Sea Hares are herbivorous, eating red, green, brown algae such as hair algae, sea lettuce and algae of the Gracilaria sp. Great addition to your clean up crew. Okay seahorse tank mate.
The sea hares are Opisthobranches or Sea slugs with missing or reduced shells of the order Anaspidea. They are named for their rabbit ear-like projections called rhinophores (used for taste, current detection), and two anterior-projecting oral tentacles. They are of the Family Aplysiidae: In old Hawai’i sea hares were called Kualakai and some were cooked in an imu wrapped in ti leaves… and consumed. There are some 2,000 species worldwide, and about 150 of these can be found in Hawaiian waters.
The Aplysia are hermaphroditic with functional female and males in one body although cross-fertilization is the general rule. Sea Hare eggs lay eggs in long yellow stringy gelatinous like egg masses laid on any surface such as sea lettuce or your aquarium glass. Eggs hatch out to pelagic trochophore larvae which metamorphose into veligers. Seahorse fry as well as many other small mouthed sea critters love to feast on the motile free swimming larval forms. After several weeks they settle and metamorphose into miniatures of their parents.
The sea hare can release a purplish ink as a defense mechanism, not only when they die, but whenever they feel sufficiently threatened or irritated. However, this ink is not particularly toxic (although it is certainly a stressful irritant to most species), but it is a potential hazard for pollution and stress if not removed from the aquarium. Fortunately, the ink is easily removed with the use of activated carbon or chemipure, or by water changes. If your tank has adequate chemical filtration, a sea hare poses no real threat to your aquarium inhabitants.
If you don’t have adequate filtration with activated carbon or plenty of macroalgae in your tank for them to eat, then don’t consider keeping this reef critter. They are sensitive to water quality, including high nitrates.
** These are the eggs.