Light reductions drive macroinvertebrate changes in Amphibolis griffithii seagrass habitat

摘要

ABSTRACT: Numerous anthropogenic activities can significantly reduce the amount of light reaching seagrass habitats. Typically these result in morphological and physiological changes to the plant and associated algal epiphytes. However, the flow-on effects to seagrass-dependent fauna induced by these disturbances has yet to be examined. This study investigated the effects of different light reduction intensity (high: ~92% reduction; moderate: ~84% reduction), duration (3, 6 and 9 mo) and timing (post-winter and post-summer) on the density and biomass of macroinvertebrate epifauna within an Amphibolis griffithii seagrass ecosystem (Western Australia). There were generally lower epifauna densities and biomass within shaded seagrass plots. When moderate intensity shading was imposed at the end of winter, total density in unshaded controls was 31% lower at 3 mo, and 78% lower at 9 mo. When high intensity shading was imposed, total density was 38% lower than in controls at 3 mo, and 89% lower by 9 mo. Although densities varied, similar magnitudes of decline occurred in post-summer shaded treatments. Taxa-specific responses were variable in terms of time, rapidity and magnitude of response. Amphipod, isopod and gastropod densities generally declined in response to shading. Bivalve densities declined with shading post-summer, but not post-winter. Ostracod densities had an inconsistent response to moderate shading. Changes in epifaunal density were largely associated with declines in algal biomass, leaf variables and stem biomass, indicating food and habitat limitations. It is likely that the significant declines in epifauna observed in this experiment would have flow-on consequences to higher trophic levels.