Patterns of coral community composition along Suva, a Pacific Island urban reef system

Hard corals (Order Scleractinia) form complex, heterogeneous communities that underpin reef ecosystem functions but are increasingly threatened by anthropogenic stressors, particularly in urbanised coastal settings. This study characterised coral community composition and juvenile coral distribution within the urban reef systems adjacent to Fiji’s capital, Suva. We recorded 27 coral genera, with Acropora and Porites together contributing over 56% of total coral cover. Coral cover varied among reef zones, peaking at reef crests (mean coverage ± SE; 44.11 ± 2.41%), and declining on reef flats (23.58 ± 2.06%) and back reefs (17.27 ± 1.90%). Juvenile analyses focused on the four most common genera: Acropora, Porites, Goniopora, and Pocillopora. Acropora juveniles were the most abundant and broadly distributed, while Porites exhibited highly clustered spatial patterns. Juvenile Goniopora distribution was restricted to back reefs, and Pocillopora displayed a dispersed, sporadic distribution. These patterns indicate strong habitat-driven zonation and genus-specific sensitivities, with Acropora more abundant in high-quality, stable environmental conditions and Porites and Goniopora tolerating more nutrient-rich, turbid conditions. Although all surveyed reefs fall within the broader urbanised area, differences among zones and reef systems were noted, reflecting varying exposure to local stressors (e.g., turbidity, nutrient loading, and sedimentation) rather than a strict urban/non-urban contrast. Thus, our findings describe ecological variability within an urban reef system rather than comparing urban and non-urban reefs. Conservation and restoration of Suva’s reefs should therefore prioritise improving local water quality through strengthened wastewater management and reduced land-based runoff and implementing targeted, habitat-specific interventions informed by environmental sensitivities. Collectively, these results underscore both the resilience and vulnerabilities of urban reef systems and highlight the need for adaptive, habitat-based management strategies in Fiji and comparable Pacific settings.