VERTICAL DISTRIBUTION AND COMPOSITION OF ICHTHYOPLANKTON AND INVERTEBRATE ZOOPLANKTON ASSEMBLAGES IN THE EASTERN TROPICAL PACIFIC

Abstract

The composition an vertical distribution of ichthyoplankton an invenebrate zooplankton of the upper 100 m of the northwest eastern tropical Pacific have been described using data from 23 neuston and 166 stratified bongo samples. Máximum invenebrate zooplankton abundance (numbers 10 m-2) occurs at the botton of the mixed layer (~ 40 m; defined by XBT casts) by day, and in the upper mixed layer at night; high concentrations (numbers x 1000 m-3) also occur in the neuston layer both day and night. Máximum ichthyoplankton abundance and diversity (numbers of taxa) occur in the upper thermocline, and most individuáis and species occur below the depths of máximum abundance of major invenebrate zooplankton taxa. The deep ichthyoplankton distribution and numerical dominance by species which are “deep living" as larvae and actively migrating “surface" feeders as adults are unique, and distinguish the eastern tropical Pacific fish fauna from that of the North Pacific central gyre. Structure of the eastern tropical Pacific fish assemblage may result in part from high surface layer zooplankton concentrations which provide (a) abundant food for actively migrating adults; and (b) intense food competition with and/or predation upon.shallow-living larvae. The deep larval fish distributions may also result in part from extreme heterogeneily in mixed layer thermal structure across the eastern tropical Pacific area.