Foraging, growth and habitat choice in turbid water: an experimental study with fish larvae in the Baltic Sea

Eutrophication is a large problem in many marine and brackish-water areas. One of the consequences is algae-induced turbidity affecting visually feeding organisms, and behavioural changes of fish and other animals are common in turbid water. The aim of this study was to compare the performance of larval pike Esox lucius in turbid and clear water. We experimentally studied habitat choice, prey attacks and swimming activity of newly hatched larvae in the presence of a predator and competitors in relation to algae-induced turbidity. Our results demonstrated that the larvae spent less time in vegetation, performed more prey attacks and spent less time swimming in turbid water than in clear conditions. The presence of competitors increased the number of prey attacks, while the presence of a visual predator decreased the number of attacks. We also showed that pike larval weight was lower in high turbidity than in low turbidity. Our results show that algae-induced water turbidity affects both direct (i.e. feeding and habitat choice) and indirect qualities (i.e. weight) of pike larvae and may therefore affect larval survival and potentially even recruitment into the population.