Dive Dry with Dr. Bill

#462: Brittle "Stars"

Some of my readers may remember that I have an interest in astronomy as well as the marine environment. A few of you joined my Halley's Comet watching events on the island back in 1986, and some of the lovely ladies may remember my promise to make you "see stars" after the bars closed at 2:00 am. Yes, I later heard that a few of you were disappointed when you found out I meant looking at them through the telescope on my sun (star?) deck.

As John Steinbeck and my icon Ed "Doc" Ricketts once said, immortalized in The Log from the Sea of Cortez, "It is advisable to look from the tide pool to the stars and then back to the tide pool again." To truly understand life on Earth, one has to understand the origin and evolution of the Universe. I don't adhere to Bishop James Ussher's declaration that the world began in 4004 BC. As a scientist, I believe it originated many billions of years ago from a primordial mixture of hydrogen and helium. Only after stars formed and began creating heavier elements like carbon, oxygen and nitrogen in their thermonuclear cores did life become possible.

To understand life one must progress from the stars, to the creation of the elements, to the appearance of life on our planet and its subsequent evolution. Am I leaving God out of the picture? Not necessarily. Why wouldn't an all-knowing God put the ingredients out there and enjoy watching as things came together through such a process? Why not take a few billion years instead of concentrating that Herculean effort into just six Earth days?

Of course I digress. The topic of today's column is not stellar evolution. I will instead focus on the "stars" in the sea, specifically the brittle stars who are relatives of the sea stars (formerly known as starfish until the P.C. crowd figured people would confuse them with real fish... sheez!). During my years at Harvard, one of my mentors was an expert on the Phylum Echinodermata to which these "stars" belong along with sea urchins and sea cucumbers. When I arrived on Catalina, it was natural for me to show an interest in them as well. Here on Catalina's leeward coast, I rarely see them because they are usually well hidden under rocks and in crevices to escape potential predators like sheephead. However during my recent dives on the oil rigs off Long Beach with the Roddenberry Dive Team, I had plenty of opportunity to film them! How fitting that brittle "stars" and the son of the creator of Star Trek would be linked together!

Brittle stars got their common name from the fact that their arms often break off when a predator attempts to snatch them up for dinner (or breakfast or lunch or just a midnight snack). This is a defense mechanism in which a part of the body is sacrificed so the entire animal doesn't die a prolonged death in the digestive acids of some fish, perhaps a sheephead or rock wrasse. Like their relatives the sea stars, brittle stars (known scientifically as ophiuroids) can grow the missing appendage back over time. Wouldn't it be wonderful if those who put their lives on the line for us in combat could do the same?

One of my favorite brittle stars is Ophiothrix spiculata. I first encountered them in 1969 when I began studying the marine life found on drifting kelp "rafts." One of the rafts we found had well over 1,000 of them on the holdfast which illustrated what a great method kelp rafting was in allowing marine life to disperse across the San Pedro Channel to Catalina. The colonists on the Mayflower and in Jamestown numbered far fewer than that! To be fair, this species has been found down to over 6,000 feet and the Channel only reaches a maximum depth of about 3,500. I suppose some could suggest these invertebrates could "walk" across the bottom to reach Catalina. However, I don't think an individual ophiuroid would live long enough to make the crossing... and still have the energy to reproduce!

This species lives anywhere there is adequate protection for it in rocky reefs and kelp forests from Moss Beach, CA, to Peru. In areas where predators are few (such as over fished regions or in very deep water), they can even be found out in the open covering the bottom to a depth of an inch or more! The population density can be extremely high with millions of them scattered over the ocean floor.

The central disk is about 3/5ths of an inch in diameter and the arms may be 3 1/2 inches long. Each arm has long spines extending along the margin, and tube feet (like sea stars). They feed on plant plankton and organic matter captured by the arms, which they extend out of the cracks and crevices, and often from kelp holdfasts. One of the things I love about these brittle stars is the range in coloration. They may be orange, brown, tan, yellow or green and exhibit various patterns. The colors are reportedly derived from the carotenoid pigments in the plant plankton they feed on. However, I do have to wonder why one sees different colored Ophiothrix in the same site since they should be feeding on the same munchies. Perhaps there is also a genetic component to their individual fashion sense!

The presence of thick mats of these brittle stars on the offshore oil rigs was interesting. Of course this current swept habitat would provide a veritable smorgasbord of plant plankton drifting by at any time of the day or night. Munching would not be a problem there. However, there were relatively few hiding places for them, mostly within the encrusting invertebrate growth that dominated the rigs. Billions and billions of them were in the open, and therefore exposed to predators. Perhaps the thing that saved them was the relatively low numbers of fish predators such as sheephead or rock wrasse. After all, there is strength in numbers... a fact that schooling baitfish know very well!

© 2011 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Masses of the brittle star Ophiothrix spiculata on white anemones and a scallop shell;
one on my glove and another falling from the oil platform (it landed safely).

This document maintained by Dr. Bill Bushing.
Material and images © 2011 Star Thrower Educational Multimedia