Natural Solutions

Basic Principles

Throughout history, humans have been drawn to coastal areas, running the risks of storms and inundation for the great benefits these areas provide: rich food resources, building materials and transport routes. Recent population growth has also been disproportionately represented in the coastal zone, with immigration adding to natural growth, leading to rapid expansion of coastal settlements, aquaculture and agriculture. Unfortunately, the vulnerability of coastal peoples has also risen disproportionately.

Sea level rise, warming waters and changes in storm patterns are already affecting coastal areas. Natural ecosystems may help to counter their impacts: binding sediments, reducing waves and growing upwards as sea levels rise, thereby protecting coastal lands and populations from erosion, inundation and storm impacts.

This capacity of natural ecosystem to provide protection is important in many locations: where nature provides other critical services, for food or recreation; where engineered defenses are too costly; or where adjacent lands are of low value and considered not worth extensive investment. The ability of ecosystems to perform these functions is highly variable, however, and so it is vital that we understand when and where ecosystems can help to protect coastlines. Such natural coastal protection depends on the local conditions and the structure of the ecosystems themselves. This is explored in more detail in ecosystem-specific pages, but the table below gives and indication of some the elements that make coastal ecosystems more or less suitable as a form of coastal defense.

Coastlines are among the most dynamic environments on earth. They are constantly shaped by waves, winds, tides and storms. Natural ecosystems thrive amidst this change, and indeed have developed the capacity to shape that change. Mangroves and salt marshes capture the moving sediments and help to reduce waves. Offshore coral reefs act as breakwaters, and further create the rock and sand to build islands and beaches.

Habitats

Coastal mangrove forest in the area of the Sandy Island Oyster Bay Marine Protected Area (SIOBMPA) at Carriacou, Grenada. Sandy Island Oyster Bay Marine Protected Area, designed with the support of the Conservancy, was officially launched by Grenada in July 2010. The new reserve is one of three new marine protected areas the country will launch to help improve the management of the country’s marine resources and protect coastlines from errosion . Grenada and St. Vincent and the Grenadines are located at the Southern end of the Lesser Antilles. Photo Credit: Marjo Aho.

Mangroves grow in the upper inter-tidal zone and are found predominantly in the warm coastal areas from the tropics to some warm temperate regions, where they can form extensive forests. Mangroves are highly productive ecosystems, especially in areas where freshwater from rivers or rainfall enhances growth. They provide critical coastal protection from waves and storms, habitat or nursery areas for fish and shellfish and support the lives and livelihoods of millions of people world-wide through the provision of food, timber and fuelwood.

While large areas of mangroves are being lost through coastal development and the expansion of aquaculture, several studies have shown that mangroves are natural coastal engineers.

The following reports are available for download and show that around the globe, mangroves reduce wind swell and waves, reduce storm surge along coasts, and that mangrove surfaces are rising at similar rates to sea level rise in a number of locations.

For more resources (reports on mangroves) visit the Coastal Resilience Resource Library on the Conservation Gateway

Limestone islands surround a sheltered lagoon where hard corals grow within centimeters of the low tide line. Wayag, Raja Ampat, Papua, Indonesia, Pacific Ocean. Photo credit: Ethan Daniels

Coral reefs, shellfish reefs and some other hard physical structures built by corals, molluscs, worms or even algae, act like physical breakwaters, dampening the power and force of waves. Reefs face growing threats yet there is opportunity to guide adaptation and hazard mitigation investments towards reef restoration to strengthen this first line of coastal defense.

Coral reefs alone provide substantial protection against natural hazards by reducing the strength of waves. Experts estimate that approximately 100 million or more people around the world benefits from healthy coral reefs. Studies show that coral reefs can provide comparable protection against harmful waves as artificial breakwaters (such as sea walls).

For more resources (reports and journal articles) on coral reefs visit the Coastal Resilience Resource Library on the Conservation Gateway.

For more information about coral reef resilience, visit the Reef Resilience Network.

TNC’s oyster reef restoration work along Jeremy Island in South Carolina. Photo credit: Clay Bolt

Oysters are filter feeders – they filter suspended particles (sediments, algae) out of the water column, leading to increased water clarity. Increasing water quality can enable more sea grass to grow providing more juvenile fish and crab habitat. Healthy oyster reefs filtering coastal waters could decreases number of harmful algae blooms, and associated fish kills and beach closures.

Oysters provide substrate in an otherwise flat world – oysters grow in 3-D reef structures that provide habitat for many other species including recreational and commercial fish, create nursery habitat for fish and crabs and can provide small animals shelter from larger predators. Reefs provide attachment points for other colonizing species which can be important food sources for fish, shrimp, and crabs.

Shellfish reefs are natural breakwaters that can stabilize shorelines, help to build wetlands, reducing runoff and the amount of suspended sediment in the water column, thus increasing water quality.

For more resources (reports and journal articles) on the value of services provided to humans by oyster reefs visit the Oyster Goals Project on the Conservation Gateway.

Spoonbills and Woodstorks in saltmarsh wetlands, an important feeding ground for many coastal birds. Ossabaw Island, GA Photo credit: Kathy Knight

Saltmarshes are widespread over vast stretches of low-energy coastlines and sheltered bays and estuaries. They are increasingly being described as important buffers between land and sea – binding sediments and reducing wave action.

For more resources (reports and journal articles) on salt marshes visit the Coastal Resilience Resource Library on the Conservation Gateway.

Healthy Seagrass Bed in the Exuma Cays Land and Sea Park, Bahamas. The Nature Conservancy works closely with partners such as the Bahamas National Trust and the government of the Bahamas to protect the marine habitat of the Exuma Cays and achieve the goal for the long term protection of national parks through the Caribbean Challenge. PHOTO CREDIT: Jeff Yonover

Seagrasses are subtidal plants that can build large meadows. Their role in coastal protection is not always so well understood, but they appear to reduce sediment suspension and in some places they create deep tightly matted soils – capturing sediments and raising the elevation of the sea bed. For more resources (reports and journal articles) on seagrasses visit the Coastal Resilience Resource Library on the Conservation Gateway.

Natural Coastal Protection

The Conservancy’s Natural Coastal Protection project is a collaborative work to review the growing body of evidence as to how, and under what conditions natural ecosystems can and should be worked into strategies for coastal protection. This site is intended to be a dynamic portal for that work, communicating to partners and practitioners, explaining the science, providing more detailed scientific reviews as downloads, and linking to the work of partners and to other related work.

This work falls within the Coastal Resilience Program at the Conservancy. This Program includes a broad array of research and action bringing together science and policy in review, support and case study efforts to enable the development of resilient coasts, where nature forms part of the solution.

Natural coastal protection is the protection of coastal lands and populations from erosion, inundation and storm impacts by natural systems.

Ecosystem Based Adaptation

Societies across the world are facing the need to adapt to changing conditions associated with natural disasters and climate change. Farmers are altering crops and agricultural methods to deal with changing rainfall and rising temperature; architects and engineers are redesigning buildings; planners are looking at managing water supplies to deal with droughts or flooding.

Most ecosystems show a remarkable ability to adapt to change, and also to buffer surrounding areas from the impacts of change. Forests can bind soils and hold large volumes of water during times of plenty, releasing it through the year; floodplains can absorb vast volumes of water during peak flows; coastal ecosystems can hold out against storms – attenuating waves and reducing erosion. Beyond this, other ecosystem services – such as food provision, timber, materials, medicines and recreation – can provide a valuable buffer to societies in the face of changing conditions.

Ecosystem Based Adaptation has been defined as “The use of biodiversity and ecosystem services as part of an overall adaptation strategy to help people to adapt to the adverse effects of climate change. This includes the sustainable management, conservation and restoration of specific ecosystems that provide key services.”*

For more resources (reports and journal articles) on Ecosystem Based Adaptation visit the Coastal Resilience Resource Library on the Conservation Gateway.

* Convention on Biological Diversity’s ad hoc Technical Expert Group on Biodiversity and Climate Change (AHTEG)