Food quality matters in the deep
“Organic matter will be consumed by the ocean floor organisms if the ‘quality’ is good enough”, stated Lara Pozzato in her PhD Thesis. The quality is more important than, for example, the amount of oxygen in the environment. Pozzato studied the interactions among organic matter and organisms at sea floors in different settings. She will defend her PhD thesis on November 16, at the Utrecht University.
In oceanic sediment, there are a lot of interactions among organic matter and organisms. Organic matter can be processed by bacteria, protozoa or animals, or can be stored in the sea floor. Under different circumstances, different organisms live in or at the sea floor. In some areas of the deep sea, there is a limited amount of oxygen, so there are other organisms living there, compared with the seafloor in shallow waters with more oxygen. Pozzato did research in oxygen-poor circumstances in the Arabian Sea and in more oxygen-rich circumstances in the Western Mediterranean and Eastern Atlantic.
The deep sea covers about 50% of our planet. It’s an unknown territory, that we are starting to exploit. But before doing this, we need knowledge of the environment, the organisms living in the deep sea and how they interact, i.g. in the carbon cycle. Deep sea sediment is a permanent carbon storage (about 150 Gt per year) that can therefore sequestrate CO2. It’s important to know how much carbon is removed from the system and the impact on the global CO2 cycle.
Pozzato found that the amount of organic matter that is not processed, but accumulated on the sea floor, is not dependent on the type of organisms living on the sea floor, but mainly due to the quality of the organic matter itself. A high quality means fresh organic matter with a lot of degradable compounds, the more refractory the organic matter the lower its quality.
Community structure and temperature do not seem the main factors regulating organic matter processing.
There is a big difference in the processing of organic matter, depending on its form. Dissolved organic matter could only be processed by bacteria and the carbon derived by its consumption was not transferred up the food chain. Conversely, other organisms depend only on particulate organic matter.
More complex organisms, such as bivalves, process and utilize organic matter in different ways than i.e. bacteria or protozoans. Laboratory experiments with the common cockle (Cerastoderma edule) provided new insights on the synthesis of carbohydrates, amino acids as well as specific fatty acids (PLFAs) production. Cockles use different food sources for different metabolic processes. Therefore, a mixed diet is necessary for the animals to thrive. Pozzato concluded that you are not what you eat, but what you make of your food.
This thesis was accomplished with financial support from the Netherlands Organisation for Scientific Research (NWO), Darwin Center for Biogeosciences and the European Science Foundation (ESF).
Lara Pozzato (1979) was born in Italy. She got a Masters degree in Environmental marine science from the University of Trieste in 2006. Since 2008 she worked at NIOZ Yerseke at her PhD research.
Photo’s:
Deep-sea sediment cores obtained via multicorer.
Branched foraminifera.
Lara Pozzato.
An oxygen minimum zone sediment core. Hard shelled foraminifera.
Endemic oxygen minimum zone polychaete, Flagellate green algae in culture.
Linopherus sp.