Zoological Studies

Vol. 54, 2015

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

Dina Amanda Gonçalves1, Sónia Cotrim Marques1*, Ana Lígia Primo1, Filipe Martinho1, Maria Donas-Bôtto Bordalo2 and Miguel Ângelo Pardal1

1Department of Life Sciences, Centre for Functional Ecology—CFE, University of Coimbra, Calçada Martins de Freitas, Coimbra 3000-456, Portugal
2Department of Biology and CESAM, University of Aveiro, Campus Universitário de Santiago, Aveiro 3810-193, Portugal

Background: 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.
Copepods dominated the biomass during spring (0.585 ± 0.671 mg C m3), summer (0.287 ± 0.383 mg C m3), and winter (0.221 ± 0.128 mg C m3). 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.

Conclusions: The considerable 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) regulatethe seasonal variations in zooplankton biomass and production in the Mondego estuary.

Key words: Mondego estuary; Estuarine copepods; Biomass and secondary production; Seasonal and diel variations.

*Correspondence: E-mail: scotrim@ci.uc.pt