How Sedimentation, Nutrient Enrichment, and Overfishing Impact a Coral Reef Ecosystem Immediately Following a Disturbance

by Natalie Ireland

Coral reefs are regularly disturbed by natural phenomena such as bleaching, storms, and outbreaks of predators, such as the corallivorous sea star Ancanthaster planci. Corrallivores are animals that eat coral polyps. Coral reef ecosystems are resilient, and are often able to recover from large-scale disturbances quickly. However, anthropogenic stressors such as overfishing, nutrient enrichment, and sedimentation can prevent coral reefs from recovering. Nutrient enrichment, caused by terrestrial runoff, creates the perfect environment for benthic algae to grow on disturbed and broken coral reefs. Overfishing, working in tandem with nutrient enrichment, causes an overgrowth of algae if there are not enough fish to graze it, and the successive degradation of the reef. Sedimentation is also another side effect of terrestrial runoff. Sedimentation buries corals, which blocks light from reaching them and potentially stops coral recovery. However, sedimentation, when not paired with any other stressor, can also stop the growth of algae by burying surfaces for algae to grow on. Gil et. al. (2016) set out to test the interactive effects that overfishing, sedimentation, and nutrient enrichment have on coral reefs in French Polynesia. They hypothesized that these anthropogenic disturbances, when working interactively, will negatively impact corals, while promoting algal cover. Continue reading

The Important Role Small Herbivores Play on Degraded Coral Reefs

by Natalie Ireland

Biodiversity is constantly being altered by anthropogenic and natural variants. Due to ocean acidification, and rising ocean temperatures, coral reef systems have degraded, and algae has come to dominate some of these systems. Macroalgae are aggressive and quickly colonize areas where coral has been degraded, and heavy algae cover of dead coral substrates prevents recovery of dead coral communities. A study conducted by Kuempel and Altieri (2017) set out to discover how coral reefs adapt to changing environments and how individual species living along the reefs promote resilience. The presence of herbivores, such as parrotfish, sea urchins, and other small grazing fish around degraded coral reefs likely halts the shift from coral-dominated areas to algae-dominated areas. Understanding the rate of recovery for coral reef dynamics can help scientists predict future coral resiliency and aid conservation efforts.

Kuempel and Altieri studied coral reefs on the Caribbean coast of Panama after a recent hypoxic event killed over 90% of coral on some reefs in that area. They chose to study this area because it has high anthropogenic stress, increasing the chance of a higher rate of algal dominance after coral disturbances. Using field surveys, herbivore manipulation, caging, and algal transplant, Kuempel and Altieri were able to study the relationships between herbivore populations, pressures that herbivores face, and grazing importance in relation to other algal mitigating factors.

This study found that there was no correlation between mass coral reef deaths and high rates of macroalgae cover. A large number of herbivores, mostly small grazing fish and invertebrates, around dead coral areas was almost always able to prevent macroalgae from colonizing. Many species of smaller herbivores were able to escape the pressures of overfishing and effectively graze coral reefs in place of large keystone herbivores. This prevented macroalgae from aggressively colonizing places where live coral cover was very low. Initial diversity in coral reef fish species is important in degraded coral reefs to overcome anthropogenic pressures and stifle macroalgae growth. Further research must be done to determine whether grazing by small herbivores can shift a coral degraded area into a coral dominated area and how this will impact future coral resilience.

Kuempel, C.D., Altieri, A.H., 2017. The Emergent Role of Small-Bodied Herbivores in Pre-empting Phase Shifts on Degraded Coral Reefs. Scientific Reports 7, 10:1038.

https://www-ncbi-nlm-nih-gov.ccl.idm.oclc.org/pmc/articles/PMC5215077/pdf/srep39670.pdf

 

 

Using Projected Climate Change Impact on Coral Reefs to Explore a New Framework for Equity

by Wendy Noreña

The effect of greenhouse gas (GHG) emissions on ecosystem services is a subject of major concern in climate policy and conservation. Coral reefs are considered an especially vulnerable ecosystem as they are projected to be highly affected by ocean warming and acidification, both of which are generally thought to be likely consequences of climate change. While much research has already been conducted to determine the damage coral reefs will suffer as a result of climate change, surveys of how individual countries will be affected by coral reef devastation have not yet been implemented. Wolff et al. model both in this study, showcasing projected climate stress on reefs from 1875 to 2050 alongside measures of vulnerability and equity for individual countries and regions based on GHG emissions per capita and expected reef devastation. The study finds an alarming decoupling between total GHG emissions and reef impact, indicating that, in general, countries that emit the most GHG will often experience less reef impact while the opposite is true for countries that emit very little GHG. Continue reading

Conservation Measures and using the Fates of Past Reefs to project Future Scenarios

by Dawn Barlow

Kennedy et al. (2013) examine the structural and ecological human-caused damage on coral reefs in the Caribbean since the 1960s and then generate modeled predictions for what coral reefs in the Caribbean might look like between now and the year 2080 if practices of local conservation and global action were to be implemented. They examine driving ecological factors of Caribbean reefs, reconstructing past disturbances to address the important roles that all of the many pieces play in contributing to overall health of the reefs. Some of these disturbances between the 1960s and the 2000s include depletion of the reef due to overfishing, loss of branching corals because of disease, bleaching, and bioerosion, hyperabundance of urchins because their predators were lost to overfishing, loss of urchins because of disease, poor watershed management that has led to changes in nutrient abundance, and ongoing climate change since the 1960s. In order for a coral reef to maintain its structure, the rate at which carbonate is produced must be greater than the rate of erosion—the carbonate budget must be positive. In order to maintain a carbonate budget that is either positive or at equilibrium, Kennedy et al. suggest that local management for the protection of grazers such as parrotfishes is important and can create a positive carbonate budget for reefs starting out with higher coral cover and keep reefs with lower coral cover to begin with near equilibrium, at least in the short term. In the long term however, aggressive mitigations will need to take effect on a global scale for there to be hope of maintaining a carbonate budget near equilibrium. Continue reading

Reef State and Resilience in a Climatically Changing Environment

by Kimberly Coombs

Climate change has been impacting coral reefs all over the world, and many models have been created to predict how coral reefs are going to respond to global climate change, in particular, global warming. It has been reported that the effects of greenhouse gas emissions have reduced coral reefs resilience, causing them to be more susceptible to stressors in their environment. As a result, coral reef state, the percent of coral cover, has begun to be greatly lessened, with a noticeable shift from coral dominated environments to macroalgae environments. Continue reading

Algal Symbionts may make Corals Resistant to Rising Sea Temperatures

by Kimberly Coombs

Corals share a mutualistic relationship with algal symbionts, but with increasing sea temperatures, these symbionts become expelled from the coral. The loss of symbionts causes the corals to become bleached and there have been declines of coral cover worldwide. Recent research has shown that there may be symbionts that are thermotolerant, such as the genus Symbiodinium, which may help reduce the amount of bleaching episodes seen amongst corals. Symbiodinium is divided into nine subgeneric clades, A-I, and the Symbiodinium D1a has been documented showing thermotolerance. Continue reading

A Strategy for Response to Climate Change in Marine Conservation

by Weronika Konwent

     An effect of global warming is an increase in sea-surface temperatures (SST), which impacts the distribution and range of corals. As temperatures increase, coral distribution will shift poleward. This is problematic because current marine protected areas do not take into account the distribution effects of climate change. Continual shifting of MPAs as conditions worsen is more than likely to meet political and logistical roadblocks. Makino et al (2014) established an integrative system by which to determine priority selection of habitats for MPAs. This research aims to create a process through which climate change can be factored into subsequent MPA planning, and will cater to coral distribution trends not only now but in the future as well. Continue reading

Potential Coral Reef Structure Changes from Climate Change

by Kimberly Coombs

Coral reefs vary in structural architecture, meaning that the structure can be very complex or relatively simple. The more structurally complex a coral reef is, the more species diversity may be supported. The reef building corals that create the complex coral reef structures need to have a sustainable carbonate budget in order to continue the processes of accretion and erosion to build the coral reefs. These corals have been experiencing reductions in their carbonate budget; as a result, they have declined around the world. Continue reading

Just Released! “Energy, Biology, Climate Change”

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Our newest book, published on May 6, 2015 and available at Amazon.com for $19.95.

The focus of this book is the interactions between energy, ecology, and climate change, as well as a few of the responses of humanity to these interactions. It is not a textbook, but a series of chapters discussing subtopics in which the authors were interested and wished to write about. The basic material is cutting-edge science; technical journal articles published within the last year, selected for their relevance and interest. Each author selected eight or so technical papers representing his or her view of the most interesting current research in the field, and wrote summaries of them in a journalistic style that is free of scientific jargon and understandable by lay readers. This is the sort of science writing that you might encounter in the New York Times, but concentrated in a way intended to give as broad an overview of the chapter topics as possible. None of this research will appear in textbooks for a few years, so there are not many ways that readers without access to a university library can get access to this information.

This book is intended be browsed—choose a chapter topic you like and read the individual sections in any order; each is intended to be largely stand-alone. Reading all of them will give you considerable insight into what climate scientists concerned with energy, ecology, and human effects are up to, and the challenges they face in understanding one of the most disruptive—if not very rapid—event in human history; anthropogenic climate change. The Table of Contents follows: Continue reading

The Economic Value of Coral Reefs

by Kimberly Coombs

Coral reefs are known for supporting a habitat rich in species diversity and abundance. Besides the benefit coral reefs provide to other species, they also offer a benefit to humans. Coral reefs provide a source of economic gain in terms of tourism and fisheries, usually bringing in about $30 billion each year. However, climate change is threatening to diminish this revenue as corals become bleached and experience higher rates of mortality.

Chen et al. (2015) conducted a study to estimate the global economic impact from loss of corals as a result of climate change. They identified three main factors from climate change that impact coral reefs the most: sea surface temperatures, CO2 concentrations in the water, and sea level rise. In order to assess the impact of these factors on coral reefs, Chen et al. used a threshold model in which they found that there are two temperature thresholds that may negatively impact coral reefs. When sea surface temperatures are between 22.37 and 26.85, coral cover may increase; conversely, when sea surface temperatures drop below 22.37 or rise above 26.85, coral cover decreases. Chen et al. found that increasing CO2 concentrations also cause a decrease in coral cover, while sea level fluctuations were found to have no significant effect.

In order to evaluate the value of coral reefs, Chen et al. used a meta-analysis that incorporated the percent coral cover, number of visitors to the reefs, GDP per capita, and the tourism expenditure for each visitor. They found that when coral cover decreased, reef value was reduced. The number of visitors correlates negatively with coral reef value because visitors prefer to visit uncrowded coral reefs. The GDP per capita and the tourism expenditure for each visitor were found to have positive effects on coral reef value.

Lastly, Chen et al. developed four different mitigation scenarios in response to climate change to evaluate coral reef value. The impact of these different mitigation scenarios on tourism and recreation revenue varies as coral cover varies under these scenarios. The economic loss ranges from $1.88 billion to $12.02 billion by the year 2100. Chen et al. noted that this result only represents the coral reef value from tourism and recreation and that there are many other factors that will be impacted by a decline in coral cover; therefore, they create a crude economic loss estimate under these four mitigation scenarios that ranges from $3.72 billion to $23.78 billion.

Overall, CO2 and sea surface temperatures will affect coral cover, which will reduce the coral reef value. A reduction in coral reef value reduces the recreation and tourism expenditures amongst other factors; therefore, ensuring coral cover remains high will give a higher guarantee that recreation, tourism.

Chen, P., Chen, C., Chu, L., McCarl, B., 2015. Evaluating the economic damage of climate change on global coral reefs. Global Environmental Change, 30, 12-20.