A review of the paper:
Haas, A.F., Nelson, C.E.Wegley K.L., Carlson, C.A., Rohwer, F.,Leichter, J.J., Wyatt, A., Smith, J.E., (2011), Effects of Coral Reef Benthic Primary Producers on Dissolved Organic Carbon and Microbial Activity, PLoS One, 6, (11), e27973
It has been shown that dominant primary producers release much of their photosynthates back into the surroundings as dissolved organic carbon (DOC). In the case of macroalgae and hermatypic corals associated with coral reefs, the released DOC affects the activity of the surrounding microbes. Due to the fact that the majority of reef production enters the food web via microbial consumption, this release of DOC is thought to fuel the food web. However, an increase in marine microbe production can lead to hyperoxia and coral death, making this an important area of research. The aim of this paper was to examine how benthic primary producers affect the seawater chemistry and examine the impact of DOC on the reef bacterioplankton.
Three samples were taken from three macroalgal genera (Phaeophyta, Rhodophyta and Chlorophyta), one from a mixed consortium of reef turf algae, one from a crustose coralline algae (CCA) and one from a hermatypic coral. These samples were then inclubated and water samples were tested for DOC levels. Dissolved oxygen (DO) was also measured using a specialised instrument and the photosynthetically active radiation (PAR) was measured using a diving-PAM. The water that remained after these incubations was then used to test whether the DOC affected the ambient microbial community. These samples were used for dark dilution culture incubations. Changes in the concentrations of DOC, DO and bacterioplankton were recorded and the microbial oxygen and DOC consumption was worked out.
It was found that all six taxa had a significant but varying effect on the DOC, DO and the microbial populations. At least 10% of the fixed organic carbon was exuded by the turf and macroalgae; coral exuded the smallest amount. All of the species released more oxygen during the day and consumed oxygen at night but the turf algae released the most. It was shown that bacterial growth rates on the substrates released from the primary producers were nearly double of the other ambient bacteria. The primary producers with a higher surface area (turf algae) released this substrate containing DOC more quickly, which creates a more rapid and inefficient respiration from the bacteria. However, the growth rates of the bacteria were found to be unrelated to the DOC release rates and more related to the quality of the DOC released. The final set of data suggested that the DOC released from corals may support a different assortment of bacteria than that released by algae.
The associations between primary producers, DOC and microbes is important in the transition between coral and algae dominated habitats. After having read Coral reefs in the microbial seas (Forest Rohwer), this was put into a wider context as it is this increase in DOC that can potentially destroy a coral reef ecosystem. An increase in nutrients (ie pollution) and overfishing, increases the amount of algae that can grow, which increases the amount of DOC released. It also changes the type of bacteria supported, as coral DOC supports a different community to algal DOC. This increases the biomass of microbes in the waters and creates a shift in community, which leads to an increased number of pathogens and an unhealthy reef.
4 comments:
This is interesting. So the microbial community that comes with coral invading algae is completely different and harms the coral more? Did the paper say how the DOC released from the algae is different to select a different microbial community to coral DOC?
No it didnt say anything, apart from the number of microbes depends on the "quality" of the DOC rather than the amount released but didnt really explain what that meant either! I find it really interesting though and would love to find out what that means, will have to do a bit more research I think!
I've actually just given it another quick read, and it says that the coral that was studied, released the smallest amount of DOC and actually takes it up sometimes. So it didn't say how it was different, but it does produce less so maybe isn't enough to cross the threshold into a shift in microbial community?
That would make sense. just a small amount will support one microbial community but a large amount from the algae could support all sorts and therefore shift it to something harmful.
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