Disconnect between settlement and fishery recruitment driven by decadal changes in nearshore habitats

Abstract

Submerged vegetation is critical to marine ecosystems and can function as recruitment habitats for commercially targeted species, such as the highly valuable Western Rock Lobster Panulirus cygnus. The development of vegetation indices for marine remote sensing has made tracking the extent and change of submerged vegetation in space and time possible. Vegetation changes may directly or indirectly affect the recruitment and population dynamics of animals that depend on these habitats. Previous studies have found that extreme climate events, such as marine heatwaves, can cause declines in submerged vegetation extent, but these studies have been limited spatially and temporally. Here, we present multidecadal extents of submerged vegetation and settlement indices for five coastal locations throughout the range of Western Rock Lobster and explore how these vegetation trends relate to an index of recruitment. We found that the correlations of vegetative extent, climate and undersize lobster catch varied significantly between the monitored locations. For some locations, particularly those with a high composition of preferential recruitment habitat (i.e., seagrass), vegetation extent in the previous two years significantly explained variation in undersize catch rates. Regions with a time series of undersize lobster and settlement data combined with consistent remotely sensed imagery allowed for the disentanglement of the influence of habitat change and post-settlement recruitment. Whereas, at locations with poor quality historical data, often due to the combined effect of turbidity and a relatively steep coastal shelf or limited catch data, the recruitment index was not improved by information on submerged vegetation. We have found that decadal changes in nearshore habitats at representative locations have driven the disconnect between settlement and fishery recruitment. We suggest that monitoring marine habitats can complement long-term fishery data collection and coastal management.