Patterns of colonization of mobile epifauna in a Western Australian seagrass bed

Abstract

Daily turnover of mobile benthic macrofauna within an Amphibolis seagrass bed at Seven Mile Beach, Western Australia, was estimated using both defaunation and neutral red staining methods. The two methods showed generally high daily turnover rates for epifauna ( x = 30% ), and consistent rates for different species. Defaunation methods were subsequently used to determine spatial and temporal variability in animal mobility. Epifaunal settlement on seagrasses at Seven Mile Beach varied substantially between the three habitats studied ( Amphibolis and Halophila seagrass beds and bare sand patches), and also with the height at which defaunated substrata were placed. The diel cycle also influenced the rate of epifaunal colonization, while the lunar cycle had no clear effect. Both the abundance and number of species settling on defaunated seagrasses were greater during the night than during the day, with double the number of species settling on defaunated Amphibolis plants tethered in the water column at night. Significant day/night differences in settlement rates were, however, detected for only three of the 12 most common epifaunal species. Defaunated Amphibolis plants placed into the Amphibolis bed were colonized at much lower rates than defaunated Amphibolis plants placed into an adjacent Halophila seagrass meadow. Present within the Halophila bed was a highly mobile guild of four amphipod species, Te hygenia sp. 1, Paradexamine churinga , Allorchestes compressa and Atylus sp., which selectively located decaying algae, including the epiphytes on seagrasses subjected to the defaunation process. These amphipods were also most rapidly attracted to defaunated plants isolated from other seagrasses on sand patches. Assemblages of scavenging herbivorous amphipods are possibly a widespread feature of seagrass habitats.