scholarly journals High-resolution modeling of thermal thresholds and environmental influences on coral bleaching for local and regional reef management

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e4382 ◽  
Author(s):  
Naoki H. Kumagai ◽  
Hiroya Yamano ◽  
Keyword(s):  
Coral Reefs ◽  
Uv Radiation ◽  
Coral Bleaching ◽  
Coral Cover ◽  
Environmental Influences ◽  
Thermal Indices ◽  
Reef Management ◽  
Water Turbidity ◽  
Thermal Thresholds ◽  
Cooling Effects

Coral reefs are one of the world’s most threatened ecosystems, with global and local stressors contributing to their decline. Excessive sea-surface temperatures (SSTs) can cause coral bleaching, resulting in coral death and decreases in coral cover. A SST threshold of 1 °C over the climatological maximum is widely used to predict coral bleaching. In this study, we refined thermal indices predicting coral bleaching at high-spatial resolution (1 km) by statistically optimizing thermal thresholds, as well as considering other environmental influences on bleaching such as ultraviolet (UV) radiation, water turbidity, and cooling effects. We used a coral bleaching dataset derived from the web-based monitoring system Sango Map Project, at scales appropriate for the local and regional conservation of Japanese coral reefs. We recorded coral bleaching events in the years 2004–2016 in Japan. We revealed the influence of multiple factors on the ability to predict coral bleaching, including selection of thermal indices, statistical optimization of thermal thresholds, quantification of multiple environmental influences, and use of multiple modeling methods (generalized linear models and random forests). After optimization, differences in predictive ability among thermal indices were negligible. Thermal index, UV radiation, water turbidity, and cooling effects were important predictors of the occurrence of coral bleaching. Predictions based on the best model revealed that coral reefs in Japan have experienced recent and widespread bleaching. A practical method to reduce bleaching frequency by screening UV radiation was also demonstrated in this paper.

scholarly journals High-resolution modeling of thermal thresholds and multiple environmental influences on coral bleaching for regional and local reef managements

2017 ◽  
Author(s):  
Naoki H. Kumagai ◽  
Hiroya Yamano ◽  
Keyword(s):  
High Resolution ◽  
Uv Radiation ◽  
Coral Bleaching ◽  
Environmental Influences ◽  
Thermal Indices ◽  
Water Turbidity ◽  
Thermal Index ◽  
Thermal Thresholds ◽  
Cooling Effects ◽  
Global And Local

AbstractCorals are one of the communities most threatened by global and local stressors. Excessive summer sea temperatures can cause coral bleaching, resulting in decreases in living coral coverage. Coral bleaching may begin with rising sea temperatures, although the widely used threshold of 1 °C over the local climatological maximum sea temperature has been reconsidered. In this study, we refine thermal indices predicting coral bleaching at high resolution (1 km) by statistically optimizing the thermal threshold and multiple environmental influences on bleaching, such as ultraviolet (UV) radiation, water turbidity, and cooling effects on corals. We use a dataset of coral bleaching events observed during 2004–2016 in Japan derived from the Web-based monitoring system, the Sango (Coral) Map Project, aiming at regional to local conservation of Japanese corals. We show how the ability to predict coral bleaching is improved by the choice of thermal index, statistical optimization of thermal thresholds, usage of multiple environmental influences, and modeling methods (generalized linear model and random forest). After optimization, the differences among the thermal indices in the ability to predict coral bleaching were slight. Among environmental influences, cooling effects, UV radiation, and water turbidity, in addition to a thermal index, well explain the occurrence of coral bleaching. Prediction based on the best explanatory model reveals that recent Japanese coral reefs are experiencing bleaching in many areas, although we show a practical way to reduce bleaching frequency significantly by screening UV radiation. Thus, our high-resolution models may provide a quantitative basis for the management of local reefs under current global and local stressors. The results of this study may be useful to other researchers for selecting a predictive method according to their needs or skills.

scholarly journals Climate Change Induced Thermal Stress Caused Recurrent Coral Bleaching over Gulf of Kachchh and Malvan Marine Sanctuary, West Coast of India

2021 ◽  
Author(s):  
Mohit Arora ◽  
Kalyan De ◽  
Nandini Ray Chaudhury ◽  
Mandar Nanajkar ◽  
Prakash Chauhan ◽  
...  
Keyword(s):  
Thermal Stress ◽  
Coral Reef ◽  
Coral Reefs ◽  
Coral Bleaching ◽  
Large Scale ◽  
Heat Waves ◽  
Southern Oscillation ◽  
Coral Cover ◽  
Imminent Threat ◽  
Marginal Reefs

Coral reefs are one of the most sensitive, productive, and invaluable biological resources on the earth. However, coral reefs are facing unprecedented stress due to ongoing climate changes and intensified anthropogenic disturbances globally. Elevated Sea Surface Temperature (SST) has emerged as the most imminent threat to the thermos-sensitive reef-building corals. The 2010–2014-2016 El Niño Southern Oscillation (ENSO) caused prolonged marine heat waves (MHWs) that led to the most widespread coral bleaching and mortality in the tropical Indi-Pacific regions. Coral bleaching prediction is vital for the management of the reef biodiversity, ecosystem functioning, and services. Recent decades, satellite remote sensing has emerged as a convenient tool for large-scale coral reef monitoring programs. As thermal stress is a critical physical attribute for coral bleaching hence, the present study examines the effectiveness of the elevated SSTs as a proxy to predict coral bleaching in shallow water marginal reefs. Advanced Very High-Resolution Radiometer (AVHRR) satellite data from the NOAA Coral Reef Watch’s (CRW) platform has been used for this study. Coral bleaching indices like Bleaching Threshold (BT), Positive SST Anomaly (PA), and Degree Heating Weeks (DHW) are computed to analyze the thermal stress on the coral reefs. The computed thermal stress from satellite-derived SST data over regions concurrence with the mass coral bleaching (MCB) events. This study concludes that in the last decades (2010 to 2019) the coral cover around these regions has dramatically declined due to higher SST, which indicates that the thermal stress induced recurrent bleaching events attributed to the coral loss.

scholarly journals STATUS OF CORAL REEFS IN THE LEMBEH STRAITS AND ADJACENT WATER, NORTH SULAWESI

2015 ◽  
Vol 37 (2) ◽  
pp. 57-61
Author(s):  
Suharsono
Keyword(s):  
Water Quality ◽  
Coral Reefs ◽  
Coral Cover ◽  
Water Discharge ◽  
River Mouth ◽  
Marine Biota ◽  
Live Coral ◽  
Reef Management ◽  
Habitat Variability ◽  
North Sulawesi

Lembeh reefs and its water surrounding are among the richest and most diverse in marine biota in Indonesia. The biota and reefs in this area have an important contribution to the province’s economy in the form of tourisms and fishery activities. An inventory using line intercept transect and free collection on the coral diversity has been conducted in four different locations showed that live coral cover ranging from 12.2–60.7% while sand rubble ranged from 4.67 to 78.67%. Among the life form categories, sponge dominated other biota with 0.47–21.97% coverage. Macro algae and turf algae cover were low at all sites, with average less than 2.07%. A total of 193 corals species belonging to 68 genera were recognized from this area. The differences among sites may be consequences of water quality, habitat variability and condition of the land base activities. Water turbidity in the coastal area of Kema was high due to the effects of water discharge from river mouth. Further, poor land management, development of port and human settlement leading to sedimentation, water pollution and poor water quality, remain the primary causes of reefs declines. Busy harbor and local sea transportation will be the major cause of coral reef degradation in the near future. There is a need to increase awareness of local people about the important of coral reefs and to develop management and conservation efforts involving scientists, academe and tourist operators. In addition, it is a need to strengthen the capabilities and capacities of institutions that concern reef management and enforce legislation. 

scholarly journals Coral reefs in the Gilbert Islands of Kiribati: Resistance, resilience, and recovery after more than a decade of multiple stressors

PLoS ONE ◽  
2021 ◽  
Vol 16 (8) ◽  
pp. e0255304
Author(s):  
Sara E. Cannon ◽  
Erietera Aram ◽  
Toaea Beiateuea ◽  
Aranteiti Kiareti ◽  
Max Peter ◽  
...  
Keyword(s):  
Climate Change ◽  
Heat Stress ◽  
Phase Shift ◽  
Coral Reefs ◽  
Coral Bleaching ◽  
Coral Cover ◽  
Hard Coral ◽  
Turf Algae ◽  
The World ◽  
Coral Communities

Coral reefs are increasingly affected by a combination of acute and chronic disturbances from climate change and local stressors. The coral reefs of the Republic of Kiribati’s Gilbert Islands are exposed to frequent heat stress caused by central-Pacific type El Niño events, and may provide a glimpse into the future of coral reefs in other parts of the world, where the frequency of heat stress events will likely increase due to climate change. Reefs in the Gilbert Islands experienced a series of acute disturbances over the past fifteen years, including mass coral bleaching in 2004–2005 and 2009–2010, and an outbreak of the corallivorous sea star Acanthaster cf solaris, or Crown-of-Thorns (CoTs), in 2014. The local chronic pressures including nutrient loading, sedimentation and fishing vary within the island chain, with highest pressures on the reefs in urbanized South Tarawa Atoll. In this study, we examine how recovery from acute disturbances differs across a gradient of human influence in neighboring Tarawa and Abaiang Atolls from 2012 through 2018. Benthic cover and size frequency data suggests that local coral communities have adjusted to the heat stress via shifts in the community composition to more temperature-tolerant taxa and individuals. In densely populated South Tarawa, we document a phase shift to the weedy and less bleaching-sensitive coral Porites rus, which accounted for 81% of all coral cover by 2018. By contrast, in less populated Abaiang, coral communities remained comparatively more diverse (with higher percentages of Pocillopora and the octocoral Heliopora) after the disturbances, but reefs had lower overall hard coral cover (18%) and were dominated by turf algae (41%). The CoTs outbreak caused a decline in the cover and mean size of massive Porites, the only taxa that was a ‘winner’ of the coral bleaching events in Abaiang. Although there are signs of recovery, the long-term trajectory of the benthic communities in Abaiang is not yet clear. We suggest three scenarios: they may remain in their current state (dominated by turf algae), undergo a phase shift to dominance by the macroalgae Halimeda, or recover to dominance by thermally tolerant hard coral genera. These findings provide a rare glimpse at the future of coral reefs around the world and the ways they may be affected by climate change, which may allow scientists to better predict how other reefs will respond to increasing heat stress events across gradients of local human disturbance.

scholarly journals Synergistic impacts of global warming on the resilience of coral reefs

2015 ◽  
Vol 370 (1659) ◽  
pp. 20130267 ◽  
Author(s):  
Yves-Marie Bozec ◽  
Peter J. Mumby
Keyword(s):  
Global Warming ◽  
Coral Reefs ◽  
Chronic Stress ◽  
Coral Bleaching ◽  
Regime Shift ◽  
Acute Stress ◽  
Coral Cover ◽  
Basin Of Attraction ◽  
Somatic Growth ◽  
Caribbean Coral Reefs

Recent epizootics have removed important functional species from Caribbean coral reefs and left communities vulnerable to alternative attractors. Global warming will impact reefs further through two mechanisms. A chronic mechanism reduces coral calcification, which can result in depressed somatic growth. An acute mechanism, coral bleaching, causes extreme mortality when sea temperatures become anomalously high. We ask how these two mechanisms interact in driving future reef state (coral cover) and resilience (the probability of a reef remaining within a coral attractor). We find that acute mechanisms have the greatest impact overall, but the nature of the interaction with chronic stress depends on the metric considered. Chronic and acute stress act additively on reef state but form a strong synergy when influencing resilience by intensifying a regime shift. Chronic stress increases the size of the algal basin of attraction (at the expense of the coral basin), whereas coral bleaching pushes the system closer to the algal attractor. Resilience can change faster—and earlier—than a change in reef state. Therefore, we caution against basing management solely on measures of reef state because a loss of resilience can go unnoticed for many years and then become disproportionately more difficult to restore.

scholarly journals In Situ Observations of Foraminiferal Bleaching in the Maldives, Indian Ocean

2018 ◽  
Vol 48 (1) ◽  
pp. 75-84 ◽  
Author(s):  
Silvia Spezzaferri ◽  
Akram El Kateb ◽  
Chiara Pisapia ◽  
Pamela Hallock
Keyword(s):  
Oxidative Stress ◽  
Coral Reefs ◽  
Coral Bleaching ◽  
Solar Irradiance ◽  
Reef Management ◽  
Recent Onset ◽  
The North ◽  
Management Plans ◽  
In Situ Observations

Abstract Coral reefs are threatened worldwide by a variety of natural and human-induced stressors; anomalous temperatures are presently among the most serious threats by causing extensive coral bleaching. Amphistegina spp. exhibit similar bleaching as corals in the presence of photo-oxidative stress induced by either light or temperature, especially during times of maximum solar irradiance. At 11 islands (34 sampling sites) in the North Ari Atoll in the Maldives, bleaching in Amphistegina was observed a few weeks before the onset of an extensive El Niño-related coral bleaching that was more severe than expected for this region. Assessment using the Amphistegina Bleaching Index (ABI) showed that the proportions of bleached specimens of Amphistegina in April–May 2015 can be explained by photo-inhibitory stress associated with temperatures exceeding 30°C during peak seasonal solar irradiance and water transparency. Importantly, the ABI indicates that environmental conditions are suitable for Amphistegina and other calcifying symbioses at most of the investigated sites, and that either chronic or relatively recent onset of photo-oxidative stress was present at the time of sampling. The observed bleaching in Amphistegina further demonstrates the potential of these unicellular protists to identify stressors in coral reefs; such applications should be considered in future reef-management plans.

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