Urgent Search for Malaysia’s Super Corals

Beneath the paradisical island veneer of Pulau Lang Tengah, Terengganu, is an amazing scientific race against warming seas to save Malaysian corals from extinction.

Text by: SL Wong | Images by SL Wong, and Coralku & collaborators

Edited by: Yao Hua Law

Published: 8 June 2023

Which corals are best to restore reefs? Considering how quickly seas are warming, it would make sense to plant corals that can withstand high temperatures. To figure out which these ‘super corals’ are, scientists in Lang Tengah, Terengganu are subjecting individuals to heat stress tests. (SL Wong)

This idyllic 700m stretch of lagoon belies a frenetic underwater laboratory run by non-profit Coralku. At depths of 9—12 m are multiple ‘nurseries’ where scientists are growing corals. There are ‘trees’, frames, steel nets and floating grids. In all, they supply 1,000 individuals a year from at least 12 species for restoration. (SL Wong)

Protected from the monsoon, the nurseries sit in the largely sand-and-rubble Pasir Besar reef. The main restoration site where most corals are planted is Batu Kuching in the south, with 1,500 corals already planted in a 150 m by 150 m area. The objective is to save Lang Tengah corals from extinction as temperatures rise.

The project began 3 years ago. The team runs numerous scientific experiments. Coral fragments on these PVC ‘trees’  come from healthy coral colonies and storm-broken pieces. The project is a model of rare rigour in Malaysian coral restoration. Coralku knows where each coral fragment comes from, in which nursery it is grown, its growth and survival rates, diseases and predators, and where and how well it does when planted. (Affendi Yang Amri)

Each month, the nursery corals are measured. Survival rates have been 34–94% over a 14-month study period, “depending on species, nursery and its genetics,” says project lead Sebastian Szereday. In terms of planted corals, Batu Kuching records over 650 days show survival rates of 9–62%, again depending on species and local sites. (Natasha Zulaikha)

To see which corals can best tolerate heat, Szereday and co-lead scientist KL Chew cut 3 cm fragments from nursery specimens. The fragments are then heat-stressed. The most resilient individuals – the ‘super corals’ – are then selected and planted. (Natasha Zulaikha)

On land, the coral fragments undergo a standardised experimental heat stress test called the Coral Bleaching Automated Stress System (CBASS). Developed in the Red Sea 3 years ago, it is an affordable, simple, portable, on-site system. The developer of the CBASS concept, marine geneticist Christian Voolstra, is also a collaborator in Coralku’s project, along with Universiti Malaya’s coral reef ecologist Affendi Yang Amri. (SL Wong)

In CBASS, corals are heated for 18 hours in tanks at 4 temperatures: normal (the historical maximum average sea temperature, which is 30 °C in Lang Tengah), 4 °C above normal, 6 °C above normal, and 9 °C above normal. The coral’s stress level is measured by how well its microalgae uses light to photosynthesise. As the temperature increases, this ability drops. Corals then reject the microalgae and become bleached. (SL Wong)

So far, Coralku has identified individuals from three ‘super coral’ species that are heat resilient: Acropora florida, Echinopora horrida, and Acropora gemmifera. Pictured is Hydnophora rigida (Lemon squeezer coral). It does well in nurseries and when planted, and its bleaching thresholds are “okay”. Szereday hopes that “rather than taking a wild guess” about which corals to plant, CBASS screening will become a standard nationwide. (SL Wong)

Coralku has planted about 500 nursery fragments of the heat-resilient species in the restoration reefs. But they can’t heat test individuals fast enough. So they also continue to plant non-resilient and untested corals. They want to try and stave off local and regional extinction. By the year end, they would have planted 3,000 fragments and are monitoring them all. As an impending El Niño phenomenon seems set to raise sea temperatures, it is a race against time. (Atkinson Tan)

This is part of Macaranga’s #SeaWorld series. Read the main story here:  Nature’s Forts Key to Weathering Storms. The series is supported by the Embassy of France in Kuala Lumpur.

Update: 14 July 2023: Text was corrected to reflect that when it gets too hot, corals reject the algae rather than the algae abandoning corals.

Bahasa Malaysia | 中文版  | Français

Further reading:

Coralku. Our Coral Reef Research Projects. 2021.

Henry, J.A., et al. (2023), Using relative return-on-effort scoring to evaluate a novel coral nursery in Malaysia. Restoration Ecology, 31: e13767.

Szereday, S., et al. Highly variable response of hard coral taxa to successive coral bleaching events (2019-2020) and rising ocean temperatures in Northeast Peninsular Malaysia. bioRxiv 2021.11.16.468775

Voolstra, CR, et al. Extending the natural adaptive capacity of coral holobionts. Nature Reviews Earth and Environment 2, 747–762 (2021).

Voolstra, CR, et al. Standardized short-term acute heat stress assays resolve historical differences in coral thermotolerance across microhabitat reef sites. Global Change Biology. 2020; 26: 4328– 4343.

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