Deep-sea corals are of conservation concern in the North Atlantic due to prolonged disturbances associated with the exploitation of natural resources and a changing environment. As a result, two research cruises in the Gulf of Maine region during 2014 and 2017 collected samples of two locally dominant coral species, Primnoa resedaeformis and Paramuricea placomus, at six locations to investigate reproductive ecology. Remotely operated vehicles (ROVs) were used to collect specimens that were examined via paraffin histology, and coincident video surveys were used to determine size class distributions. Both species were identified as gonochoristic, and sampled locations exhibited dissimilarities in spermatocyst development and oocyte size except for those in close geographic proximity. Fecundities exhibited substantial ranges across sample locations and average oocyte sizes (±SD) were 140 ± 117 μm for P. resedaeformis and 64 ± 46 μm for P. placomus. In addition, colony size distributions were also significantly different across sampling locations. Notably, the Outer Schoodic Ridge sample location, with larger colony and oocyte sizes, was identified as a potential key source population of reproductive material in the Gulf of Maine. These data were used to calculate differences in reproductive potential based on relationships between colony morphology and reproductive output using height as a predictive proxy. Furthermore, calculated age at first reproduction, 7.6–19.8 years for P. resedaeformis and 20.7–37 years for P. placomus, which may be dependent on sex of the colony, provides a metric for estimating the amount of time these coral habitats will take to recover. This investigation, in response to historical population impacts and environmental change, links reproductive and morphometric relationships to inform population scale reproductive models, while also establishing an understanding of regional scale gametogenic variability within the Gulf of Maine region.
Equatorial corals were previously thought not to spawn synchronously at the assemblage level. However, recent studies have reported multi-specific coral spawning events in equatorial regions. Here, we report the reproductive activity of 21 Acroporaspecies in the Karimunjawa Archipelago over five consecutive years (2008–2012). We also infer the month of spawning for Acropora humilis, Acropora gomezi, and Acropora muricata from the presence of mature oocytes. We found that Acroporaassemblages exhibit a high degree of inter-specific reproductive seasonality. The highest proportion of colonies with mature oocytes was observed in March 2011 (65%, n = 80). Oocytes likely developed during June–March, 6 to 10 months before spermatogenesis. Spermatocytes were observed in samples collected during March; however, the onset of spermatogenesis could not be precisely determined as samples were not collected in January and February. This was because of weather constraints and difficulty in detecting the early stages of spermatogenesis. Multi-specific spawning events were observed during the first transition period (March–April) and the second transition period (September–October) between monsoons. The number of species containing mature oocytes was higher during March–April (12 species) and September–October (8 species). Spawning patterns likely follow the lunar cycle. However, two distinct spawning events coincided with two periods of higher temperature (March–April and September–October). Daily temperature records indicate that spawning occurred on days where temperature dropped before the expected spawning time during the warming period. During the period of rising temperature, wind speeds were lower, which might serve as a signal leading to the multi-specific spawning of corals in the tropics, at least in the Karimunjawa Archipelago of Indonesia.
Corals in the Persian/Arabian Gulf are the most thermally tolerant in the world, but live very near the thresholds of their thermal tolerance. Warming sea temperatures associated with climate change have resulted in numerous coral bleaching events regionally since the mid-1990s, but it has been unclear why unusually warm sea temperatures occur some years but not others. Using a combination of 5 years of observed sea-bottom temperatures at three reef sites and a meteorologically linked hydrodynamic model that extends through the past decade, we show that summer sea-bottom temperatures are tightly linked to regional wind regimes, and that strong ‘shamal’ wind events control the occurrence and severity of bleaching. Sea bottom temperatures were primarily controlled by latent heat flux from wind-driven surface evaporation which exceeded 300 W m-2 during shamal winds, double that of typical breeze conditions. Daily temperature change was highly correlated with wind speed, with breeze winds (<4 m s-1) resulting in increased warming, while faster winds caused cooling, with the magnitude of temperature decline increasing with wind speed. Using observed and simulated data from 2012 to 2017, we show that years with reported bleaching events (2012, 2017) were characterized by low winds speeds that resulted in temperatures persisting above coral bleaching threshold temperatures for >5 weeks, while the cooler intervening years (2013–2016) had summers with more frequent and/or strong shamal events which repeatedly cooled temperatures below bleaching thresholds for days to weeks, providing corals temporary respite from thermal stress. Using observed data from 2012 onward and simulated data from 2008 to 2011, we show that the severity of bleaching events over the past decade was linked to both the number of cumulative days above bleaching thresholds (rather than total days, which obfuscates the cooling effects of occasional brief shamal events), as well as to maxima. We show that winds of 4 m s-1 represents a critical threshold for whether or not corals cross bleaching threshold temperatures, and provide simulations to forecast sea-bottom temperature change and recovery times under a range of wind conditions. The role that wind-driven cooling may play on coral reefs globally is discussed.
Coral reefs are subject to multiple stressors. Global stressors include climate changeand ocean acidification, while local stressors include overfishing and eutrophication. Some stressors stem from land-based activities, like intensive agriculture or sewage production, while others are sea-based, like fishing or diving. Processes that aim to tackle coral degradation are transpiring on different levels. These include the UNDP's Sustainable Development Goal 14, and the Coral TriangleInitiative, which foresees the installation of marine protected areas and conservation planning. This paper uses Evolutionary Governance Theory (EGT) to understand the current processes of changes in governance influencing coral reef health. EGT sees the change of governance as an evolutionary process. It emphasises that discourses play a crucial role in understanding governance evolution. Power, in particular power-knowledge in the Foucaultian sense, plays a crucial role as a driving factor. Governance does not change in a vacuum, but according to EGT is shaped by path, inter- and goal dependencies. Of late, the role of materiality - ecological and technological conditions - has been stressed as an important driver of governance change. The paper considers the main threats to corals identified in the literature and analyses how those factors mentioned by EGT help us to understand the observed governance changes. The case of coral reefs was chosen as it represents an example of extremely diverse processes of institutional changes. Therefore, it is well suited to learn if EGT helps in understanding governance changes observed in the marine sector.
The degradation of coastal habitats, particularly coral reefs, raises risks by increasing the exposure of coastal communities to flooding hazards. The protective services of these natural defenses are not assessed in the same rigorous economic terms as artificial defenses, such as seawalls, and therefore often are not considered in decision making. Here we combine engineering, ecologic, geospatial, social, and economic tools to provide a rigorous valuation of the coastal protection benefits of all U.S. coral reefs in the States of Hawaiʻi and Florida, the territories of Guam, American Samoa, Puerto Rico, and Virgin Islands, and the Commonwealth of the Northern Mariana Islands. We follow risk-based valuation approaches to map flood zones at 10-square-meter resolution along all 3,100+ kilometers of U.S. reef-lined shorelines for different storm probabilities to account for the effect of coral reefs in reducing coastal flooding. We quantify the coastal flood risk reduction benefits provided by coral reefs across storm return intervals using the latest information from the U.S. Census Bureau, Federal Emergency Management Agency, and Bureau of Economic Analysis to identify their annual expected benefits, a measure of the annual protection provided by coral reefs. Based on these results, the annual protection provided by U.S. coral reefs is estimated in:
- avoided flooding to more than 18,180 people;
- avoided direct flood damages of more than $825 million to more than 5,694 buildings;
- avoided flooding to more than 33 critical infrastructure facilities, including essential facilities, utility systems, and transportation systems; and
- avoided indirect damages of more than $699 million in economic activity of individuals and more than $272 million in avoided business interruption annually.
Thus, the annual value of flood risk reduction provided by U.S. coral reefs is more than 18,000 lives and $1.805 billion in 2010 U.S. dollars. These data provide stakeholders and decision makers with spatially explicit, rigorous valuation of how, where, and when U.S. coral reefs provide critical coastal storm flood reduction benefits. The overall goal is to ultimately reduce the risk to, and increase the resiliency of, U.S. coastal communities.
As the Earth's temperature continues to rise, coral bleaching events become more frequent. Some of the most affected reef ecosystems are located in poorly‐monitored waters, and thus, the extent of the damage is unknown. We propose the use of Marine Heatwaves (MHWs) as a new approach for detecting coral reef zones susceptible to bleaching, using the Red Sea as a model system. Red Sea corals are exceptionally heat‐resistant, yet bleaching events have increased in frequency. By applying a strict definition of MHWs on >30‐year satellite‐derived sea surface temperature observations (1985–2015), we provide an atlas of MHW hotspots over the Red Sea coral reef zones, which includes all MHWs that caused major coral bleaching. We found that: 1) if tuned to a specific set of conditions, MHWs identify all areas where coral bleaching has previously been reported; 2) those conditions extended farther and occurred more often than bleaching was reported; and 3) an emergent pattern of extreme warming events is evident in the northern Red Sea (since 1998), a region until now thought to be a thermal refuge for corals. We argue that bleaching in the Red Sea may be vastly underrepresented. Additionally, although northern Red Sea corals exhibit remarkably high thermal resistance, the rapidly rising incidence of MHWs of high intensity indicates this region may not remain a thermal refuge much longer. As our regionally‐tuned MHW algorithm was capable of isolating all extreme warming events that have led to documented coral bleaching in the Red Sea, we propose that this approach could be used to reveal bleaching‐prone regions in other data‐limited tropical regions. It may thus prove a highly valuable tool for policy‐makers to optimise the sustainable management of coastal economic zones.
Coastal water quality and light attenuation can detrimentally affect coral health. This study investigated the effects of light limitation and reduced water quality on the physiological performance of the coral Acropora tenuis. Branches of individual colonies were collected in 2 m water depth at six inshore reefs at increasing distances from major river sources in the Great Barrier Reef, along a strong water quality gradient in the Burdekin and a weak gradient in the Whitsunday region. Rates of net photosynthesis, dark respiration, and light and dark calcification were determined at daily light integrals (DLI) of moderate (13.86–16.38 mol photons m−2d−1), low (7.92–9.36 mol photons m−2 d−1) and no light (0 mol photons m−2 d−1), in both the dry season (October 2013, June 2014) and the wet season (February 2014). Along the strong but not the weak water quality gradient, rates of net photosynthesis, dark respiration and light calcification increased towards the river mouth both in the dry and the wet seasons. Additionally, a ∼50% light reduction (from moderate to low light), as often found in shallow turbid waters in the Burdekin region, reduced rates of net photosynthesis and light calcification by up to 70% and 50%. The data show the acclimation potential in A. tenuis to river derived nutrients and sediments at moderate DLI (i.e., in very shallow water). However, prolonged and frequent periods of low DLI (i.e., in deeper water, especially after high river sediment discharges) will affect the corals’ energy balance, and may represent a major factor limiting the depth distribution of these corals in turbid coastal reefs.
Coral reefs cover approximately 0.10 to 0.25% of the marine environment, and yet are home to around 25% of marine species and support the livelihoods of more 500 million people. They face a wide range of threats, with the impact of global warming gaining most attention due to its frequently claimed causal link to coral bleaching. Here we review a decade of research into the micrometeorology of Heron Reef, a lagoonal platform coral reef in the southern Great Barrier Reef, Australia. Using novel pontoon mounted eddy covariance systems we show that often > 80% of net radiation is partitioned into heating the water overlying the reef, the reef benthos, and substrate. Significant spatial variability in energy and trace gas exchanges occurs over the reef in response to different geomorphic and hydrodynamic conditions. Synoptic weather patterns that bring light winds, clear skies and high humidity, result in reef scale meteorology that appears to have a greater influence on coral bleaching events than the background oceanic warming trend. The reef develops its own convective internal boundary layer, with potential to influence cloud development and therefore the surface energy balance. Knowledge of such local effects is lacking, so it is recommended that future research is needed into reef scale processes and how they interact with larger scale forcing.
Manmade antibiotics are emerging organic pollutants widely detected in the marine environment. In this study, 14 out of 19 target antibiotics were detected in corals collected from coastal and offshore regions in the South China Sea. The average total antibiotic concentrations (∑19ABs) in the two regions were similar: 28 ng/g for coastal corals and 31 ng/g for offshore corals, based on dry tissue weight (dw). Fluoroquinolones (FQs) were predominant antibiotics in the coastal corals (mean ∑FQs: 18 ng/g dw), while sulfonamides (SAs) predominated in the offshore corals (mean ∑SAs: 23 ng/g dw). However, corals living in coastal regions tend to excrete more mucus than corals in offshore habitat. We found 53% by average of ∑19ABs in the mucus of the coastal corals; while in offshore corals, most antibiotics (88% by average) were accumulated in the tissues. In addition, the tissue-mucus mass distribution differs among individual antibiotics. Sulfonamides were mainly accumulated in tissues while fluoroquinolones were present mainly in mucus. The results of this study suggest that mucus played an important role in the bioaccumulation of antibiotics by corals. It may resist the bioaccumulation of antibiotics by coral tissue, especially for the coastal corals. Additionally, corals were compared with other marine biotas in the study area and found to be more bioaccumulative towards antibiotics.
Concern about the condition of Philippine coral reefs has prompted a recent reassessment of the status of the nation's reefs, the results of which are reported here. This paper presents the largest updated dataset on Philippine coral cover and generic diversity. The dataset was obtained from equally-sized sampling stations on fore-reef slopes of fringing reefs in six biogeographic regions using identical methods. A total of 206 stations were surveyed from 2014 to 2017, and another 101 stations were monitored from 2015 to 2018.
The weighted average hard coral cover (HCC) was 22.8% (±1.2 SE) and coral generic diversity averaged 14.5 (±0.5 SE). Both were highest in the fully-formed reefs of the Sulu Sea biogeographic region and lowest in the eastern Philippines. Comparisons of findings with those of previous assessments show the continued decline in coral cover over a larger time scale, with the loss of about a third of the reef corals over the last decade. However, no consistent changes were evident in the 101 monitoring stations from 2015 to 2018 despite the global coral bleaching event. An expanded monitoring program, not just one-off assessments, is recommended to improve reef management in the Philippines.