Depth affects the population dynamics on a soft coral-dominated reef on the Great White Wall, Fiji

Abstract

Soft corals (order Alcyonacea) are an important component of tropical coral reefs, and often form locally abundance dense carpets. Some soft coral species are prone to bleaching and heat stress like scleractinian, reef-forming corals, but others appear resistant to bleaching stressors. Despite the importance of soft corals in tropical reefs, there is limited knowledge regarding their demographic ecology. Spatial point process analysis (SPPA) enables inference of ecological processes underlying spatial distributions of individuals in a community by investigating the fit of models of known processes to observed spatial patterns. SPPA can also quantify how these underlying ecological processes change with environmental gradients (such as depth). We used SPPA to investigate the population ecology on the Great White Wall (GWW), Fiji—a vertical reef dominated by Nephtheidae soft corals alongside other filter feeders and algae. We found that a combination of reproductive and habitat association processes best explained the spatial patterns on the GWW. We found that the best-fit underlying ecological processes changed with depth, and that Nephtheidae soft corals became more dominant on deeper parts of the wall, likely due to a combination of reproductive lability, fast growth rates, and increasing suitable habitat associated with filter-feeding. Even where the Nephtheidae were most dominant, other filter feeders were able to persist. This mixed community composition could be because the Nephtheidae feed in periods of high current, and temporal niche partitioning in feeding could be permitting biodiversity on the GWW, allowing for hydroids and sponges to coexist with the Nephtheidae.

Bibliographic Information