Modelling susceptibility of Abrolhos reefs to coral bleaching

Coral reefs suffer many threats, including coral bleaching, which occurs mainly in response to environmental variables such as positive temperature anomalies. However, there is a need to explore potential synergies between environmental and anthropogenic variables. The objective of this work is to use multi-criteria analysis to explore associations between environmental and anthropogenic variables in order to estimate in a spatially explicit way the susceptibility of the different Abrolhos reefs in Bahia, Brazil, to coral bleaching. Our results show that from 2001 to 2016 there was a sharp increase in the reef areas with higher susceptibility to bleaching. While in 2001, 20% of the reef area presented low susceptibility to bleaching and 80% showed medium susceptibility, in 2016, 19% of the area showed medium and 81% showed high susceptibility. 2016 presented the highest susceptibility among the years used in the study, suggesting a higher percentage of bleached colonies, which is corroborated by the fact that this year was considered by NASA and NOAA as the hottest year since 1880. Results also show that bleaching pattern is spatially differentiated. The reefs from the coastal arch of Abrolhos present the greater susceptibility to bleaching. Exception is Timbebas reefs which, although located in the coastal arch, are more similar to the outer arch reefs, wich are less susceptible to bleaching

Climate change vulnerability and adaptation assessment for Fiji

All nations, including Fiji, that are signatories to the United Nations Framework Convention on Climate Change(UNFCCC) are obliged to provide National Communications to the Conference of Parties (COP) of the UNFCCC. The COP4 stressed the need for parties to the Convention to take into account the need for establishing implementation strategies for adaptation to climate and sea-level changes. As such, Fiji is required to submit a National Communication document that shall include information on climate change vulnerability and adaptation implementation policies and strategies. The methodology used in this assessment is based on the Intergovernmental Panel on Climate Change (IPCC) technical guidelines (Carter et al, 1994) for assessing climate change impacts and adaptation. Firstly, the present conditions are examined and key sectors identified. Then, future climatic and non-climatic scenarios are used to examine the possible effects of climate and sea-level changes on the various sectors identified. These then form the basis for identifying possible adaptation response measures for endorsement, adoption and implementation by the Fiji government. Because of the many gaps in present knowledge, and the fact that this study is focussed only on Viti Levu, the recommendations in this report should be seen as starting point for an on-going process of vulnerability and adaptation assessment in Fij

Measuring the Impact of Thermal Stress on Coral Resilience in Hawai\u27i Using Large-Area Imagery

Coral reefs worldwide are declining due to several anthropogenic stressors, but rising ocean temperature is the most serious threat to coral reef persistence. Developing models that document changes in coral communities following thermal stress events and forecast trends in reef recovery is crucial in identifying resilient reefs. Traditional approaches to generating the coral vital rates necessary for demographic modeling are time consuming and field intensive; however, by leveraging Structure-from-Motion photogrammetry, we can accurately track populations over time at a large spatial scale. In this study, I assessed the population dynamics of the dominant coral species across the Hawaiian archipelago and investigated the impact of thermal stress on coral populations. The annual growth, survival and recruitment of 3,852 coral colonies (5,636 unique colony-level transitions) for 3 genera was recorded at 16 sites spanning the Hawaiian archipelago across 14 intervals from 2013 to 2019, including 3 bleaching events. These data were used to estimate vital rates (growth, survival, and recruitment) and build integral projection models to determine the impact of thermal stress on population growth. To overcome the inherent challenges in estimating coral reproduction, I modeled recruitment in four different ways and present a comparison of datarich to data-poor estimation methods. Degree Heating Week output from the NOAA Coral Reef Watch daily global 5km satellite was used to estimate thermal conditions at each site by calculating temperature stress severity (the mean of all maximum thermal anomalies) and frequency (number of thermal stress events per 10 years). I found that all three coral genera, which have different morphologies and life-history strategies, had negative population growth rates. As expected, smaller colonies experienced faster growth, but large colonies had a high probability of shrinking, due to partial mortality. Large, multi-fragmented colonies had high survivorship and it may be advantageous for larger colonies to fragment into smaller pieces to avoid total mortality. Population dynamics were primarily driven by coral growth and survival and should be targeted in future restoration and adaptation projects. Additionally, across all taxa, population growth rates (λ) varied spatiotemporally, but most sites exhibited a declining population growth rate (λ \u3c 1). While increased severity and frequency of thermal stress events negatively impacted the population growth rate of massive Porites corals, there was no signal of this effect on encrusting Montipora corals. I demonstrate that despite variations in the responses observed among taxa, there is an overall expected population decline across the Hawaiian archipelago. While most coral population growth rates are higher following bleaching events, signifying recovery, the projected increase in both the severity and frequency of thermal anomalies may overwhelm corals’ ability to recover and threaten coral population persistence

Marine heatwave hotspots in coral reef environments: physical drivers, ecophysiological outcomes and impact upon structural complexity

A changing climate is driving increasingly common and prolonged marine heatwaves (MHWs) and these extreme events have now been widely documented to severely impact marine ecosystems globally. However MHWs have rarely recently been considered when examining temperature-induced degradation of coral reef ecosystems. Here we consider extreme, localised thermal anomalies, nested within broader increases in sea surface temperature, which fulfil the definitive criteria for MHWs. These acute and intense events, referred to here as MHW hotspots, are not always well represented in the current framework used to describe coral bleaching, but do have distinct ecological outcomes, including widespread bleaching and rapid mass mortality of putatively thermally tolerant coral species. The physical drivers of these localised hotspots are discussed here, and in doing so we present a comprehensive theoretical framework that links the biological responses of the coral photo-endosymbiotic organism to extreme thermal stress and ecological changes on reefs associated after MHW hotspots. We describe how the rapid onset of high temperatures drives immediate heat-stress induced cellular damage, overwhelming mechanisms that would otherwise mitigate the impact of gradually accumulated thermal stress. The warm environment, and increased light penetration of the coral skeleton due to the loss of coral tissues, coupled with coral tissue decay support rapid microbial growth in the skeletal microenvironment, resulting in the widely unrecognised consequence of rapid decay and degeneration of the coral skeletons. This accelerated degeneration of the coral skeletonson a reef scale hinder the recovery of coral populations and increase the likelihood of phase shifts towards algal dominance. We suggest that MHW hotspots, through driving rapid heat-induced mortality, compromise reefs' structural frameworks to the detriment of long term recovery. We propose that MHW hotspots be considered as a distinct class of thermal stress events in coral reefs, and that the current framework used to describe coral bleaching and mass mortality be expanded to include these. We urge further research into how coral mortality affects bioerosion by coral endoliths

Brazilian coral reefs in a period of global change: A synthesis

Brazilian coral reefs form structures significantly different from the well-known reef models, as follows: (i) they have a growth form of mushroom-shaped coral pinnacles called "chapeirões", (ii) they are built by a low diversity coral fauna rich in endemic species, most of them relic forms dating back to the Tertiary, and (iii) the nearshore bank reefs are surrounded by siliciclastic sediments. The reefs are distributed in the following four major sectors along the Brazilian coast: the northern, the northeastern and the eastern regions, and the oceanic islands, but certain isolated coral species can be found in warmer waters in embayments of the southern region. There are different types of bank reefs, fringing reefs, isolated "chapeirões" and an atoll present along the Brazilian coast. Corals, milleporids and coralline algae build the rigid frame of the reefs. The areas in which the major coral reefs occur correspond to regions in which nearby urban centers are experiencing accelerated growth, and tourism development is rapidly increasing. The major human effects on the reef ecosystem are mostly associated with the increased sedimentation due to the removal of the Atlantic rainforest and the discharge of industrial and urban effluents. The effects of the warming of oceanic waters that had previously affected several reef areas with high intensity coral bleaching had not shown, by the time of the 2010 event, any episodes of mass coral mortality on Brazilian reefs.Os recifes de coral do Brasil formam estruturas significativamente diferentes dos modelos conhecidos: (i) possuem uma forma de crescimento de pináculos coralíneos em forma de cogumelo, chamados "chapeirões", (ii) são construídos por uma fauna coralínea com baixa diversidade e rica em espécies endêmicas, sendo grande parte destas formas relíquias do período Terciário e (iii) os recifes costeiros estão num ambiente dominado por sedimentos siliciclásticos. Os recifes estão distribuídos em quatro áreas ao longo da costa brasileira: regiões norte, nordeste, leste, e nas ilhas oceânicas, mas espécies isoladas de coral podem ser encontradas em águas mais quentes nas enseadas da região sul. Diferentes tipos de banco recifais, recifes em franja, "chapeirões" isolados e um atol estão presentes ao longo da costa brasileira. Corais, milleporídeos e algas coralinas incrustantes constroem a estrutura rígida dos recifes. As áreas em que ocorrem os maiores recifes de coral correspondem às regiões nas proximidades de centros urbanos que estão experimentando crescimento acelerado e rápido desenvolvimento do turismo. Os principais efeitos antropogênicos sobre o ecossistema recifal estão associados, essencialmente ao aumento da sedimentação devido à remoção da mata atlântica e as descargas de efluentes industriais e urbanos. Os efeitos do aquecimento das águas oceânicas que vem afetando várias áreas de recifes, com alta intensidade de branqueamento de coral, não causaram mortalidade em massa nos recifes brasileiros até o evento de 2010

Modelling coral reefs to support their local Management : A case study in the Spermonde Archipelago, Indonesia

The potential of simulation models to provide insights on ecological questions that are crucial for the management of marine resources has become more relevant in light of the apparent demise of coral reefs. Multiple coral reef stressors can interact in nonlinear ways, confounding ecological interpretation through field studies alone. Theoretical computer modelling offers a platform to test ecological hypotheses about multiple stressors and their systemic impacts. The main purpose of this thesis was to use coral reef ecological theory to create a model as a basis for a scientifically sound, user-friendly decision support tool for the local management of coral reefs. Four major objectives were established: (1) develop a local coral reef model representing the impacts of simultaneous stressors on key ecological groups, (2) turn it into a user-friendly decision-support tool to explore different management options, (3) collect qualitative and quantitative information on the artisanal fishery of Spermonde (Indonesia) to help understand its social drivers, and (4) apply the model to real case scenarios to project the trajectory of selected coral reef response variables. Chapter two contains the description of SEAMANCORE (Spatially Explicit simulation model for Assisting the local MANagement of COral REefs) and its development. The model has two distinct compartments, benthos and fish, which run at different spatiotemporal scales and are affected by each other and by the three modelled stressors: fishing, bleaching and nutrients. Chapter three outlines an assessment of the coral reef fishery in Spermonde, focusing on the role of the patron-client system in the fishing behaviour of individual fishermen. This study contributes to the body of scientific literature on social drivers influencing fishing behaviour by empirically showing catch and behavioural differences between fishermen within the patron-client system and independent fishermen. Quantitative data on catches obtained in this study were used to parameterize fishing scenarios in Spermonde for a real case application of the model. Chapter four stems from the previous studies and adds ecological field collected data to parameterize SEAMANCORE. First, basic scenarios of nutrients and fishery were run under standardized conditions to appraise the stressorsa effects on the modelled response variables. Fishery scenarios included a fishery ban, subsistence fishery, commercial fishery, and commercial combined with destructive fishing practices. In the second part, ten-year simulations were run for four sites in Spermonde (Indonesia) exposed to varying degrees of human impacts and different initial conditions to project their local coral reefa s trajectories. Chapter 5 summarizes the contributions of this dissertation, highlighting the limitations of the modelling approach, and provides recommendations on research directions for modelling local coral reefs and management of their associated artisanal fisheries

Development and validation of computational fluid dynamics models for the coupled simulation of heat transfer and fluid flow in the coral microenvironments

This thesis explored the temperature deviations between coral surface temperature and ambient seawater temperature that likely determines the microscale processes involved in coral bleaching. The work presented here applied Computational Fluid Dynamics (CFD) technique coupled with hydrodynamic modelling and ray-tracing to predict coral surface warming due to the effects of stressors. This thesis demonstrates that modelling microscale temperature could yield important insights into thermoregulation in corals, which may lead to a more effective reef management