The reproductive biology of the depressed river mussel, Pseudanodonta complanata (Bivalvia: Unionidae), with implications for its conservation

Pseudanodonta complanata is listed as ‘Near Threatened’on the IUCN Red List (IUCN, 2006) and is a species of conservationpriority on the UK Biodiversity Action Plan. The UK is hostto some of the largest populations of this species, but littleis known about their reproductive biology. Two populations werestudied in the Great Ouse catchment and the Waveney and Yarecatchment, East Anglia, UK. Both populations are reproductivelyactive, producing viable glochidia. Small mussels (<30 mmlength) in both catchments indicate that recruitment is occurring.A short non-gravid period in May is followed by three monthsof glochidial formation in June, July and August; by Septembermussels contain mature glochidia ready for release the followingApril. Females brood between 5,000 and 50,000 glochidia, andthis scales with mussel length L (mm) as: n_glochL^2.1. The sexratio is skewed towards females (2.5 females:1 male), and malesare larger than females. No hermaphrodites were found duringthe histological examination of the gonads of 24 mussels. Thein vivo examination of demibranchs is shown to be an effectivenonsacrificial means of determining sex and gravidity. Conservationrecommendations include: minimizing management operations inriver stretches containing large populations; avoiding formsof management which preferentially remove large mussels (i.e.males and the most fecund females); performing management duringthe non-gravid period to avoid causing the premature releaseof glochidia; leaving sufficient time between management operationsfor populations to recover; and temporarily translocating musselsto refugia during management operations. (Received 9 February 2005; accepted 2 May 2007)