Spatial and temporal shifts in the diet of the barnacle Amphibalanus eburneus within a subtropical estuary

The success of many sessile invertebrates in marine benthic communities is linked to their ability to efficiently remove suspended organic matter from the surrounding water column. To investigate the diet of the barnacle Amphibalanus eburneus, a dominant suspension feeder within the Indian River Lagoon (IRL) of central Florida, we compared the stable isotopes ratios (delta C-13 and delta N-15) of barnacle tissue to those of particulate organic matter (POM). Collections were carried out quarterly for a year from 29 permanent sites and at sites impacted by an Aureoumbra lagunensis bloom. delta C-13 and delta N-15 values of Amphibalanus eburneus varied across sites, but delta N-15 was more stable over time. There was a range of delta N-15 values of Amphibalanus eburneus tissue from 6.0%o to 10.5%o across sites. Because land-based sources such as sewage are generally enriched in N-15, this suggests a continuum of anthropogenic influence across sites in the IRL. Over 70% of the variation in delta N-15 values of Amphibalanus eburneus across sites was driven by the delta N-15 values of POM, supporting a generalist feeding strategy on available sources of suspended organic matter. The dominance of this generalist consumer in the IRL may be linked to its ability to consume spatially and temporally variable food resources derived from natural and anthropogenic sources, as well as Aureoumbra lagunensis cells. Generalist consumers such as Amphibalanus eburneus serve an important ecological role in this ecosystem and act as a sentinel species and recorder of local, site-specific isotopic baselines.