May 1, 2014 | 1
Male octopuses don’t usually wine and dine prospective mates. But prior to mating, both males and females do seem to be in the mood for one date-worthy food: crab, according to new research published online in the Journal of Shellfish Research.
Scientists studied two-spot octopuses (Octopus bimaculatus) in the Bay of Los Angeles in the Gulf of California in Mexico for nine months to see what they were eating—and when.
Studying octopuses’ dietary preferences, however, can be a tricky endeavor. Scientists have long relied on counting and classifying shells and bones in an octopus’s stomach or around its den. But as the researchers of the new paper point out, “only prey with hard pieces can be identified.” In the case of ingested animals, the identification is often hampered because “the mechanical action of the beak” breaks down many would-be calcified clues. And for crustaceans, such as large crabs and lobster, the octopus can pre-digest the animal tissue inside the exoskeleton before slurping it out—leaving the traces of that meal to be carried away by the currents.
The other option is to send scientists down below the waves to observe octopuses actually consuming their dinners. This “gives a better approximation to the feeing habits,” the authors note. But it is of course a bit costly.
So these researchers took a mixed approach and did all three. They captured 261 two-spot octopuses during the study period. The ready-to-lay females were the biggest, measuring up to nine and a half inches and weighing up to seven and a half pounds.
For the final analysis, the researchers found traces of prey from 76 different animals. It turns out that octopuses like to feed on their own (broadly defined) kind, with mollusks being among the most common prey. Arthropods (such as crustaceans) were also common, as were bivalves (including clams, hold the casino), echiura (spoon worms) and gastropods (think escargot). The favorite octopus meals in this study were mud crabs (xanthidae) and chocolate clams (Megapitaria squalida). In the springtime, the mud crabs dominated these octopuses’ diets, the researchers report. And male’s chose more clams as their secondary food whereas females went for the worms.
Growing octopuses preferred bivalves. And ready-to-lay females were the most likely to be expanding their diet to include more fish, echinoderms (such as starfish and urchins) and, yes, other octopuses. The ability to target specific animals as a “specialist predator,” the researchers note, “can be a function of the octopuses’ ability to learn individually and which prey are more available or found more easily during foraging.” And in the Bay of Los Angeles, these octopuses are presented with plenty of prey options. So, their preference for good, meaty meals makes sense, the authors continue. “When food density is high, predators specialize on good-quality prey and ignore prey with lower food value.”
But octopus food choices aren’t just a curiosity. In addition to helping us learn what to feed these animals in captivity, “octopuses play an important role in the marine environment as both predators and prey,” the authors note. And understand another piece of that complex web is an important step in helping to preserve it.
Learn more about how octopuses tidy up after their feasts–and often take home food for later–in Octopus! The Most Mysterious Creature In the Sea.
Illustration courtesy of Ivan Phillipsen