Project: RAPID: Human-Driven Trophic Cascades: Mesopredator Release and Recreational Fishing in Estuaries

NSF Award Abstract:
Human activity affects natural populations of organisms directly through exploitation and indirectly by changing how species interact with each other. This project is investigating the effect of fishing on an estuarine food web. In the oyster reef food chain, newly settled oysters are eaten by crabs, and the crabs are in turn eaten by fish. More fish predators mean fewer crabs and more oysters. Fish also reduce foraging by crabs, which further benefits oysters. Although small-scale experimental studies have measured the impact of fish exclusion on oyster reefs, the links between fishing, fish populations and oyster reefs require an estuary-scale experiment. Stay-at-home orders associated with the COVID-19 pandemic has curtailed fishing activity throughout estuaries. This project combines empirical experiments and fisheries monitoring data from before, during and after COVID-19-related restrictions to investigate how changes in fishing activity influence oyster reef food webs. Building on 10+ years of preexisting observations the dataset encompasses a 100-year flood, a hurricane, and now a pandemic, a rare opportunity to investigate the effects of low fishing pressure in the absence of other disturbances. The broader impacts of this study contribution of data towards optimizing management and conservation of marine resources. Oyster reefs are essential habitat that perform ecosystem services such as water filtration and shoreline stabilization, but they are also harvested as a commercial fishery. Interest in estuarine systems for recreation and fishing is high along the Gulf of Mexico. Public displays and outreach activities at the Dauphin Island Sea Lab will include results from this project to increase awareness of the effect of human activity on local ecosystems.

The loss of top predators can destabilize ecosystems by making them more prone to invasions, altering nutrient fluxes within and between habitats, and impeding recovery after disturbances. Overfishing reduces the abundance of higher order predators, leading to higher abundances of intermediate consumers or mesopredators. Mesopredator release can increase predation pressure on basal trophic levels, including foundation species. In estuaries, fin fish, many of which are targeted by both commercial and recreational anglers, provide an important trophic link and their removal or experimental exclusion can trigger mesopredator release. However, the extent that fishing alters communities remains poorly understood. Estuarine systems along the Gulf of Mexico have experienced nearly continuous and widespread exploitation for over a century, and the few examples of temporary releases from fishing pressure have co-occurred with other natural disasters. The COVID-19 pandemic has curtailed fishing and has provided a unique research opportunity. Using a Before After Control Impact (BACI) design, the effects of fishing pressure on top-down control is being investigated in a model system, oyster reefs. Fishing activity and fish stock assessments are compared with field experiments to determine top predator feeding activity, mesopredator abundances, and recruitment and growth of oysters. To gauge changes in the structure of estuarine food webs, the data are being compared with 10+ years of preexisting results to isolate the effect of fishing activity from confounding factors associated with natural disasters like hurricanes and floods.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.