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.
Highlights
Coral reefs are among the most biodiverse ecosystems on the planet, supporting roughly three million species and approximately 25% of all marine life
Over the 15 year study period (2005–2019) the density of Stegastes increased from 0.05 to 0.24 fish per m2. This increase was not associated with changes in the cover of live hard corals, macroalgae, or algal turf inside or outside the Marine Protected Area (MPA) (Fig. 2)
While we found no relationship between predator density and S. nigricans densities in the same year, a significant negative relationship was found across the whole study period outside of MPAs when considering predator density from the previous year, and this negative relationship was significant both inside and outside of MPAs during periods where predator density was relatively high (e.g. 2005–2010) (Fig. 3)
Summary
Coral reefs are among the most biodiverse ecosystems on the planet, supporting roughly three million species and approximately 25% of all marine life. Species do not affect surrounding biodiversity and keystone species refer to those that disproportionately large effect compared to their abundance[12] They influence ecosystem processes, such as by regulating prey populations (predators), regulating predator populations (prey), supporting other species through cooperative interactions (mutualists), linking mutualistic species (hosts, clients or partners), and by creating habitats that. Naim et al.[28] showed that algal turf abundance increased significantly between 1993 and 2002 due to the expansion of Stegastes territories over time in some coral reefs at Reunion Island During their monitoring across 64 Mesoamerican reefs, Randazzo-Eisemann et al.[26] showed that the density of algal-gardening damselfish increased from 1.5 individuals per 100m2 in 2006 to 4.7 individuals per 100m2 in 2016, and that their density was strongly correlated with fleshy macroalgae cover. If predator populations are reduced due to overfishing, the farming damselfish population may increase[26]
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