The emergent effects of ocean acidification

Ocean acidification is considered a threat to global marine ecosystems. It is caused by rising atmospheric carbon dioxide (CO2) concentrations, which reduce seawater pH and drive large-scale changes in the carbonate chemistry. This process of ocean acidification is underway and will accelerate with CO2 emissions. Many marine organisms are sensitive to changes in the carbonate chemistry, and their physiological/behavioral responses to ocean acidification could lead to profound ecological shifts in marine ecosystems. However, the ecosystem responses to ocean acidification are still largely unknown. Most experiments measure the responses of a single species to extreme conditions over short time periods, and may not accurately predict the consequences to ecosystems. Additionally, there is a limited ability to make inferences about ecosystem effects from single species experiments because the responses of marine communities are likely to be complicated by species interactions. Despite these challenges, it is critical that scientists describe the effects of ocean acidification on marine communities and ecosystems to inform effective management.

My dissertation research utilizes naturally occurring seawater pH gradients from these volcanic CO2 vents to examine community and ecosystem-level responses to ocean acidification. Volcanic CO2 vents are naturally occurring sources of submarineCO2. They provide a novel opportunity to examine the broad ecological consequences of ocean acidification because the associated changes in seawater chemistry occur over ecologically relevant temporal and spatial scales. Vents persist for hundreds of years and incorporate ecological processes in the ecosystem response. Additionally, the acidification surrounding vents affects entire communities and allows researchers to examine important changes in species interactions. A series of CO2 vents off the coast of Ischia, Italy reduce seawater pH, and have been correlated with reduced species richness. While the benthic marine communities surrounding the vents are typical of Mediterranean rocky reefs (i.e., diverse communities with abundant calcifying organisms) the communities directly adjacent to the vents are dominated by fleshy algae and devoid of calcifying organisms such as sea urchins, gastropods, and coralline algae.

I was awarded the Arthur C. Giese Award for Distinguished Research in Marine Biology for my research quantifying the resilience of the benthic communities along the naturally occurring pH gradient from the Ischia vents. Resilience is a measure of ecosystem function and can be estimated by the rate of recovery and resistance to disturbance. Ecological resistance is defined as the amount of disturbance a system can withstand without fundamentally changing the structure and function. Communities with low functional redundancy, the number of taxonomically distinct species that fill the same ecological functions, may have lowered resistance because the loss of any single species can alter community structure. This may be important in low pH communities, which have been shown to have lower species richness.

The funds from the Giese Award allowed me to attend a workshop on the Best Practices in Ocean Acidification Research in Kiel, Germany in 2010. This opportunity has been incredibly beneficial for my dissertation research, and I am incredibly grateful to have had the opportunity!

Kristy Kroeker, Hopkins Marine Station News, Article.

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