Zooplankton in Kone Lagoon (New Caledonia): Natural variability versus mining effects

The objective of this study is to assess the potential impact of nickel mining activity on zooplankton communities in a coral reef channel lagoon (Voh Koné, New Caledonia). During a multidisciplinary campaign in February 2018, we analyzed the variation in zooplankton abundance, biomass and taxonomic diversity, as a function of the distance from the metallurgical plant site and of hydrodynamic conditions and environmental variables. We also compared these results with those obtained in an earlier study conducted in 2009 prior the mining. The results show the high variability of planktonic variables between stations and periods, mainly related to natural factors (hydrodynamics, climatic events). However, lagoon zooplankton also appears to be affected by mining development, and in particular by the increase in sediment inputs and consequent turbidity. Zooplankton taxonomic richness and diversity were negatively correlated with non-algal particle concentrations (C_NAP considered as an indicator of turbidity) with 10 more sensitive taxa completely absent at the highest concentrations. We interpret these negative relationships as the result of the degradation of food quality by mixing with inedible and less assimilable non-algal particles. The effect of metal toxicity cannot be excluded, even though the metal concentrations recorded in the lagoon are far from known toxic concentrations, but this hypothesis should be further developed. Overall, our results highlight the good resilience of lagoon zooplankton probably partly related to the high renewal rate of the lagoon water.