Sea hares are sea slugs that get their name from looking somewhat like a crouching rabbit in profile. But they also provide an interesting lesson in reproductive strategies. It’s probably fair to say that sea hares breed like rabbits, although the two kinds of organisms are separated by a wide evolutionary gap. And in fact, when it comes to producing potential offspring, sea hares leave rabbits so far behind in the dust that they aren’t even visible on the horizon.
While sea hares can be quite abundant on rocky reefs along the California coast, every individual supports a complete and functional set of female and male reproductive systems simultaneously once they become sexually mature. With this collection of reproductive abilities, sea hares are referred to as simultaneous hermaphrodites. Among species that are simultaneous hermaphrodites, some are capable of self-fertilization, while others are prevented from it by either anatomical barriers, or by having their two reproductive systems active at different times. Sea hares are among those animals that are simultaneous hermaphrodites with anatomical barriers to self-fertilization. The benefit is that any two sea hares can mate. No need to hope you have a male and a female. But sea hares don’t seem content to mate with just one other sea hare. Normally you will see clusters of sea hares mating on reefs off the California coast.
In today’s photo, a group of eight or nine brown sea hares are busily mating with the other members of the group. In such groups an individual sea hare could either be supplying sperm to the female gonads of another animal, or receiving sperm from another individual. They may even be donating as well as receiving sperm simultaneously.
The result of all this mating activity is the production of masses of eggs. Each sea hare can lay as many as 80 million yellow eggs in long strings that resemble cooked spaghetti from a distance. With eight or nine individuals in a mating cluster, nearly a billion eggs could be produced.
You can see masses of eggs immediately below this cluster, as well as a two egg masses on the large rock at the bottom of the photo. It is possible that these eggs were produced by the sea hares in the photo. While most of these eggs will never produce a new sea hare, you can see how sea hares compare more than favorably with the reproductive prowess of the rabbits after which they’re named.
This photo was taken with a Canon EF17-40 mm f/4L USM lens zoomed to 35 mm on a Canon EOS 5D Mk III in an Ikelite underwater housing. Lighting was provided by two Ikelite DS161 strobes set to eTTL exposure mode. The exposure was set to 1/45 sec at f/11 and ISO 200.