Symbiotic Relationships

Symbiotic relationships, when two different species form close and long-lasting interactions, occur in all of the ocean’s ecosystems. From enormous sharks with their tag-along remoras, to the tiny microscopic zooxanthellae that live within the tissues of corals, many organisms have found that working together toward a common goal is the most efficient way to procure food and escape predation.

A sea anemone hosting a clownfish.

There are a number of common and not-so-common organisms that are perfectly suited for aquarium life. A tank dedicated to or featuring these pairs is not only a more realistic slice of the reef, but often provides a more appropriate living environment, leading to healthier livestock.

One of the most common animals involved in symbiosis are anemones. In the wild, anemones of all shapes and sizes host hundreds of different fish and invertebrate species. Clownfish are probably the most well-known anemone symbionts, but other species of damselfish, namely Dascyllus trimaculatus, are also known to host with anemones in the wild. The anemone provides shelter for the fish within its stinging tentacles, and the fish return the favor by bringing bits of food back to the anemone.

Anemones also host other types of life. Tiny, translucent shrimp, most commonly in the genus Periclimenes, are the most commonly found, and can be very entertaining to watch as they move in and out of the anemone’s tentacles harmlessly feeding on its mucus. Porcelain crabs, Neopetrolisthes ohshimai, are another popular invert for hosting with anemones. These crabs use the anemone for protection as they wave around their feeding appendages, waiting for food to float by.

The important thing to remember here is that neither the anemone or the animal hosting it are dependent on the other for survival. Anemones will love long, happy lives without any animals living within their tentacles. Clownfish will often host other types of corals if an anemone is absent, and have even been known to host inanimate objects like powerheads. Periclimenes shrimp are also natural hosts of corallimorphs like Ricordea sp. in the wild, and will mirror that relationship in a biotope tank. In the same way, porcelain crabs will find a suitable coral substitute to provide them with cover. Don’t think that you must have an anemone in order to set up a biotope based on symbiosis – a 10g tank stocked to the brim with Ricordea and ten or fifteen Periclimenes shrimp would be a fascinating sight.

If you do decide to keep an anemone, however, there are some special considerations to keep in mind regarding their care. Generally, anemones require high light and high flow to survive well in home aquaria. Their requirements are much the same as SPS corals, however anemones tend to wander around their tank stinging indiscriminately, and should only be housed with other corals with caution. A future installment of this series will go into more detail on anemone-only tanks.

An Alpheid shrimp and its symbiotic goby.

Another popular symbiotic pair are pistol shrimps of the genus Alpheus and their partner gobies. This combination is truly amazing to observe. The shrimp digs a burrow in which to live. In return for shelter, the goby keeps a keen eye out, and at the first sign of danger alerts the shrimp and both dart into the hole. Because the shrimp is nearly blind, it has at least one antenna in contact with the goby at all times as a means of communication. This would be the perfect pair for a small nano tank, where the interaction can be observed up close.

When designing a biotope based on a symbiotic relationship, always be sure to take the needs of the both parties into consideration. In cases where one animal is more difficult to keep alive than the other, it is best to design the system with the needs of the more fragile species in mind. For example, Christmas tree worms (Spirobranchus sp.) are beautiful, but depend on their host Porites coral for survival. If you cannot keep the Porites alive, the worms are doomed. Since the worms don’t require any sort of special care, you would design your system around the coral, providing high light and random, chaotic flow.