Seascape connectivity of temperate fishes between estuarine nursery areas and open coastal reefs.
Abstract
While estuaries are considered valuable nurseries for many harvested fish species, little quantitative data exist about the spatial scales over which estuaries supply individuals to coastal reefs and how this influences coastal metapopulations. Quantifying this connectivity between estuaries and coastal reefs will assist the sustainable management of fisheries and key fish habitat. This information is particularly pertinent considering estuaries world-wide are experiencing degradation and habitat loss. We examine how the relative abundance and body length of three exploited fishes (Chrysophrys auratus, Pseudocaranx georgianus and Nemadactylus douglasii) varied in relation to the proximity and size of the nearest estuary, predicting that estuarine dependent species (i.e. C. auratus) would be smaller and more abundant on reefs close to large estuaries. As a network of 'no-take' marine reserves exist across the study area, we also assessed for reserve effects and if these were influenced by the proximity and size of estuaries. Fish assemblages were surveyed using baited remote underwater video systems deployed on 629 rocky reefs across 417 km of coastline in south-eastern Australia. As predicted, C. auratus were smaller and more abundant on reefs adjacent to estuaries (<8.5 km), which is consistent with the species being heavily reliant on estuaries as nursery habitats. Neither the length nor abundance of N. douglasii and P. georgianus were influenced by the proximity or size of estuaries. Marine reserves consistently had higher abundances and larger C. auratus, regardless of their proximity to estuaries. However, reserve effects were more variable for both N. douglasii and P. georgianus. Synthesis and applications. Our results suggest that the dispersal of subadult Chrysophrys auratus from estuarine nurseries to coastal reefs occurs across relatively small spatial scales, highlighting that conserving the ecological functioning of estuaries is paramount to sustaining recruitment to nearby coastal fisheries. Estuary size and proximity had little influence on populations of both Nemadactylus douglasii and Pseudocaranx georgianus as these species are not greatly dependent on estuaries. We also found that the proximity to estuaries did not enhance reserve effects, instead these effects were consistent across the study area.