Tidal and diel variations in abundance and schooling behavior of estuarine fish within an intertidal salt marsh pool

Abstract

Tidally driven fluctuations lead to rapid variations in hydrological properties that can have profound effects on the dynamic and functions of salt marshes. During low tides, many nektonic species find refuge from predatory fish in shallow intertidal pools. The utilization of shallow pool refuges also exposes fishes to fitness costs that fluctuate between day and night. Yet, how aggregated fish using an intertidal pool modulate their schooling behavior over the diel cycle remains unknown. Using high-resolution imaging sonar (ARIS), we monitored an intertidal pool over a 3-day period and quantified fish abundance, size, and schooling behavior relative to the diel and tidal cycles. Higher fish abundance was found during low tides than high tides when the section was connected with the subtidal waters. At low tide, no differences in fish abundance and size were detected in the pool between day and night, but larger schools formed at night than day. Our results suggest that biotic and abiotic factors affecting fish schooling behavior in the low tide refuge may vary over the diel cycle. We present possible functional explanations for the shifts in schooling tendency between nocturnal and diurnal utilization of the pool.