Review of nekton patterns and ecological processes in seagrass landscapes

Abstract

We reviewed seagrass landscape studies on nekton (fish and larger mobile crustaceans) to summarise: (1) patterns of nekton abundance in relation to patch attributes; and (2) models used to explain processes underpinning observed patterns. The response of nekton to landscape attributes is highly variable. Different taxa showed increasing densities with: increasing and decreasing patch size (12 and 11 taxa, respectively), increasing and decreasing proximity within a patch to edge (9, 14), increasing and decreasing distances from nearest seagrass patch (4, 11), and with patches perpendicular and parallel to currents (1, 2). The majority of taxa (213 out of 281, or 82%) showed no relationships. Landscape scale patterns are important for some species but evidence so far does not demonstrate major landscape effects overall. The lack of pattern might reflect the overriding importance of other factors such as within-patch characteristics, water depth or position within an estuary. It might also result from measurements at the wrong scale. The rigour of surveys can be improved by avoiding confounding of patch attributes by other factors, increasing awareness of statistical power, and more considered survey designs for attributes such as edge effects. The predation model is the most frequently invoked and tested model. Other explanatory models are based on disturbance, rates of encounter, food availability, larval supply, migration and reproductive success, but in many cases are not based on observed patterns. The best experimental work has been done on nekton species for which landscape studies have been built on a detailed understanding of the ecology of the species, such as for blue crabs (Callinectes sapidus). As this basic ecological platform is laid for more species, the landscape approach will become increasingly fruitful.