Roles of free-living and particle attached bacteria in subarctic estuarine systems.

In particle rich subarctic estuarine systems, like the Hudson Bay, free living and particle-attached bacteria play an integral role in recycling and exportation of particulate organic matter. To help us to understand the global carbon cycle and estimate biological pump efficiency we need to develop our knowledge of the transfer of particulate organic matter within the food web, its movement through the water column and the processes involved with recycling it

Particle attached bacteria are often larger then free living bacteria so it is assumed that their metabolic activity is believed to be more active on a per cell basis, however the opposite has been observed. In particle rich estuarine systems particle attached bacteria may reach more than 60% of the total bacterial abundance. As a result of this dominance they have been shown break down a larger fraction of the organic matter associated with sinking particles then free living however as a result of a discrepancy called “particle decomposition paradox” particle attached bacteria hydrolyse organic much faster compared to their uptake of the end product. So only a small portion is of POC is respired by particle attached. Making the free living bacteria are the main recyclers during sedimentation.

The objectives of the study were first to determine abundance, cell size, sinking velocity of particle attached and free living bacteria and their relationship with environmental conditions. The second to develop a carbon budget to consider the potential contribution of particle attached bacteria to total POC sinking export and to total carbon loss through bacterial respiration. They predicted that particle attached bacteria will have sinking velocities higher than predicted by Stoke’s law therefore can potentially contribute to POC sinking flux. Also that particle attached would dominate bacterial abundance.

The results showed that particle attached bacteria are dependent on the number and or size of particles available for attachment this was demonstrated by the positive relationships between bacterial biomass and POC concentration. They did not observe any significant difference between sampling depths, 50% of surface irradiance and the deepchlorophyll a maximum, despite large differences in the environmental conditions. This is likely to be the result of a balance between bacterial growth rates and grazing pressure.

This study is an important contribution to our understanding of these systems as to the author’s knowledge no other study has addressed these bacteria’s dual role in recycling and exporting of POM. This study for the first time combines the settling column method with flow cytometry which allows them to simultaneously determine: characteristics, abundance and sinking velocities of the target bacteria. Particles called Microaggregates (marine snow) have been studied extensively while they have taken a different approach and focused on the bacteria attached to them and most notably on the protist cells. It is integral for us to develop our understanding of these relationships because as climate change causes permafrost to melt there will be an increase in particle load into the estuarine systems like The Hudson Bay. This will lead to a massive increase in the abundance of particle attached bacteria meaning they will play an even larger role in the organic carbon cycling process

A review of: A. Lapoussiere et al Role of free-living and particle-attached bacteria in the recycling and export of organic material in the Hudson Bay system. Journal of Marine systems 88 (2011) 434-445