How does ocean acidification affect carbon dioxide sequestration in coccolithophores?

Methods

Summary

At the Leibniz Centre for Tropical Marine Ecology, we will initially collect surface samples from the North Sea and culture the plankton with ordered Emiliania huxleyi from UTEX. We will grow multiple generations in culture batches by following the procedures described by Dr. Bach and co-authors. We will then transport specimens into three separate mesocosm tanks, each with different controlled CO₂ levels. For further information on our lab space, readers can follow the MAREE lab link to learn more.

Our results will be analyzed in three components. Through growth rates and overall coccolith abundance, we will observe physiological changes in coccolithophore. We will determine changes in mesocosm calcification rates by calculating changes in abundant particulate inorganic carbon (PIC). In addition, our various forms of microscopy and eDNA analysis will discern our plankton community structures. The following methods of analysis illustrate the impacts of ocean acidification on coccolithophores, environmental calcification productivity, and plankton biodiversity.

Challenges

One of the greatest challenges of this project is the replication of the natural environment. A failure here may skew our results towards artificial community responses and may belie plankton adaptations to ocean acidification in the natural environment. To avoid this risk, we will model our mesocosms after the environments where we collect field samples. We will record environmental conditions, like water temperature, pH, light, and various nutrient levels, and culture the plankton from our chosen sites. Consequently, we will incorporate the natural environmental parameters and plankton communities into our mesocosm studies.

These ecological variables, such as temperature and pH levels, are also components of ocean acidification and will impact plankton assemblages. As we aim for a holistic research project, we will include these parameters into our analysis and observe variable changes through temperature and pH gauges. Based on available mesocosm tanks, we will repeat our methods to simultaneously altering CO2, temperature, and pH levels for a closer replication of ocean acidification.

Pre Analysis Plan

After an experimental period of two months, we will measure the effects of rising CO₂ on coccolithophores through physiological and chemical analysis. By utilizing both  light microscopy and scanning electron microscopy (SEM), we will determine coccolithophore population sizes and coccolith abundance We will calculate cellular growth rates based on the growth equation from Bach et al., 2013. Additionally, we will use Gasbench analysis to measure particulate inorganic carbon (PIC) levels.               

Community structure identification will begin with low vacuum and backscatter SEM observations of our field specimens. When paired with eDNA analysis, we will identify the local coccolithophore and phytoplankton species in our samples. Coccolithophore classification will rely on the following identification guide. After we complete the mesocosm experiments, we will repeat SEM and eDNA analysis to compare how community structures change after increased CO₂ levels.