Harbour swimming nets: a novel habitat for seahorses

1. Artificial structures are becoming increasingly important in conserving biodiversity in urban ecosystems, by providing habitat for endangered or rare species. Their role in providing habitat for such species has, however, been largely unexplored. 2. In Sydney Harbour, Australia, seahorses were observed among the netting used to keep sharks Out of swimming enclosures. Over a 2-year period, the relative densities of two species of seahorses observed on netting was measured at swimming enclosures with permanent netting and at swimming areas that were only enclosed with netting during the summer months. 3. The rate of colonization by seahorses to new netting was also examined over a period of 10 months. 4. Numbers of seahorses on permanent swimming enclosures were 10 to 100 times greater than numbers present on swimming enclosures that were only set up during the summer months. 5. This large difference may have been attributed to the slow rate of colonization of seahorses to new habitat. Seahorses were not observed at experimental nets that were deployed in two areas in the harbour until at least 4 months after the netting was deployed. 6. Swimming pool nets are a habitat for species of seahorses in Sydney Harbour and, consequently, the removal or disturbance of swimming nets may impact the survival of these fish. Management of these artificial habitats may therefore best be focused on providing a permanent habitat that may help to compensate for the loss of netting during winter months. Copyright (c) 2007 John Wiley & Sons, Ltd.