A horrible photo of a sea hare. Photo by me from Lover’s Point.
Some of you are probably curious why I am deciding to do a Creature Feature on the lowly sea hare. Well the answer comes in two parts. Firstly, I found myself reading some issues of Skin Diver Magazine that Bill had given me and started wondering how Bill was doing since I hadn’t heard from him in AGES (these are one of Bill’s favorite creatures). Secondly I myself was curious about these creatures because you can see them in Monterey, but only in the springtime. Without further ado, I present to you the Amazing Lives of California Brown Sea Hares (hereto forth known as the sea hare)!
An awesome photo of a sea hare. Photo by Janice.
Let’s start with the basics. What is it? Well the sea hare is actually a sea slug (there are no rabbits with gills, except rabbitfish (bad pun, sorry)). If you look at it though, it does look like a rabbit and it acts like a rabbit (I’ll get into that later). Sea hares are part of the phylum mollusca (things with shells) and the class gastropoda (slugs and snails). You could say sea hares are cousins to octopuses and nudibranchs and share similar traits. Some of the “cooler” traits sea hares have include producing ink like octopuses and being hermaphrodites like nudibranchs.
Sea hare inking. Photo from The Aquarium of the Pacific.
How do I identify one? Well, it has a color pattern consisting of spots and lines. It also looks like a rabbit. Their “rabbit ears” are called rhinophores and they are often seen just “mowing” down the algae (also similar to rabbits eating grass). Unfortunately color is not a good way to identify them. Their color varies from brown to tan to green to red. Their coloration depends on what they eat. Their “mantle” (or the area where their shell would be) is covered by wing-like flaps of skin called “parapodia.” These cover the gills and overlap on their back.
Sea hares can grow to be 16 inches long and weigh 5 pounds. The body length depends on whether their body is extended or not (like slugs sometimes their body is scrunched together or lengthened). 16 inches is a rare size, but regardless these sea hares are one of the largest gastropods in Southern California. The only gastropod larger than these guys are the black sea hares (38 inches and 30 pounds).
Where are these creatures found? These sea hares are found around Southern California, Japan, and the Sea of Cortez to El Salvador. Although, during spring time they move up to central California (Monterey area) and mate. Suddenly they appear and then just as suddenly they disappear. No one is really sure why.
Since I brought up mating, this is a perfect segue into reproduction. Their unusual reproduction method is what draws the attention of divers. They reproduce in orgies (officially they are called mating chains). These orgies can last hours or days. Each sea hare is, according to the Cabrillo Marine Aquarium, “…male to the one in front and female to the one behind, so each sea hare is both a mother and a father.” After mating is done, the eggs are laid. The egg masses look like yellow silly string. All eggs are laid in a central pile to reduce predation pressure and they also release pheromones to encourage more sea hares to visit, mate, and add their eggs to the pile. Each sea hare can lay up to 80 million eggs! That is very impressive. When you think about it, many creatures want to eat eggs because they are an easy target. Laying a lot of eggs in one place increases the eggs’ chances for survival.
A sea hare mating chain. Photo from the Tide Chaser Blog.
Sea hare orgy. Photo from http://www.diver.net.
When all is said and done and the mood is over, all that remains are the eggs. Photo from http://www.oceanwildthings.com.
The eggs will hatch within 10-12 days. Then the clock starts ticking. Sea hares will only live about a year and then will die after laying eggs. After hatching, the larvae will swim in the water column for about 30 days and then settle into water about 60 feet deep. The young eat so much in the next 3 months that their weight will double every 10 days. As they grow older, the sea hares will start to migrate into shallower water. As the sea hares get older, they don’t have to worry about predators as much (please excuse my anthropomorphization). Brown sea hares are herbivorous. They mainly eat red algae which helps them produce ink and accumulate chemicals in their body which makes them undesirable to eat. Their main predator when they are smaller is the giant green anemone. This anemone will only eat select parts of the sea hare that don’t contain chemicals. Other predators of small sea hares include sea stars and lobsters. The larger a sea hare becomes, the fewer predators it has to worry about.
Fun fact: Sea hares are studied in neurobiology labs because they have the largest neurons in the animal kingdom (and very few of them). This makes it easier to figure out which neurons target which behaviors. These creatures have been used in studying behavior, memory, and learning. The sea hares used in these studies are often born and bred in captivity. Who knows, maybe in the future my memory will be saved by a sea slug (I will never step on another slug again).
As you can see, these creatures are more than just blobs and are fairly interesting. Next time you encounter one on a dive, I hope you will take the time to observe its behavior. I hope you enjoyed this blog Bill (wherever you are) and learned a little something about these cool creatures!
It kind of looks like a rabbit. Shamelessly stolen from the internet.
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