Restoration and protection of coral and oyster reefs

Objective
Adaptation
Sectors
Coastal zones
Organisation
UNEP-DHI Partnership – Centre on Water and Environment
Technology group
Retreat
CTCN Keyword Matches
Restoration and protection of coral reefs

Description

Reefs are underwater ecosystems formed as a ridge of sand, rock or coral that rise up close to the water surface. Coral reefs are highly productive ecosystems held together by calcium-carbonate structures that are secreted by the corals. Oyster reefs are large communities of oysters that form on stony substrates. Reef protecting and restoration is vital as they are decreasing in size and distribution due to a number of threats, including sedimentation, pollution, disease, over-fishing, underwater construction in coastal areas, and changes in water conditions (e.g. temperature, pH) as a result of climate change. Reefs can be protected through legal means and monitoring, which minimizes potential threats.

Restoration efforts include structural restoration, such as ship sinking or large rock relocation to expand coral habitat range, and biological restoration, such as culturing coral larvae or oysters, or collecting and rehabilitating broken coral pieces to assist growth. Reefs are important for coastal climate change adaptation efforts as they act as buffers, protecting coastlines from large waves and strong currents during storm events. Similar to other green infrastructure solutions, coastal reefs not only mitigate wave impact, but also provide a range of vital ecosystem services that directly and indirectly benefit humans and the environment, for example species habitats, recreational and aesthetic values, and income

generation possibilities for local communities).

Implementation

For reef protection:

1. Any potential or ongoing degradation drivers (e.g. land based pollution sources, tourism activities damaging coral reefs, etc.) should be stopped or mitigated to the extent possible.

2. Monitoring systems (for example the Coral Reef Early Warning System, or CREWS, in the Caribbean) should be established to measure environmental conditions (temperature, salinity, pressure, tidal levels, etc.) that are indicators for reef threats

3. Legal protection of reefs, for example by designating them as marine protected areas, can improve survival rates, particularly when communities are involved in their management

For oyster reef restoration:

1. For site location, certain conditions must be met - a suitable substrate (e.g. rock for oysters), and appropriate salinity, water temperature and chlorophyll concentration. An analysis to determine a suitable site must therefore be completed.

2. Cultch material (hard substances which support oyster growth) is dispersed at the site. It can include old oyster shells, clam shells, porcelain and limestone marl.

3. Oysters should naturally recolonize the cultch material. To speed up the process, young “seed” oysters can be relocated from highly productive oyster reefs.

4. Reef height and area should be measured and monitored to assess its state of over time and mitigate potential threats. Local community involvement in monitoring and protection can be particularly beneficial.

For coral reef restoration:

1. Reefs that have been damaged (e.g. coral has been dislodged, coral boulders have cracked, etc.) may require physical restoration by reattaching corals or filling cracks in the boulders with cement. Physical restoration repairs  and encourages natural regeneration.

2. Nurseries can be established using nets, plastic mesh or cement blocks to rear coral for transplantation and speed up colonization.

3. Environmental conditions (temperature, currents, salinity, coral species) at the nursery site should correlate to those at the intended relocation site.

4. Once reared in the nursery, coral fragments are carefully moved to the relocation site and attached to a suitable substrate.

5. Reef height, reef area and species composition should be measured and monitored to assess the reef’s state over time.

Artificial reefs:

1. An analysis focusing on conditions that support coral/oyster growth must be done for site selection.

2. Potential pollutants such as tires should be avoided when selecting the site. If choosing a shipwreck, ensure that oil and other toxic substances are cleaned up.

3. The reef can be established by anchoring reef structures (pillars, rocks) or sinking the wreck and planting of propagated nursery corals.

4. Reef development needs to be monitored. Maintenance work may be required, for example reshifting reef construction or removing invasive/unwanted species.

Environmental Benefits

- Creates high value biodiversity hotspots.

- Decreases the force and velocity of waves, protecting coastlines from the effects of storms and flooding.

- Reduces wave impacts, mitigating shore erosion and land retreat.

- Filters water (oyster reefs), positively effecting overall water quality.

Socioeconomic Benefits

- Reduces or avoids maintenance costs of built infrastructure for shoreline protection.

- Reduces human injury or loss of life risks by mitigating negative coastal impacts.

- Provides an important source of food and income for local livelihoods, for example coral reefs can be used for tourism.

- Provides recreational and aesthetic value.

- Contains marine organisms with chemical compounds that have potential for medical use.

Opportunities and Barriers

Opportunities:

- If well-managed and stress is kept to minimum, reef self-resilience improves and little

restoration is required

- Provides climate change adaptation benefits along with a host of other ecosystem services

crucial for human and environmental well-being

Barriers:

- Protection activities can be complex technologically and politically – particularly when stress sources are found upstream in the rivers and significant economic development activities need to be foregone to protect the reefs

- A major driver of reef degradation is climate change (increased sea temperatures and acidity), which cannot be managed and eliminated on a local level

- Not all artificial reefs establishment is successful

- Management and local community involvement are crucial to curb illegal activities threatening reefs

Implementation considerations*

Technological maturity: 3-4

Initial investment: 3-5

Operational costs: 1-3

Implementation timeframe: 2-4

* This adaptation technology brief includes a general assessment of four dimensions relating to implementation of the technology. It represents an indicative assessment scale of 1-5 as follows:

Technological maturity: 1 - in early stages of research and development, to 5 – fully mature and widely used

Initial investment: 1 – very low cost, to 5 – very high cost investment needed to implement technology

Operational costs: 1 – very low/no cost, to 5 – very high costs of operation and maintenance

Implementation timeframe: 1 – very quick to implement and reach desired capacity, to 5 – significant time investments needed to establish and/or reach full capacity

This assessment is to be used as an indication only and is to be seen as relative to the other technologies included in this guide. More specific costs and timelines are to be identified as relevant for the specific technology and geography

Sources and further information