Coral Gardening
Reviving Watamu's Coral Reefs: A Story of Resilience and Restoration
Watamu Marine National Park (WMNP), established in 1968, is one of the world’s oldest marine parks. This 10 km² protected area, managed by the Kenya Wildlife Service (KWS), safeguards a precious coral reef ecosystem. Research on Watamu’s corals has been ongoing for over 40 years, with the first quantitative data collected in 1983. This data provides a valuable baseline for understanding changes over time.
A History of Coral in Watamu and the Challenge of Bleaching:
Corals, related to jellyfish and anemones, are fascinating animals. They thrive through a symbiotic relationship with algae (zooxanthellae) living within their tissues. These algae use photosynthesis to provide energy to the corals, much like plants do on land. However, this delicate balance is disrupted when ocean temperatures rise even just 1°C above the average temperature for an extended period (over a month). This warming causes the corals to expel the algae, leading to coral bleaching. Bleached corals appear white, are stressed, and are more vulnerable to disease and death.
Watamu’s reef was once considered healthy, boasting 40-50% coral cover. However, a devastating global bleaching event in 1997-1998 drastically changed the landscape. The reef turned completely white, and coral cover dropped from 38% to a mere 10% between 1998 and 1999. Coral bleaching remains the most significant threat to Watamu’s corals, although local human impacts are effectively managed by the KWS.
The Importance of Resilience and Recruitment:
Coral reef recovery depends on resilience – the ability to bounce back from thermal stress. Key processes like recruitment (new coral “babies” settling on the reef), growth, and survival are essential. Successful recruitment requires a supply of larvae from nearby or distant reefs and suitable, clean substrate free of competing algae and sediment. Rapid coral growth requires clear, low-nutrient water and minimal competition from macroalgae. Thermally sensitive branching corals tend to grow faster than the more thermally tolerant, massive coral forms.
While corals can recover from bleaching, this depends on the thermal adaptation and regrowth of corals outpacing the rate of rising sea temperatures. Corals that survive bleaching often exhibit increased thermal resistance, making them more likely to survive future events.
Coral Gardening: A Beacon of Hope for Watamu's Reefs
Recognizing the urgent need for intervention, we have embraced coral gardening as a key restoration strategy. This involves actively growing and transplanting corals, particularly those that have shown resilience to bleaching. In Watamu, while adult coral colonies have survived relatively well since 1998, a lack of new recruits has hindered natural recovery. The 2020 and 2024 bleaching events further underscored the need for active restoration. Many corals survived these events, and these thermally resistant colonies have become the focus of our propagation efforts. Propagating and planting these colonies back onto the reef could help overcome the issue of low recruitment and speed up the recovery of Watamu’s reefs.
The Coral Gardening Process
Coral gardening involves the collection, propagation, and transplantation of coral fragments to restore degraded reefs. This process includes sourcing Corals of Opportunity (COOs) and Thermally Resistant Colonies (TRCs) to enhance genetic diversity and improve reef resilience in the face of climate change.
1. Collecting Coral Fragments
Two types of coral fragments are collected:
- Corals of Opportunity (COOs): These are naturally broken fragments that would likely die if left in unstable environments. Collecting them gives them a second chance. Our marine team collects COOs from various genera (including Acropora, Pocillopora, and Porites). COOs play a crucial role in coral restoration, as they reduce reliance on healthy donor colonies while contributing to reef recovery.
- Thermally Resistant Colonies (TRCs): TRCs are coral colonies that have naturally adapted to withstand higher temperatures without bleaching or suffering mortality. These corals provide an essential source of genetically resilient stock for reef restoration, ensuring that future reef structures can better cope with rising ocean temperatures. They are identified from “hot pocket” areas (like Kanani, where corals experience naturally higher temperatures) or through long-term monitoring data.
2. Nursery Development
Collected coral fragments are taken to underwater nurseries. These nurseries provide a safe environment where the corals can grow and recover before being transplanted to the reef. Different methods are used to secure the fragment. COOs are glued onto plugs or zip-tied to nursery tables for stabilization while TRCs from outside the park (like from Kanani) are placed in nurseries to monitor growth before transplantation. Local TRCs are directly transplanted to reefs after collection.
3. Reef Transplantation
Once the corals in the nurseries have grown to a suitable size, they are carefully transplanted back onto degraded reef areas. Our marine team attaches the corals to the reef structure. TRCs are often prioritized for planting in areas most affected by bleaching.
4. Monitoring and Maintenance
The transplanted corals are regularly monitored to track their survival, growth, and health. This includes checking for signs of disease, predation, or bleaching. Our team also weeds the substrate and the nurseries regularly.
The Impact of Coral Gardening and Community Involvement
Coral gardening offers a proactive approach to reef restoration, accelerating recovery and increasing coral cover and biodiversity. By focusing on resilient corals, it also enhances the reef’s ability to withstand future bleaching events. Reef restoration is a resource-intensive process, but it can be supported through donations and volunteer programmes. The work being done in Watamu provides a powerful example of how science and community involvement can work together to protect these vital ecosystems. By supporting these efforts, we can contribute to the long-term health and resilience of Watamu’s coral reefs.
This project, Coral Gardening, is in its pilot phase, only having started late last year (2024). The results so far, have been encouraging. We are looking forward to what we will achieve, and learn through the process.