TEMPORAL DYNAMICS OF FISH COMMUNITIES ON AN EXPOSED SHORELINE IN HAWAII

Environmental conditions on higher latitude coral reefs can be extreme ly variable, and may structure fish communities in ways not previously observed in the more stable, low latitude locations where communities have usually been studied. Temporal changes in fish community structu re were examined in an intensive two-year study of the reef fishes of Hanalei Bay, Kauai, Hawaii. Hanalei Bay is directly exposed to winter swells with high surf, as well as frequent heavy winter rainfall and h igh river discharge. Twenty-two transects (25 x 5 m) were established in a wide variety of habitats and censused monthly (N = 1052 censuses) . Over 121 000 sightings of individuals from 150 species were made dur ing the study. Seasonal patterns in number of species, number of indiv iduals, species diversity, and evenness were observed, with winter val ues usually lowest. Values of these ensemble variables tended to be hi gher at deeper sites and at sites with greater habitat complexity. Sur f height and degree of wave exposure were negatively correlated with s everal measures of community organization. Groups of fishes with diffe rent levels of spatial mobility tended to occupy depths consistent wit h their various abilities to respond to events of heavy weather. The r ank abundance of fish taxa tended to be more stable seasonally at site s with less exposure to high wave energy. These seasonal effects may s uggest some type of short-range movement from more exposed and monotyp ic habitats to locations that are deeper or otherwise provide refuge f rom seasonally heavy seas.