Distribution and patterns of emergence of suprabenthic and pelagic crustaceans in a shallow temperate estuary (Ria de Aveiro, Portugal)

Abstract

Ecology and dynamics of the zooplankton in the Ria de Aveiro, Portugal, were researched to understand the correlation between the patterns of abundance of suprabenthic and zooplanktonic crustaceans and its tidal, day/night and lunar cycles. This study involved the collection of a series of samples during nine 25 h sampling cycles, separated weekly, at a fixed station located near the mouth of the lagoon. In each 25 h cycle, the samples were collected every 2 h with a 500 μm net, at three depths, at the surface, mid-water and over the bottom. The overall effect of the phases of tide and day and depth on the vertical position of the organisms was further investigated through a three-way analysis of variance (ANOVA), in which the phase of the tide (ebb, flood), the phase of the day (day, night) and depth (surface, mid-water, bottom) constituted the three factors in the analysis. The distribution of the species in the water column exhibited distinct tidal, day/night, and lunar patterns, reflecting the ecological particularities of the different species in relation to their seasonal occurrence and behavioural relationships. This distribution showed that for the dominant species, there was a significant interaction between behavioural strategies and cyclic changes of environmental conditions.