Spatial patterns of macrofaunal assemblages in intermittently closed/open coastal lakes in New South Wales, Australia

Many intermittently closed and open lakes and lagoons (ICOLLs) in New South Wales are affected by development in their catchments and along their shores. Impacts are exacerbated because ICOLLs can be closed for long periods. To improve water-quality and reduce the risk of flooding, local authorities frequently open lakes by bulldozing or dredging the mouths. These interventions provide an opportunity to examine patterns in the abundance and distribution of macrofauna in these habitats. Multivariate analyses of data from four surveys showed that assemblages in open lakes were consistently different from those in closed lakes. Differences in the composition of polychaetes accounted for most of the dissimilarity between different reaches within lakes, although oligochaetes and amphipods were also important. Taxonomic diversity was higher in open than in closed lakes where assemblages exhibited a high degree of dominance. Abundance decreased with distance from the sea in open lakes, but increased towards the inner reaches of closed lakes. Differences between managed and natural lakes become more apparent when open and closed lakes were examined separately. These differences were much smaller than those between open and closed lakes. The results are discussed in relation to the ecological effects of prolonged closure and isolation from the sea.