Estuarine tidal flats are very productive ecosystems,and
most of this productivity comes from the microphytobenthos (MPB). MPB
communities are commonly dominated by motile diatoms that undergo vertical
migration pattern following tidal/dial cycles. Due to this migration pattern
MPB communities are periodically exposed to variable and extreme environmental
conditions. Laviale et al.,(2015) set out to study the combined effects of high
light (HL) and high temperature (37°C versus 27°C) on the physiology of
intertidal diatom-dominated MPB communities. Light stress recovery experiments
(LSRE) were performed on MPB from two locations in France (FR) and Portugal
(PT) with different solar and temperature regimes.
Community structure was
slightly different between the two sites with the PT site dominated by Navicula phyllepta sensu lato (relative abundance: 44%),
whereas FR site was
co-dominated by N.
spartinetensis (33%)
and N. phyllepta
s.l. (28%).
Higher temperatures significantly increased photoinhibition
of epipellic MPB biofilm. Samples from the PT site were more resistant to the
couples HL-temperature stress in comparison to the samples from the FR site.
The PT communities were adapted to a higher light and temperatures environment,
and hence more resistant than the FR ones. Photoinhibiton was higher in the FR
site, but it increased 3-fold with temperature for both sites. Vertical
migration to the photoprotection zone remained below 15% for both sites but was
always lower in PT communities. ΦPSII and NPQ measurements were
comparable between the sites and showed the same general trend under HL stress.
However, PT samples appear to be less affected by HL as the ΦPSII
recovered faster under low light indicating a strong physiological
photoprotective response. TBARS values were also significantly higher in PT
samples compared to the FR samples.
As the authors hypothesised, motile diatoms can
migrate down through the biofilm to cope with high irradiance and temperatures.
A wider range of temperatures as well as HL for longer periods of time should
also be used in the future to help represent more gradual changes in
temperature as well as climatic events such as heat waves. It is also
interesting to see how community structure could potentially change with rising
sea temperatures. Diversity is likely to decrease and N. spartinetensis and N. phyllepta s.l. dominated communities could shift to a N. phyllepta s.l. only dominated structure. More
resilient non-native species could also proliferate in those conditions further
affecting the community structure. Since MPB are major contributors to primary
productivity, any effect on the microalgae community would have knock on effects on the rest of the ecosystem.
Laviale, M.,
Barnett, A., Ezequiel, J., Lepetit, B., Frankenbach, S., Méléder, V., ... &
Lavaud, J. (2014). Response of intertidal benthic microalgal biofilms to a
coupled light‐temperature stress: evidence for latitudinal
adaptation along the Atlantic coast of Southern Europe. Environmental
microbiology.
Hi Maria,
ReplyDeleteThis is an interesting paper showing the possible effect of light and temperature increase on MPB community structure. Could you possibly clarify what NPQ measurements are and what they convey, and also what TBARS are. Did you come across any information or studies whilst looking at this paper which addressed OA effect on community structure along with increased temperature and light?
Thanks
Emma
Hi Emma,
ReplyDeleteNPQ refers to non-photochemical quenching, a protective mechanisms through which both plants and algae dissipate excess energy (from high intensity light) as heat. Higher NPQ values indicate a stronger physiological photoprotective response allowing those organisms to be less affected by high intensity light. TBARS (thiobarbituric acid reactive substances) is a lipid peroxidation assay that conveys information about the oxidative degradation of lipids (mostly cell membranes). It is used as an indicator of oxidative stress. I haven’t found any studies that look at both OA and increased temperature and light yet. OA is likely to alter the bioavailability of sediment-bound metals, and thus their toxicity, so it would probably put further stress on MPB communities. It would be interesting to see if these stressors combined would have a additive or synergistic effect. Hope this answers your questions.
Hi Maria,
ReplyDeleteThanks for the reply, it makes it a lot clearer. I am very surprised in the work I have done so far I haven't come across NPQ, its great to be able to share these areas we know with each other. This is an interesting subject I will be keeping an eye out for further work looking at the areas we have discussed (OA, temp and light).