Iron, cadmium, and chromium in seagrass (Thalassia testudinum) from a coastal nature reserve in karstic Yucatán.

The management of protected areas in karstic regions is a challenge because flooded cave systems form there and provide underground hydrological conducts that may link different zones. As a consequence, affectations to the protected areas can possibly occur as a consequence of human activities in remote areas and may therefore pass undetected. Thus, the monitoring of possible contaminants in these regions is becoming imperative. In this work, we analyze the concentration of essential (iron) and non-essential metals (cadmium and chromium) in the seagrass Thalassia testudinum that grows in Yalahau Lagoon, located in a near-to-pristine protected area of the Yucatán Peninsula, close to the rapidly developing touristic belt of the Mexican Caribbean. Salinity and silicate patterns show that Yalahau is an evaporation lagoon, where groundwater discharge is important. High iron (> 400 µg/g), cadmium (>4 µg/g), and chromium (≈ 1 µg/g) concentrations were found in the area of highest groundwater input of the lagoon. High levels (5.1 µg/g) were also found near the town dump. In the rest of the sampling sites, metal concentrations remained near to background levels as estimated from other works. Temporal changes of concentrations in the seagrass tissues show also a local input and an input from the groundwater that could provoke an environmental problem in the Yalahau Lagoon in the near future.

Newly deceased Caribbean reef-building corals experience rapid carbonate loss and colonization by endolithic organisms.

Coral mortality triggers the loss of carbonates fixed within coral skeletons, compromising the reef matrix. Here, we estimate rates of carbonate loss in newly deceased colonies of four Caribbean reef-building corals. We use samples from living and recently deceased colonies following a stony coral tissue loss disease (SCTLD) outbreak. Optical densitometry and porosity analyses reveal a loss of up to 40% of the calcium carbonate (CaCO3) content in dead colonies. The metabolic activity of the endolithic organisms colonizing the dead skeletons is likely partially responsible for the observed dissolution. To test for the consequences of mass mortality events over larger spatial scales, we integrate our estimates of carbonate loss with field data of the composition and size structure of coral communities. The dissolution rate depends on the relative abundance of coral species and the structural properties of their skeletons, yet we estimate an average reduction of 1.33 kg CaCO3 m-2, nearly 7% of the total amount of CaCO3 sequestered in the entire system. Our findings highlight the importance of including biological and chemical processes of CaCO3 dissolution in reef carbonate budgets, particularly as the impacts of global warming, ocean acidification, and disease likely enhance dissolution processes.

Sclerochronological characteristics of Orbicella faveolata in Cayo Arenas, a remote coral reef from the Gulf of Mexico.

During coral calcification in massive scleractinian corals, a double annual banding of different densities (high- and low-density) is formed in their skeletons, which can provide a retrospective record of growth and the influence of environmental conditions on the coral's lifespan. Evidence indicates that during the last decades, the reduction in coral calcification rate is attributed to the combination of global stress factors such as Sea Surface Temperature (SST) and local anthropic stressors. Yet, coral growth trajectories can vary between regions and coral species, where remote locations of coral reefs can act as natural laboratories, as they are far from the harmful effects of direct anthropogenic stressors. The present study reports historical chronology over a 24-year period (1992-2016) of coral extension rate (cm yr-1), skeletal density (g cm-3), and calcification rate (g cm-2 yr-1) of the reef-building coral Orbicella faveolata at the remote reef Cayo Arenas, Campeche Bank, in the south-eastern Gulf of Mexico. The relationships between the three sclerochronological features show that O. faveolata uses its calcification resources to build denser skeletons. Chronological trends indicate that coral extension increased, skeletal density and calcification rate decreased (33% calcification rate) over time. The results reveal that despite the remoteness of the locality the maximum SST has been increased, and the coral calcification rate decreased over time. If the temperature continues to rise, there is a conceivable risk of experiencing a decline in reef-building coral species. This scenario, in turn, could pose a significant threat, endangering not only the framework of coral reefs but also their ecological functionality, even within remote Atlantic reef ecosystems.

The δ15N in Orbicella faveolata organic matter reveals anthropogenic impact by sewage inputs in a Mexican Caribbean coral reef lagoon.

Coral-reef ecosystems provide essentials services to human societies, representing the most important source of income (e.g., tourism and artisanal fishing) for many coastal developing countries. In the Caribbean region, most touristic and coastal developments are in the vicinity of coral reefs where they may contribute to reef degradation. Here we evaluated the influence of sewage inputs in the coral reef lagoon of Puerto Morelos during a period of 40 years (1970-2012). Annual δ15N values were determined in the organic matter (OM) extracted from coral skeletons of Orbicella faveolata. Average protein content in the OM was 0.33 mg of protein g-1 CaCO3 (±0.10 SD) and a 0.03% of OM relative to the sample weight (n =100). The average of N g-1 CaCO3 was 0.002% (± 0.001 SD). The results showed an increase (p < 0.001) in δ15N over the time, positively correlated with population growth derived from touristic development. These findings emphasize the need to generate urban-planning remediation strategies that consider the impact on natural environments, reduce sewage pollution, and mitigate local stressors that threaten the status of coral-reef communities in the Caribbean region.

Coral calcification and carbonate production in the eastern tropical Pacific: The role of branching and massive corals in the reef maintenance.

Hermatypic corals have the potential to construct calcium carbonate (CaCO3 ) reef-framework, maintain habitats tridimensionality and contribute to both the biogeochemical and the geo-ecological functionality of coral reefs. However, in the past decades, coral reef growth capacity has been affected by multiple and cumulative anthropogenic stressors, threating the reef functionality and their ecosystem goods and services provision to humankind. This study evaluated temporal changes in geobiological growth characteristics as a function of live coral cover, calcification rate (extension rate and skeletal density) and coral carbonate production at Islas Marias archipelago from the eastern tropical Pacific, using historical data obtained in 2007 (López-Pérez et al., 2015, Marine Ecology, 37, 679) and data obtained through field and laboratory research between 2015 and 2018. Overall, live coral cover decreased (82%), where Pocillopora spp. corals reduced from 26% in 2007 to 4% in 2018, in contrast, Pavona spp. declined from 4.1% to 3.7% over the same period. Coral carbonate production ranged between 1.78 and 10.65 kg CaCO3  m-2  yr-1 , with a significant difference (threefold) between reef zones (shallow vs deep), highlighting the higher carbonate production at deep-reef sites. Coral cover, carbonate production and sclerocronological characteristics showed a decrease rate (between 30 and 60%) associated with thermal anomaly events such as La Niña (2010-2011) and El Niño (2014-2016), with positive sights of recovery (twofold) during the following years 2017-2018. This study provides evidence that massive Pavona and branching Pocillopora corals are key reef-building species at Islas Marias archipelago, due to their capability of sustaining live coral coverage and carbonate through thermal disturbance periods. Revealing, that corals at mid-water depths (>10 m) may significantly contribute to the long-term stability of biogenic reef-framework, and geo-ecological functionality of the eastern tropical Pacific reefs.

Plutonium in coral archives: A good primary marker for an Anthropocene type section.

While we officially live in the Holocene epoch, global warming and many other impacts of global change have led to the proposal and wide adoption of the Anthropocene to define the present geological epoch. The Anthropocene Working Group (AWG) established that it should be treated as a formal stratigraphic unit, demonstrated by a reference level commonly known as "golden spike", still under discussion. Here we show that the onset of bomb-derived plutonium recorded in two banded massive corals from the Caribbean Sea is consistent (1955-1956 CE), so sites far from nuclear testing grounds are potentially suitable to host a type section of the Anthropocene. Coastal coral demonstration sites are feasible, could foster economic development, and may serve as focal points for scientific dissemination and environmental education.

Uncertainty and variability of extension rate, density and calcification rate of a hermatypic coral (Orbicella faveolata).

Skeleton growth variables of hermatypic corals, such as extension rate, density and calcification rate, are widely used to study coral response to environmental stressors, establish chronological age models and reconstruct the evolution of key climate variables. In this work, we addressed methodological aspects of the measurement of coral growth variables and the implications of their variability. A core of Orbicella faveolata was collected from the Puerto Morelos coral reef, in the Mexican Caribbean, and we measured and analysed 10 parallel transects of a core slab, covering 30 years. Density calibration was performed by measuring a high-quality and well-characterised wedge of Tridacna maxima, and the interval of interest was adjusted to the measured coral optical densities. The measurement uncertainties of extension rate, density and calcification rate were 0.011%, 1.1% and 1.6%, respectively. However, for density and calcification rate, overall variability was 29% and 33%, respectively, of which about half was attributed to intra-band growth variability. The intra-band variability of extension rate was only 0.68%, indicating the suitability of extension rate as a precise environmental proxy. These results likely differ by coral species, environments and experimental conditions, such as the exact location of the core within the colony and the method used to determine density. Uncertainties of coral growth variables should be carefully considered when reconstructing past environmental conditions.

Calcification and growth rate recovery of the reef-building Pocillopora species in the northeast tropical Pacific following an ENSO disturbance.

Pocilloporids are one of the major reef-building corals in the eastern tropical Pacific (ETP) and also the most affected by thermal stress events, mainly those associated with El Niño/Southern Oscillation (ENSO) periods. To date, coral growth parameters have been poorly reported in Pocillopora species in the northeastern region of the tropical Pacific. Monthly and annual growth rates of the three most abundant morphospecies (P. cf. verrucosa, P. cf. capitata, and P. cf. damicornis) were evaluated during two annual periods at a site on the Pacific coast of Mexico. The first annual period, 2010-2011 was considered a strong ENSO/La Niña period with cool sea surface temperatures, then followed by a non-ENSO period in 2012-2013. The linear extension rate, skeletal density, and calcification rate averaged (±SD) were 2.31 ± 0.11 cm yr-1, 1.65 ± 0.18 g cm-3, 5.03 ± 0.84 g cm-2 yr-1 respectively, during the strong ENSO event. In contrast, the respective non-ENSO values were 3.50 ± 0.64 cm yr-1, 1.70 ± 0.18 g cm-3, and 6.02 ± 1.36 g cm-2 yr-1. This corresponds to 52% and 20% faster linear extension and calcification rates, respectively, during non-ENSO period. The evidence suggests that Pocillopora branching species responded positively with faster growth rates following thermal anomalies, which allow them to maintain coral communities in the region.

Biological responses of the coral Montastraea annularis to the removal of filamentous turf algae.

Coral reef degradation increases coral interactions with filamentous turf algae (FTA) and macroalgae, which may result in chronic stress for the corals. We evaluated the effects of short (2.5 month) and long (10 month) periods of FTA removal on tissue thickness (TT), zooxanthellae density (ZD), mitotic index (MI), and concentration of chlorophyll a (Chl a) in Montastraea annularis at the beginning and end of gametogenesis. Ramets (individual lobes within a colony) consistently surrounded by FTA and ramets surrounded by crustose coralline algae (CCA) were used as controls. FTA removal reduced coral stress, indicated by increased TT and ZD and lower MI. The measured effects were similar in magnitude for the short and long periods of algal removal. Ramets were more stressed at the end of gametogenesis compared with the beginning, with lower ZD and Chl a cm(-2), and higher MI. However, it was not possible to distinguish the stress caused by the presence of FTA from that caused by seasonal changes in seawater temperature. Ramets surrounded by CCA showed less stress in comparison with ramets surrounded by FTA: with higher TT, Chl a cm(-2) and ZD, and lower MI values. Coral responses indicated that ramets with FTA suffered the most deleterious effects and contrasted with those measured in ramets surrounded by CCA. According to published studies and our observations, there could be at least six mechanisms associated to FTA in the stress caused to M. annularis by FTA. Owing to the high cover of FTA (in contrast to macroalgae and CCA) in the Caribbean, the chronic stress, the overgrowth and mortality that this functional algal group can cause on M. annularis species complex, a further decline of this important reef-building coral in the Caribbean is expected.

Shifts in coral-assemblage composition do not ensure persistence of reef functionality.

Coral communities are changing rapidly worldwide through loss of coral cover and shifts in species composition. Although many reef-building corals are likely to decline, some weedy opportunistic species might increase in abundance. Here we explore whether the reshuffling of species can maintain ecosystem integrity and functioning. Using four common Caribbean reef-building coral genera we modeled rates of reef construction and complexity. We show that shifting coral assemblages result in rapid losses in coral-community calcification and reef rugosity that are independent of changes in the total abundance of reef corals. These losses are considerably higher than those recently attributed to climate change. Dominance patterns of coral assemblages seem to be the most important driver of the functioning of coral reefs and thus, the future of these ecosystems might depend not only on reductions of local and global stressors, but also on the maintenance of keystone coral species.

Avoiding coral reef functional collapse requires local and global action.

Coral reefs face multiple anthropogenic threats, from pollution and overfishing to the dual effects of greenhouse gas emissions: rising sea temperature and ocean acidification. While the abundance of coral has declined in recent decades, the implications for humanity are difficult to quantify because they depend on ecosystem function rather than the corals themselves. Most reef functions and ecosystem services are founded on the ability of reefs to maintain their three-dimensional structure through net carbonate accumulation. Coral growth only constitutes part of a reef's carbonate budget; bioerosion processes are influential in determining the balance between net structural growth and disintegration. Here, we combine ecological models with carbonate budgets and drive the dynamics of Caribbean reefs with the latest generation of climate models. Budget reconstructions using documented ecological perturbations drive shallow (6-10 m) Caribbean forereefs toward an increasingly fragile carbonate balance. We then projected carbonate budgets toward 2080 and contrasted the benefits of local conservation and global action on climate change. Local management of fisheries (specifically, no-take marine reserves) and the watershed can delay reef loss by at least a decade under "business-as-usual" rises in greenhouse gas emissions. However, local action must be combined with a low-carbon economy to prevent degradation of reef structures and associated ecosystem services.

Sensitivity of calcification to thermal stress varies among genera of massive reef-building corals.

Reductions in calcification in reef-building corals occur when thermal conditions are suboptimal, but it is unclear how they vary between genera in response to the same thermal stress event. Using densitometry techniques, we investigate reductions in the calcification rate of massive Porites spp. from the Great Barrier Reef (GBR), and P. astreoides, Montastraea faveolata, and M. franksi from the Mesoamerican Barrier Reef (MBR), and correlate them to thermal stress associated with ocean warming. Results show that Porites spp. are more sensitive to increasing temperature than Montastraea, with calcification rates decreasing by 0.40 g cm(-2) year(-1) in Porites spp. and 0.12 g cm(-2) year(-1) in Montastraea spp. for each 1°C increase. Under similar warming trends, the predicted calcification rates at 2100 are close to zero in Porites spp. and reduced by 40% in Montastraea spp. However, these predictions do not account for ocean acidification. Although yearly mean aragonite saturation (Ω(ar)) at MBR sites has recently decreased, only P. astreoides at Chinchorro showed a reduction in calcification. In corals at the other sites calcification did not change, indicating there was no widespread effect of Ω(ar) changes on coral calcification rate in the MBR. Even in the absence of ocean acidification, differential reductions in calcification between Porites spp. and Montastraea spp. associated with warming might be expected to have significant ecological repercussions. For instance, Porites spp. invest increased calcification in extension, and under warming scenarios it may reduce their ability to compete for space. As a consequence, shifts in taxonomic composition would be expected in Indo-Pacific reefs with uncertain repercussions for biodiversity. By contrast, Montastraea spp. use their increased calcification resources to construct denser skeletons. Reductions in calcification would therefore make them more susceptible to both physical and biological breakdown, seriously affecting ecosystem function in Atlantic reefs.