Four Seasons Team Diaries: July 2024

At Landaa this month, we transplanted 28 new coral frames, kindly sponsored by guests (13), the Resort (11), and online (4), adding 1380 coral fragments to the reef. We monitored (cleaned, repaired, photographed) a total of 286 established coral frames at various sites around Landaa and Voavah.

A total of 20 frames (10 small, 10 medium) were sponsored by a group staying at Landaa, and built in a single day as part of an event held at Voavah. The group engaged enthusiastically with the activity, and we were delighted to see the Voavah reef looking healthy at the time of fragment collection.

To see the progress of your frame, please visit our dedicated Four Seasons monitoring page where we upload new photos every 6 months or so.

Maldives Coral Bleaching Season

Bleaching Experiment: Nature vs Nurture

To determine the extent to which bleaching susceptibility depends on a colony’s genetic resistance as opposed to its environment, we halved each colony on a mature, healthy frame that has grown in shallow water (3m) and planted these halves on a deep water frame (12m). Over time, we will monitor bleaching for both frames and see to what extent depth correlates with bleaching susceptibility for genetically identical colonies. [PHOTOS, below]

Anga Faru: Reef Restoration Project

Anga Faru is located to the east of Dhonfanu Island, and lies between popular dive sites Dhonfan thila and Dhigu thila. Anga Faru was designated as a protected area in 2009 and is recognized as an important nursery site for grey reef sharks. Anecdotal evidence suggests that although Anga Faru was previously considered to have high coral coverage and biodiversity, in recent years the reef has been severely affected by coral bleaching. As a result, the reef is now considered to be highly degraded by local users.

On 27 July, our Reefscapers team conducted a survey of Anga Faru (at the request of Baa Atoll Biosphere Reserve and Baa Atoll Council) to assess the reef for its suitability as a site for a coral restoration project. In this survey, we aimed to assess the overall live coral cover across the reef, as well as the suitability of the substrate for the placement of coral frames. The findings of this survey have been passed back to the Biosphere Reserve team, who will use this as part of their application for a new coral restoration project at the site.

Site Survey: The reef consists of a ring of shallow top reef (1-3m depth) with a central lagoon and has a small sandbank on its southern side. The outside of the reef slopes down to a depth of 20-30m on all sides before leveling off. Visual assessment and video transects were used to approximate live coral coverage across the site. Species diversity was estimated using direct observations to family level (eg. Acropora). Suitability of locations within the site for restoration were based on visual assessments of live coral coverage, reef slope angle, degree of sedimentation and reef rugosity. In total, 3 areas around Anga Faru were assessed:

Site 1: The north side of the island presented a sparse top reef (1.5m depth) with stable substrate consisting of rubble, <5% coral cover consisting of Pocillopora spp. and encrusting/massive genera including Cyphastrea, Montipora, Porites and Astreopora. Some healthy Acropora was found 7m down a steep reef slope, but coverage of this family was sparse. The north reef also showed relatively high levels of sedimentation, with prominent sand coverage on all but the steepest slopes. The reef slope was noted to be approximately 90 degrees between 1.5 and 16 metres, with some broad shelves located between 5 and 8 metres sloping approximately 45-50 degrees. Below 16m depth, the substrate became sand sparsely interspersed with boulders.

Photos, from left: the shallow top reef showed coral coverage less than 5%, several broad sloping shelves were located between 5 and 8 metres deep. At 15-17 metres the reef slope leveled off, the steep higher reef slope showed high levels of sedimentation. 

Site 2: The south-east side of the island presented a top reef with 10-15% coral cover, dominated by Pocillopora spp. and encrusting/massive genera. The substrate was stable and consisted of rubble and larger boulders with a higher rugosity on both the top reef and reef slopes than site 1. The top reef was slightly deeper at between 2 and 3 metres, with a shallower reef slope of approximately 45 degrees descending to below 25 metres depth.

Photos, below. The south-east side of Anga Faru showed higher species diversity, reef rugosity and overall coral coverage than site 1. Healthy coral recruits were also noted, indicating good environmental conditions for coral growth at this site.

Site 3: The south-west side of the reef presented a top reef with stable substrate and 15-20% coral cover, dominated by Pocillopora spp. and encrusting/massive genera. The overall topography of the reef was broadly similar to site 2 with a top reef of 2-3m and a slope angle of approximately 45 degrees, leveling off and becoming sand substrate between 15 and 20 metres. Coral cover increased towards the centre of the south side, with a good diversity of Leptoria, Platygyra, Goniastrea, Montipora, Porites and some larger healthy Acropora below 3m. At both sites 2 and 3, higher numbers of the coral predator Culcita schmideliana (spiny cushion star) were noted.

Photos, below. Larger colonies of living Acropora corals were found below 3 metres but were more concentrated at the bottom of the reef slope, between 12 and 15 metres. The higher reef slope (right) consisted of stable rubble and boulders with similar numbers of recruits as site 2.

Secondary Site Report: In addition to Anga Faru, surveys were carried out at three additional sites to assess their suitability as donor sites: Gaaviligili, Bodhu Gaafaru, Olhugiri.
1) Gaaviligili (south-western edge of Baa Atoll) – large healthy colonies of Heliopora coerulea. This site anecdotally has high coverage of healthy coral on the west side, including a large area of Montipora foliosa, but due to strong currents it was not possible to fully assess the site.
2) Bodhu Gaafaru – shallow reef flat with similar topography to Anga Faru. The reef here was highly degraded, with <5% live coral cover. The site had many recently dead table corals, likely casualties of the 2024 mass coral bleaching event, and was considered unsuitable as a donor site.
3) Olhugiri Reef – protected area, with restrictions on access to protect the fragile mangrove habitat of the island. The reef was degraded, with few colonies of healthy Acropora and Pocillopora but higher coverage of massive coral species. Olhugiri reef has potential as a small-scale donor site.

Recommendations:
– The top reef of both sites surveyed on the south side of Anga Faru (sites 2 and 3) are suggested as suitable locations for conducting coral restoration through the coral frame method.
– None of the donor sites can be recommended as donor reefs at this stage, and further surveys are required to identify suitable sites. However, Gaaviligili reef merits further examination before it’s exclusion as a donor reef due to the anecdotal reports of high coral cover at this site.

At Kuda Huraa this month, we transplanted 5 new coral frames. To see the progress of your frame, please visit our dedicated Four Seasons monitoring page where we upload new photos every 6 months or so.

Maldives Coral Bleaching Season

Coral Bleaching

Following coral bleaching events, numbers of corallivorous species can increase rapidly as they devour any sick coral colonies. This month, we removed the following coral-eating species from the reef and from our frames: 2 crown-of-thorns starfish, 8 cushion starfish, 300+ corallivorous snails.

Coral bleaching continued in corals around Kuda Huraa during July. The coral mortality rate has slowed, and we are seeing increased recovery in natural colonies and on coral frames around the island. This includes recovery in a few purple Acropora humilis colonies (at Seastar and Water Villas sites), surprising as these two sites have some of the highest mortality rates, and A. humilis was one of the species hit hardest by bleaching. We have also observed soft corals regain symbionts and healthy colouration this month.