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Abstract: Lake Buluan, the third-largest lake in the Philippines, sustains rich aquatic biodiversity and supports extensive aquaculture. However, decades of anthropogenic pressures, including domestic wastewater, aquaculture effluents, and agricultural runoff, have degraded water quality. This study assessed morphologically, the composition and distribution of freshwater diatoms across six stations inside and outside fish pens to evaluate their potential as bioindicators of ecological change. Nineteen species were recorded, with 11 present in both inside (IFB) and outside (OFB) fish pens. Dominant taxa—Nitzschia serpentiraphe, Gomphonema montanum, and Aulacoseira islandica—occurred at nearly all stations and are linked to nutrient-rich sediments and organic pollution. Site-specific patterns emerged: Nitzschia liebethruthii dominated IFB1 and IFB3 but was absent in IFB2 and most OFB sites, whereas Nitzschia inconspicua showed the opposite trend. The exclusive occurrence of Eunotia monodon and Cymbella tumida in OFB stations suggests more acidic or oligotrophic conditions outside enclosures. Rare taxa (Sellaphora sp., Grammatophora angulosa) contributed to richness in non-enclosed areas. Moreover, next-generation sequencing (NGS) data confirmed the dominance of Nitzschia spp., indicating mild environmental stress and ecological plasticity which is, typical for tropical shallow lakes. Findings underscore diatom monitoring as a sensitive, cost-effective tool for assessing aquaculture impacts and advocate its integration into freshwater ecosystem management.
Key Words: diatom, lake, bioindicators, aquaculture
