Reefscapers Diary 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).

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!