David I. Kline

Reef-building corals maintain intracellular photosymbiosis with dinoflagellate algae, allowing them to use photosynthetic products as metabolic fuel. Carbon dioxide (CO ₂ ) is a key substrate for photosynthesis, but its rapid increase in the global ocean due to anthropogenic emissions (known as “ocean acidification”) may disrupt coral symbiosis. We examined the effects of elevated CO ₂ on photosynthetic O ₂ production, oxidative damage, and antioxidant systems in the Caribbean reef-building corals Porites astreoides and Orbicella franksi . Coral colonies collected at 3m depth in Bocas del Toro (Panama) were exposed to control (∼390 μatm CO ₂ , pH ∼8.00) or elevated CO ₂ (∼1,060 μatm CO ₂ , pH ∼7.70) conditions in outdoor flow-through aquaria for 10 days. Flowing seawater had higher O ₂ concentrations in elevated CO ₂ tanks, with the largest differences at higher irradiance. Microsensor measurements confirmed that acute and chronic exposure to elevated CO ₂ significantly stimulated photosynthetic O ₂ production in both species. Despite increased O ₂ production. neither species showed significant changes in lipid peroxidation, reduced glutathione, or superoxide dismutase, catalase, and glutathione-S- transferase activities. Protein oxidation was unchanged in O. franksi but significantly decreased in P. astreoides . These results are consistent with partial relief of carbon limitation in P. astreoides symbionts under elevated CO ₂ , potentially improving photosynthetic efficiency and decreasing reactive oxygen species production. These findings support the resilience of P. astreoides to OA and suggest that elevated CO ₂ may increase daytime O ₂ levels on future reefs, with implications for the aerobic metabolism of reef organisms.

Aim: The symbioses between corals and endosymbiotic dinoflagellates have been described as a flexible relationship whose dynamics could serve as a source of resilience for coral reef ecosystems. However, the factors that drive the establishment and maintenance of this co‐evolutionary relationship remain unclear. We examined the environmental and geographical factors structuring dinoflagellate communities in a wide‐ranging Indo‐Pacific coral to begin to address this gap.Location: Djibouti, Oman, Taiwan and French Polynesia.Taxon: Cauliflower corals (Pocillopora spp.), dinoflagellates (family Symbiodiniaceae).Methods: We analysed publicly available amplicon sequence data from the nuclear ribosomal DNA internal transcribed spacer 2, originating from Pocillopora spp. We also compiled environmental data such as sea surface temperature (SST) and time since the last local mass bleaching event. We ran generalized least squares models, PERMANOVAs and indicator species analyses, to understand how thermal regimes and geographical distances impacted Pocillopora spp.'s Symbiodiniaceae community composition.Results: Sea surface temperature was the most important factor driving Symbiodiniaceae community differences, with the largest effect size of the statistically significant factors. When focusing on individual Symbiodiniaceae genera, SST was likewise the most important factor. Our indicator species analyses revealed that specimens that had recently bleached were characterized by roughly equal proportions of Cladocopium spp. and Durusdinium spp., while specimens that had not recently bleached had a similar proportion of Durusdinium spp. as those that had recently bleached, but also showed a reduction in Cladocopium spp., with this deficiency made up by the presence of Symbiodinium spp.Main Conclusions: We provide further support for the hypothesis that coral's Symbiodiniaceae communities could facilitate host resilience to thermal stress. Our work is in direct conversation with a larger body of biogeography literature that highlights how local environmental regimes can impact contemporary population structure, even in marine taxa with widespread distributions.

To better understand the decline of one of earth’s most biodiverse habitats, coral reefs, many survey programs employ regular photographs of the benthos. An emerging challenge is the time required to annotate the large volume of digital imagery generated by these surveys. Here, we leverage existing machine-learning tools (CoralNet) and develop new fit-to-purpose programs to process and score benthic photoquadrats using five years of data from the Smithsonian MarineGEO Network’s biodiversity monitoring program at Carrie Bow Cay, Belize. Our analysis shows that scleractinian coral cover on forereef sites (at depths of 3–10 m) along our surveyed transects increased significantly from 6 to 13% during this period. More modest changes in macroalgae, turf algae, and sponge cover were also observed. Community-wide analysis confirmed a significant shift in benthic structure, and follow-up in situ surveys of coral demographics in 2019 revealed that the emerging coral communities are dominated by fast-recruiting and growing coral species belonging to the generaAgariciaandPorites. While the positive trajectory reported here is promising, Belizean reefs face persistent challenges related to overfishing and climate change. Open-source computational toolkits offer promise for increasing the efficiency of reef monitoring, and therefore our ability to assess the future of coral reefs in the face of rapid environmental change.

Marine multicellular organisms host a diverse collection of bacteria, archaea, microbial eukaryotes, and viruses that form their microbiome. Such host-associated microbes can significantly influence the host’s physiological capacities; however, the identity and functional role(s) of key members of the microbiome (“core microbiome”) in most marine hosts coexisting in natural settings remain obscure. Also unclear is how dynamic interactions between hosts and the immense standing pool of microbial genetic variation will affect marine ecosystems’ capacity to adjust to environmental changes. Here, we argue that significantly advancing our understanding of how host-associated microbes shape marine hosts’ plastic and adaptive responses to environmental change requires (i) recognizing that individual host–microbe systems do not exist in an ecological or evolutionary vacuum and (ii) expanding the field toward long-term, multidisciplinary research on entire communities of hosts and microbes. Natural experiments, such as time-calibrated geological events associated with well-characterized environmental gradients, provide unique ecological and evolutionary contexts to address this challenge. We focus here particularly on mutualistic interactions between hosts and microbes, but note that many of the same lessons and approaches would apply to other types of interactions.

Up to 90% of global coral reefs are predicted to be severely degraded by 2050 under “business-as-usual” scenarios. To meet the scale and scope of this challenge, we propose designing and demonstrating a multi-modal system that can incorporate data from remote sensing (satellites, aircraft, and aerial drones), acoustics, genetics, sensor arrays, and low-cost imaging systems. The latter will be collected by low-cost smart sensing and autonomous underwater vehicles (AUVs) guided by adaptive sampling modeling software and rapidly analyzed using automated machine learning systems. Development and deployment will be linked to extensive and diversity-enhancing training programs. The Coral Sentinel System will be globally deployed to enable rapid-response adaptive management and to build public engagement in conservation interventions to save coral reefs.Phase 1 (Year 1) will involve testing assumptions, coalition building, fundraising, and initial system development. Phase 2 (Years 2‐4) will focus on engineering and development with a pilot deployment in the Caribbean. Phase 3 (Years 5‐6) will involve system expansion and iteration along the Tropical Eastern Pacific corridor. Phase 4 (Years 7‐10) will involve global deployment to over 50 reef sites. This will lead during the following decade (Phase 5) to provisioning of low-cost Sentinel systems to coastal communities globally.

Climate change is causing major changes to marine ecosystems globally, with ocean acidification of particular concern for coral reefs. Using a 200 d in situ carbon dioxide enrichment study on Heron Island, Australia, we simulated future ocean acidification conditions, and found reduced pH led to a drastic decline in net calcification of living corals to no net growth, and accelerated disintegration of dead corals. Net calcification declined more severely than in previous studies due to exposure to the natural community of bioeroding organisms in this in situ study and to a longer experimental duration. Our data suggest that reef flat corals reach net dissolution at an aragonite saturation state (Ω_AR) of 2.3 (95% confidence interval: 1.8–2.8) with 100% living coral cover and at Ω_AR > 3.5 with 30% living coral cover. This model suggests that areas of the reef with relatively low coral mortality, where living coral cover is high, are likely to be resistant to carbon dioxide-induced reef dissolution.

In the UK, some of the oldest oil and gas installations have been in the water for over 40 years and have considerable colonisation by marine organisms, which may lead to both industry challenges and/or potential biodiversity benefits (e.g., artificial reefs). The project objective was to test the use of an automated image analysis software (CoralNet) on images of marine biofouling from offshore platforms on the UK continental shelf, with the aim of (i) training the software to identify the main marine biofouling organisms on UK platforms; (ii) testing the software performance on 3 platforms under 3 different analysis criteria (methods A–C); (iii) calculating the percentage cover of marine biofouling organisms and (iv) providing recommendations to industry. Following software training with 857 images, and testing of three platforms, results showed that diversity of the three platforms ranged from low (in the central North Sea) to moderate (in the northern North Sea). The two central North Sea platforms were dominated by the plumose anemone Metridium dianthus; and the northern North Sea platform showed less obvious species domination. Three different analysis criteria were created, where the method of selection of points, number of points assessed and confidence level thresholds (CT) varied: (method A) random selection of 20 points with CT 80%, (method B) stratified random of 50 points with CT of 90% and (method C) a grid approach of 100 points with CT of 90%. Performed across the three platforms, the results showed that there were no significant differences across the majority of species and comparison pairs. No significant difference (across all species) was noted between confirmed annotations methods (A, B and C). It was considered that the software performed well for the classification of the main fouling species in the North Sea. Overall, the study showed that the use of automated image analysis software may enable a more efficient and consistent approach to marine biofouling analysis on offshore structures; enabling the collection of environmental data for decommissioning and other operational industries.

Object recognition memory is the ability to identify previously seen objects and is an adaptive mechanism that increases survival for many species throughout the animal kingdom. Previously believed to be possessed by only the highest order mammals, it is now becoming clear that fish are also capable of this type of memory formation. Similar to the mammalian hippocampus, the dorsolateral pallium regulates distinct memory processes and is modulated by neurotransmitters such as dopamine. Caribbean bicolour damselfish ( Stegastes partitus ) live in complex environments dominated by coral reef structures and thus likely possess many types of complex memory abilities including object recognition. This study used a novel object recognition test in which fish were first presented two identical objects, then after a retention interval of 10 min with no objects, the fish were presented with a novel object and one of the objects they had previously encountered in the first trial. We demonstrate that the dopamine D ₁ -receptor agonist (SKF 38393) induces the formation of object recognition memories in these fish. Thus, our results suggest that dopamine-receptor mediated enhancement of spatial memory formation in fish represents an evolutionarily conserved mechanism in vertebrates.

Massive coral bleaching events associated with high sea surface temperatures are forecast to become more frequent and severe in the future due to climate change. Monitoring colony recovery from bleaching disturbances over multiyear time frames is important for improving predictions of future coral community changes. However, there are currently few multiyear studies describing long‐term outcomes for coral colonies following acute bleaching events. We recorded colony pigmentation and size for bleached and unbleached groups of co‐located conspecifics of three major reef‐building scleractinian corals (Orbicella franksi,Siderastrea siderea, and Stephanocoenia michelini;n = 198 total) in Bocas del Toro, Panama, during the major 2005 bleaching event and then monitored pigmentation status and changes live tissue colony size for 8 years (2005–2013). Corals that were bleached in 2005 demonstrated markedly different response trajectories compared to unbleached colony groups, with extensive live tissue loss for bleached corals of all species following bleaching, with mean live tissue losses per colony 9 months postbleaching of 26.2% (±5.4SE) forO. franksi,35.7% (±4.7SE) forS. michelini, and 11.2% (±3.9SE) forS. siderea. Two species,O. franksiandS. michelini, later recovered to net positive growth, which continued until a second thermal stress event in 2010. Following this event, all species again lost tissue, with previously unbleached colony species groups experiencing greater declines than conspecific sample groups, which were previously bleached, indicating a possible positive acclimative response. However, despite this beneficial effect for previously bleached corals, all groups experienced substantial net tissue loss between 2005 and 2013, indicating that many important Caribbean reef‐building corals will likely suffer continued tissue loss and may be unable to maintain current benthic coverage when faced with future thermal stress forecast for the region, even with potential benefits from bleaching‐related acclimation.