Changes in Biotic and Abiotic Processes Following Mangrove Clearing

Mangrove forests, important tropical coastal habitats, are in decline worldwide primarily due to removal by humans. Changes to mangrove systems can alter ecosystem properties through direct effects on abiotic factors such as temperature, light and nutrient supply or through changes in biotic factors such as primary productivity or species composition. Despite the importance of mangroves as transitional habitats between land and sea, little research has examined changes that occur when they are cleared. We examined changes in a number of biotic and abiotic factors following the anthropogenic removal of red mangroves (Rhizophora mangle) in the Panamanian Caribbean, including algal biomass, algal diversity, algal grazing rates, light penetration, temperature, sedimentation rates and sediment organic content. In this first study examining multiple ecosystem-level effects of mangrove disturbance, we found that areas cleared of mangroves had higher algal biomass and richness than intact mangrove areas. This increase in algal biomass and richness was likely due to changes in abiotic factors (e.g. light intensity, temperature), but not biotic factors (fish herbivory). Additionally the algal and cyanobacterial genera dominating mangrove-cleared areas were rare in intact mangroves and included a number of genera that compete with coral for space on reefs. Interestingly, sedimentation rates did not differ between intact and cleared areas, but the sediments that accumulated in intact mangroves had higher organic content. These findings are the first to demonstrate that anthropogenic clearing of mangroves changes multiple biotic and abiotic processes in mangrove forests and that some of these changes may influence adjacent habitats such as coral reefs and seagrass beds. Additional research is needed to further explore the community and ecosystem-level effects of mangrove clearing and their influence on adjacent habitats, but it is clear that mangrove conservation is an important aspect of managing tropical coastal systems

Bridging the Marine-Terrestrial Disconnect to Improve Marine Coastal Zone Science and Management

Coastal zone ecosystems sit between larger terrestrial and marine environments and, therefore, are strongly affected by processes occurring in both systems. Marine coastal zone systems provide a range of benefits to humans, and yet many have been significantly degraded as a result of direct and indirect human impacts. Management efforts have been hampered by disconnects both between management and scientific research and across linked marine–terrestrial systems. Management jurisdictions often start or end at the shoreline, and multiple agencies at different levels of government often have overlapping or conflicting management goals or priorities, or suffer from a lack of knowledge or interest. Scientists also often fail to consider connections among linked marine–terrestrial systems, and communication among agencies, among scientists in different disciplines, and between scientists and managers is often inadequate. However, despite the institutional and scientific challenges inherent in improving coastal zone management, there are examples of increased coordination and cooperation among different organizations. We discuss a number of examples— including where the marine–terrestrial and science–management disconnects persist and where better integration has led to successes in coastal zone management—and provide recommendations to scientists and managers on how to better link their efforts in science and management across marine and terrestrial systems

Spatial Variation in the Chemical Composition of Natal Otholiths from a Reef Fish in the Galápagos Islands

Over the past decade, researchers have used variation in the chemical composition of fish otoliths (earstones) to address a number of ecological questions, such as stock assessment and assessing rates of movement of individuals among habitats or life-history stages. However, these methods have yet to be applied successfully to the study of larval connectivity, a major unanswered question in marine ecology. Accomplishing this task requires a reference collection of pre-pelagic natal otoliths and accurate measurement of the chemical signatures of otoliths cores of recruits. We analyzed the chemical composition of natal otoliths from near-term benthic eggs of a damselfish (Stegastes beebei) from all regions of the Galápagos Archipelago. There was no consistent variation in chemical signature at the largest scale, among regions in the archipelago (separated by ~100 to 150 km). However, we found significant variation among islands within each region (10s of km), and among clutches within islands. In addition, we found that otolith cores of newly settled recruits often differed chemically from natal otoliths (which ultimately make up the otolith core as the fish grows). Variation at smaller spatial scales but not larger ones implies that otolith chemistry will only be usable if larvae disperse short distances in this system, and additional work is required to understand the relationship between the chemistry of natal otoliths and recruit cores. Otolith chemistry has the potential to address questions of connectivity, but our data suggest that these methods should be applied cautiously

Automating Deep-Sea Video Annotation Using Machine Learning

As the world explores opportunities to develop offshore renewable energy capacity, there will be a growing need for pre-construction biological surveys and post-construction monitoring in the challenging marine environment. Underwater video is a powerful tool to facilitate such surveys, but the interpretation of the imagery is costly and time-consuming. Emerging technologies have improved automated analysis of underwater video, but these technologies are not yet accurate or accessible enough for widespread adoption in the scientific community or industries that might benefit from these tools. To address these challenges, we developed a website that allows us to: (1) Quickly play and annotate underwater videos, (2) Create a short tracking video for each annotation that shows how an annotated concept moves in time, (3) Verify the accuracy of existing annotations and tracking videos, (4) Create a neural network model from existing annotations, and (5) Automatically annotate unwatched videos using a model that was previously created. The website was seeded with 50 hours of high-resolution underwater videos that were generously provided by the Monterey Bay Aquarium Research Institute (MBARI). The biology students that were part of the project created more than 30,000 annotations that range over more than 20 concepts. About 3,000 of these annotations were then verified for accuracy by our marine biology experts. Using both validated and unvalidated annotations and automatically generated annotations from trackings, our software was able to count the number of Rathbunaster californicus (starfish) and Strongylocentrotus fragilis (sea urchin) with count accuracy of 97% and 99%, respectively, and F1 score accuracy of 0.90 and 0.81, respectively

Discriminant Function Analysis in Marine Ecology: Some Oversights and their Solutions

Marine ecologists commonly use discriminant function analysis (DFA) to evaluate the similarity of distinct populations and to classify individuals of unknown origin to known populations. However, investigators using DFA must account for (1) the possibility of correct classification due to chance alone, and (2) the influence of prior probabilities of group membership on classification results. A search of the recent otolith chemistry literature showed that these two concerns are sometimes ignored, so we used simulated data sets to explore the potential pitfalls of such oversights. We found that when estimating reclassification success for a training data set, small sample sizes or unbalanced sampling designs can produce remarkably high reclassification success rates by chance alone, especially when prior probabilities are estimated from sample size. When using a training data set to classify unknown individuals, maximum likelihood estimation of mixture proportions and group membership afforded up to 20% improvement over DFA with uninformative priors when groups contributed to the sample unequally. Given these results, we recommend the use of (1) randomization tests to estimate the probability that reclassification success is better than random, and (2) maximum likelihood estimation of mixture proportions in place of uninformative priors

Protective Capactiy of Mangroves During Tropical Storms: A Case Study from \u27Wilma\u27 and \u27Gamma\u27 in Belize

Globally threatened mangrove forest habitat is often considered an important buffer protecting coastlines from wave and storm impacts and coastal erosion. However, there is little empirical data quantifying the protective effects of mangroves during storms, primarily because of the difficulty of predicting where and when a storm will intersect the shoreline, to facilitate data collection before and after storm events. In 2005, opportunistic results from an ongoing study quantifying differences between intact and cleared mangrove areas on Turneffe Atoll, Belize, provided such pre- and post-storm data from tropical storms ‘Wilma’ (later a Category 5 Hurricane) and ‘Gamma’. We compared differences in equipment retention rates of 3 types of experimental devices previously installed in adjacent intact and cleared mangrove areas. Retention rates were greater in intact mangrove areas, empirically demonstrating the protective capacity of mangroves during moderate magnitude storm events. The results support the assumption that removal of mangroves diminishes coastal protection not only during catastrophic storm events such as hurricanes or tsunamis, but also during less energetic but more frequent events, such as tropical storms. This highlights the importance of improved coastal zone management, as storm events may increase in frequency and intensity with changing climate, and coastal mangrove forest habitats continue to decline in size and number

Spatial and Temporal Variation in the Natal Otolith Chemistry of a Hawaiian Reef Fish: Prospects for Measuring Population Connectivity

One of the most compelling unanswered questions in marine ecology is the extent to which local populations are connected via larval exchange. Recent work has suggested that variation in the chemistry of otoliths (earstones) of fishes may function as a natural tag, potentially allowing investigators to determine sources of individual larvae and estimate larval connectivity. We analyzed the spatial and temporal variation in natal otolith chemistry of a benthic-spawning reef fish from the Hawaiian Islands. We found no consistent chemical variation at the largest scale (\u3e100 km, among islands), but found significant variation at moderate scales (sites within islands, tens of kilometres) and small scales (clutches within sites), and chemistry of otoliths was not stable between years. These results imply that we may be able to use otolith chemistry to track larval dispersal only if the scales of dispersal match those of variation in natal otolith chemistry, and that separate natal otolith collections may be needed to track different cohorts of larvae. Finally, we found that elemental composition of recruit cores often did not match that of natal otoliths, suggesting that additional methodological development is required before we can effectively apply methods in otolith chemistry to the study of larval dispersal

Resource Partitioning Along Multiple Niche Axes Drives Functional Diversity in Parrotfishes on Caribbean Coral Reefs

The recent loss of key consumers to exploitation and habitat degradation has significantly altered community dynamics and ecosystem function across many ecosystems worldwide. Predicting the impacts of consumer losses requires knowing the level of functional diversity that exists within a consumer assemblage. In this study, we document functional diversity among nine species of parrotfishes on Caribbean coral reefs. Parrotfishes are key herbivores that facilitate the maintenance and recovery of coral-dominated reefs by controlling algae and provisioning space for the recruitment of corals. We observed large functional differences among two genera of parrotfishes that were driven by differences in diet. Fishes in the genus Scarus targeted filamentous algal turf assemblages, crustose coralline algae, and endolithic algae and avoided macroalgae, while fishes in the genus Sparisoma preferentially targeted macroalgae. However, species with similar diets were dissimilar in other attributes, including the habitats they frequented, the types of substrate they fed from, and the spatial scale at which they foraged. These differences indicate that species that appear to be functionally redundant when looking at diet alone exhibit high levels of complementarity when we consider multiple functional traits. By identifying key functional differences among parrotfishes, we provide critical information needed to manage parrotfishes to enhance the resilience of coral-dominated reefs and reverse phase shifts on algal-dominated reefs throughout the wider Caribbean. Further, our study provides a framework for predicting the impacts of consumer losses in other species rich ecosystems

Potential Environmental Effects of Deepwater Floating Offshore Wind Energy Facilities

Over the last few decades, the offshore wind energy industry has expanded its scope from turbines mounted on foundations driven into the seafloor and standing in less than 60 m of water, to floating turbines moored in 120 m of water, to prospecting the development of floating turbines moored in ~1,000 m of water. Since there are few prototype turbines and mooring systems of these deepwater, floating offshore wind energy facilities (OWFs) currently deployed, their effects on the marine environment are speculative. Using the available scientific literature concerning appropriate analogs, including fixed-bottom OWFs, land-based wind energy facilities, wave and tidal energy devices, and oil and gas platforms, we conducted a qualitative systematic review to estimate the potential environmental effects of deepwater, floating OWFs during operation, as well as potential mitigation measures to address some of the effects. We evaluated six categories of potential effects: changes to atmospheric and oceanic dynamics due to energy removal and modifications, electromagnetic field effects on marine species from power cables, habitat alterations to benthic and pelagic fish and invertebrate communities, underwater noise effects on marine species, structural impediments to wildlife, and changes to water quality. Our synthesis of 89 articles selected for the review suggests that many of these potential effects could be mitigated to pose a low risk to the marine environment if developers adopt appropriate mitigation strategies and best-practice protocols. This review takes the necessary first steps in summarizing the available information on the potential environmental effects of deepwater, floating OWFs and can serve as a reference document for marine scientists and engineers, the energy industry, permitting agencies and regulators of the energy industry, project developers, and concerned stakeholders such as coastal residents, conservationists, and fisheries

Herbivory and the Resilience of Caribbean Coral Reefs: Knowledge Gaps and Implications for Management

Herbivory is a key process on coral reefs that can facilitate reef-building corals by excluding algae that otherwise negatively impact coral settlement, growth, and survivorship. Over the last several decades, coral cover on Caribbean reefs has declined precipitously. On many reefs, large structurally complex corals have been replaced by algae and other non-reef-building organisms, resulting in the collapse of physical structure and the loss of critical ecosystem services. The drivers of coral decline on Caribbean reefs are complex and vary among locations. On many reefs, populations of key herbivores have been greatly reduced by disease and overfishing, and this has resulted in the proliferation of algae that hinder coral recovery following major disturbances. Yet, evidence that increases in herbivory can promote coral recovery on Caribbean reefs has been mixed. Here, we discuss key contingencies that will modify the relationships between herbivores, algae, and corals and identify critical knowledge gaps that limit our ability to predict when and where herbivores are most likely to facilitate coral persistence and recovery. Impacts of herbivores on coral reef ecosystems will vary greatly in space and time and will depend on herbivore diversity and species identity. While there are still a large number of knowledge gaps, we make several management recommendations based on our current understanding of the processes that structure reef ecosystems. Reversing the fate of Caribbean coral reefs will require the development of integrated management strategies that simultaneously address multiple stressors in addition to the impacts of fisheries on herbivore assemblages