Predicting the bleaching responses of corals is crucial in light of frequent heat stress events to manage further losses of biodiversity and ecosystem functioning, especially for reefs impacted by urbanisation. We examined if the coral cover and community at various Singapore sites changed during the 2016 global coral bleaching event. Bleaching prevalence varied widely among sites in June 2016, and was best explained by site and coral species. While some sites were minimally impacted, others registered significant decreases in coral cover and community changes persisting till March 2017, when normal colouration was mostly regained by corals. Bleaching susceptibility was associated with larger corallites in hermaphrodites and smaller corallites in gonochores (probably due to the cost of maintaining dual sexual functions in hermaphrodites), and with increasing proximity between polyps (likely because thermal damage would be less contained among polyps with greater physiological integration). However, bleaching resilience—the capacity to regain baseline pigmentation—was poorly explained by the traits studied. Our findings suggest that the interplay between local conditions and species composition strongly affects bleaching outcomes on urbanised reefs, and underscore the utility of coral traits for predicting bleaching responses to help in formulating appropriate management strategies.
Successful recruitment of new individuals is essential for recovery of degraded coral reefs. Enhancing supply of coral larvae increases initial settlement, however post-settlement survival can be influenced by density-dependent processes. We investigated the influence of larval density on settlement, colony abundance and growth to 24 months for Acropora tenuis in the north-western Philippines, to determine whether larval supply can be optimised to maximise successful recruitment. Thirty different densities of coral larvae were enclosed for five days around settlement tiles and highest total settlement occurred on tiles with highest larval densities. After 12 months, however, colony abundance and coral cover was lower on high density tiles (supplied with ~2,500–5,000 larvae) than tiles supplied with ~1,000–2,000 larvae. Coral cover at 24 months remained highest on tiles supplied with ~1,000–2,500 larvae. Larval density influenced larval substratum selection, with proportionally fewer larvae settling in typically preferred locations as density increased. We conclude that larval density can influence post-settlement colony abundance and coral cover to 12 months, with coral cover trends persisting to 24 months. We show that optimising larval densities can maximise coral recruitment and growth, however oversupply of larvae at very high densities can have negative outcomes for larval restoration.
Over the last three decades corals have declined precipitously in the Florida Keys. Their population decline has prompted restoration effort. Yet, little effort has been invested in understanding the contemporary niche spaces of coral species, which could assist in prioritizing conservation habitats. We sought to predict the probability of occurrence of 23 coral species, including the critically endangered Acropora cervicornis, using observations at 985 sites from 2011–2015. We ran boosted regression trees to evaluate the relationship between the presence of these corals and eight potential environmental predictors: (i) bathymetry (m), (ii) mean of daily sea surface temperature (SST) (°C), (iii) variance of SST (°C), (iv) range of SST (°C), (v) chlorophyll-a concentration (mg m3), (vi) turbidity (m-1), (vii) wave energy (kJ m-2), and (viii) distance from coast (km). The Marquesas and the lower and upper Florida Keys were predicted to support the most suitable habitats for the 23 coral species examined. A. cervicornis had one of the smallest areas of suitable habitat, which was limited to the lower and upper Florida Keys, the Dry Tortugas, and nearshore Broward-Miami reefs. The best environmental predictors of site occupancy of A. cervicornis were SST range (4–5°C) and turbidity (K490 between 0.15–0.25 m-1). Historically A. cervicornis was reported in clear oligotrophic waters, although the present results find the coral species surviving in nearshore turbid conditions. Nearshore, turbid reefs may shade corals during high-temperature events, and therefore nearshore reefs in south Florida may become important refuges for corals as the ocean temperatures continue to increase.
The stony-coral-tissue-loss disease (SCTLD) has recently caused widespread loss of coral along the Florida reef tract. Yet little is known about where, when, and why this coral disease outbreak occurred. In the absence of a definitive pathogen, it is essential to characterize the ecology of the disease and document the spatio-temporal dynamics of the outbreak. Here, we investigate the epizootiology of the SCTLD at multiple spatial and temporal scales along the Florida reef tract from May 2014 to December 2017. We used spatial interpolation to characterize the disease hotspots, Ripley’s K analysis to examine contagion, a spatio-temporal model to assess rates of spread, and a Bayesian model to examine ecological and environmental covariates that may have influenced the occurrence and severity of the outbreak. Our results show that the disease affected reefs at the scale of hundreds of kilometers, with significant clusters of up to 140 km. The epizootic clearly followed a contagion model, suggesting that the disease was highly contagious. The rate of spread of the epizootic was linear and moved slightly faster to the north (∼100 m d–1) than to the south (∼92 m d–1). The difference in rate of spread between the north and south direction may indicate currents facilitated transmission. The analyzed dataset showed that the epizootic affected at least 19 coral species and that deep and diverse sites were at greater risk of the disease than shallow and low diversity sites.
Severe coral bleaching events in the Gulf of Thailand and along the Andaman Sea coast of Thailand caused widespread coral mortality in 1998 and 2010. The consequent decrease in coral populations impacted the structure, health, and services of Thai coral reefs. However, most colonies in the offshore reef of Losin were still alive after the coral bleaching events. Therefore, this study was conducted by the Department of Marine and Coastal Resources in order to help to establish a proposal for making it a Marine Protected Area (MPA). Surveys on coral diversity were conducted to produce a checklist of reef-building corals. Seventy-six coral species were found, with the most dominant species being Porites lutea and Acropora communities, such as A. intermedia, A. grandis, A. muricata, A. cytherea, and A. valenciennesi. This area is expected to be designated as a restricted MPA area, under the “Act on the Promotion of Marine and Coastal Resources Management B.E. 2558 (2015).” The high diversity of hard corals discovered in this study assists in promoting an Announcement of the Losin Marine and Coastal Resources Protected Areas following Ministerial Regulation.
Coral reefs are biologically diverse and structurally complex ecosystems, which have been severally affected by human actions. Consequently, there is a need for rapid ecological assessment of coral reefs, but current approaches require time consuming manual analysis, either during a dive survey or on images collected during a survey. Reef structural complexity is essential for ecological function but is challenging to measure and often relegated to simple metrics such as rugosity. Recent advances in computer vision and machine learning offer the potential to alleviate some of these limitations. We developed an approach to automatically classify 3D reconstructions of reef sections and assessed the accuracy of this approach. 3D reconstructions of reef sections were generated using commercial Structure-from-Motion software with images extracted from video surveys. To generate a 3D classified map, locations on the 3D reconstruction were mapped back into the original images to extract multiple views of the location. Several approaches were tested to merge information from multiple views of a point into a single classification, all of which used convolutional neural networks to classify or extract features from the images, but differ in the strategy employed for merging information. Approaches to merging information entailed voting, probability averaging, and a learned neural-network layer. All approaches performed similarly achieving overall classification accuracies of ~96% and >90% accuracy on most classes. With this high classification accuracy, these approaches are suitable for many ecological applications.
The objective of this report is to review the existing models of temporal/spatial dynamics of coral communities available for the Great Barrier Reef (the Reef), with the specific aim at evaluating their strengths and weaknesses for the assessment and reporting of coral reef health within the Reef 2050 Integrated Monitoring and Reporting Program (RIMReP). Focusing on peer-reviewed articles available by 28 February 2018, we found that a variety of modeling approaches exists yet with different scope, level of complexity, and ability to represent the various processes driving the dynamics of coral populations. Tools available to model Reef coral population dynamics also vary in their capacity to capture the spatial heterogeneity of coral populations and their environment, the variability of disturbance impacts and the uncertainty around current reef state and possible future trajectory. The various characteristics and properties exhibited by coral reef models means they have different capacities to complement reef monitoring and assessment on the Reef. This review provides guidance for integrating a modeling component to RIMReP by identifying the modeling approaches that offer the strongest support to reef monitoring and management.
The report is organised as follows: In section 1, we list the potential benefits of ecological models for monitoring programs and explain how models can complement monitoring data and support the assessment of reef status and trends across the Reef. Section 2 provides an overview of the general characteristics and properties of ecological models, with the aim of facilitating the technical comparison of available coral reef models. In section 3, we summarise what we think are the key processes that influence the dynamics of coral populations. This provides a mechanistic framework allowing a comparison of models based on their ecological realism, i.e. their ability to reproduce changes in coral populations from the compounded action of individual demographic mechanisms. Section 4 provides an overview of the candidate coral models for the Reef, with their summary characteristics (model type, state variables, time steps), the ecological processes embedded, their parametrisation and model’s ability to capture the spatial dynamics of corals in a heterogeneous environment. For each model we highlight their strengths and weaknesses in complementing monitoring data to inform about status and trends across the Reef. Finally, we synthesise in section 5 the best candidate models, highlight their ability to inform management priorities for the Reef and make a number of recommendations for a successful integration into RIMReP.
The Coral Reef Expert Group (CREG) was one of eight expert groups, which all followed a prescribed process to recommend a design for their thematic component.
The tasks of the expert groups included:
- Synopsis of the theme, to include discussion on current state, primary drivers, pressures and responses using DPSIR framework.
- Review of all current monitoring and modelling activities relevant to the expert group theme.
- Identify candidate indicators that can be monitored and would provide information about trend, status or forecasting of value or the system.
- Evaluation of the adequacy and confidence of current monitoring and modelling of candidate indicators, determined by their ability to meet the objectives of the RIMReP and management needs provided by the Authority.
- Identification and discussion of gaps and opportunities in current monitoring and modelling of such indicators.
- Evaluation of new monitoring technologies for their potential to increase efficiency or statistical power and their compatibility with long-term datasets.
- Recommendations for monitoring design including consideration of primary indicators, continuity of data sets, how the design addresses management needs, modification to existing programs, costing and transition strategies.
Addressing growing threats of overexploitation to the world’s oceans is especially challenging in the High Seas, where limited data and international jurisdiction make it difficult to determine where and when conservation measures are necessary. Of particular concern are vulnerable marine ecosystems (VMEs)—special habitats on the seafloor that are highly sensitive to disturbance and slow to recover. To ensure the long-term conservation and sustainable use of marine resources, regional fisheries management organizations are committed to identifying the locations of VMEs and responding to prevent significant adverse impacts (SAIs). For over 50 years, Cobb Seamount—a shallow underwater volcanic mountain in the Northeast Pacific Ocean—has been commercially fished by multiple nations using various types of gear. Here we have assimilated data from fisheries records and a recent visual survey on the seamount. Our findings show a variety of habitat-forming emergent biological structures widely distributed on Cobb Seamount and generally depth-stratified into high-density assemblages (≥1 m–2). Our spatial analyses show that fishing has also been widely distributed, overlapping the habitat of the biological structures. We found fewer cold-water corals, sponges, and other biological structures in areas with higher recent fishing effort and documented evidence of fishing impacts, such as extensive mats of coral rubble and a high abundance of derelict fishing gear entangled with dead or damaged organisms. Based on the average density of “lost” gear (2,785 ± 1,003 km–2), we can confidently estimate that hundreds of thousands of items of derelict fishing gear are currently entangled with the seafloor of Cobb Seamount and that these pose an ongoing threat to biological structures, the biogenic habitats they create, and the species they support. Such impacts can persist for decades or centuries to come. This study contributes and discusses new information on the condition and distribution of biological structures, VME indicator taxa, physically complex biogenic ecosystems, and human impacts on Cobb Seamount. These data will be necessary to identify the location(s) of potential VMEs and SAIs on this heavily fished seamount in the High Seas.
The Phoenix Islands Protected Area, in the central Pacific waters of the Republic of Kiribati, is a model for large marine protected area (MPA) development and maintenance, but baseline records of the protected biodiversity in its largest environment, the deep sea (>200 m), have not yet been determined. In general, the equatorial central Pacific lacks biogeographic perspective on deep-sea benthic communities compared to more well-studied regions of the North and South Pacific Ocean. In 2017, explorations by the NOAA ship Okeanos Explorer and R/V Falkor were among the first to document the diversity and distribution of deep-water benthic megafauna on numerous seamounts, islands, shallow coral reef banks, and atolls in the region. Here, we present baseline deep-sea coral species distribution and community assembly patterns within the Scleractinia, Octocorallia, Antipatharia, and Zoantharia with respect to different seafloor features and abiotic environmental variables across bathyal depths (200–2500 m). Remotely operated vehicle (ROV) transects were performed on 17 features throughout the Phoenix Islands and Tokelau Ridge Seamounts resulting in the observation of 12,828 deep-water corals and 167 identifiable morphospecies. Anthozoan assemblages were largely octocoral-dominated consisting of 78% of all observations with seamounts having a greater number of observed morphospecies compared to other feature types. Overlying water masses were observed to have significant effects on community assembly across bathyal depths. Revised species inventories further suggest that the protected area it is an area of biogeographic overlap for Pacific deep-water corals, containing species observed across bathyal provinces in the North Pacific, Southwest Pacific, and Western Pacific. These results underscore significant geographic and environmental complexity associated with deep-sea coral communities that remain in under-characterized in the equatorial central Pacific, but also highlight the additional efforts that need to be brought forth to effectively establish baseline ecological metrics in data deficient bathyal provinces.