Temporal and spatial variability in recruitment of a temperate, seagrass-associated fish is largely determined by physical processes in the pre- and post-settlement phases

Post-settlement King George whiting Sillaginodes punctata were sampled every 3 to 4 d from mid-September to the end of October 1993, at 3 seagrass sites within Port Phillip Bay, Australia. The site closest to the entrance (St Leonards) showed short-lived pulses of recruits in low numbers. The site of intermediate distance into the bay (Grassy Point) showed a similar pattern; however, in this case there was a marked accumulation of recruits over time. In contrast, recruitment was low at the site furthest into the bay (Grand Scenic), and the pattern was unlike the other sites. We simulated the transport of S. punctata larvae into Port Phillip Bay over this period using 2- and 3-dimensional hydrodynamic and dispersal models. A high proportion (two-thirds) of the variation in recruitment at St Leonards and Grassy Point could be explained by 2 factors: the predicted arrival of larvae based on passive transport by currents, and disturbance of individual seagrass sites by wave action. Patterns of recruitment at Grand Scenic, however, a site that was at the Limit of larval dispersal into the bay, were unrelated to model predictions or environmental variables. The daily pattern of arrival of larvae to Port Phillip Bay was estimated from recruits using a transition in otolith microstructure. The daily pattern of arrival estimated for individuals collected from St Leonards was significantly correlated with westerly wind stress and residual sea level, and negatively correlated with barometric pressure. It appears that strong westerly winds and low barometric pressure associated with the passage of weather systems lead to positive sea level anomalies in Port Phillip Bay, and the passive transport of larvae into the bay. Interannual variability in weather patterns would be expected to lead to interannual variability in larval supply to Port Phillip Bay.