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Waquoit Bay, from the National Estuarine Research Reserve boathouse.

Studying Bacterial Ecology in Waquoit Bay

Marine bacteria are key players in the ocean’s carbon cycle. They are the only organisms that are able to recycle the large pool of dissolved organic carbon that is ultimately derived from algal photosynthesis. The major part of this carbon is respired by bacteria but the remaining fraction that is incorporated into bacterial cell growth is important in fueling marine microbial food webs. Both processes, photosynthesis and bacterial production, are likely to be affected by global warming in ways that we are only beginning to understand. For example, experimental work has suggested a disruption of the bacteria-phytoplankton relationship at higher temperatures.

To study these processes, Xosé Anxelu G. Morán, a Spanish microbial ecologist on sabbatical at the Ecosystems Center, is conducting fieldwork in the Waquoit Bay estuary. Coastal embayments and estuaries in heavily populated areas such as this one, where bacterial respiration exceeds total photosynthetic production, have been identified as net sources of carbon dioxide to the atmosphere. This is due to the presence of large amounts of dissolved organic carbon from sewage and fertilizers that leach into the groundwater. Waquoit Bay, part of the National Estuarine Research Reserve System, is a perfect location for studying how carbon supply controls bacterial metabolism and for testing hypotheses about possible future directions of change.

Waquoit Bay has been extensively studied by Ecosystems Center scientist Ivan Valiela and other researchers, but knowledge of the role of bacteria in the transformation of dissolved organic carbon is scarce. Dr. Morán’s project will help to fill this gap. So far, Morán has sampled four different sites within the Waquoit Reserve in May, June, July, August and October. Each time, three samples are taken at each of three sub-estuaries, which vary greatly in their inorganic nutrient (nitrogen) and organic nutrient (dissolved organic carbon) loading: Childs River, Quashnet River and Sage Lot Pond, together with a site outside Waquoit Bay entrance canal in Vineyard Sound. The samples are then analyzed in the Ecosystems Center analytical laboratory and flow cytometry facility to determine bacterial abundance and biomass, single-cell physiological structure and bacterial production, as well as nutrients, dissolved organic carbon, dissolved organic nitrogen and chlorophyll and rates of photosynthesis and dissolved organic carbon exudation.

Dr. Morán is with the Instituto Español de Oceanografía (IEO) in Xixón, Asturies, in northern Spain. His sabbatical with Ecosystems Center director Hugh Ducklow is funded by the Spanish Ministry of Education and Science. Dr. Morán has been assisted in his work by Ecosystems Center senior research assistant Matthew Erickson, MBL-Brown graduate student Yawei Luo, and summer undergraduate student intern from Switzerland, Stephane Aebischer.