Green gravel is an innovative method developed to restore marine habitats. This technique involves preparing small pieces of rock or substrate with kelp, which are then deployed into the ocean. It represents a scalable and accessible solution for addressing the widespread decline of underwater kelp forests globally.
Understanding Green Gravel
Green gravel is a restoration technique that utilizes small pieces of gravel onto which kelp propagules are seeded and grown in a laboratory setting. It’s called “green” because of the living kelp attached. These small pieces are easily deployed, often by scattering them from a boat. The gravel size can vary, from small pebbles to larger cobbles.
The gravel acts as a stable base for the young kelp to begin their growth in controlled conditions. After the kelp matures to a certain size, typically around 2-3 centimeters, the gravel with the attached kelp is then out-planted into the ocean. This approach bypasses the need for intensive underwater work, making it an efficient and less labor-intensive method.
The Ecological Challenge It Addresses
Green gravel directly addresses the widespread loss of kelp forests worldwide. These underwater ecosystems, often called “rainforests of the sea,” are declining due to various environmental pressures. Major factors contributing to this loss include ocean warming, marine heatwaves, pollution, overexploitation, and coastal development.
The degradation of kelp forests reduces biodiversity and vital ecosystem services, including providing food and shelter for marine life, improving water quality, and sequestering carbon. The scale of kelp forest loss is substantial, estimated at thousands of square kilometers annually, making effective and scalable restoration methods like green gravel important.
The Mechanism of Green Gravel
The mechanism of green gravel involves providing a stable, pre-cultivated base for kelp to establish and grow in degraded marine environments. The process begins with collecting fertile kelp plants, from which reproductive tissues are isolated to release microscopic spores. These spores are then used to create a zoospore suspension in a laboratory.
Small, inert gravel pieces, such as basalt or crushed laterite, are introduced into trays containing this spore solution. The kelp spores then settle and germinate on the gravel, developing into male and female gametophytes. These gametophytes reproduce, forming microscopic sporophytes that attach firmly to the gravel surface.
The young kelp are reared in controlled aquarium tanks for several months, often for up to 9-12 months, allowing them to grow robustly. Once sufficiently developed, the gravel pieces are deployed into target ocean restoration areas. The kelp eventually grows larger, overgrowing the gravel and attaching themselves to the underlying natural reef substrate, effectively re-establishing kelp populations.
Real-World Applications and Contributions
Green gravel is being explored and implemented for kelp forest restoration, showing promising results in trials conducted in Norway and Australia. It is being tested with local kelp species like Ecklonia radiata and Saccharina latissima. The technique is beneficial because it can be scaled up to treat large degraded areas.
Organizations and research groups globally, such as the Green Gravel Action Group and Seaforester in Portugal, are coordinating efforts to test and optimize this method for different environmental conditions and kelp species. For example, a project in Western Australia aims to restore 1,000 square meters of kelp forest. This approach also allows for “future-proofing” restoration efforts by using resilient kelp species or strains that may better withstand future climate change impacts.