DAILY ANALYSIS OF ABUNDANCE AND SIZE VARIABILITY OF FISH LARVAE IN RELATION TO OCEANIC WATER INTRUSIONS IN COASTAL AREAS*

Abstract

The daily variability of the summer ichthyoplankton assemblage in the Gulf oí Arauco (37°05'S, 73°20'W) was studied to characterize its composition, relative abundance, size distribution of larvae, and its response to environmental conditions. Three well defined environmental changes were observed during the 11 day study period: (1) sinking of isotherms and temperature increase of the surface layer, (2) a sharp decrease in chlorophyll concentration. Both (1) and (2) occurred on the 6th day of sampling, and (3) a storm on the 8th day. The first two events were due to onshore flow of oceanic water, which could have been enhanced by downwelling during the storm. The ichthyoplankton assemblage showed: (1) high concordance in the ranking of specific relative abundance among samples (Wc = 0.87, P < 0.01), (2) temporal concordance in the variations of relative abundance for larvae of the eight most dominant species (Wc = 0.35, P < 0.01), (3) presence of larger fish larvae after the storm for the four dominant species (P < 0.03), and (4) predominant ordination of samples into a pre-storm group and a post-storm group (Bray-Curtis índex). Implications of transport processes in the dynamics and structure of Coastal ichthyoplankton are discussed.