Dietary contribution of polychlorinated biphenyl contaminated Ulva to Fundulus heteroclitus in the New Bedford Harbor, MA, Superfund site

Macroalgal blooms are associated with a wide range of negative consequences impacting the growth and survival of primary producers and benthic consumers, but are generally not viewed as serious threats to higher trophic level consumers. A recently discovered polychlorinated biphenyl (PCB) contaminated Ulva bloom located in the New Bedford Harbor (NBH), MA, Superfund site challenges this idea, but its potential to increase the bioavailability of PCBs to the upper NBH food web has not previously been evaluated. In this investigation, the dietary contribution of Ulva to the common NBH mid-trophic consumer Fundulus heteroclitus was assessed between fall 2011 and fall 2012 using a combined approach of gut content analysis (GCA) and stable isotope analysis (SIA). Monthly GCA performed on samples collected between May and October, 2012 showed a seasonal pattern of Ulva consumption correlated to algal presence, trends in invertebrate prey abundance, and environmental conditions. Ulva was a dominant gut component found between early August and mid September following a dietary shift from invertebrate to Ulva consumption. When pooling all analyzed Fundulus samples, peak Ulva gut presence in early August (75.37+/-3.81%) equated to an estimated peak daily Ulva consumption of 42.3+/-8.4 mg Ulva dry weight and coincided with dense algal presence (607.3+/-238.6 g/m2). SIA results inversely showed a higher Ulva contribution to Fundulus diet in the fall compared to summer with a consistently high dietary contribution of grass shrimp ( Palaemonetes pugio). Combined evidence suggests that Fundulus are consuming Ulva as a by-product of prey foraging. Increased ingestion during the fall of P. pugio feeding upon Ulva may compensate for decreased direct Ulva ingestion and result in increased relative contribution of Ulva to the Fundulusdiet. Findings of this study demonstrate that Ulva can be a source of PCBs in the NBH food web. Future research should focus on the trophic transfer of PCBs between the bloom and Fundulus and the trophic transfer of PCBs from Fundulus to higher-level consumers in the NBH system such as striped bass.