Nutrient exchanges between marine and terrestrial ecosystems:: the case of the Galapagos sea lion Zalophus wollebaecki

1. The movement of materials and organisms between ecosystems is a common process in nature. 2. In the present study we investigate the hypothesis that the transport of nutrients by low-mobility species and their effect on terrestrial ecosystems depends on habitat topography. Specifically, we hypothesized that the influence of a marine organism with low mobility on terrestrial environments would be spatially restricted. 3. To address this hypothesis we analysed the distribution (both geographical and local scales) of Galapagos sea lion colonies, and quantified the spatial extent of their influence on terrestrial ecosystems (soil and plants). 4. Our results showed that the influence of Z. wollebaecki on Galapagos terrestrial habitats is restricted to shorelines with low elevations, but that it is it is geographically ubiquitous across the Archipelago. 5. Our study demonstrated that Z. wollebaecki is an effective vector for the transport of marine nutrients to terrestrial ecosystems. Transported nutrients occur in high concentrations in the soils and are used by shoreline plants. These effects are spatially restricted to the areas where seals occur and the most parsimonious explanatory variable for these patterns is the islands' topography (or elevation).