The Mediterranean deep-sea contains a mosaic of ecosystems and habitat types. Among them, cold-water corals provide shelter to a large and unique variety of organisms as well as ecosystem services. Scientific findings over the last decade have strengthened this fact and further supported the identification of cold-water corals habitats as sites of conservation interest and high vulnerability. Given the semi-enclosed nature of the Mediterranean basin and the significant anthropogenic pressure on its ecosystems, most, cold-water corals species have been listed as threatened as they are found at areas which are frequently the focus of resource exploitation (e.g. deep-sea fisheries, oil and gas prospections among others) or are affected directly by other human activities (e.g. marine debris, pollution events) as well as by the increasing impacts of climate change including ocean acidification. Nowadays, conservation and protection of such important species and ecosystems largely depend upon the proper development and implementation of marine policies. Here, we analyze the most important policy framework in place to protect these species in the Mediterranean Sea and we consider the most recent developments and opportunities for improving the situation. The management of cold-water corals involves important challenges. This is partly due to their remote location, limited political awareness, as well as incomplete information available on the occurrence, distribution and resilience of these cold-water coral species and their associated fauna, to impacts and disturbances. Specific actions are discussed to increase the protection of deep-sea ecosystems hosting cold-water corals through good governance and to establish effective area-based conservation measures to safeguard Mediterranean deep-sea biodiversity.
Lead concentrations in long-lived Corallium species of known age, from the Mediterranean Sea, Atlantic and Pacific Oceans, were determined by laser ablation, inductively coupled plasma mass spectrometer (LA-ICPMS). Lead concentrations in a 2000-year-old sub-fossil Mediterranean C. rubrum are ca 0.09 ± 0.03 μg/g. For the period 1894–1955, lead concentrations in C. rubrum skeletons from the Mediterranean are stable within the range 0.2–0.4 μg/g; concentrations increase to about 1–1.2 μg/g during the period 1960–1978, then decrease progressively to stabilize and reach values in the range 0.2–0.4 μg/g in present-day corals. These variations can be related to the lead gasoline pollution event that (1) started in the early 1950s with the increase of the numbers of cars in the world, and (2) was mitigated by the implementation of new regulations starting in 1975, leading to a return to pre-1950 levels in 2000. In the Pacific, lead concentrations in C. japonicum and C. konojoi are lower than in the Mediterranean C. rubrum, with values close to 0.17 ± 0.03 μg/g. The lowest lead concentrations in present-day samples (0.11 μg/g) are found in C. johnsoni and C. niobe from the Azores islands in the Atlantic, and in a Mediterranean C. rubrum from Montecristo Island, one of the least accessible and most protected areas in the Mediterranean Sea. Using lead concentrations in C. rubrum and in the Mediterranean seawaters, a partition coefficient Kd = [Pb/Ca]calcite / [Pb/Ca]seawater of 13 ±3 is estimated; it allows calculating past and present lead contents in seawater in which corals grew. Application to Coralliumspecies indicates that values endangering human health or threatening the preservation of aquatic ecosystem on long terms were nearly reached or exceeded in Mediterranean seawaters at the maximum of the lead gasoline pollution event in the 1980s. Measurements in C. rubrum from different places in the Mediterranean indicate that present-day seawater concentrations vary between 40 and 200 pmol/kg. As expected, the lowest concentrations come from protected areas insulated from human activities, while the highest come from places close to lead mining or processing sites.
Estimates of coral reef ecosystem calcification (Gnet) and productivity (Pnet) provide insight into coral community health and functionality in response to short- and long-term stressors such as ocean warming and acidification. Here, we investigate spatial variability in calcification and organic production at One Tree Island (OTI) and compare our new observations to sporadic metabolic rates reported over the previous 50 years on the same reef flat. Gnet and Pnet estimates at the nearshore site were 50% and 166% lower than an offshore site with a shift in organic production from net productive to net respiratory. Contrary to expectations, calcification rates in 2017 (145.7 ± 20.2 mmol m-2 d-1) were comparable to the 1970s estimate (125.0 ± 12.5 mmol m-2d-1) and 400% greater than similar observations in 2014. Our results indicate only weak associations between Gnet and aragonite (Ωar). A local increase in coral cover from 18% in 2014 to 31% in 2017 was the likely driver of increased calcification. A steeper TA–DIC slope in 2017 demonstrates a greater control of calcification on seawater carbonate chemistry than prior years. Overall, these results highlight the importance of site selection and replication when comparing metabolic datasets, and demonstrate major short-term variability in metabolic rates. The predictive capabilities of ecosystem metabolism studies may be constrained by using the available short-term datasets to represent long-term calcification trends.
The world's coral reefs are rapidly transforming, with decreasing coral cover and new species configurations. These new Anthropocene reefs pose a challenge for conservation; we can no longer rely on established management plans and actions designed to maintain the status quo when coral reef habitats, and the challenges they faced, were very different. The key questions now are: what do we want to conserve on Anthropocene reefs, why, and how? Trends in reef management over recent decades reveal rapid shifts in perceived threats, goals and solutions. Future reefs will be unlike anything previously seen by humans, and while their ability to support tourism or fisheries may be relatively resilient, our capacity to manage them may be constrained by their new species configurations. Furthermore, there is a growing spatial mismatch between the escalating scale of threats and current or planned responses. We present a blueprint for future reef conservation that recognizes the need to better understand the processes that maintain Anthropocene reefs, and the growing imperative to reform conservation efforts to address both specific local issues and larger-scale threats. The future of coral reef conservation is no longer one solely of localized action and stewardship; it requires practices and institutions operating at far larger scales than today.
Climate and environmental conditions are determinant for coral distribution and their very existence. When changes in such conditions occur, their effects on distribution can be predicted through species distribution models, anticipating suitable habitats for the subsistence of species. Mussismilia harttii is one of the most endangered Brazilian endemic reef-building corals, and in increasing risk of extinction. Herein, species distribution models were used to determine the present and future potential habitats for M. harttii. Estimations were made through the maximum entropy approach, predicting suitable habitat losses and gains by the end of the 21st century. For this purpose, species records published in the last 20 years and current and future environmental variables were correlated. The best models were chosen according to the Akaike information criterion (AIC) and evaluated through the partial ROC (AUCratio), a new approach which uses independent occurrence data. Both approaches showed that the models performed satisfactorily in predicting potential habitat areas for the species. Future projections were made using the International Panel on Climate Change (IPCC) scenarios for 2100, with different levels of greenhouse gas emission. Representative Concentration Pathways (RCPs) were used to model the Future Potential Habitat (FPH) of M. harttii in two different scenarios: stabilization of emissions (RCP 4.5) and increase of emissions (RCP 8.5). According to the results, shallow waters to the south of the study area concentrate most of the current potential habitats for the species. However, in future scenarios, there was a loss of suitable areas in relation to the Current Potential Habitat (RCP 4.5 46% and RCP 8.5 59%), whereas there is a southward shift of the suitable areas. In all scenarios of FPH, the temperature was the variable with the greatest contribution to the models (> 35%), followed by the current velocity (> 33%) and bathymetry (>29%). In contrast, there is an increase of deep (50–75 m) suitable areas FPH scenarios, mainly in the southern portion of its distribution, at Abrolhos Bank (off Espirito Santo State). These deeper sites might serve as refugia for the species in global warming scenarios. Coral communities at such depths would be less susceptible to impacts of climate change on temperature and salinity. However, the deep sea is not free from human impacts and measures to protect deeper ecosystems should be prioritized in environmental policies for Brazilian marine conservation, especially the Abrolhos Bank, due to its importance for M. harttii.
Coralline algae are foundation species in many hard-bottom ecosystems acting as a settlement substrate, and binding together and even creating reefs in some locations. Ocean acidification is known to be a major threat to coralline algae. However, the effects of ocean warming are less certain. Here we bring multiple lines of evidence together to discuss the potential impacts of ocean warming on these ecologically crucial taxa. We use a meta-analysis of 40 responses within 14 different studies available which assessed the effects of increasing temperature on coralline algal calcification in laboratory experiments. We find a net negative impact of increasing temperature on coralline algal calcification at 5.2°C above ambient conditions. Conversely, negative effects are observed when temperature drops below 2.0°C from ambient conditions. We propose that some coralline algae will be more capable of both acclimatizing and locally adapting to increasing ocean temperatures over the coming decades. This is because many species possess short generation times, the ability to opportunistically rapidly utilize open space, and relatively high phenotypic plasticity. However, less resistant and resilient species will be those that are long-lived, those with long generation times, or with narrow thermal tolerances (e.g., tropical taxa living close to their thermal maxima). Additionally, ocean warming will occur simultaneously with ocean acidification, a potentially greater threat to coralline algae, which could also reduce any tolerance to ocean warming for many species. To maximize the potential to accurately determine how coralline algae will respond to future ocean warming and marine heatwaves, future research should use environmentally relevant temperature treatments, use appropriate acclimation times and follow best practices in experimental design.
Populations of Acropora palmata and Orbicella faveolata, two important reef-building corals, have declined precipitously across the Caribbean region since at least the 1970s. Recruitment failure may be limiting population recovery, possibly due to lack of suitable settlement habitat. Here, we examine the effects of algal turfs and algal turfs + sediment, two widely abundant substrate types across the Florida Keys, on the settlement of these two ecologically-important species. We show that sedimentsignificantly impedes coral settlement, reducing settlement 10- and 13-fold for A. palmata and O. faveolata, respectively, compared to turf algae alone. This result is corroborated by our field survey data that showed a strong, negative relationship between the abundance of turf + sediment and the abundance of juvenile corals. Turf algae alone did not reduce coral settlement. Our results suggest that sediment-laden turf algae are detrimental to settling corals, but that turf algae alone may be relatively benign.
Climate change and human disturbance threatens coral reefs across the Pacific, yet there is little consensus on what characterizes a “healthy” reef. Benthic cover, particularly low coral cover and high macroalgae cover, are often used as an indicator of reef degradation, despite uncertainty about the typical algal community compositions associated with either near-pristine or damaged reefs. In this study, we examine differences in coral and algal community compositions and their response to human disturbance and past heat stress, by analysing 25 sites along a gradient of human disturbance in Majuro and Arno Atolls of the Republic of the Marshall Islands. Our results show that total macroalgae cover indicators of reef degradation may mask the influence of local human disturbance, with different taxa responding to disturbance differently. Identifying macroalgae to a lower taxonomic level (e.g. the genus level) is critical for a more accurate measure of Pacific coral reef health.
Although the existence of zooxanthellate corals in mesophotic coral ecosystems (MCEs; light-dependent coral ecosystems from 30 to 150 m in depth) has been known since the nineteenth century and focused scientific exploration of MCEs began over 50 years ago, more than 70% of all research on MCEs has been published only within the past seven years. MCEs represent approximately 80% of potential coral reef habitat worldwide, yet very little is known about them in comparison to shallow reefs. Many MCE species new to science have been discovered in the past decade, and many more await discovery. The term MCEs has been widely adopted by the scientific community since its 2008 inception; however, there is considerable inconsistency in how it is subdivided into “upper” and “lower” (and sometimes “middle”) zones. Moreover, doing so may lead to artificial boundaries when habitats and ecological communities at different depth zones may blend together. Growing evidence suggests that MCEs harbor proportionally more geographically endemic species than their shallow-water counterparts, and initial indications are that major biogeographic patterns described for shallow reef organisms may not apply to MCEs. Although MCEs may serve as refugia for some shallow species, they are increasingly recognized as unique ecosystems, important in their own right. Future research on MCEs should aim to address gaps in our understanding of the basic physical and biological characteristics of MCEs including geography, taxonomic composition, depth distribution, ecology, physiology, and connectivity. Improving knowledge of MCEs would benefit from combining different technologies to leverage the strengths of each.
Ecological restoration of forests, meadows, reefs, or other foundational ecosystems during climate change depends on the discovery and use of individuals able to withstand future conditions. For coral reefs, climate-tolerant corals might not remain tolerant in different environments because of widespread environmental adjustment of coral physiology and symbionts. Here, we test if parent corals retain their heat tolerance in nursery settings, if simple proxies predict successful colonies, and if heat-tolerant corals suffer lower growth or survival in normal settings. Before the 2015 natural bleaching event in American Samoa, we set out 800 coral fragments from 80 colonies of four species selected by prior tests to have a range of intraspecific natural heat tolerance. After the event, nursery stock from heat-tolerant parents showed two to three times less bleaching across species than nursery stock from less tolerant parents. They also retained higher individual genetic diversity through the bleaching event than did less heat-tolerant corals. The three best proxies for thermal tolerance were response to experimental heat stress, location on the reef, and thermal microclimate. Molecular biomarkers were also predictive but were highly species specific. Colony genotype and symbiont genus played a similarly strong role in predicting bleaching. Combined, our results show that selecting for host and symbiont resilience produced a multispecies coral nursery that withstood multiple bleaching events, that proxies for thermal tolerance in restoration can work across species and be inexpensive, and that different coral clones within species reacted very differently to bleaching.