Spatially explicit risk assessment for coastal invaders under different management scenarios

Biological invasions are particularly challenging in marine environments, where control strategies are scarce and efforts to reduce the abundance of the invader are costly and difficult, often representing insurmountable challenges. However, the magnitude of the impact of the invasion depends not only on the characteristics of the invading species, but also on the inherent features of the receiving environment; managing the environmental matrix could therefore be the best option for preventing or reducing undesired effects. The objective of the present work was to develop a spatially explicit risk-based approach to evaluate the effectiveness of different management practices designed to mitigate the potential impacts of the Pacific oyster (Crassostrea gigas) in the Bahía Blanca estuary (38°50′S, 62°20′W). A Risk Index (RI) was constructed to assess the potential negative impact of oyster bed expansion on environmental values and human health. RI maps were built to compare the potential effects of different management options in terms of risk reduction. An integral sanitation program within the coastal zone produced the largest reduction in the areas previously ranked as under very low, low, medium, high, and very high risk. Treatment of domestic sewage produced a major reduction in the areas under high and medium risk, mainly in the inner zone of the estuary, but changes in the area under very high risk were negligible. Removal of oysters at specific locations had a modest effect on risk reduction in terms of the whole area, but produced significant improvements at a local scale.