Reefscapers Diary 2023

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.

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

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).

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

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).

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

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!