Mesozooplankton biomass and copepod estimated production in a temperate estuary (Mondego estuary): effects of processes operating at different timescales.

Dina Amanda Gonçalves,Filipe Martinho,Miguel Ângelo Pardal,Sónia Cotrim Marques,Maria Donas-Bôtto Bordalo,Ana Lígia Primo

doi:10.1186/s40555-015-0135-6

Dina Amanda Gonçalves, Filipe Martinho + Show 4 more

Open Access

https://doi.org/10.1186/s40555-015-0135-6

Copy DOI

Journal: Zoological studies	Publication Date: Aug 11, 2015
Citations: 29	License type: cc-by

Affiliation: University of Coimbra, University of Aveiro

Abstract

A fundamental step in characterizing marine planktonic communities is the knowledge of the variability of their biomass and production, in order to assess the flux of matter through the food web and estimate the fate of this energy. The zooplankton assemblage's dynamics of the Mondego estuary (Portugal) have been extensively characterized, but none have focused on biomass and secondary production. In the present study, zooplankton biomass and secondary production were investigated with a seasonal basis in a fixed station, located at the mouth of the Mondego estuary (Portugal), with emphasis on the copepod community. In order to study the influence of physical processes operating at different temporal scales, sub-surface and near-bottom samples were collected every 2 h in diel and tidal cycles, over neap tides. Copepodsdominated the biomass during spring (0.585 ± 0.671 mg C m-3),summer (0.287 ± 0.383 mg C m-3), andwinter (0.221 ± 0.128 mg C m-3).Lower observed biomass values were probably due to the higher mesh size used in comparison to previous studies in other estuarine systems. No differences were detected between seasons in total zooplankton biomass. Concerning diel cycle, significant variation occurred mainly in spring and winter, with substantially higher biomass values being registered at night for both the surface and bottom. Moreover, copepod biomass was consistently higher at the bottom during winter. In this season, bottom samples presented higher copepod biomass both at ebb and flood tides. From the GLM analyses run for each season, chlorophyll a, diel phase, and depth were significant factors. Theconsiderable complexity in the processes structuring the dynamics and composition of biomass and production rates has been shown. Our results demonstrated that along spring and winter, secondary production varied according to diel phase and depth. In winter, night and bottom samples revealed consistently higher daily secondary production rates. From this, it is possible to conclude that local factors (river flow, predation, food limitation) regulate the seasonal variations in zooplankton biomass and production in the Mondego estuary.

Highlights

A fundamental step in characterizing marine planktonic communities is the knowledge of the variability of their biomass and production, in order to assess the flux of matter through the food web and estimate the fate of this energy
The copepod community of the Mondego estuary is dominated by the Acartia genus (Azeiteiro et al 1999, Vieira et al 2003)
In order to better comprehend the role of zooplankton in the material flow of this ecosystem, the principle aims of this study were as follows: (1) to quantify zooplankton biomass categorized by taxonomic groups; (2) to estimate copepod production by using the global model of Huntley and Lopez (1992); (3) to evaluate the effect of processes operating at different timescales on biomass transport at the interface between the estuary and the adjacent coast: seasons, tidal, and diel cycles

Summary

Introduction

A fundamental step in characterizing marine planktonic communities is the knowledge of the variability of their biomass and production, in order to assess the flux of matter through the food web and estimate the fate of this energy. Water circulation and land influence induce high variability on the distribution and structure of planktonic populations, which tend to be spatially and temporally heterogeneous when compared to other aquatic systems (Marques et al 2007). All estuaries show a gradual reduction in diversity but not in abundance or productivity of species when compared to adjacent aquatic habitats (Elliott and McLusky 2002) Due to their significant abundance and biomass in estuarine and nearshore areas, zooplankton play a key role as major grazers in aquatic food webs, being critical intermediaries in the flow of energy and matter through marine food chains, from primary producers to consumers at higher trophic levels, such as fish, marine mammals, and turtles (Leandro et al 2014, Richardson 2008). These organisms reproduce throughout the year, and several annual growth generations can be found in temperate systems like this one because of favorable temperatures and high food availability (Kleppel 1992, Leandro et al 2007)

Objectives

Methods

Results

Discussion

Conclusion