Exploitation of natural food sources by two sympatric, invasive suspension-feeders: Crassostrea gigas and Crepidula fornicata

Abstract

The natural diets of the introduced suspension-feeders Crassostrea gigas (Thunberg) and Crepidula fornicata (L.) were determined at a mid-latitudinal oyster-farming site within their European range (Bourgneuf Bay, France). Carbon and nitrogen stable isotope deviations of Pacific oysters and slipper limpets were compared with potential food sources on 3 sampling dates (March, July and November 2003). Four end-members were assimilated by the 2 species: C 3 angiosperm detritus, macroalgae-C 4 plant detritus, marine phytoplankton and benthic diatoms. Given the lack of source digestibility data for suspension-feeders, and these 2 species in particular, extreme feasible combinations of relative end-member contributions were calculated according to 2 assimilation scenarios, using either IsoSource software or a concentration-dependent model. For both Crassostrea gigas and Crepidula fornicata, benthic and planktonic microalgae dominated diets on the 3 sampling dates. Planktonic microalgae were ingested in greater proportions than benthic species in July and November; however, benthic diatoms also formed a constant and significant part of diets in these months, and were consumed in greater proportions than planktonic species in March. Plant (especially macroalgal) detritus played a major role in the diets of the 2 suspension-feeders, notably in March 2003 when it became the principal ingested source. The substantial contribution of plant detritus to the natural diets of these species has not previously been reported. Although Crassostrea gigas and Crepidula fornicata showed significantly different isotopic deviations in March and July 2003, trophic niches of Crassostrea gigas and Crepidula fornicata overlapped on all 3 sampling dates, with a greater ingestion of identical sources in November. These 2 invasive species could therefore be trophic competitors in the context of end-member supply limitation. Contrary to previous analyses conducted on these 2 species in Europe, this study reports significant dietary overlap. Ecosystemspecific diet studies of invasive species are thus necessary in order to understand trophic overlap/ competition as a function of the diversity and availability of local food sources.

Distribution and dynamics of intertidal macrobenthos predicted from remote sensing: response to microphytobenthos and environment

“…Some species, such as Macoma balthica, may feed on both sources, depending on for instance life stage or food availability (Taghon et al 1980, Herman et al 2000, Riisgård & Kamermans 2001, Rossi et al 2004). Microphytobenthos can, when resuspended, also provide food for suspension feeders (Decottignies et al 2007), whereas phytoplankton can deposit during calm conditions and becomes incorporated in the microphytobenthos , Safi 2003. In our study, the response of most trophic groups and species was best explained using a combination of environmental variables, including sediment properties and food resources.…”

Multi-scale spatial variation in stable isotope and fatty acid profiles amongst temperate reef species: implications for design and interpretation of trophic studies

“…Additionally, as the part of the plant that is eaten directly by the consumer is often unknown, or contributes to the diet of the consumer via the detrital pathway (e.g. Jaramillo et al 2003, Guest et al 2004, Tala & Edding 2005, Decottignies et al 2007), a composite sample that provides an average isotope signature of the autotroph is recommended.…”

“…Additionally, as the part of the plant that is eaten directly by the consumer is often unknown, or contributes to the diet of the consumer via the detrital pathway (e.g. Jaramillo et al 2003, Guest et al 2004, Tala & Edding 2005, Decottignies et al 2007), a composite sample that provides an average isotope signature of the autotroph is recommended.Intra-plant variability of carbon isotopes has previously been reported for macroalgae. The distal parts of Ecklonia radiata (Fenton & Ritz 1989) and Laminaria longicruris (Stephenson et al 1984) were more depleted (i.e.…”

Satellite remote sensing reveals a positive impact of living oyster reefs on microalgal biofilm development

“…MPB can contribute up to 50 % of total primary production in estuarine and coastal ecosystems (Underwood and Kromkamp, 1999) and is an important food source for higher trophic levels . After resuspension in the water column (De Jonge and Van Beuselom, 1992), benthic microalgae become available for filter feeders such as oysters (Decottignies et al, 2007). However, MPB and oyster interactions are more complex than a simple predator-prey relationship.…”