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.



Global Climate Change Inequity: Who’s Carrying Whom?

by Coco Coyle

Because the Earth’s atmosphere intermixes globally, all areas of the globe are equally exposed to greenhouse gas emissions (GHGs). However, some countries are more vulnerable to the effects of these emissions, while some countries release more GHGs into the atmosphere than others. Althor et al. (2016) compare each country’s vulnerability to climate change to its creation of GHGs for the years 2010 and 2030. They found that the countries least vulnerable to climate change were higher GHG emitters, and the most vulnerable countries were least responsible for GHG emissions. By 2030 the inequity will have worsened. The authors call for climate change policies that place more responsibility for mitigating climate change on the high-emitters. Continue reading

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

Symbionts Impact the Behavior of Coral Larvae

by Kimberly Coombs

Climate change is known for causing adults corals to become bleached, but it is also affecting the early life stages of corals. The larval stage of a coral reef’s lifecycle is very important to its survivorship. Corals disperse their larvae out into the water, then the larvae are responsible for finding a suitable substrate to settle on. After settlement, corals are able to start growing accumulate symbionts. Several studies have observed how different symbionts influence juvenile coral growth rates and thermotolerance; however, no data currently show if there are any influences from symbionts on the coral larvae before settlement occurs. 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

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