Organic enrichment negatively impacts meiobenthic copepods on Argentinean coasts

Abstract

Organic enrichment is a growing threat to coastal environments, yet its effects on meiobenthic copepods in marine sediments remain poorly understood. In this large-scale observational study conducted in Buenos Aires Province, Argentina, we evaluated the impact of riverine input—particularly the organic matter transported by rivers—on the structure of meiobenthic copepod communities. We hypothesized that the amount of organic matter and other abiotic factors, influenced by river discharge, modify environmental conditions and affect copepod abundance and richness. Sampling was conducted in low intertidal zones associated with the mouth of eight rivers on three dates between 2019 and 2020. At each site, we collected samples at three coastal positions—river mouth, 200 m west, and 200 m east—to assess copepod richness and abundance, organic matter content, temperature, pH, salinity, and grain size. Our findings indicate that riverine input played a key role in shaping copepod community structure, with temperature emerging as the primary environmental driver of community composition. Organic matter content and salinity were also critical abiotic variables influencing abundance and richness. Salinity modulated the effect of organic matter, with negative impacts on abundance becoming more pronounced under high-salinity conditions. These patterns support the hypothesis that organic enrichment negatively impacts meiobenthic copepod communities, as even slight increases in organic matter content were linked to decreases in both abundance and richness.