CoccoTrait: Revealing Coccolithophore Trait diversity and its climatic impacts

Thanks to tiny organisms called phytoplankton, the ocean plays a crucial role in regulating atmospheric CO2 and hence our climate. Phytoplankton are primary producers and use CO2 and light to grow. Despite being tiny, they grow in enormous quantities in the ocean, making them one of the most important primary producers of the planet. One marine phytoplankton, the coccolithophores, are particularly important because they take up CO2 and calcify simultaneously. Calcification is also vital because it changes the ocean's ability to take up CO2. Coccolithophores calcify beautifully ornamented plates of distinctive shapes. Each shape occupies a different ocean region, proving that morphology is critical at controlling coccolithophore distribution and contribution of the ocean CO2 uptake. About 250 species of coccolithophore live in the ocean, showing a variety of morphology, cell size and calcite content. However, most studies of coccolithophores rely on a single species. This species is the most abundant but one of the smallest and least calcified coccolithophore species; hence it is not representative of the coccolithophore community as a whole.

CoccoTrait aims to re-assess the role of coccolithophore in our climate system by including a fuller appreciation of its biodiversity. We will take advantage of new data that describe coccolithophore's main traits (e.g., size, morphology, calcite content) and apply combined statistical and mechanistic methods to address two goals:

(1) Defining the key species that characterise coccolithophore biodiversity. Not all species matter, so it is critical to identify the ones that matter the most for the carbon cycle. To do that, we will use trait-based ecology, which recognises groups of species with similar traits and functions, allowing us to study complex biological systems in a simple yet meaningful way.

(2) Determining the influence of coccolithophore diversity on the ocean carbon cycle and how it will change with climate change. Once we identify the critical coccolithophore species, we will estimate how much they contribute to ocean carbon productions and vary with climate change. Coccolithophores are already impacted by ocean warming and acidification, changing which species influence the ocean carbon cycle. We will use state-of-the-art modelling to assess their global contribution to modern and future climate.

The project combines statistical and mechanistic methods, which is unique in studying marine plankton ecology but essential to accurately estimate the climatic impacts of ocean biodiversity. We will validate this approach with coccolithophore, showing the potential to fully represent the complex ecology of other plankton to map their role in the climate system.