Complexities of disturbance response in a marine food web

Abstract

A primary aspect of applied marine ecology assesses how food webs change in response to ecosystem disturbances. In 2010, the drilling rig Deepwater Horizon (DWH) discharged ~3.19 million barrels of crude oil into the northern Gulf of Mexico. The spill, followed by widespread dispersant application to enhance oil degradation, represented a significant anthropogenic disturbance in the region. We created network models of four multi-year periods, to represent the acute and chronic food web responses to the DWH spill. Using ecological network analysis (ENA) and information theory, we compared multiple food web metrics among these periods in the context of food web resilience theory. This analysis was conducted at three levels of hierarchical organization: whole ecosystem, nekton community, and individual nekton taxa. We analyzed how individual taxa contribute to resilience of the food web with a novel informational index: Redundancy/Ascendency. Apparent responses to the disturbance differed across hierarchical levels. Some metrics dependent on biomass change and flow distribution temporarily increased during the years immediately following the discharge and subsequently returned to pre-DWH levels. Metrics of energy flow linked to primary production rose in the last two periods, perhaps reflecting eutrophication. Other metrics changed little or had no obviously explainable patterns. Overall, our results indicate the nektonic food web in this region is flexible to disturbance and likely has redundant energy pathways explaining the reported ecosystem resilience to the DWH spill. We show that an ENA, when applied to multiple levels of ecosystem hierarchy, may aid understanding of marine food web resilience.