Mark Eakin - Academia.edu (original) (raw)

Papers by Mark Eakin

Scientific Reports, 2019

Increasing heat stress due to global climate change is causing coral reef decline, and the caribb... more Increasing heat stress due to global climate change is causing coral reef decline, and the caribbean has been one of the most vulnerable regions. Here, we assessed three decades (1985-2017) of heat stress exposure in the wider caribbean at ecoregional and local scales using remote sensing. We found a high spatial and temporal variability of heat stress, emphasizing an observed increase in heat exposure over time in most ecoregions, especially from 2003 identified as a temporal change point in heat stress. A spatiotemporal analysis classified the Caribbean into eight heat-stress regions offering a new regionalization scheme based on historical heat exposure patterns. The temporal analysis confirmed the years

Current Biology, 2019

Graphical Abstract Highlights d Marine heatwaves lead to rapid coral mortality and microbial biof... more Graphical Abstract Highlights d Marine heatwaves lead to rapid coral mortality and microbial biofilm formation d Microbial metabolic activity results in rapid dissolution of the coral skeleton d Dissolution reduces skeletal hardness and density and increased porosity In Brief Due to climate change, coral reefs are now being subjected to extreme marine heatwave (MHW) conditions. Leggat et al. show that large-scale mortality due to MHWs and microbial colonization leads to a previously undescribed rapid dissolution of the coral skeleton.

Coral Reefs, 2019

The global coral bleaching event of 2014-2017 resulted from the latest in a series of heat stress... more The global coral bleaching event of 2014-2017 resulted from the latest in a series of heat stress events that have increased in intensity. We assessed global-and basin-scale variations in sea surface temperature-based heat stress products for 1985-2017 to provide the context for how heat stress during 2014-2017 compared with the past 3 decades. Previously, undefined ''Heat Stress Year'' periods (used to describe interannual variation in heat stress) were identified for the Northern and Southern Hemispheres, in which heat stress peaks during or shortly after the boreal and austral summers, respectively. The proportion of reef pixels experiencing bleaching-level heat stress increased through the record, accelerating during the last decade. This increase in accumulated heat stress at a bleaching level is a result of longer stress events rather than an increase in the peak stress intensity. Thresholds of heat stress extent for the three tropical ocean basins were established to designate ''global'' events, and a Global Bleaching Index was defined that relates heat stress extent to that observed in 1998. Notably, during the 2014-2017 global bleaching event, more than three times as many reefs were exposed to bleaching-level heat stress as in the 1998 global bleaching.

Coral Reefs, 2019

2014-2017 was an unprecedented period of successive record-breaking hot years, which coincided wi... more 2014-2017 was an unprecedented period of successive record-breaking hot years, which coincided with the most severe, widespread, and longest-lasting global-scale coral bleaching event ever recorded. The 2014-2017 global-scale coral bleaching event (GCBE) resulted in very high coral mortality on many reefs, rapid deterioration of reef structures, and far-reaching environmental impacts. Through the papers in this special issue of Coral Reefs entitled The 2014-2017 Global Coral Bleaching Event: Drivers, Impacts, and Lessons Learned, as well as papers published elsewhere, we have a good analysis of the 2014-2017 GCBE and its impacts. These studies have provided key insights into how climate change-driven marine heatwaves are destroying coral reef ecosystems: (a) The 2014-2017 GCBE is unique in the satellite record in its spatial scale, duration, intensity, and repetition of bleaching. (b) The impacts have been the most severe ever seen at many reefs. (c) Timing of observations matters and needs to be considered during the analysis of impacts. (d) On both global and local scales, the intensity of heat stress and impacts varied. (e) We continue to see important differences among and within coral taxa, with key roles played by algal symbionts and the microbiome. (f) Heat stress and bleaching both play a role in subsequent disease, which plays a key role in mortality. (g) Impacts ripple far beyond corals, with significant changes to the fish and invertebrate community that may last decades. (h) The structure of both individual coral's skeletons and entire reefs has been eroded much more quickly than previously realized. (i) The 2014-2017 GCBE provided little support for the proposed ''lifeboat'' hypothesis, whereby deep or mesophotic reefs serve as a means of coral reef salvation. (j) While marine protected areas (MPAs) provide protection from local stressors, they not only do not protect reefs from global-scale stressors, but also here is also little evidence they provide significant resilience.

Scientific Reports, 2016

Coral reefs across the world's oceans are in the midst of the longest bleaching e... more Coral reefs across the world's oceans are in the midst of the longest bleaching event on record (from 2014 to at least 2016). As many of the world's reefs are remote, there is limited information on how past thermal conditions have influenced reef composition and current stress responses. Using satellite temperature data for 1985-2012, the analysis we present is the first to quantify, for global reef locations, spatial variations in warming trends, thermal stress events and temperature variability at reef-scale (~4 km). Among over 60,000 reef pixels globally, 97% show positive SST trends during the study period with 60% warming significantly. Annual trends exceeded summertime trends at most locations. This indicates that the period of summer-like temperatures has become longer through the record, with a corresponding shortening of the 'winter' reprieve from warm temperatures. The frequency of bleaching-level thermal stress increased three-fold between 1985-91 and 2006-12 - a trend climate model projections suggest will continue. The thermal history data products developed enable needed studies relating thermal history to bleaching resistance and community composition. Such analyses can help identify reefs more resilient to thermal stress.

Coral Reef, 1996

El o related coral mortality and a subsequent increase in crustose coralline algae and sea urchin... more El o related coral mortality and a subsequent increase in crustose coralline algae and sea urchins have resulted in profound changes to the coral reef ecosystem at Uva Island, Panama (Pacific coast). New data and a model are presented that analyze the budget of the reef. The model accounts for production by corals and coralline algae, erosion by Diadema, infauna,

ABSTRACT In response to growing and widespread threats to coral reefs, in December 2012 NOAA Fish... more ABSTRACT In response to growing and widespread threats to coral reefs, in December 2012 NOAA Fisheries proposed list-ing 66 species of coral under the Endangered Species Act.

Nature Communications, 2011

Ocean acidification causes declines in calcification rates of corals because of decreasing aragon... more Ocean acidification causes declines in calcification rates of corals because of decreasing aragonite saturation states (Ω(arag)). Recent evidence also indicates that increasing sea surface temperatures may have already reduced growth and calcification rates because of the stenothermic threshold of localized coral populations. Density banding in coral skeletons provides a record of growth over the coral's lifespan. Here we present coral extension, bulk density and calcification master chronologies from seven subtropical corals (Montastraea faveolata) located in the Florida Keys, USA with a 60-year common period, 1937-1996. Linear trends indicate that extension increased, density decreased and calcification remained stable while the most recent decade was not significantly different than decadal averages over the preceding 50 years for extension and calcification. The results suggest that growth rates in this species of subtropical coral have been tolerant to recent climatic changes up to the time of collection (1996).

Mar Biol, 1991

Reproductive ecology of two major reef-building corals in the eastern Pacific [Pocillopora damico... more Reproductive ecology of two major reef-building corals in the eastern Pacific [Pocillopora damicornis (Linnaeus) andPocillopora elegans Dana] was investigated between 1984 and 1990 in Costa Rica, Panama (Gulf of Chiriqui and Gulf of Panama), and the Galapagos Islands (Ecuador) following the 1982–83 El Niño disturbance. Mature spermatocytes and oocytes were found in both species and were usually present in the

Coral Reef, 1996

El Niño related coral mortality and a subsequent increase in crustose coralline algae and sea urc... more El Niño related coral mortality and a subsequent increase in crustose coralline algae and sea urchins have resulted in profound changes to the coral reef ecosystem at Uva Island, Panama (Pacific coast). New data and a model are presented that analyze the budget of the reef. The model accounts for production by corals and coralline algae, erosion by Diadema, infauna,

Journal of Operational Oceanography, 2014

ABSTRACT Mass coral bleaching results from periods of elevated sea temperature. Satellite monitor... more ABSTRACT Mass coral bleaching results from periods of elevated sea temperature. Satellite monitoring of thermal stress has enhanced the capacity for the management of coral bleaching events worldwide. Satellite-based monitoring tools provide reef managers with cost-effective observations of temperature conditions to monitor the risk of bleaching and to target in situ observations in areas under stress. This paper describes improvements to satellite remote sensing products from NOAA's Coral Reef Watch to enhance product coverage and to correct identified errors in the production of coral reef-specific metrics for thermal stress. In addition, threats to the operational production of the thermal stress metrics are considered and a contingency plan is described to ensure continuity of operations.

Ecology Letters, Feb 1, 2011

Bulletin of Marine Science, 2007

Prior to the 10th International Coral Reef Symposium in Okinawa, Japan, in June 2004, symposium ... more Prior to the 10th International Coral Reef Symposium in Okinawa, Japan, in June
2004, symposium participants and members of the International Society for Reef Studies were surveyed to obtain their opinions about the major threats facing coral reef ecosystems. Responses from 286 participants were analyzed and compared to results obtained in a similar survey conducted in 1993. Respondents tended to rank highest those threats associated with human population growth, coastal develop- ment, and over shing. While coral bleaching was ranked much more highly than in the 1993 survey, about two-thirds of the respondents felt that direct human impacts were worse threats than those associated with global climate change.

Bulletin of Marine Science Miami, Jun 30, 2001

Abstract: Numerous changes have occurred at the Uva Island reef since the original calcium carbon... more Abstract: Numerous changes have occurred at the Uva Island reef since the original calcium carbonate budget model was published (Eakin, 1996). Minor bleaching events occurred during the 1990s and a widespread event occurred in 1997-98. In 1989 and 1993, reef flat ...

Earth Sci Rev, 2007

This paper is a review of published modern coral δ18O and Δ14C isotopic records that are at least... more This paper is a review of published modern coral δ18O and Δ14C isotopic records that are at least 30 and 20 years long, respectively. The data are presented to show basin-scale trends in both of these proxy records on decadal-to-centennial timescales. The goal was to qualitatively integrate the general inter-annual-to-centennial timescale variability revealed in these data, as well as the statistical and modeling output results that have been produced using these coral records. While many review papers typically include a representative subset of the data available, this review aims to include as much of the available data as possible. In general, coral δ18O records show a long-term warming and/or freshening throughout the tropical oceans, and agree with the NOAA Extended Reconstruction Sea Surface Temperature 2 (ERSST) on decadal timescales. In the western Pacific, it is most likely a freshening of the seawater δ18O that dominates the signal. El Niño Southern Oscillation (ENSO) variability dominates most δ18O records either by varying local seawater temperature or salinity, depending on the regional oceanography/climatology. Outside of the Pacific, ENSO affects seawater temperature and salinity via atmospheric or oceanic teleconnections. Post-bomb coral Δ14C records collectively show that the uptake of 14C has been greatest in gyre-water fed sites, followed in descending order by western boundary current areas, equatorial upwelling regions, and eastern tropical Pacific upwelling sites. These surface water Δ14C values indicate the proportion of surface water and/or the residence time of water at the surface at a given location, and can be used to model water mass mixing rates. Such models have only begun to be run and show that the amount of eastern Pacific water entering the central South Pacific increases during El Niños and that the Indonesian throughflow is supplied year-round by the North Pacific. Comparing ocean circulation models with coral Δ14C-modelled circulation enables researchers to explore the mechanisms that drive seawater Δ14C variability and fine-tune their models. In addition, our comparison between the rate of coral Δ14C increase between 1960 and 1970 and total anthropogenic CO 2 uptake rates show general agreement, demonstrating the value of coral records in understanding past carbon fluxes. Overall, coral δ18O and Δ14C proxy records represent natural archives of seawater conditions and are critical for studying the natural variability in local and regional patterns within, and teleconnection patterns between, the tropics, extra-tropics, temperate, and Polar Regions on intra-annual-to-centennial timescales.

ABSTRACT As humans increase levels of carbon dioxide in the atmosphere, climate change and ocean ... more ABSTRACT As humans increase levels of carbon dioxide in the atmosphere, climate change and ocean acidification are modifying important physical and chemical parameters in the oceans with resulting impacts on coral reef ecosystems. On one hand, rising CO2 is warming the world’s oceans and causing corals to bleach, or expel their symbiotic algae (zooxanthellae) with both alarming frequency and severity. Warmer oceans also have contributed to a rise in coral infectious diseases. Both bleaching and infectious disease can result in coral mortality and threaten one of the most diverse ecosystems on Earth and the important ecosystem services they provide. At the same time, rising CO2 is reducing the pH of the oceans and reducing the availability of carbonate ions needed by corals and many other marine organisms to build structural components like skeletons and shells. It further reduces cementation, reducing the integrity of reef structures. Ocean acidification may even be increasing the susceptibility of corals to thermally induced bleaching. Using a variety of observations and models, this talk will explore the consequences of these two stressors on corals and the importance of limiting absolute levels of atmospheric CO2—not just emissions. There is growing evidence that these stressors not only threaten reefs, but perhaps species loss as well. At least one coral species is likely to have gone extinct, others extirpated, and others at high risk due to climate change. This will only get worse as CO2 rises. At somewhere between 450-500ppm coral reefs are probably going to be unable to grow quickly enough to exceed natural forces of erosion and dissolution, resulting in net reef loss. The safe upper limit for atmospheric CO2 is probably somewhere below 350ppm, a level we passed decades ago, and for temperature is a sustained global temperature increase of less than 1.5°C above pre-industrial levels. As humans continue to increase stress on coral reefs, local actions are even more important to sustain coral reefs until we can restore more favorable environmental conditions.

Scientific Reports, 2019

Increasing heat stress due to global climate change is causing coral reef decline, and the caribb... more Increasing heat stress due to global climate change is causing coral reef decline, and the caribbean has been one of the most vulnerable regions. Here, we assessed three decades (1985-2017) of heat stress exposure in the wider caribbean at ecoregional and local scales using remote sensing. We found a high spatial and temporal variability of heat stress, emphasizing an observed increase in heat exposure over time in most ecoregions, especially from 2003 identified as a temporal change point in heat stress. A spatiotemporal analysis classified the Caribbean into eight heat-stress regions offering a new regionalization scheme based on historical heat exposure patterns. The temporal analysis confirmed the years

Current Biology, 2019

Graphical Abstract Highlights d Marine heatwaves lead to rapid coral mortality and microbial biof... more Graphical Abstract Highlights d Marine heatwaves lead to rapid coral mortality and microbial biofilm formation d Microbial metabolic activity results in rapid dissolution of the coral skeleton d Dissolution reduces skeletal hardness and density and increased porosity In Brief Due to climate change, coral reefs are now being subjected to extreme marine heatwave (MHW) conditions. Leggat et al. show that large-scale mortality due to MHWs and microbial colonization leads to a previously undescribed rapid dissolution of the coral skeleton.

Coral Reefs, 2019

The global coral bleaching event of 2014-2017 resulted from the latest in a series of heat stress... more The global coral bleaching event of 2014-2017 resulted from the latest in a series of heat stress events that have increased in intensity. We assessed global-and basin-scale variations in sea surface temperature-based heat stress products for 1985-2017 to provide the context for how heat stress during 2014-2017 compared with the past 3 decades. Previously, undefined ''Heat Stress Year'' periods (used to describe interannual variation in heat stress) were identified for the Northern and Southern Hemispheres, in which heat stress peaks during or shortly after the boreal and austral summers, respectively. The proportion of reef pixels experiencing bleaching-level heat stress increased through the record, accelerating during the last decade. This increase in accumulated heat stress at a bleaching level is a result of longer stress events rather than an increase in the peak stress intensity. Thresholds of heat stress extent for the three tropical ocean basins were established to designate ''global'' events, and a Global Bleaching Index was defined that relates heat stress extent to that observed in 1998. Notably, during the 2014-2017 global bleaching event, more than three times as many reefs were exposed to bleaching-level heat stress as in the 1998 global bleaching.

Coral Reefs, 2019

2014-2017 was an unprecedented period of successive record-breaking hot years, which coincided wi... more 2014-2017 was an unprecedented period of successive record-breaking hot years, which coincided with the most severe, widespread, and longest-lasting global-scale coral bleaching event ever recorded. The 2014-2017 global-scale coral bleaching event (GCBE) resulted in very high coral mortality on many reefs, rapid deterioration of reef structures, and far-reaching environmental impacts. Through the papers in this special issue of Coral Reefs entitled The 2014-2017 Global Coral Bleaching Event: Drivers, Impacts, and Lessons Learned, as well as papers published elsewhere, we have a good analysis of the 2014-2017 GCBE and its impacts. These studies have provided key insights into how climate change-driven marine heatwaves are destroying coral reef ecosystems: (a) The 2014-2017 GCBE is unique in the satellite record in its spatial scale, duration, intensity, and repetition of bleaching. (b) The impacts have been the most severe ever seen at many reefs. (c) Timing of observations matters and needs to be considered during the analysis of impacts. (d) On both global and local scales, the intensity of heat stress and impacts varied. (e) We continue to see important differences among and within coral taxa, with key roles played by algal symbionts and the microbiome. (f) Heat stress and bleaching both play a role in subsequent disease, which plays a key role in mortality. (g) Impacts ripple far beyond corals, with significant changes to the fish and invertebrate community that may last decades. (h) The structure of both individual coral's skeletons and entire reefs has been eroded much more quickly than previously realized. (i) The 2014-2017 GCBE provided little support for the proposed ''lifeboat'' hypothesis, whereby deep or mesophotic reefs serve as a means of coral reef salvation. (j) While marine protected areas (MPAs) provide protection from local stressors, they not only do not protect reefs from global-scale stressors, but also here is also little evidence they provide significant resilience.

Scientific Reports, 2016

Coral reefs across the world's oceans are in the midst of the longest bleaching e... more Coral reefs across the world's oceans are in the midst of the longest bleaching event on record (from 2014 to at least 2016). As many of the world's reefs are remote, there is limited information on how past thermal conditions have influenced reef composition and current stress responses. Using satellite temperature data for 1985-2012, the analysis we present is the first to quantify, for global reef locations, spatial variations in warming trends, thermal stress events and temperature variability at reef-scale (~4 km). Among over 60,000 reef pixels globally, 97% show positive SST trends during the study period with 60% warming significantly. Annual trends exceeded summertime trends at most locations. This indicates that the period of summer-like temperatures has become longer through the record, with a corresponding shortening of the 'winter' reprieve from warm temperatures. The frequency of bleaching-level thermal stress increased three-fold between 1985-91 and 2006-12 - a trend climate model projections suggest will continue. The thermal history data products developed enable needed studies relating thermal history to bleaching resistance and community composition. Such analyses can help identify reefs more resilient to thermal stress.

Coral Reef, 1996

El o related coral mortality and a subsequent increase in crustose coralline algae and sea urchin... more El o related coral mortality and a subsequent increase in crustose coralline algae and sea urchins have resulted in profound changes to the coral reef ecosystem at Uva Island, Panama (Pacific coast). New data and a model are presented that analyze the budget of the reef. The model accounts for production by corals and coralline algae, erosion by Diadema, infauna,

ABSTRACT In response to growing and widespread threats to coral reefs, in December 2012 NOAA Fish... more ABSTRACT In response to growing and widespread threats to coral reefs, in December 2012 NOAA Fisheries proposed list-ing 66 species of coral under the Endangered Species Act.

Nature Communications, 2011

Ocean acidification causes declines in calcification rates of corals because of decreasing aragon... more Ocean acidification causes declines in calcification rates of corals because of decreasing aragonite saturation states (Ω(arag)). Recent evidence also indicates that increasing sea surface temperatures may have already reduced growth and calcification rates because of the stenothermic threshold of localized coral populations. Density banding in coral skeletons provides a record of growth over the coral's lifespan. Here we present coral extension, bulk density and calcification master chronologies from seven subtropical corals (Montastraea faveolata) located in the Florida Keys, USA with a 60-year common period, 1937-1996. Linear trends indicate that extension increased, density decreased and calcification remained stable while the most recent decade was not significantly different than decadal averages over the preceding 50 years for extension and calcification. The results suggest that growth rates in this species of subtropical coral have been tolerant to recent climatic changes up to the time of collection (1996).

Mar Biol, 1991

Reproductive ecology of two major reef-building corals in the eastern Pacific [Pocillopora damico... more Reproductive ecology of two major reef-building corals in the eastern Pacific [Pocillopora damicornis (Linnaeus) andPocillopora elegans Dana] was investigated between 1984 and 1990 in Costa Rica, Panama (Gulf of Chiriqui and Gulf of Panama), and the Galapagos Islands (Ecuador) following the 1982–83 El Niño disturbance. Mature spermatocytes and oocytes were found in both species and were usually present in the

Coral Reef, 1996

El Niño related coral mortality and a subsequent increase in crustose coralline algae and sea urc... more El Niño related coral mortality and a subsequent increase in crustose coralline algae and sea urchins have resulted in profound changes to the coral reef ecosystem at Uva Island, Panama (Pacific coast). New data and a model are presented that analyze the budget of the reef. The model accounts for production by corals and coralline algae, erosion by Diadema, infauna,

Journal of Operational Oceanography, 2014

ABSTRACT Mass coral bleaching results from periods of elevated sea temperature. Satellite monitor... more ABSTRACT Mass coral bleaching results from periods of elevated sea temperature. Satellite monitoring of thermal stress has enhanced the capacity for the management of coral bleaching events worldwide. Satellite-based monitoring tools provide reef managers with cost-effective observations of temperature conditions to monitor the risk of bleaching and to target in situ observations in areas under stress. This paper describes improvements to satellite remote sensing products from NOAA's Coral Reef Watch to enhance product coverage and to correct identified errors in the production of coral reef-specific metrics for thermal stress. In addition, threats to the operational production of the thermal stress metrics are considered and a contingency plan is described to ensure continuity of operations.

Ecology Letters, Feb 1, 2011

Bulletin of Marine Science, 2007

Prior to the 10th International Coral Reef Symposium in Okinawa, Japan, in June 2004, symposium ... more Prior to the 10th International Coral Reef Symposium in Okinawa, Japan, in June
2004, symposium participants and members of the International Society for Reef Studies were surveyed to obtain their opinions about the major threats facing coral reef ecosystems. Responses from 286 participants were analyzed and compared to results obtained in a similar survey conducted in 1993. Respondents tended to rank highest those threats associated with human population growth, coastal develop- ment, and over shing. While coral bleaching was ranked much more highly than in the 1993 survey, about two-thirds of the respondents felt that direct human impacts were worse threats than those associated with global climate change.

Bulletin of Marine Science Miami, Jun 30, 2001

Abstract: Numerous changes have occurred at the Uva Island reef since the original calcium carbon... more Abstract: Numerous changes have occurred at the Uva Island reef since the original calcium carbonate budget model was published (Eakin, 1996). Minor bleaching events occurred during the 1990s and a widespread event occurred in 1997-98. In 1989 and 1993, reef flat ...

Earth Sci Rev, 2007

This paper is a review of published modern coral δ18O and Δ14C isotopic records that are at least... more This paper is a review of published modern coral δ18O and Δ14C isotopic records that are at least 30 and 20 years long, respectively. The data are presented to show basin-scale trends in both of these proxy records on decadal-to-centennial timescales. The goal was to qualitatively integrate the general inter-annual-to-centennial timescale variability revealed in these data, as well as the statistical and modeling output results that have been produced using these coral records. While many review papers typically include a representative subset of the data available, this review aims to include as much of the available data as possible. In general, coral δ18O records show a long-term warming and/or freshening throughout the tropical oceans, and agree with the NOAA Extended Reconstruction Sea Surface Temperature 2 (ERSST) on decadal timescales. In the western Pacific, it is most likely a freshening of the seawater δ18O that dominates the signal. El Niño Southern Oscillation (ENSO) variability dominates most δ18O records either by varying local seawater temperature or salinity, depending on the regional oceanography/climatology. Outside of the Pacific, ENSO affects seawater temperature and salinity via atmospheric or oceanic teleconnections. Post-bomb coral Δ14C records collectively show that the uptake of 14C has been greatest in gyre-water fed sites, followed in descending order by western boundary current areas, equatorial upwelling regions, and eastern tropical Pacific upwelling sites. These surface water Δ14C values indicate the proportion of surface water and/or the residence time of water at the surface at a given location, and can be used to model water mass mixing rates. Such models have only begun to be run and show that the amount of eastern Pacific water entering the central South Pacific increases during El Niños and that the Indonesian throughflow is supplied year-round by the North Pacific. Comparing ocean circulation models with coral Δ14C-modelled circulation enables researchers to explore the mechanisms that drive seawater Δ14C variability and fine-tune their models. In addition, our comparison between the rate of coral Δ14C increase between 1960 and 1970 and total anthropogenic CO 2 uptake rates show general agreement, demonstrating the value of coral records in understanding past carbon fluxes. Overall, coral δ18O and Δ14C proxy records represent natural archives of seawater conditions and are critical for studying the natural variability in local and regional patterns within, and teleconnection patterns between, the tropics, extra-tropics, temperate, and Polar Regions on intra-annual-to-centennial timescales.

ABSTRACT As humans increase levels of carbon dioxide in the atmosphere, climate change and ocean ... more ABSTRACT As humans increase levels of carbon dioxide in the atmosphere, climate change and ocean acidification are modifying important physical and chemical parameters in the oceans with resulting impacts on coral reef ecosystems. On one hand, rising CO2 is warming the world’s oceans and causing corals to bleach, or expel their symbiotic algae (zooxanthellae) with both alarming frequency and severity. Warmer oceans also have contributed to a rise in coral infectious diseases. Both bleaching and infectious disease can result in coral mortality and threaten one of the most diverse ecosystems on Earth and the important ecosystem services they provide. At the same time, rising CO2 is reducing the pH of the oceans and reducing the availability of carbonate ions needed by corals and many other marine organisms to build structural components like skeletons and shells. It further reduces cementation, reducing the integrity of reef structures. Ocean acidification may even be increasing the susceptibility of corals to thermally induced bleaching. Using a variety of observations and models, this talk will explore the consequences of these two stressors on corals and the importance of limiting absolute levels of atmospheric CO2—not just emissions. There is growing evidence that these stressors not only threaten reefs, but perhaps species loss as well. At least one coral species is likely to have gone extinct, others extirpated, and others at high risk due to climate change. This will only get worse as CO2 rises. At somewhere between 450-500ppm coral reefs are probably going to be unable to grow quickly enough to exceed natural forces of erosion and dissolution, resulting in net reef loss. The safe upper limit for atmospheric CO2 is probably somewhere below 350ppm, a level we passed decades ago, and for temperature is a sustained global temperature increase of less than 1.5°C above pre-industrial levels. As humans continue to increase stress on coral reefs, local actions are even more important to sustain coral reefs until we can restore more favorable environmental conditions.