Abstract
Blooms of gelatinous zooplankton can represent dramatic environmental perturbations for aquatic ecosystems. Yet, we still know little about how blooms impact fitness-related behaviours of fish caught within their areas of effect, especially for freshwater systems. Here, we documented the behavioural impacts of freshwater hydrozoan (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 with non-bloom conditions, V. moorii individuals in the midst of blooms reduced their swimming and territory defence activities (each by approx. 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. Establishing the consequences of these behavioural changes is important for understanding the effects of gelatinous zooplankton blooms in freshwater systems.
Highlights
The factors that promote the rapid growth, i.e. ‘blooms’, of gelatinous zooplankton populations in our oceans and freshwater systems have been a focus of considerable research to date [1,2,3,4,5]
We show that near-shore L. tanganjicae jellyfish blooms can alter the activity levels and behaviours of cichlid fishes caught within their areas of effect
Many of the fishes that live and breed in these shallow rocky habitats are spatially restricted to the few square metres of substrata comprising their territories, and many of these fish remain on their territories as jellyfish blooms arrive
Summary
The factors that promote the rapid growth, i.e. ‘blooms’, of gelatinous zooplankton populations in our oceans and freshwater systems have been a focus of considerable research to date [1,2,3,4,5]. ‘blooms’, of gelatinous zooplankton populations in our oceans and freshwater systems have been a focus of considerable research to date [1,2,3,4,5]. More recent research examining the interactions between fish populations and blooms of gelatinous organisms suggests that their relationships can be complex [6]. Blooms may be beneficial by providing an important food source for certain fishes [11,12,13], and even by providing nursery and foraging space for juveniles of other species [4,14,15]. The impact of gelatinous zooplankton blooms on individual fish and fish populations can be highly nuanced and depend on a wide range of ecological and species-specific factors
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
