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Many organisms exhibit depressed metabolism when resources are limited, a change that makes it possible to balance an energy budget. For symbiotic reef corals, daily cycles of light and periods of intense cloud cover can be chronic causes of food limitation through reduced photosynthesis. Furthermore, coral bleaching is common in present-day reefs, creating a context in which metabolic depression could have beneficial value to corals. In the present study, corals (massive Porites spp.) were exposed to an extreme case of resource limitation by starving them of food and light for 20 days. When resources were limited, the corals depressed area-normalized respiration to 37% of initial rates, and coral biomass declined to 64% of initial amounts, yet the corals continued to produce skeletal mass. However, the declines in biomass cannot account for the declines in area-normalized respiration, as mass-specific respiration declined to 30% of the first recorded time point. Thus, these corals appear to be capable of metabolic depression. It is possible that some coral species are better able to depress metabolic rates than others; such variation could explain differential survival during conditions that limit resources (e.g. shading). Furthermore, we found that maintenance of existing biomass, in part, supports the production of skeletal mass. This association could be explained if maintenance supplies needed energy (e.g. ATP) or inorganic carbon (i.e. CO2) that otherwise limits the production of skeletal mass. Finally, the observed metabolic depression can be explained as a change in pool sizes, and does not require a change in metabolic rules. [ABSTRACT FROM AUTHOR]

We quantified benthic community structure on shallow (10 m isobath) reefs separated by 3-130 km on four islands in the south Pacific, and evaluated the roles of disturbances vs. coral recruitment as causes of spatial heterogeneity. Reefs were surveyed in 2013 on Moorea, Tahiti, Tetiaroa, and Maiao, with community structure sampled at two sites on each island using photoquadrats. The effects of coral recruitment on population structure were evaluated through genetic analyses of Pocillopora on three of the islands. Benthic community structure with functional group resolution differed among islands and generally among sites, but coral community structure (generic resolution) differed among islands, but generally not among sites. Genetic analyses of Pocillopora using the open reading frame of host mtDNA revealed varying relative abundances of Pocillopora meandrina/Pocillopora eydouxi, Pocillopora verrucosa, Pocillopora effuses, and two unnamed haplotypes on each island. These results suggest that corals on each island represent unique samplings of genetically discrete larval assemblages rather than random samplings of a single larval assemblage. Together, our findings emphasize the extent to which coral community structure varies over a scale of <200 km, and suggests that recruitment from spatially discrete pools of coral larvae plays an important role in creating spatial variation in community structure, even where reefs are connected by prevailing currents. [ABSTRACT FROM AUTHOR]

Global climate change and other anthropogenic stressors have heightened the need to rapidly characterize ecological changes in marine benthic communities across large scales. Digital photography enables rapid collection of survey images to meet this need, but the subsequent image annotation is typically a time consuming, manual task. We investigated the feasibility of using automated point-annotation to expedite cover estimation of the 17 dominant benthic categories from survey-images captured at four Pacific coral reefs. Inter- and intra- annotator variability among six human experts was quantified and compared to semi- and fully- automated annotation methods, which are made available at . Our results indicate high expert agreement for identification of coral genera, but lower agreement for algal functional groups, in particular between turf algae and crustose coralline algae. This indicates the need for unequivocal definitions of algal groups, careful training of multiple annotators, and enhanced imaging technology. Semi-automated annotation, where 50% of the annotation decisions were performed automatically, yielded cover estimate errors comparable to those of the human experts. Furthermore, fully-automated annotation yielded rapid, unbiased cover estimates but with increased variance. These results show that automated annotation can increase spatial coverage and decrease time and financial outlay for image-based reef surveys. [ABSTRACT FROM AUTHOR]

Tropical coral reefs exemplify ecosystems imperiled by environmental change. Anticipating the future of reef ecosystems requires understanding how scleractinian corals respond to the multiple environmental disturbances that threaten their survival. We analyzed the stability of coral reefs at three habitats at different depths along the south shore of St. John, U.S. Virgin Islands, using multivariate autoregression (MAR) models and two decades of monitoring data. We quantified several measures of ecosystem stability, including the magnitude of typical stochastic fluctuations, the rate of recovery following disturbance, and the sensitivity of coral cover to hurricanes and elevated sea temperature. Our results show that, even within a ~4 km shore, coral communities in different habitats display different stability properties, and that the stability of each habitat corresponds with the habitat's known synecology. Two Orbicella-dominated habitats are less prone to annual stochastic fluctuations than coral communities in shallower water, but they recover slowly from disturbance, and one habitat has suffered recent losses in scleractinian cover that will not be quickly reversed. In contrast, a shallower, low-coral-cover habitat is subject to greater stochastic fluctuations, but rebounds more quickly from disturbance and is more robust to hurricanes and seawater warming. In some sense, the shallower community is more stable, although the stability arguably arises from having little coral cover left. Our results sharpen understanding of recent changes in coral communities at these habitats, provide a more detailed understanding of how these habitats may change in future environments, and illustrate how MAR models can be used to assess stability of communities founded upon long-lived species. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) research seeks to understand how marine ecosystems and global elemental cycles will respond to changes in seawater carbonate chemistry in combination with other environmental perturbations such as warming, eutrophication, and deoxygenation. Here, we discuss the effectiveness and limitations of current research approaches used to address this goal. A diverse combination of approaches is essential to decipher the consequences of OA to marine organisms, communities, and ecosystems. Consequently, the benefits and limitations of each approach must be considered carefully. Major research challenges involve experimentally addressing the effects of OA in the context of large natural variability in seawater carbonate system parameters and other interactive variables, integrating the results from different research approaches, and scaling results across different temporal and spatial scales. [ABSTRACT FROM AUTHOR]

In 1983 to 1984, a mass mortality event caused a Caribbean-wide, >95% population reduction of the echinoid grazer, Diadema antillarum. This led to blooms of algae contributing to the devastation of scleractinian coral populations. Since then, D. antillarum exhibited only limited and patchy population recovery in shallow water, and in 2022 was struck by a second mass mortality reported over many reef localities in the Caribbean. Half-a-century time-series analyses of populations of this sea urchin from St. John, US Virgin Islands, reveal that the 2022 event has reduced population densities by 98.00% compared to 2021, and by 99.96% compared to 1983. In 2021, coral cover throughout the Caribbean was approaching the lowest values recorded in modern times. However, prior to 2022, locations with small aggregations of D. antillarum produced grazing halos in which weedy corals were able to successfully recruit and become the dominant coral taxa. The 2022 mortality has eliminated these algal-free halos on St. John and perhaps many other regions, thereby increasing the risk that these reefs will further transition into coral-free communities. [ABSTRACT FROM AUTHOR]

Early life stages of the coral Seriatopora caliendrum were used to test the hypothesis that the depression of dark respiration in coral recruits by high pCO2 is caused by perturbed protein metabolism. First, the contribution of protein anabolism to respiratory costs under high pCO2 was evaluated by measuring the aerobic respiration of S. caliendrum recruits with and without the protein synthesis inhibitor emetine following 1 to 4 days at 45 Pa versus 77 Pa pCO2. Second, protein catabolism under high pCO2 was evaluated by measuring the flux of ammonium (NH4+) from juvenile colonies of S. caliendrum incubated in darkness at 47 Pa and 90 Pa pCO2. Two days after settlement, respiration of recruits was affected by an interaction between emetine and pCO2, with emetine reducing respiration 63% at 45 Pa pCO2 and 27% at 77 Pa pCO2. The interaction disappeared 5 days after settlement, when respiration was reduced 27% by emetine under both pCO2 conditions. These findings suggest that protein anabolism accounted for a large proportion of metabolic costs in coral recruits and was affected by high pCO2, with consequences detected in aerobic respiration. Juvenile S. caliendrum showed net uptake of NH4+ at 45 Pa pCO2 but net release of NH4+ at 90 Pa pCO2, indicating that protein catabolism, NH4+ recycling, or both were affected by high pCO2. Together, these results are consistent with the hypothesis that high pCO2 affects protein metabolism in corals. [ABSTRACT FROM AUTHOR]

Juvenile colonies of massive Porites spp. were exposed to manipulated pH and bicarbonate ([HCO3-]) in situ to test the hypothesis that ocean acidification (OA) does not affect respiration and calcification. Incubations lasted 28 h and exposed corals to ambient temperature and light with ecologically relevant water motion. Three treatments were applied: (1) ambient conditions of pH 8.04 and 1751 µmol HCO3- kg-1 (Treatment 1), (2) pCO2-induced ocean acidification of pH 7.73 and 2011 µmol HCO3- kg-1 (Treatment 2), and (3) pCO2 and HCO3--enriched seawater of pH 7.69 and 2730 µmol HCO3- kg-1 (Treatment 3). The third treatment providing elevated [HCO3-] was used to test for stimulatory effects of dissolved inorganic carbon on calcification under low pH and low saturation of aragonite (Ωarag), but it does not reflect conditions expected to occur under CO2-driven OA. Calcification of juvenile massive Porites spp. was affected by treatments, with an 81% elevation in Treatment 3 versus Treatment 1, but no difference between Treatments 1 and 2; respiration and the metabolic expenditure concurrent with calcification remained unaffected. These findings indicate that juvenile massive Porites spp. are resistant to short exposures to OA in situ, and separately, that they can increase calcification at low pH and low Ωaragif [HCO3-] is elevated. Juvenile Porites spp. may therefore be limited by dissolved inorganic carbon under ambient pCO2 conditions. [ABSTRACT FROM AUTHOR]

The Moorea Coral Reef Long Term Ecological Research program affords a unique opportunity to study the implications of ocean acidification (OA) for coral reefs, as ongoing ecological and physical monitoring there provides a context in which the patterns of community change attributed to OA can be detected. We used mesocosms to study the impacts of OA on corals and calcified algae, and conducted experiments to compare multiple species and evaluate how they are affected by changing concentrations of the different forms of dissolved inorganic carbon. Our results reveal taxonomic variation in the response to OA, with some corals and algae showing signs of resistance to OA conditions. This discovery is informing an urgent debate over the form in which coral reefs will survive (if at all) in the future. [ABSTRACT FROM AUTHOR]

The Moorea Coral Reef Long Term Ecological Research project funded by the US National Science Foundation includes multidisciplinary studies of physical processes driving ecological dynamics across the fringing reef, back reef, and fore reef habitats of Moorea, French Polynesia. A network of oceanographic moorings and a variety of other approaches have been used to investigate the biological and biogeochemical aspects of water transport and retention processes in this system. There is evidence to support the hypothesis that a low-frequency counterclockwise flow around the island is superimposed on the relatively strong alongshore currents on each side of the island. Despite the rapid flow and flushing of the back reef, waters over the reef display chemical and biological characteristics distinct from those offshore. The patterns include higher nutrient and lower dissolved organic carbon concentrations, distinct microbial community compositions among habitats, and reef assemblages of zooplankton that exhibit migration behavior, suggesting multigenerational residence on the reef. Zooplankton consumption by planktivorous fish on the reef reflects both retention of reef-associated taxa and capture by the reef community of resources originating offshore. Coral recruitment and population genetics of reef fishes point to retention of larvae within the system and high recruitment levels from local adult populations. The combined results suggest that a broad suite of physical and biological processes contribute to high retention of externally derived and locally produced organic materials within this island coral reef system. [ABSTRACT FROM AUTHOR]

We use a mathematical model to show that gradual environmental changes depress the abundance reef-building corals more strongly when acute disturbances are more frequent or severe, and when they impact colony growth and mortality, as opposed to recruitment. GLO:69VH/01jan21:bes21817-fig-0001.jpg PHOTO (COLOR): . gl Photo 1: Coral communities on the outer reef of Mo'orea, French Polynesia at 9-10 m depth, shown in January-May 2019. (A) and (C) show communities on Mo'orea's north shore; (B) shows a community on Mo'orea's east shore. [Extracted from the article]

We tested the effects of pCO2 on Seriatopora caliendrum recruits over the first 5.3d of post-settlement existence. In March 2011, 11–20 larvae were settled in glass vials (3.2mL) and incubated at 24.0°C and ~250μmolquantam−2 s−1 while supplied with seawater (at 1.4mLs−1) equilibrated with 51.6Pa pCO2 (ambient) or 86.4Pa pCO2. At 51.6Pa pCO2, mean respiration 7h post-settlement was 0.056±0.007nmolO2 recruit−1 min−1, but rose quickly to 0.095±0.007nmolO2 recruit−1 min−1 at 3.3d post-settlement, and thereafter declined to 0.075±0.002nmolO2 recruit−1 min−1 at 5.3d post-settlement (all±SE). Elevated pCO2 depressed respiration of recruits by 19% after 3.3d and 12% overall (i.e., integrated over 5.3d), and while it had no effect on corallite area, elevated pCO2 was associated with weaker adhesion to the glass settlement surface and lower protein biomass. The unique costs of settlement and metamorphosis for S. caliendrum over 5.3d are estimated to be 257mJrecruit−1 at 51.6Pa pCO2, which is less than the energy content of the larvae and recruits. [ABSTRACT FROM AUTHOR]

The article presents a study on long-term changes in the concentration of zooplankton and particulate material over a fringing reef in Saint John, U.S. Virgin Islands. Seawater quality was evaluated from concentrations of particulate matter (PM), particulate organic matter (POM) and zooplankton. The hypothesis that seawater quality over Caribbean reefs has changed over forty years is said to be consistent with the results of the study.

The article presents a study on the effect of rising temperature to juvenile Caribbean corals' respiration. It notes that the rising temperature has its vital role to determine the effect of climatic changes to the coral population. Moreover, temperature elevation measures the oxygen diffusion boundary layer (DBL) in darkness at a constant flow speed. Accordingly, the result shows insignificant effect of temperature to DBL thickness, however, interactive effects of temperatures and the taxon on oxygen concentration which is adjacent to respiration rates and tissue are observed. Furthermore, kinetic model of the effects of temperature on aerobic respiration is inconsistent with the trends and its behavioral effects reflects on the metabolic activity changes of the coenosarc.

Focuses on free-living colonies of porites in Moorea, French Polynesia. Greater abundance of unattached colonies than attached colonies in some locations; Abundance and size of free-living colonies; Likely modes of transformation of the colonies.

Presents information on a study which determined whether sceractinian corals are free of allometric constraints by quantifying metabolic scaling measured as aerobic respiration in small colonies of Siderastrea siderea. Discussion on the relationship between surface area and volume and isometry in colonial modular organisms; Methodology and results; Analysis of results.

Several species of crustose coralline algae (CCA) and their associated microbial biofilms play important roles in determining the settlement location of scleractinian corals on tropical reefs. In recent decades, peyssonnelid algal crusts (PAC) have become spatial dominants across large areas of shallow Caribbean reefs, where they appear to deter the recruitment of scleractinians. Our genetic investigations of PAC in St. John, US Virgin Islands, amplifying the large-subunit ribosomal RNA and psbA protein D1 marker genes, revealed them to be identical to Ramicrusta textilis previously reported overgrowing corals in Jamaica. Specimens of PAC sampled from the Honduras were likewise identical, confirming that this crustose alga inhabits the easternmost and westernmost regions of the Caribbean. We also analysed 16S rDNA tag amplicon libraries of the biofilms associated with PAC and sympatric CCA, which is favoured for coral settlement. Our results show that the microbial communities on PAC (vs. CCA) are characterized by significantly lower numbers of the epibiotic bacterial genus Pseudoalteromonas, which facilitates the recruitment and settlement of marine invertebrates. From these data, we infer that PAC are therefore unlikely to be attractive as settlement sites for coral larvae. Given the significant ecological change anticipated on these reefs due to increasing cover of PAC, there is an urgent need to further investigate competitive interactions between PAC and scleractinian corals, and elucidate the role of PAC and their associated microbiomes in accentuating phase shifts from coral to algae on tropical reefs. [ABSTRACT FROM AUTHOR]

This study tested the hypothesis that sponge assemblages on the reefs of St. John, US Virgin Islands (18.315°N, 64.716°W), changed from 1992 to 2017. Sponges were identified to species or genus in photoquadrats and were quantified at 2–3 y intervals by density, with linear dimensions used to estimate volume as a proxy for biomass. From 1992 to July 2017, overall sponge density (pooled among taxa) increased, although trends varied among the most common species for which density increased (four species), decreased (one species), or showed no linear relationship with time (2 species). Hurricanes Irma and Maria caused a 51% decline in overall sponge density from July to November 2017, with density in November 2017 being 31% lower than in 1992. For the common sponges, densities of 6 declined by 82–100% between July and November 2017, but densities in November 2017 were 13–736% higher than in 1992 for four species, and 47–100% lower than in 1992 for 3 species. Sponge volume did not change linearly between 1992 and November 2017, but it was reduced by 54% following the hurricanes. Multivariate variation over time in benthic community structure was not strongly associated with sponge density alone, although a significant association with rainfall highlighted the potential roles of this environmental factor in directly, or indirectly, mediating changes in community structure. Overall, the mean density of sponges, as well as most of the common sponge species, trended upwards prior to the hurricanes, but these trends reversed following the storms. [ABSTRACT FROM AUTHOR]