Effects of landscape configuration on the exchange of materials in seagrass ecosystems

Landscape (or seascape) attributes play an important role in modulating the flow rates of materials between habitats in the coastal marine environment. Seagrass meadows are known to both export and import organic matter, thus establishing links with other habitats. Most of those links remain unexplored, and little is known about the relevance of landscape configuration on these flows. We studied the relationships between landscape configuration (continuous meadows, patchy meadows in a sand matrix and patchy meadows in a rock matrix) and the exchange and accumulation of detrital material. Moreover, we evaluated the impact of landscape configuration on (1) plant nutrient content and (2) the diet of a model deposit feeder (holothurians). We determined detritus stocks in seagrass meadows as well as the carbon and nitrogen elemental and isotopic composition of plants, detritus and other food sources (e.g. suspended organic matter). Based on this, we identified, by applying mixing models, the different contributions of these sources to the diets of deposit feeders. Our results showed that landscape configuration influences the exchange of materials across the coastal seascape. Less accumulation of detrital seagrass leaves was found in patchy meadows, although no effects were found for allochthonous materials. In addition, patchy seagrass meadows showed significantly lower nitrogen concentrations in leaves compared to continuous meadows. Landscape configuration had no effect on the diet of the deposit feeder studied. These findings highlight the importance of landscape-level processes in coastal waters and specifically warn of the possible effects of changes in meadow size on seagrass performance.