The Mighty Mower

The Tasseled Sea Hare (Aplysia sp.) got its common name from the tassels it wears and its prodigious ability to consume nuisance hair algae. They're among the largest of the sea slugs you'll see in the home aquarium and can get up to eight inches long. They're graceful and beautiful critters that are captivating additions to the home marine aquarium. They often reflect their diet in appearance and specimens that are fed a diet of primarily green algae will often take on a green hue, and the same is true of individuals that exist on a diet of algae that has a red shade. Most of them are a pale brown to nearly white and are covered in little “tassels” that can be yellow, brown and sometimes even polka dotted with a darker shade over the lighter color.

The primary challenge to successfully keeping Sea Hares is the same thing that makes them so attractive to so many hobbyists. They eat hair algae, and they do it at an incredible pace. The hard part is making sure they get enough of it. They can very quickly deplete the natural supply in an aquarium that is well kept, and so supplemental feeding will be required. They will happily eat both the Nori and Ogo from Nutramar, as long as these are well hydrated before affixing them in place with a rock or clip in the aquarium, directly in the path of the sea slug. Many hobbyists will keep a spare tank in direct sunlight that has some small (marine tank appropriate) chunks of rock in it. This tank is usually either unfiltered or gently filtered with an air stone. A small, hardy fish like a damsel can be kept in this algae farm as well to help keep the nutrient supply high enough to maintain algal growth. These rocks will quickly develop a handsome crop of hair algae and can then be moved to the main display for the Tasseled Sea Hare to eat off of. Once the rock is stripped clean, it goes back to the algae farm and a new crop-rock is moved from the farm to the main display. This is one of the best ways to keep your Hare thriving long term. We've seen reports of Sea Hares eating algae wafers and algae-based shots but can't verify this.

The large size, and specific diet of this critter translates to an aquarium that might be bigger than what you would expect in regard to keeping one. We suggest a tank that is at least 55 gallons, which will give the Sea Hare plenty of territory to graze on and will also enhance the stability of the tank in regard to water chemistry and general parameters. We'll touch on this topic again. Lighting should be as bright as you can get, and the daylight timing of the tank can be longer than what you would usually use to help encourage algae growth. Don't be afraid to run your lights for eight hours or more. Some internet sleuths have hypothesized that in consuming algae, that the Tasseled Sea Hare also consumes the photosynthetic cells (called chloroplasts), and in so doing, become somewhat of a photosynthetic critter itself. To our knowledge this is only true of sea slugs in another grouping (clade), but Aplysia sp. won't be harmed by reef-intensity lighting of long duration regardless. Flow is important but shouldn't be crazy. Aim for five to ten times the volume of the tank in flow, including the filtration. Avoid all situations where flow is direct and laminar (in one direction).

Part of the difficulty of keeping Sea Hares well fed is that they also like very clean water and stable parameters, but the algae they feed on likes nutrients. Home hobbyists often add a sea hare to deal with an algae problem which is often partially the result of a water quality problem (and environment that is challenging for the Hare). Make sure the aquarium is nice and stable before adding a Tasseled Sea Hare. Keep nitrates under 10ppm, and temperatures in the 70–78-degree range (Fahrenheit obviously). Specific gravity should be kept nice and high 1.025-1.026 and the pH should remain between 8.0 and 8.4 at all times.

You can keep Tasseled Sea Hares with other fish and invertebrates. The Hare won't bother corals unless they are covered with algae (which is usually a dead/dying coral anyway). They are fine with fish, unless the fish like to pick on things. The tassels of the Hare do look like algae flowing in the current, and it is not unusual for Tangs and Rabbitfish to pick on them. Avoid very aggressive nippers like most Triggers and all Pufferfish.

Sea Hares that get picked on too much can succumb to these repeated wounds. The other way they die in aquariums is usually underfeeding. They are not very long-lived species, and generally don't live more than a couple years, even in captivity. If your Sea Hare is losing color or has become inactive for longer than is usual, remove it to a hospital tank immediately. If you don't see it for more than a day, start looking for it more carefully. Once they die, they can release a large whack of compounds that are not good for anything in the home aquarium and these chemicals are difficult to filter out quickly enough to prevent complications.

Over time, Sea Hares have gotten such a good reputation for their epic algae removal skills that some Local Fish Stores even rent them. You pick them up, add them to the tank with the issue, the Tasseled Sea Hare mows the lawn, then you pull them out and take them back to the store. Not all stores are going to be interested in doing this, but some will. Remember that Sea Hares don't like a lot of fluctuations, so handle them carefully and always drip acclimate them slowly, we recommend at least an hour. Try not to expose them to air; while they do have a rudimentary internal structure, they don't have a skeleton as such, and need the support of the water.

The Tasseled Sea Hare is one of the most beautiful things you can keep in a home aquarium, and among sea slugs, they are some of the easiest to keep. Make sure the aquarium is mature and stable, and get them enough food and your sea slug will happily keep any algae in your tank in check. If this sounds like an invert you'd like to see in your display, head to your LFS and ask them about getting you one from Quality Marine!