Dive Dry with Dr. Bill

#279: The Sunflower Starfish

It has been some time since I last dove the northern Channel Islands. In the past I've dived all of them... Anacapa, Santa Cruz, Santa Rosa and even remote San Miguel. Most of my diving off our "sister" islands was in the days I taught at UCSB and was a member of the UCSB Scuba Club. Thanks to my membership, I was able to get a 50% discount on the Truth Aquatics boats, among the best in our region.

I miss the northern islands. Their colder, more nutrient rich and productive waters have a number of species we don't see down here in the toasty southern Channel Islands. Others are much more abundant up there than here, or found at shallower depths than we see them off Catalina. I would love to go back and spend a few weeks gathering footage there with my high definition camcorder.

One species I see fairly commonly up there, but not down here, is the sunflower starfish. Although it is known from Alaska to San Diego, and even into Baja according to some sources, it is not considered common below Monterey. In the northern part of their range they may be found in the low intertidal, and down to depths of 1,450 feet although most are found no deeper than 400 feet. Of course that's well outside my diving range, at least until I get my own bathyscaph! They can live on rocky or soft bottoms.

These are truly starfish on steroids, reaching total diameters exceeding three feet. This is the largest and heaviest of the Pacific coast starfish, weighing up to 11 pounds. Their color varies from pink to purple to brown but may also be red, orange or yellow as well.

Baby sunflower stars are much more similar to their other starfish relatives, and have only five arms. However, as they grow, the adults begin adding new arms until they have 20 to 24 of them. I guess they just need to count higher than the young 'uns. These arms help them trap food that includes sea urchins and sand dollars, clams and mussels, chitons, snails, worms, hermit crabs, crabs, sea cucumbers, dead or dying squid, fish and even some of their starfish relatives. On our West Coast, sea urchins make up 21 to 98% of their diet.

Although they can evert their stomach, extending it outside the body cavity like many other sea stars if necessary, they are able to swallow most prey whole. Most starfish have rigid exoskeletons, but that of the sunflower star is composed of a few unconnected plates which allow them greater flexibility and enable them to open their mouths wide to swallow larger prey. That would also be a benefit if they ever had a toothache, but they don't have teeth.

Like other starfish, they may regenerate arms which are broken off or eaten by predators which may include king crabs or sea otters up north. When an arm is broken off (autotomized), the injured starfish releases chemicals into the water as an alarm to warn other sunflower stars in the area which then flee. Since these sea stars have few predators, their population is limited by food rather than by predation. Sunflower stars also use their many arms in a form of combat when they encounter another of their species.

An individual sunflower star may have over 15,000 tube feet, the little leg-like structures that allow them to grip onto food... or onto the bottom substrate. They are capable of moving across the bottom at up to 10 feet a minute, which is fast for an echinoderm, but makes them competitors for the tortoise rather than the hare. They are capable of moving along the bottom for distances of nearly two miles.

Male and female sunflower stars look alike externally. Eggs are produced from December through June, although some sources report March through July. They fertilize externally by broadcasting sperm and eggs into the water. When they spawn, they may stand up on the tips of their many arms to release their gametes higher above the bottom. The larvae are pelagic, drifting with the ocean currents and feeding on other plankton. Unfortunately, Catalina does not appear to be on their list of destinations. After 9-10 weeks they settle onto the substrate to begin their benthic or bottom-dwelling stage.

© 2008 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 "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles," "Gentle Giants: Giant Sea Bass," "Common Fish and Invertebrates of the Sea of Cortez" or the new "Sharks and Rays of Southern California" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

Images of the sunflower star on the rocky reefs of the northern Channel Islands.

This document maintained by Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia