Assessing the impacts of beach scraping on the macroinvertebrates of New Brighton beach, northern New South Wales

As part of an assessment of mitigation strategies for coastal erosion and associated recession of the back beach erosion escarpment, Byron Shire Council undertook trial beach scraping at New Brighton beach in August and September 2010. Sand was removed to a depth of up to 0.5m along a 1.31-km section of intertidal beach. Using a bulldozer and excavators, this sand was moved to the back (upper) beach to increase sand reserves in the dune system. We assessed the impact of scraping on the small invertebrates living within the beach (upper strandline to the lower tidal limit). We established 2 sites in the impact area and 2 control sites well away from the beach scraping works, and sampled 5 beach levels before the impact, and 1 day, 1 week, 2 weeks and 4 weeks after scraping. We extracted replicated cores of sand from which macroinvertebrates were removed, identified and counted, and subsequently analysed the data to determine: i) the size of the immediate impact; and ii) the temporal scale of recovery should an impact be detected. Remarkably, none of the variables assessed in this study (species richness, abundance, community structure) displayed unambiguous evidence of immediate effects and the primary trend was of high dynamism across the entire study area. Assessments of community structure suggested that patterns were mostly dependent on the date of sampling. Thus, macroinvertebrate assemblages were more similar within a specific sampling period at all sites than within a site over time. This study confirms suggestions from similar research that beaches are highly dynamic and thus have the capacity to recover rapidly from some forms of physical disturbance.In this study, natural disturbances, such as periods of high swell, appear to have had more of an effect than the mechanical removal of sand from the beach face.