Coral Reef Fish - Adaptations For Life on the Reef
By William Alevizon, Ph.D.
Of the myriad creatures that inhabit coral reefs, none are more obvious, colorful, or fascinating to watch than the fishes that live there. Hundreds of species may be found in relatively small areas of reef, with many of these small, well camouflaged, or hidden.
Coral reefs are unusually complex and colorful marine environments. The physical structure of these unique marine habitats differs radically from the open water habitats that comprise over 99% of the world's oceans, with a diversity of life unmatched in any other marine ecosystem. Therefore, it is not surprising that resident fishes have developed a number of specialized adaptations for life in these colorful and complex habitats.
Body Shape
The body shape of most species of fish that associate closely with coral reefs differs substantially from the shapes of "typical" open water fishes. The latter are generally built for speed, and have evolved appropriate torpedo-like shapes that offer low frictional resistance to movement through water. However. in the complex reef environment, a premium is placed upon maneuverability rather than sheer speed. Thus, coral reef fish have evolved a body plan that maximizes their ability to make rapid turns, avoiding swift predators by quickly dodging into fissures in the reef or swiftly circling around coral heads.
The essence of this design is a deep and laterally compressed body (shaped like a pancake), as well exemplified by the angelfishes and butterflyfishes. A less obvious but critical aspect of this altered body plan includes a shift (compared to open water fishes) in the placement and orientation of the pectoral and pelvic fins, which act in concert with the flattened body shape to maximize maneuverability.
Coloration
Perhaps the most striking feature of coral reef fishes is the variety of brilliant and sometimes bizarre color patterns that adorn them. Again, the use of such color patterns in reef fishes contrasts starkly with the usual color patterns of open water fishes which typically are silvery.
The reasons for such bright and varied color patterns been debated for some time. In some cases, the patterns appear to facilitate concealment under certain conditions, as when the fish is resting in particular places. In other cases, coloration may be used in species recognition to assure mating success. Sometimes, bright contrasting colors are used to warn predators of venomous spines or flesh so as to avoid "mistaken" attacks.
Feeding Structures
With the unusual variety of prey items available to coral reef fishes, it is not surprising that many species have evolved highly specialized jaws, mouths and teeth suited to particular kinds of prey.
For example, "food specialists" like the butterflyfishes (Chaetodontidae) have evolved protruding mouths that are in essence forceps armed with fine teeth - a combination well suited to nipping the coral polyps that are the primary food source of these fishes. Similarly, the parrotfishes (Scaridae) have evolved a beak-like mouth ideally suited for scraping algae from hard coral surfaces.
In contrast, many other common reef-dwelling fishes such as snappers (Lutjanidae) are generalized feeders that have retained a more "typical" mouth and jaw structure that enables them to utilize a wide variety of prey.
There is still much to learn about this fascinating group of fishes, and the adaptations that have collectively made them such a diverse and successful part of the reef fauna.
