First report on the proliferation of the sessile vermetid Dendropoma cf. maximum in Southeast Sulawesi: synergistic impacts of nickel mining sedimentation and destructive fishing on coral reef phase-shifts

Abstract

Coral reef ecosystems in Pomalaa, Southeast Sulawesi, are subjected to compounding anthropogenic pressures: chronic sedimentation from nickel mining overburden runoff and physical substrate degradation from historical and ongoing blast fishing. This study presents the first report on the localized population proliferation of the sessile vermetid gastropod Dendropoma cf. maximum across these dually disturbed reef matrices and evaluates the environmental correlates associated with this ecological shift. We evaluated benthic community structures and environmental parameters along a spatial disturbance gradient across three discrete sampling zones: High-Impact Zone (HIZ/DRM), Moderate-Impact Zone (MIZ), and Comparative Reference Sites (CRS/RS). Field surveys conducted monthly from October 2025 to February 2026 revealed a severe spatial phase-shift. In the HIZ/DRM, where the Smothering Index reached 3.8 ± 0.2, Total Suspended Solids (TSS) averaged 92.4 ± 15.6 mg/L, and Live Coral Cover collapsed to 4.2 ± 1.8%, D. cf. maximum exhibited high ecological resilience, reaching extraordinary population densities of 212 ± 28 ind/m² and forming massive biogenic crusts. Concurrently, gastropod diversity in this zone dropped drastically to H' = 0.42 ±0.12. Conversely, reference sites (CRS/RS) characterized by minimal sediment stress (Smothering Index: 0.2 ± 0.1; TSS: 6.4 ± 1.2 mg/L) and high structural complexity (Live Coral Cover: 74.8 ± 5.6%) maintained D. cf. maximum at baseline densities of 4 ± 2 ind/m². Multiple linear regression modeling confirmed that D. cf. maximum density strongly correlates with sediment smothering (r = 0.92, p < 0.001) and coral rubble cover (r = 0.89, p < 0.001). Blast fishing may have cleared native benthic competitors, while persistent lateritic overburden sedimentation likely excludes key predators. This synergistic mechanism provides vacant hard substrates that D. cf. maximum opportunistically colonizes via its sediment-tolerant mucus-net feeding strategy.