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Dive Dry with Dr. Bill

#507: With Spines... or Not With Spines?

Last month while filming giant sea bass with the crew from Japan Underwater Films (JUF) for a documentary to appear on NHK, Japan's public television station, the director (Nobu) wanted to film sequences of the good doctor at work in his office. That's me in case you were wondering. Now, of course, I wear a suit to work almost every day... it's part of the dress code at my office. Yes, I'm referring to a wetsuit (but no tie)... and my office is 60 feet under or thereabouts.

The sequences were to be filmed at Goat Harbor on the relatively shallow sandy bottom before we dropped down to look for the gentle giants. Since I'm a kelp forest ecologist, I prefer working around the rocky reefs and ocean floor where our giant kelp forests develop. Over the sand I had to look for interesting critters that I could observe intently and film in front of the JUF cameras. That's not always easy because many sandy bottom dwellers bury into the sand and aren't very visible.

During a dive there earlier that week I had been surprised to find lots of spiny sand stars out on the sand. I had never seen so many in the open even when I dive Avalon Bay during the annual Underwater Cleanup. One of the few places I've dived that they were abundant was over the shallow, sandy slopes of La Jolla Shores. They also frequent muddy bottoms... which I avoid like the plague due to generally poor visibility. Kelp does too due to the possibility of the young sexually reproducing plants getting buried. Yes, giant kelp reproduces both sexually and with spores.

This starfish (or sea star for the PC crowd) is either Astropecten armatus or A. verrilli according to some scientists, but others believe the "two" are the same species. I'll leave that determination up to the marine biologists who sit day and night in their lab drinking Starbucks and studying the number and structure of plates, spines or tube feet; or extract their DNA to compare it with that of other sea stars to determine the "correct" ID. Of course regardless of whether physical characteristics or genetics are used, it is still a human judgment call... I'm sure the sea star already knows the answer after a long search for its own identity.

Whatever its true name is, the sand star is gray in color and sports five arms that are bordered with plates and spines. The spines are not sharp. One distinction suggested is that A. verrilli does not posses spines whereas A. armatus does. I think that would be a substantial distinction! Spiny sand stars reach a diameter of about five inches (although objects do look larger underwater!). Unlike starfish from rocky areas, they do not possess "suction cups" on their tube feet. Trying to stick to a grain of sand rather than a solid rocky reef to move forward would be a difficult proposition. However, they are quite capable of moving on top of the shifting sand... or even plowing under it in search of prey or to hide from predators.

Their primary food, like that of many sea stars, consists of escargot... snails, especially the purple olive (Olivella). They don't dip them in butter and garlic though like the delicious ones I ate at the Drake Hotel in Chicago thanks to Packy Offield's mom. These snails are (gasp) swallowed whole! The empty shells are ejected out through the same opening that serves as both anus... and mouth. If they need a more varied diet, these sea stars will munch on sea pansies (Renilla kollikeri), sand dollars or even dead fish.

In addition to Goat Harbor and La Jolla Shores, the spiny sand star may be found from San Pedro south to as far as Ecuador. Although the ones I observed were in fairly shallow water (20-30 ft), they may range from the lower intertidal to depths of 180 ft, although I don't remember seeing them several years ago when I was routinely diving as deep as 200 ft. If A. verrilli is a separate species, its range is from Point Reyes to Baja, thus placing its distribution north of A. armatus. The depth range for this presumed species is believed to be about 1,500 feet. I won't dive there... wouldn't be prudent!

© 2012 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. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). 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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Astropecten covered with sand and one nearly clean; spiny sand star moving across bottom
and one doing morning calisthenics.

This document maintained by Dr. Bill Bushing.
Material and images © 2012 Star Thrower Educational Multimedia