Abstract
Since 2010, the northern Gulf of Mexico (NGoM) has experienced two unique environmental stressors. First, the 2010 Deepwater Horizon oil spill (DWH) impacted a broad range of taxa and habitats and resulted in declines of small demersal reef fish over the study area (88.5°-85.5° W, 29°-30.5° N). Then, from 2011-2014 the invasive Indo-Pacific lionfish (Pterois volitans) underwent exponential population growth, leading to some of the highest densities in their invaded range. The primary objective of this study was to evaluate the effect of these stressors on reef ecosystems, and specifically how invasive lionfish and fishing may have impacted recovery following DWH. Site-specific datasets on fish density and diet composition were synthesized into an Ecopath with Ecosim food web model of a NGoM reef ecosystem. The model consisted of 63 biomass groups and was calibrated to time series of abundance from 2009-2016. The model accounted for mortality from the DWH using forcing functions derived from logistic dose-response curves and oil concentrations. Eight stressor scenarios were simulated, representing all combinations of DWH, lionfish, and fishing. Simulated biomass differed across model groups due to singular and cumulative impacts of stressors and direct and indirect effects arising through food web interactions. Species with high exploitation rates were influenced by fishing more than lionfish following DWH. Several small demersal fish groups were predicted to be strongly influenced by either the cumulative effects of lionfish and DWH or by lionfish alone. A second group of small demersal fish benefited in the stressor scenarios due to reduced top-down predation and competition in the combined stressor scenarios. We conclude that lionfish had a major impact on this ecosystem, leading to slower recoveries following DWH and lower fish biomass and diversity. Additionally, the lack of recovery for some groups in the absence of lionfish suggests system reorganization may be preventing return to a pre-DWH state. We intended for this work to improve our understanding of how temperate reef ecosystems, like those in the NGoM, respond to broad scale stressors and advance the state of applied ecosystem modeling for resource damage assessment and restoration planning.
Highlights
The world’s marine and freshwater ecosystems are increasingly being affected by multiple environmental and anthropogenic stressors
We intended for this work to improve our understanding of how temperate reef ecosystems with complex food webs, like those in the northern Gulf of Mexico (NGoM), respond to broad scale stressors and advance the state of applied ecosystem modeling for resource damage assessment and restoration planning
Biomass dynamics were predicted for all model groups, including invertebrates and primary producers, we focused our analysis on the reef fish community because they contain informative data spanning the period before and after the Deepwater Horizon oil spill (DWH) and lionfish invasion on which we can evaluate model performance; and because reef fishes and their habitats were prioritized for restoration funds following the DWH, with at least $200 million USD allocated to research, monitoring, and enhancement of these resources since 20101
Summary
The world’s marine and freshwater ecosystems are increasingly being affected by multiple environmental and anthropogenic stressors. In marine and estuarine systems, common stressors include overexploitation, eutrophication, hypoxia, habitat loss, pollution, acidification, harmful algal blooms, tropical cyclones, rising temperatures, and invasive species. These stressors can have system-wide impacts and affect multiple trophic levels when major energy pathways or habitat types are altered (O’Connor et al, 2009; Ullah et al, 2018), leading to changes in community structure and diversity (Flaherty and Landsberg, 2011; Worm and Lotze, 2016; Lewis et al, 2020), and impact the abundance, behavior, and fitness of individuals (Watterson et al, 1998; Hernandez et al, 2016). The natural variability and large observation error exhibited in marine ecosystems adds to the difficulty in detecting significant effects of multiple stressors
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