Vertical distribution and gas bladder inflation/deflation in postlarval anchoveta Engraulis ringens during upwelling events

Abstract

Vertical distribution of fish larvae can be modified by a series of physical processes occurring in the water column at different time and spatial scales and also by biological processes occurring during larval development. To assess the factors affecting the vertical distribution of larval anchoveta Engraulis ringens during austral spring, meteorological and oceanographic features were measured and stratified ichthyoplankton sampling was carried out in central Chile during active upwelling events. In November 2001, during the upwelling season, southerly winds dominate, and intrusion of low dissolved oxygen occurred in nearshore waters; preflexion larvae of E. ringens were collected in the mixed layer of the water column (the Ekman layer) irrespective of day and night hours. Larvae larger than 10 mm showed an inflated gas bladder during night collections, and non-inflated gas bladder during day hours. Larvae with inflated gas bladders were located significantly at shallower depths during night than at day hours, indicating a direct relationship between gas bladder inflation, diel vertical migration of larval E. ringens and decrease of wind-induced turbulence at night. We discuss the potential implications of larval E. ringens vertical distribution and its variability on the horizontal transport off coastal waters during the upwelling season off central Chile as a biophysical coupling to enhance coastal retention.