Impact and Resilience of Benthic Foraminifera in the Aftermath of the Deepwater Horizon and Ixtoc 1 Oil Spills

Abstract

Benthic foraminifera, which are single-celled protists that primarily produce calcite shells, have been commonly used as bioindicators of anthropogenic and natural perturbations. Numerous surveys of benthic foraminifera conducted in the Gulf of Mexico (GoM) prior to any major oils spills allow for a fair assessment of impact, response, and resilience during and following the Deepwater Horizon (DHW) oil spill in the northern GoM (2010) and Ixtoc 1 oil spill in the southern (1979--1980). Initially, in the aftermath of DWH, there was an 80--93{\%} decrease in benthic foraminifera density and a 30--40{\%} decrease in species richness and heterogeneity in the northern GoM. From 2010 to 2012, there was a continuous depletion in benthic foraminifera calcite stable carbon isotopes related to increased deposition of petroleum carbon (PC). This depletion has subsequently been preserved in the sedimentary record. Following this period of impact, benthic foraminifera density and diversity reached a resilient state of equilibrium from 2013 to 2015, suggesting that the rate of resilience for the benthic habitat is on the order of 3 years following an event like the DWH. Secondly, the sedimentary records of benthic foraminifera were used to assess the impact, resilience, and subsequent preservation of the Ixtoc oil spill. A noticeable decrease in benthic foraminifera density as well as a depletion in the stable carbon isotopes of benthic foraminifera calcite occurred in the sedimentary interval corresponding to 1979--1980. These results have implications for determining the long-term preservation of oil spills, assessing PC mineralization and burial, and contributing to overall oil spill budgets. Overall, benthic foraminifera have proven to be valuable indicators of impact, response, and resilience of the benthos and can provide useful information concerning benthic habitat suitability following oil spills in the future.