In a study led by SECORE Internationl, scientists pioneered the development of a novel approach to
simply sow coral recruits onto degraded reefs like farmers scatter seedlings on
a field. Formerly, handling of coral outplants have been truly costly and
time-consuming. With this innovative approach,
handling and cost can be minimized and it may therefore allow for effective
large-scale reef restoration.
In the last decade, the troubling loss of coral reefs worldwide has prompted
scientists and conservationists to assist the reefs’ recovery through active
restoration approaches. Thereby, corals
are transplanted on degraded reefs to help them to recover. Until now,
actual restoration has been done manually by divers, who had to attach each
coral, whether a fragment or a coral recruit settled on a substrate,
Today, reef degradation
occurs at a scale of hundreds and thousands of square kilometers. In contrast,
restoration activities happen on less than one hectare in scale; limited by the
labor-intensive, and therefore costly, techniques that are currently available.
does it work?
”If we want restoration to
play a more meaningful role in coral reef conservation, we need to think in new
directions. We have developed our sowing approach
to allow the handling of
large numbers of corals in a very short amount of time at significantly lower
costs. This is an important step towards making coral restoration happen on a
meaningful scale”, says Dr. Dirk Petersen, Executive Director SECORE
In the sowing approach, coral
larvae are settled on specifically designed substrates, coral and substrate
together called 'Seeding Units'. Those Seeding Units are sown on the reef by
simply wedging them in crevices as they self-stabilize due to their shape and
do not require manual attachment. After a while, they become attached to the
reef via natural processes, for instance, cemented to the ground by Crustose
Coralline Algae (CCA). In the future, the Seeding Units could be sown from a
boat or by a drone.
To give an example: transplanting
10,000 individual corals on one hectare using common methods requires several
hundred to a few thousand person-hours. “Sowing the same number of corals could
be achieved in less than 50 person-hours, a time saving of over 90 percent.
Additionally, material costs could be reduced up to one third, representing a
substantial advance for future restoration work”, says SECORE’s Research Director Dr. Margaret Miller .
sexual reproduction & genetic diversity
On Curaçao, the team
collected larvae released by colonies of golf ball corals (Favia fragum). “Shortly after collection, we settled the coral
larvae on specially designed tetrapod-shaped substrates made of cement”,
explains Dr. Valérie Chamberland, who led the field research for this study on
sexually propagated corals maintains genetic diversity. Different gene
combinations, so-called genotypes, arise within the population by
recombination―the reshuffling of the genetic characteristics of parents among
their offspring. New genetic combinations may then equip some coral offspring
with capabilities to better cope with today's and future conditions than their
struggling parents. “This is of vital importance for any coral species in the
face of climate change. In this way, we may get corals that, for example, are
more resilient to raising water temperatures”, says Dirk Petersen.
Three weeks later, the settled
coral larvae had turned into initial coral polyps and the units were sown on
the reef in front of the Curaçao Sea Aquarium. “The specific shape of the
tetrapod substrates allowed us to simply wedge the Seeding Units into natural
crevices of the reef. Most Seeding Units were stable within a few weeks, either
secured in crevices or naturally cemented on the reef’s framework“, says
baby corals to survive
The design of the substrates
not only promotes the attachment on the reef, but it also enhances
the survival of the coral settlers. On the substrates, the little baby corals
can find a sheltered place to settle. “The different orientations of the
Seeding Units’ surfaces and their integrated grooves create micro-habitats for
coral settlers. There, competition and predation affecting the young and very
fragile corals is reduced compared to when larvae settle directly on the reef.
This is crucial, as our results show that the early post-settlement life stage
is the bottleneck for the survival of young corals”, says Dirk Petersen.
In the twelve months
following the sowing, the scientists closely monitored substrate attachment to
the reef and the survival rates of coral settlers. “We settled between 20-30
larvae on each substrate to ideally have one coral established per Seeding Unit
in the long term. After one year, more than half of the units were recovered
and still harbored at least one coral, meeting this target required to
eventually yield a successful restoration outcome”, explains Valerie
the next step
So far, sowing settled corals
was tested in a research pilot―now it needs to be tested on a much larger
scale. The processing of 50,000 to 100,000 substrates within a single location
and spawning season will involve major logistical and engineering challenges.
SECORE and partners are currently working to overcome these challenges in the
course of the recently launched Global Coral
study in Nature's Scientific Reports: New Seeding
Approach Reduces Costs and Time to Outplant Sexually Propagated Corals for Reef
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