Bivalves ( Mollusca : Bivalvia ) in Malaysian Borneo : status and threats

Species checklists enlist the species existing within a distinct geographical biome and assist as an indispensable input for evolving conservation and administration strategies. The arenas of conservation ecology and biology face the challenge of exaggerated biodiversity, accredited to the non-recognition of taxonomic inconsistencies. The study’s goals are to organize all scattered taxonomic information regarding bivalve molluscs from Malaysian Borneo, i.e. Sarawak and Sabah, under one umbrella. Available literature regarding Malaysian Borneo was reviewed. The published taxonomic data on bivalve species, conservation status, inconsistencies, habitats (marine, fresh, and brackish), research aspects, threats, and conservation strategies are presented. A critical review of the checklists and distributional records of the class Bivalvia from Malaysian Borneo and subsequent validation of species names with the World Register of Marine Species (WoRMS) database revealed that currently 76 bivalve species from 12 orders and other entities, 18 superfamilies, and 27 families have been recorded from the area. Twenty-six inconsistencies with WoRMS were found, and the corrected names are presented. The study indicates most of the enlisted bivalve species have not been evaluated by the IUCN Red List authority and have ‘Least Concern’ or ‘Data Deficient’ status for Malaysian Borneo. To date, published documents on conservation decision strategies and guidelines for future research are not good enough. Nevertheless, potential threats and their remedies for bivalves in the enriched Malaysian Borneo ecosystems are discussed herein.


INTRODUCTION
The establishment of a database and checklist of regionally present species is crucial in managing and conserving them from alpha to global ecosystem (Amano & Sutherland 2013). The lack of sufficient information at the local level regarding rare and/or endemic species potentially at risk of extinction may lead to strategies taken by different organizations, including the government, that are inadequate to avoid their extinction (Işik 2011). Nowadays, humankind faces some traumatic events, including the so-called "sixth extinction crisis". The previous five extinctions were caused by massive atmospheric, climatic, and universal phenomena, but the prediction of the next mass extinction is putting the finger on human interference in natural ecosystems (Braje & Erlandson 2013).
At regional and local level, species decline faster than the prediction of ecologists (Collen et al. 2011;Işik 2011), but this can be modified to a sustainable level if the conservation efforts would focus on protecting certain species (Reydon 2019). For example, some aquatic animal recovered their extinction risk by the conservation approach with a proper policy, legislation, and effective conservation measures. Recently, the Bangladesh government and department of fisheries initiated the conservation of red fin mahseer (Tor tor Hamilton, 1822). The proper breeding program and management helped this species regain their confined population (Kabir et al. 2018). Similarly, the reproduction and conservation management of butter catfish Ompok pabda (Hamilton-Bouchanan, 1822) changes their IUCN status from 'Near Threatened' to 'Endangered' species (Chakraborty et al. 2010;IUCN Bangladesh 2015). Now, aquaculture is very extensive for Ompok pabda (Hamilton-Bouchanan, 1822) in Bangladesh and the Indian region (Chaklader et al. 2016;Alam et al. 2020).
Another is to protect specific areas with high biodiversity, including rare and/or endemic species. Now governments and third-party stakeholders recognize the value of biodiversity conservation, and they convey efforts, finances, and human resources to the conservation of nature. The first step in this process is to know the present status of biodiversity (Groves et al. 2002;Martin et al. 2016), where a checklist and relevant information are considered to be essential documents to step forward. Establishing a database of locally and regionally present species allows management of the national and transboundary continental conservation process (National Research Council 1992).
Bivalves (two valves), are abundant in marine, brackish and freshwater ecosystems, both infaunal and epifaunal in nature. Most are filter-feeders, but some are carnivores. They influence food webs and aquatic ecosystems via nutrient cycling and habitat modification and act as a bio-indicator (Vaughn & Hoellein 2018). In many countries, bivalves are consumed by humans for which they are harvested from the wild, including freshwater and marine habitats (Köhler et al. 2012;Wijsman et al. 2019). As molluscs are rich in protein and fat, along with essential nutrients including vitamins and macro-micro nutrients, restaurants around the world serve them as delicious and luxury food (e.g., Venugopal & Gopakumar 2017;Olivier et al. 2020). Bivalve shells, including the waste of such meals, are also used as buffer material for soil fixation; for instance, Korean scientists applied oyster waste to increase soil pH and other micromacro nutrients (Lee et al. 2008).
In East Malaysia (Sarawak and Sabah, including the federal territory of Labuan), bivalves are considered a delicacy, and highly nutritious consumable commodities (Hamli et al. 2012b). Some previous studies described the bivalve fauna of Peninsular Malaysia (Idris et al. 2012;Jasin 2015;Zieritz et al. 2016;Zieritz & Lopes-Lima 2018). Some studies have been conducted in the Malaysian province of Sarawak and Sabah covering different habitats, including mangroves (Hamli et al. 2015;Abu Hena et al. 2016), seagrass (Al-Asif et al. 2020), wetlands (Idris et al. 2021), and freshwater . Noticeably, the bivalve species from freshwater environments have a more than four to six times higher risk of extinction than those in marine habitats (Agudo-Padrón 2011).
Currently there is no monograph of bivalves (or molluscs in general) covering Malaysian Borneo. Thus far only a small fraction of the bivalve fauna of Malaysian Borneo has been recorded. The first bivalves from modern history of Malaysian Borneo were recorded from the Pantai river, Sarawak (Turner & Santhakumaran 1989) and Sematan mangrove forest, Sarawak (Ashton et al. 2003), although the first record can be tracked back in 1791, from the Federal territory of Labuan (A small island near coast of Sarawak and Sabah in Malaysian Borneo), with the report of native bivalve species Marcia japonica (Gmelin, 1791) (reported as Venus japonica Gmelin, 1791) (Gmelin 1791). With time, the number of published documents (taxonomic and ecological studies) has increased, but the list of bivalve fauna from East Malaysia remains very incomplete. Numerous species are recorded in Huber (2010Huber ( , 2015, but his records 'north Borneo' or just 'Borneo' are not specific enough to be included here. Similar taxonomic J TT and conservation work was published on fish species of Bangladesh in which the implementation of conservation measures on local fish habitats was proposed (Parvez et al. 2019). Similarly, the current investigation intends making a checklist of bivalves in the Malaysian part of Borneo, including their conservation status. This study also discusses the existing research initiatives, future research prospective, and recommended measures toward conserving this vital living resource.

MATERIALS AND METHODS
The current study is based on published records regarding Malaysian Borneo (Sarawak and Sabah; Figure 1), including monographs, reviews, checklists, catalogues, posters, conference papers and posters, websites, and fishery reports from 1791 and 2020, but no additional material was collected. For each reported species the scientific names were confirmed based on the World Register of Marine Species (WoRMS) 2021 and MolluscaBase eds (2021) (validating unaccepted names, emendations, alternate, and representations).
The identifications were not checked for correctness. In most cases this was not possible, as most publications contain no photographs of the recorded species. New records should be accompanied by photographs as misidentifications are commonplace.
The species list comprises, orders, superfamilies, family name, accepted name, unaccepted names, and emendations. The contribution (%) of different orders within the class Bivalvia and various superfamilies and families in the class was estimated. The statistical data, total species counts, and graphical presentation were analyzed using Microsoft Excel.

Bivalves in Malaysian Borneo
Abdulla-Al-Asif et al.

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A critical review of the published checklists revealed that the current literature included 26 incorrect names for bivalve species from nine orders/ infraclasses/ superorders/ subclasses and 14 families. Of these inconsistencies in the bivalve checklist over 53.84 % (14 species) was due to names not accepted in WoRMS (2021), spelling mistakes (15.38 %; 4 entities), alternative representation and inconsistency in family name (both 11.54 %; 3 entities each), and inconsistencies in author and year (both 3.85 %; 1 entity each) ( Figure 3).

Knowledge gap on bivalve research in Malaysian Borneo
In the current century, macro benthic surveys were first conducted in Malaysian territory in 1981 (Morris & Purchon 1981;Way & Purchon 1981). In East Malaysia, Turner & Santhakumaran (1989) and Ashton et al. (2003) performed the first baseline study of bivalves in the Pantai River and Sematan mangrove forest, Sarawak. After that, extensive taxonomic studies were conducted by Hamli et al. (2012b); whereas Wong & Arshad (2011) published a significant checklist of bivalves. In a publication that reported edible bivalves and gastropods from different markets in Sarawak and that was published very recently which dealt with the morphometric and diversity investigation, we excluded that publication from our checklist due to the time span (1791-2020) in which it was published; however, the paper reported one new record Arcuatula arcuatula (Hanley, 1843) and rest of the species were already    (Idris et al. 2021). There are now a total of 19 published publications accessible, including a book, on the subject (Zieritz & Lopes-Lima 2018). Among the published papers, 10 were published in Scopus indexed journals, the other nine in local nonindexed journals. Six published documents discuss marine bivalves, another six discuss brackish habitats; whilst the papers cover freshwater and freshwatermarine habitats.

DISCUSSION
A comprehensive checklist on Malaysian marine molluscs by Wong & Arshad (2011) documented 581 species. Before this, Way & Purchon (1981) and Morris & Purchon (1981) reported 398 species (330 gastropods and 68 bivalves) from Malaysia and its adjacent coastal waters. In our study, we found bivalves from order Venerida (19 species) has the highest number of species, followed by Ostreida (12) and the freshwater order Unionida (10 species), while the rest of the orders or other entities have less than ten members. Among superfamilies, the Veneroidea (14 species) has the highest number of species, followed by the freshwater Unionoidea (10 species), and the rest of the superfamilies has less than 10 species (Figure 4). The family Veneridae comprises 14 species which is the highest among all families, following that the freshwater family Unionidae (10 species) has the second-highest number and the remaining 25 families comprise less than ten species each (Table 1).
For several recorded species it is evident the names are erroneous, as those species only occur in other continents. They are marked in the checklist ( Additionally, some species may have been misidentified, but this cannot be determined without photographs or voucher material. In the literature we

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found many inconsistencies, while the present analysis revealed most inconsistencies were "unaccepted" according to WoRMS (2021) (i.e., the genus or species name is no longer valid); the rest were misspellings, alternative representations, changes in families, changes in author, and changes in year (Table 2) Hamli et al. (2015) revealed morphological differences between these two taxa which lead to considered as they were both valid species.
The current study demonstrates that current bivalve research knowledge (ecological, taxonomic, and other aspects) are insufficient to serve as a foundation for academic, conservation, and aquaculture initiatives in Malaysian Borneo. A thorough literature search was conducted using a variety of databases (e.g., SCOPUS, Web of Science, university websites (for thesis), and CNKI), but the number of published papers on Borneo bivalves was determined to be insufficient. Bivalve research in Borneo is strongly encouraged, and areas such as populations, threats, life history, and breeding biology for aquaculture initiatives can all be considered significant research fields. While taxonomy, habitat ecology, conservation actions, area-based management initiatives, and approaches to recovery and reintroduction are all fundamental, harvesting trends are also critical Zieritz et al. 2020). A comprehensive checklist of bivalves in Malaysian Borneo is necessary to fill this knowledge gap. It is recommended that additional research on bivalves be conducted as a basis for conservation measures, as they contribute to both the ecology and economy of Malaysia.

Present status IUCN status of bivalves in Borneo and their habitats
According to the IUCN red list status, 66 bivalve species have not been evaluated by the IUCN or any other institution that are present in Malaysian Borneo, and it is quite clear that a plethora of research work can be conducted to evaluate only the IUCN unevaluated species. Whereas nine species were determined to be least concerned and one species was determined to have data deficiency ( Figure 5). Thus, these species must be protected wherever they occur in Malaysian Borneo through the imposition of reserve areas, restricted areas, or national/regional conservation sites. It is observed that 76 species of bivalve fauna have been reported from Malaysian Borneo, including 61 marine species (17 species can be found in both marine and estuarine or brackish water), three brackish water, and 12 freshwater species (one species can be found in both fresh and brackish water).

Threats to the biodiversity of bivalve species
Sarawak and Sabah (the Malaysian portion of Borneo) are rich in biodiversity. Certain areas of Borneo Island remain pristine due to the lack of human intervention. Commercial logging and forest destruction due to palm plantations, on the other hand, have increased rapidly in various parts of these two provinces (Bryan et al. 2013;Shevade & Loboda 2019). As a result of soil runoff into the South China Sea, secondary pollution of marine and coastal ecosystems occurs (Morni et al. 2017). Harvesting edible bivalves from wild sources indiscriminately is also a significant threat to sustainable populations. Most importantly, there is no government or local government initiative to initiate commercial aquaculture of these bivalves in order to conserve their indigenous characteristics. A model of the global declination of bivalves was proposed by Lopes-Lima et al. (2018), in which they showed that in the Indo-Pacific region, pollution (45%) is the significant reason of decline in bivalve species, whilst freshwater bivalve species decline more rapidly than the marine species (Agudo-Padrón 2011). Other factors contributing to the decline of bivalve fauna include overexploitation (20 %), habitat modification (15 %), and urbanization (10 %) (Figure 6), mining activities, agriculture and aquaculture, transportation infrastructure, climate change and temperature rise, recreational activities, and various geological events, such as tsunamis caused by earthquakes.  Taxa | www.threatenedtaxa.org | 26 September 2021 | 13(11): 19553-19565 19561

Conservation prospects
Conservation is critical to preventing the extinction of vulnerable species. After discussing possible causes of bivalve species decline in the Indo-Pacific region, including Malaysia, we propose some conservation strategies for sustainable use of bivalve natural bio resources based on the global model developed by Lopes-Lima et al. (2018) (Figure 8).
To begin, bivalves are aquatic Mollusca that cannot survive without water (marine, brackish, or freshwater), and thus protection of water and water-adjacent land (40 %) should be prioritized for bivalve species conservation. Additionally, awareness-raising among stakeholders (including government, the general public, universities, non-governmental organizations, and the local populace) and communication with the local populace must be implemented (25 %). Water and adjacent land management (12 %), species management through proper conservation procedures (10 %), and incentives for local stakeholders who will carry out the conservation process (4 %) can all contribute significantly to the conservation of bivalves in Borneo. While the existing policies and regulations are sufficient for a sustainable conservation process, additional research is necessary to determine whether any revisions to those policies and regulations are necessary (3 %). Ex situ conservation (2 %) and proper enforcement of policies, legislation, and regulation (2 %). Any threatened species and those that have been suppressed by stressors, including human intervention, should be recovered through the application of appropriate management guidelines and procedures (1 %). Conservation strategies can be integrated into formal national curricula; consequently, future leaders and stakeholders should be concerned about bivalve biodiversity conservation (0.5 %). Reintroduction of species from another source is sometimes feasible. The general training received by common people, stakeholders, conservationists, and government officials is sufficient in the Indo-Pacific region and Malaysia, as there are ample training facilities and current conservation legislation is adequate, but conservation measures for bivalves should be prioritized.
Another research by Lopes-Lima et al. (2014) suggested that research on different aspects of taxonomy, systematics, anatomy, physiology, ecology, and conservation of freshwater bivalves will be helpful to conserve and reduce the extinction risk. Omics approach will also be helpful to conserve the bivalve fauna (Carducci et al. 2020). In contrast, a recent study from China suggested that awareness among people regarding ecological protections can be a helpful tool for   protecting the habitat of bivalves. Reduce or suspend the commercial capture of wild bivalves, establish sanctuaries for habitat protection, extend the fishing or capture ban period which might helpful to conserve the bivalve fauna (Cao et al. 2018).

Prospects and future research
The status of bivalves in Malaysian Borneo as a whole has not yet been determined. Numerous research groups comprised of provincial governments, universities, and the federal government can work in various ecological niches to determine the true number J TT

Given Family
Corrected Family Given name of species  Regrettably, there is far too little information at the moment, but provincial governments could declare some species vulnerable and also establish some protected zones in accordance with the IUCN Red List. Numerous awareness campaigns, including posters, television programmes, telecasts, documentaries, films, and cartoons, can be produced to educate the public about the critical nature of bivalve conservation. For example, state governments can take steps similar to the Chinese Giant Panda conservation approach, which is called 'Panda Diplomacy' (Buckingham et al. 2013), where China showed public awareness and scientific efforts are effective in the conservation process. Lopes-Lima et al. (2018) proposed some research aspects that will help Journal of Threatened Taxa | www.threatenedtaxa.org | 26 September 2021 | 13(11): 19553-19565 19563 J TT retain the bivalve diversity's sustainability. According to them, the primary focus on bivalve research should be on the assessment of populations and their distribution (32 %), assessment of threats (28 %), and on studying their life history / breeding for future aquaculture purposes (20 %) (Figure 7). Whereas the taxonomy of specific bivalve species, the habitats and ecology of each species, the population trends of bivalves in Borneo, the harvest trends of fishers including aquaculture, recovery actions if any species faces imminent extinction, management plans for multi-ground stakeholders, and further action by various organizations can be considered as significant research arenas. Kumar & Ravinesh (2016) recommended that the importance of taxonomic research be disseminated; thus, taxonomic knowledge can be included in national level curricula, for example, high school and college students can learn this science with joy. This initiative can be incorporated into the provincial and regional curricula of Malaysian Borneo. Additionally, they emphasized the importance of establishing accurate species databases and repositories, which will aid in future research and analysis. Kumar & Ravinesh (2016) also emphasized the resolution of scientifically dubious name categories, such as 'taxon inquirendum' and 'nomen dubium', which is commendable, and the protocols may be beneficial for the Malaysian Borneo ecosystem as well. They proposed that an integrative taxonomic approach incorporating detailed biogeography and evolutionary genetic materials could be beneficial for bivalve fauna conservation in Malaysian Borneo. Finally, citizen scientists and civil society approaches are very common and widely adopted in many developed countries; for this, a person does not have to be a scientist; rather, a keen interest in nature and biodiversity can also be beneficial for nature conservation. The research on the aforementioned criteria may be adopted and contribute to the conservation of biodiversity in Malaysian Borneo in the coming years and decades.
The current checklist is prepared by reviewing the previously published documents from Malaysian Borneo, although the published documents are few. Some of the papers we had collected were very general, and the author did not provide an appropriate format of species scientific names (Al-Asif et al. 2020). Misidentification is a widespread issue in taxonomy, and some published documents reported different bivalve species out ranged of their original distribution region. For example, the distribution of Ctenoides scaber (Born, 1778) (Turgeon et al. 2009) is well known from North America, but the previous study reported this species from the southeastern Asian region. This might happen because the author found similarities with southeastern Asian bivalve species with North American species or is entirely misidentified.
On the other hand, we can say it is considered either misidentification of these species or they introduced to the Malaysian habitat. Most of the published papers we had handled did not provide any pictures of bivalve species, which can be considered a considerable gap of the bivalve research in Malaysian Borneo (Shabdin 2010). In contrast, the papers that were published on the ecological phenomena or on the ecological subject matter did not include photographs or appropriate scientific nomenclature, and the samples that had been gathered were not stored in a permanent and easily accessible repository for future study. The island of Borneo does not have a natural history museum, although there is a tiny part of the 'Sarawak State Museum' that is known as the 'Natural History Museum', but there are no depositing facilities or a permanent repository in the Malaysian part of this island Shabdin 2010). Given the foregoing, Malaysian Borneo urgently requires a permanent and accessible repository for the collection of samples. New expeditions to different rivers and creeks in the interior of Borneo can be conducted to determine the exact number of bivalve species found in Malaysian Borneo.

CONCLUSIONS
The current work produced a comprehensive checklist of bivalves recorded from Malaysian Borneo, crosschecked with WoRMS (2021) and MolluscaBase (2021). An accurate checklist of bivalves aids appropriate resource allocation for the conservation process, and at the same time has many other functions. Accurate data on bivalve species under one umbrella will provide insight which species are present in Malaysian Borneo. It will also help revise and update the national list of molluscan fauna and periodic update of bivalve taxonomic information.