JPR Advance Access originally published online on February 2, 2006
Journal of Plankton Research 2006 28(3):297-312; doi:10.1093/plankt/fbi126
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Zooplankton and ichthyoplankton communities in a temperate estuary: spatial and temporal patterns
IMAR – Institute of Marine Research, Department of Zoology, University of Coimbra, 3004-517 Coimbra, Portugal
* Corresponding Author: scotrim{at}ci.uc.pt
Received April 3, 2005; accepted in principle January 18, 2006; accepted for publication January 27, 2006; published online February 2, 2006
Communicating editor: R.P. Harris
Zooplankton and ichthyoplankton assemblages were studied from January 2003 to June 2004 in a temperate shallow estuary (Mondego estuary, Portugal). Monthly sampling was performed at five stations at high and low tides, with subsurface tows with 335 and 500 µm mesh Bongo nets. Analysis of variance (ANOVA) showed a significant effect (P < 0.05) of the mesh size of the net on the abundance of main zooplankton groups. On average, the abundance of the 500 µm taxocenosis was 67 and 102 times lower than the 335 µm taxocenosis at high and low tides respectively, especially in the south arm. More than 80 species were identified in the zooplankton samples. The upper reaches of northern arm are dominated by freshwater crustacean mesozooplankton like Acanthocyclops robustus and Diaptomus spp. and the cladocerans Daphnia, Ceriodaphnia and Bosmina, often being codominant. In the southern arm, the resident estuarine copepod Acartia tonsa was dominant, eventually being the most abundant taxon. Marine reaches of estuary are usually dominated by the marine calanoid copepods Acartia clausi and Temora longicornis and the siphonophores Muggiaea atlantica. Concerning the ichthyoplankton, this was dominated by the larvae of estuarine resident species, mainly Pomatoschistus sp., and eggs of Engraulis encrasicolus. The abundance of Pomatoschistus sp. larvae was positively correlated with water temperature. Statistical analysis (canonical correspondence analysis) used to determine the spatiotemporal structure of the zooplankton assemblages and its correlation with environmental variables showed that salinity and temperature were the main factors influencing the distribution of zooplankton. The results obtained also showed that abundance was strongly influenced by the hydrological circulation pattern and direct or indirect human impacts that occur in each arm of the estuary.
This article was presented at Plankton Symposium III, held at Figuera da Foz, portugal, between 17 and 20 March 2005, under the auspices of the University of Coimbra and the University of Aveiro, and coordinated by Mário Jorge Pereira and Ulisses M. Azeiteiro.