Density‐dependence mediates coral assemblage structure

Abstract

Density dependence (DD) controls community recovery following widespread mortality, yet this principle rarely has been applied to coral assemblages. The reefs of Mo'orea, French Polynesia, provide the opportunity to study DD of coral population growth, because coral assemblages in this location responded to declines in abundance with high recruitment and an increase in cover during which recruitment of pocilloporid corals was inversely associated with density. This study tests for DD in this system, first, by describing the context within which it operates: coral cover changed from 46% in 2005, to <1% in 2010 following an outbreak of a corallivorous sea star and a cyclone, and then increased to 74% by 2017, in large part through inverse density‐associated pocilloporid recruitment. Second, a test for DD of recruitment was conducted by decreasing Pocillopora spp. cover from 33% to 19%: one year later, the density of Pocillopora spp. recruits was 1.65‐fold higher in the low vs. high cover treatment. Finally, the effects of DD were investigated by comparing simulated and empirical distributions of pocilloporid colonies: as predicted by DD, small colonies were randomly distributed, while large colonies were uniformly distributed. Together these results demonstrate DD of population regulation for Pocillopora spp. corals, thus revealing the potential importance of this ecological principle in determining the resilience of coral assemblages.

The spatial footprint and patchiness of large‐scale disturbances on coral reefs

“…To model stochastic background mortality, we randomly selected, each year, 40% of all reefs and reduced coral cover on each selected reef by 15%. The latter two processes involve the stock‐recruitment dynamics of corals, which are complex, scale‐dependent and involve multiple processes (gamete production, fertilization, dispersal, settlement, post‐settlement survivorship), each of which are often nonlinear functions of local coral abundance (Doropoulos et al, 2017; Edmunds et al, 2018; Oliver & Babcock, 1992; Vermeij & Sandin, 2008). We assumed that propagule production scales quadratically with local cover, to mimic fertilization‐suppressed larval production at low gamete densities.…”

Diversity, structure and demography of coral assemblages on underwater lava flows of different ages at Reunion Island and implications for ecological succession hypotheses

“…Moreover, our study focused on coral assemblages and was conducted several years after the last volcanic eruption, which may have had an impact on the outcomes of this study. It would be interesting to examine coral assemblages and their biotic interactions with other taxa (such as spatial competition, allelopathy and density-dependent mechanisms) during the first months of the recolonization processes, as subtle changes in these early stages may have profound and long-lasting effects on coral dynamics 29,36,75,76 .…”

“…A rapid recolonization driven by high recruitment of juvenile corals has also been documented four years after the eruption of the Hunga Tonga-Hunga Ha'apai volcanic island 35 . In some cases, the ecological processes driving the recovery dynamics have been examined (e.g., density-dependence 36 ), but in the majority of cases, the underlying ecological processes associated to recovery trajectories of coral assemblages, such as recruitment, early mortality and growth, remain elusive, and therefore so do the mechanisms of ecological succession 29,37,38 . In the context of "coral reef crisis" and the pessimistic projections for the future of this ecosystem, examining succession processes is not only important for understanding changes and recovery trajectories of coral communities, but is also critical to better evaluate the potential colonization of climate change refugia, such as non-reef marginal tropical environments or high-latitude temperate regions [39][40][41][42] .…”

Facilitating corals in an early Silurian deep‐water assemblage

“…2020) as well as investigating mortality due to adult proximity (Gibbs & Hay 2015) or density‐dependence (Edmunds et al . 2018). However, to our knowledge SPPA has not been used to analyse coral palaeocommunities.…”