Julia Cox1, Henry M Page1, Robert Miller1
1University of California Santa Barbara, USA
Fishing impacts temperate reef ecosystems by altering predation, competition, and food web structure. Targeted removal of key species or size classes can lessen competition for food, leading to changes in diet and community restructuring amongst remaining fish populations. Understanding the impacts of fishing on food webs is essential to preserving ecosystem services such as fishery-based food and economies. Marine Protected Areas (MPAs) that limit or prohibit fishing frequently cause increased densities and sizes of fished species within their boundaries. Lack of fishing in MPAs provides an opportunity to utilize the protected areas as natural fishing exclusion experiments to infer the effects of fishing on food webs. In the Santa Barbara Channel (California, USA), we sampled paired MPA and unprotected rocky reef sites for two fish species that are harvested both commercially and recreationally (Paralabrax clathratus and Sebastes atrovirens) and one species that does not support a fishery (Oxyjulis californica). We identified and enumerated fish gut contents and utilized isotope ratio mass spectrometry to infer diet and trophic position from fish tissue. We used nitrogen isotope ratios to estimate trophic level, and compared isotopic data and gut contents across reefs, species, standard length, and protection status. Preliminary results show variability in trophic level across reefs for all three fish, suggesting variability in trophic structure across reefs and emphasizing the need for specific management practices informed by the unique dynamics of each reef. There was a positive relationship between standard length and trophic level for P. clathratus and S. atrovirens, indicating that size structure affects trophic structure. This work provides insight into food web dynamics of temperate reef ecosystems, and has potential to inform conservation and management practices to preserve essential ecosystem services derived from fisheries.
Biography
Julia Cox is a PhD student in the Interdepartmental Graduate Program in Marine Science at the University of California, Santa Barbara. She studies kelp forest food web dynamics and fisheries in the Santa Barbara Channel, using stable isotope analysis (SIA) to examine organisms’ roles within the food web and conducting SCUBA surveys of reefs. Julia’s interest in fisheries began during her position at a federal fish hatchery, where she spent summers raising fish and connecting with the public.