Metaecosystem dynamics of marine phytoplankton alters resource use efficiency along stoichiometric gradients

Metaecosystem theory addresses the link between local (within habitats) and regional (between habitats) dynamics by simultaneously analyzing spatial community ecology and abiotic matter flow. Here, we experimentally address how spatial resource gradients and connectivity affect resource use efficiency (RUE) and stoichiometry in marine phytoplankton at local and regional scales. We created gradostat metaecosystems consisting of five linearly interconnected patches, which either were arranged in countercurrent gradients of nitrogen (N) and phosphorus (P) supply or with a uniform spatial distribution of nutrients, and which had either low or high connectivity. Gradient metaecosystems were characterized by higher remaining N and P concentrations (and N:P ratios) than uniform ones, a difference reduced by higher connectivity. The position of the patch in the gradient strongly constrained elemental stoichiometry, local biovolume production and RUE. Expectedly, algal C:N, biovolume
and N-specific RUE decreased towards the N-rich end of gradient metaecosystem, whereas the opposite was observed for most of the gradient for C:P, N:P and P-specific RUE. However, at highest N:P supply, unexpectedly low C:P, N:P, and P-specific RUE values were found, indicating that the low availability of P inhibited efficient use of N and biovolume production. Consequently, gradient metaecosystems had lower overall biovolume at the regional scale, but higher dissimilarity in species composition. Thus, the performance of phytoplankton in metaecosystems strongly depended on the stoichiometry of resource supply and spatial connectivity between patches.