Search

A survey conducted in Fall 2017 by US Navy scientists around the small, uninhabited island of Farallon de Medinilla (FDM) documented severe bleaching related to extended regional heat stress. Three of the dominant scleractinian genera at FDM, Pocillopora, Leptastrea, and Astreopora, were severely impacted, with more than 90% of colonies from many species exhibiting bleaching. In contrast, several species of Porites corals, another dominant genus at FDM, fared better, with less bleaching (7%–68% by species) than the island average (78%). Bleaching was somewhat higher at shallower depths (1 knot that precluded diving, rare but potentially hazardous ordnance items, survey requirements for georeferenced imagery, and quantitative data collection. The survey protocol designed to accommodate these challenges is presented here, as are lessons from an unsuccessful attempt to delineate bleached coral colonies in photographs using automated object-based image analysis.

Metal release rates were measured from four different copper alloy-based materials used by the aquaculture industry: copper sheet machined into a diamond mesh, copper alloy mesh (CAM), silicon bronze welded wire mesh, and copper sheeting, and compared with conventional nylon aquaculture net treated with a cuprous oxide antifouling (AF) coating. Release rates were measured

Studies using paleoecological and historical data can inform coral reef management by providing accurate ecological baselines and by pinpointing the timing, magnitude, and drivers of ecosystem declines. However, these studies have rarely been incorporated into policy and management frameworks. This working group brings together paleontologists, historical ecologists, ecologists, fisheries scientists, and conservation practitioners to develop pathways for incorporating long-term ecological data into decision-making to advance the sustainable management of reef ecosystems. Our group is focusing on Caribbean coral reefs, a geography with an abundance of historical ecological data and a track record of collaboration between reef scientists and managers. This spirit of collaboration is enhanced by the immediacy of conservation needs for reef ecosystems in this region. We are focusing on the application of long-term data to two pressing management issues for Caribbean coral reefs, which together address the most urgent local human drivers of ecosystem change – fishing and land-based pollution. In this talk, I will outline our working group’s aims and progress to date.

Caribbean coral reef ecosystems have declined dramatically since systematic monitoring began in the 1970s. Over the past 50 years, they have lost between 50-80% of reef-building corals, their principal ecosystem architects. These declines have been attributed to climate change, introduction of invasive species, overfishing, and land-based pollution. Although recognized as a major stressor to corals, the role of land-based pollution in Caribbean coral declines has not been quantified due to the lack of consistent reef water quality monitoring. As part of our CPN-funded working group “Integrating paleo and historical data into coral reef management and policy”, we compiled several metrics of reef water quality from paleoecological data and disparate monitoring efforts across the Caribbean to document multidecadal-scale change over a period of intensifying coastal land alteration. We then compared water quality trends with trends in living coral cover from these same reefs to assess the role of water quality declines from land-based runoff on coral reef ecosystem health. These analyses show that (1) an array of historical data exist for reconstructing trends in Caribbean reef water quality that are in disparate repositories and remain mostly untapped, (2) reefs across the Caribbean have experienced water quality declines over the past half century, even offshore sites that were previously thought to be unaffected by land-based runoff, (3) correlations between reef water quality and coral abundance trends are detected at select sites where water quality monitoring protocols were consistent and sustained for multiple decades, and (4) water quality declines are asynchronous across sites and are likely related to differing timing and histories of land alteration.

Ocean warming is negatively impacting coral reef ecosystems and considerable effort is currently invested in projecting coral reef futures under 21st century climate change. A limiting factor in these projections is lack of quantitative data on the thermal thresholds of different reef communities, due in large part to spatial and temporal gaps in bleaching observations. Here we apply a coral bleaching proxy, skeletal stress bands, to reconstruct the history of bleaching on eight coral reefs in the central equatorial Pacific (CEP) and use this information to constrain the thermal thresholds of their coral communities. First, three genera of massive corals collected on both Pacific and Caribbean reefs are used to derive a calibration between the proportion of corals that form stress bands during a bleaching event, and the total observed bleaching incidence in the community of mixed coral taxa. The correlation is highly significant, indicating that stress bands in massive corals reflect community-level bleaching severity (R2 = 0.945, p

Frequent occurrences of coral bleaching and associated coral mortality over recent decades have raised concerns about the survival of coral reefs in a warming planet. The El Niño-influenced coral reefs in the central Gilbert Islands of the Republic of Kiribati, which experience years with prolonged heat stress more frequently than 99% of the world’s reefs, may serve as a natural model for coral community response to frequent heat stress. Here we use nine years of survey data (2004–2012) and a suite of remote sensing variables from sites along gradients of climate variability and human disturbance in the region to evaluate the drivers of coral community response to, and recovery from, multiple heat stress events. The results indicate that the extent of bleaching was limited during the 2009–2010 El Niño event, in contrast to a similar 2004–2005 event, and was correlated with incoming light and historical temperature variability, rather than heat stress. Spatial and temporal patterns in benthic cover suggest growing resistance to bleaching-level heat stress among coral communities subject to high inter-annual temperature variability and local disturbance, due to the spread of “weedy” and temperature-tolerant species (e.g., Porites rus) and the cloudy conditions in the region during El Niño events.

Improved understanding of marine terrace development and morphology can provide better estimates of historical sea levels and tectonic uplift rates. Using a numerical model, this study explored the relative influence of environmental controls on late Pleistocene marine terrace widths on San Clemente Island (SCI) and in the Santa Cruz region (SCZ) in southern and central California, respectively. The model was calibrated/validated based on SCI and SCZ terrace observations using digital elevation models (DEMs), modeled nearshore wave climate, as well as data from existing SCI and SCZ marine terrace studies. In total, 648 simulations were conducted considering a range of wave height decay rates, rock resistance, initial topographic slope, and tectonic uplift rates. The model outcomes were generally consistent qualitatively with observations of SCI and SCZ terrace widths from published work and the DEMs presented here. Modeled terrace widths increased with decreasing topographic slope and increasing tectonic uplift rates; terrace widths were less well correlated with variations in wave and rock strength parameters in this study. Overall, the results suggest that topographic slope and tectonic uplift rates influence terrace widths more than wave- and rock-related properties. Some of the model assumptions and modeling outcomes contrast with existing rock coast and marine terrace studies, and additional research is necessary.

Coral bleaching caused by heat stress (warm water) will arguably be the greatest driver of coral reef loss in the coming decades. Understanding how corals have adapted to distinct oceanographic regimes on multiple scales can provide insight into future tolerance and persistence, information critical to directed intervention or targeted protections. The northern Line Islands span a gradient in oceanographic regimes across latitudes, with seawater becoming warmer, fresher, more oligotrophic, and more saturated with aragonite away from the equator. The combination of this regional gradient and island-scale (local) conditions was used as a natural experiment against which to test how massive Porites corals respond to these background conditions and episodic heat stress. We found that coral condition, represented by a metric combining tissue thickness, lipids, and calcification, was similar at almost all islands, though there were differences in how corals allocate resources among these biological parameters. Corals at Teraina, the most densely inhabited island, showed evidence for reduced calcification, potentially associated with human impacts and/or outflow of freshwater from the island. In contrast, Porites corals at Palmyra, a wildlife reserve, exhibited unexpectedly high tissue-condition metrics for its latitude, suggesting an additional food source, possibly plankton-rich lagoonal outflow. We did not find a strong relationship between human habitation and the response of Porites corals to recent heat stress. However, differences in coral calcification rates and energy stores between observed values and those expected based solely on the regional oceanographic gradient, suggests local effects have indirect impacts on these corals.

Figure 2 in the original article has been updated with this figure 2 due to discrepancies related to incorrect mapping with one of the islands.

In our paper describing a new coral record from Butaritari, we hypothesized that comparing the temporal trends in our records to coral records from farther east in the equatorial Pacific may support the evidence for a weakening of a Walker circulation, documented elsewhere in the literature [Power and Smith, 2007; Tokinaga et al., 2012]. Weakening of the Walker circulation is expected under global warming due to an imbalance in the rate of change in different aspects of the hydrological cycle [Vecchi and Soden, 2007]. We thank Karnauskas et al. [2015] for recognizing the value of our Butaritari coral climate reconstruction, and we appreciate their critique of our study. The Karnauskas et al. [2015] analyses strengthen our argument regarding the utility of interisland coral-proxy derived sea surface temperature (SST) gradients as a Walker circulation metric, but we disagree with their interpretation of decadal variability in our records. Here we provide additional analyses, which confirm that our reconstruction [Carilli et al., 2014] shows a long-term weakening of the Walker circulation over 1972-1998. We also document that significant decadal variations in Walker circulation strength, and for particular choices of start and end years over which trends are calculated, are able to show slight Walker strengthening. Overall, we conclude that Walker circulation variations are more nuanced than either our original publication [Carilli et al., 2014] or the subsequent Karnauskas et al. [2015] comment would suggest. Karnauskas et al. [2015] also provide a detailed analysis of Equatorial Undercurrent (EUC) activity near the Gilbert Islands and argue that the EUC does not strongly affect Butaritari. Our original publication did not claim to find significant EUC/Butaritari linkages, and we appreciate the diligence of Karnauskas et al. [2015] for ruling this out as a possibility.

This work was supported by an Australian Nuclear Science and Technology Organization Postdoctoral Fellowship (J.C.), a Natural Sciences and Engineering Research Council of Canada Discovery Grant (S.D.), a National Science Foundation Ocean Sciences Postdoctoral Fellowship (S.S.), and ARC Discovery Project grant DP1092945 (H.V.M.), and an AINSE Fellowship grant (H.V.M.).

Microplastics (less than 5 mm) are a recognized threat to aquatic food webs because they are ingested at multiple trophic levels and may bioaccumulate. In urban coastal environments, high densities of microplastics may disrupt nutritional intake. However, behavioural dynamics and consequences of microparticle ingestion are still poorly understood. As filter or suspension feeders, benthic marine invertebrates are vulnerable to microplastic ingestion. We explored microplastic ingestion by the temperate coral Astrangia poculata . We detected an average of over 100 microplastic particles per polyp in wild-captured colonies from Rhode Island. In the laboratory, corals were fed microbeads to characterize ingestion preference and retention of microplastics and consequences on feeding behaviour. Corals were fed biofilmed microplastics to test whether plastics serve as vectors for microbes. Ingested microplastics were apparent within the mesenterial tissues of the gastrovascular cavity. Corals preferred microplastic beads and declined subsequent offerings of brine shrimp eggs of the same diameter, suggesting that microplastic ingestion can inhibit food intake. The corals co-ingested Escherichia coli cells with microbeads. These findings detail specific mechanisms by which microplastics threaten corals, but also hint that the coral A. poculata , which has a large coastal range, may serve as a useful bioindicator and monitoring tool for microplastic pollution.

Multi-decadal variability in coral growth rates has been documented throughout the Caribbean over the past 150–200 years. Analyses of observational and model data suggest that anthropogenic aerosols were a key driver of variations in coral growth in the western Caribbean in the second half of the twentieth century.

Coral bleaching, during which corals lose their symbiotic dinoflagellates, appears to be increasing in frequency and geographic extent, and is typically associated with abnormally high water temperatures and solar irradiance. A key question in coral reef ecology is whether local stressors reduce the coral thermal tolerance threshold, leading to increased bleaching incidence. Using tree-ring techniques, we produced master chronologies of growth rates in the dominant reef builder, massive Montastraea faveolata corals, over the past 75–150 years from the Mesoamerican Reef. Our records indicate that the 1998 mass bleaching event was unprecedented in the past century, despite evidence that water temperatures and solar irradiance in the region were as high or higher mid-century than in more recent decades. We tested the influence on coral extension rate from the interactive effects of human populations and thermal stress, calculated here with degree-heating-months (DHM). We find that when the effects of chronic local stressors, represented by human population, are taken into account, recent reductions in extension rate are better explained than when DHM is used as the sole predictor. Therefore, the occurrence of mass bleaching on the Mesoamerican reef in 1998 appears to stem from reduced thermal tolerance due to the synergistic impacts of chronic local stressors.

For the past few centuries, multidecadal climate variability in North Atlantic sea surface temperatures has been modulated by the Atlantic Multidecadal Oscillation (AMO). A coral-based temperature reconstruction reveals that the AMO is a transient climate feature that only became significant after AD 1730.

Anthropogenic threats, such as increased sedimentation, agrochemical run-off, coastal development, tourism, and overfishing, are of great concern to the Mesoamerican Caribbean Reef System (MACR). Trace metals in corals can be used to quantify and monitor the impact of these land-based activities. Surface coral samples from the MACR were investigated for trace metal signatures resulting from relative differences in water quality. Samples were analyzed at three spatial scales (colony, reef, and regional) as part of a hierarchical multi-scale survey. A primary goal of the paper is to elucidate the extrapolation of information between fine-scale variation at the colony or reef scale and broad-scale patterns at the regional scale. Of the 18 metals measured, five yielded statistical differences at the colony and/or reef scale, suggesting fine-scale spatial heterogeneity not conducive to regional interpretation. Five metals yielded a statistical difference at the regional scale with an absence of a statistical difference at either the colony or reef scale. These metals are barium (Ba), manganese (Mn), chromium (Cr), copper (Cu), and antimony (Sb). The most robust geochemical indicators of land-based activities are coral Ba and Mn concentrations, which are elevated in samples from the southern region of the Gulf of Honduras relative to those from the Turneffe Islands. These findings are consistent with the occurrence of the most significant watersheds in the MACR from southern Belize to Honduras, which contribute sediment-laden freshwater to the coastal zone primarily as a result of human alteration to the landscape (e.g., deforestation and agricultural practices). Elevated levels of Cu and Sb were found in samples from Honduras and may be linked to industrial shipping activities where copper–antimony additives are commonly used in antifouling paints. Results from this study strongly demonstrate the impact of terrestrial runoff and anthropogenic activities on coastal water quality in the MACR.

A number of marine and freshwater organisms, including scleractinian and proteinacious corals, coralline algae, sclerosponges, and bivalve mollusks, secrete skeletons that grow larger over time and may record environmental contaminants over the lifespan of an individual. Most of these organisms also form periodic growth patterns (growth increments, lines or bands) that can be used to accurately date contaminant archives produced from chemical or physical analysis of sequential skeletal samples (termed sclerochronology). The majority of records produced from these organisms thus far have focused on paleoclimate reconstructions, but there is a vast potential for information on changes in contaminant levels over time. Importantly, sclerochronological archives offer the potential for pre-anthropogenic baselines of naturally occurring substances to estimate the magnitude of anthropogenic pollution. This chapter presents an overview of existing contaminant records and discusses the limitations and potential for future work using archives derived from marine organism skeletons.

Anthropogenic 236U (t½=23.4 My) is an emerging isotopic ocean tracer with interesting oceanographic properties, but only with recent advances in accelerator mass spectrometry techniques is it now possible to detect the levels from global fall-out of nuclear weapons testing across the water column. To make full use of this tracer, an assessment of its input into the ocean over the past decades is required. We captured the bomb-pulse of 236U in an annually resolved coral core record from the Caribbean Sea. We thereby establish a concept which gives 236U great advantage – the presence of reliable, well-resolved chronological archives. This allows studies of not only the present distribution pattern, but gives access to the temporal evolution of 236U in ocean waters over the past decades., Highlights ► This is the first ever annually-resolved record of 236U from global fall-out. ► We demonstrate the usefulness of 236U as oceanic tracer using coral cores. ► Using the record a value for the total global fall-out of 236U has been determined.

Coral bleaching is the breakdown of symbiosis between coral animal hosts and their dinoflagellate algae symbionts in response to environmental stress. On large spatial scales, heat stress is the most common factor causing bleaching, which is predicted to increase in frequency and severity as the climate warms. There is evidence that the temperature threshold at which bleaching occurs varies with local environmental conditions and background climate conditions. We investigated the influence of past temperature variability on coral susceptibility to bleaching, using the natural gradient in peak temperature variability in the Gilbert Islands, Republic of Kiribati. The spatial pattern in skeletal growth rates and partial mortality scars found in massive Porites sp. across the central and northern islands suggests that corals subject to larger year-to-year fluctuations in maximum ocean temperature were more resistant to a 2004 warm-water event. In addition, a subsequent 2009 warm event had a disproportionately larger impact on those corals from the island with lower historical heat stress, as indicated by lower concentrations of triacylglycerol, a lipid utilized for energy, as well as thinner tissue in those corals. This study indicates that coral reefs in locations with more frequent warm events may be more resilient to future warming, and protection measures may be more effective in these regions.

The Mesoamerican Reef, the second-largest barrier reef in the world, is located in the western Caribbean Sea off the coasts of Mexico, Belize, Guatemala, and Honduras. Particularly in the south, the surrounding watersheds are steep and the climate is extremely wet. With development and agricultural expansion, the potential for negative impacts to the reef from land-based runoff becomes high. We constructed annually resolved century-scale records of metal/calcium ratios in coral skeletons collected from four sites experiencing a gradient of land-based runoff. Our proxy data indicate that runoff onto the reef has increased relatively steadily over time at all sites, consistent with land use trends from historical records. Sediment supply to the reef is greater in the south, and these more exposed reefs will probably benefit most immediately from management that targets runoff reduction. However, because runoff at all sites is steadily increasing, even distal sites will benefit from watershed management.

Coral bleaching, during which corals lose their symbiotic dinoflagellates, typically corresponds with periods of intense heat stress, and appears to be increasing in frequency and geographic extent as the climate warms. A fundamental question in coral reef ecology is whether chronic local stress reduces coral resistance and resilience from episodic stress such as bleaching, or alternatively promotes acclimatization, potentially increasing resistance and resilience. Here we show that following a major bleaching event, Montastraea faveolata coral growth rates at sites with higher local anthropogenic stressors remained suppressed for at least 8 years, while coral growth rates at sites with lower stress recovered in 2–3 years. Instead of promoting acclimatization, our data indicate that background stress reduces coral fitness and resilience to episodic events. We also suggest that reducing chronic stress through local coral reef management efforts may increase coral resilience to global climate change.

Caribbean coral reefs have been massively altered in recent decades due to human impacts, resulting in a dramatic reduction of live coral cover but quantitative data before the 1970s have not been available to assess how these changes came about1,2,3. We produced master chronologies of growth rates in massive Montastrea faveolata corals from the Mesoamerican reef tract that provide a method for extending records of coral health further back into the past. Our records reveal a unique reduction in growth rate associated with the 1998 coral bleaching event that has no parallel in the past 75 to 150 years. Of 92 cores collected from live coral heads in 2006-2007, 94% have severely reduced growth rates and 14% exhibit partial mortality scars in 1998-1999 whereas only 3 stress bands are found in single cores prior to 1998, and none of these cores exhibited earlier partial mortality. Some corals returned to pre-1998 extension rates by 2001, although corals in areas affected by sediment-laden runoff or high human population density still had not fully recovered by the time of sample collection eight years later. Previous episodic stresses like hurricane strikes and a warming event in 1983 more severe than 1998 had little to no effect on M. faveolata growth rates. The 1998 event apparently surpassed a threshold in coral tolerance precipitating a catastrophic shutdown in growth that had lasting effects throughout the Mesoamerican reef system but was particularly prolonged in areas exposed to other stressors. These findings suggest that projected increases in global temperatures over the next century are likely to result in drastic reductions in growth rather than a gradual decline in coral health, but that corals with fewer local stresses will be better able to survive bleaching events, underscoring the need for local conservation measures.

Acknowledgments Coral samples were collected and exported with appropriate collection and CITES export permits from Belize and Honduras. We thank R. Bundy, D. Moguillansky, E. Effner, T. Wong and A. Hartmann for help with isotopic analyses, and K. Hughen, H. Wong and M. Dore for Sr/Ca analyses. We thank C. Reich at the United States Geological Survey for in situ salinity data. J. Carilli was supported by a Mia Tegner Memorial Grant, B. Katz and two anonymous donors. The molecular work was supported by National Science Foundation (NSF) grant #OCE09-62721 to F. Azam. M. Garren was supported by an NSF Graduate Research Fellowship and The Robert and Patricia Switzer Foundation.