Caribbean Coral Reef Ecosystems Research Articles

Stony coral tissue loss disease: a review of emergence, impacts, etiology, diagnostics, and intervention

Stony coral tissue loss disease (SCTLD) is destructive and poses a significant threat to Caribbean coral reef ecosystems. Characterized by the acute loss of coral tissue, SCTLD has impacted over 22 stony coral species across the Caribbean region, leading to visible declines in reef health. Based on the duration, lethality, host range, and spread of this disease, SCTLD is considered the most devastating coral disease outbreak ever recorded. Researchers are actively investigating the cause and transmission of SCTLD, but the exact mechanisms, triggers, and etiological agent(s) remain elusive. If left unchecked, SCTLD could have profound implications for the health and resilience of coral reefs worldwide. To summarize what is known about this disease and identify potential knowledge gaps, this review provides a holistic overview of SCTLD research, including species susceptibility, disease transmission, ecological impacts, etiology, diagnostic tools, host defense mechanisms, and treatments. Additionally, future research avenues are highlighted, which are also relevant for other coral diseases. As SCTLD continues to spread, collaborative efforts are necessary to develop effective strategies for mitigating its impacts on critical coral reef ecosystems. These collaborative efforts need to include researchers from diverse backgrounds and underrepresented groups to provide additional perspectives for a disease that requires creative and urgent solutions.

Broadscale coral disease interventions elicit efficiencies in endemic disease response

The presence and abundance of reef-building corals are crucial to the long-term existence of Caribbean coral reef ecosystems, providing both direct and indirect, local and global, ecological, economic, and social benefits. In 2014, stony coral tissue loss disease (SCTLD) was first identified in southeast Florida and remains endemic to the region, while continuing to spread throughout the Caribbean. Effective in situ intervention treatments using antibiotic paste can halt lesion progression on Montastraea cavernosa up to 90% of the time. This study investigated intervention activities over a three-year period to identify efficiencies in disease response. Since May 2019, 1,037 corals, >85% of which were M. cavernosa, were treated during disease intervention dives in southeast Florida. Treated coral density, the number of treated corals per meter along a dive track, was significantly higher in the first year compared to subsequent years and displayed annual peaks in late summer each year. Season significantly influenced treatment density, leading to higher values in the wet season across all years, 2019 to 2022. Areas of highest treatment density were identified between Haulover Inlet and Government Cut near Miami and Hillsboro Inlet in northern Broward County. Areas with the highest treatment density were only identified in the first year, suggesting that broadscale interventions may have decreased disease prevalence in subsequent years. Results indicate that in endemic areas with sporadic and dynamic disease prevalence, intervention efforts should be weighted proportionally across space and time to maximize intervention efficiency. This study provides optimistic results for the potential of interventions reducing disease prevalence and supports that disease interventions are an effective coral restoration tool that can decrease the increasing burden on post hoc coral restoration.

Long-Term Change in Caribbean Reef Water Quality and Ecosystem Health

Caribbean coral reef ecosystems have declined dramatically since systematic monitoring began in the 1970s. Over the past 50 years, they have lost between 50-80% of reef-building corals, their principal ecosystem architects. These declines have been attributed to climate change, introduction of invasive species, overfishing, and land-based pollution. Although recognized as a major stressor to corals, the role of land-based pollution in Caribbean coral declines has not been quantified due to the lack of consistent reef water quality monitoring. As part of our CPN-funded working group “Integrating paleo and historical data into coral reef management and policy”, we compiled several metrics of reef water quality from paleoecological data and disparate monitoring efforts across the Caribbean to document multidecadal-scale change over a period of intensifying coastal land alteration. We then compared water quality trends with trends in living coral cover from these same reefs to assess the role of water quality declines from land-based runoff on coral reef ecosystem health. These analyses show that (1) an array of historical data exist for reconstructing trends in Caribbean reef water quality that are in disparate repositories and remain mostly untapped, (2) reefs across the Caribbean have experienced water quality declines over the past half century, even offshore sites that were previously thought to be unaffected by land-based runoff, (3) correlations between reef water quality and coral abundance trends are detected at select sites where water quality monitoring protocols were consistent and sustained for multiple decades, and (4) water quality declines are asynchronous across sites and are likely related to differing timing and histories of land alteration.

A century of warming on Caribbean reefs

The world’s oceans are warming at an unprecedented rate, causing dramatic changes to coastal marine systems, especially coral reefs. We used three complementary ocean temperature databases (HadISST, Pathfinder, and OISST) to quantify change in thermal characteristics of Caribbean coral reefs over the last 150 years (1871–2020). These sea surface temperature (SST) databases included in situ and satellite-derived measurements at multiple spatial resolutions. We also compiled a Caribbean coral reef database identifying 5,326 unique reefs across the region. We found that Caribbean reefs have been warming for at least a century. Regionally reef warming began in 1915, and for four of the eight Caribbean ecoregions we assessed, significant warming was detected for the latter half of the nineteenth century. Following the global mid-twentieth century stasis, warming resumed on Caribbean reefs in the early 1980s in some ecoregions and in the 1990s for others. On average, Caribbean reefs warmed by 0.18°C per decade during this period, ranging from 0.17°C per decade on Bahamian reefs (since 1988) to 0.26°C per decade on reefs within the Southern and Eastern Caribbean ecoregions (since 1981 and 1984, respectively). If this linear rate of warming continues, these already threatened ecosystems would warm by an additional ~1.5°C on average by 2100. We also found that marine heatwave (MHW) events are increasing in both frequency and duration across the Caribbean. Caribbean coral reefs now experience on average 5 MHW events annually, compared to 1 per year in the early 1980s, with recent events lasting on average 14 days. These changes in the thermal environment, in addition to other stressors including fishing and pollution, have caused a dramatic shift in the composition and functioning of Caribbean coral reef ecosystems.

Development of a reef fish biological condition gradient model with quantitative decision rules for the protection and restoration of coral reef ecosystems

Coral reef ecosystems are declining due to multiple interacting stressors. A bioassessment framework focused on stressor-response associations was developed to help organize and communicate complex ecological information to support coral reef conservation. This study applied the Biological Condition Gradient (BCG), initially developed for freshwater ecosystems, to fish assemblages of U.S. Caribbean coral reef ecosystems. The reef fish BCG describes how biological conditions changed incrementally along a gradient of increasing anthropogenic stress. Coupled with physical and chemical water quality data, the BGC forms a scientifically defensible basis to prioritize, protect and restore water bodies containing coral reefs. Through an iterative process, scientists from across the U.S. Caribbean used fishery-independent survey data and expert knowledge to develop quantitative decision rules to describe six levels of coral reef ecosystem condition. The resultant reef fish BCG provides an effective tool for identifying healthy and degraded coral reef ecosystems and has potential for global application.

Socio-ecological dynamics of Caribbean coral reef ecosystems and conservation opinion propagation

The Caribbean coral reef ecosystem has experienced a long history of deterioration due to various stressors. For instance, over-fishing of parrotfish – an important grazer of macroalgae that can prevent destructive overgrowth of macroalgae – has threatened reef ecosystems in recent decades and stimulated conservation efforts such as the formation of marine protected areas. Here we develop a mathematical model of coupled socio-ecological interactions between reef dynamics and conservation opinion dynamics to better understand how natural and human factors interact individually and in combination to determine coral reef cover. We find that the coupling opinion and reef systems generates complex dynamics that are difficult to anticipate without use of a model. For instance, instead of converging to a stable state of constant coral cover and conservationist opinion, the system can oscillate between low and high live coral cover as human opinion oscillates in a boom-bust cycle between complacency and concern. Out of various possible parameter manipulations, we also find that raising awareness of coral reef endangerment best avoids counter-productive nonlinear feedbacks and always increases and stabilizes live coral reef cover. In conclusion, an improved understanding of coupled opinion-reef dynamics under anthrogenic stressors is possible using coupled socio-ecological models, and such models should be further researched.

Invasive lionfish preying on critically endangered reef fish

Caribbean coral reef ecosystems are at the forefront of a global decline and are now facing a new threat: elimination of vulnerable species by the invasive lionfish (Pterois spp.). In addition to being threatened by habitat destruction and pollution, the critically endangered social wrasse (Halichoeres socialis), endemic to Belize’s inner barrier reef, has a combination of biological traits (small size, schooling, and hovering behavior) that makes it a target for the invasive lionfish. Based on stomach content analyses, this small fish comprises almost half of the lionfish diet at the inner barrier reef in Belize. The combination of lionfish predation, limited range, and ongoing habitat destruction makes the social wrasse the most threatened coral reef fish in the world. Other species with small range and similar traits occur elsewhere in the Caribbean and face similar risks.

Shifting Baselines and The Extinction of The Caribbean Monk Seal

The recent extinction of the Caribbean monk seal Monachus tropicalis has been considered an example of a human-caused extinction in the marine environment, and this species was considered a driver of the changes that have occurred in the structure of Caribbean coral reef ecosystems since colonial times. I searched archaeological records, historical data, and geographic names (used as a proxy of the presence of seals) and evaluated the use and quality of these data to conclude that since prehistoric times the Caribbean monk seal was always rare and vulnerable to human predation. This finding supports the hypothesis that in AD 1500, the Caribbean monk seal persisted as a small fragmented population in which individuals were confined to small keys, banks, or isolated islands in the Gulf of Mexico and the Caribbean Sea. This hypothesis is contrary to the assumption that the species was widespread and abundant historically. The theory that the main driver of monk seal extinction was harvesting for its oil for use in the sugar cane industry of Jamaica during the 18th century is based primarily on anecdotal information and is overemphasized in the literature. An analysis of reported human encounters with this species indicates monk seal harvest was an occasional activity, rather than an ongoing enterprise. Nevertheless, given the rarity of this species and its restricted distribution, even small levels of hunting or specimen collecting must have contributed to its extinction, which was confirmed in the mid-20th century. Some sources had been overlooked or only partially reviewed, others misinterpreted, and a considerable amount of anecdotal information had been uncritically used. Critical examination of archaeological and historical records is required to infer accurate estimations of the historical abundance of a species. In reconstructing the past to address the shifting baseline syndrome, it is important to avoid selecting evidence to confirm modern prejudices.

Reef Sharks Exhibit Site-Fidelity and Higher Relative Abundance in Marine Reserves on the Mesoamerican Barrier Reef

Carcharhinid sharks can make up a large fraction of the top predators inhabiting tropical marine ecosystems and have declined in many regions due to intense fishing pressure. There is some support for the hypothesis that carcharhinid species that complete their life-cycle within coral reef ecosystems, hereafter referred to as “reef sharks”, are more abundant inside no-take marine reserves due to a reduction in fishing pressure (i.e., they benefit from marine reserves). Key predictions of this hypothesis are that (a) individual reef sharks exhibit high site-fidelity to these protected areas and (b) their relative abundance will generally be higher in these areas compared to fished reefs. To test this hypothesis for the first time in Caribbean coral reef ecosystems we combined acoustic monitoring and baited remote underwater video (BRUV) surveys to measure reef shark site-fidelity and relative abundance, respectively. We focused on the Caribbean reef shark (Carcharhinus perezi), the most common reef shark in the Western Atlantic, at Glover's Reef Marine Reserve (GRMR), Belize. Acoustically tagged sharks (N = 34) were detected throughout the year at this location and exhibited strong site-fidelity. Shark presence or absence on 200 BRUVs deployed at GRMR and three other sites (another reserve site and two fished reefs) showed that the factor “marine reserve” had a significant positive effect on reef shark presence. We rejected environmental factors or site-environment interactions as predominant drivers of this pattern. These results are consistent with the hypothesis that marine reserves can benefit reef shark populations and we suggest new hypotheses to determine the underlying mechanism(s) involved: reduced fishing mortality or enhanced prey availability.

Diel movements of fishes linked to benthic seascape structure in a Caribbean coral reef ecosystem

Many common fishes associated with Caribbean coral reef ecosystems use resources from more than 1 patch type during routine daily foraging activities. Few studies have provided direct evidence of connectivity across seascapes, and the importance of benthic seascape structure on movement behavior is poorly known. To address this knowledge gap, we coupled hydro-acoustic technology to track fish with seafloor mapping and pattern analysis techniques from landscape ecol- ogy to quantify seascape structure. Bluestriped grunts Haemulon sciurus and schoolmaster snapper Lutjanus apodus were tracked over 24 h periods using boat-based acoustic telemetry. Movement pathways, and day and night activity spaces were mapped using geographical information system (GIS) tools, and seafloor structure within activity spaces was mapped from high-resolution aerial photography and quantified using spatial pattern metrics. For both fish species, night activity spaces were significantly larger than day activity spaces. Fish exhibited a daytime preference for seascapes with aggregate coral reef and colonized bedrock, then shifted to night activity spaces with lower- complexity soft sediment including sand, seagrass, and scattered coral/rock. Movement path com- plexity was negatively correlated with seascape complexity. This demonstrates direct connectivity across multiple patch types and represents the first study to apply quantitative landscape ecology techniques to examine the movement ecology of marine fish. The spatially explicit approach facili- tates understanding to the linkages between biological processes and the heterogeneity of the land- scape. Such studies are essential for identifying ecologically relevant spatial scales, delineating essen- tial fish habitat and designing marine protected areas.

Complex migration and the development of genetic structure in subdivided populations: an example from Caribbean coral reef ecosystems

A matrix‐based projection model is used in conjunction with the results of a coupled bio‐physical dispersal model to examine the spread of alleles through subdivided populations over time, and the associated development of genetic structural patterns. Applying this approach, it becomes possible to quantitatively evaluate the contribution of spatially explicit migration towards patterns of genetic structure observed in the field. To provide a concrete example, the model was used to examine genetic dispersal between coral reef patches of the Caribbean. Using generic life‐history parameters, the model shows the formation of a strong genetic break between eastern and western patches, as well as the development of a gradient along the length of the Bahamian archipelago, corresponding with evidence previously collected for coral and fish species. The data also suggest that Jamaica and the Cayman Islands are important stepping stones between the reefs of the northern Caribbean (Hispaniola and the Bahamas) and the Mesoamerican Barrier Reef. The model provides an effective means of evaluating regional‐scale genetic connectivity through time and identifying natural clusters of genetic exchange.

New tools for resolving phylogenies: a systematic revision of the Convolutidae (Acoelomorpha, Acoela)

Molecular sequence data, morphological characters of spermatozoa, and newly obtained morphological characters of penis musculature are used here to revise the systematics of the family Convolutidae (Acoela). Species having isodiametric penes with non-anastomosing longitudinal muscles are transferred to the family Isodiametridae fam. nov. Species with longitudinal penis muscle fibres that anastomose or cross-over each other remain in the Convolutidae. Some species of the genera Convoluta and Conaperta (Convolutidae) are transferred to the genus Isodiametra gen. nov. (Isodiametridae fam. nov.). The genus Stomatricha (Otocelididae) is transferred to the family Convolutidae. Convoluta opisthandropora (Convolutidae) is transferred to the genus Pseudohaplogonaria (Haploposthiidae). Aphanostoma sanguineum (Convolutidae) is transferred to the genus Pseudactinoposthia (Actinoposthiidae). Zusammenfassung Molekulare Sequenzdaten, Spermien-Morphologie und erstmals ermittelte morphologische Merkmale der Penismuskulatur werden herangezogen, um die Verwandtschaftsverhaltnisse innerhalb der Familie Convolutidae (Acoela) neu zu beleuchten. Dabei werden Arten mit isodiametrischen Penes mit nicht anastomosierender Langsmuskulatur in die neue Familie Isodiametridae gestellt, wahrend Arten mit longitudinalen Penis-Muskelfasern, die sich verbunden oder einanderuberkreuzen, innerhalb der Convolutidae belassen. Einige Arten der Gattungen Convoluta und Conaperta (Convolutidae) werden in die neue Gattung Isodiametra gen. nov. (Isodametridae fam. nov.) gestellt. Die Gattung Stomatricha (Otocelididae) wird in die Familie Convolutidae uberfuhrt. Convoluta opisthandropora (Convolutidae) wird in die Gattung Pseudohaplogonaria (Haploposthiidae) gestellt und Aphanostoma sanguineum (Convolutidae) in die Gattung Pseudactinoposthia (Actinoposthiidae).

Mass mortality of a Caribbean sea urchin: Immediate effects on community metabolism and other herbivores

The echinoid Diadema antillarum Philippi was an important herbivore in many areas of the Caribbean prior to the mass mortality that eliminated 95-99% of the individuals throughout the Caribbean in 1983-84. Five days after the mass mortality in St. Croix, U.S. Virgin Islands, algal biomass increased by 20% and algal community primary productivity dropped on both a per unit area basis (37% decrease) and per unit algal biomass basis (61% decrease). This accompanied a 50% decrease in the amount of algal biomass removed by herbivores. Concurrent with the changes in the algal community were increases in the rates of grazing by herbivorous fishes, suggesting that exploitative competition for food was occurring between D. antillarum and some herbivorous fish species. These results suggest that D. antillarum has an important role in structuring both the producer and consumer components of Caribbean coral reef ecosystems.