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RESEARCH ARTICLE
Contents Vol 57(4)

Effects of a freshwater canal discharge on an ovoviviparous isopod inhabiting an exposed sandy beach

Juan Pablo Lozoya A and Omar Defeo A B
+ Author Affiliations
- Author Affiliations

A UNDECIMAR, Facultad de Ciencias. Iguá 4225, Montevideo 11400, Uruguay.

B Corresponding author. Email: odefeo@fcien.edu.uy

Marine and Freshwater Research 57(4) 421-428 https://doi.org/10.1071/MF05067
Submitted: 9 April 2005  Accepted: 21 March 2006   Published: 14 June 2006

Abstract

The present study evaluates the effects of an artificial freshwater discharge (Canal Andreoni) on the ecology of the ovoviviparous isopod Excirolana armata. Bimonthly, 17 environmental variables plus isopod abundance, biomass, fecundity, growth and mortality were compared between three sites: ‘Barra del Chuy’ (undisturbed), at 13 km from the canal, ‘Coronilla’ (moderately disturbed), at 1 km, and ‘Andreoni’ (grossly disturbed), at the canal mouth. Environmental (salinity, slope, beach width, and swash width) and some biological (isopod abundance, biomass and growth rates) variables significantly decreased towards Canal Andreoni. Salinity was the most important explanatory variable of spatial trends in isopod biomass. However, the reproductive output, fecundity, survival and individual weight were not affected, suggesting that E. armata is regulated by density-dependent and abiotic factors operating together: the former were more intense on undisturbed conditions, whereas the latter prevailed in impacted ones. Internal brooding counteracts the effect of fresh water, which explains the lack of effect of environmental harshness on reproductive traits.

Extra keywords: Excirolana, freshwater discharges, internal brooding, Uruguay.


Acknowledgments

This paper is part of the MSc thesis of J.P.L. We wish to express our gratitude to the ‘Benthic Ecology Group’ of UNDECIMAR for field and laboratory assistance. J.P.L. especially thanks Cate, Amelia and Paco for their continuous encouragement. Suggestions by three anonymous referees substantially improved the final manuscript. Financial support from CONICYT (Projects N° 1018 and 4034), PEDECIBA and PDT (Project S/C/OP/07/49) is acknowledged.


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