Aim The aim of this study was to understand whether the large-scale biogeographical patterns of the species-area, species-island age and species-isolation relationships associated with marine shallow-water groups in the Atlantic Ocean vary among marine taxa and differ from the biogeographical patterns observed in terrestrial habitats.Location Atlantic Ocean.Methods Reef fish, gastropod and seaweed species richness as well as reef fish endemic species data were obtained for 11 Atlantic oceanic islands. Using a multimodel inference approach based on linear and nonlinear regressions, we tested hypotheses regarding the variation in species richness and endemism as a function of island area, age and isolation. Best models were selected using ratios between Akaike weights corrected for small sample size (AIC c ). Results were compared between the three shallow-water species groups and contrasted against previous studies of marine and terrestrial systems.Results Island area was the best single predictor of gastropod and seaweed richness, although it was not an improvement compared to the null model for reef fish. Island age explained richness in all taxa and was the best single predictor of reef fish richness. Isolation was a good predictor of seaweed richness but not of fish and gastropod richness, possibly because of their overall higher dispersal capacity. Reef fish endemism was influenced solely by island isolation.Main conclusions This work reveals large-scale island biogeographical patterns for marine shallow-water organisms in the Atlantic Ocean. Our results suggest that reduced gene flow is a potentially important mechanism for the maintenance of reef fish endemism in oceanic islands. The role of island age regarding the species richness of all taxa emphasizes the importance of habitat history for the geographical distribution of marine shallow-water biodiversity. Finally, we show that some island biogeographical patterns differ not only between marine and terrestrial ecosystems but also, importantly, within marine shallow-water environments, where the biogeographical patterns are highly taxon-dependent.

We investigated the paradox of why Amazonian manatees Trichechus inunguis undergo seasonal migrations to a habitat where they apparently fast. Ten males were tracked using VHF telemetry between 1994 and 2006 in the Mamirau´a and Amana˜Sustainable Development Reserves, constituting the only long-term dataset on Amazonian manatee movements in the wild. Their habitat was characterized by analysing aquatic space and macrophyte coverage dynamics associated with the annual flood-pulse cycle of the River Solimo˜es. Habitat information came from fieldwork, two hydrographs, a three-dimensional model of the water bodies and classifications of Landsat-TM/ETM + images. We show that during high-water season (mid-May to end-June), males stay in várzea lakes in association with macrophytes, which they select. We then show that, during lowwater (October-November), the drastic reduction in aquatic space in the várzea leads to the risk of their habitat drying out and increases the manatees' vulnerability to predators such as caimans, jaguars and humans. This explains why males migrate to Ria Amana˜. Based on data on illegal hunting, we argue that this habitat variability influences females to migrate too. We then use published knowledge of the environment's dynamics to argue that when water levels are high, the habitats that can support the largest manatee populations are the várzeas of white-water rivers, and we conjecture that rias are the species' main low-water refuges throughout Western Amazonia. Finally, we warn that the species may be at greater risk than previously thought, because migration and low-water levels make manatees particularly vulnerable to hunters. Moreover, because the flooding regime of Amazonian rivers is strongly related to large-scale climatic phenomena, there might be a perilous connection between climate change and the future prospects for the species. Our experience reveals that the success of research and conservation of wild Amazonian manatees depends on close working relationships with local inhabitants.

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