Dive Dry with Dr. Bill

#170: 'Tis the Season of the (Bat) Star

I violated many of my safety principles two weekends ago when I dove to capture the images for this week's newspaper column. As long-time readers know, after a serious OOA (out of air) incident a few summers ago, I have always dived with my pony bottle for backup. Recently it went out of date before I realized it, and can't be filled legally. By the time you read this, I will have replaced it with a slightly larger bottle so I can keep writing these scintillating columns for your reading delight!

The second "rule" I violated was not diving deep (past 100 ft.) without a buddy. When I descend into the realm where nitrogen narcosis may cloud my already feeble judgment, I feel better if there is a buddy there to "sober" me up and bring me back to reality (especially if she is pretty... oops, I said reality!). I don't seem to get narcosis to any significant degree, but the deeper I go, the greater the possibility. The King Neptune was anchored at Ship Rock in 150 ft of water. All the other divers on board were instructors or their students so there was no one to buddy up with.

Taking a calculated risk (ok, so I just used my abacus and not my Pentium computer), I descended to the base of the Ship Rock pinnacle. I was looking for two species which eluded me, perhaps because it was a bit dark and I didn't want to waste my video light battery. Instead I observed a field of beautiful bat stars that covered the bottom between 110 and 133 ft. This turned out to be the deepest dive I've ever done in Catalina waters... at least as far as I can remember (dives in the 60's don't count because I was there, kind of... just kidding). Given that Christmas is just a few days away, these beautiful starfish or sea stars make an appropriate subject this week.

The BBC states that they are the most common sea star on North America's West Coast. I often encounter numerous bat stars in the colder waters of the northern Channel Islands. They are more rare here, so seeing so many at once was a great surprise. I see only a few small ones in the dive park each year, and they are almost always orange in color. The bat stars at Ship Rock had more varied hues that were only brought out when I turned on my video lights since reds and oranges don't penetrate to such depths.

Bat stars are known from Sitka, Alaska (brrr) to Cedros Island off Baja, and are more common north of Pt. Conception. They can be found in the intertidal, on rocky reefs and sandy bottoms down to nearly 1,000 ft (won't "go there!"). They lack the spines and pedicellariae of the fragile and knobby sea stars. This species may reach a diameter of 8" or more. It differs from many sea stars in that there is webbing between the arms. They usually possess five arms, but may have between four and nine. I have observed that most bat stars seem to raise the tip of their arms slightly and move with some of their tube feet extended. This probably allows them to chemically sense or touch things as they approach them.

These starfish feed on a variety of plant and animal material, living or dead. Because of their varied diet, they are referred to as omnivores (like me) and scavengers (unlike me). I found several feeding on algal detritus. They do so by extending their stomachs out of the body to engulf the food like many other sea stars. Many invertebrates that show a flight reaction to other predatory starfish do not react when a bat star is near.

When they encounter one another, bat stars may engage in gentle fisticuffs, pushing one another with their arms, or a form of arm wrestling in which they pin the other's arm to the bottom with theirs. Imagine arm wrestling with up to nine arms! This seems to space these individuals out and affects the area they can successfully feed in without fighting (batting?) one another. Perhaps humans should space themselves further apart to ensure Peace on Earth... at least in the large cities on the "Big Island" across the San Pedro Channel.

Bat stars apparently mate throughout the year (another similarity with yours truly), but may peak from May to July (unlike me). Ripe individuals release their eggs and sperm into the water so fertilization is outside the body (no comment). The eggs and larvae may disperse with ocean currents. Based on my observations it appears that they may settle in shallower water and then work down to deeper water as they grow.

For those of my readers who celebrate the Christmas holiday, these beautiful bat stars are quite appropriate for this weekend. For those who celebrate Hanukkah, you will notice I did find a six-sided "Star of David" bat star as well. I must admit I was not as successful trying to locate appropriate symbols for my Buddhist, Muslim, Hindu, Scientologist and heathen friends (oh, wait, I did find an empty wine bottle for the latter). I hope all of you will celebrate your respective holidays in your own tradition as is granted us by our guarantee of freedom of religion.

© 2005 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. Look for my new DVD on the giant sea bass to be released in January.

The "Christmas" bat star and the "Star of David" bat star; two bat stars fighting
(not in the spirit of the season) and the stomach of a bat star extended
outside the body to feed (always in the season!).

This document maintained by Dr. Bill Bushing.
Material and images © 2005 Star Thrower Educational Multimedia