Dive Dry with Dr. Bill

#377: The Spiny Sand Star

It's pouring rain as I write this column, so the only way I'm going to get wet this weekend is to walk downtown. Yes, I'm a fair weather diver. We need the rain to fill the reservoir and I've got editing to do on my two video submissions for the Long Beach SCUBA Show film festival coming up in May. If you are interested in diving and have never attended it, you should... it's the largest such show in the country for SCUBA enthusiasts. I find it a great way to reconnect with diving friends from all over the country, and also love the wealth of information on dive travel opportunities. Even with the specials offered due to the downturn in the economy and travel industry, I'd still have to rob our local bank a few times to complete my "bucket list" of dive destinations. Of course I'm still looking for that lovely and intelligent mermaid with a dive boat... and trust fund!

Dr. Bill, get to the point... what's the subject of this week's column? Oops, sorry. I thought I'd focus on one of the critters I encountered during last weekend's harbor clean-up dive. I'm referring to the spiny sand star (Astropecten armatus). As a kelp forest ecologist, I spend most of my time diving rocky bottoms which provide kelp with a point of attachment. One rarely finds kelp over sandy bottoms, although I have seen such forests off Yellowtail Point and Torqua Springs, and they exist off Santa Barbara as well. Soft bottom environments are a completely different habitat requiring quite unique adaptations for survival.

This species of sea star, formerly known as starfish, is gray to tan in color, occasionally with hints of rose. Individuals may reach six to nine inches in diameter. The disk's upper surface is covered with elevated, granular plates known as paxillae, each with a cluster of spines on top. The five arms are all bordered with plates and spines.

The sand star is rarely seen exposed on the surface, so I was quite fortunate in finding this one. They usually burrow under the sand to search for their prey, and as a means of protection. When I first located it, this one was still covered with sand. Most rocky bottom critters aren't capable of boring through their substrate (although some clams, sea urchins and others do). However, many sandy bottom species are adept at burrowing in these dynamic habitats.

My readers are most likely familiar with the suction cups found on the ends of the tube feet on most starfish (er, sea stars). You won't find them on the sand star. It is close to impossible to use suction to adhere to tiny grains of sand, although they work well on the rocky reefs where other species are found. An additional adaptation to sand is that the arms are pointed which also assists in movement on the soft, shifting surface.

If a sand star were to dine at a fine restaurant (or even the ones I frequent), what would be on the menu? One delicacy (or is it more like a staple?) would be escargot... the purple olive snail that also burrows under the sand. It is reported that the sand star can detect these molluscs from a distance, approach them quickly and trap them with its arms. The snails are swallowed whole, digested internally and the empty shells discarded through the mouth. You can invite me to dine on escargot any time I'm not like them and because I'm not like them... I pull the snail from the shell so I don't have to spit it out. Sand stars also feed on other snails, sea pansies, their distant cousins the sand dollars and even dead fish.

Scientists are still a bit confused about this species of sea star, so you're allowed to be too. Some recognize it as existing from San Pedro to Ecuador at depths from the lower intertidal to 180 feet. I found mine at just 10 feet. They identify a second species of sand star, Astropecten verrili, whose geographic distribution ranges from Point Reyes, California, to Baja California, Mexico, in depths up (down?) to 1,600 feet. You can bet I'm not sampling any there! Other scientists believe the two are the same species. Perhaps it's time for a little DNA testing?

© 2010 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM 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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Sand star at surface still covered with sand, central disk without sandy coating;
spines and regenerating arm and sand star reburying itself.

This document maintained by Dr. Bill Bushing.
Material and images © 2010 Star Thrower Educational Multimedia