Trophic relationships between the farmed pearl oyster Pinctada margaritifera and its epibionts revealed by stable isotopes and feeding experiments

Abstract

Bivalve cultures support a host of epibionts, mainly suspension feeders, which can compete for food resources with the cultivated bivalves. However, the magnitude of interspecific competition for food in bivalve aquaculture settings remains inconclusive, especially in tropical areas. We investigated the interactions for food between the farmed pearl oyster Pinctada margaritifera and its epibionts, using stable isotope analysis and feeding experiments. Inter-and intraspecific variations of δ 13 C and δ 15 N stable isotope ratios (SIRs) were determined for oysters in the presence or absence of epibionts. The diet of the most abundant epibionts, Herdmania momus and Didemnum sp., was specified using isotope measurements and flow cytometry during feeding experiments, to determine the main phytoplankton groups consumed by these ascidians in natural conditions. The absence of intraspecific variation in SIRs among oysters with or without epibionts suggested that the diet of P. margaritifera was not affected by the presence of epibionts, indicating a reduced diet overlap and no food limitation. The δ 13 C signature of ascidians (−21 ‰) was lower than that of oysters (−18 ‰), indicating a difference in organic matter sources ingested by these filter feeders despite receiving the same food mixture. While the main carbon source of oysters came from large particulate organic matter (POM) > 20 µm, our results showed that the diet of ascidians mainly came from smaller particles (POM < 20 µm) and reflects the composition of ambient water (mainly picophytoplankton < 2 µm), which confirmed their lack of food selectivity. In the studied conditions, food competition between oysters and epibionts, specifically ascidians, was not a limiting factor, in spite of a diet overlap for nanophytoplankton.

Effect of species diversity on particle clearance and productivity in farmed bivalves

“…Species within the suspension-feeding guild have considerable overlap in the size of particles they can acquire. Yet, some suspension feeders do partition available food resources to minimize interspecific competition (Peterson 1982, Lesser et al 1992, Kang et al 2009, Lacoste et al 2016, Novais et al 2016. We propose that in this study, the bivalve polyculture removed more suspended seston than monocultures due to variations in particle capture processes and differences in dietary requirements or preferences exhibited by the 4 focal species.…”

Shellfish culture: a complex driver of planktonic communities

“…; Lacoste & Gaertner‐Mazouni ; Lacoste et al . ). The reason for this is that biofouling organisms include many filter‐feeder species, such as ascidians, gastropods, polychaetes, bryozoans or hydrozoans (review in Dürr & Watson ), which contributes to significantly increasing the total grazing pressure on a planktonic community (Woods et al .…”

“…; Lacoste et al . ). Therefore, the combined influence of all these communities (reared bivalve species and epibionts) on the planktonic community should be considered more closely.…”

Potential of Ascidians as Extractive Species and Their Added Value in Marine Integrated Multitrophic Aquaculture Systems–From Pests to Valuable Blue Bioresources

“…Various approaches have shown that the diet of ascidians mainly comes from smaller particles [particulate organic matter (POM) < 20 µm] (Ju et al, 2015(Ju et al, , 2016, picophytoplankton (<2 µm), and phytoplankton biomass (Riisgärd and Larsen, 2016). Moreover, Lacoste et al (2016) verified an overall lack of food selectivity. The retention efficiency increased for particle sizes 2-5 µm (Armsworthy et al, 2001), in which particles from 2 to 3 µm were completely retained (Randløv and Riisgärd, 1979) and retention efficiency decreased for particles above 4.5 µm (Pascoe et al, 2007).…”