Highly Variable Taxa-specific Coral Bleaching Responses to Thermal Stresses

Complex histories of chronic and acute sea surface temperature (SST) stresses are expected to trigger taxon- and location-specific responses that will ultimately lead to novel coral communities. The 2016 El Niño-Southern Oscillation provided an opportunity to examine large- scale and recent environmental histories on emerging patterns in 226 coral communities distrib- uted across 12 countries from East Africa to Fiji. Six main coral communities were identified that largely varied across a gradient of Acropora to massive Porites dominance. Bleaching intensity was taxon-specific and was associated with complex interactions among the 20 environmental variables that we examined. Coral community structure was better aligned with the historical temperature patterns between 1985 and 2015 than the 2016 extreme temperature event. Addi- tionally, bleaching responses observed during 2016 differed from historical reports during past warm years. Consequently, coral communities present in 2016 are likely to have been reorganized by both long-term community change and acclimation mechanisms. For example, less disturbed sites with cooler baseline temperatures, higher mean historical SST background variability, and infrequent extreme warm temperature stresses were associated with Acropora-dominated communities, while more disturbed sites with lower historical SST background variability and frequent acute warm stress were dominated by stress-resistant massive Porites corals. Overall, the combination of taxon-specific responses, community-level reorganization over time, geographic variation, and multiple environmental stressors suggest complex responses and a diversity of future coral communities that can help contextualize management priorities and activities

Large Geographic Variability in the Resistance of Corals to Thermal Stress

Aim: Predictions for the future of coral reefs are largely based on thermal exposure and poorly account for potential geographic variation in biological sensitivity to ther- mal stress. Without accounting for complex sensitivity responses, simple climate ex- posure models and associated predictions may lead to poor estimates of future coral survival and lead to policies that fail to identify and implement the most appropri- ate interventions. To begin filling this gap, we evaluated a number of attributes of coral taxa and communities that are predicted to influence coral resistance to thermal stress over a large geographic range. Location: Western Indo-Pacific and Central Indo-Pacific Ocean Realms. Major taxa studied: Zooxanthellate Scleractinia – hard corals. Methods: We evaluated the geographic variability of coral resistance to thermal stress as the ratio of thermal exposure and sensitivity in 12 countries during the 2016 global-bleaching event. Thermal exposure was estimated by two metrics: (a) histori- cal excess summer heat (cumulative thermal anomaly, CTA), and (b) a multivariate index of sea-surface temperature (SST), light, and water flow (climate exposure, CE). Sensitivity was estimated for 226 sites using coordinated bleaching observations and underwater surveys of coral communities. We then evaluated coral resistance to ther- mal stress using 48 generalized linear mixed models (GLMMs) to compare the poten- tial influences of geography, historical SST variation, coral cover and coral richness. Results: Geographic faunal provinces and ecoregions were the strongest predic- tors of coral resistance to thermal stress, with sites in the Australian, Indonesian and Fiji-Caroline Islands coral provinces having higher resistance to thermal stress than Africa-India and Japan-Vietnam provinces. Ecoregions also showed strong gradients in resistance with highest resistance to thermal stress in the western Pacific and Coral Triangle and lower resistance in the surrounding ecoregions. A more detailed evaluation of Coral Triangle and non-Coral Triangle sites found higher resistance to thermal stress within the Coral Triangle, associated with c. 2.5 times more recent historical thermal anomalies and more centralized, warmer, and cool-water skew SST distributions, than in non-Coral Triangle sites. Our findings identify the importance of environmental history and geographic context in future predictions of bleaching, and identify some potential drivers of coral resistance to thermal stress. Main conclusions: Simple threshold models of heat stress and coral acclimation are commonly used to predict the future of coral reefs. Here and elsewhere we show that large-scale responses of coral communities to heat stress are geographically variable and associated with differential environmental stresses and histories

Temporal and Spatial variability in Reef fish Density and Biomass within the Dar es Salaam Marine Reserve System, Tanzania

This study was conducted within the Dar es Salaam Marine Reserve System with the aim of investigating temporal and spatial variations in reef fish biomass and density. Benthic cover which is a key factor for fish distribution was also estimated. Sampling was conducted from August 2014 to April 2015. Underwater Visual Census (UVC) techniques were used for the assessment of reef fish density and biomass, and line intercept transect (LIT) was used for the estimation of benthic cover. Results showed that there was a significant seasonal and temporal variation in fish density and biomass at both Mbundya and Bongoyo Islands. Benthic cover of live coral was significantly higher at Mbudya than at Bongoyo. It was concluded that Mbudya Island has less seasonal variation than Bongoyo due to the existence of a larger fraction of live coral cover. These results have implications for the management of marine reserves with regard to destructive fishing practices, a key factor impacting the stability and biomass of reef fish populations

Assessment of reef fish and benthic cover of the North and South Dar es Salaam Marine Reserves system before the 2016 El Niño

The status of reef fish density, diversity, species richness, biomass and coral cover was evaluated by comparing the conditions in two Dar es Salaam Marine Reserves (DMRs); the North Dar es Salaam Marine Reserve (NDMR; gazetted in 1975), and the South Dar es Salaam Marine Reserves (SDMRs; gazetted in 2007), before the 2016 El Niño. A 10 m line-intercept transect was used to characterize benthic cover and a 50 m belt transect was used to assess reef fish population status. Sampling occurred between August 2014 and April 2015. The results showed that fish biomass in the (NDMRs) was 2.7 times higher than that in the (SDMRs) and live hard coral cover was 3 times higher. Higher reef fish density, biomass, diversity, species richness and live hard coral cover were revealed before 2016 El Niño in NDMRs as compared to the SDMRs. Differences in status are linked to differences in time of gazetting and level of effective management in the marine protected areas (MPAs), where NDMRs has a General Management Plan (GMP) while SDMRs does not, and the differences in management are likely to have contributed to the differences in fish biomass and coral cover

Spatial genetic differentiation correlates with species assemblage turnover across tropical reef fish lineages

Aim: Evaluating the similarity of diversity patterns across micro- to macroevolutionary scales in natural communities, such as species-genetic diversity correlations (SGDCs), may inform on processes shaping community assembly. However, whether SGDCs not only hold across communities but also across lineages has never been explored so far. Here we investigated SGDCs across co-distributed taxa for different spatial components (alpha, beta, gamma), and formally tested the influence of dispersal traits on beta-SGDCs.Location: Western Indian Ocean.Time period: 2016-2017.Major taxa studied: Tropical reef fish species with contrasting dispersal traits.Methods: Using double-digest restriction-site associated DNA sequencing (ddRADseq) Single Nucleotide Polymorphism data for 20 tropical reef fishes and distribution data of 2,446 species belonging to 12 families, we analysed the correlations between within-species genetic diversity and within-family species diversity (i.e., lineage diversity) for the three spatial components (alpha, beta, gamma-SGDCs). We then related the strength of beta-SGDCs per species to proxies of larval dispersal abilities.Results: We detected positive and significant lineage-based SGDC only for the beta component, that is, the families showing the greatest level of species turnover among sites contain the species with the greatest levels of genetic differentiation. We showed that the Monsoon Drift mainly explained the beta-diversity patterns at both intraspecific and interspecific levels. Higher beta-SGDCs were found for species with short pelagic larval duration and weak larval swimming capacity.Main conclusions: Our study reveals a strong correlation between genetic and species beta-diversity, a result explained by the presence of a 'soft' barrier and mediated by larval dispersal processes. This suggests that vicariance and dispersal limitation are major processes shaping beta-diversity patterns from microevolutionary to macroevolutionary scales in tropical reef fishes.ISSN:1466-822XISSN:1466-823

Species ecology explains the spatial components of genetic diversity in tropical reef fishes

Generating genomic data for 19 tropical reef fish species of the Western Indian Ocean, we investigate how species ecology influences genetic diversity patterns from local to regional scales. We distinguish between the α, β and γ components of genetic diversity, which we subsequently link to six ecological traits. We find that the α and γ components of genetic diversity are strongly correlated so that species with a high total regional genetic diversity display systematically high local diversity. The α and γ diversity components are negatively associated with species abundance recorded using underwater visual surveys and positively associated with body size. Pelagic larval duration is found to be negatively related to genetic β diversity supporting its role as a dispersal trait in marine fishes. Deviation from the neutral theory of molecular evolution motivates further effort to understand the processes shaping genetic diversity and ultimately the diversification of the exceptional diversity of tropical reef fishes

Temperature patterns and mechanisms influencing coral bleaching during the 2016 El Niño

Under extreme heat stress, corals expel their symbiotic algae and colour (that is, ‘bleaching’), which often leads to widespread mortality. Predicting the large-scale environmental conditions that reinforce or mitigate coral bleaching remains unresolved and limits strategic conservation actions1,2. Here we assessed coral bleaching at 226 sites and 26 environmental variables that represent different mechanisms of stress responses from East Africa to Fiji through a coordinated effort to evaluate the coral response to the 2014–2016 El Niño/Southern Oscillation thermal anomaly. We applied common time-series methods to study the temporal patterning of acute thermal stress and evaluated the effectiveness of conventional and new sea surface temperature metrics and mechanisms in predicting bleaching severity. The best models indicated the importance of peak hot temperatures, the duration of cool temperatures and temperature bimodality, which explained ~50% of the variance, compared to the common degree-heating week temperature index that explained only 9%. Our findings suggest that the threshold concept as a mechanism to explain bleaching alone was not as powerful as the multidimensional interactions of stresses, which include the duration and temporal patterning of hot and cold temperature extremes relative to average local conditions

Corrigendum: exploring associations between gaze patterns and putative human mirror neuron system activity

A corrigendum on:Exploring associations between gaze patterns and putative human mirror neuron systemactivityby Donaldson, P. H., Gurvich, C., Fielding, J., and Enticott, P. G. (2015). Front. Hum. Neurosi. 9:396.doi: 10.3389/fnhum.2015.0039