Determination of microalgal diversity in three selected coastal locations of Sri Lanka with varying degrees of water pollution

Abstract

Microalgae is expected to play a vital role in a bio-based economy in Sri Lanka due to its rich biodiversity in marine and coastal environments. However, many human activities causing water pollution are identified as threats for the biodiversity in selected coastal locations. The current study was carried out to determine the microalgal diversity in three selected west-coast locations of Sri Lanka, with varying degrees of water pollution: Ulhitiyawa (UL, 7.34’N, 79.83’E), Mattakkuliya (MK, 6.97´N, 79.87´E), and Uswetakeiyawa (UK, 6.59´N, 79.52´E). The sampling of water was done from January to February 2023 and physico-chemical parameters (pH, EC, TDS, TSS, Na+, NO3 -, PO4 3-, Ca2+ etc.) of water samples were measured analyzed. Morphological identification of microalgae species was carried out using a Digital Light Microscope (OPTIKA-B- 290 TB). The relative abundance of each species was determined using a Petroff-Hausser bacteria counting chamber and biodiversity indices (Shannon-Wiener Index, Simpson’s Index and Margalef’s Index) were calculated. While the water from MK was brackish, it was saline (Na+ ion concentration) in the other two locations (UH 7950.00 ± 1394.74b ppm, UW 7623.33± 1296.70b ppm). Total Dissolved Solid (TDS) values decreased when the distance from seashore to the sampling site increased. The phosphate concentration in MK (0.45 ± 0.09 mg/L) was higher compared to UL (0.30± 0.01b mg/L) and UK (0.04± 0.02a mg/L), possibly due to the water pollution in MK (p < 0.05). Forty-two species of phytoplankton present in the water column and scoop samples from the three locations and were phenotypically characterized into four groups (Chlorophyta, Cyanophyta, Bacillariophyta and Euglenophyta). The highest mean species diversity and richness were observed in UK followed by UL while the highest mean species dominance was observed in MK. The most abundant microalgae species in UL was Coelastrella vacuolata while Ankistrodesmus sp. and Licmophora abbreviata were the most abundant species in UK. In MK, Chlorella vulgaris was the highest abundant species. Correlation analysis revealed a significant relationship between the physico-chemical parameters of seawater and the microalgal diversity. A positive correlation between F- (+0.913), Na+(+0.889) and Ca2+(+0.883) and species diversity was found while a negative correlation was observed with PO4 3- (-0.868) TDS (+0.755) was positively correlated with species richness while EC (-0.959), NO3 - (-0.698), NH4 +(-0.814) and Total Solids (-0.833) were negatively correlated with species dominance.