Environmental plastics in the context of UV radiation, climate change, and the Montreal Protocol.

There are close links between solar UV radiation, climate change, and plastic pollution. UV-driven weathering is a key process leading to the degradation of plastics in the environment but also the formation of potentially harmful plastic fragments such as micro- and nanoplastic particles. Estimates of the environmental persistence of plastic pollution, and the formation of fragments, will need to take in account plastic dispersal around the globe, as well as projected UV radiation levels and climate change factors.

Plastics in the environment in the context of UV radiation, climate change and the Montreal Protocol: UNEP Environmental Effects Assessment Panel, Update 2023.

This Assessment Update by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) considers the interactive effects of solar UV radiation, global warming, and other weathering factors on plastics. The Assessment illustrates the significance of solar UV radiation in decreasing the durability of plastic materials, degradation of plastic debris, formation of micro- and nanoplastic particles and accompanying leaching of potential toxic compounds. Micro- and nanoplastics have been found in all ecosystems, the atmosphere, and in humans. While the potential biological risks are not yet well-established, the widespread and increasing occurrence of plastic pollution is reason for continuing research and monitoring. Plastic debris persists after its intended life in soils, water bodies and the atmosphere as well as in living organisms. To counteract accumulation of plastics in the environment, the lifetime of novel plastics or plastic alternatives should better match the functional life of products, with eventual breakdown releasing harmless substances to the environment.

Browning, nutrient inputs, and fast vertical mixing from simulated extreme rainfall and wind stress alter estuarine phytoplankton productivity.

Browning and nutrient inputs from extreme rainfall, together with increased vertical mixing due to strong winds, are more frequent in coastal ecosystems; however, their interactive effects on phytoplankton are poorly understood. We conducted experiments to quantify how browning, together with different mixing speeds (fluctuating radiation), and a nutrient pulse alter primary productivity and photosynthetic efficiency in estuarine phytoplankton communities. Phytoplankton communities (grazers excluded) were exposed simultaneously to these drivers, and key photosynthetic targets were quantified: oxygen production, electron transport rates (ETRs), and carbon fixation immediately following collection and after a 2-d acclimation/adaptation period. Increasing mixing speeds in a turbid water column (e.g. browning) significantly decreased ETRs and carbon fixation in the short term. Acclimation/adaptation to this condition for 2 d resulted in an increase in nanoplanktonic diatoms and a community that was photosynthetically more efficient; however, this did not revert the decreasing trend in carbon fixation with increased mixing speed. The observed interactive effects (resulting from extreme rainfall and strong winds) may have profound implications in the trophodynamics of highly productive system such as the Southwest Atlantic Ocean due to changes in the size structure of the community and reduced productivity.

A roadmap to integrating resilience into the practice of coral reef restoration.

Recent warm temperatures driven by climate change have caused mass coral bleaching and mortality across the world, prompting managers, policymakers, and conservation practitioners to embrace restoration as a strategy to sustain coral reefs. Despite a proliferation of new coral reef restoration efforts globally and increasing scientific recognition and research on interventions aimed at supporting reef resilience to climate impacts, few restoration programs are currently incorporating climate change and resilience in project design. As climate change will continue to degrade coral reefs for decades to come, guidance is needed to support managers and restoration practitioners to conduct restoration that promotes resilience through enhanced coral reef recovery, resistance, and adaptation. Here, we address this critical implementation gap by providing recommendations that integrate resilience principles into restoration design and practice, including for project planning and design, coral selection, site selection, and broader ecosystem context. We also discuss future opportunities to improve restoration methods to support enhanced outcomes for coral reefs in response to climate change. As coral reefs are one of the most vulnerable ecosystems to climate change, interventions that enhance reef resilience will help to ensure restoration efforts have a greater chance of success in a warming world. They are also more likely to provide essential contributions to global targets to protect natural biodiversity and the human communities that rely on reefs.

Seventeen-year study reveals fluctuations in key ecological indicators on two reef crests in Cuba.

Reef crests in the Caribbean have lost approximately 80% of the foundational habitat-forming coral Acropora palmata (Lamarck, 1816), with declines registered as early as the 1950s mainly from anthropogenic causes. We studied two reef crests in the northwestern region of Cuba over 17 years (2005 to 2021) to evaluate temporal changes in coral cover, dominated by A. palmata, and their potential drivers. The density of A. palmata generally showed a negative trend at both reefs, with the lowest density recorded in 2021 at 0.2 ± 0.05 col. m-2 at Playa Baracoa and 1.0 ± 0.1 col. m-2 at Rincon de Guanabo. The mean size of the colonies in the two reefs also decreased over time. In Playa Baracoa, the mean diameter of A. palmata colonies decreased from 2012 at 67 ± 5.9 cm to 2013 at 34 ± 2.2 cm, whereas in Rincon de Guanabo, a change in diameter was evident from 2015 at 44.3 ± 2.3 to 2021 at 21.6 ± 0.9 cm. Adult colonies (10 cm-50 cm diameter) predominated in most years on both reefs. The populations of A. palmata on both reefs were healthy, with an average of 70% colonies in good condition during the study period. However, A. palmata cover decreased by almost half by 2021, to 8.6% in Playa Baracoa and 16.8% in Rincon de Guanabo. By contrast, macroalgal cover increased two-fold to 87.1% in Playa Baracoa and four-fold to 77.2% in Rincon de Guanabo. The density of the sea urchin Diadema antillarum was higher in Playa Baracoa than in Rincon de Guanabo. The highest densities were 2.8 ± 0.2 ind. m-2 in Playa Baracoa in 2005 and 0.1 ± 0.03 ind. m-2 in Rincon de Guanabo in 2008. Although our results show an overall decline of A. palmata (density and percent cover) and an increase in macroalgae, these two reef crests are in better condition than most reefs in the Caribbean in terms of the density and health of A. palmata populations, and the density of D. antillarum at Playa Baracoa. Our results are important in establishing a management plan to ensure the condition of these reef crests does not degrade further.

Long-term survival, growth, and reproduction of Acropora palmata sexual recruits outplanted onto Mexican Caribbean reefs.

Acropora palmata is a foundational yet endangered Caribbean reef-building coral species. The lack of recovery after a disease outbreak and low recruitment has led to widespread use of fragmentation to restore populations. Another option is the production of sexual recruits (settlers) via assisted reproduction to improve the genetic diversity of depleted populations; however, the viability of this approach has not been tested over the long term. In 2011 and 2012, A. palmata larvae were cultured, settled, and the sexual recruits raised in an ex-situ nursery. Survival and growth were monitored over time. In 2014, these two F1 cohorts were moved to an in-situ nursery and after one year, a subset (29 colonies) was outplanted onto Cuevones Reef in the Mexican Caribbean. Growth and survival of these colonies were monitored periodically and compared to colonies that remained in the in-situ nursery. In 2019, samples were collected and analyzed for fertility and fecundity. 53% of the colonies were gravid and fecundity was 5.61 ± 1.91 oocytes and 3.04 ± 0.26 spermaries per polyp. A further 14 colonies from these two cohorts were outplanted in 2020 onto Picudas Reef and monitored during the subsequent spawning seasons. Two years after outplanting onto Picudas Reef, all colonies were alive and spawning of three of these colonies was recorded in 2022 in synchrony with the wild population. Gametes were collected from two colonies and crossed, with 15% fertilization success. Spermatozoa from wild colonies were then added and fertilization success increased to 95%. The resultant larvae followed normal development and symbiont uptake was visible within two weeks. The F2 generation was settled, maintained in an ex-situ nursery, and monitored for survival and growth. Both F1 and F2 generations followed a Type III survival curve with high initial mortality while in the ex-situ nursery and low later-stage mortality. The growth rates of these colonies increased three-fold after outplanting when compared to their growth rates in the ex-situ and in-situ nurseries. All colonies survived while in the in-situ nursery and for an additional nine years after outplanting onto Cuevones Reef. Overall, our results show that colonies produced by assisted breeding, once outplanted, may contribute to the genetic diversity and establishment of self-sustaining sexually-reproducing populations, which is an overarching goal of coral restoration programs.

Coral affected by stony coral tissue loss disease can produce viable offspring.

Stony coral tissue loss disease (SCTLD) has caused high mortality of at least 25 coral species across the Caribbean, with Pseudodiploria strigosa being the second most affected species in the Mexican Caribbean. The resulting decreased abundance and colony density reduces the fertilization potential of SCTLD-susceptible species. Therefore, larval-based restoration could be of great benefit, though precautionary concerns about disease transmission may foster reluctance to implement this approach with SCTLD-susceptible species. We evaluated the performance of offspring obtained by crossing gametes of a healthy P. strigosa colony (100% apparently healthy tissue) with that of a colony affected by SCTLD (>50% tissue loss) and compared these with prior crosses between healthy parents. Fertilization and settlement were as high as prior crosses among healthy parents, and post-settlement survivorship over a year in outdoor tanks was 7.8%. After thirteen months, the diseased-parent recruits were outplanted to a degraded reef. Their survivorship was ∼44% and their growth rate was 0.365 mm ± 1.29 SD per month. This study shows that even diseased parent colonies can be effective in assisted sexual reproduction for the restoration of species affected by SCTLD.

Building consensus around the assessment and interpretation of Symbiodiniaceae diversity.

Within microeukaryotes, genetic variation and functional variation sometimes accumulate more quickly than morphological differences. To understand the evolutionary history and ecology of such lineages, it is key to examine diversity at multiple levels of organization. In the dinoflagellate family Symbiodiniaceae, which can form endosymbioses with cnidarians (e.g., corals, octocorals, sea anemones, jellyfish), other marine invertebrates (e.g., sponges, molluscs, flatworms), and protists (e.g., foraminifera), molecular data have been used extensively over the past three decades to describe phenotypes and to make evolutionary and ecological inferences. Despite advances in Symbiodiniaceae genomics, a lack of consensus among researchers with respect to interpreting genetic data has slowed progress in the field and acted as a barrier to reconciling observations. Here, we identify key challenges regarding the assessment and interpretation of Symbiodiniaceae genetic diversity across three levels: species, populations, and communities. We summarize areas of agreement and highlight techniques and approaches that are broadly accepted. In areas where debate remains, we identify unresolved issues and discuss technologies and approaches that can help to fill knowledge gaps related to genetic and phenotypic diversity. We also discuss ways to stimulate progress, in particular by fostering a more inclusive and collaborative research community. We hope that this perspective will inspire and accelerate coral reef science by serving as a resource to those designing experiments, publishing research, and applying for funding related to Symbiodiniaceae and their symbiotic partnerships.

A low-cost benthic incubation chamber for in-situ community metabolism measurements.

Benthic incubation chambers facilitate in-situ metabolism studies in shallow water environments. They are used to isolate the water surrounding a study organism or community so that changes in water chemistry can be quantified to characterise physiological processes such as photosynthesis, respiration, and calcification. Such field measurements capture the biological processes taking place within the benthic community while incorporating the influence of environmental variables that are often difficult to recreate in ex-situ settings. Variations in benthic chamber designs have evolved for a range of applications. In this study, we built upon previous designs to create a novel chamber, which is (1) low-cost and assembled without specialised equipment, (2) easily reproducible, (3) minimally invasive, (4) adaptable to varied substrates, and (5) comparable with other available designs in performance. We tested the design in the laboratory and field and found that it achieved the outlined objectives. Using non-specialised materials, we were able to construct the chamber at a low cost (under $20 USD per unit), while maintaining similar performance and reproducibility with that of existing designs. Laboratory and field tests demonstrated minimal leakage (2.08 ± 0.78% water exchange over 4 h) and acceptable light transmission (86.9 ± 1.9%), results comparable to those reported for other chambers. In the field, chambers were deployed in a shallow coastal environment in Akumal, Mexico, to measure productivity of seagrass, and coral-, algae-, and sand-dominated reef patches. In both case studies, production rates aligned with those of comparable benthic chamber deployments in the literature and followed established trends with light, the primary driver of benthic metabolism, indicating robust performance under field conditions. We demonstrate that our low-cost benthic chamber design uses locally accessible and minimal resources, is adaptable for a variety of field settings, and can be used to collect reliable and repeatable benthic metabolism data. This chamber has the potential to broaden accessibility and applications of in-situ incubations for future studies.

Differential sensitivity of coral larvae to natural levels of ultraviolet radiation during the onset of larval competence.

Scleractinian corals are the major builders of the complex structural framework of coral reefs. They live in tropical waters around the globe where they are frequently exposed to potentially harmful ultraviolet radiation (UVR). The eggs and early embryonic stages of some coral species are highly buoyant and remain near the sea surface for prolonged periods of time and may therefore be the most sensitive life stages with respect to UVR. Here, we analysed gene expression changes in five developmental stages of the Caribbean coral Montastraea faveolata to natural levels of UVR using high-density cDNA microarrays (10 930 clones). We found that larvae exhibit low sensitivity to natural levels of UVR during early development as reflected by comparatively few transcriptomic changes in response to UVR. However, we identified a time window of high UVR sensitivity that coincides with the motile planula stage and the onset of larval competence. These processes have been shown to be affected by UVR exposure, and the transcriptional changes we identified explain these observations well. Our analysis of differentially expressed genes indicates that UVR alters the expression of genes associated with stress response, the endoplasmic reticulum, Ca(2+) homoeostasis, development and apoptosis during the motile planula stage and affects the expression of neurogenesis-related genes that are linked to swimming and settlement behaviour at later stages. Taken together, our study provides further data on the impact of natural levels of UVR on coral larvae. Furthermore, our results might allow a better prediction of settlement and recruitment rates after coral spawning events if UVR climate data are taken into account.

Discovery and characterization of Hv1-type proton channels in reef-building corals.

Voltage-dependent proton-permeable channels are membrane proteins mediating a number of important physiological functions. Here we report the presence of a gene encoding Hv1 voltage-dependent, proton-permeable channels in two species of reef-building corals. We performed a characterization of their biophysical properties and found that these channels are fast-activating and modulated by the pH gradient in a distinct manner. The biophysical properties of these novel channels make them interesting model systems. We have also developed an allosteric gating model that provides mechanistic insight into the modulation of voltage-dependence by protons. This work also represents the first functional characterization of any ion channel in scleractinian corals. We discuss the implications of the presence of these channels in the membranes of coral cells in the calcification and pH-regulation processes and possible consequences of ocean acidification related to the function of these channels.

Anthropogenic pollution of aquatic ecosystems: Emerging problems with global implications.

Aquatic ecosystems cover over two thirds of our planet and play a pivotal role in stabilizing the global climate as well as providing a large array of services for a fast-growing human population. However, anthropogenic activities increasingly provoke deleterious impacts in aquatic ecosystems. In this paper we discuss five sources of anthropogenic pollution that affect marine and freshwater ecosystems: sewage, nutrients and terrigenous materials, crude oil, heavy metals and plastics. Using specific locations as examples, we show that land-based anthropogenic activities have repercussions in freshwater and marine environments, and we detail the direct and indirect effects that these pollutants have on a range of aquatic organisms, even when the pollutant source is distant from the sink. While the issues covered here do focus on specific locations, they exemplify emerging problems that are increasingly common around the world. All these issues are in dire need of stricter environmental policies and legislations particularly for pollution at industrial levels, as well as solutions to mitigate the effects of anthropogenic pollutants and restore the important services provided by aquatic ecosystems for future generations.

Coral reef restoration efforts in Latin American countries and territories.

Coral reefs worldwide are degrading due to climate change, overfishing, pollution, coastal development, coral bleaching, and diseases. In areas where the natural recovery of an ecosystem is negligible or protection through management interventions insufficient, active restoration becomes critical. The Reef Futures symposium in 2018 brought together over 400 reef restoration experts, businesses, and civil organizations, and galvanized them to save coral reefs through restoration or identify alternative solutions. The symposium highlighted that solutions and discoveries from long-term and ongoing coral reef restoration projects in Spanish-speaking countries in the Caribbean and Eastern Tropical Pacific were not well known internationally. Therefore, a meeting of scientists and practitioners working in these locations was held to compile the data on the extent of coral reef restoration efforts, advances and challenges. Here, we present unpublished data from 12 coral reef restoration case studies from five Latin American countries, describe their motivations and techniques used, and provide estimates on total annual project cost per unit area of reef intervened, spatial extent as well as project duration. We found that most projects used direct transplantation, the coral gardening method, micro-fragmentation or larval propagation, and aimed to optimize or scale-up restoration approaches (51%) or provide alternative, sustainable livelihood opportunities (15%) followed by promoting coral reef conservation stewardship and re-establishing a self-sustaining, functioning reef ecosystems (both 13%). Reasons for restoring coral reefs were mainly biotic and experimental (both 42%), followed by idealistic and pragmatic motivations (both 8%). The median annual total cost from all projects was $93,000 USD (range: $10,000 USD-$331,802 USD) (2018 dollars) and intervened a median spatial area of 1 ha (range: 0.06 ha-8.39 ha). The median project duration was 3 years; however, projects have lasted up to 17 years. Project feasibility was high with a median of 0.7 (range: 0.5-0.8). This study closes the knowledge gap between academia and practitioners and overcomes the language barrier by providing the first comprehensive compilation of data from ongoing coral reef restoration efforts in Latin America.

Ultraviolet radiation reduces the photoprotective capacity of the marine diatom Phaeodactylum tricornutum (Bacillariophyceae, Heterokontophyta).

This study demonstrates that UV radiation (UVR) reduces the photoprotective capacity of the diatom Phaeodactylum tricornutum by affecting xanthophyll cycle (XC) activity. The short-term reduction of photosystem II (PSII) maximum efficiency of charge separation (F(v)/F(m)) in cells exposed to UVR could be explained mainly by a reduced photoprotective capacity under this condition. Phaeodactylum tricornutum cells acclimated to two different photosynthetically active radiation (PAR) intensities, high light (HL, 200 micromol quanta m(-2) s(-1)) and low light (LL, 50 micromol quanta m(-2) s(-1)), were exposed to saturating irradiance (1100 micromol quanta m(-2) s(-1)) in the presence (PAR + UVR) and absence of UVR (PAR). HL cells exhibited a greater reduction in F(v)/F(m) in PAR + UVR when compared with the PAR treatment that was related to a reduction in the de-epoxidation of XC pigments. In contrast, in LL cells, UVR did not considerably affect XC de-epoxidation even though the reduction in F(v)/F(m) was greater than in HL cells. The negative effect of UVR on photoprotection was more pronounced in HL cells because they synthesized more XC pigments than LL cells. This was confirmed when XC activity was blocked with dithiothreitol and when PSII repair was inhibited with chloramphenicol (CAP). The differential reduction of F(v)/F(m) between PAR + UVR and PAR treatments disappeared when XC was blocked in HL cells. A higher reduction and an incomplete recovery of F(v)/F(m) were observed in cells incubated with CAP in the presence of UVR. Such responses confirm that UVR had a negative effect on photoprotective mechanisms causing an enhancement of damage by PAR, especially in HL-acclimated cells in which heat dissipation is important for PSII regulation.

Settlement and post-settlement survival of Orbicella annularis and Orbicella faveolata (Scleractinia: Merulinidae) on substrates with coatings

Introduction: One of the main bottlenecks in restoration projects based on sexual reproduction is post-settlement survival, mainly due to competition for substrate with fleshy algae and predation. Therefore, substrates of different shapes and materials have been created and tested, seeking to optimize these processes with attractive surfaces for the larvae and structures where the recruits are protected from predation, and competition is reduced. Objective: To improve settlement and post-settlement survival of two important Caribbean reef-building corals, using different coatings on substrates. Methods: To determine whether substrate coatings properties are favourable to larval settlement in Orbicella annularis, and O. faveolata, collected in Puerto Morelos, Mexican Caribbean, we evaluated their settlement for three weeks on six coatings with a combination of properties. Each coating was designed to provide a combination of two out of three properties: 1) water repellence (hydrophobicity), 2) phosphorescence-based colour, and 3) mineral-enriched surface chemistry. In a separate experiment larvae settlement was tested using coatings with a single property. Finally, we determined the post-settlement survival of O. annularis and O. faveolata on the different coatings for seven weeks. Results: The combination of high hydrophobicity and light blue phosphorescent microparticles and high hydrophobicity and red-orange phosphorescent microparticles resulted in a higher settlement of O. annularis and O. faveolata when compared with other coatings (30.8 - 66.7 % higher). No significant differences were found in the number of larval settled when the water-repellence and the phosphorescence-based were evaluated independently. Post-settlement survival time on substrates was low, with a maximum of 34 days after settlement for O. annularis and 42 days for O. faveolata. Conclusions: In terms of the larval settlement, the combination of the coatings properties appears to play an essential role in the choice of microhabitat for both O. annularis and O. faveolata. But individually these properties did not generate an advantage in the larval settlement. Moreover, some chemical components associated with the coatings may be counterproductive to the survival of the polyps over time.

Introducción: Uno de los principales cuellos de botella en proyectos de restauración basada en reproducción sexual es la supervivencia de las larvas posterior al asentamiento, principalmente por la competencia por el sustrato con algas filamentosas y la depredación. Por ello, se han creado y analizado sustratos de diferentes formas y materiales, buscando optimizar estos procesos con superficies atrayentes para las larvas, y estructuras donde los reclutas se encuentran protegidos de la depredación y se disminuya la competencia. Objetivo: Mejorar el asentamiento y la supervivencia de dos importantes corales formadores de arrecifes del Caribe, utilizando diferentes recubrimientos en sustratos. Métodos: Para determinar si las propiedades de la superficie del sustrato son favorables para el asentamiento de larvas de Orbicella annularis y O. faveolata, recolectadas en Puerto Morelos, Caribe mexicano, evaluamos su asentamiento durante tres semanas en seis recubrimientos con una combinación de propiedades. Cada recubrimiento fue diseñado para proporcionar una combinación de dos de tres propiedades: 1) repelencia al agua (hidrofobicidad), 2) fosforescencia y 3) química superficial enriquecida con minerales. En un experimento separado se evaluó el asentamiento de larvas en sustratos con recubrimientos de una sola propiedad. Finalmente, se determinó la supervivencia posterior al asentamiento de O. annularis y O. faveolata sobre los diferentes recubrimientos durante siete semanas. Resultados: La combinación de alta hidrofobicidad y micropartículas fosforescentes azules y alta hidrofobicidad y micropartículas fosforescentes rojo-naranja dio como resultado un mayor asentamiento de O. annularis y O. faveolata en comparación con otros recubrimientos (30.8 - 66.7 % mayor). No se encontraron diferencias significativas en el número de larvas asentadas cuando se evaluaron de forma independiente la repelencia al agua y la fosforescencia. El tiempo de supervivencia posterior al asentamiento en los sustratos fue bajo, con un máximo de 34 días después del asentamiento para O. annularis y 42 días para O. faveolata. Conclusiones: En el asentamiento de larvas, la combinación de las propiedades del recubrimiento parece desempeñar un papel importante en la elección del microhábitat tanto para O. annularis como para O. faveolata. Pero de forma individual estas propiedades no generaron una ventaja en el asentamiento larvario. Además, algunos componentes químicos asociados con los recubrimientos pueden ser contraproducentes para la supervivencia de los pólipos a lo largo del tiempo.

Optimization of DNA extraction from a scleractinian coral for the detection of thymine dimers by immunoassay.

Ultraviolet (UV)-B is known to cause DNA damage, principally by the formation of thymine dimers, but little research has been conducted in coral reef environments where UV doses are high. The majority of tropical reef-dwelling corals form a mutualistic symbiosis with the dinoflagellate Symbiodinium but few studies have been conducted on in situ DNA damage in corals and none have investigated the symbiotic components separately. The aim of this research was to quantify DNA damage in both the coral host and the dinoflagellate symbiont. The first step in this investigation was to optimize the extraction of DNA from the host, Porites astreoides, as well as the symbiont. The optimization was divided into a series of steps: the preservation of the samples, separation of the coral tissue from the skeleton, separation of the host tissue from the algal cells to prevent cross contamination as well as the extraction and purification of genomic DNA from the algae that are located intracellularly within the invertebrate animal tissue. The best preservation method was freezing at low temperatures without ethanol. After scraping with a razor blade, the coral tissue can be divided into host and algal components and the DNA extracted using modifications of published techniques yielding DNA suitable for the quantification of thymine dimer formation using antibodies. Preliminary data suggest that in P. astreoides collected from 1 m depth, thymine dimers form approximately 2.8 times more frequently in the host DNA than in the DNA of its symbionts.

Global change feed-back inhibits cyanobacterial photosynthesis.

Cyanobacteria are an important component of aquatic ecosystems, with a proliferation of massive cyanobacterial blooms predicted worldwide under increasing warming conditions. In addition to temperature, other global change related variables, such as water column stratification, increases in dissolved organic matter (DOM) discharge into freshwater systems and greater wind stress (i.e., more opaque and mixed upper water column/epilimnion) might also affect the responses of cyanobacteria. However, the combined effects of these variables on cyanobacterial photosynthesis remain virtually unknown. Here we present evidence that this combination of global-change conditions results in a feed-back mechanism by which, fluctuations in solar ultraviolet radiation (UVR, 280-400 nm) due to vertical mixing within the epilimnion act synergistically with increased DOM to impair cyanobacterial photosynthesis as the water column progressively darkens. The main consequence of such a feed-back response is that these organisms will not develop large blooms in areas of latitudes higher than 30°, in both the Northern and Southern Hemispheres, where DOM inputs and surface wind stress are increasing.

Intraspecific diversity among partners drives functional variation in coral symbioses.

The capacity of coral-dinoflagellate mutualisms to adapt to a changing climate relies in part on standing variation in host and symbiont populations, but rarely have the interactions between symbiotic partners been considered at the level of individuals. Here, we tested the importance of inter-individual variation with respect to the physiology of coral holobionts. We identified six genetically distinct Acropora palmata coral colonies that all shared the same isoclonal Symbiodinium 'fitti' dinoflagellate strain. No other Symbiodinium could be detected in host tissues. We exposed fragments of each colony to extreme cold and found that the stress-induced change in symbiont photochemical efficiency varied up to 3.6-fold depending on host genetic background. The S. 'fitti' strain was least stressed when associating with hosts that significantly altered the expression of 184 genes under cold shock; it was most stressed in hosts that only adjusted 14 genes. Key expression differences among hosts were related to redox signaling and iron availability pathways. Fine-scale interactions among unique host colonies and symbiont strains provide an underappreciated source of raw material for natural selection in coral symbioses.

Response of Millepora alcicornis (Milleporina: Milleporidae) to two bleaching events at Puerto Morelos reef, Mexican Caribbean.

Two naturally occurring colonies of Millepora alcicornis were monitored during 1997 and 1998, both years in which this species bleached in the Mexican Caribbean. One colony (HL) was naturally exposed to a high light environment and another nearby colony (LL) was exposed to 5.9 times lower light levels due to shadowing by a pier. For 10 days in August 1997, seawater temperatures in the surrounding reef lagoon rose up to 1.5 degrees C above the 6-year August average. The HL colony bleached to white during this period, whereas, the LL colony remained dark-brown colored. The HL colony recovered its normal dark-brown coloration (reversible bleaching) within several weeks, during which time the seawater temperatures returned to average. The following year, for 10 days, seawater temperatures rose up to 3 degrees C above the 7-year August average and both colonies bleached to white and neither colony recovered (irreversible bleaching). Both colonies were rapidly overgrown by algae and hydroids and, as of June 2003, no recovery has taken place. Prior to the 1997 bleaching, experiments using solar radiation showed that the quantum yield of photosystem II charge separation of branches from HL and LL colonies were affected for several hours by exposure to ultraviolet radiation (UVR, 280 to 400 nm), but recovered by the same evening, suggesting that UVR does not have long-term effects on photochemistry in M. alcicornis. In situ effective quantum yield of photosystem II charge separation (deltaF/Fm') measurements before the 1998 bleaching event indicate that both colonies were healthy in terms of the physiological status of their endosymbionts. During and after the 1998 bleaching event, both colonies showed a reduction in deltaF/Fm' and consequently an increase in excitation pressure on photosystem II. The data suggest that temperature is not the only factor that causes bleaching and that solar radiation may play an important role in coral bleaching.