Assessing the large-scale and long-term changes in the southern Gulf of Mexico benthic ecological status under natural and human-induced disturbances

Abstract

Monitoring benthic fauna in the Gulf of Mexico is needed to assess its ecological status under multiple human pressures and natural variability. The knowledge about the large-scale and long-term variability of the benthic ecological status still needs to be improved. Here, AZTI's Marine Biotic Index (AMBI) and multivariate AMBI (M-AMBI) assess benthic ecological status under human pressures and natural disturbances. The total number of samples analyzed was 1123 (from the coast to the deep sea), obtained during a relatively long period (nine yearly sampling events) and a wide area (the southern Gulf of Mexico -436,000 km2), in which benthic fauna, environmental and contaminant data were obtained. AMBI and M-AMBI were able to identify the effects on the benthic communities from natural and human disturbance: 1) benthic assemblages responded to climate pat-terns, such as El Nin similar to o events and other natural disturbances (i.e. dry and windy seasons); 2) these natural dis-turbances were associated to an exacerbation of contamination, mainly metals, hydrocarbons, and potential redox that exceeded the sediment quality guidelines; 3) the contamination can be related to human pressures, such as pollutant discharges from land-based activities and the oil industry. AMBI and M-AMBI provide baseline guidelines for determining the benthic ecological status of each sedimentary environment identified within the area since the entire region is affected by chronic and sublethal pollution, harmful in the long term to the benthic biota.