Benthic foraminifera records of complex anthropogenic environmental changes combined with geochemical data in a tropical bay of New Caledonia (SW Pacific)

During the 1950s, open-cast mining led to an increasing input of heavy-metal-rich terrigenous particles in the bays near Nouméa, detected by geochemical and sedimentological analyses. Even though most of terrigenous metal is unavailable, an impact on the benthos was suspected. Simultaneously, the population of Nouméa increased dramatically, which may impact the neighboring bays. Foraminifera were used for assessing this double impact. Thirteen surface samples were collected as a basis for the interpretation of 27 samples from a 54 cm long core. Paradoxically, the general trends in foraminiferal assemblages with time were consistent with a decreasing impact of pollution and continental influence (e.g., increasing species richness, diversity, density, and decreasing percentages of Ammonia tepida). Explanations were found in the urban planning that led to a decrease of freshwater and pollutant inputs. Multiple and contradictory impacts of anthropic activities could be assessed only by a set of complementary tools (i.e., geochemistry and bioindicators).