Wang et al (2014) describes phytoneuston as phytoplankton communities that dominate the sea-surface microlayer (SML). The SML differs from sub surface water (SSW) and sub bottom water (SBW) as they are comprised of different community compositions and biomass, which is the focus of this study. The SML is a 1000 micron biogeochemical boundary between the atmosphere and the sea that has distinct roles in processes like gas and heat exchange, particle cycling, microbial loops (as larvae feed on microalgae), etc. The SML phytoneuston also provides an insight to increase in temperature, nutrients and UV rays, decrease in oxygen concentrations, etc (Wang et al 2014). Dapeng Cove in the Daya Bay in the South China Sea was used as the study area for this experiment, which experiences reduced water flux and elevated nutrient levels (40-fold increase in the nitrogen: phosphorus ratio).
A volume of 0.5L of the SML sample was collected using a glass plate sampler with the plate having been submerged vertically and withdrawn gently. The SSW and the SBW samples were collected with a Niskin bottle sampler at 0.5m below the surface and equally above the bottom, respectively. The subsamples for chlorophyll A and dissolved nutrients (like total nitrogen and total phosphorus) were filtered in the field and analysed. Water temperature, salinity, and dissolved oxygen were determined in situ.
Based on microscopic observations of phytoplankton communities, species in the phytoneuston were different to other phytoplankton groups in the underlying column. This suggests that the SML harbour favourable micro-niches for these organisms to thrive in, which eliminates factors such as physical transportation via mixing; and that there is almost a shift from phytoplankton dominance to cyanobacteria dominance.
Although the total diversity in the SML was significantly high (with abundant phosphorous), cyanobacteria were highly enriched in the SML with Lyngbya, Oscillatoria and Synechococcus as the principal contributors (Wang et al 2014). Their increased abundance in the SML (especially in temperate regions during the summer) is suggested to be due to buoyancy strategies (photo-protective accessory pigments), high growth rates, high temperature and UV radiation resilience (despite natural warming as well as receiving large volumes of discharged warm water), lowered grazing pressure, production of antioxidants, etc. Cyanobacteria correlates positively with nutrients, water temperature and salinity and inversely correlate with dissolved oxygen, diatoms and phytoplankton. This is because cyanobacteria are able to exploit remineralized organic compounds produced as a result of diatom (and other phytoplankton) mortality (Wang et al 2014).
The results of this study also showed that diatoms dominated the SSW and the SBW and only 10% of the SSW and the SBW were in the SML as they have a low tolerance to high temperature and UV rays. They suggested that the small fraction of diatom densities that were measured was due to mixing. Dinoflagellates (Alexandrium tamarense) and chlorophyll A also showed the same trend, due to actively motile cells in flagellates and high temperatures and UV radiation damaging chlorophyll A as well as grazing by protists.
This study highlights how environmental parameters can be established by studying the composition of the phytoneuston community of a certain area. This can be used to determine the fate of aquaculture and the communities inhabiting these waters due to aquaculture as well as increased human population. This paper serves as a good base as it provides evidence for positive correlation between phytoplankton and diatoms, and an inverse relationship between the two and cyanobacteria. However, the microscopic methods used should be associated with size-fractionated pigment analysis and other molecular methods to further gain an understanding of the phytoneuston community, as small flagellates and picoplankton could have been ignored under the microscope. Another potential future study could be to understand the extent and type of protist grazing and to also understand how phytoneuston overcome this pressure (if at all).
Reviewed Paper:
A volume of 0.5L of the SML sample was collected using a glass plate sampler with the plate having been submerged vertically and withdrawn gently. The SSW and the SBW samples were collected with a Niskin bottle sampler at 0.5m below the surface and equally above the bottom, respectively. The subsamples for chlorophyll A and dissolved nutrients (like total nitrogen and total phosphorus) were filtered in the field and analysed. Water temperature, salinity, and dissolved oxygen were determined in situ.
Based on microscopic observations of phytoplankton communities, species in the phytoneuston were different to other phytoplankton groups in the underlying column. This suggests that the SML harbour favourable micro-niches for these organisms to thrive in, which eliminates factors such as physical transportation via mixing; and that there is almost a shift from phytoplankton dominance to cyanobacteria dominance.
Although the total diversity in the SML was significantly high (with abundant phosphorous), cyanobacteria were highly enriched in the SML with Lyngbya, Oscillatoria and Synechococcus as the principal contributors (Wang et al 2014). Their increased abundance in the SML (especially in temperate regions during the summer) is suggested to be due to buoyancy strategies (photo-protective accessory pigments), high growth rates, high temperature and UV radiation resilience (despite natural warming as well as receiving large volumes of discharged warm water), lowered grazing pressure, production of antioxidants, etc. Cyanobacteria correlates positively with nutrients, water temperature and salinity and inversely correlate with dissolved oxygen, diatoms and phytoplankton. This is because cyanobacteria are able to exploit remineralized organic compounds produced as a result of diatom (and other phytoplankton) mortality (Wang et al 2014).
The results of this study also showed that diatoms dominated the SSW and the SBW and only 10% of the SSW and the SBW were in the SML as they have a low tolerance to high temperature and UV rays. They suggested that the small fraction of diatom densities that were measured was due to mixing. Dinoflagellates (Alexandrium tamarense) and chlorophyll A also showed the same trend, due to actively motile cells in flagellates and high temperatures and UV radiation damaging chlorophyll A as well as grazing by protists.
This study highlights how environmental parameters can be established by studying the composition of the phytoneuston community of a certain area. This can be used to determine the fate of aquaculture and the communities inhabiting these waters due to aquaculture as well as increased human population. This paper serves as a good base as it provides evidence for positive correlation between phytoplankton and diatoms, and an inverse relationship between the two and cyanobacteria. However, the microscopic methods used should be associated with size-fractionated pigment analysis and other molecular methods to further gain an understanding of the phytoneuston community, as small flagellates and picoplankton could have been ignored under the microscope. Another potential future study could be to understand the extent and type of protist grazing and to also understand how phytoneuston overcome this pressure (if at all).
Reviewed Paper:
Zhao-Hui Wang, Shu-Hua Song, Yu-Zao Qi (2014). A comparative study of phytoneuston and the phytoplankton community structure in Daya Bay, South China Sea. Journal of Sea Research 85, 474-482.
Hi Ankitha,
ReplyDeleteThank you for the blog it was a very interesting read and a very good summary.
You mention the two sampled areas had elevated nutrient concentrations. Did the authors confirm whether this was a natural occurrence, from the diatoms, plus other phytoplankton you mention or, was it due to our activity? If down to our activity it is a generalised 'bit of every form of pollution' or just one specific activity, such as an industrial plant?
Thank you,
Sophie,
Hi Sophie,
DeleteThank you for your question.
The two sampled areas were at Dapeng Cove, the site of the two nuclear power stations (the Daya Bay Nuclear Power Station and the Lingao Nuclear Power Station). So yes, these sites are strongly influenced by human activity as well as mariculture which has led to eutrophication which has in turn led modification of the dinoflagellate and diatom communities.
Hope this answers your question,
Ankitha
Hi Ankitha,
DeleteThank you, it does thank you, although it would be great to see the effect of cleaning up these areas and the change in the communities, whether back to pre-polluted (if this data exists) or not.
It was very interesting so thank you.
Sophie,
Hi Ankitha,
ReplyDeleteI enjoyed reading your post. As you say cyanobacteria are enriched due to increased temperature tolerance etc., I was just wondering if the authors suggested what impact ocean warming will have on the SML? Presumably there will be a limit to their tolerance. Certainly understanding the current environmental conditions on the composition of the SML is important as it is so central biogeochemical processes.
Many thanks,
Amelia
Hi Amelia,
DeleteThank you and I'm glad you enjoyed it.
The authors did not mention any thresholds as far as I am aware, but yes, you are right, there will definitely be limits to their tolerance. I am unsure of how easy it is to determine their thresholds and put a value to it.
A book by Liss and Duce (1997) mentions that primary production in this layer as well as neustonic eggs and larvae are threatened by high temperature, UV and chemical contamination and I think this suggests a trade off. However, long term effects in this layer is difficult to estimate due to vertical mixing, photo repair and adaption, etc.
Apologies if this didn't fully answer your question but I hope it helps.
Thanks,
Ankitha
Reference :
Liss, P. and Duce, R. (1997). The sea surface and global change. Cambridge: Cambridge University Press, pp.48-56.