Short-term fish predation destroys resilience of zooplankton communities and prevents recovery of phytoplankton control by zooplankton grazing

Abstract

Planktivorous fish predation directly affects zooplankton biomass, community and size structure, and may indirectly induce a trophic cascade to phytoplankton. However, it is not clear how quickly the zooplankton community structure and the cascading effects on phytoplankton recover to the unaffected state (i.e. resilience) once short-term predation by fish stops. The resilience has implications for the ecological quality and restoration measures in aquatic ecosystems. To assess the short-term zooplankton resilience against fish predation, we conducted a mesocosm experiment consisting of 10 enclosures, 6 with fish and 4 without fish. Plankton communities from a natural lake were used to establish phytoplankton and zooplankton in the mesocosms. High biomasses (about 20 g wet mass m -3 ) of juvenile planktivorous fish (perch, Perca fluviatilis ) were allowed to feed on zooplankton in fish enclosures for four days. Thereafter, we removed fish and observed the recovery of the zooplankton community and its cascading effect on trophic interactions in comparison with no fish enclosures for four weeks. Short-term fish predation impaired resilience in zooplankton community by modifying community composition, as large zooplankton, such as calanoids, decreased just after fish predation and did not re-appear afterwards, whereas small cladocerans and rotifers proliferated. Total zooplankton biomass increased quickly within two weeks after fish removal, and at the end even exceeded the biomass measured before fish addition. Despite high biomass, the dominance of small zooplankton released phytoplankton from grazer control in fish enclosures. Accordingly, the zooplankton community did not recover from the effect of fish predation, indicating low short-term resilience. In contrast, in no fish enclosures without predation disturbance, a high zooplankton:phytoplankton biomass ratio accompanied by low phytoplankton yield (Chlorophyll-a:Total phosphorus ratio) reflected phytoplankton control by zooplankton over the experimental period. Comprehensive views on short and long-term resilience of zooplankton communities are essential for restoration and management strategies of aquatic ecosystems to better predict responses to global warming, such as higher densities of planktivorous fish.

Lateral hydrological connectivity differentially affects the community characteristics of multiple groups of aquatic invertebrates in tropical wetland pans in South Africa

“…Daphnia) while favouring small cladocerans (e.g. Bosmina, Chydorus), copepods, and rotifers (Ersoy, Brucet, Bartrons, & Mehner, 2019;Jakobsen, Hansen, Jeppesen, Grønkjaer, & Søndergaard, 2003). This is in line with our study where, small bodied zooplankton species, such as Bosmina longirostris, Dunhevedia sp.…”

“…are good swimmers, they are mostly restricted to fishless waters because their large body size and active behaviour also makes them highly sensitive to visual predation by fish (Kerfoot & Lynch, 1987;Nhiwatiwa et al, 2009). Bosmina, Chydorus), copepods, and rotifers (Ersoy, Brucet, Bartrons, & Mehner, 2019;Jakobsen, Hansen, Jeppesen, Grønkjaer, & Søndergaard, 2003). In this study, the large branchiopods were not observed in sites with high LHC.…”

Grazing resistance in phytoplankton

“…Co-evolution of zooplankton grazers to sizes that would allow them to ingest even the largest phytoplankton cells, colonies, and aggregates is strongly constrained as zooplankton themselves are on the menu of visually hunting predators (Lass & Spaak, 2003;Sommer et al, 2012). Even short-term fish predation events may lead to longer-term reduction in large-bodied grazers (Ersoy et al, 2019). Visually, hunting fish may induce several defenses in zooplankton too, such as Daphnia becoming smaller (Lass & Spaak, 2003), where smaller animals also have a lower maximum size of particles they can ingest (Burns, 1968).…”

Phytoplankton Community Response to Nutrients, Temperatures, and a Heat Wave in Shallow Lakes: An Experimental Approach

“…It is commonly accepted that communities with higher species richness have an advantage in resource use efficiency (RUE, the amount of biomass produced per unit of supplied resource) [23,24] and this has also been shown for phytoplankton communities [25,26]. RUE often decrease with increasing grazing pressure on phytoplankton [27,28] and zooplankton grazing is another important factor determining the diversity and community structure of phytoplankton [29,30]. The biomass ratio of zooplankton to phytoplankton is a crude estimate of the zooplankton grazing pressure [31] and this ratio is also highest under mesotrophic conditions [22,32].…”