The uptake and release of suspended and dissolved material by oysters and mussels in Marennes-Oléron Bay

Abstract

The uptake and release of material by oysters (Crassostrea gigas) and mussels (Mytilus edulis) in Marennes-Oléron Bay (SW France) were measured in situ using benthic ecosystem tunnels (BEST). There was a large variation in seston concentrations, owing to high sedimentationlerosion dynamics. Organic matter was diluted by resuspended sediment, but had a low C/N ratio, i.e. a high quality, owing to resuspension of microphytobenthos. In many cases a significant decrease of chlorophyll concentrations was observed in tunnels with oysters and mussels. Average clearance rates per tidal cycle ranged from 4 to 7, and from 0.9 to 2.7 1.g-'AFDW.h-' throughout the season, for oysters and mussels respectively. Calculation of the filtration pressure (the fraction of the primary production filtered per day), indicated that bivalves in the bay were able to filter much more than the daily pelagic primary production. It seemed obvious that the bivalve stocks depended not only on phytoplankton but also on microphytobenthos. Significant regeneration of nitrogen could be demonstrated from musselbeds on the sediment, at higher rates than direct excretion of ammonium. No significant release of nutrients was obsewed for the oysters or mussels, when they were put on tables, as practised by the oyster farmers. lt seemed likely that biodeposits were flushed away from the tunnels in this case, and mineralization occurred elsewhere. It was concluded that the canying capacity of the bay for herbivores is extensively exploited by the shellfish. Mineralization of bivalve biodeposits represent a large potential for nitrogen regeneration.

Impact of Brown Ring Disease on the energy budget of the Manila clam Ruditapes philippinarum

“…In the field, Manila clams live mainly in the intertidal zone and filtration is not possible during low tide. Moreover, food concentration may vary with the tidal cycle and over short time scales (Smaal and Haas, 1997;Smaal and Zurburg, 1997). Consequently, for such an intertidal bivalve, food is available during a limited period only; thus, decreased filtration capacity should lead to a pronounced loss of efficiency in the exploitation of available trophic resources.…”

Open water integrated multi-trophic aquaculture: constraints on the effectiveness of mussels as an organic extractive component

“…4). Organic matter in mussel feces was assumed to be 5% carbon (Smaal & Zurburg 1997). Total DW and carbon egestion rates were calculated for comparison with results from previous model predictions.…”

Temporal scaling and relevance of bivalve nutrient excretion on a tidal flat of the Seto Inland Sea, Japan

“…However, uncertainty about the actual contribution of animal excretion to the total flux may still remain due to the additional effect of local variables. These include nutrient release due to microbial mineralization of vegetative detritus (Falcao & Vale 1990) and anirnal biodeposits (Hennksen et al 1983, Gardner et al 1993, Smaal & Zurburg 1997. The nutrient release from sediments may also be enhanced by bioturbation and irrigation currents due to benthic infauna species (Callender & Hamrnond 1982, Hennksen et al 1983, Yamada & Kayama 1987, Aller 1988, Luther et al 1998).…”

“…Further, a factor which has been given httle attention in quantifying the animal contnbution to the processes of nutrient regeneration is the temporal variability of the macrozoobenthic communities. In intertidal zones, major studies on the release of nutnents by dense populations of bivalves have been based on 1 (Dame et al 1984, Dame & Dankers 1988 or relatively few sampling occasions (Pnns , Smaal & Zurburg 1997. Other studies have investigated the year-round seasonal variation of animal nutrient excretion through in situ chamber incubations (Yamada & Kayama 1987, Boucher & Boucher-Rodoni 1988, Schlüter & Josefsen 1994.…”