MEPS 543:37-54 (2016)  -  DOI: https://doi.org/10.3354/meps11567

ABSTRACT: Benthic filter feeders have key functional roles in coastal ecosystems as an intermediate trophic level in food webs and as bioengineers. The food available to such species depends on the local composition of the water column, reflecting factors operating across multiple spatial scales. Here, we examined how upwelling and biogeography influence their dietary signatures. The diet regimes of 2 mussels and 1 barnacle were investigated using fatty acid (FA) and stable isotope (SI) analyses across 13 sites spanning 3000 km across 3 biogeographic regions corresponding to the west, south and east coasts of South Africa. SI and FA signatures showed similar patterns for all taxa. δ¹⁵N signatures of filter feeders increased from the oligotrophic east to the eutrophic west coast, with no difference between upwelling and non-upwelling sites, while δ¹³C signatures significantly decreased at upwelling sites. The lower δ¹³C signature associated with upwelling indicates different food sources from non-upwelling sites. FA signatures changed among coasts, with west coast samples differing from the south and east coasts. Upwelling affected the FA signature of filter feeders only on the west coast, where upwelling events are stronger. These specimens were enriched in polyunsaturated FA, a marker of high food quality. Hence, a powerful effect of upwelling was detectable in filter feeder diets, but depended on upwelling intensity and frequency, and was nested within the overriding effects of biogeography.

KEY WORDS: Trophic ecology · Fatty acids · Stable isotopes · Spatial scale · Intertidal ecology · Mytilus galloprovincialis · Perna perna · Chthamalus dentatus