There's no smell like home: how sensory ontogeny plays a role in the early life histoy of estuarine-dependent fishes

The spatial distribution and connectivity of marine organisms and their populations are largely determined by biophysical and behavioural factors affecting dispersal during the larval phase. While biophysical modelling is... [ view full abstract ]

The spatial distribution and connectivity of marine organisms and their populations are largely determined by biophysical and behavioural factors affecting dispersal during the larval phase. While biophysical modelling is shedding new light on larval processes, the question of how larval behaviour interacts with biophysical factors needs more investigation, particularly outside of warm-water marine species. Understanding what abilities fish larvae have and when these develop is critical to effective modelling and management of fish populations, and while most studies to date have focused on settlement-stage responses little is known about pre-settlement behaviours. Here, we studied the ontogeny of olfactory responses to habitat cues in larvae of two temperate estuarine-dependant species reared at Port Stephens Fisheries Institute, NSW. Since the critical period of movement from coastal waters to estuary areas was of interest we compared olfactory cues from the coastal zone with those from the upper estuary to test preference behaviour. Our results show a dynamic sensory ontogeny in the early life history of these species. While larvae did not respond to different chemical cues at flexion both species developed a preference for coastal water from ca. 7mm SL. While this preference persisted in Mulloway with further growth, Australian Bass larvae experienced a significant shift in preference towards estuary cues from ca. 8mm SL. Subsequent trials indicate that the presence of chemicals cues from organic matter such as seagrass drive the dynamics in behavioural changes observed more so than different levels of pH or salinity. This research into pre-settlement behaviour of early-stage temperate fishes supports the hypothesis that sensory ecology plays a role in larval transport from ocean to estuary.