DYNAMICS OF FISH LARVAL DIVERSITY IN THE COX'S BAZAR COAST, BANGLADESH: SPATIOTEMPORAL DISTRIBUTION AND ENVIRONMENTAL RELATION

Abstract

Fish larval abundance, diversity, and ecological indices along the southeast coast of Cox's Bazar were assessed at five sampling stations: Moheshkhali Para (S1), Naf River Estuary (S2), Bakkhali River Estuary (S3), Rezukhal Estuary (S4), and St. Martin (S5). Monthly sampling covered three seasons from January to December 2022. Samples were collected with a Bongo net. Water volume was determined with a flow meter and hydrological data (Temperature, pH, alkalinity, and salinity) were collected. Fish larvae were identified morphologically at the family level. The relationship between larval occurrence and environmental factors was investigated through Canonical Correspondence Analysis (CCA). A total of 3,082 larvae under 32 families were found. S2 had the most families (24), while S5 had the fewest (16). Clupeidae, Engraulidae, Gobiidae, Ambassidae, and Sillaginidae were most abundant. S3 had the highest count (40.11 ± 71.08) per 1000 m3 , whereas S1 had the lowest (17.44 ± 22.17). Larval counts were greater in the monsoon and summer than in winter, and number of fish family was highest in the monsoon. S1 had the highest species richness (Margalef's index: 2.26 ± 1.26), diversity (Simpson's Index: 0.83 ± 0.09, Shannon-Weiner Index: 1.95 ± 0.52), and evenness (Pielou's evenness index: 0.84 ± 0.01). In contrast, S5 had the lowest (1.54 ± 0.70, 0.69 ± 0.09, 1.47 ± 0.29, and 0.64 ± 0.15). No significant variation (p > 0.05) was found in the indices among stations. Regarding seasons, Simpson's Index and Shannon-Weiner Index (H) exhibited significant variation (p < 0.05). Temperature, pH, total alkalinity, and salinity ranged from 22.7-32.9 °C, 6.6-8.5, 78-126 mg/L, and 15.3- 37 ppt, respectively. Ambassidae and Mugillidae had positive correlations with alkalinity and pH and Engraulidae with temperature. These findings may enhance the understanding of coastal and marine fish larval research in Bangladesh