Effects of experimental in situ seabed disturbance on deep-sea macrofaunal communities of Chatham Rise, Southwest Pacific

Abstract

ABSTRACT With the possibility of deep-sea mining of mineral resources occurring, it is necessary to understand potential impacts on benthic communities. Previous simulated mining experiments revealed direct benthic impacts; however, indirect impacts of sedimentation are not well understood. A disturbance experiment was conducted on Chatham Rise, New Zealand, to assess the resilience of benthic communities to sedimentation that could result from future deep-sea phosphorite mining. Macrofaunal and sediment samples were collected before, immediately after, and one year after a disturbance in areas directly physically disturbed and subjected to induced sedimentation (DI), and undisturbed or subjected to sedimentation only (UI). Macrofaunal abundance significantly decreased in DI areas but not in UI areas. However, abundance-based community structure changed in both areas; in DI areas this was mostly driven by decreases in dominant fauna, but in UI areas by changes in more sensitive fauna. One year after disturbance, abundance-based community structure had recovered in both areas and was correlated most strongly with variations in sediment C:N molar ratios. Biomass-based community structure in DI areas differed one-year post disturbance from communities sampled at the two earlier periods. These results are useful for informing the management of impacts from offshore industries where sedimentation is an issue.