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Dive Dry with Dr. Bill

#450: Death by "Demonic" Acid?

My Sea Trek monitoring has taken me to Descanso Bay frequently this summer, but not to enjoy the benefits of buffalo milk on the beach and lovely ladies in bikinis. It's all work, no play for the good doctor! However, with the warming of our waters and the great visibility, it has been very nice to cruise over there in Tim Mitchell's yacht (er, I mean skiff) to take the water samples and dive to clean the light sensors. Reminds me of the days when I owned my own boat, the 30 ft St. Pierre dory Agape (named after one I saw in the Greek islands). Sadly that vessel sank shortly after I put half a year's salary into rebuilding the engine, tricking it out and (gulp) renaming it the Eleutheria (the Greek word for freedom). At least I still had Toyon's old launch, the K.V., to conduct my classes with and take my students diving. Ah, the life of a sailor (er, stinkboat captain)!

Last month, while suiting up on the Sea Trek float to dive, I noticed a sea lion hauled out on the beach. Many of the beach's patrons were closing in on it to take pictures. Please remember that harassment of marine mammals is defined as interfering with or altering the behavior of the animal. Of course it is human nature to be curious. According to those who had closer encounters with this pinniped than I did, it appeared to be sick with signs of disorientation. Two days later I was diving there again and located a dead sea lion lying on the bottom in relatively shallow water. The following day I had to relocate one of the light sensors and took my high definition video rig out to film it. There were no signs of injury, either by shark or boat propeller. The only thing I noted was that scavengers had already taken the eyes and nibbled away at the rear flippers, nostrils and ears. Interestingly, the carcass had disappeared a few days later. Hmmm.

Given the lack of obvious injury, and the reported behavior of the sea lion on the beach, I suspect this animal may have died of domoic acid poisoning. Wikipedia defines domoic acid as "a kainic acid analog, heterocyclic amino acid." Now I was a chemistry "major" in high school and won the American Chemical Society award, but had to do some research to find out what all this meant. Kainic acid is a natural acid found in certain marine algae. Wikipedia further confused me by calling that "a specific agonist for the kainate receptor used as an ionotropic glutamate receptor which mimics the effect of glutamate." Heck, as an 8th grade I won an Outstanding Award at the Illinois State Science Fair for my work with amino acids, but those brain cells must have been wiped out by my advancing age! Let's simplify things a bit for my readers (not to mention for me!).

The Japanese isolated domoic acid from a red alga known as Chondria armata back in 1958. That seaweed is known from tropical and subtropical waters of the western Pacific and Indian Oceans, but is not found on our West Coast. However, domoic acid is also produced by the microscopic diatom Nitzschia navis-varingica and others in the genus Pseudo-nitzschia. Just in case you were wondering, diatoms are largely what encrusts the salt water toilet bowls on our island if we don't keep the lid down to prevent light from reaching them. Yep, that's one argument for putting the seat and lid down that I can agree with! Don't worry though, these diatoms are not a threat to your health as you peruse your favorite reading material!

Diatoms are also at the base of food chains in the marine environment. These tiny "munchies" are filtered out by shellfish and eaten by plankton-feeding fish including anchovies and sardines. Like DDT or mercury, domoic acid is bioaccumulated up through the food chain. That means that for each level we go up (via predators and scavengers), the concentration increases. While the domoic acid may not hurt the fish or shellfish that initially consume the diatoms, it does increase in their tissues. When another critter such as a sea lion decides to munch on a school of baitfish, they acquire an increased load of this toxin which can then be amplified enough in their bodies to cause harm or even death.

Domoic acid is a neurotoxin that causes short-term memory loss and brain damage, and thus impacts behavior in those animals affected by it. I don't eat sardines or anchovies, much less sea lions, so that can't explain my problems (nor can my psychiatrist)! It may also cause seizures and tremors. The areas of the brain that are most affected are the hippocampus, which is important in movement and navigation, and the amygdaloid nucleus, associated with memory and emotion. The damage is caused by excessive amounts of calcium entering the brain cells, which causes the cells to die.

The diatoms most likely responsible for producing the domoic acid in the first place are naturally occurring, as is domoic acid itself. It is only when these diatom species bloom, increasing in great numbers, that they truly pose a problem for our ocean's food chains. Such blooms can occur naturally when important nutrients or other conditions for the diatoms are optimal. However, there is a growing body of research that strongly suggests blooms are also formed along populated coastal regions due to anthropogenic causes such as pollution and nutrient runoff. They appear to be increasing in frequency and extent. Sadly, incidents of domoic acid poisoning in marine mammals are as well.

I hate to leave my readers on such a sour note, especially during such a gorgeous summer. While navigating through the mooring's in Tim's skiff, I occasionally called out to the owners of the larger yachts in our harbor asking if they wanted to trade. I was sure I could placate Tim by offering him the yacht's dinghy. Now one group of three gentlemen responded positively... but I had a feeling they had consumed one too many "adult beverages" already (and it wasn't even midday!). The lovely ladies in bikinis sunning themselves on the decks took one look at yours truly and "his" vessel... and turned the other way. Sniff.

© 2011 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. 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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Image of Pseudo-nitzschia diatom (credit: NOAA), chemical composition of domoic acid (Wikipedia);
dead sea lion in Descanso Bay with forensic expert Gary Garibaldi inspecting it.

This document maintained by Dr. Bill Bushing.
Material and images © 2011 Star Thrower Educational Multimedia