{"id":4155,"date":"2023-02-28T09:51:47","date_gmt":"2023-02-28T06:51:47","guid":{"rendered":"https:\/\/www.coa.sua.ac.tz\/animal\/?p=4155"},"modified":"2023-03-01T21:53:31","modified_gmt":"2023-03-01T18:53:31","slug":"low-genetic-diversity-and-lack-of-genetic-structure-among-populations-of-the-sandfish-holothuria-metriatyla-scabra-on-the-tanzanian-coast","status":"publish","type":"post","link":"https:\/\/www.coa.sua.ac.tz\/animal\/research-news\/low-genetic-diversity-and-lack-of-genetic-structure-among-populations-of-the-sandfish-holothuria-metriatyla-scabra-on-the-tanzanian-coast","title":{"rendered":"Low genetic diversity and lack of genetic structure among populations of the sandfish Holothuria (Metriatyla) scabra on the Tanzanian coast"},"content":{"rendered":"

By Valeli J. Bugota and Cyrus Rumisha<\/span><\/p>\n

Summary<\/strong><\/span><\/p>\n

Sandfish (Holothuroids<\/em>) or sea cucumbers in general play important ecological roles in the ecosystem. One role is remineralising large quantities of organic nutrients through their feeding and burying activities, which increases the benthic productivity of coral reefs. Further, the role of sea cucumbers in the dissolution of CaCO3<\/sub> sediment provides an important source of alkalinity and may play a role in buffering ocean acidification at least at local scales on coral reefs.<\/span><\/p>\n

The tropical sandfish Holothuria (Metriatyla)<\/em> scabra Jaeger, 1833 has been severely depleted in <\/span>the Western Indian Ocean because it is easy to catch and in high demand. In response,\u00a0<\/span>Mainland Tanzania closed the fishery; however, the fishery remains open in the semi-<\/span>autonomous islands of Zanzibar. Yet, it is unknown whether the aforementioned contrasting\u00a0<\/span>management measures are consistent with the genetic stock structure of the fishery. <\/span>Therefore, this study analysed partial sequences (706 base pairs) of the cytochrome oxidase <\/span>subunit I gene (COI) from four sandfish populations from Tanzania to assess the extent of <\/span>genetic diversity and population structure. The populations showed low haplotype (0.17\u2013<\/span>0.44) and nucleotide diversities (0.025\u20130.084%), as well as small mutation-scaled effective <\/span>size (9 \u00d7 10\u22124<\/span>\u221217 \u00d7 10\u22124<\/span>) compared to other marine macroinvertebrates from Tanzania, <\/span>suggesting that the fishery has not recovered despite the ban that was imposed 16 years\u00a0<\/span>ago. Furthermore, Analysis of Molecular Variance (AMOVA) revealed a low and non-<\/span>significant genetic differentiation index (FST = 0.0047, p > 0.05), indicating a lack of\u00a0<\/span>population structure. The lack of population structure was further supported by <\/span>phylogenetic analysis, which grouped together all COI haplotypes of sandfishes from both <\/span>Zanzibar and Mainland Tanzania. This suggests that populations in Mainland Tanzania and <\/span>Zanzibar are genetically homogeneous and that Zanzibari fishers may be targeting the same <\/span>stock that is protected in Mainland Tanzania. Therefore, the fishery should be managed as a <\/span>single unit, and management measures between Mainland Tanzania and Zanzibar should be harmonized<\/span>.<\/span><\/p>\n

 <\/p>\n

Introduction<\/span><\/strong><\/p>\n

The sandfish Holothuria (Metriatyla<\/em>) scabra Jaeger, <\/span>1833 (Echinodermata: Holothuroidea<\/em>) is a tropical sea <\/span>cucumber with a wide Indo-Pacific distribution that <\/span>stretches from east Africa to the eastern Pacific <\/span>(Tuwo et al. 2019). The sandfish is sedentary and <\/span>often shows high abundance in shallow muddy and <\/span>sandy-muddy areas among seagrass beds, particularly <\/span>those adjacent to mangrove and coral reef ecosystems <\/span>(Rahantoknam et al. 2021). The sandfish is a seasonal <\/span>spawner with two spawning periods in July and <\/span>August and December and January (Kithakeni and <\/span>Ndaro 2002). Fertilized eggs hatch into larvae within <\/span>36 h after spawning, and the larvae remain planktonic <\/span>in water for about 16\u201317 days, swimming with the help <\/span>of tiny cilia until they metamorphose into sedentary juveniles (Mercier et al. 2000; Al Rashdi et al. 2012). Due to the long planktonic larval duration, the sandfish H. scabra<\/em> has the ability to disperse over\u00a0<\/span>great distances, facilitating recruitment to various <\/span>habitats in its natural range. Dispersal is not limited <\/span>to the pelagic larval phase, but may also occur <\/span>during the benthic juvenile\/adult stages through <\/span>active buoyancy adjustment (Hamel et al. 2019).<\/span><\/p>\n

The sandfish H. scabra<\/em> is the most valuable and\u00a0<\/span>commercially important sea cucumber, ranking prob<\/span>ably number one on the world b\u00eache-de-mer market\u00a0<\/span>(Conand 2008). Because of their slow rates of move<\/span>ment and easy access to fishers, they have been\u00a0<\/span>overfished all over the world to feed the demand for\u00a0<\/span>b\u00eache-de-mer in Asia (Uthicke and Conand 2005). Con<\/span>sequently, populations of H. scabra<\/em> are estimated to\u00a0<\/span>have declined by at least 50% in the past 30\u201350\u00a0<\/span>years (Hamel et al. 2013). The decline has had a nega<\/span>tive impact on the income and livelihoods of commu<\/span>nities that rely on the sandfish fishery, particularly in <\/span>developing countries (Conand 2008). In response, <\/span>management strategies have been developed over\u00a0<\/span>the last three decades to sustainably promote develop<\/span>ment, maintenance, or regeneration of wild sandfish\u00a0<\/span>(Riquet et al. 2022). In Mainland Tanzania, a total <\/span>closure of the fishery was implemented in 2006, <\/span>which is still in effect today (URT 2009). The country <\/span>also banned the sale and export of H. scabra<\/em> and its <\/span>products, including b\u00eache-de-mer in accordance with\u00a0<\/span>Regulations 13 (11) and 67 (2) of the Fisheries (Amend<\/span>ment) Regulations, 2009 (URT 2009). However, because\u00a0<\/span>the ban was imposed without dialogue with the semi-<\/span>autonomous Zanzibar Islands (Mmbaga 2015), the\u00a0<\/span>fishery remains open in Zanzibar. As a result, there is <\/span>a potential that Zanzibari fishers are targeting the <\/span>same stock that is protected in Mainland Tanzania,\u00a0<\/span>especially if sandfish populations from these areas con<\/span>stitute a single stock. If this is the case, it may compro<\/span>mise management efforts made by Mainland Tanzania,\u00a0<\/span>rendering the ban ineffective and threatening the <\/span>fishery\u2019s sustainability despite enacted measures <\/span>(\u00c1rnason et al. 2009). Such consequences were <\/span>observed in the Atlantic cod (Gadus morhua), which <\/span>continued to decline despite enacted measures <\/span>because management approaches were not consistent <\/span>with the population genetic structure of the fishery <\/span>(Zemeckis et al. 2014). Thus, a comprehensive analysis <\/span>of the genetic structure of the sandfish populations in <\/span>Tanzania is required to inform the decision-makers on <\/span>whether the current management approach is in line <\/span>with the fishery\u2019s genetic stock structure. Therefore, <\/span>the aim of this study was to assess the extent of <\/span>genetic diversity and structure among populations of <\/span>the sandfish H. scabra<\/em> along the Tanzanian coast. The <\/span>results of this study could help Tanzanian policymakers <\/span>and decision-makers make well-informed decisions <\/span>about sandfish management and conservation.<\/span><\/p>\n

For more details:\u00a0Click here<\/strong><\/a><\/span><\/p>\n

Bugota, V.J. and Rumisha, C. (2023). Low genetic diversity and lack of genetic structure among populations of the sandfish Holothuria (Metriatyla)<\/em> scabra on the <\/span>Tanzanian coast, Marine Biology Research,<\/em> DOI: 10.1080\/17451000.2023.2176883<\/span><\/p>\n

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By Valeli J. Bugota and Cyrus Rumisha Summary Sandfish (Holothuroids) or sea cucumbers in general play important ecological roles in the ecosystem. One role is remineralising large quantities of organic nutrients through their feeding and burying activities, which increases the benthic productivity of coral reefs. Further, the role of sea cucumbers in the dissolution of […]<\/p>\n","protected":false},"author":2,"featured_media":4164,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[],"class_list":["post-4155","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research-news"],"_links":{"self":[{"href":"https:\/\/www.coa.sua.ac.tz\/animal\/wp-json\/wp\/v2\/posts\/4155","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.coa.sua.ac.tz\/animal\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.coa.sua.ac.tz\/animal\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.coa.sua.ac.tz\/animal\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.coa.sua.ac.tz\/animal\/wp-json\/wp\/v2\/comments?post=4155"}],"version-history":[{"count":5,"href":"https:\/\/www.coa.sua.ac.tz\/animal\/wp-json\/wp\/v2\/posts\/4155\/revisions"}],"predecessor-version":[{"id":4171,"href":"https:\/\/www.coa.sua.ac.tz\/animal\/wp-json\/wp\/v2\/posts\/4155\/revisions\/4171"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.coa.sua.ac.tz\/animal\/wp-json\/wp\/v2\/media\/4164"}],"wp:attachment":[{"href":"https:\/\/www.coa.sua.ac.tz\/animal\/wp-json\/wp\/v2\/media?parent=4155"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.coa.sua.ac.tz\/animal\/wp-json\/wp\/v2\/categories?post=4155"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.coa.sua.ac.tz\/animal\/wp-json\/wp\/v2\/tags?post=4155"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}