Dive Dry with Dr. Bill

#584: The Easter Hare... Er, Bunny

This Easter I expected one of three different kinds of Easter bunny to magically appear... a milk chocolate one, a stuffed and fluffy one or one like Hugh Hefner had surrounding him back in my hometown of Chicago (before he moved to the mansion here). Yes, I'm well past the stage of Easter egg hunts (although my granddaughters aren't) and don't actually celebrate it as a religious holiday either. I guess I'm something of a heathen even though I like many of the teachings and try to follow the Golden Rule common to many religions. I do think back to my childhood when Mom & Dad would sometimes get us ducklings or bunnies. Strange thing is they all disappeared once they grew up... and months later we were "treated" to some unusual meals of duck or rabbit. At that age we had no idea we were consuming our former pets.

My parents (and the neighbors) didn't mind as much when I kept snakes, turtles, butterflies, beetles, mice and other wild critters in my cages. I even created a zoo in our garage and charged my neighbors five cents to see the animals... back when a nickel was a small fortune for a kid. I don't keep pets today since I like the freedom to travel on the spur of the moment. I've found a great alternative... all my current pets reside in the waters surrounding Catalina Island. They feed themselves (and our visitors pay to feed them too), and I don't need a pooper scooper!

In keeping with the holiday I thought I'd write this week's column about a strange form of "rabbit," the California sea hare (Aplysia californica). They are called sea hares because their antenna-like rhinophores look like rabbit ears (at least to amateur biologists). Like terrestrial "bunnies," these snails feed on plant material. They just love seaweed salads. No meat in their diet, they are strict vegans. I tried that once and lost too much weight. Hmmm, maybe I need to try it again to get rid of my VET (Video Editing Tummy) aka Buddha Belly.

Now vegan critters, also known as herbivores, are often desirable prey for my kind of critter, the carnivore. Food chains begin with seaweed that converts sunlight into carbohydrates and other chemical energy. This gets munched on by herbivores such as sea hares, cows or deer. Then along comes a first or second level predator that finds converted grass (or seaweed) very tasty. To ensure they survive, animals need to develop defenses against the predators that feed on them.

Nudibranchs, the beautiful shell-less snails that often have incredible coloration, are relatives of the sea hares. Many nudibranchs have unique ways to prevent carnivores from carving them up for din din. Some simply don't taste good, and a fish that ingests one may spit it out immediately. As a child, I discovered that canned peas have a similar defense mechanism. I would hold them in my mouth like a chipmunk and ask to go to the bathroom to spit them out in the john. My parents got wise when I had to go to the toilet a dozen times during dinner. Of course you landlubbers all know that monarch caterpillars eat poisonous milkweed plants and birds avoid them because of the toxins they ingest.

Other nudibranchs munch on relatives of jellyfish like hydroids that have stinging cells known as nematocysts. Somehow they prevent the stinging cells from triggering while eating them. They then incorporate these cells into their own skin and use them to sting unsuspecting predators. Ever have a yellow jacket sting your tongue? I did the first week I arrived on Catalina when I went to take a sip from my soda can. Very effective defense!

Like nudibranchs, Aplysia has no outer shell for defense and their seaweed diet doesn't have stinging cells. However, a while back I discovered that our California sea hare does something rather unusual with its food to establish a defense mechanism of its own. I'm guessing these critters must have quite a background in chemistry. Sea hares release a red ink when threatened by a crab, lobster, garibaldi or careless diver. Researchers at the Tokyo University of Marine Science and Technology sampled this ink and tested the various compounds in it.

Now critters like squid and octopus release a black or brown ink that temporarily blinds their predators so they can escape. The sea hare's ink has a chemical in it known as aplysioviolin (APV). Sounds like something my dive buddy Karen Elaine or future dive buddy Yap Shu Mei might play in an orchestra. But no, it doesn't make beautiful music or even blind potential munchers. This chemical defense is created from a pigment in their red algae food known as phycoerythrobilin. The APV interferes with the senses of crab predators which apparently find it highly offensive.

To make things even more interesting. There is a second component to the fluids released by the sea hare when threatened. It is not in the red ink, but in a whitish component known as opaline. This compound causes hungry lobsters to forego a taste of the sea hare and begin grooming and other behaviors instead. So different chemical constituents created by the sea hare defend against different species of predators. Better living through chemistry... and they didn't even have to take Harvard's notoriously difficult Organic Chem class!

© 2014 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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Three types of Easter bunnies and a baby California sea hare on a blade of kelp;
sea hare head showing rhinophores and red ink used for defense.

This document maintained by Dr. Bill Bushing.
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