Abundance and distribution of dinoflagellate cysts in Xiamen Western Harbor

In a grid investigation, dinoflagellate cysts were collected from sediments in Xiamen Western Harbor in May of 2000,from which five species of cysts were identified: Alexandrium tamarensis, A. minutum, Lingulodinium polyedra,Gonyaulax scrippsae and Gymnodinium catenatum, account for about 21% in the species composition. The quantitative analysis of the sediments shows that the number of dinoflagellate cysts varies from 51 to 256 cysts/g of sediment, the highest value (>200 cysts/g) being recorded at the stations of the central part of the bay, while the lowest (＜100 cysts/g) at the bay mouth. A good linear relationship is found between cyst amount and fine-grained sediments. Complex physiognomies on the seabed, topographty in the bay and weak water exchange are the main factors not only in cyst accumulation but also in their distribution pattern, and have resulted in the difference in cyst densities between the inner bay and the outer bay in the harbor.     

胶州湾表层沉积物中甲藻孢囊的分布

为了解胶州湾表层沉积物中甲藻孢囊的分布特征,于2015年7月采集胶州湾12个站位的表层沉积物进行甲藻孢囊分析,共鉴定甲藻孢囊37种(分属5个类群)和2种未定种,包括自养型20种和异养型17种,优势种为膝沟藻。其Shannon-Wiener多样性指数[H′(log2)]介于2.84—3.91,平均值为3.42;均匀度指数介于0.75—0.98,平均值为0.88,总体值较高。胶州湾海域各站位的甲藻孢囊丰度介于96—969cyst/g DW(干重),平均丰度为401cyst/g DW,呈现出临近湾口处丰度较高,而湾内较低的空间分布差异特征。尤其值得注意的是,有两种产虾夷扇贝毒素(Yessotoxin,YTX)甲藻[具刺膝沟藻(Gonyaulax spinifera)和多边舌甲藻(Lingulodinium polyedrum)]的孢囊和3种产麻痹性贝类毒素(PSP)甲藻[塔玛/链状亚历山大藻(Alexandrium catenella/tamarense)、微小/相似亚历山大藻(A.minutum/affine)和链状裸甲藻(Gymnodinium catenatum)]的孢囊在胶州湾海域大多数站位均有分布,尽管其数量不高,但其广泛的分布范围仍需引起我们的重视。     

福建福宁湾表层沉积物中甲藻孢囊分布与多样性研究

孢囊是甲藻生活史中特殊的休眠阶段,被认为是赤潮发生的种源。于2018年4月采集了福建福宁湾海域表层沉积物,对沉积物中甲藻孢囊的分布规律进行了研究,重点揭示有毒有害甲藻孢囊的分布;同时测定了沉积物中生源要素含量,以揭示孢囊分布与生源要素的关系。共鉴定甲藻孢囊25种,其中别什藻(Biecheleria tirezensis)孢囊占据优势。孢囊的种类多样性指数(H'')偏低,为2.06~2.34;均匀度指数(J)为0.71~0.81。孢囊密度介于178.6~386.3 cysts/g (以干重计,下同),平均为286.0cysts/g。孢囊密度高值区位于水深较深、沉积物颗粒较细的长表岛外海域,而低值区则位于长表岛至海尾角的近岸海域。值得注意的是,研究分析鉴定出9种有毒有害甲藻的孢囊,包括麻痹性贝类毒素(paralytic shellfish poisoning,PSP)原因种奥氏亚历山大藻(Alexandrium ostenfeldii)和链状/塔玛亚历山大藻(Alexandrium catenella/tamarense)孢囊复合体、goniodomine A原因种平野亚历山大藻(Alexandrium hiranoi)、虾夷扇贝毒素(yessotoxin,YTX)原因种具刺膝沟藻(Gonyaulax spinifera)和网状原角藻(Protoceratium reticulatum)、产生鱼毒素的哈曼褐多沟藻(Pheopolykrikos hartmannii)以及赤潮藻类Barrufeta bravensis、锥状斯氏藻(Scrippsiella acuminata)和垂裂莱万藻(Levanderina fissa),其中Barrufeta bravensis、Gonyaulax spinifera和Scrippsiella acuminata的孢囊分布广泛且密度较高,需引起关注。     

Modern Dinoflagellate Cysts Distribution off the Eastern Part of Geoje Island,Korea

Distributional characteristics of dinoflagellate cysts in surface sediments were investigated in relation to environmental factors in the eastern part of Geoje Island, Korea. Samples were collected from 10 stations in February of 2004 and water temperature and salinity were measured in February, May, September and November of 2004. Total 30 taxa of dinoflagellate cysts were identified representing 19 genera, 28 species and 2 unidentified species. Among these dinoflagellate cysts,Brigantedinium spp. of which relative proportion in the total dinoflagellate cysts was 23.5%, was the most abundant at all stations except St. 1, and was followed bySpiniferites bulloideus (8.6%),Lingulodinium machaerophorum (8.2%) andDiplopsalis lenticula (6.7%). In addition, ellipsoidal cysts of the genusAlexandrium (Alexandrium catenella - tamarense type) andGymnodinium catenatum, known to be causative organisms for PSP, occurred with high concentrations.Scrippsiella trochoidea was also found; however, its cyst concentration was low. Generally, species composition in the study area was similar to these reported from Jinhae Bay and Busan Harbor and several dinoflagellate cysts reflected the eutrophic condition. Cyst distribution in the eastern part of Geoje Island seems to be influenced by the Tsushima Warm Current flowing from the southwest. The mean water temperature was 12.0°C in February, 14.7°C in May, 20.9°C in September and 17.2°C in November, which was most favorable forAlexandrium spp. growth. The abundances of dinoflagellate cysts ranged from 528 to 2,834 cysts/g dry sediment. Higher concentrations were recognized in sediments of west area of the Jisimdo than at other stations. The cyst composition of this area was closely related to these of Jinhae Bay and Busan Harbor from which currents flow into this area. Higher cyst concentration in the west area of Jisimdo might be due to formation of the gyre.     

北黄海表层沉积物中甲藻孢囊的分布特征

2009年和2010年采集北黄海15个站位的表层沉积物样品进行甲藻孢囊分析,共鉴定出甲藻孢囊28种(隶属13个属)和2种未定种,优势种为膝沟藻(Gonyaulax spp.)、塔马/链状亚历山大藻(Alexandriumcatenella/tamarense)和微小/相似亚历山大藻(Alexandrium minutu...     

福建东山湾表层沉积物中甲藻孢囊分布研究

本研究于2016年11月在福建东山湾海域采集了表层沉积物, 对沉积物中甲藻孢囊的分布规律进行了研究, 重点揭示了有毒有害甲藻孢囊的分布; 同时测定了沉积物中生源要素含量, 以揭示孢囊分布与生源要素的关系。共鉴定甲藻孢囊22种, 包括自养型14种和异养型8种, 优势种为原多甲藻孢囊。孢囊的种类多样性指数(H')偏低, 为1.70~2.38之间; 均匀度指数(J)为0.64~0.84。孢囊密度介于70.6~136.4个·g^-1, 平均为107.2个·g^-1, 在漳江口和八尺门海域较低。东山湾表层沉积物中较高的异养型甲藻孢囊百分含量(平均75.5%)在一定程度上说明了水体中较高的初级生产力及富营养化水平。值得注意的是, 本研究分析鉴定出7种有毒有害甲藻的孢囊, 包括麻痹性贝类毒素(paralytic shellfish toxin, PSP)原因种奥氏亚历山大藻(Alexandrium ostenfeldii)和链状/塔玛亚历山大藻(Alexandrium catenella/tamarense)孢囊复合体、虾夷扇贝毒素(yessotoxin, YTX)原因种具刺膝沟藻(Gonyaulax spinifera)、环胺藻毒素(azaspiracid, AZP)潜在原因种环胺藻(Azadinium sp)、产生鱼毒素的哈曼褐多沟藻(Polykrikos hartmannii)以及赤潮藻类Barrufeta bravensis和锥状斯氏藻(Scrippsiella acuminate)。整体来说, 这些有毒有害藻类的孢囊密度较低, 但具刺膝沟藻在某些站位的高密度出现需引起关注。     

Distribution of dinoflagellate cysts in Yellow Sea sediments

To investigate the distribution,abundance,and species composition of dinoflagellate cysts in the Yellow Sea,surface sediment samples were collected at 37 sites,including the Korean dump site.Twenty-one dinoflagellate cyst taxa were identified,with the assemblages dominated mainly by Spiniferites bulloideus,Operculodinium centrocarpum,and cyst of Alexandrium catenella/tamarense type.A high frequency of O.centrocarpum in the Yellow Sea was observed for the first time,and it is likely that this can be attributed to the dynamics of the Yellow Sea Cold Water Mass and the Changjiang(Yangtze) River runoff.Total cyst concentrations ranged from 23 to 48 442 cysts/g dry weight,and high cyst concentrations were recorded adjacent to the dumping site.This result suggests that anthropogenic activities such as ocean dumping stimulate the growth of dinoflagellates in the Yellow Sea,which in turn leads to high levels of dinoflagellate cyst production.     

孢囊及其与赤潮爆发关系的研究进展

某些藻类(特别是甲藻),在不适宜生长的恶劣环境条件下能形成休眠孢囊。孢囊下沉到海底,以渡过不良的生存条件。一旦环境条件适宜,孢囊就大量萌发形成浮游细胞和优势群体,从而诱导赤潮的形成。简述了当前国际上对孢囊研究的最新进展,从孢囊和营养细胞相互转化的角度探索了孢囊与赤潮形成的关系,以及分子生物学技术在赤潮生物及其孢囊的定性、定量及赤潮发生监测中的应用。     

Dinoflagellate cysts in recent marine sediment from Guangxi, China

Total of 33 species of dinoflagellate cysts were discovered from surface sediment in the searegion of Guangxi, among them 12 cyst types (Diplopsalopsis sp.1, D. sp. 2, D. sp. 3, Cochlodinium sp., Protoperidinium sp. 1, P. sp. 2, P. compressum , Scrippsiella sp. 1, S. sp. 2, Alexandrium sp. 1, A. sp. 2, A. sp. 3) were first reported from the South China Sea. And one cyst type (Cochlodinium sp.) was first reported in the world. Scrippsiella trochoidea is the dominant species in this area, accounting for 45% of all the cysts. There are 2 cysts of toxic dinoflagellate (Alexandrium tamarensis and Gymnodinium catenatum). But there is no relationship between cyst number and grain size distribution.     

大亚湾大鹏澳海域表层沉积物中浮游植物休眠体集群的季节变化

于2007年4月至2008年3月对大亚湾大鹏澳海域表层沉积物中浮游植物休眠体进行了每月1次的周年调查.本调查分析鉴定出浮游植物休眠体79种,包括甲藻孢囊50种,硅藻休眠体26种.浮游植物休眠体丰度没有明显的季节变化规律,变化范围为217～6 764 cells/cm3,平均为1 376 cells/cm3;鱼类养殖区休眠体丰度较高,平均丰度为1 999 cells/cm3.浮游植物休眠体在数量上以硅藻为主,甲藻次之,而在鱼类养殖区也出现了较高的蓝藻休眠体.硅藻休眠体的平均丰度为783 cells/cm3,百分比含量为56.9%,从而反映了该海域硅藻型浮游植物群落结构.甲藻孢囊丰度的变化范围在79～1 237 cells/cm3,位于湾口对照区丰度较高,年平均为733 cells/cm3,而鱼类养殖区和贝类养殖区平均值分别为502、388 cells/cm3.异养型甲藻孢囊的种类和数量均比较丰富,其百分比含量为26.7%～82.4%.研究结果显示,在富营养化程度较高的养殖区海域,硅藻休眠体和异养型甲藻孢囊百分率均较高,而鱼类养殖区还出现了较高蓝藻孢子丰度.本次调查中还出现了易碎藻和艉杆藻等在本海域浮游植物调查中未记录种类的孢囊,有毒有害赤潮生物的休眠体如亚历山大藻、链状裸甲藻、旋沟藻、巴哈马梨甲藻孢囊等也在此次调查中频繁出现,说明大亚湾海域存在较大的有毒有害赤潮发生的风险.     

舟山港4艘商船压舱箱沉积物中甲藻孢囊种群结构的分析

为了解商船压舱箱沉积物在海洋水生生物入侵过程中扮演的潜在媒介作用,本文利用光学显微镜观察法,研究了停泊于我国舟山港4艘商船压舱箱沉积物中甲藻孢囊的种类组成、孢囊密度、香农-威纳指数(H′)和PSP原因种,并对甲藻孢囊种群结构进行了相关性分析。结果表明,鉴定出的甲藻孢囊隶属于5大类,共24种,4份样品中甲藻孢囊的种群结构各有差异,但均检测出能产生麻痹性贝毒(Paralytic Shellfish Poisons,PSP)的甲藻孢囊,如亚历山大藻Alexandriumspp.和链状裸甲藻Gymnodium catenatum。在4艘商船的压舱箱沉积物中均检测出有硅藻分布,其中在富成轮压舱箱沉积物中还检测出3种未知种孢囊。通过相关性分析可知,甲藻孢囊H′值与PSP甲藻孢囊密度占总甲藻孢囊密度的比率呈负相关。甲藻可以通过商船压舱箱沉积物为传播媒介,以孢囊形式来扩大其生物地理分布,提高甲藻物种多样性可有助于降低PSP甲藻的破坏风险。因此,有效处理船只压舱箱沉积物、积极保护当地海洋生物物种多样性,对于降低外来甲藻物种(特别是一些有毒有害种)的赤潮风险和保持当地海洋生态系统的平衡,具有十分重要的意义。     

秋季南黄海表层沉积物中甲藻孢囊分布

2007年秋季(10月)在黄海22个站位采集表层沉积物样品进行甲藻孢囊的种类鉴定与计数,本航次中共鉴定出33种(不包括2个未确定种),优势种是锥状斯克里普藻(Scrippsiella trochoidea)、塔玛亚历山大藻(Alex-andrium tamarense)和膝沟藻属(Gonyaulaxsp.)的种类。与东海和南海甲藻孢囊的同期丰度相比,黄海的相对较低,丰度范围为10~519个/cm3,平均108个/cm3。孢囊丰度总体分布趋势从北向南递增,最高丰度区出现在长江口以北(32°19′59.88″N,122°37′5.16″E),另外,在南黄海调查海域中,中部黄海冷水团区域孢囊丰度较高,膝沟藻成为该区域的优势种,密集中心达101个/cm3。有毒甲藻孢囊在沉积物表层聚集且分布广泛,有爆发赤潮的可能。     

Environmental significance of dinoflagellate cysts from the proximal part of the Po-river discharge plume (off southern Italy,Eastern Mediterranean)

To determine the relationship between region specific dinoflagellate cyst distribution in the Po-river discharge area and oceanic environmental conditions, surface sediments of 48 sites in the middle and distal part of the discharge plume area have been studied. Establishing such a relationship is a prerequisite to create reconstructions of the eutrophication history as well as the palaeoclimatic and palaeoceanography history of the area.Literature based information about the sedimentation rates based on ²¹⁰Pb dating methods are available for 18 sites. This enables the calculation of cyst accumulation rates of individual cyst species which reflect their cyst production. Correlation of the accumulation rates of individual species with environmental parameters of the upper waters allows us to adapt and refine the ecological characteristics of a selection of cyst species. This latter is trivial since the current concepts on the ecological significance of dinoflagellate cyst have to be revised as a result of the current developments in the dinoflagellate research field. These developments have elucidated that a considerable part of the relative abundance datasets that form the basis for the present day ecological concepts of dinoflagellate cysts might have suffered from so called “closed sum effects” and have been overprinted by early diagenetic processes.The dinoflagellate cyst association reflects both upper and bottom water circulation. Based on the relative abundance data four associations can be distinguished that are characteristic for the major oceanographic settings in the region. (1) River discharge association. This association consists of Echinidinium spp., Lejeunecysta sabrina, Lingulodinium machaerophorum, Polykrikos kofoidii, Polykrikos schwarzii, cysts of Protoperidinium stellatum, Selenopemphix quanta and reworked cysts. These species have high relative abundances in sites where bottom waters are low in oxygen and upper waters are influenced by river discharge waters that are characterized by high productivity and relative low salinity. (2) Warm water association. This association consists of Spiniferites mirabilis, Spiniferites pachydermus, Spiniferites ramosus and Spiniferites spp. which have their highest relative abundances in the sites at the plume margin that are characterized by relative warm upper waters and intermediate chlorophyll-a concentrations. (3) Oxygenated bottom water group. Species of this group; Impagidinium aculeatum, Impagidinium patulum, Impagidinium sphaericum, Operculodinium centrocarpum and Operculodinium israelianum have their highest relative abundances at sites where bottom waters are formed by well ventilated Adriatic Deep Water or Eastern Mediterranean Deep Water. (4) Golfo di Taranto group consisting of round brown cysts produced by Protoperidinium species (grouped as Brigantedinium spp.).The variation in accumulation rates can be related to gradiental changes in the trophic state of the surface waters linked to river outflow. Most species show a positive relationship between cyst production and nutrient/trace element availability in upper waters. No negative correlation between cyst production and nutrient/trace element availability could be documented. Production of Brigantidinium spp., Echinidinium spp., L. sabrina, L. machaerophorum, P. kofoidii/schwarzii, Spiniferites spp., S. mirabilis and S. quanta shows the most pronounced increase with increasing nutrient/trace element availability. These species can be considered as valuable indicators for reconstructing changes in the trophic state of the upper waters within the Po-river area in palaeo-environmental studies.     

回顾与展望:关于有害藻华种类休眠体通过船舶压舱水底泥地理扩散的研究

船舶压舱水可引起外来生物入侵,国际海事组织(International Maritime Organization, IMO)因此制定了具有约束力的压舱水公约,已于2019年1月对我国正式生效。大量研究证明船舶压舱泥是有害藻华种类特别是有害甲藻孢囊的携带者。另一方面,有害藻华在我国近三十年频发,尤其是新的种类不断出现。因此,这种态势是否与压舱泥带来的外来种入侵有关是一个具有重要科学和现实意义的问题。我们最近的工作表明,此前国内外通过形态学方法对压舱泥的检测都大大地低估了甲藻孢囊的种类多样性和样品间种类组成的异质性。因此,必须通过更深入全面的实证研究对外源有害藻华甲藻通过压舱泥入侵我国海域进行风险评估。本文从如下几个方面进行了综述与讨论：(1) 船舶压舱水(泥)与有害藻华地理扩散;(2) 国内外有关压舱泥中甲藻孢囊多样性的检测与溯源研究;(3) 我们对美国港口船舶压舱泥的检测发现压舱泥中甲藻孢囊具有很高的种类多样性和样品间的异质性。最后从我们最近的工作及与文献报道的工作比较获得了几个重要的科学问题。在评述国内外研究成果和前期研究结果基础上,提出有必要通过更大量、广泛的国际船舶压舱泥和中国全海域沉积物取样、高通量测序的分子鉴定与形态观察、单孢囊分子-形态鉴定、孢囊萌发、全面生信分析相结合的技术路线,实证性地评估有害藻华种类通过压舱泥入侵中国的风险,并以此建立对新出现藻华种类溯源或判断是否外来种入侵的基本依据,同时为海关职能部门的检验执法提供依据。     

湄洲湾海域甲藻孢囊的时空分布初步调查

为了解湄洲湾海域表层沉积物中甲藻孢囊的时空分布特征,于2018年5月(春)、8月(夏)、11月(秋)和2019年2月(冬)采集湄洲湾海域7个站位表层沉积物样品,进行甲藻孢囊分析,共鉴定出甲藻孢囊6大类42种和2种未知种。异养型甲藻孢囊种类数和丰度均高于自养型甲藻孢囊,其中又以原多甲藻类孢囊的种类和丰度最高。季节间差异不明显:种类数介于34～38种之间,丰度则在397.8～569.5 cysts/g之间变化,全年平均丰度448.0 cysts/g。工业区附近的站位种类数和丰度均低于养殖区附近的站位和对照点。优势种高达16种,原多甲藻类占绝对优势,但全部优势种优势度均不大。多样性指数、丰富度指数和均匀度指数均较高,全年的平均值分别为3.45、1.55和0.92。与历史资料对比,新发现19种孢囊,但丰度相差不大。另需注意的是,在湄洲湾海域共发现6种有毒甲藻孢囊,虽然全年丰度均不高,但仍有暴发有毒赤潮的危险,需引起重视。     

Rapid flow cytometric method for the assessment of toxic dinoflagellate cyst viability

The inadvertent transfer and dispersal of non-indigenous marine species via shipping ballast water is of increasing environmental concern. Despite a major global effort to develop new ballast water treatment technologies, their acceptance has been hampered by the lack of suitable indicator species for assessing treatment effectiveness. Resistant dinoflagellate cysts are one proposed test organism, however their use has been limited due to difficulties in assessing their viability after treatment. The paper describes the development of a rapid method to determine the viability of cysts of the dinoflagellate Alexandrium catenella using staining with SYTOX Green and flow-cytometric analysis. The viability of A. catenella cysts was inversely proportional to their ability to take up the stain. There was excellent agreement between cysts measured as viable/non-viable using flow cytometry and cyst viability determined in standard long-term germination tests. Advantages of the flow-cytometric method include high test precision and rapid testing times of < 2 days, compared to > 4 weeks using existing germination methods.     

Palaeoproductivity and post-depositional aerobic organic matter decay reflected by dinoflagellate cyst assemblages of the Eastern Mediterranean S1 sapropel

In the reconstruction of bioproductivity in surface waters the extent to which a proxy has been diagenetically altered is often a matter of debate. Here we investigate how organic- and calcareous-walled dinoflagellate cysts can be used for separately estimating bioproductivity and oxygen related diagenesis. This is achieved by studying the cyst content of the most recent Eastern Mediterranean sapropel S1, that is thought to have been deposited under conditions of increased primary production in surface waters and possible anoxia in the bottom waters. Based on chemical evidence, it has been shown that the visible sapropelic layer represents only the residual lower part of what was initially a much thicker sapropel, as a result of post-depositional decay of organic matter related to oxygen penetration into the sediments. The effect of aerobic organic matter decay on the cyst associations is studied through the comparison of the unaffected, lower part of the initial sapropel and the ‘oxidised’ upper part. Comparing the unaffected sapropelic sediments with pre- and post-sapropelic material gives insight into the relationship between fossil cysts assemblages and palaeoproductivity.Impagidinium aculeatum, Impagidinium patulum, Operculodinium israelianum, Polysphaeridium zoharyi and probably Impagidinium spp., Impagidinium paradoxum and Nematosphaeropsis labyrinthus are very resistant against aerobic decay and their accumulation rates appear to be primarily related to productivity in surface waters. Protoperidinium and Echinidinium species, on the other hand, are shown to be very sensitive and can be used to recognise oxygen-related decay. The calcareous-walled dinoflagellate cysts seem to be unaffected by oxic organic matter decay in Mediterranean sediments.     

Historical deposits of Alexandrium catenella resting cysts in the sediments of Queen Charlotte Sound,New Zealand

In 2011, a large repository of resting cysts of the toxic dinoflagellate Alexandrium catenella was discovered in the sediments of the Onapua/Opua inlet located off Tory Channel, Queen Charlotte Sound. The inlet is a potential source of infection for other areas, such as the major mussel-growing areas of Port Underwood and Pelorus Sound. This study aimed to establish whether the dinoflagellate was a new arrival in the Sounds or had existed unnoticed in this isolated embayment for some time. Alexandrium catenella cysts were identified to a depth of 20–21?cm within the sediment cores, corresponding to a date estimated by radioisotope (²¹⁰Pb and ¹³⁷Cs) and Pinus radiata pollen distribution to at least the mid 1970s. Over this time span, resident populations of A. catenella have not become established beyond the confines of Queen Charlotte Sound, suggesting it does not pose an imminent threat of doing so unless increasingly intense and prolonged blooms result in more widespread cyst dispersal.     

Dinoflagellate cysts in the surface sediments of the White Sea

Dinoflagellate cysts were studied in 42 samples from the surface sediments of the White Sea. The total concentration of dinocysts varies from single cysts to 25 000 cyst/g of dry sediments, which reflects the biological productivity in the White Sea waters and the regional particular features of the sedimentation processes. The highest concentrations are observed in silts; they are related to the regions of propagation of the highly productive Barents Sea waters in the White Sea. Generally, the spatial distribution of dinocysts species in the surface sediments corresponds to the distribution of the major types of water masses in the White Sea. The cysts of the relatively warm-water species (Operculodinium centrocarpum, Spiniferites sp.) of North Atlantic origin that dominate in the sediments indicate an intensive intrusion of the Barents Sea water masses to the White Sea along with hydrological dwelling conditions in the White Sea favorable for the development of these species during their vegetation period. The cold-water dinocyst assemblage (Islandinium minutum, Polykrikos sp.) is rather strictly confined to the inner parts of shallow-water bays, firstly, those adjacent to the Onega and Severnaya Dvina river mouths.