Environmental forcing and larval fish assemblage dynamics in the Lima River estuary (northwest Portugal)

This study investigated the potential control of selected abioticparameters on an estuarine larval fish assemblage from the LimaRiver. Surveys were done fortnightly during spring tides, fromApril 2002 until April 2004, at 11 stations distributed alongthe estuary from the mouth to 7 km upstream. The surveys consistedof subsurface plankton tows of 5-min duration using a 1-m diameter,500-µm mesh net and coupled with vertical profile measurementsof temperature, salinity, dissolved oxygen, pH and turbidity.The Lima River estuary exhibited seasonal vertical stratificationof salinity during the winter period, when salinity sharplyincreased with depth and a layer of fresh water was sometimespresent at the surface. Temperature was always vertically stratified.Cooler water was typically found near the bottom of the watercolumn, except during winter, when a thermal inversion occurred.A seasonal decrease in abundance and diversity of the larvalassemblage was observed during winter, when fish larvae werealmost absent from the plankton collections. Canonical correspondenceanalysis (CCA) results showed that the first axis representeda temporal gradient and the second axis represented a spatialgradient. Seasonal variations on temperature and precipitationwere responsible for the temporal differences on the fish larvalassemblages. This study reinforced the concept that interannualclimate and hydrodynamic variations have a strong influenceon estuarine ichthyoplankton and, consequently, on the recruitmentof marine coastal fish populations. This paper was presented at Plankton Symposium III, held atFiguera da Foz, Portugal between 17 and 20 March 2005, underthe auspices of the University of Coimbra and the Universityof Aveiro, and coordinated by Mário Jorge Pereira andUlisses M. Azeiteiro.