Ocean acidification is an increasingly recognised
phenomenon, occurring as a result of the oceans absorption of CO2
produced by anthropogenic means. The severity of this process is reflected in
the predicted 0.3-0.4 decrease in pH expected over the next century, a faster
decrease than experienced for at least 300 million years. The prospect of this
dramatic change makes it important to try and assess the impacts ocean
acidification will have on microbial communities and thus the processes in
which microbes play an important role. Therefore this investigation utilises
naturally occurring areas of elevated CO2 to emulate the process of
ocean acidification and assess its impact on microbial communities. This study
was carried out using glass slides attached to floats held at 0.5 m below the
water surface at three sites around Vulcano Island, Tyrrhenian Sea. The site
was chosen due to CO2 vents around the island which acidify the
water creating a pH gradient. The amount of light reaching each slide was also
controlled and the slides were either exposed to ambient light (AL) or low
light (LL) levels. After 16 days the slides were collected.
On examination light regime was found to have the greatest
overall effect on biofilm production, however sites 2 and 3 showed visible
biofilm increase compared to site 1. Uronic acid is a significant component of
biofilm exopolysaccharide (EPS) and was measured in samples. Uronic acid levels
were found to be higher in AL biofilms and significantly elevated at sites with
higher pCO2, the same was also found with LL biofilms when exposed
to higher levels of pCO2. Reasons for the significant biomass
increase found on the slides are explained by elevated pCO2 causing
an increase in chlorophyll-a concentration and diatom abundance. Diatoms have
been shown to be responsible for EPS production and increased pCO2
has been shown to enhance photosynthesis efficiency and enhance EPS production.
Finally DGGE analysis of biofilms collected from the different sites indicate
that community variation did occurred at higher pCO2 areas, however
reasons for this change were not elucidated and are directed as an area for
further study by the authors.
Overall the results indicate that the biomass of biofilms
will greatly increase in areas of high CO2, especially when exposed
to ambient light; however it also highlights that the bacterial composition of
biofilm communities will be altered. Although not much is known about these
changes it has been suggested that the increase in biofilm biomass recognised
in this study is important in sustaining grazers such as molluscs and limpets
as they will require more energy for calcification in areas of higher pCO2.
I think that the research carried out in
this paper is an important step toward understanding ocean acidification and
its effects on coastal ecosystems. I quite enjoyed the paper and found it
relatively easy to understand, however it was slightly frustrating that there
were not clear subdivisions, such as method, results, conclusion.
Lidbury, I., Johnson,
V., Hall-Spencer, J. M., Munn, C. B., Cunliffe, M. (2012) Community- level
response of coastal microbial biofilms to ocean acidification in a natural
carbon dioxide vent ecosystem. Marine Pollution Bulletin, 1-5.
8 comments:
Hi
What were the pH levels that they tested? You spoke about the effects of ocean acidification and the drop in pH of around 0.3. However I suspect that in areas where CO2 is naturally bubbling through the substrate, the pH would be far lower and therefore have much more of an effect than ocean acidification. If the authors of this paper suggest that these two things may be linked but tested pH's alot lower than the 0.3 drop, then I would severely question their methods and hypothesis and the overall integrity of their findings.
Hi
What were the pH levels that they tested? You spoke about the effects of ocean acidification and the drop in pH of around 0.3. However I suspect that in areas where CO2 is naturally bubbling through the substrate, the pH would be far lower and therefore have much more of an effect than ocean acidification. If the authors of this paper suggest that these two things may be linked but tested pH's alot lower than the 0.3 drop, then I would severely question their methods and hypothesis and the overall integrity of their findings.
Great post Arrianna, this is a really interesting field of research because of the impact it is likely to have on many keystone organisms such as corals. It is fascinating that the potential benefit of increased energy resources for molluscs and limpets could help to counteract the increased energy demands that are associated with calcification in a lower pH environment.
I agree with your comment Adam however I would say that it could be possible that the authors have selected this area for their investigation because these hydrothermal vents provide a gradient of pH which could not only allow them to predict changes that might happen in the near future but also the effect that ocean acidification will have over an extended period of time if acidification continues to increase.
Thank you for your comment. The 0.3-0.4 pH decrease mention was an estimation explaining why the study is important and was carried out. The three sites which the authors tested varied in pH, Site 1: pH = 8.26, Site 2: pH = 8.10 and site 3: pH= 7.72. The measurements taken also showed that site 1 had the lowest amount of pCO2 (342) and site 3 had the highest pCO2 (1645) my apologies for not including this data in my blog post. It is understandable how you may think that the CO2 vents would create a much lower decrease than what has been predicted, however I think that is just further illustrates how much CO2 is being emitted from anthropogenic sources to create this kind of decrease. I hope this helps you understand it a little better.
Hi Arrainna, I really enjoyed this post! Its great to think that although ocean acidification obviously has many adverse effects, that actually it can also cause a change that can help deal with them! It is surprising the amount of C02 it takes to make such a small change, after using CO2 as a factor in my project,I understand this well!
I was just wondering whether the authors mentioned whether there was a change in community diversity as a result in a change in CO2 as well? It seems likely that different species would flourish at different pH. And I dont know whether this would be true, would this have an affect on the grazers?
Hey, Thanks I'm glad that you enjoyed the post! The DGGE analysis carried out did show that bacterial comunity composition was altered. The authors found a difference in the biofilm community between each site, however they also stated that there was at least a >50% similarity between the community compositions at all sites. I guess it is difficult to compare as there was not a control site. Apart from this there was not much more information on how the composition changed other than it varied between bacteria and Eukarya. It was also stated that not much was known about these changes and that it was an area for further research. It would be interesting to see how the whole ecosystem would be affected however the only reference made was concerning the calcification rates of grazers.
Hey,
Thats quite cool, shows that ocean acidification is really complex and maybe whacking a snail into a tank with lower pH doesnt really show the true ecological effects (i really hate those studies).
Hi Arainna,
Congratulations for this interesting review!
I think that these findings are really really important as you said, to understand the future impact of ocean acidification on ecosystems.
The fact that algae and especially diatoms, will do better with higher pH in my view, is extremely important. Diatoms, and microalgae in general are a key component of every ecosystems and innumerable are those organisms who feed on them. For this reason i guess that if the are gonna increase in the future, profound changes will occurr in the ecosystems as a whole.
For my dissertation project, i'm looking at the effects of acidification on invertebrate settlement at natural CO2 vents (same as this study). I've found that amphipods actually increase a lot at the low pH stations...no surprise why...because they feed on diatoms of course! Since amphipods and small crustaceans in general, are eaten by several marine organisms, it really seems that big changes in the trophic structure of ecosystems are likely to occurr.
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