Our Acropora Journey: Chapter 1
by Rahul Mehrotra
Wildlife conservation, depending on who you ask, has many goals. For some, it is the dedication to support the recovery or preservation of a single group of animals, or a single species, that has suffered a major population loss. For others, it is the Sisyphean struggle of preserving a whole ecosystem or habitat, thereby supporting all the creatures that live within. This story, our story, aims to show how sometimes, conserving a single group of animals is the same as conserving an ecosystem, and how we need this now more than ever. I hope that as I sit here typing this on our little island home, where the koels scream in the morning, the cicadas scream during the day, and the bats scream at night, I can help you understand one of our many vital missions and bring you along on this journey.
The protagonist of our story is a plucky, fast-growing coral called Acropora, complex in both character and substrate. Among the most diverse corals present today, this group represents well over a hundred species, most of which are found in the Indo-Pacific. Their complex structure and ability to grow over large areas makes them an important and often vital part of most established and visited coral reefs, providing the perfect home for many fish and invertebrates. In many parts of the world, they used to be a common if not dominant sight on the reef, at least until quite recently. Over the past few decades, there have been increasing and ever-frequent reports of localised loss of Acropora colonies, driven by threats such as disease, predation, anchor/diver damage, and of course everyone’s favourite, coral bleaching (often aka ocean warming aka climate change).
The best and most widely discussed example of this is in the Caribbean, where 80% of Acropora populations have been lost, driven by human activities and climate change (Cramer et al., 2020). Here in Thailand, the decline in Acropora has been reported from a multitude of locations (Phongsuwan and Changsang 2012; Yeemin et al., 2013; Scott et al., 2017). At the Koh Mun Nai archipelago, where our story starts, the prelude is a dark one. Regular monitoring by us and our colleagues at the DMCR have shown that Acropora is an uncommon sight on most reefs. The mass mortality, caused largely by the 2010 coral bleaching event, have left only a few tabulate colonies, and have almost completely wiped out the important and structurally complex ‘branching’ and ‘corymbose’ species. Despite sporadic conservation efforts by the DMCR at the island of Koh Mun Nai, our Acropora census (2020-2021) of the island found fewer than 250 colonies greater than 25cm in diameter across the whole island. Even on a small island like ours, a healthy population would make a manual SCUBA survey of individual colonies practically impossible. Almost one third of the colonies we found showed signs of fragmentation, significant recent mortality, or active entanglement in discarded fishing gear. Our reef surveys unfortunately tell us that the rest of the islands haven’t fared much better, with multiple ‘Acropora graveyards’ now largely devoid of coral (or fish) life.
Phew, those are some heavy facts, why are you even still reading? Well, for those masochists that still remain, let’s take a step back from this journey for a bit and talk about the world of conservation again. Anyone who has lived in the world of conservation for an extended period of time will tell you that everyone starts this journey with dreams of making a difference but anyone who stays, rarely does so because of an overwhelming abundance of success stories and positive change in the world. We stay for the giant sums of money, the luxury is bliss, and most of our chauffeurs accept bitcoin.
Okay, fine, we aren’t here for the imaginary loot (though conservation is only one of many under-funded causes in the world today). I’m not sure if there is a single reason why us morons stick it out. For some it’s because we feel that if we don’t, nobody will. Others perhaps stay because we cling to our little agency in our little pocket of improvement, or because we believe our efforts may ‘go viral and spread’ (too soon?). I suspect though that some of us remain, despite the integral cynicism this field can bring, because we can sense the changing tide in the world. That a portion of the digital and connected world is taking up arms against the tsunami of climate change, unsustainable practices, misinformation and the demonisation of science. If this tidal shift can get behind wildlife conservation and help reinforce or highlight the successes of the conservation and environmental realms, then we may be able to salvage something for the long term.
So lets get back to our story, and see if we can instil something to take our path in a different direction. At ATMEC, our relationship with Acropora conservation is complex and varied, with all aspects working in synergy to attempt to re-establish our protagonist within the story, and thus the future of our little archipelago. First, we try to tackle the immediate threats. Without a large number of colonies, only predators that are on a serious diet would consider travelling here. Instead, the greatest active threat to the colonies here appears to be entanglement and fragmentation from discarded fishing gear. By utilising our new MARsCI protocol, we have been able to document and clean dozens of colonies across the archipelago. This then acts to promote recovery in many colonies, and hopefully get them contributing to the reproductive population in the area.
The lack of a healthy population is, however, yet another major concern. A healthy parent population will drive recovery via sexual reproduction (aka magical coral spawning), however the opposite is also true. With so many colonies already lost in recent years, the remaining survivors are now more disconnected than ever, risking genetic bottlenecking and reduced reproductive turnover. Or to put it another way, less coral jizz spread over a large area means fewer babies, that are also avid readers of ‘The Inbreeder’s Guide to Family Planning’. The next active threat is sedimentation. The archipelago sits just a few kilometres from the mouth of the river Prasae, which inundates the whole region in silt and sand, particularly when it rains (another growing concern with climate change). The final threat of note here is the big boss itself, a warming ocean and the almost-annual threat of coral bleaching.
So, how are we trying to tackle these issues? By taking advantage of the coral’s own superpowers, asexual and sexual reproduction. First, we locate and rescue naturally broken or damaged fragments of living Acropora, by securing them onto nurseries and artificial substrates. We look for fragments across the whole archipelago, but secure them at a single site. The site is chosen based not only on it’s separation from the main archipelago, but also it’s protection from some of the most severe sedimentation stress. By bringing together fragments of colonies from multiple locations, we maximise the localised genetic diversity at a single relatively isolated spot, without artificially promoting the abundance of a single genotype/colony within the reef (I’m looking at you, coral fraggers). The structures they are secured onto are also diverse in shape and each are tested to show a greater ability to prevent sediment collection. Next, we keep the colonies in relatively close proximity (but not in direct competition) to help with the final goal of any coral conservation.
When these corals recover and mature, we hope they will be able to join the contribution to the mass coral spawning events, and hopefully maximise their chance to produce genetically diverse offspring. This year (2022), we were able to provide rare and vital data on natural coral spawning of Acropora at this archipelago, a key piece in this puzzle. These corals represent the survivors, those that have withstood the mass-mortality events of their kin, and the hope is they will be able to, with enough time, produce equally resilient offspring. We are by no means the only group working to utilise adaptation and evolution in coral conservation (and we have a lot more to learn, check out this recent article on our website). But we are using sound scientific principles and the limited resources we have, to try and give these corals a future. This story is just beginning, and there are many more twists, hurdles and hurrahs yet to have. With your support, we will be able to continue telling this story and, in turn, keeping our protagonist one step ahead of their own nemeses.
To learn more about some of these ideas and concepts, checkout these articles below, or get in touch for more fusion of science,conservation and education!
· Allchurch A. (2021) The Importance and Fragility of Natural Coral Recruitment. Aow Thai Marine Ecology Center.
· Leinbach S. (2022) Coral Recovery, But at a Cost: The Hidden Effects of Bleaching. Aow Thai Marine Ecology Center.
· Scott C. (2019). Coral Fragging Should be Banned. Conservation Diver.
· Wallace C.C. (2011) Acropora. In: Hopley D.(eds) Encyclopedia of Modern Coral Reefs. Encyclopedia of Earth Sciences Series. Springer, Dordrecht.
- Cramer, K.L., Jackson, J.B., Donovan, M.K., Greenstein,B.J., Korpanty, C.A., Cook, G.M. and Pandolfi, J.M., 2020. Widespread loss of Caribbean acroporid corals was underway before coral bleaching and disease outbreaks. Science Advances, 6(17), p.eaax9395.
- Phongsuwan, N. and Chansang, H., 2012. Repeated coral bleaching in the Andaman Sea, Thailand, during the last two decades. Phuket Marine Biological Center Research Bulletin, 71, pp.19-41.
- Scott, C.M., Mehrotra, R.,Cabral, M. and Arunrugstichai, S., 2017. Changes in hard coral abundance and composition on Koh Tao, Thailand, 2006–2014. Coastal Ecosystems, 4, pp.26-38.
- Yeemin, T., Pengsakun, S., Yucharoen, M., Klinthong, W., Sangmanee, K. and Sutthacheep, M., 2013. Long-term decline in Acropora species at Kut Island, Thailand, in relation to coral bleaching events. Marine Biodiversity, 43(1), pp.23-29.