De novo reefs: fish habitat provision by oyster aquaculture varies with farming method

Aquaculture industries have the capacity to produce positive ecosystem service benefits, such as the provision of habitat to wild animals. Oyster cultivation is the oldest and largest aquaculture industry in south-eastern Australia. Oyster spat are grown to marketable size in rackand-rail (‘racks’) or longline-and-basket (‘baskets’) configurations, which add structure to estuarine waters. This study assessed: (1) how the fish communities associated with oyster farms vary with production method; (2) how communities of fish utilise oyster infrastructure, as compared to adjacent natural habitats; and (3) whether oyster infrastructure can serve as de facto oyster reefs by supporting similar fish communities. Remote underwater video surveys, conducted during summer and winter of 2 study years, revealed that fish observations and species richness were generally greater for rack than basket cultivation. Both types of oyster farms supported at least as many species of fish as adjacent natural habitats, including oyster reef, seagrass, mangrove and bare sediment. Fish communities were, in general, most similar between racks and baskets and most dissimilar between racks and bare sediments. Oyster farms supported species of fish otherwise limited to habitats with wild oysters, and unique harvested fish species were ob served more frequently at racks. Fish use of oyster-growing infrastructure for foraging and shelter mirrored use of natural biogenic habitats. Overall, this study suggests that the oyster aquaculture infrastructure can support fish communities with species composition similar to those of natural biogenic habitats, although this service is dependent on farming method. Ecosystem services provided by aquaculture should be considered in estuarine habitat enhancement, conservation and restoration.