Conservation of coral reefs using artificial coral settlement devices (CSD)

ENTRY DATE: 26.12.2014 | LAST UPDATE: 26.12.2014

CATEGORIES:

  • Disaster Prevention
  • Coastal disaster (Hard measures)

TECHNOLOGIES MATURITY:

Ready for introduction, to be applied immediately.

Technology Owners:

The coral settlement devices described here were developed by the Tokyo University of Marine Science and Technology

Needs Address

The need to reduce the loss and bleaching of coral reefs in areas where coral reefs may be affected by sea surface temperature rise, by increased CO2 concentrations in seawater, and by increased intensity of tropical cyclones, and where the loss or bleaching of coral reefs due to human disruptions can already be observed.

Adaptation effects

  • Prevention of deterioration of natural ecosystems due to rising sea surface temperatures, rising CO2 concentrations, and increased intensity of tropical cyclones due to climate change. 
  • Prevention of flood damage caused by extreme events.
  • Disaster prevention, coastal erosion prevention, supply of sand.

Overview and Features

  • Transplantation technology for coral can be broadly divided into two methods based on type of reproduction: sexual and asexual. Below is a summary of the two methods. 

    Table: Comparison of asexual and sexual reproduction methods

     

    Sexual reproduction

    Asexual reproduction

    Transplantation method

    Coral larvae that have been fertilized in the field or indoors are transplanted by settling them on a substrate.

    A natural community is isolated and transplanted by creating fragments to be transplanted.

    Impact on donor/existing coral community

    Since larvae are used, there is no impact on any donor/existing community.

    Impacts are imposed on the community that has been isolated.

    Diversity of the transplanted community

    If larvae spawned in natural waters are used, diverse species can be transplanted.

    Transplanting is limited to species that can easily produce fragments and be anchored to the seabed Also, since genetically identical individuals are transplanted, intra-species diversity is low.

    Scale/size of restoration

    The method can be implemented on a large-scale.

    Transplanting is limited by the size of the donor/existing community.

    Ease of transplantation work

    Work can be standardized, so it is practical for major operations.

    The work of creating fragments and anchoring to seabed requires skill, so standardization of work is difficult.

    Source: "Manual for restoration of coral communities using coral larvae coral settlement devices"

  • Asexual reproduction as a method of transplantation inevitably leads to destruction of healthy coral reefs, so it is difficult to use on a large scale. Conversely, the use of sexual reproduction has come into practical use for the transplantation of juvenile coral, as this method does not damage the existing community (donor), making it possible to transplant and result in a species composition similar to the natural conditions. 

Sexual reproduction method using coral settlement devices

  • To produce juvenile corals outside, it is only necessary to install a coral settlement device for the larvae, so the production of juvenile corals can be done at a relatively low cost
  • CSDs similar to the ones depicted below are stacked vertically in a case, which is then placed on the seabed before coral spawning season, and then one waits for the larvae to settle. About a year later, the juvenile coral will have grown to a size clearly discernible to the naked eye, and the CSD can be used as it is, for the seedling transplantation. For transplantation, holes are drilled into the seabed, and waterproof bond is inserted into the bottom of CSD.
  • Since the CSD is light and can be mass-produced at low cost, it is possible to install a large number of them at one time and settle larvae, making it possible to produce a large number of transplantable coral seedlings. 

    Photos: Implantation components (left) and installation of case on coral bed ( right )

    Source: "Manual for restoration of coral communities using coral larvae coral settlement devices"

Monitoring

  • Monitoring involves follow-up studies of the survival status of transplanted seedlings and is done to adapt the management method to respond to transplant results. It is essential for adaptive management.
  • The monitoring is done for target species, one month, three months, six months and one year later after transplantation. Thereafter, monitoring should be done about twice a year, before and after typhoon season. The details to be monitored are summarized below.

    Table: Monitoring item

    Parameter

    Study content

    Species name

    Genus or family of coral. Once the larvae become big enough to identify, record name of the species.

    Diameter

    Measure the maximum diameter of the coral community in millimeters.

    Survival and mortality rates

    Measure the mortality percentage of the coral community.

    Health (vs bleaching) rating

    Rate the degree of bleaching of the coral community based on the following criteria.

    0:No bleaching visible

    1:Almost no bleaching visible (less than 5% of community)

    2:Less the 50% of the community bleached

    3:50% or more of the community

    4:Almost completely bleached (90% of the community or more)

    Damage rating

    Rate damage to the coral community based on the following criteria.

    0:No damage visible

    1:Almost no damage visible (less than 5% of community)

    2:Less the 50% of the community damaged

    3:50% or more of the community damaged

    4:Almost completely damaged (90% or more)

    Feeding damage

    Record observations of the presence of feeding damage by crown-of-thorns starfish, coral-eating snails, etc., and the type of feeder observed.

    Seaweed growth

    Record seaweed attached to top of the coral settlement devices.

    Sediment deposition

    Record the thickness of sediment deposited on the coral settlement devices.

    Inhabitors

    Record the type of animal inhabiting the coral community coral settlement devices and the number of individuals observed.

     

Cost

CSD available at low cost, but the work of transplanting, management, and monitoring is expensive. 

Ease of maintenance

  • It is necessary inspect the installed CSDs at various times, including at the time of extraction, and also after typhoons have passed. 
  • It is necessary to inspect and repair the fasteners, wire and cases that hold the CSDs in place, and to recover the CSDs that are carried away by currents. Also, as seaweed will grow on the CSDs over time, so it is necessary to remove the seaweed, and also to remove floating mud deposited on the top of the case. 

Considerations

There can be enormous variations in the number of larvae settling over space and time; even if one year at one location a large number settle, there is no guarantee that they will do so the following year. More advances are needed to enable stable production of seedlings for transplantation, including the methods for collecting of larvae slicks, as well as feeding and settling methods. 

Co-benefit, suitability for developing countries

  • Biodiversity conservation. 
  • Prevention of soil erosion due to storm surges. 
  • Supply of sand to beaches. 
  • Diversity of fish and other fisheries resources can sustain and stimulate the fishing industry. 
  • Community development due to increase in tourism. 

Information Resources

"Manual for restoration of coral communities using coral larvae coral settlement devices," (in Japanese) by the Ministry of the Environment, Kyushu Regional Environmental Office, and Naha Natural Environment 
http://www.coremoc.go.jp/report/NRPS/NRPS2007b.pdf