Upstream/downstream food quality differences in a Caribbean Island River
Résumé
Caribbean rivers are inhabited by native macrofauna with a diadromous life cycle. The factors influencing the upstream migration of diadromous species are not well understood. Suggested primary factors include species density, habitat suitability and food availability. We hypothesized that food quality could be a key parameter in the upstream migration of macrocrustaceans. We sampled the main shrimp species and their potential food sources along an altitudinal gradient in the Grand Carbet River of Guadeloupe. Lipid analyses of the different food items reveal that biofilm and drifting organic matter are main sources of eicosapentaenoic acid (EPA). Biofilm is richer in EPA upstream, while drifting material is richer in EPA downstream. These opposed altitudinal gradients are reflected in shrimp lipids depending on whether they feed on biofilm or drifting organic matter. In addition, low EPA levels in shrimp suggest that dietary EPA could be a limiting factor in this system and that this differential altitudinal distribution of EPA could influence shrimp settlement.