Seagrasses are flowering plants that grow fully submerged in marine environments, unlike seaweeds. They possess roots, stems, leaves, and produce flowers and seeds. These plants form dense underwater meadows in shallow, sheltered coastal waters, estuaries, and bays globally. They are among the world’s most productive ecosystems.
Why Plant Seagrass
Seagrass meadows provide crucial habitats for diverse marine life. They act as nurseries for many juvenile fish, crustaceans, and other marine organisms, offering shelter from predators. A single hectare supports tens of thousands of fish and millions of small invertebrates, including commercially important species. These underwater pastures also provide food for large grazers like manatees, dugongs, and green sea turtles.
Seagrass improves water quality. Their leaves trap floating sediments, filtering the water and enhancing clarity. Seagrasses absorb excess nutrients like nitrogen and phosphorus, preventing harmful algal blooms. This filtration benefits adjacent ecosystems like coral reefs by providing clearer water.
Seagrass meadows naturally defend against coastal erosion. Their roots bind sediments, stabilizing the seafloor and preventing coastal land loss. Seagrass blades reduce wave energy by up to 40% before reaching the shore, minimizing storm damage and coastal flooding. They also trap sediment, building up the seafloor and protecting coastlines from sea-level rise.
These underwater plants are allies against climate change, acting as carbon sinks. Seagrass meadows absorb and store large amounts of carbon, often called “blue carbon,” in tissues and sediments. They can sequester carbon up to 35 times more efficiently than tropical rainforests, storing an estimated 10% to 18% of the ocean’s carbon despite covering a small fraction of the seabed.
Before You Plant Seagrass
Understanding legal requirements is essential before planting seagrass, as permits vary by location. Many jurisdictions require permissions for disturbing marine habitats, including restoration. Engaging local environmental agencies early is advisable for compliance.
Site assessment prepares for successful seagrass restoration. Suitable locations have good water quality with sufficient light, as seagrasses rely on sunlight. The seafloor substrate should be appropriate (soft sand or mud), providing a stable base for roots. Sites with moderate water flow and minimal disturbances are preferred for new seagrass.
Identifying reasons for past seagrass decline addresses ongoing stressors. This might include assessing pollution, sedimentation, or excessive nutrients. Resolving or mitigating these issues before planting increases long-term success.
Sourcing healthy plant material is a consideration. Seagrass can be obtained from specialized nurseries cultivating species for restoration. Nurseries often focus on species adapted to local conditions, such as Halodule wrightii (shoal grass) or Zostera marina (eelgrass). Alternatively, plant material can be salvaged from development areas or healthy donor meadows, ensuring ethical and legal collection.
How to Plant Seagrass
Planting seagrass involves several methods, each suited to different conditions. One approach is transplanting individual shoots, often from donor beds or nurseries. These shoots include a portion of the rhizome and roots, aiding quick establishment. They can be secured to the seafloor using biodegradable anchors (like wire staples) or by burying the rhizome directly.
Another method involves planting rhizome fragments, sections of underground stem from which new shoots emerge. Fragments are often bundled or attached to a biodegradable mat before placement. Proper spacing is important for future growth and spread, typically several inches to a foot or more between planting units, depending on species and desired density.
Utilizing seeds is a viable planting strategy, particularly for larger-scale restoration. Seeds can be collected from flowering plants in healthy meadows during reproductive season. Once collected, seeds are stored in controlled conditions to prevent premature germination.
Seeds can be dispersed directly onto the seafloor, or placed into biodegradable bags with inert sand. These bags, often containing around 50 seeds, weigh down seeds and provide a growth medium, with one bag typically planted per square meter. This method protects seeds and ensures they remain in place until they germinate and establish roots. Minimize environmental disturbance during planting.
After You Plant Seagrass
Initial monitoring assesses new seagrass survival and establishment. Regular observations identify signs of stress (discoloration or blade loss), indicating water quality or environmental issues. Tracking growth and spread over the first few months provides insights into restoration success. This initial phase determines if immediate interventions, like replanting, are necessary.
Protecting the restoration site from disturbances is an aspect of post-planting care. Recreational activities like boat traffic and anchoring can damage new plantings; marking the area with buoys or establishing no-anchor zones can be beneficial. Grazing by marine animals, while natural, might need monitoring if many herbivores impact young plants.
Long-term care involves continued observation as the seagrass meadow matures. Full establishment can take time, from months to several years for faster-growing species like Zostera noltii or Cymodocea nodosa, and potentially centuries for very slow-growing species such as Posidonia oceanica. Patience is a factor in seagrass restoration, as ecosystems develop gradually. Sustained monitoring ensures the long-term resilience and health of the restored habitat.