Oxygen minimum zones (OMZs) are a phenomena of present and past. It has been confirmed that OMZs will spread in the future as a consequence of global climate change. Knowing which role these zones play in the nitrogen cycle is crucial as they are the main areas of nitrogen loss to the atmosphere through processes such as denitrification and anammox.
Increasing our knowledge of microbial communities supported within these habitats could give us further insight into such biogeochemical processes and help us predict future changes. Previous studies on the eastern tropical south pacific (ETSP) OMZs have mainly focused on bacteria and archaea or benthic meiofaunal diversity beneath OMZs. So far, little was known about pelagic eukaryote diversity in such oxygen-depleted environments however, most recently Parris et al. (2014) used 18S rRNA gene sequencing to provide an insight into pelagic microeukaryotic community structures. Organisms divided in two size fractions (0.2 - 1.6 µm, >1.6 µm) were sequenced from samples taken at seven depth increments throughout the ETSP OMZ off northern Chile. Results can be found in Figure 1 which showed a contrasting pattern:
The microbial community structure found in this study showed great variations to the ones at other OMZ sample sites. The authors spent a lot of time questioning the quality of methods and data collected; which is obviously important. Such a survey is only a snapshot in time, so replicates over a certain time period at the same site could give us more information as to whether such variations are due to sampling errors (sampling during or between blooms of particular species) or due to differing environmental factors.
In my opinion the fact that Parris et al. considered different sizes in their sampling is already very advantageous as picoeukaryotes smaller than 3µm may be among the most abundant cells in the water column, and may have been previously overlooked. The anoxic OMZ core, also known as anoxic marine zone (AMZ), was thought to be dominated by bacteria and archaea. Marine microeukaryotes and zooplankton however, can significantly affect these communities directly or indirectly. Therefore, it is of particular interest that small protist and eukaryote diversity reach their maximum in this AMZ. There is not much known about AMZs so far, and why they are also called a “microbial reactor” will be another post worth…
Parris D. J., Ganesh S., Edgcomb V. P., DeLong E. F. and Stewart F. J. (2014) Microbial eukaryote diversity in the marine oxygen minimum zone off northern Chile. Frontiers in Microbiology. 5: 543
Hi Tabea, thankyou for the read.
ReplyDeleteIt would be interesting to know what phylogenetic diversity they found at the other OMZ sites you mentioned- do you have any information on this please? I definitely agree that the authors need to use different times points, even over seasonal fluctuations, and I feel this would have been a much stronger paper if they did this- I know funding is a massive limiting factor these days but it doesn't really seem to be that significant if it isn't done in replicate form. Could you elaborate on how micro-eukaryotes and zooplankton will affect the bacteria and archaea in the AMZ- are you thinking predation wise, will the predation be of use to control the biochemical processes of archaea and bacteria such as nitrous oxide release?? Did this study sample the AMZ then- or is this for future studies? Thank you :)
Hi Elyssa,
ReplyDeleteIf you are really interested in the differences of phylogenetic diversty it propably would be best to have a look at this table: http://www.frontiersin.org/files/Articles/116310/fmicb-05-00543-HTML/image_m/fmicb-05-00543-t002.jpg
It gives you information about 14 sampling sites including this study. The authors also mention that we need to be careful with assuming differences between sites. In more recent studies technology might be more advanced and also sample size and analsis tools differ between all these studies. As you can see it would not only be important to take replicates, but also to asure that methodologies across every study (different time and place) are uniform! This study is therefore a really important starting point for the future.
Your second question was how micro-eukaryotes and zooplankton will affect the bacteria and archae:
Protists can impact major nutrient cycles through grazing on prokaryotic prey which would indirectly affect the structure and function of bacteria and archaea communities but can also affect it directly by breaking down organic matter.
Zooplankton surfaces, guts and fecal pellets form habitats for bacterial growth, therefore bacteria density can be highly increased when they are present. In our last lecture we learned about the cryptic symbiosis between ciliates and methanogenic archaea… I think this is enough to show how important it is to understand these poorly understood interactions!
Yes the study also sampled the AMZ, and as you can see in the diagram, with very surprising results (0.2-1.6 µm sized micro-eukaryotes are most diverse in these zones). However I will soon blog about another really interesting paper focusing on AMZs! I hope you will enjoy reading it. Let me know if you have any other questions!
Hi Tabea,
ReplyDeleteGreat table! Really well collaborated and useful as other research can then spin off of this table. I agree with everything you mention- especially the importance to study trophic level interactions. As the climate is changing, so many of these important relationships could be jeopardised or even enhanced! Do you know how an AMZ is created- is this just when the oxygen is completely depleted? This must be pretty difficult to get to this stage if so!? I am not sure if the results are that surprising, but could you elaborate what you mean? Thankyou
Hi Elyssa,
DeleteIt is important to know that not all OMZ necessarily have an anoxic core, however in some cases with high rates of phytoplankton productivity occurs in the upper layers and where is poor ventilation/circulation, nitrite accumulates and oxygen concentration can drop to such low levels that the can`t be detected by the most advanced technology!IApparently AMZs are commonly found in the global ocean!
That the results are surprising might have been worded a little wrong it is more very interesting! This study was the first one to do a size fractionated comparison of eukaryotic community structures in OMZs. Previous gene sequencing has been focused on larger sizes (>3.0µm). In this study, the diversity of larger micro-eukaryotes decreased in AMZs however the diversity of smaller ones increases... This suggests that most previous studies might have missed out even more than we thought, not only didn`t they detect anything smaller then 3.0µm but they also missed such contrasting patterns within a smaller size range. I Hope that helps? Thank you
Wow, thats crazy! Are they quite common in surface layers then? Would be so interesting to look deeper into these, maybe there are even some new species! Yes that clears things up, it makes you wonder doesn't it how much is really out there- great study. Thankyou :)
ReplyDelete