Squid: Smart as Dogs, Fast as Hawks

11. February 2012 · Write a comment · Categories: Marine Biology, Marine Science

Squids and their relatives, the octopus, are said to represent the ultimate in invertebrate evolution. There is little doubt that these cephalopods have highly advanced nervous systems and other evolutionary features that give them great advantage in the sea. Their ability rapidly change colors and body patterns affords them many uses, including camouflage, escape, mating, and possibly, communication. The truth is stranger than fiction, they say, and where squids are concerned, strangeness and mysteries abound.

Probably no creatures in the sea have evoked visions of monsters than the squid. Noted for their slimy writhing skulking fleshy bodies with all-too-human-like eyes, squids and their cousins, the octopus, could be likened to humans without bones, and they remind us, perhaps, somewhere in the deep recesses of our ancient consciousness, of our own primitive and terrifying origins in the sea.

Even today, giant squids as monsters of the deep find themselves scratched on the pages of terror novels and scripted on the silver screen. Consider this account from the desk of Peter Benchley, author of Jaws, the story of another monster of the sea, the Great White Shark. In the opening of his 1991 novel (and subsequent film), the Beast, he writes:

It hovered in the ink dark water, waiting.
It was not a fish, had no air bladder to give it buoyancy, but because of the special chemistry of its flesh, it did not sink into the abyss.
It was not a mammal, did not breathe air, so it felt no impulse to move to the surface.
It hovered.
It was not asleep, for it did not know sleep, sleep was not among its natural rhythms. It rested, nourishing itself with oxygen absorbed from the water pumped through the caverns of its bullet-shaped body.
Its eight sinuous arms floated on the currents; its two long tentacles were coiled tight against its body. When it was threatened or in the frenzy of a kill, the tentacles would spring forward, like tooth-studded whips…
It existed to survive. And to kill.
For, peculiarly, if not uniquely, in the world of living things, it often killed without need, as if Nature, in a fit of perverse malevolence, had programmed it to that end.

While accounts of giant squids attacking ships and boats abound, few (if any) of these have much credibility. Squid, like the octopus, are rather shy creatures and prefer darkness and seclusion. Yet the very nature of their rare and ghastly appearance, and their ability to rapidly change color and form, have placed them prominently among legendary monsters of the deep, including sea serpents, loch ness monsters, and mermaids.

Squids, octopus, cuttlefish, the chambered nautilus, and their prehistoric relatives, the ammonites, belong to the Phylum Mollusca. Because they appear to have large heads in relation to their body, they have the appearance of being all head and all feet. For that reason, they have been put in a class called Cephalopoda, which means “head foot.” Cephalopods also include cuttlefish and the chambered nautilus, one of the few cephalopods still to retain an external shell.

While on the outside they may not much appear like a snail, on the inside they are quite similar to other molluscs. First, behind the parrot-like beak of squids and octopus lies a radula. As you recall when we studied gastropods, the radula is a hard, toothlike structure used in various ways for feeding. In periwinkles and limpets, it is used for scraping algae and bacteria off of rocks. In cone shells, it is used to inject a poisonous venom into its prey. In the squids and octopus, the radula is used for stuffing food down its throat.

The second feature of cephalopods that joins them with other molluscans is the presence of a mantle cavity. The mantle cavity is a flesh fold of skin that houses the gills and, in shell-bearing molluscs, secretes the shell in which they live. The mantle cavity of squids and octopus contains their gills.

The third link to molluscs is the presence of a shell. In the squids, the shell, called a pen, is internal and runs along the squid’s back to keep the body stiff and streamlined. The chambered nautilus, as mentioned earlier, still retains a shell, as did all ancestral cephalopods. Octopus lack a shell; however, in all cephalopods, the horny beak is considered another remnant of a shell in these organisms.

What distinguishes cephalopods from other molluscs are their brains. Squids and octopus have the largest brains of any invertebrates, placing them at the pinnacle of invertebrate evolution. Their ability to sense and processes environmental information places them on an level equivalent to many vertebrates, including the fishes. The learning abilities of octopus are well documented and their intelligence has been compared to that of canine puppies.

Many unique features distinguish squid from other invertebrates, but one distinctive difference is their ability to swim. In fact, squids (and fishes and marine mammals) belong to a category of organisms known as nekton. Nekton are organisms that have developed powers of motion to propel themselves against the ocean currents. Unlike plankton, nekton are not at the mercy of the currents. Let’s take a closer look at squids and compare and contrast their bodies and behavior with other organisms.

Squid Parts and Purposes

At least 500 species of squid are known to exist. They range in size from the tiny pygmy squid, Idiosepius pygmaeus, measuring 1-2 inches in length, to the giant squid, Architeuthis sp., reaching lengths of 60 feet or more. Off the coast of California, the market squid, Loligo opalescens, averages from 8-12 inches in length. In addition to size, squid species differ in body shape and attachments; some have elaborate fins used as “swimming keels;” some have claws and hooks on their suckers; some have bioluminescent photophores covering their bodies. Most squids travel in schools, particularly when mating, and their numbers can be vast. Cousteau describes an almost solid sea of squid they happened upon one night off the coast of California, describing them as “several yards thick, of writhing squirming creatures who darted to and fro by expelling water from their funnels, like a fleet of miniature jets.”

All squids have ten arms, making them decapods, in contrast to octopus, who are octopods. In general, eight of these arms are similar in size; two longer arms are called tentacles. In most species, the tentacles are equipped with “clubs,” flattened expanded appendages at the end of the tentacles. These clubs often have wicked hooks and claws in the suckers which only appear on the flattened ends.

Like all cephalopods, squids are carnivores, eating numerous species of fish, crustaceans, shellfish, and worms. Squid feed by grabbing their prey with the two tentacles. These appendages, which are usually held close to their bodies in pouchlike sacs, shoot out like harpoons, grab the prey, and pull it into their circle of arms. Many species of squid have poison glands that inject powerful neurotoxins into the prey when it is caught. Once subdued, the horny beak chops the prey up into bite-size pieces, which are rammed down the squid’s throat and into its stomach with the file-like radula. Digestion is accomplished by digestive glands. Food passes into the intestine, which loops back in the body and exits as the anus near the funnel. Similar to bivalves, the squid ejects its fecal matter in the excurrent stream of its siphon.

The squid’s role as a predator is enormously enhanced by its ability to swim rapidly. Squids have been called “invertebrate athletes” that “inch for inch…compete in swimming power with any other creature that lives in the sea.” How do squid swim so fast? Like other cephalopods, squids make use of jet propulsion. The basic swimstroke is described as follows:

  1. The squid sucks in water through the mantle opening
  2. The squid shuts the mantle, a kind of locking mechanism
  3. The squid tell its mantle muscles to contract! (using the brain and giant axon)
  4. The squid propels forwards or backwards as water jets out it funnel

Water enters the mantle cavity at the mantle collar by expansion of the circular muscles that line the mantle. By closing the collar, water is forced outwards through the funnel. When the squid needs speed, it rapidly contracts the mantle which forces water out the funnel and rapidly propels the squid in the direction opposite to that in which the funnel is pointing. Because the funnel is flexible, squid can actually move backwards or forwards, depending on which direction the funnel is pointed. Backwards movements are more effective than forwards movements; the torpedo-like shape of the body and the fins act to reduce drag and assist the squid in jetting through the water. The fins may also be used for propulsion in some species, either by undulating them or flapping them.

Another swimming advantage is realized by the location of the squid’s gills, called ctenidia. Squids have two gills attached to the inner wall of the mantle. Water coming in through the mantle collar flows over these gills, oxygen is extracted, and the water is pumped out the funnel. If the squid is swimming fast, more water is passed over the gills and more oxygen can be extracted. This arrangement allows squid to achieve high rates of motion, up to 20 knots per hour, for limited periods of time, much like a drag racer or Olympic sprinter!

The oxygen available to squid is further enhanced by the squid’s blood, which contains the copper-based hemocyanin, which is less viscous and easier to pump than hemoglobin. The circulatory system of squids has three “hearts” which pump blood through these ctenidia. The right and left branchial hearts pump blood through the gills where it is returned to the ventricular heart. This heart pumps blood forward and backwards through aorta to the rest of the body. Circulation and breathing are vital to the survival of the squid; low oxygen concentrations cause them to quickly lose strength. Aquariums which successfully keep squid must supply well-oxygenated water to keep them alive.

Despite the squid’s swimming abilities, its abilities as a high jumper should not be overlooked. Instances where squid have leaped more than 40 feet out of the water are not uncommon. Apparently, when trying to avoid their predators, which can be numerous, entire schools of squid will leap and fall into the sea simultaneously, in one balletic motion. Consider this account by Thor Heyerdahl and his companions aboard the Kon-Tiki in 1947:

One sunny morning we all saw a glittering shoal of something which shot out of the water and flew through the air like large rain drops, while the sea boiled with pursuing dolphins. At first we took it for a shoal of flying fish, for we had already had three different kinds of these on board. But when they came near, and some of them sailed over the raft at a height of four or five feet, one ran straight into Bengt’s chest and fell slap on deck. It was a small squid. Our astonishment was great.

The squids ability to avoid predators is probably what has kept it alive over the eons. Squids are prey for nearly all fishes in the ocean, many marine mammals, and even birds. Man, too, is quite fond of squid; thus, squid have evolved an entire arsenal of tools to avoid being eaten.

One tool animals employ to avoid predation is camouflage and squids are masters in this regard. The skin of squids contains dense concentrations of pigment-filled star-like cells called chromatophores. The elastic walls of these cells, controlled by muscles under nervous control, can be contracted and expanded, producing a dazzling array of spots, stripes, ripples, and changing hues of all colors. These color changes surpass the chameleon in terms of speed and versatility. Squids change colors to blend in with their environment, turning light-colored in shallow waters and deeper hues in darker waters. Squids even employ startle responses, rapidly changing their hues to temporarily confuse or startle their predators. For a squid, a few milliseconds delay in a predator’s attack can mean the difference between escape or death.

The highly developed sensory system of squids also gives them an advantage over their predators. The squid “brain” consists of two fused nerve centers that are linked down the length of the body by two giant nerve axons. The giant axons are bundles of fused nerve fibers that transmit nerve signals very rapidly, making them ideal for escape response. In fact, so highly developed are these nerves that they provide ideal material for the study of nerve impulses. For more than 60 years, the giant nerve axons of squids have answered many fundamental questions about neurophysiology. Giant nerve axons still serve as an active subject of research, providing a vast store of information and intrigue to biophysicists, biochemists, pharmacologists, and neurophysiologists to this day.

No less significant are the squid’s eyes and provide an excellent example of convergent evolution, where similar characteristics are developed in evolutionarily-distinct animals to solve a similar problem. Squids have eyes very much like human eyes, having a retina composed of rods and cones that may enable squids to distinguish fine detail and even color. Squid eyes also have eyelids and a pupil that can expand and contract. In fact, squids can focus each eye separately, providing them with vision that may be “twice as good as humans.” The nerve impulses from each eye travel through huge optic nerves that feed into the brain for processing information. These rapid-fire nerve fibers allow them to quickly respond and maneuver in any situation.

An interesting feature of a squid’s nervous system is its connection to structures called statocysts. These fluid-filled vesicles contain calcareous particles which allow the animal to orient itself to the gravitational field. Paired statocysts are embedded in the brain of the squid and allow them to remain aware of their orientation and movement in a three-dimensional manner.

One other well-known “escape” response of squids is their ability to eject black ink. Inside the mantle cavity of squids lies an ink sac. When disturbed, they eject a cloud of ink which temporarily confuses the squid’s predators. The ink is believed to function like a smoke screen to create a diversion while the squid escapes. One species of squid turns black all over its body, emits a cloud of black ink, then turns white and slips away, all within the space of a second. All that’s left for the predator is a cloud of ink. Another species of squid, which spends all of its life in the dark abyss, ejects a cloud of luminescent bacteria instead. In this way, it’s predator might even be temporarily blinded, just long enough for the squid to escape.

The squid’s highly developed nervous system allows them to compete well with fishes. As expressed by two Canadian scientists in a recent publication, “there are too many things that fish do well that squid either do poorly or not at all…however, there are a few things that squid do much better.” Squid devote as much of their body weight to the nervous system as many reptiles, which are vertebrate. It is postulated that their nervous control of their circulatory system allows them to achieve the athletic feats described above. It is also postulated that their highly evolved nervous system allows them to maintain sophisticated patterns of social organization. Their gregarious nature and their use of color implies a kind of language between individuals. They have even been observed using arm signals; an upraised arm appears to mean “go away.”

Many species of squids are equipped with photophores, bioluminescent light organs that function as camouflage, luring prey, reproduction, communication, or other yet undiscovered uses. More than fifty kinds of light organs have been described in squid ranging in size from pinpoints of light to discs the size of a quarter. A wide variety of patterns, colors, and shapes of photophores are described, many having the appearance of brilliant gems. Some species have photophores on their eyes and one species, which is translucent, has photophores on its liver! The use of photophores for communication has not been adequately documented, yet the following account of a squid attack on divers filming at night makes one wonder whether schools of squid emit an “attack” signal before they move in on their prey.

In 1991, Howard Hall, a cinematographer, decided to try to capture footage of a Humboldt squid (ranging up to 6 feet in length) following a hooked fish to the surface, a phenomenon often observed by Mexican fisherman. “Not a good idea,” said one of the fisherman. Hall hung at about thirty feet, filming while a thresher shark was being reeled in. Suddenly, he noticed “rapid-fire strobes going off about 5 times per second…flashing from bright red to ivory white.” Hall noticed a school of 5-foot long squid ascending from the depths. They attacked the shark and then turned their attention to Hall’s dive buddy.

Alex was behind me in the darkness. He had no movie lights to ward off the squid. A group ascended from the depths below, frenzied by the smell of blood in the water. Three large squid grabbed Alex at the same time. Suddenly, he felt himself rushing backward and down. A tentacle reached around his neck and ripped off his pre-Columbian gold pendant and chain, tearing the skin on his neck. Another squid ripped his decompression computer off his pressure gauge. Tentacles tore his dive light from his wrist and his collection bag off his waist. Then, as suddenly as they had grabbed him, the squid were gone.

Whether the “red-and-white” flashes were group signals to attack or not is pure speculation on my part. Notwithstanding, it seems to me that the squid attacked the divers with the speed and skill of a well-seasoned team of navy commandos! The suddenness with which they left also attests to some kind of communication between the squids. And somewhere, I imagine, there is a squid with a gold chain around his neck and another with a computer record of all his dives.

Squid Mating Rituals

Finally, we come to the mating activities of these fascinating creatures. Off the coast of southern California in spring (and possibly in fall), thousands of Loligos gather for their annual mating ritual. Sexes are separate in squids. Eggs are produced by ovaries inside the mantle cavity; sperm is produced from a penis also located inside the mantle cavity. Ducts from the gonads lead to the funnel, where the eggs or sperm can be easily manipulated. When it comes time to mate, male squids flash their own unique signal using their chromatophores. If a female finds favor with his “pattern,” they will embrace head to head by intertwining their arms. A packet of sperm will emerge from the funnel of the male, which he will grasp with one of his arms and place it in a pocket beneath the mouth of the female, in some species, or cement them inside the mantle, in others. The female will release all of her eggs and hold them in her arms, triggering the sperm packets to open and fertilize the eggs. (How all this occurs is still somewhat of a mystery!)

Once fertilized, the eggs will be released into the water, the squids will separate, and, if capable, swim away. However, the frenzy of copulation and the rigors of mating weaken the squid and those that do not die outright are quickly munched by the many sea lions, sharks, and dolphins that gather in the wings during such “festivals.”

Egg masses are released as clusters; in some species, a single female may lay millions of eggs. The jelly-like substance that surrounds the eggs appears to be distasteful to other marine organisms so that they don’t get eaten. However, once hatched, the miniature squid are easy prey for any number of animals. In addition, unlike other molluscs, squid eggs hatch miniature adults directly; there is no planktonic larval stage like there is for other molluscs.

Of all the invertebrates in the sea, squids and octopus must certainly be one of the most fascinating. Their long history with man is documented in numerous legends and folktales dating back to the Greeks. The knowledge of nerve conduction gained from our studies of squid giant axons surpasses that of any other organism. Still, there are many things we don’t understand about these organisms and our continued exploitation of their populations and environment may prevent our ever knowing all of their habits. Only by continued research and judicious restrictions on squid harvesting can we hope to understand the true mysteries of these amazing creatures.

Matthew Maury: The Father of Physical Oceanography

26. January 2012 · Write a comment · Categories: Historical Oceanography, History of Science, Marine Science, Ocean Science, Physical Oceanography

Having credited James Hutton with fathering geology, it follows that we should cite another scientific father, Matthew Fontaine Maury. In his pioneering book, The Physical Geography of the Sea and Its Meteorology, published in 1855, Maury established a clear link between scientific observations and navigation of the sea. His global compilations of data on winds, currents, weather and a number of other important oceanographic phenomena combined with the appeal of his charming and sometimes emotional prose produced a work that drew favor from a wide audience, including merchant seamen, Navy officers and the general public. Despite scientific inaccuracies in the book—even for its time—and its theological arguments to explain nature’s design—similar to Hutton’s—, there is little doubt that his book has had an impact on oceanography and oceanographers. How else can you explain the recognition of Maury as the father of physical oceanography.

Maury undoubtedly gained an early fascination with the sea. His older brother, John, a midshipman in the U.S. Navy, sent home vivid letters of gallant ships, rolling seas and exotic adventures. To a five year old already burdened with chores on a farm, his older brother’s life must have bordered on heroic. At the age of nineteen, Maury secretly requested from Congressman Sam Houston a commission in the Navy. On February 1, 1825, his request was granted. Though his father vehemently objected and refused to pay for his transportation to Washington, Maury scraped up the money and embarked on the career of his dreams.

From 1825-1834, Maury sailed across the Atlantic, crossed Cape Horn and even circumnavigated the globe. During these voyages, Maury developed a keen interest in navigation, currents, winds and weather. At every opportunity, he sought information from schoolmasters, fellow sailors, books and just about anything he could lay his hands on. He also made careful notes of all that he observed, from currents in the Mediterranean to daily sea breezes off the coast of Valparaiso, Chile. In 1834, he began to publish articles, including one on the navigation of Cape Horn, and books, notably a training manual on navigation for ship’s officers. Then, in October 1839, a stage coach accident left Maury’s right leg permanently damaged, effectively ending his duties at sea.

In 1842, Maury was appointed as Superintendent of the Depot of Charts and Instruments for the Navy Department in Washington. It was here that Maury began to study the huge assemblage of ship’s reports in the Depot’s archives. From this information, be began to compile a global database on currents, winds and weather patterns across the globe. He began to publish his own charts which quickly gained a following. In such demand were his ocean maps that he could “hold them for ransom,” not distributing them until the ship’s captains provided the most recent logs of their journeys.

Maury’s charts soon became internationally famous. In the fall of 1853, he was appointed as the U.S. Representative to the International Congress in Brussels. He urged the recording of oceanographic data aboard naval and merchant marine vessels and soon his system of recording currents and winds was adopted world-wide.

In 1855, Maury published what is considered to be his greatest contribution to oceanography, a book called The Physical Geography of the Seas. the book contained detailed information on the Gulf Stream; bathymetric maps with contours at depths exceeding 4.5 miles deep; and a wealth of information on currents and meteorology. Some call Maury’s book “the first textbook of modern physical oceanography.”

As a result of Maury’s work, sailing times between the British Isles and California were reduced by thirty days. His charts took twenty days off trips to Australia and ten days off trips to Rio de Janiero. Of more lasting impact, Maury’s work forged the bonds between ocean science and national and commercial interests. In this respect, he did set the stage for modern oceanography.

In the introduction to the 1963 Oxford University Press printing of Maury’s Physical Geography of the Sea, John Leighly writes:

Maury had, indeed, an abundance of factual information to impart, but his presentation of it was constantly obscured by his eagerness to organize it by means of hastily formulated and poorly grounded hypotheses. The history of the application of the physical theory to the sea and the atmosphere would have been little different if the book had never been written. Its value as a document in our intellectual history lies in a more general sphere than in the contribution it made to scientific insight.

I’m afraid I disagree. To my way of thinking, Maury was among the first to recognize the importance of a global way of thinking. His zeal for oceanographic data from all parts of the world ocean and his ability to synthesize massive data sets into coherent atlases of ocean properties distinguish his work from others. Clearly, Maury was a big thinker, one who could see the big picture and appreciate its relevance to understanding ocean processes. Such thinking lent more than scientific insight; it contributed to a view of our planet as an interconnected system, one that dominates our perspective today. Thanks, dad.

iBooks Author: First Impressions

20. January 2012 · Write a comment · Categories: ebooks, iBook Author, Ocean Science, Textbooks

Apple’s release of iBooks Author today promises to change the way textbooks are written, published, and distributed. Only time will tell if it’s all that, but I thought I would give a few first impressions after a couple of hours fiddling with it.

The app is free from the App store, but only works with OS X Lion, so right out of the gate, I had to upgrade my operating system. Switching to Lion has risks (see below), ones I wasn’t willing to take previously, but given that I have backup systems, I took the plunge. It took about 1.5 hours to download it and install it. I don’t know if that’s normal, but that’s what it took on my 2.8 GHz Intel Core i7 with 8 GB of memory. Downloading iBook Author was relatively fast, and after about 10 minutes I had the app up and running.

If you’ve used Pages or Keynote, the layout and operation of the app will be very familiar to you. If not, well, then you’ll have to spend a little more time learning the interface. But for me, an experienced Keynote user, getting the hang of it was a snap.

Here’s what it looks like when you open it.

The template chooser in iBooks Author looks a lot like the ones in Keynote and Pages.

Like Pages and Keynote, it defaults to the Template Chooser. For starters, I picked the Contemporary one (Astronomy).

The main screen looks like Pages with a few extras.

This is the first screen that came up when I selected the Astronomy template.

Text and figures can be added like you would expect. It only took a couple minutes to create this section starter using images and text I already had on hand.

 

 

After a few minutes, I was able to produce a decent looking Chapter introduction.

Here’s another completed page.

Using the template, you can easily insert or copy and paste text

Note the Widgets tool. That’s the one that has all of the cool interactive features. Using this tool, you can create your own interactive figures, add movies, and add complete Keynote presentations. This is where iBook Author may really shine. I say “may” because there are size limits (2 GB) to the completed document. I don’t know about you, but my Keynote presentations get pretty large with the number of images I include. And movies, well, a 2GB movie is tiny in the movie world. So I expect that authors will have to pay close attention to reducing the size of their movie and Keynote inserts.

Here’s a few screenshots of the completed movie and Keynote inserts:

Here's what a Quicktime movie insert looks like on the page.

 

Here’s what a completed Keynote presentation looks like.

Of course, a book needs text so I copied and inserted a new page (2-column) and tried pasting three pages of text from a Word document. At first, I didn’t get what I wanted. The text was truncated at the beginning. Then I realized that the first part that I created (Section 2 in the screen shots) was still part of the text flow. After inserting a page break, the text came out perfect. iBook Author even created new pages to accommodate the text.

Text can be pasted into a 2-column template.

I’m guessing that with more practice and experience with the app, I’ll figure out all of the bells and whistles. But it’s pretty simple from the get-go, and really lets you whip together a short e-book quickly.

That said, I do have some concerns.

First, you can only preview your completed e-book on an iPad. In fact, the preview function only works when the iPad is connected to the computer. That’s a bit restricting and annoying, but I guess Apple’s reasoning is obvious: that’s how they sell iPads.

Second, use of this app to create a complete textbook will require extraordinary planning and organization. BiBA (before iBook Author), textbook authors really only had to worry about text and images (pictures, figures, graphs, that kind of thing). Now an author has to plan for interactive images, movies, and presentations within the book. While the opportunity for creativity is enormous, it does raise the bar for producing something that is meaningful and impactful.

Third, the size limit is something that authors will have to pay attention to in the planning of the book. Some of that might be sidestepped with the use of external links, something I did not explore. Otherwise, a 16-chapter textbook won’t allow for too many movies.

Finally, there are restrictions in where you can publish the book, if you want to make any money off of it. Apple retains sole distributor rights for anything created and published in iBook Author for sale. That means you’re limited to selling it in iBooks. Otherwise, if you choose to give it away, you can distribute it wherever you want. It remains to be seen how big of a limitation that might be.

Overall, I liked it, and I’d give it a 4/5 stars for starters. It’s sure to elicit lots of conversation. I hope this little review inspires you to check it out and learn more.

P.S. I’ve attached a PDF version of the book I created today. Feel free to check it out and contact me if you have any questions or comments.

Preview of The Deep Blue Sea by Sean Chamberlin

 

 

 

 

Marine Worms and Penis Fencing

17. January 2012 · Write a comment · Categories: Marine Biology

BILATERIA

Startling as it may seem, worms represent a significant evolutionary progression in the development of animals. Flatworms represent the first of the Bilateria (a taxon exhibiting bilateral symmetry) and the first animals that are triploblastic, meaning their development includes three well-defined germ layers, the ectoderm, mesoderm and endoderm. The development of bilateral symmetry in animals provided an avenue for cephalization (concentrating nervous and sensory systems in a head) and exploiting horizontal gradients and surfaces for food, which in turn may have lead to improved musculature, burrowing, and physiological specialization, such as the development of digestive systems, circulatory systems, excretion systems and reproductive systems. When you consider that the Bilateria include 99% of all species on Earth, then the evolution of this design and its implication for the success of animals becomes apparent.

The Bilateria encompass all of the remaining phyla that we will visit and itself is divided into two divisions: the Protostomes, including the worms, mollusks, arthropods and many others; and the Deuterostomes, including the echinoderms, hemichordates and chordates. Primarily, these divisions are distinguished by the type of cleavage and development of the fertilized egg, topics for a good developmental biology course. Nonetheless, as you may encounter these terms in the literature, we mention them here.

We begin our inquiries into the Bilateria with the flatworms (Phylum Platyhelminthes) and the ribbon worms (Phylum Nemertea), nearly all of whom inhabit benthic environments.

FLATWORMS

A satisfactory treatment of the flatworms fails our meager paragraphs here as the diversity in form, function and ecology of these groups is simply astounding. Free-living marine flatworms (Turbellaria) come in many sizes, from the tiny microturbellari, like the 4-mm Polychoerus carmelinsis (named after the city of Carmel where it was first found) to the 30 cm (nearly a foot long) macroturbellaria, Genus species, and colors, from the highly decorated genus species to the exotic genus species. For species that employ toxins as a chemical defense, their colors and pattern act as warning coloration to predators. Flatworms largely inhabit the sea floor (reefs and/or sediments) on, beneath, or within sand, mud, rocks, shells, seaweeds, mangroves or even its food source. Some species, like the ruffle-edged Pseudobiceros bedfordi, can swim above the reef and some are truly pelagic.

The body plan of flatworms, while diverse, generally consists of a flattened ovoid (but sometimes elongate) ciliated cell wall filled with numerous rhabdites that produce mucous for a variety of hypothesized uses. Internally, a simple or highly branched digestive system complements a well-developed musculature and a centralized nervous system. Exchange of gases and wastes primarily occurs through diffusion, for which a flat and small size is well-suited. Unlike ctenophores, flatworms have one opening that serves both as mouth and anus.

While nearly all flatworms are hermaphrodites and can reproduce by reciprocal exchange of eggs and sperm. A few species engage in a phenomenon known as penis fencing, a refined form of hypodermic insemination. This latter process involves injecting sperm beneath the skin of a mate, a technique well-known among hermaphrodites but observed rarely where sexes are separate due to the high energetic costs associated with wound-healing in the females. However, for hermaphrodites, the choice to stab or be stabbed may act as a selective pressure on individuals (the hypothesis being that it is better to stab than be stabbed). In 1998, two scientists confirmed that individuals of a marine flatworm, Pseudoceros bifurcus, did indeed attempt to avoid penetration. These flatworms were observed to raise up on the posterior half of their bodies, evert their penises and attempt to stab each other. Unsuccessful but “point-scoring” strikes by one individual typically generated an avoidance response by the other individual and once an individual had successfully inseminated another, the mating behavior stopped. In 39 “contests” between 12 pairs, these scientists observed 287 strikes and 46 inseiminations. Of these, 30 were unidirectional, meaning only one individual was inseminated. These scientists speculate that sperm donation maximizes the change of producing offspring while minimizing the energetic costs associated with wound healing. Penis fencing, as they call it, may also select for more favorable partners as, presumably, being stabbed by the best “swordsman” insures that your offspring are the strongest and most fit.

Not all reproduction in flatworms requires such efforts. Their ability to clone themselves through asexual reproduction is legendary and a subject of intense study for applications in tissue regeneration. In a famous set of experiments, often performed by students, a flatworm is chopped into three pieces—head, middle-tail—and observed as each section regenerates its body. Marine flatworms have been observed in the wild with chunks of flesh missing, presumably from the bite of a fish, with no apparent harm as the tissues will reform.

Many flatworms also exhibit symbiotic relationships. One species of flatworm lives in the gills of horseshoe crabs in a form of commensalism (one species benefits, the other is unharmed) where it receives transportation, shelter, aeration and increased food availability. Mutualism (where both species benefit), like that mentioned for corals, occurs between a small flatworm and an algal symbiont in France, where these green worms may number in the millions and paint the beach green at low tide. A number of flatworms have evolved parasitism, a symbiosis where one species benefits at considerable expense to the other. Trematodes inhabit a number of mollusks and can infect mollusk-eating fishes that may be eaten raw by humans as sushi. The World Health Organization has estimated that 40 million people may be infected by trematodes worldwide. Care when eating raw fish as well as checking with health authorities and researching fishes to avoid should prevent infection (if you are still inclined to eat sushi).

Side Note: Continuing work on flatworm phylogeny appears to suggest that some groups of flatworms may be more advanced and belong to a large group of higher animals known as Lophotrochozoa, a group that includes annelids and mollusks. The advent of molecular phylogeny continues to redistribute branches on the tree of life such that any scheme of classification should be considered a works-in-progress.

RIBBON WORMS

The ribbon worms, also known as the bootlace worms (Phylum Nemertea), may hold the record for the longest animal: a nemertean measuring 180 feet washed up on the shore of St. Andrews, Scotland, following a storm in the late 1800s. Typically, however, nemerteans range in size from a few millimeters to a few meters and display a wide range of colors and patterns. Though less diverse than flatworms, they occupy similar habitats, living in benthic environments throughout the world ocean.

Nemerteans display considerable adaptations for ambushing prey. Equipped with a formidable, eversible proboscis that may exceed the length of their bodies, they lie in wait until a suitable prey appears. At that time, a fluid-filled cavity at the front-end of the organism forcefully propels the proboscis outwards to entangle, lasso and/or harpoon their victim. A nemertean proboscis is typically sticky, owing to gland cells lining the proboscis. It may also be equipped with stylets (calcareous barb) and supplied with paralytic venom in some species.

Two “improvements” in the body plan of nemerteans are evident. Unlike flatworms, nemerteans have a one-way digestive system with a separate mouth and anus. They have a simple circulatory system, consisting of two lateral blood vessels that run the length of their body in which blood circulates (albeit not always in the same direction) as a result of circular muscle within the blood vessels. With these systems, nemerteans are better able to supply energy and nutrients to their tissues and, presumably, maintain a more active lifestyle than their flatworm relatives.

Like flatworms, nemerteans may fragment and clone asexually. Many of them fragment easily, which makes them hard to collect and study. However, unlike flatworms, nemerteans have separate sexes with simple male and female reproductive organs. Mating involves aggregation in some species or construction of a burrow or cocoon. The resultant gamete turns into a planktotrophic larva known as a pilidium, easily recognized in plankton samples by its helmet-shaped appearance and tufts of cilia.

Both flatworms and ribbon worms likely play important ecological roles in the transfer of energy and materials in marine food webs. However, because they are difficult to observe and study under natural conditions, the significance of their role remains uncertain.

The Cnidaria: Animals That Sting!

13. January 2012 · Write a comment · Categories: Marine Biology, Ocean Conservation

BENTHIC CNIDARIA

The Cnidaria (pronounced nye_DARE-ee-uh), which include the familiar sea anemones, jellyfishes and corals, derive their name from a specialized cell called a cnidoblast or nematocyst, unique to all cnidarians. These cells act like miniature, hollow harpoons to inject poisons into their prey and enemies. Anyone who has been stung by a jellyfish can attest to the power of these cells. Beyond their sting, cnidarians play an enormously important role throughout the world ocean. Corals have been called the “canary in the coal mine” of global warming; along with jellyfish, corals may act as early warning systems for negative human alterations of marine ecosystems.

Because of their radial symmetry (having a symmetrical arrangement around a central point), the cnidarians have been called “the flowers of the animal kingdom.” Certainly, a tidepool of sea anemones with their tentacles waving give the impression of a flower garden and many cnidarians “farm” algal symbionts. Yet most of the 9000+ species of cnidarians are flesh-eating carnivores, feeding on a range of animals from small zooplankton to small fish.

We focus our attention here on two groups of cnidarians: 1) the Anthozoa, a class that includes sea anemones, solitary corals, hard corals, soft corals, sea fans and sea pens, among others; and 2) the hydrocorals, benthic members of the class Hydrozoa, who, like corals, are reef-builders.

Anthozoa

The anthozoans (Class Anthozoa) evoke images of faraway tropical isles and crystal clear blue waters. That’s because many anthozoans—especially the reef-building stony corals—inhabit the tropics, where warm temperatures and oligotrophic waters favor their growth and reproduction. Yet equally stunning in their beauty are the deep-sea corals that inhabit the cold and deep waters of the world. These reef-building corals—the shallows and the deep—provide food, protection and shelter to tens, perhaps hundreds, of thousands of marine organisms. Their handiwork even dwarfs that of humans: the Great Barrier Reef in Australia is the most massive structure built by any organism and plainly visible from space.

Given their widespread extent, it should be no surprise that the anthozoans represent the largest class of cnidarians and host a diverse number of species, including sea anemones, tube anemones, solitary corals, stony corals, black corals, blue corals, soft corals, sea fans and sea pens, among others. Equally diverse are the kinds of habitats in which they are found: from the intertidal to the sea floor, from the tropics to the poles. While most attach to hard substrates, The soft-body forms, like the anemones, can burrow in sediments.

Despite the stony exterior of the reef-building corals with which those of us who have visited souvenir shops are most familiar, they are, in fact, built by soft-bodied anemone-like polyps that inhabit the pores and interstices of the calcium carbonate matrix. As such, the anemones provide a good model for the body plan of anthozoans. A typical sea anemone consists of a muscular cylinder with a foot (basal disk) at one end and a flattened mouth (oral disk) surrounded by tentacles at the other. The interior of the anemone may be divided into a series of partitions (septa) in which digestive and reproductive processes can tale place. Food is caught with the nematocyst-containing tentacles and carried to the oral groove where it is moved by a pharynx into the central gastric cavity. Reproduction may be asexual, in which the anemone simply splits in two (self-cloning) or sexual, in which gametes may released by males, females or hermaphrodites into the water (or held in brood pouches). Fertilized eggs develop into a planula which may drift and feed before settling to the bottom.

Reproduction in corals follows the pattern for anemones, except that on coral reefs, like the Great Barrier Reef (and other reefs), the timing and release of gametes is highly synchronized  and coordinated among coral species, a phenomenon known as mass spawning or mass broadcasting. From October to December each year, a few to several days following a full moon, more than 140 coral species release their gametes into the water over a period of four to five days. Because the eggs and sperm of different species don’t cross-fertilize, this synchronized spawning is thought to offer “survival in numbers” and to take advantage of ideal current patters that insure the return of the planula to a suitable location. (e.g., Harrison et al., 1984; Wilson and Harrison, 2003).

In corals—hard or soft—the skeleton is excreted by the ectoderm (outer skin layer) in folds of tissue at the polyp’s base. The resultant coral cup exhibits a series of radial ridges called septa. Any number of new polyps may bud from the original, giving rise to a colony of polyps, each of whom build their own cup. In an almost fractal-like way, a colony of polyps creates the architecture of the coral colony type, ranging from the tree-like staghorn coral to the maze-like brain corals to the mushroom-like plate corals. Except for the solitary corals, all corals that you see are colonies of individuals.

While many types of corals are able to build skeletons, the most well-known and the most numerous are the reef-building or hermatypic corals in the order Scleractinia, commonly called the stony corals. These corals require an algal symbiont—a dinoflagellate—to carry out the metabolic processes for building their calcium carbonate skeleton, a symbiotic relationship known as mutualism, where both species benefit. The symbiont not only provides energy in the form of fixed, organic carbon but it also provides essential compounds in the biochemical pathways that enable calcium carbonate secretion. In turn, the coral animal provides essential nitrogen compounds to the symbiont. For these reasons, stony corals are confined to shallow waters where light is abundant and warm waters, typically where temperatures remain above 73° F (although cold-water hermatypic corals are known).

The nature of this symbiotic relationship between corals and algae has been the subject of intense research due to worldwide increases in the incidence of coral bleaching, a phenomenon whereby the coral expels its symbionts. Bleaching is presumably caused by prolonged elevated seawater temperatures but other factors may contribute as well. For reasons that are not entirely understood, higher-than-tolerable temperatures cause a breakdown in the relationship between a coral and a symbiont and the algae are expelled. If conditions improve, the coral may recover its symbionts and survive. If stressful conditions are prolonged, the coral may die. While coral bleaching occurs even under natural conditions, the increasing number of bleaching episodes has led to international efforts to monitor and report conditions where bleaching may occur. NOAAs Tropical Ocean Coral Bleaching Indices web site provides near real-time information and maps on thermal stresses for 24 selected reef “hot spots” around the globe.

While increasing ocean temperatures as a result of global warming certainly play a role in bleaching, a number of other factors also appear to be important, including disease, sedimentation, eutrophication, habitat destruction and species-shifts associated with fishing. The rate of coral bleaching appears to be severe and a number of scientists have predicted catastrophic decline and extinctions of coral reefs worldwide. Nonetheless, continued research will be needed to assess the long-term temporal and spatial effects and the degree to which these communities adapt or exploit new habitats to overcome anthropogenic disturbances.

While the degree to which humans are responsible coral bleaching and the worldwide decline in coral reefs may be debated, the rapid decline in populations of deep-sea corals has only humans to blame. Long-known but only recently appreciated, these cold-water corals, many of them hundreds of years old, have borne the effects of deep-sea trawling for more than a century. Increasing use of this type of fisheries in recent decades has exacerbated an already existing problem. The photographs of deep-sea coral communities before and after trawling provide striking evidence of the destruction these trawlers leave in their wake.

In response to concerns that these organisms were being eliminated before their ecological role or potential benefit to humans could be evaluated, more than 1,136 scientists from 69 countries called upon the United Nations to halt fishing techniques that lead to the destruction of deep-sea corals and sponges. In their statement to the UN, submitted on February 15, 2004, the scientists wrote: “As marine scientists and conservation biologists, we are profoundly concerned that human activities, particularly bottom trawling, are causing unprecedented damage to the deep-sea coral and sponge communities on continental plateaus and slopes, and on seamounts and mid-ocean ridges.” While some nations have already banned these methods in their waters, increased efforts will be needed to insure that deep-sea communities are managed responsibly.

Hydrozoa

The hydrocorals, well-represented in Florida and California, feature polyp stages that produce hard skeletons of calcium carbonate. Like their cousins, the true corals (Class Anthozoa), these animals are important reef builders, particularly in temperate environments. Off Carmel, California, tree-like colonies more than 100-years old have been found. The hydrocorals also include the encrusting fire corals, some of which can be quite painful to the touch, as experienced by Chamberlin diving off Palm Beach, Florida, as a youth. Hydrocorals also appear to be sensitive to changes in seawater temperatures brought about by climatic events: in Panama, two species of hydrocorals were eliminated (presumably to extinction) by the 1982-83 El Niño. While some hydrocorals produce planula that swim for a few hours, most complete their entire life as benthic organisms.

Conclusion

In modern times, coral reefs have been called the “canary in the coal mine” as a way of expressing the concern that human-induced changes in our global environment threaten the survival of our species. While it is not the role of scientists to decide whether or not this statement is true, science can provide the kind of objective and self-consistent observations that enable citizens and policy makers to make informed decisions. Oftentimes, the answers are not clear cut and definitive conclusions are not possible. However, by educating yourself in the science behind these issues, you can, at least, present an opinion based on the best available facts. Such an approach is far preferable to making decisions based on hearsay or advocacy.

The Sponge

10. January 2012 · Write a comment · Categories: Marine Biology · Tags: , , , , ,

The skeletons of sponges (the Porifera or “pore bearers”) have graced the backs of bathing humans since antiquity. Today, natural sponges are still prized for their beauty and soft texture. But what most people don’t realize is that sponges possibly represent our most ancient ancestors. Based on a comparison of a particular gene in sponges with the same gene in worms, insects, mammals and other organisms, Mitch Sogin at The Marine Biological Laboratory at Woods Hole, Massachusetts, has concluded that the sponge genome represents the basal blueprint from which all other multicellular animals emerged. While this interpretation is still debated (e.g. Ender and Shierwater, 2003), there appears to be wide agreement that sponges represent are among the most primitive animals on our planet, the basal metazoans.

Sponges have been enormously successful, occurring in a wide range of oceanic and freshwater habitats from the intertidal to the deep sea. Scientists have described more than 8000 species of sponges in a dazzling array of colors, shapes and sizes, from a few centimeters to a few meters (notably the basket sponge). Their body plan is remarkably simple: sponges lack the muscles, nervous and digestive systems present in nearly all other animals. Nonetheless, some are capable of limited movement (Bond, 1992), some have been observed to expand and contract (Ruppert, 2004) and some have been shown to transmit electrical impulses in response to tactile stimuli (Leys et al, 1999). And while most sponges are considered to be filter-feeders, removing fine particles of food and detritus from the water column, at least one species has been shown to use a type of living Velcro to capture small zooplankton (Vacelet et al, 1995).

Three layers of cells comprise the sponge. The outer layer consists of tile-like cells called pinacocytes, which function much like the epithelium of higher animals. A network of incurrent pores (formed by contractile pore cells) perforates this outer layer and provide for the intake of seawater for food and gas exchange. Inside the sponge, lining its inner cavity (sometimes called a vase), are a group of cells known as collar cells, which bear a long flagellum (a whiplike hair) that beats and provides the “motor” for the circulation of seawater. Surrounding each collar cell is a ring of microvilli (tiny hairs) that capture food particles in a mucous web and ingest them. In the middle layer, called the mesohyl, the mesenchyme cells, move about like amoeba within the sponge and transfer food particles, receive partially digested food particles from the collar cells, digest food, remove debris and generally act like living forklifts to move materials and energy about the sponge. A large excurrent vent generally in the center of the sponge expels waste.

Comprising 95% of all sponges, the demosponges (class Deomspongiae), exhibit a more complex architecture than the simple body plan presented here. A series of flagellated chambers and channels interconnect to control and modify the flow of seawater through the sponge. This arrangement, called the leuconoid type, enables these sponges to more efficiently move greater volumes of seawater and grow to a larger size. (Ruppert Invertebrate Zoology, 2004)

Holding the sponge together and embedded in its middle layer is a skelton composed of spicules (crystals of calcium carbonate in the shape of multi-pronged spikes) and/or spongin (the tough elastic proteinaceous collagen that gives the sponge its sponginess). Though spongin is prized by sponge divers and their customers, scientists hold great interest in spicules for their possible clues to evolutionary relationships and even climate change. One group of scientists examine spicules as one would examine tree rings for the possible information they hold on past ocean conditions.

Sponges play an important and perhaps underappreciated role in the environments where they occur. Because they filter water, they help remove organic debris that might otherwise stimulate harmful bacterial growth. They also serve as a food source for nudibranchs (sea slugs), starfish, turtles and some fish, although sponges are toxic to many fish. As a result, sponges also provide habitat and shelter to a number of organisms in a type of symbiosis known as commensalisms, where both species benefit but the relationship is not obligatory.

Beyond beauty and science, sponges also hold great promise for their medical potential. Studies on the aggregation and immune system response of sponge cells have provided insights into these processes in higher animals. The discovery of chemicals in sponges (secondary metabolites) with potential therapeutic applications has spurred an interest in sponge phylogeny, physiology and ecology as scientists desire to learn more about the kinds of sponges that produce these chemicals and the conditions that favor their production. These discoveries have stimulated research in “spongiculture”, the development of techniques for growing harvestable quantities of sponges and/or their cells. (See Pomponi et al., 1998)

Day of the Dolphin

06. January 2012 · Write a comment · Categories: Marine Biology, Marine Mammals, Marine Science · Tags: , , , , , ,

Studies of cetacean behavior and its relationship with life history and ecology belong to a field of study known as behavioral ecology. Behavioral ecologists attempt to discern how behavior(s) enable an organism to survive and reproduce in its environment. Variations in behavior in response to changes in the environment are also important.

The study of behaviors by cetologists—scientists who study cetaceans—has historically been a qualitative endeavor. From John Lilly’s early attempts to communicate with dolphins to behavioral studies on captive animals to tracking of wild populations, cetologists have struggled to find ways to quantify what are largely descriptive and somewhat anecdotal observations. How do you put a number on play? Aggression? Mating behaviors? How do you quantify complex sounds in a meaningful way? Fortunately, new tools, new approaches and new understandings have put cetology on the threshold of a major transition “from qualitative, descriptive natural history to focused, quantitative analyses of the social interactions and social relationships of individuals” (Samuel and Taylor 2000).

The key to the transformation of cetacean science lies in an increasing arsenal of techniques that enable scientists to identify individuals, distinguish between sexes (not always easy in cetaceans), determine their genetic relationships, track and record their movements and classify and statistically analyze their behaviors and sounds, among others. Recognition of the unique natural markings of individual animals have enabled observations of the movements and activities of individuals and built a long-term data set from which hypotheses about cetacean behavior could be constructed. Advances in animal behavior theory from other disciplines provided a framework for cetacean studies and has led to the development of rigorous methods suited for testing hypotheses. Like much of oceanography, studies on cetaceans increasingly rely on quantitative methods and statistics to better understand the complex and intricate behaviors of these animals.

Most behaviors are grouped into categories based on function. Behavioral ecologists ask “what problem does this behavior solve?” (after Tyack 2000; following Alcock 1998). The major functional behaviors of cetaceans include:

1)    protection: predator avoidance and defense

2)    agonistic behavior: competition with other animals or between individuals

3)    socialization: social interactions

4)    sexual behavior: finding, courting, choosing mate

5)    parenting: care and protection of young

6)    travel: dispersal and migration

7)    foraging—finding, identifying, capturing and consuming prey (discussed above)

Behaviors may vary in space and time, they may involve single or multiple interactions and they may occur between two or more individuals. They may occur above or below the surface of the water, they may be associated with any of a number of other activities, like swimming, diving or resting, and they may change during the course of an animal’s life. As you might suspect, cetacean behavior and its study can be quite complex.

Most cetacean behaviors also involve a system of communication that includes tactile, visual, acoustic and/or chemical signals. So far as we know, chemical communication does not occur in cetaceans (as it does in many terrestrial animals). Communication, as traditionally defined, involves a two-way exchange of information between a sender and receiver with the requirement that received signals are acted upon in some manner or that the information “reduces uncertainty” in the receiver. Peter Tyack (2000) promotes a broader and perhaps more pragmatic view of animal communication that encompasses a range of possible signals that function to transmit information in ways that may not be included in the classic definition. These communication signals are intimately associated with the functional behaviors listed above and include:

1)    advertisement: a signal designed to influence the decision of the receiver, i.e., mating songs of male humpback whales

2)    tonic signals: the classic transmission-response form of communication, i.e., mother-calf responses after separation

3)    deception: a signal designed to mislead the receiver, i.e., threat displays

4)    environmentally altered: variations in signals caused by the presence of an object or substance in the environment (physical, geological, chemical or biological) from which information may be gleaned, i.e. locating another individual’s depth and range based on their echo

5)    interception: recognizing or intercepting a signal intended for another receiver, i.e., find prey by listening to their acoustic signals

6)    learned signals: recognizing the signals of other species and what they mean, i.e., dolphin attraction to fishing vessels when the winch is activiated

Though this list may appear somewhat abstract, I invite you to explore future postings as well the scientific literature for a close look at this rapidly advancing and exciting field of science.

 

 

Marine Habitats: Definitions and Challenges

05. January 2012 · Write a comment · Categories: Marine Biology, Marine Science, Ocean Science · Tags: , , , , ,

Roughly speaking, a habitat is where an animal lives. In terrestrial terms, a habitat encompasses the geologic landscape, the climate and unique physical and chemical circumstances that may characterize a particular location. However, in aquatic environments, the term habitat takes on quite a different meaning. In addition to an undersea landscape punctuated by mountains, trenches and canyons that are taller and deeper than anything on land, the watery world imparts a three-dimensional, moving, changing, turbulent and fluid character to aquatic habitats. Imagine if land-bound species were suddenly permitted to float around in the sky at the whim of the winds and movements of air masses. The nature of our world would change drastically yet this is the world experienced by many marine organisms.

On the broadest level, we can divide the marine realm into two parts: 1) the benthos, the region defined by the surface of the earth beneath the sea; and 2) the pelagos, the region that encompasses all the watery parts of the sea. Though different in character, these two primary habitats provide the protection, nourishment and support systems for the survival and reproduction of marine organisms. As we shall see, some organisms take advantage of the unique properties of both habitats, spending part of their lives in both realms.

The benthic environment is defined largely by the type of substrate of which it is composed and may vary from very fine muds and sands, called soft-bottom benthos, to cobbles, boulders and solid rock, called hard-bottom benthos. The composition and nature of the substrate determines whether organisms may live within the substrate as infauna or upon the substrate as epifauna. Infauna typically inhabit soft bottoms where they may burrow into and/or move freely within the sediments but it may also include organisms that can penetrate solid substrates, like rock-boring clams. Epifauna may occur on either soft or hard bottoms where they live and/or travel upon the surface of sediments or rock. Some very tiny organisms may even live between the grains of sediments. These interstitial organisms can be found from the seashore to the abyss.

The pelagic environment exhibits less obvious differences in structure and composition. Nonetheless, the pelagic environment is quite diverse in its physical and chemical properties, the nature of which affects benthic habitats as well. Variations in light intensity differentiate the surface waters from the deeper waters. Sunlight generally penetrates to about 200 meters in the upper ocean, defining a region called the epipelagic zone. From 200 to 1000 meters, light is very dim, defining what is called the mesopelagic or twilight zone. Beneath 1000 meters, the bathypelagic and abyssopelagic zones are completely dark. Pressure also exerts its influence on marine organisms: the weight of one atmosphere is added for every 10 meters of depth. Thus, at 1000 meters, the water pressure is 100 atmospheres, or 1,460 pounds per square inch! Only organisms that can withstand these crushing pressures survive here. Temperature plays an important role in the distribution of pelagic organisms both with depth and latitude. Tropical regions tend to have warm and stable temperatures while temperate and polar regions may vary in temperature considerably, especially in the upper ocean. Currents that bring cold or warm water into a particular location will also alter the habitat of organisms suited for narrow ranges of temperature. The concentration of dissolved salts, the salinity, affects the physiology of marine organisms and, as a result, influences where certain organisms may live. Thus, while the pelagic environment may appear homogeneous at first glance, its physical and chemical properties create very specific habitats that may be exploited by marine organisms.

Marine scientists define both the spatial (geographic) and temporal (time-varying) properties of an environment to define the range of conditions to which organisms are subjected. The combination of geological, chemical and physical conditions and their variations with space and time determine, to a large degree, the types of organisms that may inhabit a particular location. Organisms that are adapted to a wide range of temperature conditions, for example, are called eurythermal because they can tolerate changes in temperature. On the other hand, organisms that have very specific requirements are termed stenothermal because they have a very narrow range of temperature tolerance. Similar terms have been defined to describe the range of tolerance to salinity, pressure or other physical and chemical conditions. For organisms permanently attached to a subtrate, these variations in seawater properties mean the difference between life and death. If an organism is not adapted to a particular suite of conditions, it will die. On the other hand, more mobile organisms may simply relocate or migrate to maintain its preferred conditions. In general, tropical regions tend to exhibit stable conditions in which conditions change very little from place to place through the seasons. Temperate regions experience both temporal and seasonal variability and may represent the region of greatest fluctuations in an organism’s habitat. Polar regions, though extreme, offer another type of stable environment in which conditions change minimally thoughout the seasons. Of course, climate and other scales of change influence the year-to-year variations in a particular habitat. The ability of a species to adapt to such changes determines whether it will survive through the eons or go extinct. The fossil record reveals a long history of marine organisms who failed to make the cut!

The Midi-Chlorians

03. January 2012 · Write a comment · Categories: Ocean Movies

ANAKIN

Sir…I’ve been wondering, sir…what are midi-chlorians?

QUI-GON
A microscopic life form that resides within all living cells and communicates with the Force. The midi-chlorians are actually one vast entity that encompasses the Universe, but is broken into an infinite number of small pieces that reside in every living thing.

ANAKIN
They live inside of me?

QUI-GON
In your cells. We are symbionts with the midi-chlorians.

ANAKIN
Symbionts?

QUI-GON
Living together for mutual advantage. Without the midi-chlorians, life would not exist, and we would have no knowledge of the Force. They speak to you all of the time, telling you the will of the Force.

ANAKIN
They do?

QUI-GON
Some call it intuition…the voices within you. When you learn to quiet your mind, you will hear them speaking to you.

ANAKIN
I don’t understand.

QUI-GON
With time and training you will. (You will!)

Star Wars Episode One — The Phantom Menace, Act III, 1999

Welcome to the Undersea World!

03. January 2012 · Write a comment · Categories: Ocean Science

When Jacques Cousteau entered the “silent world” with his crude aqualung in 1943, the world of undersea exploration entered a new era. No longer were humans confined to the terrestrial parts of our planet. Now humans, or menfish, as Cousteau called them, could spend extended periods of time underwater roaming as freely as time, pressure and air capacity permitted. Though arguably as significant a leap for mankind as Neil Armstrong’s first steps on the moon, no television crews or news reporters recorded that momentous day. Instead, Cousteau enjoyed his first aqualung “flight” collecting lobsters. To celebrate this historic moment, Cousteau’s wife, Simone, and his partners and co-inventors, Phillipe Taillez and Frederic Dumas, feasted while begging Cousteau for every little detail of his experience.

For those of us fortunate to have dove beneath the sea—either as skin or Scuba divers—the undersea world offers a special sense of serenity and wonder that cannot be experienced anywhere else. Far from a silent world, the undersea world crackles with the activities of noisy shrimps and fishes. Colors and patterns, though subdued and cast in a bluish hue, in deeper waters, have a language of their own. Flashes of movement in a school of fish, the quick dart of a ornate worm, the dark shadow of a large predator at the edge of your vision lend to an otherworldly environment in which we are only visitors. An undersea experience can intoxicate, hypnotize, and fill you with a sense of overpowering wonder or uncontrollable fear. Despite the cold, the dim light, the dry air and the uncomfortable gear, it’s a rare dive that does not end in a laugh or smile.

As peculiar and alien as this environment may feel at first, a look around often uncovers a few familiar faces or at least something that looks familiar. Although the dinner plate is not the most conscientious place to start when describing marine life, it does provide a good point of reference. Crabs, lobsters, shrimp, mussels and many types of fishes may be known to us prior to our first visit. Yet it’s the animals with which we have no experience, that have no description in our vocabulary, which we might not even recognize as animals at first that give us pause. “What was that?” you might ask a companion upon your return to dry land. What was that, indeed?

Like characters in an epic space movie or a legendary fantasy novel, the marine animals offer their own splendid variety of peculiar armaments, bizarre behaviors and wily personalities. They provide a glimpse into the roots of our own ancient world, a world from which our own evolutionary emerged. Most importantly, knowledge of marine animals gives us a sense of the living world that covers most of our planet: some 99% of all living space on Earth is in the ocean. And you’ll gain an appreciation for the important role they play in human ecosystems. Dive in, explore and wonder.

Blue Whale, Dana Point, August 8, 2008

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