Short term variability in larval fish assemblages of the Sydney shelf:tracers of hydrographic variability

The among-and within-night changes in the vertical and horizontal distribution of ichthyoplankton assemblages across the Sydney continental shelf, SE Australia, were examined in relation to concurrent changes in hydrography.Of the environmental factors examined, spatial position (sampling depth, distance from shore), water temperature and sampling depth relative to the base of the mixed layer gave the best explanation for variability in assemblage distnbutlons.There was good agreement between observed changes in ichthyoplankton distributions and among-night variability in the crossshelf temperature and current fields Ichthyoplankton assemblages functioned as short term, biological tracers of hydrographic variability.Our observat~ons suggest several cross-shelf ad\~ect~ve processes, including a recirculation cell over the shelf, could retain passively drlfting ichthyoplankton within the shelf region and also minimise longshore drift.The multivariate analysis used was an effective method of examining patterns within and between large, highly variable biological and environmental data sets.