Faunal Assemblages of Seagrass Ecosystems

Abstract

Seagrass habitats support diverse animal assemblages and while there has been considerable progress in the study of these fauna over the last few decades, large knowledge gaps remain. There are biases in our knowledge of taxonomic and functional information that favour the temperate regions over the tropics, some seagrass genera over others, shallow habitats compared to deeper meadows and larger animals over smaller ones, with many invertebrate communities poorly described. In many areas of Australia, invertebrate identification to low taxonomic resolution is difficult due to a lack of resources, but new approaches , such as genetic barcoding, may one day surpass traditional methods of classification and overcome this issue. Many studies have demonstrated greater biodiversity of fauna in seagrass compared to adjacent bare habitats with explanations for this ranging from habitat and seascape processes to food availability and trophic interactions. Within seagrass ecosystems, meadows can be highly heterogeneous, and habitat factors such as structural complexity, patch size , edges, gaps and corridors influence associated faunal communities. Broader seascape processes that occur across multiple connected habitats, including seagrass meadows , bare sediments, mangroves, saltmarshes and coral and rocky reefs, influence faunal productivity and/or diversity through the movement of organisms for recruitment and migration, and the transport of detritus and nutrients . The study of seagrass food webs has highlighted the importance of bottom-up processes in shaping the faunal assemblages through assessments of the role of invertebrate prey in influencing the productivity of consumer species and manipulative experiments that show prey resources affecting spatial patterns of predators. In addition, top-down consumptive and non-consumptive effects of predators such as their modification of prey behaviour also affect the structure of faunal communities. A large number of natural and anthropogenic perturbations to seagrass meadows influence their resident animals. These disturbances can modify seagrass-associated fauna in several ways; directly where seagrass fauna are more sensitive to perturbation than their seagrass habitat, indirectly through habitat modification, and additionally through interventions that reduce connectivity between habitats that fauna use for part of their life cycle. Animals can also play a significant role in structuring seagrass meadows through processes such as herbivory and bioturbation that can have both positive and negative effects on seagrass habitat.