A seafloor sensitivity index to oil spills in tropical marine protected areas

Abstract

Oil spills are a global environmental challenge with ecological impacts at local and regional scales. In 2019, a major oil spill from an unknown source reached the Brazilian margin and strongly affected tropical marine habitats with high biodiversity. It is therefore important to establish a quick and accessible approach to assist decision-makers for oil spill responses. Based on current Brazilian legislation, only very specific companies (such as organized ports, port facilities, platforms and their auxiliary facilities) are obliged to maintain marine oil spill response structures. This paper aims to develop an approach for mapping seafloor sensitivity to oil spills for continental shelf areas with limited resources and materials. The study was conducted using a pre-existing bathymetric dataset, at mega- and meso-habitat scales. The assessed area extends over 933 km2, between the 10 and 90 m isobaths, comprising tropical marine areas of intense maritime traffic due to the strategic location for important international routes and also due to the presence of ports, terminals and shipyards. From the megahabitat-scale analyses (30 m resolution grid), the areas with greatest topographic complexity were selected for subsequent detailed analysis and the development of a seafloor sensitivity index at a mesohabitat-scale (10 m resolution grid). The results revealed that 12.7% of the area was classified at a high seafloor sensitivity index (SIseafloor), 28.7% was classified at relatively moderate sensitivity, and 58% was classified at low sensitivity. The seafloor sensitivity methodology presented here can be easily applied to other locations to prepare recovery operations, monitoring plans, and for other forms of environmental planning.