Into the Great Wide Ocean by Sönke Johnsen

Author:Sönke Johnsen
Language: eng
Format: epub
Publisher: Princeton University Press
Published: 2024-07-24T00:00:00+00:00

The Paddlers

There are a large number of oceanic animals that paddle (i.e., push) their way through the ocean. These include crustaceans (shrimp and shrimp-like animals), and animals that are seen by fewer people, such as pelagic snails, pelagic worms, and comb jellies. There is enormous diversity of form among these animals, and of what they use to paddle with.

In some ways, one can think of crustaceans as the insects of the sea. Like insects, they are arthropods, which means they have a stiff external skeleton and many pairs of jointed legs. Also like insects, they are impossibly abundant and diverse. If the terrestrial god had “an inordinate fondness for beetles,” as British evolutionary biologist J.B.S. Haldane supposedly said after noting how many beetle species there were, Neptune had a thing for crustaceans. Pelagic crustaceans include the tiny, usually one-eyed copepods, the ostracods (think tiny shrimp swimming inside a tiny clam), and an absolute host of shrimp and shrimp-like animals of all sizes, shapes, and colors. Although some shrimp can move quickly by rapidly curling their tail (the part we eat), this “tail flip” can be done only a few times in a row and is reserved for escaping from predators. Otherwise, all the crustaceans move by paddling some subset of their appendages. In the case of copepods, the appendages are their legs or a pair of oar-like antennae. Ostracods primarily use the middle pair of three pairs of legs on their thorax, extending them outside their spherical shell like some secretive rower. The shrimp and shrimp-like animals typically have paddle-like appendages on the rear half of the body. On average, they move slowly, though I have seen some species, such as krill and amphipods, zip around in large spirals. Even the fastest aren’t remotely as speedy as a fish, though. They’re of course much smaller, but at the same time the bigger ones tend to be even slower.

The pelagic snails and worms are two groups of animals that make me happy to be a biologist. In addition to being eerily beautiful, they are such a departure from their relatives on land and on the seafloor. From childhood, our image of a snail is an animal so overwhelmed by its shell that it barely moves, and our image of a worm is an animal that leaves the soil only to die on the sidewalk after a heavy rain. But in the pelagic realm, they’ve both been released to soar like butterflies from a cocoon. Watching them is like watching turtles fly—which I suppose they actually do in the form of sea turtles. Many pelagic snails are called pteropods, which means “winged feet,” and the normally flat foot you see in most snails has been split in two and stretched out into wings that allow the snails to fly underwater. The smaller ones are typically heavy for their size and so must flap their wings frantically to keep from dropping, as we discussed in chapter 2, but the larger ones are less dense and move through the water in the stately fashion of jellyfish.

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