The zooplankton prey field for rock lobster phyllosoma larvae in relation to oceanographic features of the south-eastern Indian Ocean

Abstract

The western rock lobster, Panulirus cygnus, provides Australia's most valuable wild caught fishery but, in recent years, there has been a dramatic decline in settlement of the post-larval phase into their natal coastal habitat. One hypothesis for this decline was that the oceanographic conditions no longer favour the survival, feeding and growth of the larval (phyllosoma) phase. To explore this, the oceanography and corresponding zooplankton prey field along five latitudinal transects in the south-eastern Indian Ocean were quantified during July 2010. Leeuwin Current Water (LCW) and Sub-Tropical Surface Water (STSW) were distinguished and a prominent front at ∼30°S characterized by strong eastward flow separated them. Although zooplankton abundance increased towards the north, the prey field was unevenly distributed with patches of higher prey concentration associated mainly with LCW. Chaetognaths were the most abundant prey item (means: 17.2 and 4.1 m−3 in LCW and STSW, respectively) and were positively correlated with chlorophyll a in both water masses. Panulirus cygnus phyllosoma had a highly patchy distribution but, despite lower prey concentrations, were more abundant in STSW than LCW, particularly south of the front. Our results suggest that LC meso-scale features with strong fronts may be implicated in phyllosoma aggregations and shoreward transport of late-stage larvae and that this warrants further investigation.