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Bacterial Degradation of Marine Particles: Colonisation, Dispersal, and Impact on Vertical Export in the Ocean

Final Report Summary - BACPAC (Bacterial Degradation of Marine Particles: Colonisation, Dispersal, and Impact on Vertical Export in the Ocean)

The aim of the project BacPac was to provide new knowledge on the role of heterotrophic bacteria in the oceans biological carbon pump, i.e. the export of particulate organic matter from the productive surface layer of the ocean to the deep sea. The specific objectives were to investigate whether sinking particles are colonised by the same bacterial communities as those present in the ambient water column, how efficiently they degrade sinking organic particles, and if these patterns differ spatially and temporally. While providing improved knowledge of marine ecosystem functioning, the objectives are also highly relevant for a better understanding of the factors controlling microbial diversity in the ocean.

In important objective was to provide the researcher Dr. Tamelander with fresh research skills in molecular techniques and bioinformatics, and complementary skills that would improve his academic competence and possibilities to become established as an independent scientist.

To meet the objectives, both field-based research and controlled laboratory-based experiments were performed during BacPac. Patterns in the bacterial community composition and activity in suspended and sinking particles were studied in the field in North Atlantic and Arctic settings, allowing the comparison between oceanographic regions and seasons. This study it importantly showed that sinking particles are primarily colonised in the surface layer where particle formation takes place, and that the community is retained during transit to depth. Hence, sinking particles may provide an input of new bacterial taxa to the deep-sea environment. There was also a trend towards higher hydrolytic enzyme activity of bacteria associated with sinking particles.

Zooplankton faecal pellets typically comprise an important part of the sinking organic matter in the marine environment due to their fast sinking speed. To further evaluate the role of phytoplankton-zooplankton interactions for the colonisation process, an experiment using the lab-reared copepod species Acartia grani was performed. In this experiment, the copepods were fed either of three different phytoplankton species or starved, and the bacterial community composition developing on the copepods and in the egested faecal pellets were monitored over time. This experiment will help resolve whether the bacterial community in zooplankton faecal pellets, which are an important component in the vertical flux of organic matter from the productive surface layer, stem from the diet or from the gut of the consumers. This is an important question, since the degradation rate of faecal pellets likely will be affected by the environmental conditions the pellet-associated bacteria are adapted to (zooplankton gut or in association with phytoplankton cells).

BacPac has further investigated zooplankton as “marine particles”, determining the variation in the bacterial community composition associated with different zooplankton species form the Western Mediterranean Sea (seasonal variation) and along a transect from the eastern to the western part of the Mediterranean Sea and the East Atlantic Ocean. Large-sized zooplankton has the ability to migrate between density-separated water layers, and may therefore contribute to two-directional exchange of bacterial taxa between the surface layer and deeper layers. Preliminary analyses revealed that the zooplankton-associated bacterial communities generally had low species numbers compared to the ambient water-column, but included taxa rarely found in the marine environments. These analyses also indicated feeding by the zooplankton on picocyanobacteria, which are highly abundant in the marine environment but are considered too small in size to be grazed by most zooplankton.

In order to solve these questions, BacPac invested significantly in the development of researcher skills. Training the researcher in molecular biological methods and bioinformatics were emphasized, in order to promote the use of these methods in ecological studies. This is considered a fruitful way forward in marine biogeochemistry, and the scientific community will benefit significantly from scientists whose expertise encompass both biogeochemical, classical ecological, as well as molecular methods and bioinformatics needed to analyse data from next generation sequencing technologies.

Dissemination activities (conference contribution, seminars, publication activities) during BacPac have increased Tamelander’s international contacts and improved his presentation and teaching skills. As a sign of success, Tamelander’s application and trial lecture for the academic title “docent” at the University of Helsinki were evaluated positively in May 2014. This title is used in particular at universities within the Nordic countries as a sign of competence in teaching and eligibility for professorship. Hence, activities during his Mare Curie Fellowship have clearly strengthened his academic qualifications.

The results obtained through BacPac will directly benefit the scientific community by providing new knowledge on bacterial community characteristics and degradation activity on organic matter that is exported from the oceans productive surface layer. This is highly relevant to the successful development of biogeochemical models used to delineate the marine carbon cycle.

Given the pressure on the marine environment globally from human activity (eutrophication, rising levels of carbon dioxide, increasing temperature and sea ice loss in Polar Oceans), society has a need for the development of successful environment management strategies in order to ensure sustainable use of marine resources. Crucial to this is a thorough understanding of the factors regulating structure of marine food webs and processes regulating elemental cycles. By providing new knowledge on essential biogeochemical and ecological processes, BacPac will in the long run benefit such efforts.

The training has also contributed to the increased competence of a researcher, thereby improving the demand for highly qualified research personal within the ERA and strengthening the competitiveness of European science. Before the termination of BacPAc, Tamelander was recruited to a research position in Finland where he aims to establish his own research group.