Free Octopus by Roland C. Anderson Page B

deciding whether this hermit crab or that snail was worth a try. Besides, they were gaining weight. But while hunting, their appearance was disguised and they were always looking for predators. One false move and they would be prey themselves.
    Part of the wide choice of prey species may be because of octopus energetics. Unlike homeotherms, such as mammals that keep their bodies heated and spend a lot of energy doing so, octopuses are poikilotherms: their metabolism slows down in cooler water, and they become less active and waste less energy. A major amount of an octopus’s energy can be spent on digestion, so energy expenditure for foraging may loom less large in their energy equation. They don’t have to eat regularly just to keep going. In the lab, our healthy young pygmy octopuses didn’t eat anything at all some days. Octopuses are so efficient at converting food calories to body weight that energy output may be a smaller part of their daily budget than it is for us.
    Every researcher has found prey species that their octopuses wouldn’t eat. Two-spot octopuses from California and the day octopus of Hawaii wouldn’t touch one species of top snail; giant Pacific octopuses didn’t eat hairy crabs; and Bermuda common octopuses seldom touched chitons. Perhaps the answer to this issue is preference; we don’t know.
    Eat or be Eaten
    If predation limits octopus foraging time and food intake, maybe keeping an octopus with predators would cut down on both its time out hunting and the weight of crabs it consumed. In Hawaii, I tried to test for this predator influence. I kept two Hawaiian day octopuses at a time in a small outdoor saltwater pond and gave them lots of crabs as prey. As ten days passed, the crab supply got depleted and the crabs got more wary. The octopuses hunted longer and caught fewer of them. When I put a moray eel predator in the pond with them, the octopuses did not limit their foraging time as they should have if they were wary of the predator. Maybe the pond was too small for them. Maybe it was because octopuses don’t stay in one territory in the ocean, and if they have no place loyalty, they could just leave if a predator menaces. And maybe it’s because moray eels hunt by sneaking in and around the rocks, so not going out wasn’t going to help the octopus. This is a good example of the researcher’s lament: find the answer to one question and it raises two or three more.
    â€”Jennifer A. Mather
    Prey species have evolved many ways to avoid being caught by octopuses. Many mollusks count on their protective shell to save them from predators. While providing some resistance, the shell doesn’t stop predation by a variety of animals. Scallops can swim away by clapping the valves together, a successful method for avoiding capture by slow sea star predators but not for avoiding the jet-propelled grab of an octopus. The fragile-shelled, scalloplike file clam hides in crevices; scavenging wrasse can’t get them but they are vulnerable to the common octopuses with its flexible arms. Octopuses normally hunt by feeling around in the landscape, with touch and chemical receptors in their suckers probably helping them recognize sources of prey. The approach is an effective one. We timed common octopuses in Bermuda, and it took five minutes for them to snake an arm into a crevice, capture the prey, throw away the shell, and start to digest the meat.
    Crabs, being mobile, are a tougher challenge for octopuses to catch than the slower snails and often immobile clams. If you lift a rock, crabswill scrabble out from under it and hide under one nearby, and when you pick up the second rock, they will scurry back under the first rock. Foraging common octopuses and Hawaiian day octopuses are often trailed by wrasse and other fishes as they move across the bottom, and perhaps the fish are planning to eat the small animals escaping from the octopus’s menace. We watched a