Manipulating artificial habitats to benefit seahorses in Sydney Harbour, Australia

1. Artificial habitats are a common feature of urban marine environments and usually support different assemblages of marine organisms in contrast to neighbouring natural habitats. Despite these differences, artificial habitats can be managed to benefit biodiversity, either by the addition of structures to provide habitat where little natural habitat remains, or by engineering existing structures to better support native populations. 2. Seahorses are listed as protected species in New South Wales, Australia, and are of conservation concern worldwide. The physical structure of nets used to protect popular swimming beaches in a highly urbanized estuary, Sydney Harbour, was manipulated to test the hypotheses that more structurally complex habitats would support higher abundances of the seahorse Hippocampus whitei that use these structures and their potential prey (mobile crustaceans). 3. The simple addition of frayed net material to construct a more structurally complex net habitat supported higher abundances of H. whitei than unmanipulated nets in a field experiment over 53 days. Habitat preference assays in the laboratory supported the hypothesis that the patterns of distribution observed in the field were due to the preferences of individual seahorses for the more complex habitats. 4. The habitats manipulated to add structural complexity supported much higher abundances of the mobile epifauna (amphipods, copepods) that are consumed by seahorses. The potential therefore exists to engineer artificial structures in urban estuaries to provide habitats that are preferred by vulnerable fauna and their food sources. Copyright (C) 2011 John Wiley & Sons, Ltd.