Changes and drivers of freshwater mussel diversity and distribution in northern Borneo

Abstract

Human activities are threatening Borneo's unique biodiversity, but little is known on the status of freshwater invertebrates. We assessed changes in diversity and distribution of freshwater mussels (Bivalvia: Unionida) in northern Borneo, and identified drivers of present distribution and threats. Past distribution data were collected from literature and museum resources. Present distribution data were collected from 21 river basins, and 47 water quality, climatic, landscape and human variables explored as potential predictors of species presence/ absence. Species delimitations were identified by morphology and COI barcoding, and haplotype networks generated. Our data indicate that over the past 50 years, four of originally five native species have become very rare or possibly locally extirpated. Since these four species are endemic to Borneo, other Bornean river basins should urgently be surveyed to identify any remaining populations. In the same time span, the non-native Sinanodonta woodiana has become the most widespread freshwater mussel in northern Borneo. The fifth native species was identified as Rectidens sumatrensis and found in four Sarawakian river basins, thus contradicting previous assumptions of an endemic Bornean Rectidens species. Although a number of stable R. sumatrensis populations are retained across Sarawak, the species' strong spatial contraction in mainland Sundaland and apparent low tolerance to eutrophication suggest that it is vulnerable to further habitat alteration. Our results indicate that Borneo's (endemic) freshwater invertebrate biodiversity is declining rapidly. Comprehensive surveys targeting an array of invertebrate and vertebrate taxa are needed to identify Borneo's freshwater biodiversity hotspots, where conservation efforts should be concentrated.

Population genetic structure of Asian snakehead fish (Channa striata) in North Borneo: Implications for conservation of local freshwater biodiversity

“…Subsequently, the main pressing challenge in our effort to effectively conserve and manage freshwater biodiversity in Sabah is in identifying the minimum units of conservation (Woodruff, 1989) among these fragmented habitats. We reiterate the call by Zieritz et al (2018) to identify freshwater "biodiversity hotspots" (sensu Myers, Mittermeier, Mittermeier, da Fonseca, & Kent, 2000) in Borneo, which the authors noted would entail more thorough studies of species-level diversity. Intra-population diversity has been similarly side-lined in defining biodiversity hotspots even though incorporating molecular data could augment this approach by helping us delimit and delineate evolutionarily significant units (ESUs) within taxa, with particular interest on those with low genetic diversity and potentially low adaptive capacity.…”

New freshwater mussel taxa discoveries clarify biogeographic division of Southeast Asia

“…The Isthmus of Kra as a significant biogeographic barrier for the Unionidae. It was shown that freshwater basins of the Malacca Peninsula represent a part of the Sundaland Subregion 16,17 and that the Dawei and Tanintharyi river basins belong to the Western Indochina Subregion 4,5,7,24 . However, the location of the southern boundary of the Western Indochina Subregion was until now unclear, because freshwater mussel faunas of the southern edge of Myanmar south of the Tanintharyi Basin were almost unknown.…”

Effects of mussels on nutrient cycling and bioseston in two contrasting tropical freshwater habitats

“…Muar River is a mesotrophic river (* 7-11 m wide) that flows through a mosaic of oil palm plantation and secondary forest, several km from the nearest human settlement ( Table 1). The only mussel present in the lake is the non-native Sinanodonta woodiana Lea, 1834, which is native to China and Russia, and has been widely introduced in ponds and rivers across Malaysia (Watters, 1997;Zieritz et al, 2016Zieritz et al, , 2018b. The river features two native mussel species, Contradens contradens (Lea, 1838) and Monodontina vondembuschiana (Lea, 1840) .…”