Rapid decline of the greater European peaclam at the periphery of its distribution

¹ CBMA – Centre of Molecular and Environmental Biology, Department of Biology, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal
² CIMAR-LA/CIIMAR – Centre of Marine and Environmental Research, Rua dos Bragas 289, 4050-123 Porto, Portugal
³ ICBAS – Institute of Biomedical Sciences of Abel Salazar, University of Porto, Department of Populations Studies, Laboratory of Ecotoxicology, Lg. Prof. Abel Salazar, 2, 4099-003 Porto, Portugal
⁴ Aquamuseum of the Minho River, Parque do Castelinho, 4920-290 Vila Nova de Cerveira, Portugal

^* Corresponding author: ronaldo.sousa@ciimar.up.pt

Received: 12 January 2011
Accepted: 29 April 2011

Abstract

Extirpation or even extinction of freshwater invertebrate species is a neglected conservation issue; declines in abundance and spatial distribution for freshwater invertebrates are far less documented than for vertebrate species. In the Minho River tidal freshwater wetlands (northwest of Iberian Peninsula), a rapid decline in density and biomass of the bivalve Pisidium amnicum was recorded at 16 different sites over seven years, from 2004 to 2010, without any sign of a potential recovery. Mean density values reached more than 80 ind.m⁻² in 2004, but declined to less than 1 ind.m⁻² in 2009 and 2010. An identical declining trend was observed for biomass. A significant reduction in the spatial distribution also occurred. The abiotic changes resulting from the 2005 heat wave and possibly the negative interactions imposed by the non-indigenous invasive bivalve Corbicula fluminea were the main factors responsible for the declining trends. Given the very low density, P. amnicum is facing a serious risk of extirpation in this ecosystem and conservational measures are urgently needed.