Ecological Effects of Macroalgal Harvesting on Beaches in the PeelHarvey Estuary, Western Australia

Macrophyte harvesting is used to manage macroalgal accumulations in eutrophic estuaries throughout the world. Despite the widespread use of harvesting as a management tool, little research has addressed the effects on beach ecosystems. This paper reports on experimental investigations into the short- and long-term effects of macroalgal harvesting on beaches in the Peel-Harvey estuarine system, Western Australia. The short-term effects were examined of a single harvesting event on macrophyte biomass, sediment organic content and the density, species richness and composition of macroinvertebrates and fish of intertidal habitats of a regularly harvested beach. Long-term effects of harvesting were assessed by comparing this area with nearby beaches that have never been harvested. Harvesting caused an immediate decrease in the biomass of macrophyte detritus and densities of epifauna and fish. All of these variables recovered to values similar to non-harvested areas within two months. There was no effect on surface sediment organic matter or densities or richness of benthic infauna. The beach that had been harvested for several years had similar macroinvertebrate assemblages to those on a non-harvested beach at which macroalgae did not accumulate. In contrast, both beaches had different faunal assemblages to a beach that had never been harvested and on which algal accumulations occur. It was concluded that at regularly harvested sites the disturbance caused by harvesting is temporary (in the order of days to weeks). In the long-term, harvesting may mimic the natural flushing of beaches, preventing the detrimental effects of algal accumulation and producing faunal assemblages not unlike those found at beaches without accumulations. In highly eutrophic systems, such as the Peel-Harvey estuarine system, harvesting may be an effective beach management tool.