Monthly report updates from our Reefscapers coral biologists at Kuda Huraa and Landaa Giraavaru.

Reefscapers healthy small frame covered in coral growth

You may also be interested in:

  • Our previous Reefscapers Diaries from 2016 onwards (including our extensive 2016 coral bleaching report).
  • The ground-breaking lab work and unique photography (Oct-Nov 2021) in our Coral Spawning Reports.
  • Sponsoring your very own coral frame as part of our Reefscapers coral propagation and reef regeneration projects;
  • Viewing the latest photographs of your coral frame (uploaded every 6 months) – see our Coral Frame Collection.

Reefscapers Diary April 2023

Corals (Montipora) thriving in shallow warm waters Maldives

Wild Montipora corals thriving in the shallow warm waters at Kuda Huraa’s water villas site

Coral Propagation – Monthly Progress

At Landaa this month, we transplanted 38 new coral frames, kindly sponsored by guests (23), the Resort (12), and online orders (three), which in total added ~2100 coral fragments onto the reef. In addition, we monitored (cleaned, repaired, photographed) a total of 600 coral frames around the island. We have also lifted a total of 78 buried frames out of the sand at various sites, and repopulated with new fragments where necessary.
To celebrate Earth Day (22 April) the Resort sponsored a commemorative coral frame, which was built by guests and staff. A big thank you to everyone who came to participate and support the event. 🙏

At Kuda Huraa this month, we monitored and mapped a total of 182 existing frames, and transplanted seven new frames around the island, kindly sponsored by guests (two), the Resort (two), and online orders (three). In addition, we relocated 108 frames at the Water Villas site to provide the coral with shading and reduce stresses over the warmest period of the year.

NOAA Bleaching Warnings

According to NOAA’s Coral Reef Watch Bleaching Forecast for the Maldives area, Malé Atoll was in a “No Stress” state at the start of the month. By 4 April we were at “Watch” status, elevating to “Warning” levels by 21 April.

Coral Bleaching Monitoring

Here in the Maldives, we are currently in the high ocean temperature season (March to May), so our team is actively monitoring for signs of coral stress, paling and coral bleaching. Our bi-weekly surveys of five sites around Kuda Huraa are monitoring 300 coral colonies (135 coral frames, nine coral species).

This month, we conducted 20 hours of bleaching monitoring (two dives and nine snorkels), and our results so far show 17% colonies are paling and 1% are bleached, with the shallow Water Villas site currently most impacted by the warmer ocean temperatures. We also observed the impacts of fish predation on colonies in the Shallow House Reef area – see photos (below) that represent the kind of damage that fish can cause on our healthy coral colonies (the stressed corals then go on to pale and bleach).

NOAA coral bleaching status Maldives
Acropora before-after fish predation Reefscapers Maldives
Acropora before-after fish predation Reefscapers Maldives

Addu Coral Festival

Members of our team attended the 2023 ‘Coral Festival’ on S. Hithadhoo from 27-30 April (organised by the Maldives Coral Institute). Our Reefscapers stall was visited by global government representatives, NGOs, charities, international conservationists, and many interested members of the public from nearby local islands. It was an ideal platform to showcase the full range of our work to fellow marine biologists and passionate conservationists.

On the second evening, our 2023 coral spawning documentary was screened, alongside videos from the Manta Trust and the recent Nekton deep sea expedition. Throughout, our team attended various lectures, including:

  • keynote presentations by prominent coral scientists Prof Callum Roberts and Prof Madeline Van Oppen
  • workshops on artificial intelligence in ocean science
  • panel discussions on coral restoration and conservation
Addu Coral Festival 2023 Maldives (5) stall
Addu Coral Festival 2023 Maldives (2) presentations

Reefscapers Diary March 2023

Coral Propagation – Monthly Progress

At Landaa during March, we transplanted 32 new coral frames, kindly sponsored by guests (17), the Resort (13), and online orders (two), which in total added ~1200 coral fragments onto the reef. In addition, we monitored (cleaned, repaired, photographed) a total of 646 coral frames at various sites around the island.

This month, we have also been recycling and lifting coral frames around Landaa, including 12 coral frames buried in the sand at the Turtle and Blue Hole sites, and recycling 290 coral fragments at the Turtle and Bissie’s Reef.

At Kuda Huraa this month, we monitored a total of 235 existing frames (mainly at the House Reef site), and transplanted 6 new frames around the island, kindly sponsored by guests (4), and the Resort (2). We also retagged 23 frames, remapped 73 heart-formations (Deep House Reef site), and retransplanted 27 frames (House Reef and Channel sites).

Reefscapers monthly coral monitoring & maintenance Maldives
Reefscapers monthly coral monitoring & maintenance Maldives

Coral Bleaching Monitoring

From late March to late May, the Maldives experiences higher than average ocean temperatures. This is associated with the transition of the monsoons from the North-Easterly to the South-Westerly, resulting in calm periods with little wind and rain. These conditions can be extremely stressful for the corals, and can result in paling initially, followed by possible bleaching and eventual mortality.

Temperature loggers have been deployed at various locations to record hourly SST (sea surface temperature). We will also log additional environmental data, including: UV levels, air temperatures, precipitation, wind speed/direction.

We plan to monitor the severity of any coral bleaching, to determine which species demonstrate the greatest resilience and which locations offer the best protection. Our bi-weekly surveys will attempt to identify the external stressors by assessing the paling and bleaching of selected coral colonies:

  • 300 coral colonies, on 135 coral frames, representing nine different species, at five sites around Kuda Huraa
Reefscapers coral frame photography
Reefscapers coral bleaching Maldives examples

“Project Crack”

On the Eastern side of Kuda Huraa, a single coral species (Montipora digitata) has been growing rapidly. This would normally be great news! But unfortunately, these dense patches of corals are severely restricting water flow in the adjacent areas, especially at low tide, creating a dead zone of low ocean current and higher water temperatures.

From an aerial study, we have seen the water flow pooling between the two main coral blocks (rb1 and rb2), isolating the North side of the island. To alleviate this, we plan to remove a section of these corals on the northern block of reef, creating a ‘crack’ in reef block rb1, to allow the current to flow more freely again. Map legend >

  • Yellow: coral blocks (rb1 and rb2), restricting water flow
  • Red: ‘dead zone’
  • Blue: coral frames affected by low current
Reefscapers project CRACK

Reefscapers Diary February 2023

Coral Propagation – Monthly Progress

At Landaa this month, we transplanted 38 new coral frames, all kindly sponsored by guests (18), the Resort (11), and online orders (nine), which in total added more than 2,000 coral fragments onto the reef.
In addition, we monitored (cleaned, repaired, photographed) 208 coral frames at various sites around the island.
We have also repaired frames at the Turtle site and Bissie’s Reef (using 1970 fragments), and lifted 252 coral frames that had become buried in the seasonal shifting sands (at the Turtle and Blue Hole sites).

At Kuda Huraa during February, we monitored a total of 164 existing frames, retransplanted 40 existing frames, and transplanted eight new frames around the island, kindly sponsored by guests (four), the Resort (one), and online orders (three).

Our team spent time maintaining the House Reef site. Over several dives, we lifted 60 coral frames from the seasonal shifting sands, retransplanting them with new coral fragments. This site can be challenging to maintain – the depth necessitates SCUBA gear, many of the frames are untagged and arranged randomly, and there are many corallivores due to the healthy biodiversity. This means the whole operation requires a coordinated team effort, with one team member remaining with the boat.

Temperature Loggers

We added two extra temperature loggers at Landaa’s House Reef (at depths of 2m and 5m) and two loggers at the ‘watersports bommie’, where we witnessed wild coral colonies spawning in November 2022. We also transplanted an experimental frame with fragments that spawned in November 2022 (A. humilis, A. secale, A. globiceps). We want to see if these corals will spawn next season, or whether they put all their energy into growth.

Valentine’s Day! 💙

On 14 February, we organised an event with our Resort colleagues to build a commemorative heart-shaped coral frame [VIDEO].

Reefscapers coral frame healthy heart

Coral Thermotolerant Experiments

  • Hypothesis: Coral reared at high temperature will survive best at elevated temperatures in the future.
  • Key research question: Does rearing juvenile coral at higher temperatures early in the life-stage make them more resistant to higher temperatures?

In published literature on elevated ocean temperatures, less than 5% of research has studied coral juveniles. We therefore decided to run our new thermotolerant experiments utilising our newly settled Acropora secale from the November 2022 coral spawning event.

  • McLachlan, R. H., Price, J. T., Solomon, S. L., & Grottoli, A. G. (2020).
    Thirty years of coral heat-stress experiments: a review of methods. Coral Reefs (Vol. 39, Issue 4).

Gamete Collection, Fertilisation and Settlement

During the November mass coral spawning event at Landaa Giraavaru, we collected gamete bundles of Acropora secale from the reef and our coral frames. The bundles were processed and allowed to fertilise in our Fish Lab. The embryogenesis stages were closely monitored, and successful settlement was observed (onto pre-conditioned ceramic coral fragment plugs). The settled planulae metamorphosed into juvenile corals, and symbiodinium (zooxanthellae) were uptaken.

Rearing at Ambient Temperature

The newly settled A. secale recruits were grown in ambient seawater temperatures (27-28°C) for around two months. We selected 28 individual juveniles from the upper surface substrate, to ensure consistency in light conditions.

Each recruit was photographed on: day 0 (T0), day 7 (T1), day 14 (T2), day 21 (T3), day 30 (T4).

To assess survivorship and health, we followed the standard bleaching category chart (Oliver, 2004) with an additional category 5 (‘dead’). After 30 days, we assessed health and survival rates.
Recruits were then subjected to seven days (T5) of elevated temperature, followed by seven days at ambient temperature. Survivorship and health were monitored and assessed throughout.

Three Thermotolerant Treatments

  • Treatment 1: CONTROL (x1 tank of 28 recruits): Recruits were reared at ambient sea temperature only (27-28°C)
  • Treatment 2: HOTTEST TIME OF DAY (x2 tanks of 28 recruits each): Recruits were subjected to three hours of high temperature (32°C) for 30 days
  • Treatment 3: CONSTANT (x2 tanks of 28 recruits each): Recruits were subjected to 30 days of constant heat stress. The ambient temperature was increased by 1°C for five days, to reach 32°C

Results

A total of 144 recruits were assessed for this study. At 14 days (T2), survivorship remained 100% in all treatments. After 21 days (T3), all treatments had a reduction in health and survivorship. Surprisingly, the results after 30 days showed low survivorship in our control. Unfortunately, due to electrical problems, the final seven days (T5) were disrupted, giving incomplete data and inconclusive results.

Future experimental ideas:

  • Re-run after the next spawning event
  • Select several species to assess differences in survival and thermotolerance capacity

Reefscapers Diary January 2023

Reefscapers coral colony close-up frame
Reefscapers coral frame healthy heart

Coral Propagation – Monthly Progress

At Kuda Huraa this month, we monitored a total of 153 existing frames, and transplanted 13 new frames around the island, kindly sponsored by guests (eleven) and online orders (two).

At Landaa, we transplanted 62 new coral frames, all kindly sponsored by guests (44 [*]), the Resort (13), and online orders (5), which in total added 3764 coral fragments onto the reef.

[*] Guest sponsors included a very generous corporate sponsorship of 35 medium-sized frames, completed thanks to a huge team effort collecting corals, constructing frames, outplanting, and monitoring, so a HUGE THANK YOU to everyone involved 🙏

In addition, we monitored (cleaned, repaired, photographed) 199 coral frames at various sites around the island. We have also been recycling and lifting coral frames around Landaa, and retransplanting 500+ coral fragments at several of our sites (Voavah, Dive, Elephant).

Coral Thermotolerant Experiments

Over 95% of coral research studies looking at elevated ocean temperatures use adult corals (with less than 5% studying settlement, and pre-/post-settlement). We have therefore decided to start our new thermotolerant experiments utilising newly settled Acropora secale from the November 2022 coral spawning event.

  • McLachlan, R. H., Price, J. T., Solomon, S. L., & Grottoli, A. G. (2020). Thirty years of coral heat-stress experiments: a review of methods. Coral Reefs (Vol. 39, Issue 4).

Read our Reefscapers Diaries for further details and photographs of our ongoing coral propagation efforts and reef regeneration experiments, both in the Lab and out in the lagoon, updated each month. You may also be interested in our ongoing research and photography, studying coral spawning.

This month, we released our coral spawning video on YouTube and social media, detailing our research and the coral spawning process here in the Maldives. To date, our video has clocked up over 1000 views!