<i>Tridacna maxima</i> ‘Rediscovered’ in the Eastern Indian Ocean
Giant clams are ecologically important coral reef animals, with many species facing imminent local extinction. While many regions have undertaken recent assessments of their biodiversity assets, persistent gaps remain even in otherwise well-surveyed areas. This study sought to understand the geograp...
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2025-05-01
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| author | Lisa Kirkendale Peter Middelfart Michael Amor |
| author_facet | Lisa Kirkendale Peter Middelfart Michael Amor |
| author_sort | Lisa Kirkendale |
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| description | Giant clams are ecologically important coral reef animals, with many species facing imminent local extinction. While many regions have undertaken recent assessments of their biodiversity assets, persistent gaps remain even in otherwise well-surveyed areas. This study sought to understand the geographic distribution of smaller-bodied and morphologically similar giant clams, specifically <i>Tridacna maxima</i> and <i>T. noae</i>, in the eastern Indian Ocean. Due to the difficulties in reliably identifying these species using morphological characters, we confirmed species identity and investigated intraspecific variation using sequence data from the mitochondrial cytochrome C oxidase subunit I gene (COI). Seventy whole animal vouchers were newly sampled from a 1500 km span of remote northwestern Australian coastline over a decade, as part of an ongoing coral reef survey expedition of the Western Australian Museum and partners. <i>Tridacna maxima</i> had a limited distribution and was only genotyped from offshore oceanic reefs in the Rowley Shoals and Cocos Keeling Islands. In contrast, <i>T. noae</i> was well established beyond Ningaloo Reef, and was abundant at inshore sites throughout the Pilbara and Kimberley, and even offshore to Ashmore Reef. Phylogeographically, <i>T. maxima</i> did not group with conspecifics from the Western Pacific Ocean, including the east coast of Australia, but instead clustered with individuals from Malaysia, China, Taiwan, and Indonesia; <i>T. noae</i> exhibited a similar pattern. The affinity of Western Australian individuals with representatives from the Indo-Malay region and not eastern Australia will be an important consideration for these commercially important species. Novel haplotypes in both tested species occur in Western Australia. Continued sampling of eastern and central Indian Ocean giant clams, especially to continue to document the range of <i>T. noae</i>, is encouraged to understand connectivity in this basin. Together, these findings contribute to an improved baseline for conservation initiatives of these iconic coral reef animals in Western Australia. |
| format | Article |
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| spelling | doaj-art-fd03d84cfcd04b329b065c9dbd5028212025-08-20T03:24:39ZengMDPI AGDiversity1424-28182025-05-0117638410.3390/d17060384<i>Tridacna maxima</i> ‘Rediscovered’ in the Eastern Indian OceanLisa Kirkendale0Peter Middelfart1Michael Amor2Collections & Research Centre, Western Australian Museum, Locked Bag 49, Welshpool DC, WA 6986, AustraliaCollections & Research Centre, Western Australian Museum, Locked Bag 49, Welshpool DC, WA 6986, AustraliaCollections & Research Centre, Western Australian Museum, Locked Bag 49, Welshpool DC, WA 6986, AustraliaGiant clams are ecologically important coral reef animals, with many species facing imminent local extinction. While many regions have undertaken recent assessments of their biodiversity assets, persistent gaps remain even in otherwise well-surveyed areas. This study sought to understand the geographic distribution of smaller-bodied and morphologically similar giant clams, specifically <i>Tridacna maxima</i> and <i>T. noae</i>, in the eastern Indian Ocean. Due to the difficulties in reliably identifying these species using morphological characters, we confirmed species identity and investigated intraspecific variation using sequence data from the mitochondrial cytochrome C oxidase subunit I gene (COI). Seventy whole animal vouchers were newly sampled from a 1500 km span of remote northwestern Australian coastline over a decade, as part of an ongoing coral reef survey expedition of the Western Australian Museum and partners. <i>Tridacna maxima</i> had a limited distribution and was only genotyped from offshore oceanic reefs in the Rowley Shoals and Cocos Keeling Islands. In contrast, <i>T. noae</i> was well established beyond Ningaloo Reef, and was abundant at inshore sites throughout the Pilbara and Kimberley, and even offshore to Ashmore Reef. Phylogeographically, <i>T. maxima</i> did not group with conspecifics from the Western Pacific Ocean, including the east coast of Australia, but instead clustered with individuals from Malaysia, China, Taiwan, and Indonesia; <i>T. noae</i> exhibited a similar pattern. The affinity of Western Australian individuals with representatives from the Indo-Malay region and not eastern Australia will be an important consideration for these commercially important species. Novel haplotypes in both tested species occur in Western Australia. Continued sampling of eastern and central Indian Ocean giant clams, especially to continue to document the range of <i>T. noae</i>, is encouraged to understand connectivity in this basin. Together, these findings contribute to an improved baseline for conservation initiatives of these iconic coral reef animals in Western Australia.https://www.mdpi.com/1424-2818/17/6/384giant clamshaplotype networks<i>Tridacna noae</i>Indian OceanphylogeographyWestern Australia |
| spellingShingle | Lisa Kirkendale Peter Middelfart Michael Amor <i>Tridacna maxima</i> ‘Rediscovered’ in the Eastern Indian Ocean Diversity giant clams haplotype networks <i>Tridacna noae</i> Indian Ocean phylogeography Western Australia |
| title | <i>Tridacna maxima</i> ‘Rediscovered’ in the Eastern Indian Ocean |
| title_full | <i>Tridacna maxima</i> ‘Rediscovered’ in the Eastern Indian Ocean |
| title_fullStr | <i>Tridacna maxima</i> ‘Rediscovered’ in the Eastern Indian Ocean |
| title_full_unstemmed | <i>Tridacna maxima</i> ‘Rediscovered’ in the Eastern Indian Ocean |
| title_short | <i>Tridacna maxima</i> ‘Rediscovered’ in the Eastern Indian Ocean |
| title_sort | i tridacna maxima i rediscovered in the eastern indian ocean |
| topic | giant clams haplotype networks <i>Tridacna noae</i> Indian Ocean phylogeography Western Australia |
| url | https://www.mdpi.com/1424-2818/17/6/384 |
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