Muddy-bottom meiofauna responses to metal concentrations and organic enrichment in New Caledonia South-West Lagoon

The New Caledonia South-West Lagoon is subject to both major terrigenous and urban inputs associated with the development of the Noumea city, which may affect its functioning. Environmental parameters, sediment biochemical characteristics, metal concentrations and benthic meiofauna were assessed to better characterize and unravel the effects of these two potential disturbances in muddy sediments. Seventeen stations were sampled along disturbance gradients within four bays located around the city of Noumea and subject to different levels of anthropogenic and terrigenous inputs. Two cruises were carried out during July (dry season) and December 2002 (beginning of the rainy season). Spatial changes were much more important than temporal ones. Temporal changes were restricted to the biochemical characteristics of superficial sediment and more specifically to its labile organic fraction. Two groups of metals were identified based on their spatial distribution. The first was composed of Cr, Mn, Co and Ni, which mainly originate from the erosion of soils and mining activities. The second was composed of Zn, Cu and Pb. which mainly originate from urban activities. All sampled bays could be considered as potentially contaminated by one or more metals. Total meiofauna density correlated negatively with bulk descriptors of organic matter (during the December cruise) and positively with EHAA/THAA ratio (during both cruises). It did not correlate with Ni, Mn, Cr and Co but did correlate negatively with Cu and Pb during the December cruise. Our results suggest that the density of meiofauna in the South-West Lagoon is positively affected by the qualitative and negatively affected by the quantitative characteristics of sedimentary organic matter. This pattern differs drastically from what is usually observed in temperate ecosystems. This discrepancy may result from the importance of the inputs of refractory organic matter of terrestrial origin in the South-West Lagoon. Metals originating from soil erosion and mining have apparently no effect on total meiofauna, whereas some metals originating from urban activities may have a negative effect on total meiofauna at least during the beginning of the rainy season. (c) 2006 Elsevier Ltd. All rights reserved.