The natural beauty of coral reefs attracts millions of tourists worldwide resulting in substantial revenues for the adjoining economies. Although their visual appearance is a pivotal factor attracting humans to coral reefs current monitoring protocols exclusively target biogeochemical parameters, neglecting changes in their aesthetic appearance. Here we introduce a standardized computational approach to assess coral reef environments based on 109 visual features designed to evaluate the aesthetic appearance of art. The main feature groups include color intensity and diversity of the image, relative size, color, and distribution of discernable objects within the image, and texture. Speci c coral reef aesthetic values combining all 109 features were calibrated against an established biogeochemical assessment (NCEAS) using machine learning algorithms. These values were generated for ∼2,100 random photographic images collected from 9 coral reef locations exposed to varying levels of anthropogenic in uence across 2 ocean systems. Aesthetic values proved accurate predictors of the NCEAS scores (root mean square error < 5 for N ≥ 3) and signi cantly correlated to microbial abundance at each site. This shows that mathematical approaches designed to assess the aesthetic appearance of photographic images can be used as an inexpensive monitoring tool for coral reef ecosystems. It further suggests that human perception of aesthetics is not purely subjective but in uenced by inherent reactions towards measurable visual cues. By quantifying aesthetic features of coral reef systems this method provides a cost e cient monitoring tool that targets one of the most important socioeconomic values of coral reefs directly tied to revenue for its local population.
When juveniles must tolerate harsh environments early in life, the disproportionate success of certain phenotypes across multiple early life stages will dramatically influence adult community composition and dynamics. In many species, large offspring have a higher tolerance for stressful environments than do smaller conspecifics (parental effects). However, we have a poor understanding of whether the benefits of increased parental investment carry over after juveniles escape harsh environments or progress to later life stages (latent effects). To investigate whether parental effects and latent effects interactively influence offspring success, we determined the degree to which latent effects of harsh abiotic conditions are mediated by offspring size in two stony coral species. Larvae of both species were sorted by size class and exposed to relatively high-temperature or low-salinity conditions. Survivorship was quantified for six days in these stressful environments, after which surviving larvae were placed in ambient conditions and evaluated for their ability to settle and metamorphose. We subsequently assessed long-term post-settlement survival of one species in its natural environment. Following existing theory, we expected that, within and between species, larger offspring would have a higher tolerance for harsh environmental conditions than smaller offspring. We found that large size did enhance offspring performance in each species. However, large offspring size within a species did not reduce the proportional, negative latent effects of harsh larval environments. Furthermore, the coral species that produces larger offspring was more, not less, prone to negative latent effects. We conclude that, within species, large offspring size does not increase resistance to latent effects. Comparing between species, we conclude that larger offspring size does not inherently confer greater robustness, and we instead propose that other life history characteristics such as larval duration better predict the tolerance of offspring to harsh and variable abiotic conditions. Additionally, when considering how stressful environments influence offspring performance, studies that only evaluate direct effects may miss crucial downstream (latent) effects on juveniles that have significant consequences for long-term population dynamics.
Oil spills cause damage to marine wildlife that lasts well past their immediate aftermath. Marine offspring that must settle and metamorphose to reach adulthood may be particularly prone to harm if the legacy of oil exposure interrupts later transitions across life stages. Following an oil spill on Curaçao, we found that oil-contaminated seawater reduced settlement of 2 coral species by 85% and 40% after exposure had ended. The effect of contamination on settlement was more severe than any direct or latent effects on survival. Therefore, oil exposure reduces the ability of corals to transition to their adult life stage, even after they move away from oil contamination. This interruption of the life cycle likely has severe consequences for recruitment success in these foundational and threatened organisms. Latent, sublethal, and behavioral effects on marine organisms—as shown in this study—are not commonly considered during oil-spill impact assessments, increasing the likelihood that harm to marine species goes underestimated or unmeasured.
Coral reefs throughout the Caribbean have suffered the effects of human activities, including overfishing, nutrient pollution, and global climate change. Yet despite systematic deterioration of reef health, there still exists appreciable variability of reef conditions across Caribbean sites. The mid-depth (20 m) fringing reefs of Bonaire and Curaçao, in the leeward Netherlands Antilles, remain healthier than reefs on many other Caribbean islands, supporting relatively high fish biomass and high coral cover. Approximately one half of the fish biomass is composed of planktivorous species, with the balance comprised of herbivorous and carnivorous species. Only a small fraction (<7%) of the fish biomass is composed of apex predators, predominantly due to the essential absence of sharks from these reefs. Coral cover across these islands averages 26.6%, with fleshy macroalgae and turf algae covering most of the remaining benthos. Coral cover was not correlated with the biomass of any fish groups, failing to provide a clear link between fish activities (e.g., herbivory) and the health and persistence of corals. However, there was a strong, positive correlation between macroalgal cover and herbivorous fish biomass. This result is in contrast to previously published reports and may identify a disparity between correlational studies conducted within islands (or nearby islands) versus studies comparing results from across islands. These data provide insights into the structure of reef communities in the southern Caribbean Sea.
On Bonaire, we studied the effects of predator abundance and habitat availability on the abundance of the threespot damselfish Stegastes planifrons, a species that creates algal gardens at the expense of live coral cover. Across 21 sites, predator biomass ranged from 12 to 193 g m−2 (mean = 55.1; SD = 49.1) and benthic cover of S. planifrons’ preferred habitat (corals of the Orbicella species complex) ranged from 2.2 to 38.0% (mean = 14.3; SD = 9.6). Across these gradients, the local abundance of S. planifrons was significantly and negatively related to preda- tor biomass, but not to habitat availability. Increased local abundance of S. planifrons corre- sponded to an increasingly larger proportion of coral colonies affected by its ‘farming behavior’, resulting in an increased prevalence of coral disease. Thus, predators indirectly affected the com- position of reef communities around Bonaire by controlling damselfish abundance. Furthermore, the abundance of S. planifrons could not be correlated with its preferred habitat, despite such cor- relations having been observed elsewhere in the Caribbean.
The GCRMN baseline scientific monitoring methods provide a basic framework for existing and developing monitoring programs to contribute data that support a regional understanding of status and trends of Caribbean coral reefs. The purpose of these methods is to collect data that will contribute to our understanding of the processes that shape coral reefs and to provide actionable advice to policy makers, stakeholders, and communities. In order to achieve these goals, the GCRMN community seeks to collect comprehensive and inter-comparable data that build from a modern scientific perspective of reef monitoring.
The GCRMN methods have been developed to provide a systematic snapshot of the ecosystem health of coral reefs and, when repeated through time, insight into temporal trends in reef condition. Based on the conclusions of a retrospective analysis of trends in reef health over the past decades, GCRMN members have agreed that there is great value in coordinating and standardizing future monitoring efforts. To date, Caribbean regional monitoring efforts often collect non-overlapping types of data about coral reefs, or the efforts use non-comparable methods for describing similar parts of the reef ecosystem. The goal of this document is to define a set of data and data collection techniques that will be used by Caribbean GCRMN members. These methods reflect long-standing, vetted scientific protocols and provide a compromise between practical applicability and ease of comparison between existing methods and long-term datasets.
The GCRMN methods describe six elements of the coral reef ecosystem – (1) abundance and biomass of key reef fish taxa, (2) relative cover of reef-building organisms (corals, coralline algae) and their dominant competitors, (3) assessment of coral health and (4) recruitment of reef-building corals, (5) abundance of key macro-invertebrate species, and (6) water quality. These elements provide an overview of the current condition of the coral reef ecosystem as well as an indication of likely future trajectories. GCRMN recognizes that by collecting information about these elements across multiple locations, with regular re-sampling through time, it will be possible to more knowingly describe the status of coral reef health in the Caribbean and to assess the effectiveness of local and regional management efforts.
These methods are designed to provide a basic and regional summary of reef health. Importantly, the elements that are included for GCRMN monitoring are not all-inclusive, and many partner members may be interested in collecting more detailed or spatially expansive data. However, the GCRMN methods should be viewed as a minimum set of measurements to provide a reliable snapshot of reef condition – data elements should not be selected individually but instead will be collected in sum. Given the inherent complexity of reef processes, a multidimensional description of coral reef health is essential to provide a coherent ‘baseline’ of coral reef condition in a dynamic and changing world.
On coral reefs, herbivorous fishes consume benthic primary producers and regulate competition between fleshy algae and reef-building corals. Many of these species are also important fishery targets, yet little is known about their global status. Using a large-scale synthesis of peer-reviewed and unpub- lished data, we examine variability in abundance and biomass of herbivorous reef fishes and explore evidence for fishing impacts globally and within regions. We show that biomass is more than twice as high in locations not accessible to fisheries relative to fisheries-accessible locations. Although there are large biogeographic differences in total biomass, the effects of fishing are consistent in nearly all regions. We also show that exposure to fishing alters the structure of the herbivore community by disproportionately reducing bio- mass of large-bodied functional groups (scraper/excavators, browsers, grazer/ detritivores), while increasing biomass and abundance of territorial algal- farming damselfishes (Pomacentridae). The browser functional group that consumes macroalgae and can help to prevent coral–macroalgal phase shifts appears to be most susceptible to fishing. This fishing down the herbivore guild probably alters the effectiveness of these fishes in regulating algal abun- dance on reefs. Finally, data from remote and unfished locations provide important baselines for setting management and conservation targets for this important group of fishes.