Many animals in the ocean seek shelter from predators by living on or among other animals. Among fishes, members of the Damselfish family (Pomacentridae) often seek protection this way. Some of these relationships also are commensal or even symbiotic.
One of the most well known symbiotic relationships in the marine world is that between anemones and fishes commonly known as ‘clownfish’ or ‘anemonefish’. Clownfish form a subfamily, Amphiprioninae, of the Dameselfish family. Each of the twenty-some species in this subfamily lives symbiotically with one or more anemone species.
Both the fishes and the anemones are believed to benefit from the relationship. The fishes are protected from predators by the stinging nematocysts of the anemeones’ tentacles; the anemones feed in part on waste matter from the fish.
In the photo at the top right of this page, an Indo-Pacific clownfish species, Amphiprion ocellaris, hides among the tentacles of an anemone (Heteractis sp) where it makes its home. The photo was taken at Bunaken Island, Indonesia.
In some cases, several species live together in the same host anemone. In the macro photo above, a juvenile Two-bar Anemonefish (Amphiprion bicinctus) — the only anemonefish species known from the Red Sea — shares its living space with some Anemone Shrimp (Periclimenes longicarpus), a commensal species. I photographed this particular anemone (Stoichactis sp.) at a reef in the Straits of Tiran. This one anemone was host to a number of these shrimp, plus an adult pair of A. bicinctus, and several juveniles. A. bicinctus also shares its anemone home at times with another Red Sea damselfish species, Dascyllus trimaculatus.
I was photographing Cerianthid ‘tube anemones’ in Hawaii one day when I noticed a very tiny fish that appeared to be sheltering among the tentacles of the individual in my viewfinder! The fish was so tiny that I could not identify it then with any confidence. Only after the photos were enlarged could I see that it was a barely post-larval Hawaiian Dascylllus (Dascyllus albisella), a damselfish species endemic to Hawaii. The image above is one of those photos. At that time I had never before seen this relationship, but I have since seen this pairing a few more times. I do not know if the relationship is commensal, or if the little fishies were merely sheltering among the Cerianthid’s tentacles until they grew large enough to migrate to the reef.
Many other species in the damselfish family find shelter not in anemones, but in branching hard corals, especially Acroporidae. It is not uncommon to see a group of these fishes hovering above a formation of ‘antler coral’. From a distance they can look like a colorful shimmering mass above the coral colony. If a predator (or a diver) approaches too quickly or too closely, the fishes drop down instantly and in unison into the branches of the coral, where they hide until the threat has passed. (The precision of this choreography is impressive.) The image above, photographed in the Red Sea, shows a number of fluorescent green fish (Chromis caerulea) snuggled in among the branches of a stand of Acropora sp.
I have seen this behavior in many species of damselfish. Interestingly, these fishes seem to practice a sort of species segregation. Only one species at a time will inhabit a given coral colony. Once a group of conspecifics has established itself at a coral colony, no other species of damselfish will be tolerated there.