Inshore Ichthyoplankton: A Distinctive Assemblage?

Our collections of larval fishes made at underwater lights on the outer shelves of coral reefs in the Caribbean yield large numbers of specimens mostly representing only a few of the families of fishes that inhabit coral reefs as adults. Although it is difficult to sample close to the reefs and methods of taking quantitative samples there have yet to be devised, preliminary comparisons of our near-reef data with those from ichthyoplankton collections made by others during extensive offshore surveys suggest that the inshore larval fishes constitute a distinctive assemblage. Not only are different taxa dominant, but few inshore larval fishes show the morphological specializations that characterize many of the offshore larvae. We postulate that tropical marine fish larvae tend to be specialized either for long distance transport or for avoiding being swept downstream by offshore currents. This seems to indicate that there are two groups of larval fishes: a far-field assemblage of larvae that are morphologically modified or behaviorally specialized for long distance transport by ocean currents and a near-field assemblage of unspecialized larvae that avoid currents and spend their entire lives in the vicinity of the reefs.