For many years it has been understood that marine microbes play a vital role in the oceans food webs. Probably the most important role is carried out by the photoautotrophic primary producers. These microbes use the energy from the sun and CO2 to produce organic molecules that are essential for life. Other marine microbes may either feed on these organisms or on dissolved organic molecules (DOM) that have found their way into the water column from these cells. The largest contributors to primary production are two genera of Cyanobacteria called Synechococcus and Prochlorococcus which are found throughout the world’s oceans.
It is easy to think of the marine food web as never changing and being a constant loop. The truth is that many things can have an impact on the way an ecosystem works. Any change in the dynamics or abundance of a primary producer like Prochlorococcus could change the whole microbial community found in that area. This in turn could affect larger organisms and continue up the food web.
In this paper the authors studied the temporal and spatial dynamics of several Prochloroccus clades, referred to in this study as ecotypes, in the Atlantic and Pacific oceans near the islands of Bermuda and Hawaii respectively. This was done in order to explore whether normal changes in environmental factors could have a significant effect on which ecotype is dominant. Samples were collected continuously over a 5 year period at depths ranging between 1 and 200m. PCR and flow cytometry were used for species identification and measure of abundance. Measurements in light, temperature and mixing of the water column were also taken to investigate environmental changes.
This study found that there seems to be a strong annual pattern of ecotype abundance and succession of which ecotype was dominant throughout the year. Two ecotypes that live close to the ocean surface that require high light levels peaked in the spring months and droped again in the winter, a third high light ecotype did not not peak until October when the other two clades had decreased in abundance and light levels were lower. Two other ecotypes that live in the lower end of the euphotic zone where light levels are already very low also peaked in the autumn. These two ecotypes are obviously very sensitive to higher irradiances as they could not be detected anywhere near the surface. These trends were repeated every year, throughout the five-year study although the Atlantic populations showed stronger trends compared to the Pacific.
I think this paper gives a good indication into the dynamics of a very important genus of Cyanobacteria. The next stage would be to study how Prochloroccus ecotypes differ in their production of DOM and the other roles they play in the marine microbial food web and how having different ecotypes dominant at different times of the year might affect these things. Undoubtedly, this would be a major task. I also think that it should be noted that this study concentrated on Prochloroccus and not Synechococcus. Synechococcus tend to be more abundant in cooler waters and it would be interesting to see whether they follow the same patterns as Prochloroccus. Especially when we consider the fact that Synechococcus tends to be concentrated more at the surface compared to Prochloroccus.
A review of:
R, Malmstrom. A, Coe. G, Kettler. A, Martiny.J, Frias-Lopez. E, Zinser and S, Chisholm. (2010) Temporal dynamics of Prochlorococcus ecotypes in the Atlantic and Pacific. The ISME Journal. 4, 1252-1264.
3 comments:
Hi Lee,
It's an interesting topic with annual variations of the Prochlorococcus, alot of the papers posted and that I have read talk about regulation of picoplankton by viruses, do you think these trends were or could have been affected by these instead of temporal shifts? or that these could have also been of importance alongside temporal shifts? did the authors mention that this could have been a possibility?
Also sorry but Did you Mean Dissolved organic molecules or Matter? I know everything is made up of molecules but the matter is the usual reference as it consists of all physical substance?
Hi Dan
unfortunately they did not really mention the impact of viruses on Prochlorococcus but no doubt they would effect the population size. I'm guessing that this would only be a major player in shaping ecotype populations when the ecotypes are blooming and at a relatively high densities, increasing cell-virus contact. For example two high light ecotypes peak in the spring which is when the highest amount of cells would probably be killed by viruses. I imagine it is a very complexe relationship they have. I think the aim of this paper was to just look at non-biological aspects affecting the ecotypes.
I did mean to write dissolved organic matter and not molecules. In my head when I think of DOM leaking from a bacterial cell I tend to think of small simple molecules, like sugars, lipids, protiens ect. When I think of matter I imagine something much larger, something I can see. Thanks for pointing it out.
Hi Lee. It's easy to think only of small molecules, but remember the concept that DOM is made of al kinds of big sticky stuff,DNA, polysaccharides, cell rag,wants etc. Remeber viruses and even small bacteria are technically DOM in operational terms, defined by the size of filters!
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