Delay:   Loop: [stop] [reverse direction]


Togetherness: the word says it all. Living together in varying degrees of intimacy is the very root of coral reef existence. The "five-dollar" word for togetherness is symbiosis and without the various symbioses of coral reef animals, there would be no coral reef. It all starts with the symbiosis of a dinoflagellate and a coral animal, and here both partners presumably benefit from the arrangement; the corals get food and the algae get protection.

Although commonly thought of as being beneficial to both parties, such arrangements, termed mutualisms, are examples of only one of several types of symbioses. The types of symbioses may be thought of as a continuum of arrangements. The "positive" extreme would be these mutualistic arrangements where both parties benefit. Probably the most well-known mutualism is between the various anemone fishes and sea anemones. Indeed, this relationship is so well known that it is virtually an icon of coral reefs. I suspect there is no true reef aquarist who doesn't, deep in his or her heart, want to have their own version of Nemo snuggled into an anemone somewhere in their system. Similar mutually beneficial relationships would be those of cleaner wrasses or cleaner shrimps and their clientele.

A different type of symbiosis is commonly described. This is an arrangement which benefits one of the partners, while neither benefitting nor is harming the other. Termed commensalisms, this is the arrangement commonly described for animals such as porcelain anemone crabs and their host anemones. These crabs are primarily suspension-feeding animals, and they use their large basket-like feeding appendages to sweep the water to get their food. They don't harm the anemones, but they benefit by gaining protection from their host. Few fish will hazard getting eaten by an anemone simply for the chance to snack on the crab.

A similar arrangement is often said to exist for the beautiful Periclimenid shrimps living on sea anemones throughout the tropics and well illustrated in these images. Here the shrimp is presumed to get the benefits of protection while the anemone gets no benefit whatsoever (See, for example, Mihalik and Brooks, 1997). These relationships, however, may be significantly more complex than this simple explanation indicates. Some of these shrimps, such as the relatively common Periclimenes pedersoni, found throughout the Caribbean, may be a cleaner shrimp (Zann, 1980). So, while the shrimp may be a commensal on its anemone, it may simultaneously be involved in a mutualistic relationship with some of the fish in its community. Yet other species of Periclimenes turn the usual shrimp and anemone relationship onto its head. Fautin and her coworkers have recently shown that Periclimenes brevicarpalis, which is found on the bulb-tipped anemone, Entacmaea quadricolor, in the Indo-Pacific, grazes on the anemone, eating its tentacles (Fautin, et al., 1995; Guo, et al., 1996). So, in this case, the shrimp is not a commensal but an ectoparasite.

The transition from a commensal relationship to true mutualism or, conversely, to a parasitic relationship, appears to be easily accomplished, and there are numerous examples of closely related animals exhibiting these different aspects of symbioses. If any reader wants to learn more about some of these relationships, I recommend he take a look at the very readable and well illustrated book, Living Together In The Sea, by Leon Zann, cited in the References. Coral reefs and our coral reef aquaria contain numerous examples of various aspects of symbioses, as are illustrated in these images. Such relationships are, however, common in all the world's seas and may been seen on a visit to the sea shore.


Fautin, D. G., C.-C. Guo and J.-S. Hwang. 1995. Costs and benefits of the symbiosis between the anemone shrimp Periclimenes brevicarpalis and its host Entacmaea quadricolor. Marine Ecology Progress Series. 129:77-84.

Guo, C. C., J. S. Hwang and D. G. Fautin. 1996. Host selection by shrimps symbiotic with sea anemones: A field survey and experimental laboratory analysis. Journal of Experimental Marine Biology and Ecology. 202:165-176.

Mihalik, M. B. and W. R. Brooks. 1997. Protection of the symbiotic shrimps Periclimenes pedersoni, P. yucatanicus, and Thor spec. from fish predators by their host sea anemones. In: den Hartog, J. C., L. P. van Ofwegen and S. van der Spoel. Eds. Proceedings of the 6th International Conference on Coelenterate Biology. Nationaal Natuurhistorisch Museum. Leiden. pp. 337-343.

Zann, L P. 1980. Living together in the sea. T. F. H. Publications. Neptune NJ. 416 pp.

Text by Ronald L. Shimek, Ph. D.
Photos by Reef Central members.

Reefkeeping Magazine™ Reef Central, LLC-Copyright © 2008