Coral Spawning Observations
The best way for reefs to recover from any disturbance is to repopulate through natural sexual reproduction, thereby increasing genetic diversity and abundance of corals on the reef. Coral spawning occurs when male and female gametes are released, fertilized and then settle on the reef to become a new coral colony. However, in the Maldives, little is known about the exact timing of this event, which is often species specific. In 2019, the Six Senses marine biology team had started surveying Six Senses Laamu house reef for spawning activity around the full moon in March and two species (Diploastrea heliopora and Porities lobata) were observed releasing male gametes 3 nights after the full moon. On the same day in 2020, a third species (Goniastrea retiformis) was observed releasing gamete bundles on this same day. Despite these observations, with 36 different coral genera have been recorded on Six Senses house reef, and 47 in Laamu, there is still much more research needed to understand this critical event. Now with a clearer idea of when spawning occurs, the Six Senses marine biology team are conducting a more detailed and targeted research project into coral spawning and recruitment success.
LIFE AFTER
BLEACHING
We are witnessing the coral reefs in the Maldives change, and not for the better. Historically, live coral covered an average of 42% of reefs in the Maldives. But, in 1998 a catastrophic event occurred. Prolonged unusually warm sea surface temperatures caused the reefs of the Maldives to fall victim to its first mass coral bleaching event. This resulted in live coral coverage to decrease by an average of 93%. Just when the reefs seemed to have recovered disaster struck again and in 2016 three weeks of unusually warm waters caused 73% of Maldivian corals to bleach. Here at Six Senses Laamu, marine biologists witnessed this first hand and documented the decline on reefs near the resort.
National Coral Reef Monitoring Program
Since 2018, Six Senses Laamu’s House Reef has been established as a permanent reef monitoring site under the Climate Change Adaptation Program (CCAP) launched by the Maldivian Ministry of Fisheries, Marine Resources and Agriculture. The program was launched following the catastrophic mass coral bleaching event in 2016, where a rise in sea surface temperature resulted in an average loss of 75% of Maldives’ shallow corals. Three years worth of data from the Six Senses Laamu’s site has been reviewed to give an indication of the reefs’ recovery up to December 2020. The results showed that total live coral cover increased from just 12% in March 2018 to an impressive 25.9% in June 2020. However, due to temperatures exceeding 30 degrees celsius, 16% of coral that year were recorded as bleached, and this likely resulted in the drop in live coral cover to 18.4% recorded in December 2020. The data proves the reefs are recovering from the 2016 mass bleaching event, but the rate of recovery is hindered by continued smaller scale bleaching events.
Coral Spawning Observation in March 2021
COLLABORATIVE FOR REEFS
IN LAAMU (CRL)
The coral spawning project has been one of Six Senses biggest projects since 2021. In 2023, this project took a big step forwards by establishing the Collaborative for Reefs in Laamu (CRL), aiming to explore an innovative restoration method in the Maldives, called larval restoration.
Since 2021we have been monitoring coral spawning on the Six Senses Laamu house reef. Corals are colonial animals and they use environmental factors like temperature and the lunar cycle to synchronize their spawning. The majority of coral species will release bundles of both eggs and sperm which then float to the surface of the water and break apart to fertilize with other coral colonies of the same species. To study this natural phenomenon the MUI team checks for the eggs developing inside the coral colonies by ‘coral cracking’. The presence and color of the eggs inside the colony can give the team an indication into which species are likely to spawn that month. The team then follows this up with night dives following the full moon. In 2023, we conducted 95 dives with 6969 minutes spent surveying and 235+ corals observed spawning. in 2023, we saw more colonies spawning than in previous years, and recorded species spawn that we have never witnessed before! Our dataset provides the necessary groundwork to understand the coral spawning patterns, vital to successfully implement larval restoration.
In March 2023, with the inception of CRL, the team welcomed four visiting researchers to trial larval restoration in Laamu. One of these researchers was Professor Peter Harrison who is a leading researcher in coral reproduction and restoration, and has been developing larval restoration for many years. Many other restoration projects focus on asexual fragmentation as a method, but this has limitations due to scalability, high maintenance, and reduced genetic diversity, leaving populations at risk from bleaching or disease. Larval restoration is an alternative method that has the potential to be scalable, and enhances the coral's natural reproductive cycle meaning the restored reefs have increased genetic diversity and adaptive capacity, which is especially important in a rapidly warming environment. Prof Peter Harrison has successfully implemented larval restoration in Australia and in the Philippines with very positive outcomes, restoring coral cover to large sections of reef.
During their visit in March 2023, the team was keeping their fingers crossed to catch a spawning event! Lucky enough, on the first night of spawning dives we spotted ‘setting’ in a branching coral species, giving the team a finite amount of time to prepare for spawning. The team and the collaborators quickly got into the action, placing spawn cones on top of the coral colonies to catch the bundles of eggs and sperm as they’re released. These cones are then carefully collected and brought to the surface to mix together for ex-situ fertilization. Then it’s a waiting game! The team nervously waited to see the first signs of fertilization. When cell division starts, it's a promising start to the larval restoration process and the beginning of new coral life!
The embryos were added to the ex-situ rearing facilities in the SHELL lab and to a large in-situ larval pool pioneered by Prof Peter Harrison where they can develop in a safe environment, away from the hungry mouths of fish! By taking regular samples to check on their development, the team can see when they are ready to settle (~6 days) and organize the release! To the ex-situ pools, the team added settlement material into the pools and watched closely as larvae settled down.
The larvae in the large in-situ pool can be released onto the reef either by lifting up the larval pool to dispense the larvae into tubs which are swam to the reef for cloud release, opening the bottom of the pool and dragging it near a degraded reef, or by doing targeted release with Floaty Boat! Floaty Boat (or otherwise affectionately known as Brie) is an Autonomous Surface Vessel kindly donated to MUI by Queensland University of Technology funded by the Ocean Kind project. Brie is specifically designed to aid the larval restoration technique in several ways: mapping of restoration sites, scooping up spawn slicks, and the release of larvae. Brie can create 3D models of the reef by driving along GPS tracks plotted by the team, this way the long-term effects of larval restoration and reef health can be tracked. Brie can also help in targeted larval release, the team attach a bag full of larvae to her, and she pumps down the larvae onto the reef in specific plots.
This pilot project in March 2023 resulted in 21,000 larvae being released onto the reef and 262 settlers growing in the ex-situ tanks. Since March 2023 we have repeated the process multiple times, making adjustments and improvements as we go, and have released an estimated 12.2 million larvae onto the Six Senses Laamu house reef. In addition to the released larvae, we have ~ 2000 settlers in the tank which will be raised ex-situ for around 2 years before being outplanted. The team is very excited about the future of this project.
In 2024 ,the team was able to successfully release nearly 3 million coral larvae onto the restoration site around Olhuvelhi Island, home of Six Senses Laamu. While egg collection was reduced compared to the previous year, the high fertilization rates of approximately 80% and the successful development of larvae underscored the potential of coral larval restoration as a critical tool for reef recovery. Over time, this restoration effort is expected to play a significant role in increasing coral cover, enhancing biodiversity, and contributing to the broader restoration goals for Laamu’s reefs.
The CRL project, while still in its early stages, offers promising results that align with the success seen in similar initiatives in the Philippines led by Professor Peter Harrison of Southern Cross University in Australia. These projects have demonstrated the feasibility and effectiveness of coral larval restoration, and the MUI team is optimistic that the techniques and methodologies used in Laamu will lead to similar successes. We look forward to continuing our efforts and scaling up the restoration work in the coming years, guided by the lessons learned and the valuable partnerships that have been formed.
This project would not have been possible without the invaluable support and collaboration of Southern Cross University, University of Bristol, Queensland University of Technology, Aquarium Connections, Coral Spawning Lab, Maldives Coral Institute, and Six Senses Laamu. Special thanks are due to Professor Peter Harrison for his pioneering work and leadership in coral larval restoration. With their help and guidance, our reefs in Laamu have hope for the future.
MICRO-FRAGMENTATION
PROTECTING RARE CORALS
In 2024, the Six Senses team added a new project to our coral restoration work, focused on saving rare coral species and rapid regeneration of coral biomass on reefs. Through the innovative technique of micro-fragmentation, we have the opportunity to actively help restore the local reefs by cloning corals and capitalising on the fact that this cutting triggers the coral’s regeneration response, which causes them to grow 25 to 50 times faster than normal.
Micro-fragmentation involves taking selected corals and cutting them into small fragments made up of just a few polyps each. Each tiny fragment of coral has the remarkable ability to grow rapidly and develop into a new adult colony. These micro-fragments are placed into our specialized coral runway systems that are specially designed to house corals and enhance their growth with constant and controlled water flow. This process essentially acts as coral cloning and can 37 be used to target rare or threatened species with low numbers on the reef.
Once the micro-fragments grow large enough, we can replant them back onto the reef, helping to maintain the underwater diversity and increasing coral cover. Guests now also have the opportunity to participate in this activity, meaning they can not only contribute directly to conservation but also gain hands-on experience in coral restoration, read more about our new guest activity here.
Currently, the Six Senses team is focusing on saving Acropora hemprichii, a now rare coral species severely impacted by the 2024 mass bleaching event. By micro-fragmenting these vulnerable corals, more colonies can be produced, increasing the chances of survival for this rare species.
