Dara Yiu1,2, Emma Elliott Smith3, Shane Farrell1,2, Douglas Rasher2
1University of Maine Darling Marine Center, USA - 2Bigelow Laboratory for Ocean Sciences, USA - 3University of New Mexico, USA
Kelps serve as foundation species in coastal seas around the world, providing habitat and energy resources that influence the structure of fish assemblages. However, the ecological linkages between fish and kelp are not well resolved in the Northwest Atlantic, where kelps (i.e., Laminaria digitata and Saccharina latissima) are rapidly declining due to ocean warming, and kelp forests are giving way to degraded reefs dominated by diminutive red turf algae. Here, we investigated reef fish communities across 250 km of the Gulf of Maine, focused on subregions in coastal Maine at varying stages of the kelp-to-turf transition. Although total reef fish biomass was unrelated to the abundance of kelp, we found that kelp forest loss had significant effects on fish resource use and trophic dynamics. Specifically, bulk tissue stable carbon and nitrogen isotope analysis of fish muscle revealed that kelp forest fishes had larger trophic niches and greater interspecific niche separation than did those on turf-dominated reefs. Additionally, essential amino acid stable carbon isotope (δ13CEAA) analysis demonstrated that predatory fishes in kelp forests derived more than 50 % of their energy from kelp. In contrast, fishes from turf-dominated reefs relied more heavily on phytoplankton-derived organic matter, rather than shifting to utilize red algae. Our findings highlight that even where fish abundance is not closely linked to foundation species, climate-driven state shifts can fundamentally alter fish trophic interactions and the flow of organic matter through temperate coastal food webs.
Biography
Dara is a PhD student studying the ecology of rocky reef fishes in the Gulf of Maine. Her dissertation investigates impacts of a ‘kelp forest to turf reef’ state shift on the fishes and food webs here. She is assessing connectivity between fishes and habitat using visual surveys and eDNA. She also aims to build a more complete understanding of the ecological role of local fishes in modern rocky reef food webs by investigating predator-prey interactions with diet analysis and stable isotopes.