Abstract
Native fauna of the tropical volcanic part of Guadeloupe is amphidromous: juveniles born in rivers but that grow in the sea need to migrate upstream to colonise their adult habitat in rivers. This migration is affected by any human-made obstacles placed in their way. Moreover, on volcanic tropical islands, streams are the main source of water catchment for the human population. This deeply affects river hydrology and characteristics. Both damming and water catchment potentially affect community diversity and species demography, but they may also alter the trophic ecology of the river fauna. Using stable isotopes and the stable isotope Bayesian ellipses approach in R (SIBER), this study aimed to assess the isotopic niche variability of riverine fauna of three persistent small rivers of Basse-Terre Island (Guadeloupe) affected by damming and water catchment. Using electrofishing, decapods and fishes (gobies) of three rivers were sampled upstream and downstream of dams. Our results demonstrated that the variability of the isotopic niches was extremely high between rivers but varied less between stations of the same river. Our results revealed complex and river-specific effects and a pattern merged with natural variability. Our two hypotheses (i.e., increase of resources upstream of dams and differential responses of trophic guilds to damming and water catchment) were only weakly supported and never in an unambiguous manner. Our study showed that it is necessary to consider the ‘noise’ generated by natural variability to observe and understand changes in the trophic ecology of associated fauna in relation to damming and water catchment.
Highlights
The volcanic part of the Guadeloupe (Basse-Terre) presents many persistent rivers that support original native communities, dominated by freshwater crustaceans (Atyidae and Palaemonidae shrimps and crabs), molluscs and fish
In the context of an increase in the human population and freshwater resource limitation due to marked dry seasons, the rivers of tropical islands are essential because they ensure the production of tap water as well as the supply of freshwater for agriculture (March et al 2003)
Despite the fact that no significant changes were observed in the basal resource isotopic composition, an important variability was observed in the stable isotope composition of the animal community in the six investigated stations
Summary
The volcanic part of the Guadeloupe (Basse-Terre) presents many persistent rivers that support original native communities, dominated by freshwater crustaceans (Atyidae and Palaemonidae shrimps and crabs), molluscs and fish (mainly Gobiidae). After several weeks in saline waters, the post larvae re-enter the freshwater ecosystems through the river mouths and migrate upstream to their adult habitats (Myers 1949; McDowall 1997) During their juvenile migration to the upstream habitats, amphidromous fauna must cross all obstacles located in the riverbeds. The adults could perform movements between refugia, feeding and spawning habitats throughout their lives In many rivers, these movements are perturbed by obstacles, with small obstacles not being as insignificant as initially thought, because they have been shown as significantly disrupting and/or obstructing their movements (Ovidio & Philippart 2002). These structures can produce a bottleneck effect in stopping juveniles and slowing down the adults in their upstream movement, increasing the densities of upstream migrating animals below the dam (i.e., crowding effect) (Benstead et al 1999)
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