Effects of tidal current-induced flow on reef fish behaviour and function on a subtropical rocky reef

Journal article, 2016

Tidal currents are important features in reef environments with high tidal range Such current-influenced areas can be attractive for fish due to transport of nutrients and foo items. Biological sampling, however, is difficult in these environments and it remains poorl understood to what degree strong currents actually shape tropical and subtropical reef fish communities We used remote underwater video to investigate effects of flow velocity on fish acros the tidal cycle at a rocky reef in southern Mozambique. Fish were recorded during flow velocitie ranging from 0 to 1.44 m s-1. Current flow velocity had no significant effect on the benthic fis assemblage, while increasing flow velocity had a negative effect on pelagic fish abundance an influenced trophic group composition. Limits for tolerated flow velocity on the pelagic assemblag were species-specific, with the highest resistance for larger predatory fish using subcarangifor swimming. Flow velocity had significant positive effects on size of Caranx spp., showing tha smaller individuals had lower tolerance to flow than larger conspecifics. Planktivorous pomacentrid and monodactylids were very abundant in flows up to 0.5 m s?1, suggesting that the are functions as an important foraging ground for planktivorous fish up to this flow velocity, whil abundance of barracudas Sphyraena spp. was higher in moderate currents compared to slac water. For the benthic assemblage, benthic structures seemed to provide sufficient flow refuge fo fish throughout the tidal cycle, highlighting the importance of structural complexity for benthi fish in this environment. Fish assemblages on reefs subjected to strong tidal currents might therefor be sensitive to habitat modifications. The ecological importance of tidal currents should b considered in marine management.