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On shallow coral reefs, coral bommies create patchy communities where interactions among patches are likely to affect a variety of ecological features. Here, we describe bommies in the back reef of Moorea, French Polynesia, and evaluate the role of select factors in determining their size, shape, and distribution. We tested the hypothesis that the distribution and growth of corals varies across the surface of bommies (i.e., north, south, east, and west sides), and therefore might play a role in determining bommie shape and their propensity for fission and fusion. Bommies were elliptical in planar shape, with their long axes parallel to ambient flow and perpendicular to the direction of offshore waves.Poritesspp. andPocilloporaspp. were the most abundant corals, and they were uniformly distributed over the surface of bommies. During April 2022, small colonies (≤ 4 cm height) ofPocilloporaspp. grew at similar rates on the north, south, east, and west sides of the bommies, among which integrated seawater flow during the experiment was similar. These results suggest that the contemporary growth and distribution of corals is unlikely to play a strong role in determining the features of present-day bommies. Evaluating how environmental conditions mediate the structure of coral bommies in shallow habitats will help to understand whether habitat mosaics can mediate coral reef resilience in the Anthropocene. 

Tropical corals are undergoing population declines due to disturbances. The implications of these trends are modulated by the ability of corals to support population recovery through recruitment. Current research underscores the importance of physical features of benthic surfaces in promoting coral recruitment, which creates opportunities to enhance recruitment by engineering surfaces to replicate these features with the goal of enhancing coral settlement. This study examined the interaction between the settlement of coral larvae and three-dimensional (3D) surfaces and employed 3D printing to enhance recruitment. We tested the effects of the features of microhabitats on the settlement preference, gregariousness, and survival of the brooding coral Pocillopora acuta. Grooved microhabitats that are common in the shallow (<7 m depth) backreef of Moorea, French Polynesia, were printed onto tiles made of polylactic acid, and were favored for settlement by freshly released larvae fromP.acuta. The percent survivorship over 20 d of coral recruits that settled in grooved microhabitats was 16.4% vs none on open flat surfaces. These results underscore the importance of naturally forming benthic features in promoting coral recruitment, and they highlight the potential for duplication of these features through 3D printing to enhance coral recruitment and accelerate reef restoration following damage. 

Abstract Understanding how foundation species recover from disturbances is key for predicting the future of ecosystems in the Anthropocene. Coral reefs are dynamic ecosystems that can undergo rapid declines in coral abundance following disturbances. Understanding why some reefs recover quickly from these disturbances whereas others recover slowly (or not at all) gives insight into the drivers of community resilience. From 2006 to 2010 coral reefs on the fore reef of Moorea, French Polynesia, experienced severe disturbances that reduced coral cover from ~46% in 2005 to <1% in 2010. Following these disturbances, coral cover increased from 2010 to 2018. Although there was a rapid and widespread recovery of corals, reefs at 17 m depth recovered more slowly than reefs at 10 m depth. We investigated the drivers of different rates of coral recovery between depths from 2010 to 2018 using a combination of time‐series data on coral recruitment, density, growth, and mortality in addition to field experiments testing for the effects of predation. Propagule abundance did not influence recovery, as the density of coral recruits (spat <6 months old) did not differ between depths. However, mortality of juvenile corals (≤5 cm diameter) was higher at 17 m, leading to densities of juvenile corals 3.5 times higher at 10 m than at 17 m depth. Yet, there were no differences in the growth of corals between depths. These results point to an early life stage bottleneck after settlement, resulting in greater mortality at 17 m than at 10 m as the likely driver of differential coral recovery between depths. We used experiments and time‐series data to test mechanisms that could drive different rates of juvenile coral mortality across depths, including differences in predation, competition, and the availability of suitable substratum. The results of these experiments suggested that increased coral mortality at 17 m may have been influenced by higher intensity of fish predation, and higher mortality of corals attached to unfavorable substratum. In contrast, the abundance of macroalgae, a coral competitor, did not explain differences in coral survival. Our work suggests that top‐down processes and substratum quality can create bottlenecks in corals that can drive rates of coral recovery after disturbance. 

Abstract Biome degradation characterizes the Anthropocene Epoch, and modern ecology is deeply involved with describing the changes underway. Most research has focused on the role of acute disturbances in causing conspicuous changes in ecosystem structure, which leads to an underappreciation of the chronic effects causing large changes through the cumulative effects of small perturbations over decades. Coral reefs epitomize this trend, because the changes in community structure are profound, yet the data to quantify these effects are usually insufficient to evaluate the relative roles of different disturbance types. Here, four decades of surveys from two coral reefs (9 and 14 m depth) off St. John, US Virgin Islands, are used to quantify the associations of acute and chronic events with the changes in benthic community structure. These reefs profoundly changed over 36 years, with coral death altering species assemblages to depress abundances of the ecologically important coralOrbicellaspp. and elevating the coverage of macroalgae and crustose coralline algae/turf/bare space (CTB). Linear mixed models revealed the prominent role of chronic variation in temperature in accounting for changes in coverage of corals, macroalgae, and CTB, with rising temperature associated with increases in coral cover on the deep reef, and declines on the shallow reef. Hurricanes were also associated with declines in coral cover on the shallow reef, and increases on the deep reef. Multivariate analyses revealed strong associations between community structure and temperature, but weaker associations with hurricanes, bleaching, and diseases. These results highlight the overwhelming importance of chronically increasing temperature in altering the benthic community structure of Caribbean reefs. 

ABSTRACT Body size profoundly affects organism fitness and ecosystem dynamics through the scaling of physiological traits. This study tested for variation in metabolic scaling and its potential drivers among corals differing in life history strategies and taxonomic identity. Data were compiled from published sources and augmented with empirical measurements of corals in Moorea, French Polynesia. The data compilation revealed metabolic isometry in broadcasted larvae, but size-independent metabolism in brooded larvae; empirical measurements of Pocillopora acuta larvae also supported size-independent metabolism in brooded coral larvae. In contrast, for juvenile colonies (i.e. 1–4 cm diameter), metabolic scaling was isometric for Pocillopora spp., and negatively allometric for Porites spp. The scaling of biomass with surface area was isometric for Pocillopora spp., but positively allometric for Porites spp., suggesting the surface area to biomass ratio mediates metabolic scaling in these corals. The scaling of tissue biomass and metabolism were not affected by light treatment (i.e. either natural photoperiods or constant darkness) in either juvenile taxa. However, biomass was reduced by 9–15% in the juvenile corals from the light treatments and this coincided with higher metabolic scaling exponents, thus supporting the causal role of biomass in driving variation in scaling. This study shows that metabolic scaling is plastic in early life stages of corals, with intrinsic differences between life history strategy (i.e. brooded and broadcasted larvae) and taxa (i.e. Pocillopora spp. and Porites spp.), and acquired differences attributed to changes in area-normalized biomass. 

Understanding population dynamics is a long-standing objective of ecology, but the need for progress in this area has become urgent. For coral reefs, achieving this objective is impeded by a lack of information on settlement versus post-settlement events in determining recruitment and population size. Declines in coral abundance are often inferred to be associated with reduced densities of recruits, which could arise from mechanisms occurring at larval settlement, or throughout post-settlement stages. This study uses annual measurements from 2008 to 2021 of coral cover, the density of coral settlers (S), the density of small corals (SC), and environmental conditions, to evaluate the roles of settlement versus post-settlement events in determining rates of coral recruitment and changes in coral cover at Moorea, French Polynesia. Coral cover, S, SC, and the SC:S ratio (a proxy for post-settlement success), and environmental conditions, were used in generalized additive models (GAMs) to show that: (a) coral cover was more strongly related to SC and SC:S than S, and (b) SC:S was highest when preceded by cool seawater, low concentrations of Chlorophyll a, and low flow speeds, and S showed evidence of declining with elevated temperature. Together, these results suggest that changes in coral cover in Moorea are more strongly influenced by post-settlement events than settlement. The key to understanding coral community resilience may lie in elucidating the factors attenuating the bottleneck between settlers and small corals. 

Monitoring coral cover can describe the ecology of reef degradation, but rarely can it reveal the proximal mechanisms of change, or achieve its full potential in informing conservation actions. Describing temporal variation in Symbiodiniaceae within corals can help address these limitations, but this is rarely a research priority. Here, we augmented an ecological time series of the coral reefs of St. John, US Virgin Islands, by describing the genetic complement of symbiotic algae in common corals. Seventy-five corals from nine species were marked and sampled in 2017. Of these colonies, 41% were sampled in 2018, and 72% in 2019; 28% could not be found and were assumed to have died. Symbiodiniaceae ITS2 sequencing identified 525 distinct sequences (comprising 42 ITS2 type profiles), and symbiont diversity differed among host species and individuals, but was in most cases preserved within hosts over 3 yrs that were marked by physical disturbances from major hurricanes (2017) and the regional onset of stony coral tissue loss disease (2019). While changes in symbiont communities were slight and stochastic over time within colonies, variation in the dominant symbionts among colonies was observed for all host species. Together, these results indicate that declining host abundances could lead to the loss of rare algal lineages that are found in a low proportion of few coral colonies left on many reefs, especially if coral declines are symbiont-specific. These findings highlight the importance of identifying Symbiodiniaceae as part of a time series of coral communities to support holistic conservation planning. Repeated sampling of tagged corals is unlikely to be viable for this purpose, because many Caribbean corals are dying before they can be sampled multiple times. Instead, random sampling of large numbers of corals may be more effective in capturing the diversity and temporal dynamics of Symbiodiniaceae metacommunities in reef corals. 

Abstract As the major form of coral reef regime shift, stony coral to macroalgal transitions have received considerable attention. In the Caribbean, however, regime shifts in which scleractinian corals are replaced by octocoral assemblages hold potential for maintaining reef associated communities. Accordingly, forecasting the resilience of octocoral assemblages to future disturbance regimes is necessary to understand these assemblages' capacity to maintain reef biodiversity. We parameterised integral projection models quantifying the survival, growth, and recruitment of the octocorals,Antillogorgia americana,Gorgonia ventalina, andEunicea flexuosa,in St John, US Virgin Islands, before, during, and after severe hurricane disturbance. Using these models, we forecast the density of populations of each species under varying future hurricane regimes. We demonstrate that although hurricanes reduce population growth,A. americana,G. ventalina, andE. flexuosaeach display a capacity for quick recovery following storm disturbance. Despite this recovery potential, we illustrate how the population dynamics of each species correspond with a longer-term decline in their population densities. Despite their resilience to periodic physical disturbance events, ongoing global change jeopardises the future viability of octocoral assemblages.