Most reef building
corals are constructed trough the association between coral polyps and their
symbiotic dinoflagellate microalgae. Besides providing the host with fixed
carbon, the zooxanthellae (genus Symbiodinium) also contribute to the
production of antioxidants to prevent oxidative damage. As part of the coral
holobiont zooxanthellae produce and process dimethylsulphoniopropionate (DMSP)
and its enzymatic cleavage product dimethylsulphide (DMS).
DMSP and DMS play a
key role in the global sulphur cycle and also in the antioxidant system of the
coral.
Depending on their
symbiotic zooxanthaellae corals respond differently to climate change. Some
clades of zooxanthallea are known to be more resistant to e.g. temperature
changes. Increasing temperature is one of the main factors for coral bleaching.
The study by
Deschaseeaux et al. (2014)
investigated the tolerance of the symbiotic zooxanthellae to increasing
temperature linked to the production of DMSP and DMS. Therefore, two different
subclades of symbiotic algae (Acropora millepora (D1)
and Acropora tenuis (C1)) were
collected in waters of Magnetic Island, Australia. Clade D is known to be more
resistant to thermal stress than clade C.
The two clades were
isolated from the coral tissue. To prevent contamination the zooxanthellae were
kept in an axenic chamber. The genotypes of the clades were identified. Clades were
examined in chambers with increasing temperature and in control chambers. DMSP
and dissolved and gaseous DMS were measured.
Relevant results were
that DMSP and DMS concentration differed between the two clades. DMSP concentration
decreased in all treatments. Although, concentration of DMSP were higher in
clade C than in D. No difference in DMSP concentration was measured between the
two treatments of clade D. For clade C the concentration of DMSP was higher in
the control chamber than in the chamber with increased temperature. The higher
concentration of DMSP in the control chamber might be a result of the enhanced
DMSP consumption in clade C with increasing temperature. Suggesting that clade
C uses DMSP to prevent oxidative stress. This is supported by the results of
measured DMS. Decreasing concentration of DMSP didn’t lead to increasing
concentration of gaseous DMS in clade C. Potentially caused by consumption of
DMS under thermal stress. All in all, clade C showed distinct response to
thermal stress, whereas clade D remained nearly unaffected.
Despite of some vague
results, this study contributes to a better understanding of coral reef
response to increasing temperature. Considering the theory that coral produced
DMS plays a role in cloud forming and therefore has an impact on local climate,
enhanced consumption of DMS(P) due to thermal stress by clade C could affect this
interaction. Secondly, it can be assumed that increasing temperature has
distinct effects on the biogenic sulphur cycle of symbiotic zooxanthellae.
Furthermore, this study focused only on the DMS(P) production by symbiotic zooxanthellae. The whole microbial holobiont should be considered for further studies.
Additionally, I would like to
recommend this paper by Nils Rรคdecker,
a master student of the Centre for Tropical Marine Ecology, Bremen. The paper
gives you a nice overview of nitrogen cycling in corals. Even with a short
video at the end: http://www.sciencedirect.com/science/article/pii/S0966842X1500075X
Since I have read the paper "A bacterial pathogen uses DMSP as a cue to target heat-stressed corals" (Garren et al. 2014) which Katherine and I presented in the seminar, I see issues in this paper. Based on their results Deschaseeaux et al. (2014) conclude that thermal stress leads to decreasing DMSP concentration and reduced DMS emission which would have a negative feedback on the DMS-CCN theory. Though, they have only measured the DMS(P) concentration of the associated zooxanthellae. In my opinion, it is necessary to consider always the entire coral holobiont to make those predictions.
ReplyDeleteIn the paper by Garren et al. (2014) they mention a fivefold increase of DMSP in the coral mucus under thermal stress. Even though they used a different coral species (still a stony coral from a reef close by) and applied a different temperature treatment, they considered the mucus from the entire coral holobiont.