Monchanin, C., Mehrotra, R., Haskin, E., Scott, C.M., Plaza, P.U., Allchurch, A., Arnold, S., Magson, K. and Hoeksema, B.W., 2021. Contrasting coral community structures between natural and artificial substrates at Koh Tao, Gulf of Thailand.
Marine Environmental Research, 172, p.105505.
Concrete cubic frames and decommissioned steel naval vessels have been deployed in Thailand liberally to act as artificial substrates for coral restoration and marine recreation. We assessed recruitment at such substrate types at Koh Tao, Gulf of Thailand, and compared the community structure of scleractinian corals between artificial substrates and nearby natural reefs. Our results from a sample of 2677 recruits from nine sites highlighted significant differences in community structure between both reef types. Investigations of variables including time since deployment, distance from the natural reef, and seafloor depth revealed only the latter as a possible influencing factor. The diversity of recruits could not be explained by dynamics in coral spawning, and were found to represent groups with lower structural complexity. Our results suggest that coral community structure on artificial and natural reefs differs and supports distinct ecological and functional roles.
Mehrotra, R., Allchurch, A., Monchanin, C. and Scott, C.M., 2021. Assessment of spatiotemporal variability of giant clam populations (Cardiidae: Tridacna) from 11 years of monitoring at Koh Tao, Thailand. Journal of Molluscan Studies, 87(4), p.eyab042.
Giant clams (Tridacninae) are an ecologically important species in coral reef habitats across the Indo-Pacific. Numerous examples of giant clam population declines of varying degrees of severity have been documented since the 1970s. These have been attributed to several reasons, such as overexploitation in regional fisheries and ornamental trades, extreme weather events and anomalous marine warming events leading to bleaching. In Thailand, this has led to extensive conservation efforts, such as legal protections and population restocking. Despite these strong measures, to date no long-term studies have been conducted on giant clam populations in Thai waters. We provide results from 11 years (2009–2019) of giant clam population monitoring, at Koh Tao, an island with a well-documented history of coral reef-associated stressors as well as conservation efforts. Surveys were conducted across two depth ranges at 18 reef sites around the island, revealing contrasting trends. Our findings indicate a significant population decline of Tridacna crocea from coral reefs in the 6–8 m depth range, from 1.41 (±0.47) individuals/100 m2 in 2010 to 0.59 (±0.17) individuals/100 m2 in 2019, with, however, no significant change in T. squamosa populations at this depth range. Data from the 3–5 m depth range indicate no significant change in the T. crocea population over the years, but a population increase of T. squamosa from 0.78 (±0.18) individuals/100 m2 in 2009 to 2.07 (±0.38) individuals/100 m2 in 2019. Abundance estimates from these sites indicate extensive heterogeneity in giant clam populations around the island, and highlight the importance of sufficient spatial resolution in identifying population trends.
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Mehrotra, R., Allchurch, A., Monchanin, C. and Scott, C.M., 2022. Recruitment of hard coral communities on giant clam shells(Cardiidae: Tridacna) differ from surrounding reef habitats at a tourist destination in the Gulf of Thailand.
Journal of Molluscan Studies, 88(4), p.eyac031.
Giant clams are organisms of significant ecological importance on coral reefs. They are known to help maintain oligotrophic conditions on reefs, to act as potential reservoirs of symbiotic dinoflagellates and as a consequence of their large, dense shells, to contribute to reef structural complexity. Despite this, little work has been done to investigate the utility of giant clam shells for coral recruitment. Here, we quantify scleractinian coral growth on living and dead giant clams around the Thai island of Koh Tao, a site with a history of environmental and anthropogenic pressure related to tourism. Transect surveys at 15 reefs around the island yielded 739 clams, of which 120 were found to support coral recruits. A total of 270 distinct corals were recorded between depths of 2.1 and 8 m (none were found at depths shallower than 2 m), with 29% found on dead shells and 71% on living clams. Differences were found in the community structure of hard corals found on clam shells vs those found in surrounding reef environments, with mushroom corals (Fungiidae) and Stylocoeniella being significantly more abundant on clam shells than on the natural reef. In contrast, corals abundant on surrounding reefs (e.g. Acropora and Porites) were disproportionately better represented on the reef than on clam shells. This suggests that giant clam shells may play a significant role in the succession of coral reefs with certain corals being preferentially supported over others.
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