Dating on land may be unpleasant, but for microscopic sea animals, searching for a mate in the sea is like looking for a needle in a haystack, where the haystack is the size of Mount Everest.
Consider copepods, distant relatives of shrimp that fuel the ocean’s food web. Tiny and packed with fat, they are the baby food of the sea, feeding countless larval crabs, fish, and squid. Crunchy on the outside, full of gooey oils on the inside, they’re also the go-to meal for enormous, swirling schools of bait fish—sardines, anchovies, herring—that in turn feed the tuna, snapper, and cod we like to eat. Attaining numbers large enough to satiate all those appetites requires copious amounts of copepod copulation, which requires some close physical contact between males and females—but the copepods’ size doesn’t make that easy. Some species are as small as a sesame seed, others about as long as your thumbnail. Even within the confines of the average home aquarium, a male copepod swimming around randomly is likely to bump into a female copepod about once per year—yet individuals may live only a few months and some only a few weeks. Not great odds for finding a partner.
So with an entire ocean to contend with, how in the world does an animal smaller than a grain of rice find an equally tiny (and transparent) mate in all that blue? Peter Franks, a professor at Scripps Institution of Oceanography, has a simple answer: Copepod singles’ bars, of course. And, as is most often the case for our own dating rituals, the males at these hotspots always make the first move.