Too close for comfort? Mesozooplankton dynamics in Marine Protected Areas adjacent to mining tailings on the...

In Brazil's Southwestern Atlantic, the contiguous Costa das Algas Environmental Protection Area and Santa Cruz Wildlife Refuge were established in 2010 to protect a highly biodiverse coastal region. In 2015, the collapse of the Fundão tailings dam released large volumes of metal-rich mining waste, which were transported to the coastal zone by the Doce River and altered local marine conditions. This study analyzed four years of mesozooplankton data to assess the influence of hydrodynamics and environmental variability on community structure within these Marine Protected Areas (MPAs). Hydrological and biological data collected at 11 sampling stations during 16 surveys conducted between 2018 and 2023 were analyzed using multivariate techniques. Mesozooplankton dynamics were primarily driven by spatial distribution and seasonal gradients in temperature, salinity, wind-driven circulation, and phytoplankton characteristics (abundance, diversity, and biomass). Interannual variability and episodic events, such as extreme river discharge and wind reversals, disrupted seasonal patterns in community structure, particularly in the inner-shelf sector. Dominant taxa varied mainly by shelf location and included Penilia avirostris, Paracalanus parvus, Temora spp., Clausocalanus furcatus, and Oithona plumifera, with community shifts reflecting changes in environmental conditions. Although direct effects of mining tailings were not clearly detected, differences in zooplankton abundance and composition following rainy seasons suggest a strong influence of variations in Doce River discharge and plume displacement. The results highlight the role of MPAs in sustaining biodiversity by protecting critical habitats and maintaining ecosystem integrity, and emphasize the importance of incorporating planktonic communities into long-term monitoring and management of protected coastal ecosystems.