Science Review 2021 - ATMEC Research Outputs

by Rahul Mehrotra

In its first full year as an academic and conservation institution, 2021 saw ATMEC begin to set strong roots in the field of independent marine biological and ecological research. Research published last year focused on two primary themes; the taxonomy and biodiversity of marine life, and fascinating (if not disturbing) ecological trends from coral reefs. Much of this research was based on data from previous years of fieldwork at Koh Tao by members of the ATMEC team, with several more projects from Koh Tao still to be concluded. It is apparent, however, that 2022 will see ATMEC branching out with research from many parts of the Gulf of Thailand and beyond (spoilers!). So, let’s summarise each paper briefly before discussing the broader implications:


A Radiograph of a Mustelus Shark © White et al., 2021

·       The first output of the year by White et al. (2021) contributed a much-needed revision of the taxonomically troublesome genus of sharks Mustelus, with a focus on the northern Indian Ocean. These benthic sharks are found across the globe and are commonly eaten in some countries. Beyond revising multiple species in this genus, this paper also described a new species of Mustelus shark, M. andamanensis, based on specimens found in fish markets in Ranong province, Thailand.


·       The next paper of 2021 was also taxonomically focused. By combining several years of field survey data from Koh Tao, Mehrotra et al. were able to update the documented biodiversity of nudibranchs and other sea slugs from Thai waters by a further 90 species. This project ran from 2012 till early 2020 and combined thousands of hours of diving and snorkelling surveys, with citizen science, resulting in a doubling of documented diversity from the Gulf of Thailand. It also added further emphasis on the hidden and often exclusive biodiversity from the muck (soft sediment habitats) of the island.


·       Moving from taxonomy to fundamental research in ecology, the paper by Monchanin et al. compiled a huge dataset on coral recruits on artificial reefs, and compared it with coral communities found on the natural fringing reefs and pinnacles near Koh Tao. This research, based on a year and a half of fieldwork, is among the most extensive on coral recruitment and communities from Thai waters. The key findings are that the diversity and composition of coral recruits on artificial reefs differ significantly from those on the natural reef, and none of the multiple variables assessed could clearly explain why. Hence, the birth of one the largest projects ATMEC intends to undertake.


P. purpurea overgrowing different coral types © Allchurch et al., 2021

·       As the year began to draw to a close, the findings by Mehrotra et al. on giant clam populations from coral reefs at Koh Tao were published. Analysis of over a decade of data collected by the Conservation Diver team from the island revealed that these keystone species in the reefs appeared to be undergoing contrasting population shifts. The fluted clam Tridacna squamosa may be benefiting from long-term population restocking efforts but the burrowing clam T. crocea appears to be declining.


·       The final paper of the year by Allchurch et al. documented biofouling and competition between several reef building corals and the sponge Pseudoceratina purpurea. The sponge was found to disproportionately grow over some coral types over others, and was present in large amounts at certain popular tourist sites while being almost absent at others. This species of sponge has never been documented to be a coral competitor (though it has been found to have potent toxic compounds!), however it is not the only known biofouling organism documented from the Gulf, with more records coming soon!


A number of coral-specific nudibranchs © Mehrotra et al., 2021

The earlier outputs in 2021 highlighted the complexity and often overlooked importance of taxonomic investigations. South-East Asia hosts among the most biodiverse habitats in the marine world, and Thailand is no exception. The immense scope, however, of investment in time and resources needed to allow for a sufficiently deep understanding of even the most remote branches of the tree of life, provide growing barriers to taxonomic research. It is therefore with great pride that ATMEC is able to contribute snippets of research in this ever-more isolated field. Sharks and sea slugs represent some of the most popular (albeit fundamentally distinct) groups in the SCUBA diving industry with contrasting roles in ecology. Most sharks face significant threats, ranging from fishing and bycatch (i.e. White et al., 2021), ghost-fishing and discarded fishing gear, active persecution (ahem Australia), habitat loss and more. A large number of species are considered endangered and there is growing concern that we may not be able to even document the true modern diversity of this ancient group of predators before they are lost. Meanwhile sea slugs show no direct conservation threats, with several new species being described every year, and their pokemon-esque alure enthralling the lives of ever-increasing numbers of marine enthusiasts. However, even these colourful blobs of joy may be beginning to face indirect threats. In this latest sea slug paper, Mehrotra et al. (2021) document many species that are associated exclusively with hard and soft corals, many of which are threatened by factors such as climate change.

This leads us to the findings in the remaining three papers, discussing the complex world of coral reef ecology. Allchurch et al. (2021) recorded that mushroom corals (Fungiidae) and Pavona corals were disproportionately affected by biofouling from P. purpurea (the latter group incidentally being shown to host very specific sea slugs). The possible causes for this proliferation of sponge are unknown but the leading hypotheses are relatively weak predation pressure of sponges, combined with a high availability of nutrients and ideal environmental conditions to reinforce sponge growth. A further case may be made that the defensive response of these specific corals may be compromised by other environmental stressors such as warming waters, tourism pressure from SCUBA diving or microbe and nutrient availability from terrestrial runoff. These same factors, while not only possibly enhancing sponge growth, were also suggested by Mehrotra et al. (2021) as a possible indirect explanation for the decline in burrowing clam populations in the 6-8m depth of Koh Tao. These clams, along with the fluted giant clams, are crucially important on our reefs due to their ability to contribute to the low-nutrient conditions needed by corals in reefs, and act as potential stores of vital zooxanthellae in their tissues and poop (cue ‘the circle of life’).

Natural and Artificial reefs surveyed by Monchanin et al., 2021

All these factors, and more, remain part of the vast and wonderfully complex picture of coral reef ecology. Which brings us to the equally wonderfully nerdy research documented in Monchanin et al. (2021) where we start to explore a whole range of large-scale trends. In an effort to explain why recruits of the aforementioned Fungiidae corals, among others, are so prevalent on the artificial reefs of Koh Tao, we began to edge closer to a giant rabbit hole, one that we’re still falling down, 4 years later.  Underlying the deepest questions of coral reef ecology, evolution, and adaptation in the modern world, is the sadly ignored topic of coral reef succession, the topic and substance lining the  frictionless walls of this rabbit hole. The dynamics of succession, or the process by which the community structure of an ecosystem changes overtime, is particularly hard to grasp in coral reefs, given how slowly they grow and change. The colonisation of new artificial substrate is an example of primary succession, where a new habitat is formed and we can see which colonisers pioneer, and which are overtaken by others. Secondary succession is where a typical succession pathway is interrupted by an event or process (climate change, habitat destruction, Thanos, etc.) leading to the partial or complete loss of certain groups, opening niches up for others. A deeper understanding of both of these is essential to developing a framework for management and conservation of coral reefs as we progress into an uncertain future. While we were unable to pin down specifically what is causing the contrasting coral communities on natural and artificial reefs at our study sites,  we are far from running out of ideas, indeed hypothesising a few of our own in the paper. We are by no means tumbling down the rabbit hole in despair, instead we are shooting head-first with a yearning to scratch the itch of the fundamental science of whatever lies at the end.  

2021 represented just the first of hopefully many chapters in our journey of discovery, and we hope you’ll stick around to support us along the way. If you would like to access/discuss any of the papers mentioned in this article, feel free to get in touch with us!