Expedition report: Little and large: surveying and safeguarding coral reefs & whale sharks in the Maldives (September 2022)

In September 2022, Biosphere Expeditions ran its tenth annual Reef Check survey expedition to the Maldives, after a two-year year hiatus in 2020/2021 due to the COVID pandemic. Local and international citizen scientists, supervised by a professional reef biologist, performed Reef Check surveys for one week in South Male’ and Vaavu atolls at exposed, semi-exposed and sheltered sites. We repeated visits to sites last surveyed in 2019 to compare reef health from three years ago, particularly those around Guraidhoo Island, which had been subjected to land reclamation work in 2020.

Coral cover for all sites surveyed at South Male’ and Vaavu varied between 42 and 15%, very similar to the range in 2019 of between 45% and 18%. Mean coral cover at all depths was 26% (27% in 2019). In 2019, development of the islands was set to increase across the country from contracts signed by the previous (2018) Maldivian government. We mapped and digitised increased landfill areas (increasing the pre-existing land area by 70% in 2020) near to Reef Check sites at Guraidhoo backreef and forereef; the former to extend the land area of a local island and the latter to extend a resort. These areas coincide with a relative decline in shallow live hard coral cover from 30 to 14% (53% decline) at sheltered backreef areas in 3-4 m of water, and 21 to 15% (29% decline) in exposed forereef waters at 5-6 m. Coral cover in deeper areas stayed the same (Guraidhoo backreef) or increased (Guraidhoo forereef) over the same three-year time period. A further site called Coral Gardens (southern area of south Ari atoll), which was previously surveyed just before the 2016 bleaching event, showed a coral cover decline from 63 to 19% (69% decline), indicative of the long-term effect of the 2016 bleaching event. Much of the substrate at Coral Gardens was colonised by Tydemania expeditionis algae with rubble dominant in the deeper section, indicative of a breakdown of previously dead coral colonies, probably from the 2016 bleaching event. Coral Gardens was also notable for high sedimentation and poor visibility, estimated at only 6 m.

Isolated bleaching was observed, but only of individual, small (less than two-year-old) colonies. Such bleaching was mostly of Pocillopora and some Acropora colonies. No Crown of Thorns were recorded during the expedition. Coral-eating Drupella gastropods were commonly recorded, with incidents of live-coral damage in three of the six sites. One site (Guraidhoo backreef) had 17 colonies affected by Drupella. Litter was largely absent from the reefs we visited, although lost fishing lines were commonly found, largely encrusted into the coral framework.

As for all previous surveys, there were moderate to large-sized grouper at all sites, with an average density of 0.25 to 4.25 grouper (above 30 cm total length) per 500m3 at outer reefs, with lower numbers (0 to 2 individuals) at inner reefs. Parrotfish (an important grazer) were present at low densities of 3.9 individuals per 500m3, with similar densities on outer and inner reefs. Densities of all species of snapper were at similar levels (3.7 individuals per 500m3), whilst sweetlips were rare (0.3 individuals) and butterflyfish predictably abundant (12.6 individuals per 500m3).

Sharks (black tip reef and whitetip) were only recorded on the first check dive (not a survey) and on the last day at Coral Gardens.

A short effort-based whale shark survey was carried out at the outer reef of South Ari Marine Protected Area on 8 September 2022. No sharks were sighted.