Dinoflagellate cyst distribution in surface sediments along the south-western Mexican coast (14.76° N to 24.75°N)

In this study, we explore the relationship between the modern assemblages of organic-walled dinoflagellate cysts and sea-surface conditions (temperature, salinity, primary productivity) and water depth and distance to the coast. Statistical treatments were performed on 95 surface sediment samples from sites located along the south-western Mexican coast (14.76° N to 24.75°N). Redundancy analysis (RDA) illustrates that the principal parameters correlated with the regional cyst distribution are the distance to the coast and the productivity in the upper water column, which is closely related to upwelling intensity. Empirical observations coupled with RDA provide insight into the spatial coverage of some cyst taxa produced by dinoflagellate species potentially responsible for harmful algal blooms along the coast. They also allow the recognition of four zones of assemblages, which are linked to the upwelling intensity and the productivity and characterize La Paz Bay, the south-western Mexican margin (from 15.95° N to 23.11° N), the northern part of the Gulf of Tehuantepec and the southern part of the Gulf of Tehuantepec.     

Control of modern dinoflagellate cyst distribution in the Irish and Celtic seas by seasonal stratification dynamics

Surface sediments from seven stations located in the seasonally stratified, frontal and mixed water regions in the Celtic and Irish seas have been analysed for their dinoflagellate cyst assemblages and dinosterol content. A total of 45 dinoflagellate cyst taxa have been identified and the assemblages related to surface and sediment conditions. Sediments from the mixed water region, at 30 m water depth, are characterised by a relatively low cyst concentration (∼2300 cysts/g dry weight) and high relative abundances of Lingulodinium machaerophorum accompanied by Spiniferites membranaceus, Brigantedinium spp. and Dubridinium caperatum. Assemblages from stratified and frontal water stations are dominated by Spiniferites ramosus associated with Operculodinium centrocarpum, Brigantedinium spp., cysts of Polykrikos schwartzii and Selenopemphix quanta. Ordination techniques performed on a restricted number of 35 taxa from the assemblages differentiated the stratified and frontal assemblages based on the abundance of the less abundant species Bitectatodinium tepikiense and Spiniferites elongatus. Among the environmental parameters (sea-surface temperature and salinity, stratification index, chlorophyll concentration and sediment grain-size classes), the seasonal stratification and sedimentological context, itself a function of tidal dynamics, explain most of the variance in the environmental conditions. These results indicate that dinoflagellate cyst analyses of shelf sediment records can be used to document the planktonic signal of seasonal stratification dynamics.     

Dinoflagellate cyst distribution in marine surface sediments off West Africa (17–6°N) in relation to sea-surface conditions, freshwater input and seasonal coastal upwelling

An organic-walled dinoflagellate cyst analysis was carried out on 53 surface sediment samples from West Africa (17–6°N) to obtain insight in the relationship between their spatial distribution and hydrological conditions in the upper water column as well as marine productivity in the study area.Multivariate analysis of the dinoflagellate cyst relative abundances and environmental parameters of the water column shows that sea-surface temperature, salinity, marine productivity and bottom water oxygen are the factors that relate significantly to the distribution patterns of individual species in the region.The composition of cyst assemblages and dinoflagellate cyst concentrations allows the identification of four hydrographic regimes; 1) the northern regime between 17 and 14°N characterized by high productivity associated with seasonal coastal upwelling, 2) the southern regime between 12 and 6°N associated with high-nutrient waters influenced by river discharge 3) the intermediate regime between 14 and 12°N influenced mainly by seasonal coastal upwelling additionally associated with fluvial input of terrestrial nutrients and 4) the offshore regime characterized by low chlorophyll-a concentrations in upper waters and high bottom water oxygen concentrations.Our data show that cysts of Polykrikos kofoidii, Selenopemphix quanta, Dubridinium spp., Echinidinium species, cysts of Protoperidinium monospinum and Spiniferites pachydermus are the best proxies to reconstruct the boundary between the NE trade winds and the monsoon winds in the subtropical eastern Atlantic Ocean. The association of Bitectatodinium spongium, Lejeunecysta oliva, Quinquecuspis concreta, Selenopemphix nephroides, Trinovantedinium applanatum can be used to reconstruct past river outflow variations within this region.     

Biogeography of dinoflagellate cysts in northwest Atlantic estuaries

Few biogeographic studies of dinoflagellate cysts include the near‐shore estuarine environment. We determine the effect of estuary type, biogeography, and water quality on the spatial distribution of organic‐walled dinoflagellate cysts from the Northeast USA (Maine to Delaware) and Canada (Prince Edward Island). A total of 69 surface sediment samples were collected from 27 estuaries, from sites with surface salinities >20. Dinoflagellate cysts were examined microscopically and compared to environmental parameters using multivariate ordination techniques. The spatial distribution of cyst taxa reflects biogeographic provinces established by other marine organisms, with Cape Cod separating the northern Acadian Province from the southern Virginian Province. Species such as Lingulodinium machaerophorum and Polysphaeridinium zoharyi were found almost exclusively in the Virginian Province, while others such as Dubridinium spp. and Islandinium? cezare were more abundant in the Acadian Province. Tidal range, sea surface temperature (SST), and sea surface salinity (SSS) are statistically significant parameters influencing cyst assemblages. Samples from the same type of estuary cluster together in canonical correspondence analysis when the estuaries are within the same biogeographic province. The large geographic extent of this study, encompassing four main estuary types (riverine, lagoon, coastal embayment, and fjord), allowed us to determine that the type of estuary has an important influence on cyst assemblages. Due to greater seasonal variations in SSTs and SSSs in estuaries compared to the open ocean, cyst assemblages show distinct latitudinal trends. The estuarine context is important for understanding present‐day species distribution, the factors controlling them, and to better predict how they may change in the future.     

Organic-walled dinoflagellate cyst production in relation to upwelling intensity and lithogenic influx in the Cape Blanc region (off north-west Africa)

Fossil dinoflagellate cyst assemblages are increasingly used in paleoclimatic research to establish paleoenvi‐ronmental reconstructions. To obtain reliable reconstructions, it is essential to know which physical factors influence the cyst production. Most information about the relationship between variations in physical parameters and cyst production is known from middle and higher latitudes. Information from the (sub)tropics is rare. To increase this information, the temporal variation in cyst assemblages from the upwelling area off north‐west Africa (off Mauritania) has been compared to environmental conditions of the upper water column. Samples were collected by the sediment trap CB9, off north‐west Africa (Cape Blanc, 21°15′2″N, 20°42′2″W) between 11 June 1998 and 7 November 1999 at 27.5‐day intervals. Off Cape Blanc, upwelling occurs throughout the year with variable intensity. This region is also characterized by frequently occurring Saharan dust storms. Seasonal variations in dust input, upwelling intensity and sea surface temperature are reflected by the production of organic‐walled dinoflagellate cyst assemblages. Several cyst taxa are produced throughout the sampling interval, with the highest fluxes at times of strongest upwelling relaxation and/or dust input (Echinidinium aculeatum Zonneveld, Echini‐din ium delicatum Zonneveld, Echinidinium granulaturn Zonneveld, Echinidinium spp., Impagidinium aculeatum (Wall) Lentin et Williams, Impagidinium sphaeri‐cum (Wall) Lentin et Williams, Protoperidinium americanum (Gran et Braarud) Balech, Protoperidinium stellatum (Wall in Wall et Dale) Rochon etal., Protoperidinium spp., Selenopemphix nephroides (Benedek) Benedek et Sarjeant and Selenopemphix quanta (Bradford) Matsuoka). Species such as, for example, Bitectatodinium spongium (Zonneveld) Zonneveld et Jurkschat and Impagidinium patulum (Wall) Stover et Evitt do not show any production pattern related to a particular season of the year or to specific environmental conditions in the upper water column. The production of cysts of Protoperidinium monospinum (Paulsen) Zonneveld et Dale is restricted to intervals with increased nutrient concentrations in upper waters when sea surface temperatures at the sampling site is below approximately 24°C.     

Dinoflagellate cyst distribution along a shelf to slope transect of an oligotrophic tropical sea (Sunda Shelf, South China Sea)

From 51 surface samples collected along a shelf to slope transect of the Sunda Shelf, South China Sea, 36 taxa of organic‐walled dinoflagellate cysts are identified. Oligotrophic tropical shelf assemblages on the Sunda Shelf are dominated by gonyaulacoids such as Spiniferites species, Operculodinium centmcarpum and Operculodinium israelianum. Concentrations of dinoflagellate cysts in the shelf sediments are generally low and correlate well with the content of fine‐grained (clay and silt fraction) sediments. Detailed comparisons of sediment grain‐size distributions to concentrations of dominant dinoflagellate taxa (Spiniferites species, 0. centmcarpum and 0. israelianum) in the shelf sediments indicate that these taxa behave in water like sediment particles with size range φ 5.75–6.25 (13–18 μm). In contrast, slope assemblages in fine‐grained sediments are dominated by protoperidinioids. This may reflect higher nutrient availability as a result of weak winter upwelling. The concentrations of dinoflagellate cysts in the shelf sediments are mainly controlled by transport and winnowing processes and are probably not representative of surface water conditions.     

Recent Dinoflagellate cyst distribution in the North Canary Basin,NW Africa

The North Canary Basin (NW Africa) falls within a major eastern boundary upwelling system. This part of the coastal upwelling system is seasonal and is characterised by the development of large filaments migrating seawards. Hence, 16 samples from this location were selected to identify an “upwelling signal” in the composition of the dinoflagellate cyst assemblages.

Samples closest to the most intense upwelling cells are dominated by L. machaerophorum and G. catenatum and Protoperidinium spp. These make up the “upwelling signal” characteristic for the system. Moreover, the “upwelling signal” can be advected offshore, with filaments that may extend as far as 300 km. Finally, the finding of cysts from G. catenatum, a toxic dinoflagellate, raises the need for a better understanding of the relationship between its presence and distribution in the region, and the coastal upwelling system.     

Seasonal and spatial variation of phytoplankton assemblages, biomass and cell size from spring to summer across the north-eastern New Zealand continental shelf

The composition, biomass and cell size of phytoplankton taxonomicgroups were determined in the Hauraki Gulf and adjacent shelfof north-eastern New Zealand. In early spring, on the innershelf, over-winter mixing and upwelling supported a bloom dominatedby large, chain-forming diatoms in a moderately turbulent watercolumn. The bloom declined in late spring because of nutrientlimitation, and the assemblage evolved initially toward smalldiatoms, and eventually to co-occurrence of dinoflagellates,small nanoflagellates and picophytoplankton in early and latesummer. Mid- to outer-shelf biomass was much lower than inshore,and was dominated by small or motile taxa which were probablylimited by grazing and light. In early summer, strong upwellingdisplaced inner shelf phytoplankton to beyond the shelf edge,whilst enriching the shelf with nutrients. However, shelf phytoplanktonbiomass increased only after the relaxation of upwelling. TheHauraki Gulf was strongly stratified from early spring throughlate summer. The flora were seasonally less variable than onthe shelf, with a thecate dinoflagellate-dominated flora inearly spring, replaced post-bloom by the co-occurrence of presumablylow-nutrient-adapted autotrophic and/or heterotrophic dinoflagellates(most of which were non-thecate, and some toxic), nanoflagellatesand picophytoplankton. The succession in floristics was consistentwith a change from an autotrophic toward a heterotrophic ecosystemfrom spring to summer. Implications for secondary production,and vertical and lateral organic carbon export on the shelf,are discussed.     

THE CALCAREOUS RESTING CYST OF PENTAPHARSODINIUM TYRRHENICUM COMB. NOV. (DINOPHYCEAE)1

While investigating dinoflagellate cyst assemblages in surface sediments of the Gulfs of Naples and Salerno (Mediterranean Sea), we found a new calcareous resting cyst. This cyst has a round to oval body surrounded by a thick mineral layer, which gives it the shape of a Napoleon hat, with a flat, oval face bearing the archeopyle and a convex keel on the opposite side. The cyst shape is variable in both natural samples and clonal cultures. The organic membrane underlying the calcareous covering is resistant to acetolysis, thus demonstrating the presence of sporopolleninlike material. The cyst germinated into a motile stage having the same morphological features and thecal plate pattern as Peridinium tyrrhenicum Balech. We believe the validity of the genus Pentapharsodinium Indelicato & Loeblich should be accepted. Based on the comparative examination of the species we collected and of a similar species, Pentapharsodinium trachodium Indelicato & Loeblich, we propose Pentapharsodinium tyrrhenicum as a new combination for Peridinium tyrrhenicum. The genus Pentapharsodinium also includes P. dalei Indelicato & Loeblich (= Peridinium faeroense Dale), which produces spiny, organic-walled cysts. The presence of species forming calcareous cysts and species producing noncalcareous cysts in the same genus raises questions about maintaining the family Calciodinellaceae. This family should only include calcareous cyst-forming peridinioids, in order to maintain a unified system of classification of fossil and recent dinoflagellates.     

High diversity dinoflagellate cyst assemblages from the Late Triassic of southern England: new information on early dinoflagellate evolution and palaeogeography

Abundant and diverse dinoflagellate cyst assemblages from the Rhaetian of southern England are characterized by the occurrence of a new species of Rhaetogonyaulax, some undescribed taxa and numerous forms with Arctic and Australasian affinities. The dinoflagellate cyst assemblages permit a discussion of the palaeogeographic distribution of dinoflagellate cysts in the Late Triassic. The hypothesis on a Late Triassic migration event of organic walled microplankton from higher latitudes to the Boreal domain is presented.     

中国渤海海域甲藻孢囊的种类多样性和生态地理分布

在渤海湾24个站位采集0–10 cm表层沉积物144份样品, 进行甲藻孢囊的种类多样性和生态地理分布研究, 并分析渤海海域水体的富营养化趋势。在渤海海域共采集鉴定出6类32种甲藻孢囊, 包括原多甲藻类孢囊11种、裸甲藻类孢囊6种、膝沟藻类孢囊7种、钙质类孢囊5种、翼藻类孢囊2种及Tuberculodinioid类孢囊1种。其中, 自养型甲藻孢囊17种, 优势种为锥状斯氏藻(Scrippsiella trochoidea)孢囊, 丰富的孢囊库为锥状斯氏藻赤潮提供种源, 可作为该海域发生锥状斯氏藻赤潮的参考依据; 异养型甲藻孢囊15种, 优势种为无纹多沟藻(Polykrikos schwartzii)和锥形原多甲藻(Protoperidinium conicum)孢囊; 发现1种产麻痹性贝类毒素的孢囊--塔玛亚历山大藻(Alexandrium tamarense)孢囊, 但是仅在S6、S8和S14三个站位发现, 且孢囊数量较少。渤海甲藻孢囊组成与世界其它海域相似, 异养型甲藻孢囊种类丰富, 提示渤海海域富营养化程度较高。每个站位沉积物样品分为3层(每层约3 cm), 春夏两季表层、中层和底层之间孢囊组成差异不大, 平均种类数为5.58–7.29, 孢囊的平均密度范围在58.82–103.57 cysts·g^–1 DW之间; 孢囊种类丰富的站点, 孢囊密度也较高, 如S9、S14站位。对渤海海区表层沉积物中甲藻孢囊的生物多样性进行了统计分析, 发现表、中、底3层甲藻孢囊的平均种类多样性指数在春季(5月)分别为1.69、1.61和1.52; 略低于夏季(8月)的1.83、1.89和1.60。     

Seasonal change of dinoflagellates cyst flux collected in a sediment trap in Omura Bay, West Japan

Sediment trap samples were harvested bimonthly from 1998 to2000 and examined to better understand the species compositionand seasonal variation of dinoflagellate cyst flux in OmuraBay in Japan. Samples’ living cyst flux clearly showedseasonal variation with the higher flux number between autumnand winter. In total, 43 different cyst taxa were recorded,and these were composed of two different ecological groups.The first group included Protoperidinium compressum and Protoperidiniumsubinerme, which increased every autumn to winter. The secondgroup included Gonyaulax spp. and Pheopolykrikos hartmanniiand was trapped throughout the year. These two groups manifestedthe different flux patterns and were, respectively, heterotrophicand autotrophic in nutrition. In the heterotrophic group, protoperidinioidcysts were dominant. Vegetative cells of protoperidinioid areknown to feed mainly diatoms. Sample diatom flux also increasedfrom autumn to winter. Therefore, the increase of protoperidinioidcysts in autumn to winter was observed to correlate with diatomblooms. In contrast, the autotrophic group mostly consistedof Gonyaulacoid cysts and were generally observed throughoutthe year, although occurrence varied between species most likelyresponding to favorable environmental conditions. The resultsindicate that cyst production is closely related to differentnutritional modes.     

Calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea: distribution patterns and influence of main environmental gradients

The distribution of calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea was quantitatively analysed. The samples contain 11 cyst species and the vegetative coccoid Thoracosphaera heimii. Cyst abundance increases towards the deeper parts of the basins and is generally higher in the eastern Mediterranean Sea. Three major distribution characteristics exist: (1) different assemblages in oceanic and neritic regions, (2) little agreement with the associations of areas studied so far like the Atlantic Ocean, and (3) a unique oceanic assemblage in the eastern Mediterranean Sea. A gradual change in cyst assemblages from the western to the eastern Mediterranean Sea was observed and statistically compared with the main environmental gradients in the upper water column. Temperature, nitrate concentration and possibly salinity appear to be the most important factors controlling cyst production. Three groups containing cysts with similar environmental preferences can be distinguished: (1) an eastern Mediterranean group related to relatively high temperature and salinity but low nitrate concentration, (2) a group of more or less consistently abundant cosmopolitan species tolerating or even preferring relatively low temperature and salinity but high nitrate concentration, and (3) a group containing species that are possibly adapted to neritic environments and have probably been transported from coastal areas into the studied regions. In contrast to other calcareous plankton, calcareous dinoflagellate cysts correlate strongly with the main environmental gradients in the Mediterranean Sea, bearing a high potential for palaeoenvironmental reconstructions.     

大窑湾养殖区赤潮甲藻孢囊种类组成及分布的研究

2006—2007年对大窑湾养殖区的甲藻孢囊进行了研究,结果检出10种甲藻孢囊,分属于4大类9种甲藻孢囊,其中原多甲藻类孢囊2种,膝沟藻类孢囊5种,钙质类孢囊1种,裸甲藻类孢囊1种,一种艉杆藻(Ensiculifera Balech)和一种易碎藻(Fragilidium mexicanum)是中国沿海新记录的两个种类,此外还有一种无法鉴定到种的一种原多甲藻孢囊。膝沟藻类孢囊的种类数占绝对优势,占50%,其次是原多甲藻类孢囊占30%,钙质类孢囊和裸甲藻类孢囊各占10%。10种孢囊中有3种异养型孢囊和7种自养型孢囊。并发现两种产麻痹性贝毒(PSP)的孢囊—塔玛亚历山大藻/链状亚历山大藻复合体(Alexandrium tamarense/A.catenella)和链状裸甲藻(Gymnodinium catenatum)。孢囊密度的季节分布呈现明显的双峰型,在2007年1月份和2007年的8月份出现了两个高峰。2007年的1月份达到了调查全年的孢囊密度最高值,达到了1.09×103 cysts/g湿重,2007年的8月份出现的第二次高峰期孢囊密度达到了0.86×103 cysts/g湿重。孢囊密度最低值出现在2007年的10月,只有280 cysts/g湿重。全年孢囊平均密度为695.5 cysts/g湿重。甲藻孢囊的多样性指数除了2007年的9月和10月以外,相差不大,变化范围为0.17—0.55,全年的平均值为0.46。     

Dinoflagellate cysts from surface sediments of Saldanha Bay, South Africa: an indication of the potential risk of harmful algal blooms

The distribution and abundance of dinoflagellate cysts from recent coastal sediments in Saldanha Bay, was investigated, and compared to the cyst assemblages of the adjacent coastal upwelling system as reflected in the sediments off Lambert's Bay on the southern Namaqua shelf. Twenty-two cyst types were identified from three sample sites off Lambert's Bay with recorded abundances between 1726 and 1863 cysts ml⁻¹ wet sediment. At least 21 distinctive cyst types were identified from 32 sample sites within Saldanha Bay. Cyst abundance in Saldanha Bay was relatively low, averaging 116 cysts ml⁻¹ wet sediment. The region off Lambert's Bay is especially susceptible to the formation of harmful algal blooms attributed to high biomass dinoflagellate blooms. Owing to these blooms and the retentive circulation characteristics of this area, cyst formation and deposition is high. Blooms can be advected into Saldanha Bay, but their development and duration in the Bay is restricted by the system of exchange that operates between the Bay and the coastal upwelling system, in that there is a net export of surface waters from the Bay. Consequently, fewer cysts are formed and deposited within the Bay thereby reducing the likelihood of in situ bloom development initiated from the excystment of cysts.     

Hundred Years of Environmental Change and Phytoplankton Ecophysiological Variability Archived in Coastal Sediments

Marine protist species have been used for several decades as environmental indicators under the assumption that their ecological requirements have remained more or less stable through time. However, a growing body of evidence suggests that marine protists, including several phytoplankton species, are in fact highly diverse and may quickly respond to changes in the environment. Predicting how future climate will impact phytoplankton populations is important, but this task has been challenged by a lack of time-series of ecophysiological parameters at time-scales relevant for climate studies (i.e. at least decadal). Here, we report on ecophysiological variability in a marine dinoflagellate over a 100-year period of well-documented environmental change, by using the sedimentary archive of living cysts from a Scandinavian fjord (Koljö Fjord, Sweden). During the past century, Koljö Fjord has experienced important changes in salinity linked to the North Atlantic Oscillation (NAO). We revived resting cysts of Pentapharsodinium dalei preserved in the fjord sediments and determined growth rates for 18 strains obtained from 3 sediment core layers at salinity 15 and 30, which represent extreme sea-surface conditions during periods of predominantly negative and positive NAO phases, respectively. Upper pH tolerance limits for growth were also tested. In general, P. dalei grew at a higher rate in salinity 30 than 15 for all layers, but there were significant differences among strains. When accounting for inter-strain variability, cyst age had no effect on growth performance or upper pH tolerance limits for this species, indicating a stable growth response over the 100-year period in spite of environmental fluctuations. Our findings give some support for the use of morphospecies in environmental studies, particularly at decadal to century scales. Furthermore, the high intra-specific variability found down to sediment layers dated as ca. 50 years-old indicates that cyst-beds of P. dalei are repositories of ecophysiological diversity.     

Development of diatom-based salinity models for paleoclimatic research from lakes in British Columbia (Canada)

Diatoms were identified and enumerated from the surface sediments of 65 lakes located on the Cariboo and Chilcotin Plateaux (British Columbia, Canada). These lakes span a large gradient in lakewater ionic concentration (fresh through hypersaline) and composition, as well as other physical/chemical variables. Almost all of the study lakes had higher salinities in the late-summer than in the spring. The lakes with spring salinities >8 g l^–1 showed the largest seasonal increases in salinity. Ionic composition was similar in the spring and late-summer for most lakes. Both ionic concentration (i.e. salinity) and composition were important environmental variables that could account for the different diatom floras in the lakes. Diatom assemblages characteristic of carbonate-dominated and sulfate-dominated waters were identified. Other variables such as water depth and phosphorus concentration were also important.The majority (87%) of diatom taxa had estimated salinity optima < 3 g l^–1 Halophilic diatom taxa had broader tolerances to salinity when compared to the fresh water taxa, however taxa with narrow and broad tolerances could be identified across the salinity gradient. Species diversity was weakly but significantly correlated to lakewater salinity (r ² = 0.18 to 0.3, P < 0.05).Salinity inference models were developed based on the relationship between the diatom assemblages and the spring, late-summer and average salinity. The correlations between the measured and diatominferred salinity, based on the spring (r = 0.95), late-summer (r = 0.94) and average (r = 0.95) salinity data, are high because there was an extremely strong correlation (r = 0.98) between the log transformed spring and late-summer measured salinities. These salinity reconstruction models provide a tool that can be used to infer past climatic changes as part of paleolimnological studies from appropriate closed-basin lakes in British Columbia.     

Composition and succession of dinoflagellates and chrysophytes in the upper fast ice of Davis Station, East Antarctica

Little is known of the wider Antarctic distribution of the upper fast ice community now comprehensively described from McMurdo Sound. We determined the fast ice protist community at Davis Station, East Antarctica and compared it with that of McMurdo Sound. As at McMurdo Sound, Davis fast ice is characterised by extreme and transitory salinities (96–2.5 psu) and temperatures (−4.5 to −0.1°C) during the spring/summer transition. Both communities are dominated by Polarella glacialis (an autotrophic dinoflagellate), chrysophytes and their life cycle stages. Furthermore, the physical parameters of brine temperature and salinity at which these successions occurred approximated those of McMurdo Sound. The high degree of similarity between the communities from the geographically disparate locations indicates that this community type has a circum-Antarctic distribution. Confirming the areal extent and seasonality of this community type will assist in future predictions of sea ice productivity.     

Late Quaternary Protoperidinium cysts as indicators of paleoproductivity in the northern Arabian Sea

The reliability of organic-walled cysts of the heterotrophic dinoflagellate Protoperidinium as paleoproductivity indicators and the influence of bottom water oxygenation on cyst preservation is assessed by using Arabian Sea records of the past 125 kyr as a natural laboratory. Multidisciplinary geochemical, micropaleontological and palynological datasets are integrated to analyze the relationship between Protoperidinium cyst concentrations and other paleoproductivity proxies. Differential preservation potential is quantified in order to establish threshold oxidative degradation values for a possible application of quantitative Protoperidinium cyst records in paleoenvironmental reconstructions. Results indicate that variations in Protoperidinium cyst concentration closely correspond to other marine productivity and/or upwelling proxies. Although oxygenation will lead to significant cyst degradation, and thus decreased concentrations, down-core patterns in Protoperidinium cyst concentration still primarily reflect changes in sea surface productivity. In view of differential preservation among dinoflagellate cysts, down-core variations in relative abundance of Protoperidinium should be treated with caution.     

Modern dinoflagellate cysts in hypertrophic coastal waters of Tokyo Bay, Japan

A survey of dinoflagellate resting cysts in surface sedimentsamples was carried out in Tokyo Bay, Japan, to document theirhorizontal distribution. At least 21 different cyst types werefound. Dominant cyst types allowed the recognition of assemblageswhich form three different dinoflagellate cyst communities:the innermost part of the Bay, the central area and the moutharea. In all stations in Tokyo Bay, heterotrophic dinoflagellatecysts always occupied more than half of the cyst populations.Cysts of Polykrikos schwartzii/kofoidii are the most abundantheterotrophic species. These assemblages may reflect highlynutrient-enriched (hypertrophic) and turbulent water conditions.Among the cyst types found were probable ellipsoidal cysts ofAlexandrium tamarense. This is the first record of toxic Alexandriumspecies cysts in Tokyo Bay sediments.