[OANNES Foro] Abiotic and biotic interactions in the diffusive boundary layer of kelp blades create a potential refuge from ocean acidification

[Mario Cabrejos]

Functional Ecology 

First published: 20 March 2018

 <https://doi.org/10.1111/1365-2435.13067>
https://doi.org/10.1111/1365-2435.13067


 


Abiotic and biotic interactions in the diffusive boundary layer of kelp
blades create a potential refuge from ocean acidification


 
<https://besjournals.onlinelibrary.wiley.com/action/doSearch?ContribAuthorSt
ored=Noisette%2C+Fanny> Fanny Noisette
<https://besjournals.onlinelibrary.wiley.com/action/doSearch?ContribAuthorSt
ored=Hurd%2C+Catriona> Catriona Hurd

 


Abstract


1.    Seaweeds are able to modify the chemical environment at their surface,
in a micro‐zone called the diffusive boundary layer (DBL), via their
metabolic processes controlled by light intensity. Depending on the
thickness of the DBL, sessile invertebrates such as calcifying bryozoans or
tube‐forming polychaetes living on the surface of the blades can be
affected by the chemical variations occurring in this microlayer. Especially
in the context of ocean acidification (OA), these microhabitats might be
considered as a refuge from lower pH, because during the day photosynthesis
temporarily raises the pH to values higher than in the mainstream seawater.

2.    We assessed the thickness and the characteristics of the DBL at two pH
levels (today's average surface ocean pH 8.1 and a reduced pH predicted for
the end of the century, pH 7.7) and seawater flows (slow, 0.5 and fast, >8
cm/s) on Ecklonia radiata (kelp) blades. Oxygen and pH profiles from the
blade surface to the mainstream seawater were measured with O2 and pH
microsensors for both bare blades and blades colonized by the bryozoan
Membranipora membranacea.

3.    The DBL was thicker in slow flow compared with fast flow and the
presence of bryozoans increased the DBL thickness and shaped the DBL
gradient in dark conditions. Net production was increased in the low pH
condition, increasing the amount of oxygen in the DBL in both bare and
epiphytized blades. This increase drove the daily pH fluctuations at the
blade surface, shifting them towards higher values compared with today's pH.
The presence of bryozoans led to lower oxygen concentrations in the DBL and
more complex pH fluctuations at the blade surface, particularly at pH 7.7.

4.    Overall, this study, based on microprofiles, shows that, in slow flow,
DBL microenvironments at the surface of the kelps may constitute a refuge
from OA with pH values higher than those of the mainstream seawater. For
calcifying organisms, it could also represent training ground for harsh
conditions, with broad daily pH and oxygen fluctuations. These chemical
microenvironments, biologically shaped by the macrophytes, are of great
interest for the resilience of coastal ecosystems in the context of global
change.

 



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