Complete mitochondrial genome sequences for Crown-of-thorns starfish Acanthaster planci and Acanthaster brevispinus

BACKGROUND: The crown-of-thorns starfish, Acanthaster planci (L.), has been blamed for coral mortality in a large number of coral reef systems situated in the Indo-Pacific region. Because of its high fecundity and the long duration of the pelagic larval stage, the mechanism of outbreaks may be related to its meta-population dynamics, which should be examined by larval sampling and population genetic analysis. However, A. planci larvae have undistinguished morphological features compared with other asteroid larvae, hence it has been difficult to discriminate A. planci larvae in plankton samples without species-specific markers. Also, no tools are available to reveal the dispersal pathway of A. planci larvae. Therefore the development of highly polymorphic genetic markers has the potential to overcome these difficulties. To obtain genomic information for these purposes, the complete nucleotide sequences of the mitochondrial genome of A. planci and its putative sibling species, A. brevispinus were determined and their characteristics discussed. RESULTS: The complete mtDNA of A. planci and A. brevispinus are 16,234 bp and 16,254 bp in size, respectively. These values fall within the length variation range reported for other metazoan mitochondrial genomes. They contain 13 proteins, 2 rRNA, and 22 tRNA genes and the putative control region in the same order as the asteroid, Asterina pectinifera. The A + T contents of A. planci and A. brevispinus on their L strands that encode the majority of protein-coding genes are 56.3% and 56.4% respectively and are lower than that of A. pectinifera (61.2%). The percent similarity of nucleotide sequences between A. planci and A. brevispinus is found to be highest in the CO2 and CO3 regions (both 90.6%) and lowest in ND2 gene (84.2%) among the 13 protein-coding genes. In the deduced putative amino acid sequences, CO1 is highly conserved (99.2%), and ATP8 apparently evolves faster any of the other protein-coding gene (85.2%). CONCLUSION: The gene arrangement, base composition, codon usage and tRNA structure of A. planci are similar to those of A. brevispinus. However, there are significant variations between A. planci and A. brevispinus. Complete mtDNA sequences are useful for the study of phylogeny, larval detection and population genetics

Seasonal and spatial variations of optical properties, chlorophyll a and turbidity in Suo-Sound of the western Seto Inland Sea, Japan

2007年の5月から11月にかけて，ほぼ毎月，周防灘全域の全水柱（ここでは，海表面から海底直上20cmまで）における水温，塩分，光量子，クロロフィルα（以下Chl.α），濁度の鉛直分布及び透明度の海域分布を調査し，アサリ生産との関連性について検討した。その結果，海底高濁度層が灘全体に見られ，特に灘南西部の浅海域（水深10m程度）では，観測期間を通じて沖合域よりも濁度は高く，Chl.αも高濃度だった。これらの浅海域を含めて，灘西部の水深20m程度以浅の海域では，一般に海表面から海底までの全水柱が有光層になっていた。周防灘のアサリ漁場は，干潟から水深5m程度までの海域にあるため，底生濾過捕食者のアサリにとって，餌料供給の点では沖合域よりは好適条件を備えていると考えられた。また，Chl.α濃度は，鉛直混合の開始初期の10月に周防灘全体で最も高く，時期的にはアサリの秋季産卵の数週間前であると考えられた。これらのことから，周防灘のアサリ生産は，地域的・季節的な環境条件の違いとそれに伴う植物プランクトンの変動に関連があることが明らかとなった。From May to November 2007, we investigated the seasonal and spatial variations of temperature, salinity, optical properties, chlorophyll-α and turbidity in Suo-Sound of the Seto Inland Sea in relation to the Manila clam (Ruditapes philippinarum) production. The bottom turbid layer was found throughout the Suo-Sound, particularly in the western shallow area (bottom depth: about 10 m) which chlorophyll a concentrations were significantly higher than offshore. Generally, the entire water column of western area (bottom depth: less than 20 m) was mostly the euphotic zone. As the fishery grounds of the Manila clam located in the mud flat and the areas less than 5 m water depth, they inhabit in potentially productive area of phytoplankton and benthic microalgae. Also, the highest chlorophyll-α concentrations were observed in October, approximately a few weeks before their autumn spawning period. These results indicate that the marina clam's production is apparently coupled with local environmental factors and seasonal events related to the phytoplankton production.本研究は，広島大学と水産総合センター瀬戸内海区水産研究所との共同研究「瀬戸内海におけるベントスの生産性評価手法の開発」の一環として行われ，「広島大学地域貢献研究」および「水産基盤整備調査委託事業：広域アサリ漁場整備開発のための海況調査」の予算支援を受けたものである

Summer distribution and short-term variation of the bottom turbid layer in Suo-sound in the Western Seto Inland Sea, Japan

2009年の6月29日-7月2日と8月22-23日に，周防灘において水温，塩分，クロロフィルα（以下chl. α），濁度の鉛直分布を調べた。6-7月にはchl. αの亜表層極大と海底高濁度層がほぼ調査海域全体に形成されていた。8月にはchl. α の亜表層極大は弱くなり，6-7月と較べて海底高濁度層の発達が顕著で，chl. α濃度の増加も見られた。6-7月と8月の両観測期間は，それぞれ小潮と大潮の時期に相当していたことから，潮汐周期が海底高濁度層の発達に影響を及ぼしている可能性が示唆された。また，両観測期間中に，灘西部の2観測点（水深10mの浅海域と30mの沖合域）において1-3時間毎の連続観測を行って日周変動を調べた。海底高濁度層は水温・塩分（および密度）の急激な変化時に最大値を示し，濁度層の分布パターン・厚さは潮汐周期と底層の水温･塩分･密度分布によく対応していた。さらに，塩分－chl. α，塩分－濁度，chl. α－濁度の関係から，粒状懸濁物を陸（河川）起源，海底高濁度層，亜表層クロロフィル極大，異水塊に由来するものに分別することができた。During June 28 to July 2 and August 22 to 23 in 2009, we investigated the distributiosn and diurnal variations of temperature, salinity, chlorophyll a (chl.α) and turbidity in Suo-sound, Seto Inland Sea. In June to July observation, the subsurface chl.α maximum layer (SCM) and the bottom turbid layer (BTL) were found throughout the Suo-sound. In August, the SCM almost diminished but the BTL significantly developed compared to June to July observations and chl.α also showed a noticeable increase in the bottom layer. June to July and August observations corresponded with a neap and spring tides, suggesting a close relation between the development of the BTL and the tidal cycle. The turbidity values of BTL showed a maximum when temperature and salinity changed rapidly, and the distribution pattern of the BTL well-corresponded to those of temperature and salinity, particularly in spring tide in August. Particulate matter was classified into four groups such as terrigeous matter, BTL, SCM, and different water mass according to salinity-chl.α, salinity-turbidity, and chl.α-turbidity relationships

Comparison of absorption coefficients between accumulated matter on the thalli of Ecklonia kurome and suspended matter in the water surrounding Ecklonia bed

海水中の懸濁物と，海藻の葉上堆積物は，ともに藻体表面に到達する光を質的かつ量的に変化させ，海藻の生産力に多大な影響を及ぼす。本研究では内湾域である広島湾における大型褐藻クロメの葉上堆積物とクロメ群落直近の海水中の懸濁物について，両者の光吸収係数を統一的手法（QFT法）に基づいて把握し，その特性を比較した。懸濁物と堆積物の全体の光吸収特性に明瞭な差は認められず，葉上堆積物の多くが沈降した懸濁物によって構成されていたことが推察された。懸濁物・堆積物ともに，デトリタスや微細藻類など多様な要素により構成されており，光合成有効波長域（400-700nm）のうち，短波長側の光は微細藻類の色素以外のデトリタスなどが，長波長側の光は微細藻類の光合成色素が吸収し，それぞれクロメの光吸収に大きく影響すると考えられた。Light is the primary limiting factor for macroalgal production. Understanding not only the quantity but also the quality of light reaching algal thalli is important to the success of algal recovery and sustainability. This study explores the optical properties of accumulated matter on the thalli of Ecklonia kurome and suspended matter in the water surrounding an Ecklonia bed in Hiroshima Bay, based on spectral absorption coefficient estimated by the quantitative filter technique (QFT) method. According to the experiments, minimal difference of optical properties between suspended matter and accumulated matter was recognized. It is assumed that suspended matter in the water formed the accumulated matter on the thalli of E. kurome. Both suspended matter and accumulated matter were composed of multiple components, various kinds of microalgae, detritus and inorganic matter. In the wavelength-specific photosynthetically active radiation (400-700nm), detritus and inorganic matter formed the primary absorber of blue light, while microalgal pigments was the primary absorber of red light. Each absorber in suspended and accumulated matter might attenuate specific wavelength and change the quality of light reaching the thalli of E. kurome

Ecological traits and their diversities of five Zostera marina populations in and around Hiroshima Bay, the Seto Inland Sea, Japan

広島湾および周辺海域の5カ所の生育地のアマモZostera marinaの生態的特性を2004年の繁茂期に調査した。調査場所は広島湾奥部の阿品（St.1），同湾央部の大黒神島（St.2），同湾口部の屋代島（St.3），柳井湾奥部の伊保庄（St.4），および同湾外部に位置する平郡島（St.5）である。アマモの分布水深は生育地により異なり，St.1，St.2では海底でのアオサ類等の堆積により，分布下限水深は1-2m（C.D.L. 基準）までである一方，他の生育地では4-6mまで分布した。アマモの平均現存量は120-180g DWm-2の範囲にあったが，アマモの株のサイズと密度は生育地により異なっていた。平均株密度は生育地により88-278 shoots m-2の範囲であり，St.3およびSt.5では特に浅所で小型の株が密生した。これらの群落では，総現存量に占める地下部現存量の割合が相対的に大きかった。一方，湾奥部に位置するSt.1とSt.4では，アマモの株は大型である一方生育密度は低かった。群落内の底質の粒度組成の相違から，波浪流動等の物理的環境が生育地間で異なることが示唆され，それぞれの場所のアマモの生態的特性はその影響を受けていると考えられた。Ecological traits of five Zostera marina populations in and around Hiroshima Bay were investigated in a luxuriant season of 2004. Study sites were located at the most inner (Ajina; St.1), center (O-kurokami-jima; St. 2) and near the mouth area (northern coast of Yahiro-jima; St. 3) of Hiroshima Bay, and at the inner area (Ihono-sho; St. 4) and the outside (Heigun-jima; St.5) of Yanai Bay which is the strait adjacent to Hiroshima Bay. The distribution depth (C.D.L.) was different among the populations. The lower depth of Zostera distribution was limited to 1-2 m at St.1 and 2 by algal-mat of Ulva spp. and other macroalgae, though it was 4-6 m at St. 3-5. Mean biomass was ranged in 120-180g DWm-2, but shoot size and density was different among the populations. Mean density ranged between 88-278 shoots m-2, and the populations at St.3 and 5 exhibited higher densities with smaller shoots especially in shallow stands of the two population. These stands also exhibited higher proportion of below-ground biomass to total biomass. On the contrary, populations in inner areas (St. 1 and 4) exhibited lower density with larger shoots. Physical conditions such as water motion induced by waves were different among the habitats which were shown in grain size compositions of the sediments, and this could affect the ecological traits of each Z. marina population.本調査は，水産庁委託「生物多様性に配慮したアマモ場造成技術開発調査事業」（平成16～18年度）の一環として実施されたものである

Current environmental status of the oyster farms on Lake Kamo in Japan; viral control of the harmful bloom of Heterocapsa circularisquama

Lake Kamo is an enclosed, low-inflow estuary connected to the open sea that is famous for oyster farming in Japan. In the fall of 2009, this lake experienced its first bloom of the dinoflagellate Heterocapsa circularisquama, which selectively kills bivalve mollusks. This species has been detected exclusively in southwestern Japan. The completely unexpected outbreak of H. circularisquama in the northern region is believed to have been caused by the contamination of purchased seedlings with this species. The water quality and nutrient data collected by our group from July through October over the past 10 years revealed that the environment of Lake Kamo has not changed significantly. However, in the open water around Sado Island, where Lake Kamo is located, the water temperature has increased by 1.80 °C in the last 100 years, which is equivalent to 2–3-fold the world average. This has resulted in a rise in the sea level, which is expected to further deteriorate the water exchange between Lake Kamo and the open sea and low dissolved oxygen in the bottom layer of the Lake and the associated dissolution of nutrients from the bottom sediment. Therefore, seawater exchange has become insufficient and the lake has become nutrient rich, making it prone to the establishment of microorganisms, such as H. circularisquama, once they have been introduced. We developed a method to mitigate the damage caused by the bloom by spraying sediments containing the H. circularisquama RNA virus (HcRNAV), which infects H. circularisquama. After ∼10 years of performing various verification tests, including field trials, this method was used at the Lake in 2019. During the 2019 H. circularisquama growth season, a small amount of sediment containing HcRNAV was sprayed on the lake three times, which resulted in a decrease in H. circularisquama and an increase in HcRNAV, indicating that this method is effective in diminishing the bloom

A New Record of Sargassum alternato-pinnatum Yamada (Fucales, Phaeophyceae) from Taiwan

This report describes Sargassum alternato-pinnatum Yamada as a newly recorded species in Taiwan. The specimens for this study were collected from a shallow tidepool in Lan-yu, Taiwan. This species is characterized by the following features: (1) small discoid holdfast, (2) terete primary branches, (3) sharp spines arising from surface of branches, (4) leaves that furcate 1–3 times, (5) spherical vesicles around the apex, (6) pseudozygocarpic receptacles with leaves or vesicle-like tissues, and (7) male and female conceptacles scattered within the receptacles. In this report, we also present a line drawing and photographs for the identification of S. alternato-pinnatum

Development of Quantitative Real-Time PCR for Detecting Environmental DNA Derived from Marine Macrophytes and Its Application to a Field Survey in Hiroshima Bay, Japan

The sequestration and storage of carbon dioxide by marine macrophytes is called blue carbon; this ecosystem function of coastal marine ecosystems constitutes an important countermeasure to global climate change. The contribution of marine macrophytes to blue carbon requires a detailed examination of the organic carbon stock released by these macrophytes. Here, we introduce a quantitative real-time polymerase chain reaction (qPCR)-based environmental DNA (eDNA) system for the species-specific detection of marine macrophytes. and report its application in a field survey in Hiroshima Bay, Japan. A method of qPCR-based quantification was developed for mangrove, seagrass, Phaeophyceae, Rhodophyta and Chlorophyta species, or species-complex, collected from the Japanese coast to investigate their dynamics after they wither and die in the marine environment. A trial of the designed qPCR system was conducted using sediment samples from Hiroshima Bay. Ulva spp. were abundant in coastal areas of the bay, yet their eDNA in the sediments was scarce. In contrast, Zostera marina and the Sargassum subgenus Bactrophycus spp. were found at various sites in the bay, and high amounts of their eDNA were detected in the sediments. These results suggest that the fate of macrophyte-derived organic carbon after death varies among species