ARTICLE

Examples of symbiosis in tropical marine fishes

John E. Randall & Arik Diamant

Introduction

The word symbiosis is from the Greek meaning living together, but present usage means two dissimilar organisms living together for mutual benefit. Ecologists prefer to use the term mutualism for this. The significance of symbiosis and its crucial role in coral reef function is becoming increasingly obvious in the world’s warming oceans. A coral colony consists of numerous coral polyps, each like a tiny sea anemone that secretes calcium carbonate to form the hard skeletal part of coral. The polyps succeed in developing into a coral colony only by forming a symbiotic relationship with a free-living yellowish brown algal cell that has two flagella for locomotion. These cells penetrate the coral tissue (the flagella drop off) to live in the inner layer of the coral polyps collectively as zooxanthellae and give the yellowish brown color to the coral colony. As plants, they use the carbon dioxide and water from the respiration of the polyps to carry out photosynthesis that provides oxygen, sugars, and lipids for the growth of the coral. All this takes place within a critical range of sea temperature. If too warm or too cold, the coral polyps extrude their zooxanthellae and become white (a phenomenon also termed bleaching). If the sea temperature soon returns to normal, the corals can be reinvaded by the zooxanthellae and survive.
The current scientific community generally agrees that if the warming of our planet from the burning of fossil fuels continues, along with deforestation, our coral reefs are doomed. The corals of the magnificent Great Barrier Reef of Australia are beginning to die, and with them all the dependent marine life will likely perish. We should learn all we are able about the biology of coral reefs. A long list of relevant publications on the ecology of coral reefs, especially with respect to fishes, is given below in References. The following are among the more important papers that report on symbiosis on coral reefs, especially in relation to fishes: Ormond (1980a, 1980b), Diamant & Shpigel (1985), and Bshary et al. (2006).
Knowing that my colleague Arik Diamant in Israel has photographs of different species of fishes that forage together, as well as fishes with octopus, I suggested that we join forces and present the best photos we can find to illustrate symbiosis in fishes. We have assembled 27 photographs for this article.