MEPS 644:91-103 (2020)  -  DOI: https://doi.org/10.3354/meps13314

ABSTRACT: Benthic suspension feeders, such as bivalves, potentially have several different food sources, including plankton and resuspended detritus of benthic origin. We hypothesised that suspension feeders are likely to feed on detritus if it is present. This inference would be further strengthened if there was a correlation between δ¹³C of suspension feeder tissue and δ¹³C of particulate organic matter (POM). Since detritus is characterised by high particulate organic matter (POC):chl a ratios, we would also predict a positive correlation between POM δ¹³C and POC:chl a. We hypothesised that increasing depth and greater distance from shore would produce a greater nutritional reliance by experimentally transplanted blue mussels Mytilus edulis on plankton rather than macrophyte-derived detritus. After deployments of 3 mo duration in 2 different years at depths from 3 to 40 m, M. edulis sizes were positively correlated with POM concentrations. POC:chl a ratios and δ¹³C of POM and M. edulis gill tissue decreased with increasing depth (and greater distance from shore). δ¹³C of POM was correlated with δ¹³C of M. edulis. Our results suggest that detritus comprised a large proportion of POM at shallow depths (<15 m), that M. edulis ingested and assimilated carbon in proportion to its availability in POM, and that growth of M. edulis was higher where detritus was present and POM concentrations were higher.

KEY WORDS: Carbon · Stable isotope analysis · Detritus · Phytoplankton · Seagrass · Kelp · Suspension feeders.