Haul-outs and halos: assessing the effect of fur seal aggregations on temperate reefs

Understanding the role of predators in shaping the dynamics of biological communities is paramount to improved conservation planning. Large predators have high metabolic and spatial needs, thereby having complex, cascading... [ view full abstract ]

Understanding the role of predators in shaping the dynamics of biological communities is paramount to improved conservation planning. Large predators have high metabolic and spatial needs, thereby having complex, cascading impacts on multiple trophic levels and entire ecosystems. In the case of central-place foragers, predators can deplete prey resources close to the colony termed a ‘halo effect’. Despite this the design of marine protected areas all too often try to incorporate aggregation sites of protected predator species whilst also trying to create havens for the recovery of target species from fishing activities. The effectiveness of such a silver bullet approach to marine conservation and resource management remains largely unknown. On the south coast of NSW, populations of Australian and long-nosed fur seals are growing rapidly, due to protection enabling a recovery from past overexploitation, and establishing breeding colonies and haul-out sites that are currently incorporated into important marine protected areas. We therefore aim to evaluate whether a recent increase in localised fur seal activity impacts benthic community and fish species assemblages compared to areas not used for hauling out by fur seals. We applied an asymmetrical experimental design (1 impact site vs. 3 control sites) incorporating two established fur seal haul-out sites each contrasted with 3 reference sites along the northern and southern ocean coast of Jervis Bay, NSW. We assessed benthic community assemblages, fish species assemblages, fish species richness and fish species biomass using underwater visual census and benthic imaging on SCUBA across all impact and control sites. Although complex, the results indicated the potential for localised effects of fur seal aggregation sites on temperate coastal reefs. Consequently, this research has important applications in marine reserve design and management, particularly for the management of expectations of reserves with regard to complex trophic interactions, a characteristic of rich and healthy ecosystems.