Community Structure and Spatial Pattern of Coral Reef Fishes in Nipah Bay, North Lombok Regency

Reef fishes are key indicators of reef condition and play an important role in linking benthic and pelagic processes. This study aimed to quantify the community structure and spatial variation of reef fishes in Nipah Bay, North Lombok. Surveys were conducted in July 2025 at three stations and two depths (3 m and 7 m) using underwater visual census along 70 × 5 m belt transects. All observed fishes were identified to species level, and total length was recorded to estimate biomass using family-specific length–weight relationships. Environmental parameters, including temperature, salinity, pH, current velocity, and total suspended solids (TSS), were measured concurrently. A total of 1,884 individuals belonging to 55 species, 32 genera, and 15 families were recorded. The assemblage was dominated by Pomacentridae, followed by Labridae and Acanthuridae, while Chaetodontidae were relatively scarce. Diversity indices indicated moderate to high diversity (H' = 2.13–3.02), high evenness (E = 0.67–0.86), and low dominance (D = 0.06–0.19). Descriptive analysis of community composition suggested variation in reef fish assemblages among stations, with relatively higher similarity between T1 and T2 compared to T3. Total fish biomass reached 58.07 g m⁻², with Acanthuridae contributing the largest proportion. Spatial variation in reef fish assemblages was likely influenced by benthic habitat characteristics, including structural complexity, substrate composition, and live coral cover, while water quality parameters were relatively homogeneous across sites. These findings provide baseline information on reef fish community structure and support future reef management and long-term monitoring in Nipah Bay.