engleski

Interactions between fish and invertebrates in the lowland area of the Sava River

Riverine ecosystems exhibit diverse and varied hydrological, geological and limnological conditions along with longitudinal and transverse profiles, where floods and droughts, two opposite natural components of streamflow regimes, are key drivers of environmental conditions and biocoenoses. The littoral zones of freshwaters are highly susceptible to extreme hydrological fluctuations caused by climate-induced changes in the water cycle. Disturbances in the hydrology could affect fish assemblages and their trophic interactions with invertebrates, which constitute a large part of fish diets. The littoral zone of the Sava River (Croatia) was studied to determine the influence of hydrological extremes on (1) fluctuations in environmental drivers and biocoenoses, and 2) the trophic relationships between fish, macroinvertebrates and zooseston, in an attempt to reveal their trophic interactions. In spring of 2014 and 2015, seven sampling sites were selected considering accessibility and representativeness in terms of different anthropogenic sources of pollution (e.g., industry, traffic, agricultural and urban activities). A range of instruments were used onsite to determine the environmental and hydrological conditions. This study contributes to the existing research upon the stressor effects of extreme hydrological events on environmental conditions and communities, reflected in a reduction in fish diversity and abundance. The hydrological extremes in precipitation and the riverine regime also altered macrozoobenthos and zooseston components due to the changes in water and sediment habitat conditions. In the food-web network among fish, macrozoobenthos and zooseston hydrological stressors caused remarkable changes in food resources and functional feeding traits. Biocoenotic components showed different tolerance to extreme discharge, resulting in remarkable reductions in fish abundance, diversity, biomass, size and, presumably due to dilution, the abundance of zooseston, which is an important food for fish larvae. By contrast, benthic macroinvertebrates did not show significant fluctuations in abundance, but the share of benthic groups of organisms was shifted during high discharge. Gastropods and amphipods were found to be important food sources for fish. The resilience and recovery of the ecosystem greatly depended on biodiversity. Climate change will likely exacerbate the extent of water cycle alterations and create more challenges for the future of ecosystem and fisheries management. The present study helps to highlight the consequences of hydrological disturbances caused by climate change: the enhancement of stressors in riverine littoral habitats and inhabited communities. The present study helps to highlight the consequences of hydrological disturbances caused by climate change: the enhancement of stressors in riverine littoral habitats and inhabited communities. Accordingly, a study of the effects of zooseston and macroinvertebrate ingestion on fish populations under varying hydrological conditions is planned.

fish ; nutrition ; zooseton ; biocoenoses

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