Dive Dry with Dr. Bill

#687: Death by Starvation?

Death is nature's way of mixing up the gene pool and helping to ensure new genetic combinations are available to increase adaptability of a species to changing conditions. Not always a pleasant thought for human beings as their post-reproductive years progress. Fortunately our species also benefits from the wisdom of age by keeping old geezers like myself alive to counsel our progeny.

Now I don't believe most marine critters contemplate their potential afterlife, but I could be wrong. Certainly they can exhibit what appears to be human-like fear as a potential predator lunges at them. But during times like this, with the sad ecological disruptions in our kelp forests, death may be slow and not easily anticipated.

Many months ago I expressed concern that the absence of giant kelp was substantially reducing the food supply for herbivores like snails. My specific concern was for our abalone, still recovering from the withering syndrome that hit them back in the 1980s. Many divers have had the thrill of extending a blade of giant kelp toward an abalone and having it reach out its "tongue" (OK, really its foot) or pounce on top of the tasty morsel.

But there has been very little giant kelp (Macrocystis pyrifera) in the dive park the past 18-20 months. With their primary food source dwindling, I could coax at least the green abalone to take the horrible tasting devil weed as a less palatable substitute. Until it begins to die, the devil weed doesn't really slough off much of nutritional value. Even when it dies off at the end of its annual life cycle, most of it drifts away at the surface where the abalone can't reach it.

Over the past few months it is hard to see anything through this thick algal invader. However, I've clawed my way to the bottom to observe what was happening near the surface of the rocky reef. I've seen a number of abalone shells lying on the bottom. Some were youngsters while others were mature and of reproductive age.

Without a nutritious food source animals begin to decline. With humans fat tissue may serve as a reserve for a while (I'm in "good shape" for that), but if the absence of healthy food continues muscle and other tissues are also consumed and the body weakened. Abalone don't have a lot of fat on them. As they begin to starve it is often the reproductive organs that are reabsorbed first, rendering them sterile.

When primary food supplies are low for long periods of time, muscle tissue gets reabsorbed and the critters weaken. Abalone (Haliotis spp.) need their strong muscular foot to hold tight to the rocks and prevent predators (including nasty poachers) from taking them. They are more vulnerable in this condition and if it continues, may die altogether.

Recently I've been witnessing what might be another native snail's demise. The wavy top snail (which has gone by several scientific names in my lifetime including Astraea undosa, Megastraea undosa and Lithopoma undosum) also loves juicy giant kelp. It normally feeds at night when shell-cracking predators like big male sheephead are snoozing.

I've seen a number of empty wavy top snails on recent dives. The ones whose shells are broken most likely met their demise in "death by sheephead" during the day. Others whose shells are empty but intact may have fallen victim to octopus. It is quite possible without their primary food source they, too, had weakened muscles and couldn't cling to the rocks tight enough to survive. They may also have starved to death.

It is especially difficult to see the abalone dying. When I first arrived on the island in the late 1960s they were so plentiful despite harvesting that I never thought they could possibly disappear. Then when the withering foot syndrome hit in the 1980s they declined sharply. In recent years they had been making a slow comeback, but now starvation may be decimating them again.

© 2016 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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Shells of young dead abalone and mature green abalone; empty shells of wavy top snails.

This document maintained by Dr. Bill Bushing.
Material and images © 2016 Star Thrower Educational Multimedia