Taxonomic Composition and Environmental Drivers of Phytoplankton in Earthen Fish Ponds (Bulgaria)
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Date
2025-06-29
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Plovdiv University Press "Paisii Hilendarski"
Abstract
This study presents a comparative analysis of phytoplankton taxonomic structure and its relationship with environmental factors in earthen aquaculture ponds located in Plovdiv and Trivoditsi, Bulgaria, during the period May–September 2024. A total of 114 phytoplankton taxa were identified across six phyla, with Chlorophyta and Cyanoprokaryota dominating the bio-mass. The results showed a pronounced shift towards higher phytoplankton biomass (PhB up to 60.3 mg L⁻¹) and chlorophyll-a concentrations (up to 133 μg L⁻¹) in the Trivoditsi ponds, associated with blooms of green algae and cyanobacteria. For the first time, the invasive and potentially toxic species Raphidiopsis raciborskii was recorded in Bulgarian aquaculture ponds, contributing up to 15.5% of the phytoplankton biomass during bloom periods. Environmental parameters such as elevated ammonium, phosphate, and COD were positively correlated with increased PhB, chlorophyll-a, and total viable counts (TVC) of heterotrophic bacteria. Redundancy analysis (RDA) highlighted the influence of nutrient enrichment and organic load on the biological variables. The observed co-variation between PhB and TVC suggests the presence of a dynamic microbial loop, where intensive primary production supports hetero-trophic bacterial growth. These findings confirm the role of eutrophic conditions and nutrient availability in shaping phytoplankton and microbial communities in earthen ponds used for aquaculture. This study provides new insights into the ecological interactions in such systems, contributing to future strategies for water quality management and sustainable aquaculture practices.
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Keywords
phytoplankton, cyanobacteria, Raphidiopsis raciborskii, aquaculture ponds, heterotrophic bacteria