Copepod community structure across the Amazon River plume gradient: linking diversity and biomass with environmental drivers

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Abstract The Amazon River plume generates strong hydrographic gradients that shape pelagic ecosystem functioning in the tropical Atlantic. We quantify the relative influence of key environmental drivers on copepod biomass and diversity and identify indicator taxa across contrasting plume regions. Using data from the AMAZOMIX expedition, we sampled three hydrographic zones, the coastal plume [Shelf Amazon River Plume (SARP)], oceanic plume (Ocean Amazon River Plume) and oligotrophic ocean (Non-Amazon River Plume). Twenty-five copepod families were recorded, reflecting high biodiversity across plume-influenced and oceanic environments. Hierarchical Bayesian models were used to assess environmental effects and to derive a Latent Ecosystem Functioning Index (LIFE), defined as a shared ecological state integrating biomass and diversity along environmental gradients. Copepod biomass peaked in the plume-influenced SARP (mean = 1 585 μg C m−3) and was positively associated with fluorescence (β = 392) and salinity (β = 257), indicating strong bottom–up control. In contrast, diversity showed weak environmental responses, suggesting stronger dependence on habitat heterogeneity than on productivity. LIFE was strongly correlated with biomass (r = 0.93) but not with diversity (r = 0.03), revealing a spatial decoupling between productivity and community structure. These findings emphasize key environmental drivers of copepod biomass and propose a latent ecosystem functioning index as an integrative tool for plume-affected ecosystems.

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