Influence of natural and anthropogenic disturbance on the soft bottom macrobenthic community of the Campeche Bank, Mexico
The structure of macrobenthic communities was investigated in carbonate and transitional carbonate-terrigenous sediments of the Southern Gulf of Mexico (Campeche Bank). The aim was to assess the influence of natural disturbance represented by winter storms and river runoff and the putative influence of oil-related activities using a regional approach. At a scale of > 100 km community composition of benthic macroinfauna was characterised as distinct assemblages within the carbonate and transitional sedimentary provinces controlled by natural disturbance. The carbonate assemblage was numerous and diverse influenced by a heterogeneous substratum. Winter storms had a severe impact with mortality probably resulting from abrasion and passive transport causing low values of number of taxa, abundance, biomass and diversity measurements. Conversely, on the transitional shelf a sequence of disturbance from river runoff and winter storms resulted in a general impoverished community due to fine sedimentation and sediment instability. Immediately after the rainy season, values of biological measures were low, but the severity of disturbance was contingent with depth. At a scale of 10s km within the transitional shelf, the combined effect from natural and anthropogenic disturbance caused extremely low values of biological measures within the so called oil exclusion zone. Despite the lack of adequate controls the effects of oil related activities were identified as severe reductions in macroinfauna densities and biomass resulting in a very simple community. Large spatial variability at this scale masks the temporal variation observed in other areas of the Campeche Bank and the relationship between biological measures and indicators of oil activities (Barium, Nickel and oil-hydrocarbons). Finally the increased variability resulting from the influence of oil activities interrupts the natural gradient of macroinfauna patterns across the shelf.