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

Abstract

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 Scenlc), and the pattern was unlike the other sites. We simulated the transport of S punctata larvae into Port Phillip Bay over t h~s penod using 2-and 3-dimensional hydrodynamic and dlspersal models. A hlgh 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 passlve 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 11m1t of larval dlspersal into the bay, were unrelated to model predictions or environmental variables. The daily pattern of arrival of larvae to Port Phllllp Bay was estimated from recruits using a transition in otolith microstructure. The daily pattern of arrlval estimated for individuals collected from St Leonards was slgnlficantly correlated with westerly wind stress and residual sea level, and negatively correlated with barometnc 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.

Small-scale dynamics of secondary dispersal in a seagrass associated fish: a caging study

“…For example, S. punctata is a percoid, has a full compliment of fin elements, and falls within a size-range similar to that of reef fishes studied. However, Jenkins & Welsford (2002) found the swimming capabilities of S. punctata post-larvae to be relatively weak, which supports the contention (gained through hydrodynamic dispersal models) that recruitment into Port Phillip Bay is largely a passive process (Jenkins et al 1997(Jenkins et al , 1999.…”

“…Early in the recruitment period, most post-larvae are close to the entrance of Port Phillip Bay, but over time numbers decrease in this area and increase in seagrass beds further inside the bay towards the Geelong Arm (Jenkins et al 1996b). At present, hydrodynamic dispersal models and known larval behaviours have failed to explain the settlement of S. punctata to seagrass beds located in the Geelong Arm on the western side of Port Phillip Bay (Jenkins et al 1997(Jenkins et al , 1999. The aim of this study, using cage inclusion experiments, was to assess whether wave disturbance generated by onshore winds can facilitate secondary dispersal in S. punctata post-larvae.…”

“…Recent studies in shallow seagrass beds suggest that wave disturbance generated by onshore winds may facilitate secondary dispersal for a number of seagrassassociated fishes (Jenkins et al 1997, Moran et al 2003. One species that may be particularly susceptible to secondary dispersal is the King George whiting Sillaginodes punctata.…”

Detecting range shifts among Australian fishes in response to climate change

“…In Port Phillip Bay (Victoria, Australia), postlarval abundances of King George whiting (Sillaginodes punctata) at seagrass sites are strongly correlated with zonal westerly winds, the main westerly wind belt over Tasmania, and are likely to be influenced by climate change (Jenkins et al 1997;Jenkins 2005).…”

“…Sea-level rise in Australia may also directly affect estuarine and marine fish during their pre-and post-settlement phases. For example, Jenkins et al (1997) showed that spatial and temporal variability in recruitment of a temperate, seagrass-associated fish, King George whiting (Sillaginodes punctata), was largely determined by physical processes, including the residual sea level (caused by changes in barometric pressure). Other Australian commercial species that might be similarly affected include pink snapper (Pagurus auratus), southern sea garfish (Hyporhamphus melanochir), Australian herring (Arripis georgianus), whiting and mullet (Fletcher and Head 2006).…”