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Promoting resilience is highly relevant to preserving biodiversity and ecosystem functioning. For coral reefs, parrotfish protection emerged as a mainstream action for reversing the degradation experienced by these systems. The rationale is that restoring their populations will increase grazing activity and reinforce control of fast‐growing macroalgae, facilitating coral cover recovery. A lack of a link between parrotfish trends and macroalgae and coral cover trends at a large scale has, however, often been the case. Suggesting more complex underlying dynamics that should be reexamined. In this review, we discuss how lumping parrotfish species as if they were functionally redundant may obscure trends. And how a lack of appreciation of other functions around the parrotfish paradigm, specifically bioerosion, may have unforeseen and potentially adverse effects on degraded reefs. We show that bioerosion responded more directly and quickly to spatial and temporal changes in parrotfish assemblages than macroalgae consumption, arguably due to the varying vulnerability among Caribbean parrotfishes to fisheries and habitat loss. For highly degraded reefs, positive changes in parrotfish populations could hence compromise the remaining coral skeleton structures and the reef framework, further accentuating reef degradation, where increases in macroalgae consumption could not necessarily compensate for higher rates of bioerosion.

Phase shifts from hard coral to macroalgae have led to the formulation of a top-down herbivory paradigm, whose assumption is that a reduction in herbivory is the primary driver of these changes. Caribbean parrotfish from Scarus and Sparisoma genera are usually known as main reef herbivorous. Yet, they are a diverse group of organisms that perform multiple functions, including the bioerosion of reef structures. Generalizing functions at the group level likely explains why the direct effects of parrotfish on macroalgae regulation are not always evident. In this study, we tested the hypothesis that parrotfish potential functions are strongly linked to the habitat’s benthic characteristics. Furthermore, we expect that the parrotfish bioerosion potential will be highly sensitive to changes in benthic conditions, while herbivory will be more robust. We conducted in situ benthic and parrotfish surveys across the diverse reefscape of the remote Alacranes Reef, the most extensive system in the Gulf of Mexico. Both bioerosion and herbivory potential were highest in the most complex and structured sites, while only macroalgae removal was high in deep low-coral cover sites dominated by fleshy macroalgae. Interestingly, both functions were highly diminished in shallow and reticulated inner reefs dominated by turf algae and cyanobacteria, suggesting that even the herbivory function can be depleted under unfavorable benthic conditions. Our findings highlight the need to reconsider parrotfish management strategies to account for the specific roles of different species and consider reciprocal benthic-fish interactions.

Diseases are major drivers of the deterioration of coral reefs and are linked to major declines in coral abundance, reef functionality, and reef-related ecosystems services. An outbreak of a new disease is currently rampaging through the populations of the remaining reef-building corals across the Caribbean region. The outbreak was first reported in Florida in 2014 and reached the northern Mesoamerican Reef by summer 2018, where it spread across the ~450-km reef system in only a few months. Rapid spread was generalized across all sites and mortality rates ranged from 94% to <10% among the 21 afflicted coral species. Most species of the family Meandrinadae (maze corals) and subfamily Faviinae (brain corals) sustained losses >50%. This single event further modified the coral communities across the region by increasing the relative dominance of weedy corals and reducing reef functionality, both in terms of functional diversity and calcium carbonate production. This emergent disease is likely to become the most lethal disturbance ever recorded in the Caribbean, and it will likely result in the onset of a new functional regime where key reef-building and complex branching acroporids, an apparently unaffected genus that underwent severe population declines decades ago and retained low population levels, will once again become conspicuous structural features in reef systems with yet even lower levels of physical functionality. A new deadly coral disease, known as stony coral tissue loss disease, has modified the coral communities across the Caribbean region by disproportionately affecting key reef-building corals and reducing reef functionality.

Caribbean reef corals have experienced unprecedented declines from climate change, anthropogenic stressors and infectious diseases in recent decades. Since 2014, a highly lethal, new disease, called stony coral tissue loss disease, has impacted many reef-coral species in Florida. During the summer of 2018, we noticed an anomalously high disease prevalence affecting different coral species in the northern portion of the Mexican Caribbean. We assessed the severity of this outbreak in 2018/2019 using the AGRRA coral protocol to survey 82 reef sites across the Mexican Caribbean. Then, using a subset of 14 sites, we detailed information from before the outbreak (2016/2017) to explore the consequences of the disease on the condition and composition of coral communities. Our findings show that the disease outbreak has already spread across the entire region by affecting similar species (with similar disease patterns) to those previously described for Florida. However, we observed a great variability in prevalence and tissue mortality that was not attributable to any geographical gradient. Using long-term data, we determined that there is no evidence of such high coral disease prevalence anywhere in the region before 2018, which suggests that the entire Mexican Caribbean was afflicted by the disease within a few months. The analysis of sites that contained pre-outbreak information showed that this event considerably increased coral mortality and severely changed the structure of coral communities in the region. Given the high prevalence and lethality of this disease, and the high number of susceptible species, we encourage reef researchers, managers and stakeholders across the Western Atlantic to accord it the highest priority for the near future.

Coral growth is an important metric of coral health and underpins reef-scale functional attributes such as structural complexity and calcium carbonate production. There persists, however, a paucity of growth data for most reef-building regions, especially for coral species whose skeletal architecture prevents the use of traditional methods such as coring and Alizarin staining. We used structure-from-motion photogrammetry to quantify a range of colony-scale growth metrics for six coral species in the Mexican Caribbean and present a newly developed workflow to measure colony volume change over time. Our results provide the first growth metrics for two species that are now major space occupiers on Caribbean reefs, Agaricia agaricites and Agaricia tenuifolia . We also document higher linear extension, volume increase and calcification rates within back reef compared to fore reef environments for four other common species: Orbicella faveolata , Porites astreoides , Siderastrea siderea and Pseudodiploria strigosa . Linear extension rates in our study were lower than those obtained via computed tomography (CT) scans of coral cores from the same sites, as the photogrammetry method averages growth in all dimensions, while the CT method depicts growth only along the main growth axis (upwards). The comparison of direct volume change versus potential volume increase calculated from linear extension emphasizes the importance of assessing whole colony growth to improve calcification estimates. The method presented here provides an approach that can generate accurate calcification estimates alongside a range of other whole-colony growth metrics in a non-invasive way.

We studied 2 seagrass beds in the Mexican Caribbean that were grazed by green turtles. Grazing impact was moderate at Puerto Morelos (<20% of the area was grazed), whereas at Akumal, 45 to 55% of the bed was grazed. The turtles practiced rotational (cultivation) grazing and thereby increased the nitrogen leaf content in the dominant seagrass Thalassia testudinum by 30 to 33%. Average seagrass leaf productivity decreased under grazing at Puerto Morelos from 3.09 to 0.93 g dry wt m−2 d−1, whereas it did not change significantly at Akumal (0.88 to 1.17 g dry wt m−2 d−1). At Puerto Morelos, the turtles maintained grazing plots for 13 mo to >2 yr, creating a mosaic of patches that were grazed, ungrazed or recovering from grazing. Cover of the faster-growing Halodule wrightii and rhizophytic algae increased in the grazing plots, whereas that of the dominant but slow-growing T. testudinum decreased. After the turtles stopped grazing the plots, the cover of T. testudinum gradually increased again, but recovery to pre-grazing conditions lasted >1 yr and was not observed in this study. Cover of Syringodium filiforme decreased when the turtles opened up new grazing areas but remained stable afterwards because the turtles usually avoided consumption of this seagrass. At Akumal, the system approached carrying capacity for grazing, and the turtles returned to grazing plots that had not fully recovered from past grazing. Here, the dominant climax seagrass T. testudinum became less abundant from 2008 until 2012, resulting in a less patchy landscape with low seagrass biomass and higher prevalence of the early seral species H. wrightii.

The ecology of coral reefs is rapidly shifting from historical baselines. One key-question is whether under these new, less favourable ecological conditions, coral reefs will be able to sustain key geo-ecological processes such as the capacity to accumulate carbonate structure. Here, we use data from 34 Caribbean reef sites to examine how the carbonate production, net erosion and net carbonate budgets, as well as the organisms underlying these processes, have changed over the past 15 years in the absence of further severe acute disturbances. We find that despite fundamental benthic ecological changes, these ecologically shifted coral assemblages have exhibited a modest but significant increase in their net carbonate budgets over the past 15 years. However, contrary to expectations this trend was driven by a decrease in erosion pressure, largely resulting from changes in the abundance and size-frequency distribution of parrotfishes, and not by an increase in rates of coral carbonate production. Although in the short term, the carbonate budgets seem to have benefitted marginally from reduced parrotfish erosion, the absence of these key substrate grazers, particularly of larger individuals, is unlikely to be conducive to reef recovery and will thus probably lock these reefs into low budget states.

Anthropogenic and natural disturbances have modified coral reef ecosystems over the last decades, ultimately, exerting negative impacts on the persistence of the carbonated matrix and the physical function. In 2014, the Caribbean region saw the onset of a new deadly coral disease, often known as the stony coral tissue loss disease. In summer of 2018, the outbreak was first reported in the Mexican Caribbean in a diving site named ‘Fish Market’. From July 2018 to March 2019, surveys were made to assess the impacts of this new outbreak in the stony coral community in terms of composition and the effect on the coral community calcification. This disease outbreak had severe consequences for this site. Several colonies of susceptible species were lost, which resulted in significant changes in the coral community composition and reductions in the gross carbonate production in a period of only 8 months.

The ecology of coral reefs is rapidly shifting from historical baselines. One key-question is whether under these new, less favourable ecological conditions, coral reefs will be able to sustain key geo-ecological processes such as the capacity to accumulate carbonate structure. Here, we use data from 34 Caribbean reef sites to examine how the carbonate production, net erosion and net carbonate budgets, as well as the organisms underlying these processes, have changed over the past 15 years in the absence of further severe acute disturbances. We find that despite fundamental benthic ecological changes, these ecologically shifted coral assemblages have exhibited a modest but significant increase in their net carbonate budgets over the past 15 years. However, contrary to expectations this trend was driven by a decrease in erosion pressure, largely resulting from changes in the abundance and size-frequency distribution of parrotfishes, and not by an increase in rates of coral carbonate production. Although in the short term, the carbonate budgets seem to have benefitted marginally from reduced parrotfish erosion, the absence of these key substrate grazers, particularly of larger individuals, is unlikely to be conducive to reef recovery and will thus probably lock these reefs into low budget states.

Diseases are major drivers of the deterioration of coral reefs and are linked to major declines in coral abundance, reef functionality, and reef-related ecosystems services. An outbreak of a new disease is currently rampaging through the populations of the remaining reef-building corals across the Caribbean region. The outbreak was first reported in Florida in 2014 and reached the northern Mesoamerican Reef by summer 2018, where it spread across the ~450-km reef system in only a few months. Rapid spread was generalized across all sites and mortality rates ranged from 94% to <10% among the 21 afflicted coral species. Most species of the family Meandrinadae (maze corals) and subfamily Faviinae (brain corals) sustained losses >50%. This single event further modified the coral communities across the region by increasing the relative dominance of weedy corals and reducing reef functionality, both in terms of functional diversity and calcium carbonate production. This emergent disease is likely to become the most lethal disturbance ever recorded in the Caribbean, and it will likely result in the onset of a new functional regime where key reef-building and complex branching acroporids, an apparently unaffected genus that underwent severe population declines decades ago and retained low population levels, will once again become conspicuous structural features in reef systems with yet even lower levels of physical functionality.