While coral transplantation is thought to be
restorative to a reef previously decimated, further works have indicated that
this may not be the case. A study conducted by Casey et al. (2015), looking into the impacts of grazer damselfish (Stegastes spp.) on the survival of
transplanted Acropora muricata,
discovered that regardless of the presence of Stegastes, transplantation of corals shifted the coral microbial community
in favour of coral disease associated pathogens.
Previous studies have debated the benefit of Stegastes presence on coral reefs; some
point towards damselfish promoting a thick growth of an epilithic algal matrix
(EAM) and so inhibiting coral growth, and others suggesting that the fish
promote recruitment/survival. Thus, the scientists investigated the microbial
composition and survival of corals outside and inside the Stegastes territory, using transplanted coral branches.
The work was completed over a year, on a reef 1-3m
deep off Lizard Island, Australia. Ten baseline coral samples were collected
from territories of Stegastes, and
controls collected from outside these areas. The transplanted fragments were directly
placed in/outside the territories, and at six months mortality was estimated. Ten
fragments from each treatment were sampled for microbial analyses, with the
same process being repeated after the one year of transplantation.
Akaike’s Information Criterion (AIC) was used to
compare generalised linear models of the data, defining the mortality as low
(0-20%), partial (20-80%) and high (80-99%). It was found that after 6 months
and a year, the corals transplanted inside the territories suffered a higher
loss of tissue and mortality than those transplanted outside.
16S rRNA gene amplicon sequencing was undertaken to retrieve
the microbial sequences collected from baseline, six months, and ten months. The
OTUs were assigned to categories: autotrophs, heterotrophs and potential pathogens,
with the abundances of less than two percent excluded. GLMs were used to
analyse differences in relative abundances of the data, taking into account
time and treatment type.
The results showed that the microbial communities had shifted in composition.
After one year, there was significant increase in abundance of autotrophs in
damselfish territories and so a more EAM population; a significant decrease of
heterotrophs, and surprisingly there were significantly higher abundances in
potential pathogens in all coral fragments regardless of fish presence/absence.
Of these pathogens sequenced, four out of the 21
genera are linked to coral disease, three of these four being associated with
black band disease (BBD). This change in coral microbial community could massively
affect the ecology of the reef, as loss of coral diversity could lead to
decreased resistance to coral disease pathogens.
This paper shows how microbial communities can
provide invaluable information about the state of corals, as well as how
different trophic interactions impact on the reef as a whole. It provides us
with food for thought as to how we can further protect reefs, most likely
involving the adaptation of known methods in order to optimise coral health and
minimise the risk of disease to already struggling systems.
Casey, J.M., Connolly, S.R. and Ainsworth,
T.D., 2015. Coral transplantation triggers shift in microbiome and promotion of
coral disease associated potential pathogens. Scientific reports, 5.
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ReplyDeleteHey Lucy,
ReplyDeleteinteresting reading. Did the author mention any possible reasons for the change in coral microbial communinity, especially towards potential pathogens? I was thinking about any solutions to overcome this problem. Any suggestions?
Hi Nuri,
DeleteThe author mentioned how the coral microbial community had taken on a similar structure to that of the EAM, which in a previous study of theirs along with others has been shown to be associated with more potential pathogens. It was suggested that the corals within the Stegastes territories would suffer more as they are routinely grazed upon by the fish in order to promote turf algae growth, and so it is difficult for the corals to grow which could cause a shift. However, as this paper shows that the shift in the community does not necessarily rely on the presence of the fish, the author does not believe that the fish are the (sole) cause.
Instead they suggest that the transplantation itself will stress the corals enough to produce a shift in the microbial community anyway, and the pathogens associated with coral disease, such as BBD mentioned in the paper, would take the opportunity to infect the corals. Coupled with the increased presence of potential pathogens being more abundant in the EAM, and that the corals are shifted over the year towards this structure, it seems inevitable that there would be an increase in pathogens.
As for solutions, the paper doesn't mention any as such, however it could be more beneficial to house the corals in an environment that could allow acclimation to the newer conditions and so when transplanted they would not be as stressed; this could help the corals combat the potential pathogens that may try to infect them. However, previous research has suggested that allowing this to happen will result in a shift in the community of microbes anyway, so this shift may just be a potential risk that is outweighed by the need to conserve the reef.
What are your thoughts?
Hi Lucy,
Deletethanks for the detailed answer. The idea of acclimation to reduce stress sounds promising to me. Additionally, I could only think of any potential probiotics which could be used to "vaccinate" the coral. Some previous studies have looked into the use of probiotics to cure or prevent coral diseases. For instance, you could dose the coral branches after removal with potential probiotic to avoid the loss of their natural micro flora till they get transplantated.
Hi Nuri,
DeleteGiven what we have been taught about probiotics, that sounds more promising than previous acclimation as you would hopefully be able to give the corals an extra boost in immune response/protection when being transplanted. The main concern from the authors was the fact that no matter what has been done in the past, the corals will have a microbial shift, with the result potentially leading to an increase in pathogens. The use of probiotics may help reduce this damaging effect.