Long-term changes in phytoplankton composition in a large mountain reservoir used for cage aquaculture. A case study with Dospat Reservoir-Bulgaria

Kostadin Dochin

Kostadin Dochin

Abstract: Current research investigates changes in phytoplankton species composition over a seven-year period (2016-2022) and compares them with previous studies. Our objective is to focus on a three-year period (2019-2022) during which rainbow trout production decreases significantly, resulting in significant changes in algae species abundance and composition. During the same period, the species diversity of phytoplankton decreased two and a half times, and its biomass reached several times lower levels than when the rainbow trout farm operated at full capacity. The number of identified cyanoprokaryotes has decreased twice, is not abundant and is almost not found among the dominant species. The adverse facts clearly confirm the impact of cage aquaculture on the eutrophication of Dospat Reservoir. We can predict with confidence that, in the next few years, the resumption of the production process will lead to a deterioration of the ecological status of the Dospat Reservoir, that will negatively affect the composition and structure of phytoplankton.

Keywords: cage fish farming; change; eutrophication; lack of production; negative impact; phytoplankton diversity

Citation: Dochin, K. (2025). Long-term changes in phytoplankton composition in a large mountain reservoir used for cage aquaculture. A case study with Dospat Reservoir – Bulgaria. Bulg. J. Agric. Sci., 31(1), 212–224.

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Date published: 2025-02-25

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