Nearshore distributional gradients of larval fish (15 taxa) and planktonic crustaceans (6 Taxa) in Hawaii

Abstract

Fifteen taxa of fish larvae (most identified to species) and 6 taxa of crustaceans (most identified to species) were studied in zooplankton samples collected 0.2, 0.5, 1.0 and 3.0 km off the leeward coast of Oahu, Hawaii in May and July 1975. The following distributional patterns were elucidated: inshore (2 spp); inshore-neritic (2 spp); neritic (7 spp); and offshore-neritic (7 spp). Three of these 18 species had age-related differences in behaviour that led to age-dependent distributional patterns, and 4 further species had a random distribution. All abundant types of fish larvae were either oceanic as adults or were hatches from the demersal or brooded eggs of reef species. The larvae of reef fishes with pelagic eggs were not abundant in the nearshore region sampled and were probably to be found more than 3 km offshore. The offshore-neritic distributional pattern evidently resulted from relatively passive movement with currents. In contrast, maintenance of inshore and neritic patterns probably required relatively active swimming by the animals. The current regime, including a tidal eddy and possible nearshore upwelling, probably helped maintain the inshore and neritic patterns of such animals. The limited area occupied by these inshore coastal plankton communities could make them particularly vulnerable to environmental changes, including anthrogenic ones.