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1. Scaling the effects of ocean acidification on coral growth and coral–coral competition on coral community recovery

   https://doi.org/10.7717/peerj.11608  

   Evensen, Nicolas R. ; Bozec, Yves-Marie ; Edmunds, Peter J. ; Mumby, Peter J. ( January 2021 , PeerJ)

   Ocean acidification (OA) is negatively affecting calcification in a wide variety of marine organisms. These effects are acute for many tropical scleractinian corals under short-term experimental conditions, but it is unclear how these effects interact with ecological processes, such as competition for space, to impact coral communities over multiple years. This study sought to test the use of individual-based models (IBMs) as a tool to scale up the effects of OA recorded in short-term studies to community-scale impacts, combining data from field surveys and mesocosm experiments to parameterize an IBM of coral community recovery on the fore reef of Moorea,more »French Polynesia. Focusing on the dominant coral genera from the fore reef, Pocillopora , Acropora , Montipora and Porites , model efficacy first was evaluated through the comparison of simulated and empirical dynamics from 2010–2016, when the reef was recovering from sequential acute disturbances (a crown-of-thorns seastar outbreak followed by a cyclone) that reduced coral cover to ~0% by 2010. The model then was used to evaluate how the effects of OA (1,100–1,200 µatm pCO 2 ) on coral growth and competition among corals affected recovery rates (as assessed by changes in % cover y −1 ) of each coral population between 2010–2016. The model indicated that recovery rates for the fore reef community was halved by OA over 7 years, with cover increasing at 11% y −1 under ambient conditions and 4.8% y −1 under OA conditions. However, when OA was implemented to affect coral growth and not competition among corals, coral community recovery increased to 7.2% y −1 , highlighting mechanisms other than growth suppression (i.e., competition), through which OA can impact recovery. Our study reveals the potential for IBMs to assess the impacts of OA on coral communities at temporal and spatial scales beyond the capabilities of experimental studies, but this potential will not be realized unless empirical analyses address a wider variety of response variables representing ecological, physiological and functional domains.« less
2. Epifaunal invertebrate assemblages associated with branching Pocilloporids in Moorea, French Polynesia

   https://doi.org/10.7717/peerj.9364  

   Pisapia, Chiara ; Stella, Jessica ; Silbiger, Nyssa J. ; Carpenter, Robert ( January 2020 , PeerJ)

   Reef-building corals can harbour high abundances of diverse invertebrate epifauna. Coral characteristics and environmental conditions are important drivers of community structure of coral-associated invertebrates; however, our current understanding of drivers of epifaunal distributions is still unclear. This study tests the relative importance of the physical environment (current flow speed) and host quality (e.g., colony height, surface area, distance between branches, penetration depth among branches, and background partial mortality) in structuring epifaunal communities living within branching Pocillopora colonies on a back reef in Moorea, French Polynesia. A total of 470 individuals belonging to four phyla, 16 families and 39 genera weremore »extracted from 36 Pocillopora spp. colonies. Decapods were the most abundant epifaunal organisms (accounting for 84% of individuals) found living in Pocillopora spp. While coral host characteristics and flow regime are very important, these parameters were not correlated with epifaunal assemblages at the time of the study. Epifaunal assemblages associated with Pocillopora spp. were consistent and minimally affected by differences in host characteristics and flow regime. The consistency in abundance and taxon richness among colonies (regardless of habitat characteristics) highlighted the importance of total habitat availability. With escalating effects of climate change and other localized disturbances, it is critical to preserve branching corals to support epifaunal communities.« less
3. Daily variation in net primary production and net calcification in coral reef communities exposed to elevated <i>p</i>CO₂

   https://doi.org/10.5194/bg-14-3549-2017  

   Comeau, Steeve ; Edmunds, Peter J. ; Lantz, Coulson A. ; Carpenter, Robert C. ( January 2017 , Biogeosciences)

   The threat represented by ocean acidification (OA) for coral reefs has received considerable attention because of the sensitivity of calcifiers to changing seawater carbonate chemistry. However, most studies have focused on the organismic response of calcification to OA, and only a few have addressed community-level effects, or investigated parameters other than calcification, such as photosynthesis. Light (photosynthetically active radiation, PAR) is a driver of biological processes on coral reefs, and the possibility that these processes might be perturbed by OA has important implications for community function. Here we investigate how CO₂ enrichment affects the relationships between PAR and community netmore »O₂ production (P_net), and between PAR and community net calcification (G_net), using experiments on three coral communities constructed to match (i) the back reef of Mo'orea, French Polynesia, (ii) the fore reef of Mo'orea, and (iii) the back reef of O'ahu, Hawaii. The results were used to test the hypothesis that OA affects the relationship between P_net and G_net. For the three communities tested, pCO₂ did not affect the P_net–PAR relationship, but it affected the intercept of the hyperbolic tangent curve fitting the G_net–PAR relationship for both reef communities in Mo'orea (but not in O'ahu). For the three communities, the slopes of the linear relationships between P_net and G_net were not affected by OA, although the intercepts were depressed by the inhibitory effect of high pCO₂ on G_net. Our result indicates that OA can modify the balance between net calcification and net photosynthesis of reef communities by depressing community calcification, but without affecting community photosynthesis.« less
4. Selective Uptake of Pelagic Microbial Community Members by Caribbean Reef Corals

   https://doi.org/10.1128/AEM.03175-20  

   Hoadley, Kenneth D. ; Hamilton, Maria ; Poirier, Camille L. ; Choi, Chang Jae ; Yung, Cheuk-Man ; Worden, Alexandra Z. ( April 2021 , Applied and Environmental Microbiology)

   Johnson, Karyn N. (Ed.)

   ABSTRACT Coral reefs are possible sinks for microbes; however, the removal mechanisms at play are not well understood. Here, we characterize pelagic microbial groups at the CARMABI reef (Curaçao) and examine microbial consumption by three coral species: Madracis mirabilis , Porites astreoides , and Stephanocoenia intersepta . Flow cytometry analyses of water samples collected from a depth of 10 m identified 6 microbial groups: Prochlorococcus , three groups of Synechococcus , photosynthetic eukaryotes, and heterotrophic bacteria. Minimum growth rates (μ) for Prochlorococcus , all Synechococcus groups, and photosynthetic eukaryotes were 0.55, 0.29, and 0.45 μ day −1 , respectively, and suggestmore »relatively high rates of productivity despite low nutrient conditions on the reef. During a series of 5-h incubations with reef corals performed just after sunset or prior to sunrise, reductions in the abundance of photosynthetic picoeukaryotes, Prochlorococcus and Synechococcus cells, were observed. Of the three Synechococcus groups, one decreased significantly during incubations with each coral and the other two only with M. mirabilis. Removal of carbon from the water column is based on coral consumption rates of phytoplankton and averaged between 138 ng h −1 and 387 ng h −1 , depending on the coral species. A lack of coral-dependent reduction in heterotrophic bacteria, differences in Synechococcus reductions, and diurnal variation in reductions of Synechococcus and Prochlorococcus , coinciding with peak cell division, point to selective feeding by corals. Our study indicates that bentho-pelagic coupling via selective grazing of microbial groups influences carbon flow and supports heterogeneity of microbial communities overlying coral reefs. IMPORTANCE We identify interactions between coral grazing behavior and the growth rates and cell abundances of pelagic microbial groups found surrounding a Caribbean reef. During incubation experiments with three reef corals, reductions in microbial cell abundance differed according to coral species and suggest specific coral or microbial mechanisms are at play. Peaks in removal rates of Prochlorococcus and Synechococcus cyanobacteria appear highest during postsunset incubations and coincide with microbial cell division. Grazing rates and effort vary across coral species and picoplankton groups, possibly influencing overall microbial composition and abundance over coral reefs. For reef corals, use of such a numerically abundant source of nutrition may be advantageous, especially under environmentally stressful conditions when symbioses with dinoflagellate algae break down.« less
5. Geographically driven differences in microbiomes of Acropora cervicornis originating from different regions of Florida’s Coral Reef

   https://doi.org/10.7717/peerj.13574  

   Williams, Sara D. ; Klinges, J. Grace ; Zinman, Samara ; Clark, Abigail S. ; Bartels, Erich ; Villoch Diaz Maurino, Marina ; Muller, Erinn M. ( January 2022 , PeerJ)

   Effective coral restoration must include comprehensive investigations of the targeted coral community that consider all aspects of the coral holobiont—the coral host, symbiotic algae, and microbiome. For example, the richness and composition of microorganisms associated with corals may be indicative of the corals’ health status and thus help guide restoration activities. Potential differences in microbiomes of restoration corals due to differences in host genetics, environmental condition, or geographic location, may then influence outplant success. The objective of the present study was to characterize and compare the microbiomes of apparently healthy Acropora cervicornis genotypes that were originally collected from environmentally distinctmore »regions of Florida’s Coral Reef and sampled after residing within Mote Marine Laboratory’s in situ nursery near Looe Key, FL (USA) for multiple years. By using 16S rRNA high-throughput sequencing, we described the microbial communities of 74 A. cervicornis genotypes originating from the Lower Florida Keys ( n  = 40 genotypes), the Middle Florida Keys ( n  = 15 genotypes), and the Upper Florida Keys ( n  = 19 genotypes). Our findings demonstrated that the bacterial communities of A. cervicornis originating from the Lower Keys were significantly different from the bacterial communities of those originating from the Upper and Middle Keys even after these corals were held within the same common garden nursery for an average of 3.4 years. However, the bacterial communities of corals originating in the Upper Keys were not significantly different from those in the Middle Keys. The majority of the genotypes, regardless of collection region, were dominated by Alphaproteobacteria, namely an obligate intracellular parasite of the genus Ca. Aquarickettsia . Genotypes from the Upper and Middle Keys also had high relative abundances of Spirochaeta bacteria. Several genotypes originating from both the Lower and Upper Keys had lower abundances of Aquarickettsia , resulting in significantly higher species richness and diversity. Low abundance of Aquarickettsia has been previously identified as a signature of disease resistance. While the low- Aquarickettsia corals from both the Upper and Lower Keys had high abundances of an unclassified Proteobacteria, the genotypes in the Upper Keys were also dominated by Spirochaeta . The results of this study suggest that the abundance of Aquarickettsia and Spirochaeta may play an important role in distinguishing bacterial communities among A. cervicornis populations and compositional differences of these bacterial communities may be driven by regional processes that are influenced by both the environmental history and genetic relatedness of the host. Additionally, the high microbial diversity of low- Aquarickettsia genotypes may provide resilience to their hosts, and these genotypes may be a potential resource for restoration practices and management.« less