Data from: Freshwater hydrozoan blooms alter activity and behaviour of territorial cichlids in Lake Tanganyika

Jellyfish blooms pose multiple threats to wild fish. Yet, we still know
little about how blooms impact fitness-related behaviours of fish caught
within their areas of effect, e.g. for littoral fish that are not able to
relocate to avoid incoming blooms of stinging jellyfish. Here, we
documented the behavioural impacts of freshwater jellyfish (Limnocnida
tanganjicae) blooms on a territorial cichlid (Variabilichromis moorii) as
well as on the wider community of cichlids in a shallow-water rocky
habitat of Lake Tanganyika. Compared to non-bloom conditions, V. moorii
individuals reduced their swimming and territory defence activities during
jellyfish blooms (each by ~ 50%), but not their foraging or affiliative
behaviours. Despite this reduction in activity, V. moorii could not
entirely avoid being stung and preferred to remain closer to the rocky
substrata as opposed to the more open demersal zone. Many other fishes
similarly hid among the benthic substrata, changing the composition of the
fish community in the demersal zone during bloom conditions. Reductions in
activity could have multiple fitness-related implications for individual
fish. Understanding these behavioural consequences is an important topic
of research as blooms are predicted to increase in severity in the future
especially along coastal habitats.