Long term relationship between farming damselfish, predators, competitors and benthic habitat on coral reefs of Moorea Island

Abstract

Understanding the processes that shape biodiversity is essential for effective environmental management. Across the world’s coral reefs, algal farming damselfish (Stegastes sp.) modify the surrounding benthic community through their creation of algae “farms”. Using a long-term monitoring dataset (2005–2019) from Moorea Island, French Polynesia, we investigated whether the density of dusky damselfish (Stegastes nigricans) is associated with benthic habitat composition, the density of predators and/or competitors, and whether the survey area was inside or outside of a Marine Protected Area (MPA). We found no evidence that benthic cover or number of competitors were associated with dusky damselfish densities, both inside and outside MPAs. In contrast, fluctuations in dusky damselfish densities were negatively associated with the density of predators (e.g. Serranidae, Muraenidae and Scorpaenidae) in the preceding year in non-MPA areas, and both within and outside of MPAs when predator densities were high (2005–2010). These results suggest that healthy predator populations may be important for regulating the abundances of keystone species, such as algal farming damselfish, especially when predator densities are high.

Effects of onshore development and damselfish (Stegastes nigricans) on coral richness in Opunohu Bay and Cook’s Bay in Moorea, French Polynesia

“…This may be due to the variation in relationship directions per coral taxa (negative, neutral, or positive) neutralizing any net effect of S. nigricans on coral cover. This lack of significant relationship aligns with other studies in Moorea (Feeney et al 2021) and the Caribbean (Vermeij et al 2015). Ultimately, the long-term relationship between farmer damselfish and corals remains unknown.…”

Emerging insights on effects of sharks and other top predators on coral reefs

“…Despite a lack of consistent variation in total herbivore biomass across a dramatic gradient of predator biomass in the northern Line Islands, there was strong evidence of prey release among the subset of herbivorous damselfish [30]. Similar negative associations of predators and territorial damselfish have been observed across a within-island gradient in Bonaire [59], a multi-region study of the GBR [44], and through survey years on Moorea [60]. Indeed, across a broad gradient of fisheries activity in the tropical Pacific, areas with more fisheries protections (and, ostensibly, higher predator densities) support lower densities of herbivorous damselfish [61].…”

Deep Learning for Semantic Segmentation of Coral Images in Underwater Photogrammetry

“…Possible causative agents of this disturbance are: sedimentation effects, cyclones, weak bleaching events, outbreaks of Acanthaster planci, algal spreading, predator populations and microbial diseases. (Faurea, 1989;Adjeroud, 1997;Feeney et al, 2021). In particular, it is worth pointing out that when Acanthaster planci erupts, they can cause great damage to corals, and their concentrated outbreaks on the reef floor are closely related to ocean water temperature warming and nutrient enrichment caused by human development.…”