1 Phytoplankton Species in Hong Kong Coastal Waters 香港海域浮游植物 ZHANG Xiaodong 張曉東 LIU Hongbin 劉紅斌 The Hong Kong University of Science and Technology 香港科技大學 2024
3 Preface 前言 My first encounter to marine phytoplankton was in the class of Marine Plankton during my undergraduate studies in Xiamen University. Later, I had an opportunity to study the isolation, cultivation, and identification of marine diatom Skeletonema at the Third Institute of Oceanography, Ministry of Natural Resources, and started my journey in the world of phytoplankton. Phytoplankton are extremely small and with the exception of a few species, they are not visible to the naked eyes of a human being. Despite their small size, phytoplankton play a crucial role in marine ecosystems and global biogeochemical cycles due to their fast growth rate, wide distribution, and extremely high abundance. 我第一次接觸海洋浮游植物是在廈門大學讀本科時的海洋浮游生物學課程。 隨後 有幸在自然資源部第三海洋研究所學習分離、培養、鑒定海洋硅藻骨條藻，從此走 進了浮游植物的世界。 浮游植物極為微小，除少数物種外都不為人類肉眼所見。 儘管粒徑微小，浮游植物由於生長速度快，分佈廣泛，豐度極高，在海洋生態系統 和全球生物地球化學循環中起到了極為關鍵的作用。 There are many islands and bays in Hong Kong. The eastern, western, and southern regions exhibit different environmental characteristics. The diverse habitats result in high diversity of phytoplankton species in Hong Kong. Based on data from Agriculture, Fisheries and Conservation Department, Hong Kong (AFCD), there may be over 800 species of phytoplankton in Hong Kong. However, research on the diversity of phytoplankton in Hong Kong waters remains limited. Since 2018, we have conducted a two-year monitoring of phytoplankton species composition and abundance at 25 sampling stations in 10 water control zones of Hong Kong waters, through a project in collaboration with the Hong Kong Environmental Protection Department (Development of Supplementary Criteria to Improve Water Quality Assessment on Impacts of Nutrient Enrichment, Ref: 17-04208), and identified more than 250 species of phytoplankton.
4 Different species were photographed under a microscope and a total of 102 common species, including diatoms, dinoflagellates, and other phyla (cyanobacteria, diatoms, haptophytes, green algae, cryptophytes, and raphidophytes), sorted by Latin name according to class, order, family, genus, and species, were included in this book. The publication of this book not only supplements research on the diversity of phytoplankton in Hong Kong, but also serves as a reference tool for phytoplankton research and monitoring in Hong Kong. 香港境內海島、港灣眾多，東部、西部以及南部區域都呈現了不同的環境特徵。 多 樣化的生境可能導致香港浮游植物物種多樣性極高。基於香港漁農自然護理署的 數據，香港浮游植物物種可能超過800 種。然而有關香港海域浮游植物多樣性的 研究仍然十分匱乏。自2018年來，我們藉助於和香港環境保護署合作的項目（香 港海域富營養化影響的水質評價補充標準研究，Ref：17-04208）對香港海域的10 個水質控制區25 個採樣站位進行了兩年的浮游植物物種組成和豐度監測，鑒定出 浮游植物超過250 個物種。我們在顯微鏡下對不同物種進行拍照，整理成圖冊。本 書涵蓋硅藻、甲藻以及其他門類（藍藻、矽鞭藻、定鞭藻、綠藻、隱藻以及針胞藻） 共102個常見物種，按照綱、目、科、屬、種的拉丁名排序。本書的出版不僅為香 港浮游植物多樣性的相關研究補充資料，還可作為本港科研以及海洋監測的參考 工具書。 The publication of this book is supported by Environment and Conservation Fund, Hong Kong. We are grateful for the support of Dr. You Yanchun from Xiamen University and Ms. Fang Xihe from the Hong Kong University of Science and Technology on the photo collection and typesetting process of this book. The cover and inserting pages were designed by Ms. Fang Xihe. Due to the constraints of the editor's expertise and time limitations, this book may contain imperfections and inaccuracies. We sincerely invite experts and readers to offer criticisms and corrections. 本書的出版得到了香港環境及自然保育基金的支援，特此致謝。本書照片收集、 排版過程中承蒙廈門大學尤艷春博士、香港科技大學方熹鶴女士的支持，封面及
5 插頁由方熹鶴女士設計，特此致謝。 由於編者水平和時間有限，本書難免存在 缺點和錯誤，誠懇地希望各位讀者給予批評指正。 ZHANG Xiaodong 張曉東 March 2024 2024年3月
6 Contents 目錄 Chapter 1. Introduction........................................................................................................ 13 Chapter 2. Diatoms ............................................................................................................... 27 Bacillaria paxillifera .......................................................................................................................... 30 Cylindrotheca closterium .................................................................................................................. 33 Nitzschia ................................................................................................................................................ 36 Nitzschia longissimi ............................................................................................................................ 39 Nitzschia lorenziana ........................................................................................................................... 42 Nitzschia sigma .................................................................................................................................... 45 Nitzschia ventricosa ............................................................................................................................ 48 Pseudo-nitzschia .................................................................................................................................. 51 Pseudo-nitzschia pungens ................................................................................................................. 54 Licmophora abbreviata ...................................................................................................................... 57 Licmophora flabellata ........................................................................................................................ 60 Amphiprora sulcata ............................................................................................................................ 63 Navicula ................................................................................................................................................. 66 Pinnularia ............................................................................................................................................. 69 Meuniera membranacea ................................................................................................................... 71 Pleurosigma .......................................................................................................................................... 74 Pleurosigma acutum ........................................................................................................................... 76 Pleurosigma pelagicum ..................................................................................................................... 79 Grammatophora marina ................................................................................................................... 82 Asterionellopsis glacialis ................................................................................................................... 85 Thalassionema frauenfeldii .............................................................................................................. 88 Thalassionema nitzschioides ............................................................................................................ 91 Thalassiothrix longissima ................................................................................................................. 94 Amphora coffeaformis ....................................................................................................................... 97 Phaeodactylum tricornutum ........................................................................................................... 100
7 Asteromphalus cleveanus ................................................................................................................ 103 Corethron criophilum ...................................................................................................................... 106 Coscinodiscus ..................................................................................................................................... 109 Coscinodiscus wailesii...................................................................................................................... 112 Palmerina hardmaniana ................................................................................................................. 115 Melosira moniliformis...................................................................................................................... 118 Guinardia delicatula ......................................................................................................................... 121 Guinardia flaccida ............................................................................................................................ 124 Guinardia striata ............................................................................................................................... 127 Pseudosolenia calcar-avis ............................................................................................................... 130 Rhizosolenia cochlea ........................................................................................................................ 133 Rhizosolenia crassispina ................................................................................................................. 136 Rhizosolenia hyalina ........................................................................................................................ 139 Rhizosolenia imbricata .................................................................................................................... 142 Rhizosolenia robusta ........................................................................................................................ 146 Rhizosolenia setigera ........................................................................................................................ 149 Rhizosolenia styliformis .................................................................................................................. 152 Stephanopyxis turris ......................................................................................................................... 155 Bellerochea horologicalis ............................................................................................................... 158 Bacteriastrum ..................................................................................................................................... 161 Chaetoceros ........................................................................................................................................ 164 Chaetoceros lorenzianus ................................................................................................................. 167 Chaetoceros pseudocurvisetus ....................................................................................................... 170 Leptocylindrus danicus .................................................................................................................... 173 Odontella mobiliensis ....................................................................................................................... 176 Odontella sinensis ............................................................................................................................. 179 Eucampia zodiacus ........................................................................................................................... 183 Hemiaulus ........................................................................................................................................... 186 Ditylum brightwellii .......................................................................................................................... 189 Ditylum sol .......................................................................................................................................... 192 Helicotheca tamesis .......................................................................................................................... 195
8 Proboscia alata................................................................................................................................... 198 Lauderia annulata ............................................................................................................................ 201 Skeletonema ........................................................................................................................................ 204 Skeletonema costatum...................................................................................................................... 207 Skeletonema dohrnii ......................................................................................................................... 210 Skeletonema tropicum...................................................................................................................... 213 Detonula pumila ................................................................................................................................ 216 Planktoniella blanda ........................................................................................................................ 219 Planktoniella sol ................................................................................................................................ 222 Thalassiosira eccentrica .................................................................................................................. 225 Thalassiosira leptopus...................................................................................................................... 228 Thalassiosira pseudonana .............................................................................................................. 231 Thalassiosira rotula .......................................................................................................................... 234 Chapter 3. Dinoflagellates .................................................................................................. 239 Akashiwo sanguinea ......................................................................................................................... 242 Amphidinium carterae ..................................................................................................................... 245 Dinophysis caudata ........................................................................................................................... 248 Tripos furca ........................................................................................................................................ 251 Tripos fusus ........................................................................................................................................ 254 Tripos muelleri ................................................................................................................................... 257 Tripos trichoceros ............................................................................................................................. 261 Alexandrium tamarense .................................................................................................................. 264 Gambierdiscus .................................................................................................................................... 267 Gymnodinium catenatum ................................................................................................................ 270 Pyrocystis lunula ............................................................................................................................... 273 Gyrodinium spirale ........................................................................................................................... 276 Protoperidinium oceanicum ........................................................................................................... 279 Prorocentrum donghaiense ............................................................................................................ 282 Prorocentrum gracile ....................................................................................................................... 285 Prorocentrum lima ............................................................................................................................ 288 Prorocentrum micans....................................................................................................................... 291
9 Prorocentrum minimum .................................................................................................................. 294 Scrippsiella trochoidea..................................................................................................................... 297 Noctiluca scintillans ......................................................................................................................... 300 Chapter 4. Others ............................................................................................................. 305 Trichodesmium erythraeum ........................................................................................................... 306 Ebria tripartita ................................................................................................................................... 309 Hermesinum adriaticum ................................................................................................................. 312 Dictyocha fibula ................................................................................................................................ 315 Dictyocha octonaria .......................................................................................................................... 318 Isochrysis galbana ............................................................................................................................ 321 Phaeocystis globosa .......................................................................................................................... 324 Platymonas helgolandica ................................................................................................................ 327 Chlamydomonas ................................................................................................................................ 330 Dunaliella salina ............................................................................................................................... 333 Rhodomonas salina .......................................................................................................................... 336 Chattonella marina ........................................................................................................................... 339 Heterosigma akashiwo ..................................................................................................................... 342 Chapter 5. Appendix ........................................................................................................ 347 Appendix 1． Glossary ................................................................................................................. 347 Appendix 2． Literatures list for phytoplankton identification in this book ............. 351 Appendix 3． Checklist of Red Tide Causative Species from 1975 -2023 ................... 353 Appendix 4． Species name index............................................................................................. 357 Appendix 5． References list ...................................................................................................... 367
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13 Chapter 1. Introduction 第一章 序言 The term phytoplankton originates from the Greek words φυτόν (phyton), meaning 'plant', and πλαγκτός (planktos), meaning 'wanderer' or 'drifter'. Phytoplankton are small photosynthetic organisms that are typically not visible to the naked eyes. They generally possess pigments and obtain energy through photosynthesis, as terrestrial plants do. Lacking adequate motility, phytoplankton rely on water flow for movement. They can be found in all aquatic environments, from freshwater ponds, to vast oceans. Typically inhabiting euphotic layers to access light, phytoplankton can also be found in coastal sediments and deep ocean waters, with some species exhibiting epiphytic behavior on surfaces such as rocks, sand, macroalgae, or seagrass in intertidal zones. Serving as primary producers in marine ecosystems, phytoplankton, despite their small size, play a crucial role in global biogeochemical cycles and marine food webs due to their high abundance and rapid growth. Phytoplankton are the base of marine food chain, so changes in the abundance and composition of phytoplankton could greatly influence the stability of marine ecosystem. 浮游植物這個名詞來自於希臘單詞φυτόν（phyton，植物）和 πλαγκτός （planktos， 浮游）的結合。 浮游植物是一類微小的自養生物，絕大多數肉眼不可見。 和陸生 植物一樣，他們一般具有色素，通過光合作用獲取能量。浮游植物沒有較強的運動 能力，大多數時候只能隨著水流移動。浮游植物能夠在從淡水池塘到多種海洋生境 的所有的水生環境中發現。儘管浮游植物為了獲得足夠的光一般生活在真光層，他 們在近岸的沉積物以及大洋的深層也有發現，一些物種还可以附生在潮間帶的岩 石、砂礫、大型海藻和海草表面。 浮游植物是海洋生態系統中的初級生產者。儘 管粒徑小，但歸因於極高的豐度以及快速生長，浮游植物在海洋生態系統以及全球 生物地球化學循環中起到了關鍵的作用。浮游植物是海洋食物鏈的基礎，其豐度和 組成的變化會極大影響海洋生態系統的穩定性。
14 Main phytoplankton groups 浮游植物主要類群 Phytoplankton are highly diverse, exhibiting distinct niche segregation in various habitats. They are categorized by size into picophytoplankton (0.2 to 2 µm), nanophytoplankton (2 to 20 µm) and microphytoplankton (larger than 20 µm). Their abundance, biomass, and metabolic rate vary among different marine ecosystems.. Based on morphology, pigment composition and phylogenetic analysis, phytoplankton are primarily composed of cyanobacteria, diatoms, dinoflagellates, chrysophytes, raphidophytes, silicoflagellates, cryptophytes, haptophytes, euglenophytes, chlorophytes, and some others. 浮游植物多樣性高，在不同生境有明顯分化。基於粒徑大小，浮游植物可以分為超 微型浮游植物、微型浮游植物和小型浮游植物。他們在海洋生態系統中的豐度、生 物量、代謝速率都有較大差異。 基於形態結構、色素組成等特徵，海洋浮游植物 主包括藍藻、硅藻、甲藻、金藻、針胞藻、硅鞭藻、隱藻、定鞭藻、裸藻、綠藻等。 Cyanobacteria are a group of photosynthetic prokaryotes that are widely distributed across various habitats, including the estuarine, coastal, and oceanic waters. They can also be found on intertidal rocks, and as the epiphytes of macroalgae and seagrasses. Some species thrive in extreme environments like hot springs and hypersaline water. They are typically unicellular or forming colonial aggregates. Some of them, such as the filamentous Trichodesmium and certain unicellular species, are capable to fix nitrogen by converting molecular nitrogen (N2) into ammonia, a form usable by phytoplankton. The picocyanobacteria Prochlorococcus and Synechococcus are the most abundant phytoplankton in the ocean, contributing about a quarter of net oceanic primary production.
15 藍藻是分佈在不同生境的可進行光合作用的原核生物。 除了河口、近岸和大洋， 藍藻也在潮間帶岩石、大型海藻、海草以及其他基質表面生存。有些物種可以在一 些極端環境生存，如熱泉或高鹽的環境。藍藻經常為單細胞或形成聚集的群體。一 些絲狀藍藻束毛藻和一些單細胞藍藻能夠進行固氮作用，將氮氣分子轉化成其他 浮遊植物能夠利用的氨鹽。而海洋中豐度最高的浮遊植物超微型藍藻原綠球藻和 聚球藻，對海洋凈初級生產貢獻高達25%。 Diatoms and dinoflagellates are pivotal in coastal ecosystems, dominating the primary producers. Diatoms possess silicified cell wall and play the most important role in global silica cycle. Diatoms display remarkably high species diversity, with more than 16000 species recorded (Guiry, 2024) and estimated species number up to 200,000 (Mann et al., 1996). Dinoflagellates are also diverse, comprising nearly 3000 species (Guiry, 2024) varying in size, morphology, niche, and trophic strategies. Both diatoms and dinoflagellates are primary contributors to coastal blooms. 硅藻和甲藻是近岸浮遊植物的關鍵類群，是近岸初級生產力的主要貢獻者。硅藻具 有硅質化細胞壁，在全球硅循環中起到了最為重要的作用。硅藻物種多樣性極高， 已记录物種超过16000種（Guiry, 2024），數目據估計多達20萬種左右（Mann et al., 1996）。甲藻也具有極高的物種多樣性，約有超过3000 個物種记录 （Guiry, 2024），其粒徑、形態、生境、營養方式都具有很大的差異。硅藻和甲藻也是在近 岸形成紅潮的主要類群。 Other marine phytoplankton are also important parts of the marine ecosystems. Phaeocystis globosa, a haptophyte species, is known to form harmful blooms, whereas other haptophyte species like Isochrysis galbana serve as high-quality food for marine organisms such as shrimps, molluscs, and fish larvae. Coccolithophore species, through calcification, significantly influence the global carbon cycle. Haptophytes are a primary source of dimethylsulfide (DMS), the most prevalent volatile sulfur compound in seawater. DMS plays a vital role in climate regulation by promoting the formation of
16 cloud condensation nuclei, thereby affecting radiation levels. Additionally, certain raphidophyte species, such as Chattonella marina and Heterosigma akashiwo, can form harmful blooms leading to fish kills. Unicellular green algae also hold ecological significance in coastal and oceanic waters due to their high abundance. 其他海洋浮游植物類群在海洋生態系統重要的組成部分。定鞭藻球形棕囊藻可以 形成有害紅潮，而部分物種如球等鞭金藻是浮游動物和魚、蝦、貝類的優質餌料。 而顆石藻類群具有獨特的鈣化作用，在全球碳循環中起到了重要的作用。定鞭藻的 許多物種是二甲基硫的主要來源。二甲基硫是海洋中最多的揮發性硫化物，通過促 進形成雲結核改變輻射強度來調節氣候。針胞藻中的赤潮異彎藻、海洋卡盾藻也是 重要的紅潮生物，甚至可能會引發魚類死亡事件。海洋綠藻中的部分類群由於粒徑 小，豐度高，也在海洋生態系統中佔據重要作用。 Phytoplankton blooms 浮游植物紅潮 Various phytoplankton species can rapidly proliferate in estuaries, coastal areas, and even oceans under optimal conditions, forming blooms that may result in detrimental effects on marine ecosystems. These blooms have been linked to the death of fish and invertebrates due to gill clogging, oxygen depletion, and toxin release. Globally, there are more than 300 bloom forming phytoplankton species, with 86 of them documented in Hong Kong. More than 20 phytoplankton species are toxic or potentially harmful. The predominant bloom-forming phytoplankton in Hong Kong are diatoms and dinoflagellates, with frequent occurrences in coastal waters (Fig. 1). Between 1975 and 2023, 995 blooms were recorded in Hong Kong coastal waters, with dinoflagellates accounting for 62.1% of the blooms, diatoms for 14.5%, and other phytoplankton for 23.4%. Notably, Noctiluca scintillans blooms are the most common in Hong Kong waters, followed by Skeletonema and Mesodinium rubrum blooms. Approximately one-fifth of the blooms in Hong Kong coastal waters are induced by toxic or harmful species,
17 producing toxins such as paralytic shellfish poisoning (PSP), diarrhetic shellfish poisoning (DSP), neurotoxic shellfish poisoning (NSP), hemolytic toxins, okadaic acid, and domoic acid, posing risks to fish, shellfish, and human health. Blooms occur in all coastal areas of Hong Kong, with Tolo Harbour experiencing particularly frequent occurrences (Fig. 2). Seasonally, blooms are more common in spring compared to the rest of the year (Fig. 3). 浮游植物許多物種在環境適宜時可以在河口、近岸甚至大洋快速增殖形成紅潮，給 海洋生態系統帶來危害。浮游植物紅潮可能會造成魚鰓堵塞、水體缺氧、甚至毒素 分泌，造成魚類和無脊椎動物死亡。 全世界引發紅潮的浮游植物有超過300 種， 香港海域引發紅潮的浮游植物約為86 種，其中超過20 種為有毒或可能有害的物 種。 香港引發紅潮的浮游植物以硅藻、甲藻為主。 自1975年至2023年，香港海 域紅潮頻繁發生（圖1），共錄得995 宗紅潮，其中618 是甲藻引發，佔總數的 62.1%， 144宗由硅藻引起，占14.5%。其他類別的浮游植物引發233宗紅潮，佔 比23.4%。夜光藻引發的紅潮在香港海域最為常見，其次是骨條藻以及紅色中縊蟲。 香港海域紅潮近1/5 是由超過有毒有害物種引發。 浮游植物產生的典型毒素包括 失憶性貝毒，麻痹性貝毒、神經性貝毒、溶血性毒素、大田軟海綿酸、軟骨藻酸等， 會造成魚類、貝類死亡甚至會危害人類健康。香港紅潮几乎遍佈香港各海域，其中 吐露港尤為頻繁 （圖2）。此外，香港一年中春季較其他季節更為頻繁發生紅潮 （圖3）。 History of research on phytoplankton in Hong Kong 香港浮游植物研究歷史與現狀 Hong Kong, located in the subtropical region, is characterized by numerous bays and islands. The western side is impacted by the freshwater discharge from the Pearl River, which brings high concentrations of nutrients and suspended particles, whereas the eastern and southern sides are influenced by the oceanic waters of the South China Sea. Anthropogenic activities and the strength of the Zhe-Min Coastal Current modulated by monsoon play significant roles in shaping the spatial-temporal distribution of
18 phytoplankton in Hong Kong waters. The scientific exploration of phytoplankton in Hong Kong dates back to the 19th century. In 1864, Lauder conducted seasonal surveys on diatom abundance and composition in Hong Kong coastal waters, identifying 12 new species of Chaetoceros (Lauder, 1864). The earliest identification, classification, and description of Sketonema costatum, a crucial diatom species, were based on samples collected from Hong Kong coastal waters in 1866. 香港地處亞熱帶海域，海灣和島嶼眾多，西部受珠江淡水及其输入的高營養鹽以及 懸浮顆粒物影響，東部和南部則偏向於南海海水影響。來自於人類活動的影響以及 季風驅動的闽浙沿岸流强度也會深刻影響香港海域浮遊植物的時空分佈。香港的 浮游植物研究肇始於19 世紀。 早在1864 年，Lauder 在香港海域對硅藻的豐度、 組成開展季節性調查，並描述了12個角毛藻新物種（變型）（Lauder, 1864）。硅 藻中最重要的物種之一中肋骨條藻的最初的鑒定、分類以及描述，也是基於1866 年於香港採集的水樣標本。 Research on phytoplankton in Hong Kong has advanced significantly over the past two centuries. Until the early 21st century, studies were primarily focused on specific regions such as Tolo Harbour (Thompson & Ho, 1981; Hodgkiss & Chan, 1983; Chan & Hodgkiss, 1988; Lam & Ho, 1989), Victoria Harbour (Kueh, 2002), Port Shelter, and Lamma Island (Dickman et al., 2002). Recent investigations have expanded to encompass a broader examination of phytoplankton species diversity in Hong Kong waters. Li (2006) conducted an analysis of diatom species diversity across various coastal areas from September 2004 to September 2005, identifying 117 species and variants belonging to 42 diatom genera. Lin (2007) and Ye (2011) conducted seasonal and monthly surveys in different zones, identifying 254 and 206 phytoplankton species, respectively. Ye (2011) also reported a total of 388 phytoplankton species based on both current investigations and historical data. Notably, diatoms and dinoflagellates are predominant in Hong Kong coastal waters, with key species including Skeletonema, Chaetoceros, Thalassiosira, and Pseudo-nitzschia. Additionally, certain dinoflagellate species of Prorocentrum, Gymnodinium, and Scrippsiella were also dominant during the summer or autumn.
19 兩個世紀以來，香港浮游植物研究取得了長足發展。 直至21世紀初，香港海域的 浮游植物研究主要局限於特定海域，如吐露港（Thompson & Ho， 1981; Hodgkiss & Chan, 1983; Chan & Hodgkiss, 1988; Lam & Ho， 1989）、維多利亞港（Kueh， 2002）、牛尾海及南丫島（Dickman et al.， 2002）。 近年來，部分對香港海域浮 游植物物種多樣性研究拓展到全面調查。 李揚（2006）分析了2004 年9 月至2005 年9 月香港不同海域的硅藻物種多樣性，共鑒定到硅藻42 個屬，117 物種（變 型）。 基於香港不同海域不同季度/月份的調查，林旭吟（2007）和葉青（2011） 分別鑒定出254和206個浮游植物物種。 葉青（2011）結合歷史數據，統計出香 港海域388個浮游植物物種。 香港海域以硅藻和甲藻為主，其中優勢物種主要有 骨條藻、角毛藻、海鏈藻和擬菱形藻。一些甲藻如原甲藻、裸甲藻和施克里普藻在 夏季或秋季形成優勢。 The Hong Kong Agriculture, Fisheries and Conservation Department (AFCD) and the Hong Kong Environmental Protection Department (EPD) have conducted extensive investigations into the composition of phytoplankton species in the coastal waters of Hong Kong in past decades. To mitigate the impact of harmful algal blooms (HABs) on aquaculture, AFCD has established a comprehensive phytoplankton monitoring program. Through regular sampling intervals - weekly, bi-weekly, monthly, and seasonally - in various fish culture zones and offshore stations over the past decades, AFCD has identified over 800 phytoplankton species in Hong Kong's coastal waters. AFCD has also produced three illustrated books detailing bloom-forming species in the region. Concurrently, the Hong Kong EPD has been monitoring water quality at 76 stations across 10 water control zones since 1986, assessing various parameters including chlorophyll concentration. Since 2000, EPD has conducted monthly sampling surveys at 26 stations within the 10 water control zones to analyze phytoplankton species composition, abundance, and size. The findings are subsequently disseminated to the public through the annual seawater quality report.
20 香港漁農自然護理署和香港環境保護署在過去幾十年香港海域浮游植物物種組成 進行了大量調查。 為減少紅潮對水產養殖的影響，香港漁農自然護理署已實施一 項長期的浮游植物監測計劃。通過對香港主要魚類養殖與以及離岸監測站進行每 周、每兩周、每月或每季度在不同魚類養殖區和離岸站位的採樣、調查，香港漁農 自然護理署鑒定了800 多種浮游植物，並出版了三本引發红潮的浮游植物圖鑒。 香港環境保護署自1986年開始包含葉綠素濃度的香港海域水質監測。 自2000年 開始對香港海域10個26個站位每個月進行取樣調查，分析浮游植物的物種組成、 豐度和粒徑大小，並將結果在每年的海水水質年報里向公眾公佈。 Research methods of phytoplankton species diversity 浮游植物多樣性研究方法 Phytoplankton species diversity is primarily assessed through traditional and molecular methods. Water samples or plankton trawl net samples are fixed using Lugol’s solution or formalin and stored in the dark. Subsequently, the samples are gently inverted to resuspend the cells and observed under a microscope after sedimentation in a Utermöhl chamber (Fig. 4) or Sedgewick Rafter cell (Fig. 5). For species that are not easy to be identified using a light microscope alone, isolation, cultivation, and further analysis are required. Polarized light microscopy is essential for distinguishing coccolithophore species based on the morphology, dimensions, and arrangement of coccoliths. Fluorescence microscopy is particularly valuable for identifying certain dinoflagellates by observing plates on the cell surface after fluorescence staining. The application of electron microscopy has significantly advanced species identification based on ultrastructural features not visible under light microscopy. Molecular methods, involving DNA extraction, Polymerase Chain Reaction (PCR), sequencing, genome analysis, and bioinformatic analyses, offer a novel perspective on phytoplankton classification according to their phylogenetic relationships. These methods have emerged as fundamental and precise tools for recognizing phytoplankton species. The rapid and effective nature of molecular techniques has ushered phytoplankton identification, classification, and diversity investigations into the molecular era.
21 浮游植物多樣性研究一般通過常規生物學方法和分子生物學方法進行，對不同層 次的浮游植物多樣性進行研究。水樣或拖網樣品用魯格氏液或甲醛固定后暗處保 存。樣品輕輕混勻使細胞懸浮，于Utermöhl 計數框（圖4）或Sedgewick Rafter 計 數板（圖5）裡沉澱后在顯微鏡下觀察。對於一些顯微鏡下難以分辨的物種，有必 要進行分離、培養。為觀察顆石藻顆石粒的大小、形態與排布方式，偏振光顯微鏡 的應用是有必要的。此外，經過染色后，在螢光顯微鏡下人們能夠通過甲藻細胞表 面甲板特徵鑒定甲藻。電子顯微鏡下人们可以觀察到光學顯微鏡觀察不到的超顯 微結構，極大地助力了浮游植物鑒定工作。 分子生物學方法包括DNA 提取，聚 合酶鏈式反應，測序、基因組分析以及其他生物信息學分析。 分子生物學方法可 以分析浮游植物的遺傳位置，給浮游植物分類工作帶來新的視角，已經成為浮游植 物鑒定最基礎最準確的依據之一。 由於分子生物學具有快速、高效的特點，浮游 植物的鑒定、分類以及多樣性調查研究已經進入了分子時代。 In collaboration with EPD (Development of Supplementary Criteria to Enhance Water Quality Assessment on Nutrient Enrichment Impacts, Ref: 17-04208), we carried out a project focusing on monitoring phytoplankton species composition and abundance across 25 stations in 10 water control zones from October 2018 to April 2021. Water samples were preserved using Lugol’s solution (1% final concentration) and stored in darkness until analysis. Samples are gently inverted several times, and 20 ml aliquots are then allowed to settle in an Utermöhl chamber (Hydro-Bios, Germany) or Sedgewick Rafter cell. Cell images were documented using an inverted microscope. The identification and classification of phytoplankton species were conducted based on references listed in the Appendix. 我們藉助於和香港環境保護署合作的項目（香港海域富營養化影響的水質評價補 充標準研究，Ref： 17-04208），從2018 年10月至2021年4月對香港海域的10 個水質控制區25 個採樣站位進行了兩年的浮游植物物種組成和豐度監測。 水樣 用終濃度1%的魯格氏液固定后避光保存。 样品混勻后取20ml 在Utermöhl 計數
22 框或Sedgewick Rafter 计数板沉澱后在倒置顯微鏡下拍照。 浮游植物物種的分類 鑒定主要參考書列舉在附錄中。 Figure 1. Numer of red tide incidents from 1975 to 2023 (from AFCD). 圖1. 一九七五年至二零二三年香港紅潮個案数目 （AFCD）
23 Figure 2. Distribution of red tide incidents in Hong Kong coastal waters (from AFCD). 圖2. 香港海域紅潮個案分布（AFCD） Figure 3. Number of red tide incidents in each month from 1975 to 2023 in Hong Kong coastal waters (from AFCD). 圖3. 一九七五年至二零二三年香港海域每月紅潮個案数目（AFCD）
24 Figure 4. Utermöhl Chamber 圖4. Utermöhl計數框 Figure 5. Sedgewick Rafter cell 圖 5. Sedgewick Rafter 計數板
25
27 Chapter 2. Diatoms 第二章 硅藻 Diatoms are unicellular organisms characterized by a siliceous cell wall and yellowbrown chloroplasts. They occur either as solitary cells or in colonies, forming various shapes such as chains, ribbons, fans, zigzags, or stars. Most diatoms are photoautotrophic, with only a limited number exhibiting heterotrophic behavior. The observation of diatoms dates back to 1703, with the establishment of the first diatom genus in 1788. The classification of diatoms has undergone continuous evolution over the past two centuries, leading to ongoing debates and controversies at the present day. 硅藻是一類具有硅質細胞壁的單細胞生物，色素體黃褐色。硅藻一般獨立生活或形 成鏈狀、帶狀、扇形、之字形或星狀的群體。 絕大多數硅藻是光合自養，只有極 少數物種為異養。硅藻於1703年第一次被觀察到，並於1788年第一個屬被建立， 距今已二百到三百年。兩百多年來來硅藻的分類體系一直不斷變化，直到現在仍存 在許多爭議。 Diatoms exhibit a remarkably high level of species diversity, with estimates up to possibly 200,000 species, and new species being described regularly. Species differentiation in diatoms primarily relies on the overall shape and ultrastructure of their siliceous cell walls, known as frustules. The size of diatom cells typically falls within the range of 2 to 200 μm, with only a limited number exceeding 200 μm. The frustule is composed of two halves, with the epitheca slightly larger than the hypotheca. The ends of the frustules are referred to as valves, and diatom cells can be observed in two distinct views under a microscope: the valve view, which shows the top or bottom valve of the frustule, and the girdle view, which provides a side view. Diatoms are generally categorized into two
28 groups based on valve symmetry and frustule structure: centric diatoms, which are radially symmetric and often circular, and pennate diatoms, which are typically bilaterally symmetric and elongated. 硅藻物種多樣性極高，據估計可能多達二十萬個物種，且每年都會有新物種發現。 不同硅藻的主要鑒定主要依據硅質細胞壁整體外觀以及超顯微結構。大多數硅藻 細胞粒徑一般位於2 微米到200 微米之間，少數物種會大於200 微米。硅藻的硅 質壁分為兩半，其中一半（上殼）比另一半（下殼）稍大。硅質壁的頂端和底端稱 為殼面。硅藻細胞在顯微鏡下呈現兩個不同的面觀：殼面觀和殼環面觀。殼面觀是 從硅質壁頂端或底端殼面觀察，而殼環面觀則是從側面觀察。基於殼面對稱性和硅 質壁結構，硅藻一般被分成兩大類，中心硅藻和羽紋硅藻。中心硅藻一般輻射對稱， 大多數傾向於圓形，而羽紋硅藻兩側對稱，較為瘦長。 Diatoms are a prominent component of marine phytoplankton, exhibiting high abundance and widespread distribution. They inhabit the euphotic zones of various marine environments, including estuaries, coastlines, and open oceans, spanning from spanning polar to tropical regions. Additionally, certain diatom species can be found on sediment and surfaces of intertidal reefs, seagrasses, and macroalgae. Serving as the foundation of the marine food chain, diatoms contribute significantly to marine primary productivity, accounting for 40% of it, and play a crucial role in global biogeochemical cycles. Some diatoms have the capacity to form blooms in estuarine and coastal waters. Notably, in the coastal waters of Hong Kong, diatoms have caused 144 blooms between 1975 and 2023. It is important to note that certain diatom species are toxic; for instance, certain Pseudonitzschia species can produce domoic acid, leading to amnesic shellfish poisoning and posing significant threats to the aquaculture industry, ecosystem stability, and human health. 硅藻是極為重要的海洋浮游植物，豐度高，分佈廣。從極地到熱帶，從河口、近岸 到大洋的幾乎所有環境的真光層，都有硅藻發現。硅藻也能在沉積物、潮間帶礁石、
29 海草以及大型海藻表面分佈。硅藻是海洋食物鏈的基礎，貢獻了 40%的海洋初級 生產力，在生物地球化學循環中發揮極為重要的作用。部分硅藻在近岸可以形成紅 潮。香港海域自1975 年至2023年共記錄有144次硅藻紅潮。部分硅藻具有毒性， 如部分擬菱形藻物種會產生軟骨藻酸，引發失憶性貝毒，會對養殖業、生態系統穩 定性以及人類健康造成極大損失。
30 Bacillaria paxillifera 派格棍形藻 Phylum: Heterokontophyta 门：不等鞭毛门 Class: Bacillariophyceae 纲：羽紋硅藻纲 Order: Bacillariales 目：硅藻目 Family: Bacillariaceae 科：硅藻科 Morphology Cells are elongated with flat ends and are distributed in parallel to form a bamboo raftlike stacked colony. Adjacent cells could slide forward and back along each other, adhering one to another only by their ends, to perform a gliding movement and form a dynamically extending or aggregating chain. General shape of colony is very variable, rectangular to filamentous consequently. Chloroplasts are small, granular, and numerous. 形態 細胞細長，末端平截，相鄰細胞平行分佈形成竹排狀堆積群體。相鄰細胞可以前後 滑動，形成一個動態延長或聚集的鏈，只通過細胞末端相連。群體外觀也因此從矩 形到束狀不斷變形。色素體呈小顆粒狀，數量多。 Ecology and distribution Bacillaria paxillifera is a widely distributed marine planktonic and benthic species. 生態與分佈 派格棍形藻是廣泛分佈的浮游和底棲物種。 Size Length (apical axis): 70-100 μm (Hendey, 1964); 68-190 μm (Chin et al., 1965); 70-115
31 μm (Thomas et al., 1997); 80-115 μm (Al-Kandari et al., 2009); 61.6-156 μm (Gao et al., 2021); 120-135 μm (Al-Yamani et al., 2019). Width (transapical axis): 5-6 μm (Cupp, 1943; Thomas et al., 1997); 6-7 μm (Al-Yamani et al., 2019) 粒徑 長（縱軸）：70到100微米 （Hendey，1964）; 68到190 微米（金德祥等， 1965）; 70到115 微米（Thomas et al.，1997）; 80 到115微米（Al-Kandari et al.， 2009）; 61.6到156微米（高亞輝等，2021）; 120 到135微米（Al-Yamani et al.， 2019）。 寬（橫軸）：5到6微米（Cupp，1943）; 6 到7微米（Al-Yamani et al.，2019）; 5 到6微米（Thomas et al.，1997） Synonyms 同種異名 Bacillaria paradoxa J.F.Gmelin 1791 Bacillaria paxillifer (O. F. Müller) Nitzsch 1817 Diatoma paxillifera (O.F. Müller) Brébisson 1838 Homoeocladia paxillifera (O.F. Müller) Elmore 1921 Nitzschia paradoxa Grunow 1880 Nitzschia paxillifera (O.F. Müller) Heiberg 1863 Oscillaria paxillifera (O.F. Müller) Schrank 1823 Oscillatoria paxillifera (O.F. Müller) Schrank ex Gomont 1892 Vibrio paxillifer O.F. Müller 1786
32 Fig. Girdle views of Bacillaria paxillifera 圖 派格棍形藻殼環面觀
33 Cylindrotheca closterium 新月柱鞘藻 Phylum: Heterokontophyta 门：不等鞭毛门 Class: Bacillariophyceae 纲：羽紋硅藻纲 Order: Bacillariales 目：硅藻目 Family: Bacillariaceae 科：硅藻科 Morphology Cells are solitary with weakly silicified frustule. Valves are lanceolate, and abruptly narrow into long rostrate slightly bent or straight apices. 形態 細胞單個生活，細胞壁硅質化程度低。 殼面呈披針形，驟然收縮成較長的或彎曲 或直的末端。 Ecology and distribution Cylindrotheca closterium is a cosmopolitan marine to brackish water species widely distributed in temperate to tropical areas in the littoral zone. This species also occurs as epppyhytic form. 生態與分佈 新月柱鞘藻是廣泛分佈在溫帶和熱帶的近岸海洋和半鹹水物種，也可以附著生存。 Size Length （Apical axis）: 57-208 μm (Allen and Cupp, 1935); 50-80 μm (Hendey, 1964）; 20-90 μm (Chin et al.,1965); 20-180 μm (Chin et al., 1982); 32-150 μm (Isamu, 1991); 30-400 μm (Tomas, 1997); 28-67 μm (Al-Yamani et al., 2011; 2019); 12-400 μm (Law,
34 2018); 17-180 μm (Gao et al., 2021) Width (transapical axis): 5-12 μm (Allen and Cupp, 1935); 1.5-8 μm (Chin et al., 1982); 2-6 μm (Isamu, 1991); 2.5- 8 μm (Tomas, 1997); 1.5-8 μm (Law, 2018); 1.4-8 μm (Gao et al., 2021) 粒徑 長（縱軸）：57到208 微米（Allen and Cupp， 1935）;50-80 微米（Hendey， 1964）;20 到90微米（金德祥等，1965）;20-180微米（金德祥等，1982）;32 到150 微米（山 路勇1991）; 30 到400 微米（Tomas， 1997）; 28到67微米（Al-Yamani et al.， 2011， 2019）;12到400 微米（羅秉全， 2018）;17 到180微米（高亞輝等，2021） 寬（橫軸）5到12 微米（Allen and Cupp， 1935）;1.5 到8微米（金德祥等，1982）;2 到6微米（山路勇，1991）;2.5 到 8 微米（Tomas， 1997） ;1.5-8 微米（羅秉全， 2018）;1.4 到8微米（高亞輝等，2021） Synonyms 同種異名 Ceratoneis closterium Ehrenberg 1839 Nitzschia closterium (Ehrenberg) W.Smith 1853 Nitzschiella closterium (Ehrenberg) Rabenhorst 1864 Nitzschia longissima var. closterium (Ehrenberg) Van Heurck 1885 Nitzschiella tenuirostris Mereschkowsky 1901 Homoeocladia closterium (Ehrenberg) Kuntze 1898 新月筒柱藻 新月蛾眉藻
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