Global controversy in oyster systematics and a newly described species from SE Asia (Bivalvia: Ostreidae: Crassostreinae)

Abstract

The diversity of native oysters in many regions is overshadowed by the global dominance of a few economically important species. Here we describe the Muar Oyster, Crassostrea (Magallana) saidii sp. nov., first reported as an established local fishery renowned for exceptional and distinctive flavour over 160 years ago by British colonial officials in Malaysia, but as yet never formally named or described as a species. This new species has a subtle but clear morphological diagnosis dependent on three-dimensional characters, which has long been recognised by local fishers to differentiate the new species from co-occurring C. (M.) belcheri (G. B. Sowerby II, 1871). The Indo-Pacific clade Magallana Salvi & Mariottini, 2016 in Salvi and Mariottini 2017 is a phylogenetically distinct group that nonetheless cannot be morphologically separated from the broader genus Crassostrea Sacco, 1897. Fossils or species known only from shell specimens, though morphologically distinct species, cannot be classified as Magallana, Talonostrea Li & Qi, 1994, or Crassostrea s.s.; therefore, we revise these groups as sub-genera within Crassostrea. Our analysis of the COI barcoding fragment from previously published sequences of all available Magallana species found that gene is not sufficient to separate several economically important species, and revealed more than 5% of sequences in GenBank represent identification errors. The new species Crassostrea (Magallana) saidii sp. nov., which is genetically, morphologically, and gastronomically distinct, is known from only one population under potential threat from urbanisation. Many more global species of Magallana remain undescribed. The systematics of this group is critical to understand the diversity of global oysters, and to understand the sustainable use of species grown worldwide for centuries as our food.

Endemic Muar, Malaysia Oyster Crassostrea (Magallana) saidii Wong & Sigwart, 2021 Approaches Optimal Harvest Despite Year-Round Multiple Recruitments

“…This oyster generally settles on the riverbed, at curves of the river in strong currents, probably due to the lower siltation at high speed. The oyster is buried under sediment during unusual high sedimentation fluxes and can survive, keeping the ventral margin gape exposed to the water column (Sigwart et al, 2021).…”

“…The oyster Crassostrea (Magallana) saidii Wong & Sigwart, 2021 is a species new to science. It is morphologically and genetically distinct, limited to Sungai Muar, Malaysia, the only known population in the scientific record (Sigwart et al, 2021). Because of its creamy white meat and excellent quality, the species is known as the white oyster among fisherfolk and locals and is more popular with oyster fans than the Crassostrea belcheri (Axe Oyster) species, which can also be found in the estuary of Muar (Sigwart et al, 2021).…”

“…It is morphologically and genetically distinct, limited to Sungai Muar, Malaysia, the only known population in the scientific record (Sigwart et al, 2021). Because of its creamy white meat and excellent quality, the species is known as the white oyster among fisherfolk and locals and is more popular with oyster fans than the Crassostrea belcheri (Axe Oyster) species, which can also be found in the estuary of Muar (Sigwart et al, 2021). The oyster fishery in Muar estuary was first reported in 1858 by a British Captain, who described Muar oyster as a delicacy reserved for the royals and high officials (Macpherson, 1858).…”

“…Muar oysters have been farmed through bottom ranching by returning empty oyster shells to certain points of the Sungai Muar estuary, which is still practiced today. However, the small population is threatened by urbanization, pollution, and habitat destruction (Sigwart et al, 2021). Therefore, a sound biological baseline is required to ensure sustainability, protection, and management.…”

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Population dynamics provides insight into how the population changes in structure over time. The insight is especially paramount for species with limited distribution and of conservation concern, such as Crassostrea (Magallana) saidii Wong & Sigwart, 2021(Sigwart et al, 2021. The species is a recently described oyster endemic to the Muar estuary, Malaysia.

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