Alejandra, our Reefscapers coral biologist, Kuda Huraa
Relocating our artificial reefs, Landaa Giraavaru
Coral Propagation – Monthly Progress
At Landaa during June, we transplanted 33 new coral frames (17 guest-sponsored, 14 Resort-sponsored, two online orders) using almost 2000 coral fragments. We also monitored (cleaned, repaired, photographed) around 200 existing coral frames at various sites around the island.
We are continuing to build the generous guest sponsorship of 50 large frames. This month, we completed a further nine frames, giving a total of 22 frames out-planted to Mudikaashi Reef (Dive Site). To ensure genetic diversity at the site, we have spent time harvesting more than 2200 coral fragments from all around the island.
At Kuda Huraa this month, we transplanted eight new coral frames (five guest-sponsored, one Resort-sponsored, two online orders) using 500 coral fragments. In addition, we monitored the House Reef site (removing Drupella snails), retransplanted the complete Turtle site, replaced some predated Water Villas corals, and relocated 30 frames buried by the seasonally shifting sands.
Temperature Profiles and Coral Bleaching Monitoring
This year, the NOAA Bleaching Alert season started on 30 March with ‘Watch’/’Warning’, and remained active until the middle of May, when the status was lowered to ‘No Stress’. We analysed the data from our lagoon temperature loggers at Kuda Huraa, to reveal a similar date pattern to the NOAA alerts. But we found an important difference in the data, as the first major temperature peak occurred four days before the NOAA bleaching alert was issued. On 26 March, our data shows the Channel North site peaked at 34.7°C (and recorded an overall daily average of 33.7°C).
Sea surface temperatures recorded by our loggers in the lagoon at Kuda Huraa (March to May 2022)
Coral Bleaching Monitoring
By the end of the bleaching season, our Kuda Huraa results are as follows:
- Water Villas (shallow site with optimum coral health) – a total of 400 local colonies were monitored; 15% of corals were presenting signs of paleness or bleaching, but with good recovery rates and zero mortality.
- Turtle site (shallow site with Gulhifalhu rescue corals) – we monitored 200 newly introduced colonies of different species and sizes. Around 31% of corals were pale/bleached; although double the rate, this is a good result considering the inherent stresses of the large-scale relocation project (we are yet to finalise the rates of recovery and mortality).
Rescue corals recovering from stress (April to June)
Rescue Coral Health Monitoring
At Kuda Huraa, many of the Gulhifalhu rescue colonies are already encrusting to the substrate, and the mass coral import has visibly increased marine biodiversity in the area. We focused our efforts on maintaining the Turtle and House Reef sites, reattaching any fallen or broken corals.
- Boulder corals – we continue to use quadrats to monitor health and survival rates. Results show full recovery in 18 colonies that initially presented fish predation (only one colony presented new partial-death this month).
- Small-sized frame controls – data analysis revealed survival rates varying from 54% (at the Channel site) up to 75% survival.
During June, a total of 90 Drupella snails were removed from both new and local coral colonies in the House Reef and the Water Villas, shortly after displaying signs of thermal stress during April/May.
- Saponari, et al (2021). Assessing population collapse of Drupella spp. (Mollusca: Gastropoda) Two years after a coral bleaching event in the Republic of Maldives. Hydrobiologia. 848. 1-14. 10.1007/s10750-021-04546-5.
Found Drupella in aggregations of up to 62 individuals, two years after a bleaching event.
- Bruckner, et al (2017). Predation by feeding aggregations of Drupella spp. inhibits the recovery of reefs damaged by a mass bleaching event. Coral Reefs. 36. 10.1007/s00338-017-1609-2.
Found Drupella in aggregations of 250+ individuals following the 2016 bleaching event.
During June at Kuda Huraa, coral eggs were observed in two coral species on frames in the Water Villas and the Blue Hole.
- Acropora latistella – pigmented (orange) eggs found: 8 March, 26 May.
- Acropora digitifera – pigmented (pink) eggs found: 23 May, 26 May, 6 June.
- Acropora digitifera – spawning: 7 May (around new moon); 2 June; 12 June.
We recently analysed our spawning data (2021-2022):
- Gametes observed in 17 different coral species.
- Spawning events recorded in four species (A. secale, A. plantaginea, A. tenuis, Montipora digitata).
- Temperature/tide profiles were charted alongside spawning events, to aid the prediction of future spawning events.
Coral Settlement Update
Our Acropora millepora and Acropora digitifera polyps from March/April 2022 are growing nicely. Regular maintenance includes removing any competition (algae) and keeping the tanks clean.
During June, we observed immature oocytes in A. squarrosa and A. plantaginea. As we near the second coral spawning season here in the Maldives (October/November), it is important we track gametogenesis. Understanding the reproductive biology at a local and regional scale is crucial to uncover how populations maintain fecundity.
Research shows that thermal stress reduces reproductive output of coral species, which in turn could hinder their ability to recover after disturbance. It is crucial we understand the reproductive biology of Acropora species in the Maldives, to better understand life history traits.
Maldives Marine Research Symposium (MMRS)
Our proposals have been accepted by the MMRS, for presentation at their symposium in August. We have been creating infographics and slides to detail our research findings on gametogenesis, embryogenesis, and coral spawning of both wild and frame colonies. This will also include a statistical review of our dataset to identify any similarities or differences between locations on spawning synchronicity.
- Oral presentation: “Methodology for the use of coral larvae settlement ex-situ, for upscaling restoration of the declining Acropora species”.
- Poster presentation: “Observational insight into coral spawning patterns on two Maldivian Reef Ecosystems”.
Six Month A.I. Analysis
To assess growth rates and mortality since last year’s annual review, we reanalysed our coral frame photographs using our bespoke AI software. The volume (in litres) of Acropora and Pocillopora coral species have both increased as follows:
- Acropora volume was 4000L (2021 Q4), now increased to 6000L (2022 Q2)
- Pocillopora volume was at 10,000L (2021 Q4) and is now over 15,000L (2022 Q2)
- Volumes of dead corals appear to have remained steady
Increase in volume of Pocillopora corals on our articifical reefs, 2016-2022