CUHK electronic theses & dissertations collection

Crustaceans are ubiquitous in the world’s oceans and include species ranged in size from 1 m. Information on the natural diet of marine crustaceans, especially the small crustaceans such as copepods, is usually obtained by measuring gut content microscopically or by the use of electronic particle counters, by microscopic examination of gut contents and fecal pellets, and by the use of stable isotopes or taxon-specific pigment markers. Unfortunately, most of these methods involve conducting feeding experiments in artificial laboratory condition, require a high level of taxonomic expertise, and provide only coarse information on food types that are digestion-resistant. Increasingly over the past decade, DNA-based methods have been used to study the natural diet of small marine organisms such as molluscan larva and the lobster larva with high taxonomic resolution.In this thesis, the diets of two marine crustaceans are investigated. The small calanoid copepod Calanus sinicus (2.5−3.5 mm), one of the animals studied in this thesis, is a dominant member of the marine zooplankton in the continental shelf waters of China and the northwest Pacific Ocean. Copepods of the genus Calanus are generally considered to be herbivorous although information on the natural diet of C. sinicus is scarce.Another marine crustacean studied in this thesis is the hydrothermal crab Xenograpsus testudinatus. This crab is endemic to the shallow-water hydrothermal vents of Kueishan Island in the northeastern corner of Taiwan. The extreme environment inhabited by X. testudinatus is unsuitable for most marine organisms due to discharge of hot and acidic water with high content of sulphur. Although the diet of X. testudinatus has been studied by several investigations, the taxonomic resolution of the dietary information is poor.Accurate information of the diet and feeding habit of a species provides the basis for understanding its role in aquatic food webs. In my thesis, the natural diets of the marine copepod C. sinicus from Hong Kong and Taiwan and the hydrothermal vent crab X. testudinatus were investigated using Illumina sequencing of the prey DNA in the gut content. Variable regions of the 18S and 16S rRNA genes in the gut contents are amplified using DNA extracted from gut contents to determine the composition of eukaryotes and prokaryotes in the diet of the marine crustacean. The diet of X. testudinatus are compared to those of the mangrove crabs Perisesarma bidens.Gelatinous zooplankton including Hydrozoa and unclassified Ctenophora are very common in the gut contents of C. sinicus from both Hong Kong and Taiwan. C. sinicus from Hong Kong contains diatoms and dinoflagellates, while C. sinicus from northern Taiwan also feeds on Anthozoa, Ascidiacea and Malacostraca. Unclassified Proteobacteria and unclassified bacteria are common in C. sinicus from both Hong Kong and Taiwan. Cyanobacteria, mainly Synechococcus, are only found in C. sinicus from Taiwan. My results show that C. sinicus can feed omnivorously on a diverse assemblage of phytoplankton and zooplankton.The diet of X. testudinatus differs from that of P. bidens. While P. bidens feeds mainly on Magnoliopsida plant, X. testudinatus feeds on a diverse assemblage of organisms including algae, fishes, bivalves, copepods and anthozoans. Although soil bacteria such as Rodobacteraceae and cyanobacteria including Oscillatoriphycidae occur in the gut contents of both crabs, Mycoplasmataceae and Helicobacteraceae, which are suspected to be gut probiotic bacteria, are only found in the vent crabs. My findings suggest that both X. testudinatus and P. bidens are scavengers.In short, the DNA-based method can provide detailed information on the natural diets of marine crustaceans and provide accurate information on the trophic role of the marine crustaceans in the food webs.甲殻類動物在海洋上是很常見的。牠們的體型大小也有很大的差異(由 1米)。有關海洋甲殻類動物食性研究特別是一些細小甲殻類動物例如橈腳類動物通常都是利用電子計量器或以肉眼在顯微鏡下計算，利用電子顯微鏡去鑑定腸及糞便中的食物殘滓及利用穩定同位素或物種獨有的色素去鑑定。不過，這些方法包括實驗室餵食測試需要熟練的鑑定技巧而且這些方法只能夠提供粗略的資訊。例如只限於會經消化後留下硬塊的食物。雖然如此，最近有研究成功利用DNA鑑定的方法去找出一些細小海洋甲殻類動物例如龍蝦及軟體動物的幼體的食性。這篇論文主要研究兩種海洋甲殻類動物的野外食物。其中一種研究對象，細小的橈腳類動物中華哲水蚤 (2.5−3.5毫米)，在中國沿岸海域及西北太平洋是很常見的。雖然有關於中華哲水蚤在食性資料不多，但是哲水蚤類的動物一般被認為是草食性。這篇論文的另一研究對象是烏龜怪方蟹。牠在位於台灣東北部的龜山島的淺水熱噴泉是很常見的。在淺水熱噴泉的生境，由於經常有酸性高溫及含有高濃度硫磺的水噴出，所以那裡是被認為不適合生物居住的。雖然烏龜怪方蟹的食性也有被研究過，但有關牠們的攝食的物種鑑定還是不夠詳細。準確的有關生物的食性的資料可以幫助我們了解該生物在海洋食物網中角色。有見及此，在這篇論文中主要會利用DNA鑑定及Illumina定序技術來研究來自香港及台灣的中華哲水蚤及在淺水熱噴泉的烏龜怪方蟹的食性。在實驗中，腸道中的DNA的18S及16S rRNA基因中DNA序列差異大的區域會被用來鑑定腸道中的有核生物及原生生物。居住在紅樹林的雙齒近相手蟹的攝食也會用來跟烏龜怪方蟹比較。啫哩狀的浮游動物比如水息蟲類動物及櫛水母來自香港及台灣的中華哲水蚤的腸道中是很常見的。在來自香港的中華哲水蚤腸道中找到了硅藻及甲藻，而在來自台灣的中華哲水蚤的腸道中卻找到珊瑚綱動物，海蛸和軟甲綱動物。在來自香港及台灣的中華哲水蚤的腸道中找到的原核生物為不能鑑定的細菌及不能鑑定的變形菌。藍綠藻主要為聚球藻只有在來自台灣的中華哲水蚤的腸道中找到。研究的結果顯示中華哲水蚤是雜食性及攝食很多不同類型的浮游生物。研究結果顯示烏龜怪方蟹所食的食物跟雙齒近相手蟹很不同。雙齒近相手蟹主要攝食雙子葉植物綱植物，而烏龜怪方蟹所吃的食物是高生物多樣性的包括藻類，魚，雙殻綱動物，橈腳類動物及珊瑚綱動物。土壤細菌比如紅桿菌科細菌及藍綠藻都可以烏龜怪方蟹及雙齒近相手蟹的腸道及胃道中找到，而可能是腸道原生細菌的枝原體科細菌及螺旋杆菌科細菌只能夠在烏龜怪方蟹的腸道中找到。研究結果顯示烏龜怪方蟹及雙齒近相手蟹都是拾荒者。總括而言，利用DNA去研究動物食性的方法可以提供更多有關海洋甲殻類動物食性的詳細資料及提供準確的有關海洋甲殻類動物食性層次的資料。Ho, Tsz Wai.Thesis M.Phil. Chinese University of Hong Kong 2015.Includes bibliographical references (leaves 65-85).Abstracts also in Chinese.Title from PDF title page (viewed on 12, October, 2016).Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only