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Dive Dry with Dr. Bill

#563: Wasting Away

No, not me... my Buddha belly is still quite ample unfortunately, and I'm not talking about the lyrics in Jimmy Buffet's "Margaritaville" that I hear on karaoke nights at El Galleon. Friends have been reporting the death of sea stars (known as starfish by the less politically "correct" people like me) all along the West Coast from Alaska to Orange County. There are also reports of them dying along the East Coast and elsewhere around the globe as well. Mass deaths of sea stars and sea urchins are often associated with warm water events like El Niños, and I've observed them during the events of the late 1970s, late 1990s and especially the massive El Niño of 1982-84.

Echinoderms like sea stars and sea urchins have external skeletons made of calcium carbonate (CaCO-3). This mineral has a very interesting relationship with changes in temperature and pH. Most chemical compounds increase in solubility as water temperature increases, but calcium carbonate is different. Its solubility increases with colder temperatures. This is one reason coral reefs are in the tropics and not found in cooler waters like ours. Warming of the ocean should favor the formation of the echinoderm exoskeleton. However, the global ocean is also becoming more acidic too, and such changes in pH may increase solubility.

During 2006 we had a period of highly elevated water temperatures here off Catalina. Surface temperatures were in the upper 70s for weeks and most of our giant kelp died off. During this warm water episode I also observed and filmed large numbers of sea urchins that died, leaving nothing but their skeletons ("tests") behind. We refer to such occurrences as mass wasting events.

But is temperature the reason for the current wasting event in sea stars? While local water temperatures are still quite comfortable for this time of year, they aren't really that unusual and this is not an El Niño year. However, increased temperature itself is probably not the direct cause for the wasting disease. Increasing water temperature also promotes the growth of certain pathogens like bacteria. I learned that lesson well while diving in the tropical waters of Fiji as Jean-Michel Cousteau's guest at his resort near Savusavu. Rather than use my own fins, I put on some of the resort's full foot fins. They were too small and caused open sores on both my feet which quickly became infected with tropical bacteria. Fortunately I usually travel with the antibiotic Cipro and it quickly cleared up the nasty infection.

Bacteria are believed to be a primary cause of the mass wasting events in echinoderms as well. These bacteria are often members of the scientific genus Vibrio which also infect fish such as our local blacksmith. At least ten species of sea star have been affected along the West Coast with sunflower stars, ochre stars and bat stars among the most frequent victims. Lesions form on the body, become infected and rapidly progress. One scientist observed the two halves of an infected sea star literally crawl away from one another.

Death can occur very quickly with sea stars losing all their arms within seven hours. When healthy, they can regrow lost arms but those affected by the wasting disease are not able to. When infected with the wasting disease, a sea star can go from perfectly normal to completely decomposed overnight, turning into a glob of white goop.

The current mass wasting event is unprecedented in that it covers a very wide geographic range. Up in Vancouver, British Columbia, species of starfish that covered the ocean floor last year are now almost totally absent. Dr. Pete Raimondi at U. C. Santa Cruz, who is coordinating a large part of the investigation into this event, believes the loss of sea stars could potentially be in the millions. Heck, when you look up in the sky with the naked eye you can only see about 7,000 visible stars out of the billions and billions Carl Sagan commented on.

Starfish can be very important members of a marine ecosystem. Diving at depths greater than 100 feet around the island, one can see almost uncountable numbers of bat stars that feed on dead organisms, keeping the bottom clean. The ochre starfish is an important predator keeping mussel populations from overwhelming reefs and pier pilings. It has been referred to as a keystone species because of its significant ecological role. The loss of millions of sea stars could impact our marine ecosystems for decades.

So far I have not observed any evidence of wasting in our local sea stars. If you observe diseased or dead sea stars in our waters, please help collect data by noting the date, the island location, the species involved and the symptoms noted and report it to the UCSC group collecting this data (http://www.eeb.ucsc.edu/pacificrockyintertidal/data-products/sea-star-wasting/index.html#track-disease) or notify me by e-mail (bushing@post.harvard.edu) and I will report it. This disease may be comparable to having every California resident living near the ocean going out and collecting a single sea star each from our tidepools and beaches.

© 2013 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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Sunflower star, ochre star, bat star and unidentified sea star affected by wasting disease (photo courtesy of Bruce Bray)

This document maintained by Dr. Bill Bushing.
Material and images © 2013 Star Thrower Educational Multimedia