Small-scale spatial variability of food partitioning between cultivated oysters and associated suspension-feeding species, as revealed by stable isotopes

Abstract

Oyster culture structures support a host of epibionts belonging to the same suspensionfeeding guild, which are considered to be potential competitors for food with cultivated oysters. In an intertidal shellfish ecosystem on the northern French coast, an approach based on stable isotopes ( 13 C and 15 N) was used to investigate intra-and interspecific food resource partitioning among cultivated oysters and the main associated wild sessile epibionts such as polychaetes, barnacles, mussels and ascidians. The main objective of the present study was to determine inter-and intraspecific food partitioning, along with small-scale spatial variability, within the guild of suspension feeders. We demonstrated that interspecific competition was limited among co-occurring suspension-feeders (ascidians, serpulid and terebellid polychaetes, bivalves and barnacles). None of the studied species had similar δ 13 C and δ 15 N signatures, indicating that relative contributions of organic matter sources may differ for each suspension-feeding species. Spatial variability was investigated both from the view of intra-and interspecific variability. Intraspecific variability was examined with regard to species' feeding biology and the trophic plasticity of co-occurring suspension-feeders. Mantel tests indicated that spatial heterogeneity resulted not only from environmental conditions, such as elevation above sea level (a.s.l.) and sediment features, but also from the inherent spatial structure of isotopic signatures. Our results show that isotopic approaches that are limited to sampling in one area and at one time are at risk of mistaking trophic interactions.

Spatial and temporal interaction between sediment and microphytobenthos in a temperate estuarine macro-intertidal bay

“…The positive influence of silt on benthic diatoms must be involved in the long-term trends in macrozoobenthic community by increasing the trophic plasticity of the macrozoobenthic community, making possible the coexistence of a wide variety of different species in sediments surrounding oyster farms. However, interaction between MPB and macrozoobenthos must be more thoroughly examined to verify (1) whether long-term MPB development is a factor favouring the trophic plasticity in these habitats (Dubois et al 2007, Lefebvre et al 2009) and (2) the long-term trends concerning macro zoobenthic assemblage evolution (Timsit et al 2004). …”

“…Dynamics of marine systems vary widely in their temporal and spatial components due to complexity in the benthopelagic coupling (Zajac 2008). The trophic environment of benthic fauna in these systems is therefore characterised by a high degree of spatial heterogeneity, such as transition zones and patches (Deegan & Garritt 1997, Dubois et al 2007) that are related to the landscape of their habitats. It appears very relevant to understand the spatial patterns of primary producers in relation to sediment in order to elucidate the role they play in the trophic food web and to assess the respective contributions of both components to consumer's diet (Lefebvre et al 2009).…”

“…The tidal range of this macrotidal system during spring tide is about 8 m. The tidal regime is semi-diurnal and the synchronization between daytime exposure periods and solar noon occurs during neap tides. The bay contains a total area of about 117 km 2 from which 37 km 2 are intertidal flats, and current velocity can reach 3 m s −1 during flood tide and 1.5 m s −1 during ebb tide (Dubois et al 2007). The rivers Douve and Taute join together in the western Carentan Channel while 2 other rivers, Vire and Aure, converge to form the eastern Isigny Channel.…”

Trophic transfer and habitat use of oyster Crassostrea virginica reefs in southwest Florida, identified by stable isotope analysis

“…Oysters were cleaned of epibionts and kept alive for 12 h in seawater prepared with deionized water and Instant Ocean® at the salinity of collection site to allow for evacuation of their gut contents (Gearing 1991, Decottignies et al 2007, Dubois et al 2007. Tissues from individual oysters were removed from the shells and stored in pre-combusted (500°C, 4 h) 20 ml glass scintillation vials at −20°C until further processing (Dubois et al 2007). …”

Trophic typology of coastal ecosystems based on δ13C and δ15N ratios in an opportunistic suspension feeder

“…Previously, spatial variability has only been studied on small scales, generally within bays (e.g. Dubois et al 2007b) or along an estuarine gradient (e.g. Piola et al 2006), within the same system with comparable functioning.…”