Landscape pattern influences nekton diversity and abundance in seagrass meadows

We studied how spatial qualities and configuration of seagrass patches influence the diversity and abundance of resident nekton. Shallow landscapes of equal area (4225 m2) in 2 bays were mapped and sampled in the summer and fall to identify different qualities of landscape structure and the abundance and diversity of nekton. Two suites of characteristics were found to describe the natural landscape structure: (1) habitat area, connectivity, patch proximity and patch density; and (2) patch shape complexity and edge length. These were used to quantitatively distinguish between 3 naturally occurring seagrass landscape patterns: (1) small, isolated patches; (2) reticulated edge patches; and (3) continuous cover. Species evenness (Pielou’s J’) was significantly lower in small, isolated patches and reticulated edge patches compared to continuous cover. This pattern was temporally consistent despite significant seasonal differences in total nekton density and seasonal shifts in the distribution of individual species among landscape patterns. Nekton species density (no. of species per 61.2 m2 of seagrass) and species richness (no. of species per 1683 ind. sampled) did not differ significantly among landscape patterns; however, a landscape structure threshold may exist for species evenness between 45 and 85% cover. High densities of shrimp in small, isolated patches and reticulated edge patches during summer drove species evenness levels lower and overall nekton density levels higher than in continuous cover. Large expanses of continuous seagrass harbor more stable nekton communities across time. They may provide enough space for different species to feed and reproduce without depleting food resources to the point that nekton populations become unstable.