中国沿海甲藻包囊研究进展

休眠包囊是甲藻生活史中的一个重要阶段,它们对于甲藻种群的生存、延续以及扩散具有重要的生物学意义.能够形成休眠包囊的甲藻大部分时间以包囊的形式存在于沉积物中,因此研究包囊有助于揭示甲藻的物种多样性.根据沉积物中甲藻包囊的种类和数量还可以追溯各海区的富营养化历史,以及重建古海洋环境.本文介绍了甲藻包囊的研究方法,指出形态分...     

Encystment of Peridinium gatunense: occurrence, favourable environmental conditions and its role in the dinoflagellate life cycle in a subtropical lake

1. The abundance of cysts of the bloom‐forming dinoflagellate Peridinium gatunense in the sediments of Lake Kinneret and the effects of environmental conditions on encystment were studied in relation to bloom dynamics. Peak cyst formation coincided with the highest growth rate of the population, prior to bloom peak. 2. Peridinium cysts were counted in water and sediment corer samples from 2000 to 2003 and in archived sediment trap samples collected during 1993–94. The cyst data were examined in relation to ambient temperature and nutrient records, and revealed no direct correlation. 3. In laboratory encystment experiments with Peridinium cells collected from the lake, 0.2–3% of the vegetative cells encysted. Temperature, light and cell density had no significant effect on the percentage of encystment. 4. Cysts were always present in the lake sediments but their abundance in ‘non Peridinium’ years was much lower than after a massive bloom. Vegetative cells were always present in the water column after the collapse of the annual dinoflagellate bloom, potentially serving as the inoculum for the next bloom. We propose that the hardy cysts serve as an emergency ‘gene bank’ to initiate population build up following catastrophic die outs.     

Patterns of vertical cyst distribution and survival in 100-year-old sediment archives of three spring dinoflagellate species from the Northern Baltic Sea

The history of expansion of bloom-forming cold water dinoflagellates in the Northern Baltic Sea was studied using 100-year-old sediment archives of their resting cysts. Vertical cyst distributions of Biecheleria baltica and Apocalathium malmogiense, two dinoflagellates indistinguishable by light microscopy and not recognized as distinct species in monitoring, and chain-forming Peridiniella catenata were analysed in Pb²¹⁰ and Cs¹³⁷ dated layers of a sediment core from deep, hypoxic accumulation bottoms of the Gulf of Finland. Cyst profiles showed that B. baltica and A. malmogiense were already present in the Baltic spring phytoplankton community at the beginning of the 20th century. This confirms that B. baltica, which was only recognized in the late 1980s, is a native species in the area. A drastic increase in B. baltica cyst concentrations in the 1930s to 1960s coincided with the acceleration of anthropogenic eutrophication. Large cyst deposits accumulated over several decades in the sediment which, by the 1980s, amounted to the seed stock necessary to inoculate dominant blooms. In the cyst records A. malmogiense always contributed a minor fraction of the two species. P. catenata had a relatively short cyst record in Gulf of Finland sediments despite demonstrated long-term presence in the plankton, which emphasizes that cyst-based historic surveys are not suitable for all cyst-forming dinoflagellates. This was corroborated by correspondence analyses of long-term plankton and cyst records which validated the trends from the sediment archive for B. baltica and A. malmogiense, but failed to do so for P. catenata. Germination experiments with 100-year-old cysts revealed a remarkable long-term survival capacity of A. malmogiense, making this species a suitable model for resurrection studies testing adaptation in heavily impacted systems such as the Baltic Sea.     

Seasonal distribution of dinoflagellate resting cysts in surface sediments from Changjiang River Estuary

In order to understand the distribution of dinoflagellate cysts, surface sediments were collected from 15 stations in Changjiang River Estuary from 122°E to 123.5°E and from 29°N to 32°N in four cruises from May 2002 to February 2003. In the present study, 38 different cyst morphotypes representing 21 genera and 6 groups were identified, while 1 type was not identified into genus level. Species number and cell density of dinoflagellate cysts ranged from 10 to 25 species and from 12 to 587 per gram of dry weight, respectively. There were no obvious differences in cyst composition and density among seasons. However, the highest cyst species number and density were recorded in summer and winter, respectively. Cysts of heterotrophic dinoflagellates, which held 55.7% of the overall cyst density averagely, dominated cyst assemblages. Cyst density and species number increased from the west to the east, from the north to the south within the study area. Cysts of toxic dinoflagellates Alexandrium cat‐enella and Alexandrium tamarense complex distributed widely and were observed in almost all stations, with the maximum cell density of 81 per gram of dry weight.     

Dinoflagellate cyst records in recent sediments from Daya Bay, South China Sea

Nine sediment cores of 8–26 cm in length were collected from two basins of Daya Bay, the South China Sea, by Tokyo University Fisheries Oceanography Laboratory core sampler in August 2001 to investigate the distribution of dinoflagellate resting cysts. In the present study, 51 different cyst morphotypes representing 22 genera were identified from 65 sediment samples. Among them, there were 21 autotrophic species and 30 heterotrophic ones. Cyst species richness in each sample varied from 12 to 29, while the values of Shannon‐Weaver diversity index (H′) were between 0.15 and 4.13. There were an obvious increase in both species richness and values of H′in 2–6 cm sediments. Cyst concentrations varied from 154 to 113 483 cysts per gram dry weight sediment, and were much higher in upper sediments. Scrippsiella trochoidea was the most dominant cyst type, which took up over 90% of cyst assemblages in the upper sediments. The abrupt increase of S. trochoidea cysts in the surface sediments reflected the bloom of this species in Daya Bay in 2000. The results from cyst assemblages showed some trend of changes in water quality in this area, and indicated a typical type of pollution caused by cultural eutrophication, which started in the 1980s and greatly accelerated in the middle of 1990s. Cysts of Alexandrium, mainly those of Alexandrium catenella and Alexandrium tamarense complex, occurred frequently and abundantly in this area, with the highest concentration and relative frequency of 503 cysts per gram dry weight sediment and 22.3%, respectively. The high abundance of Alexandrium cysts provided rich ‘seed bed’ for Alexandrium blooms and was also an important source of paralytic shellfish poisoning toxins, especially in winter.     

Preservation of organic-walled dinoflagellate cysts in different oxygen regimes: a 10,000 year natural experiment

The occurrence of organic-walled dinoflagellate cysts in (fossil) sediments depends on several factors, including as the ecological preferences of the cyst-forming dinoflagellates, cyst production, transport and preservation. Although laboratory experiments have shown that several cyst species are sensitive to chemical treatment, no information about the selective preservation of dinoflagellate cyst species in natural environments has previously been presented. Here, we present data on the effects of oxygen availability in bottom sediments on a cyst assemblage from the ungraded Madeira Abyssal Plain f-turbidite of which only the upper layer has been oxidized. Based on differences in species composition between the oxidized and underlying, unoxidized layers of this turbidite, the influence of oxygen availability on the preservation of individual species has been estimated. Cyst species have been classified in ascending order of resistance to oxygen availability in sediments as: (1) highly sensitive (cysts formed by Protoperidinium species), (2) moderately sensitive (e.g. Spiniferites species), (3) moderately resistant (e.g. Impagidinium paradoxum and Nematosphaeropsis labyrinthus) and (4) resistant (e.g. Impagidinium aculeatum).     

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.     

Dinoflagellate cysts from sediment traps deployed in the Bellingshausen,Weddell and Scotia seas,Antarctica

Dinoflagellate cysts have been recovered from six long-term (1–2 yr) sediment trap moorings deployed in the Bellingshausen, Weddell and Scotia seas, Antarctica. These traps, mostly moored near the sea bed to sample the nepheloid layer, were located both within and to the north of the maximum sea-ice limit. The numbers of cysts, together with the composition of the assemblages, reinforce the importance of the maximum sea-ice limit as a modern biogeographic boundary for the distribution of dinoflagellate cysts. Cysts derived from heterotrophic dinoflagellates make up the highest proportions within the assemblages recovered from the traps. One trap sampled the export production, revealing little difference in cyst flux over those sampling the nepheloid layer. Cyst flux appears to be highest in areas closest to the Antarctic Convergence, north of the maximum sea-ice limit, and to high nutrient availability. There are, however, differences between the sediment trap assemblages and those recovered from core-top samples at the same or nearby sites. These differences, in the greater number of cysts, and in the higher numbers of round, brown Protoperidinium cysts in the traps, may reflect annual differences in the primary productivity and/or cyst production in the area. In some areas the sediment record may preserve little information about local surface water productivity because of the activity of bottom water currents, for example those arising from the Antarctic Circumpolar Current.     

Distributions of calcareous dinoflagellate cysts in surface sediments of the western equatorial Atlantic Ocean,and their potential use in palaeoceanography

Only very few studies focus on recent calcareous dinoflagellate cyst diversity, geographic distribution and ecology, so that information on the distribution patterns and environmental affinities of individual cyst species is extremely limited. This information is, however, essential if we want to use calcareous dinoflagellate cysts for palaeoenvironmental reconstruction. Surface sediment samples from the generally oligotrophic western equatorial Atlantic Ocean, offshore northeast Brazil, were therefore quantitatively analysed for their calcareous dinoflagellate cyst content, including the calcareous vegetative coccoid Thoracosphaera heimii. Seven calcareous dinoflagellate cyst species/morphotypes and T. heimii were encountered in high concentrations throughout the area. Substantial differences in the distribution patterns were observed. The highest concentrations of cysts are found in sediments of the more oligotrophic, oceanic regions, beyond the influence of Amazon River discharge waters. Dinoflagellates producing calcareous cysts thus appear to be capable of surviving low nutrient concentrations and produce large numbers of cysts in relatively stable and predictable environments affected by minimal seasonality. To test for the environmental affinities of individual species, distribution patterns in surface sediments were compared with temperature, salinity, density and stratification gradients within the upper water column (0–100 m) over different times of the year, using principal components analysis and redundancy analysis. T. heimii and four of the seven encountered cyst species (Sphaerodinella? albatrosiana, two morphotypes of Sphaerodinella? tuberosa and Scrippsiella regalis) relate to these parameters significantly and the variations in the cyst associations appear to be associated with the different surface water currents characterising the area. The results imply that calcareous dinoflagellate cyst distributions can potentially be used to distinguish between different open oceanic environments and they could, therefore, be useful in tracing water mass movements throughout the late Quaternary.     

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 resting cysts as factors in phytoplankton ecology of the North Sea

The occurrence and distribution of dinoflagellate resting cysts were investigated at 11 locations in the south-eastern part of the North Sea. Twenty-six known cyst species and 7 unknown cyst types, which may act as seed population for planktonic dinoflagellate blooms, have been recorded for the first time in the area. The most common cysts in recent sediments were those ofScrippsiella trochoidea, Zygabikodinium lenticulatum, Peridinium dalei, Scrippsiella lachrymosa, Protoceratium reticulatum, Protoperidinium denticulatum, andP. conicum. At all stations,S. trochoidea dominated the cyst assemblages with a maximal abundance of 1303 living cysts/cm³ in the uppermost half centimetre. Cysts of the potentially toxic dinoflagellatesAlexandrium cf.excavatum andA. cf.tamarense were scarce. In the upper 2-cm layer of sediment, dinoflagellate cysts were found in concentrations of 1.8 up to 682 living cysts/cm³. Empty cysts constituted 22–56% of total cyst abundance. The comparative distribution of the cysts showed a general increase in abundance from inshore sites to the offshore area, whereby sandy stations exhibited the lowest cyst abundance and diversity. The wide distribution of living and empty cysts ofScrippsiella lachrymosa suggests that its motile form, which has not been officially recorded in the area until now, is a common plankton organism in German coastal waters. The relatively high abundance of cysts in recent sediments demonstrates the potential importance of benthic resting stages for the initiation of dinoflagellate blooms in the study area.     

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.     

2004年春季长江口海域甲藻孢囊的分布研究

于2004年4月初,采集长江口(E122°～123°30',N29°～32°)10个站点0～15cm底泥样品,研究甲藻孢囊在这10个站点的水平和垂直分布情况。在30个样品中共鉴定出6大类24种甲藻孢囊。孢囊组成以异养型原多甲藻类孢囊为主,有13种,平均密度为157cysts·g^-1DW,为调查海域的最优势种群。两种产麻痹性贝类毒素(Paralytic shellfish poisoning,PSP)的孢囊,塔玛亚历山大藻和链状裸甲藻,在海区分布广泛但数量较低。10个站点甲藻孢囊的种类数在11～18种之间,平均密度为189～846cysts·g^-1DW,在远离河口的D6站点有一个明显的最高峰,位于最北部的D1站点孢囊密度最低。与其它海湾相比,属于孢囊密度较低的海区。Shannon-Weaver生物多样性指数(H')变化范围在2.57～3.27之间。甲藻孢囊的密度分布与生物多样性相关系数r=-0.72。3个不同深度的甲藻孢囊密度分别为351cysts·g^-1DW、412cysts·g^-1DW、432cysts·g^-1DW;生物多样性指数分别为3.22、2.95、2.98。     

Late-Holocene succession of dinoflagellates in an Antarctic fjord using a multi-proxy approach: paleoenvironmental genomics, lipid biomarkers and palynomorphs

Recent work has shown that paleoenvironmental genomics, i.e. the application of genomic tools to analyze preserved DNA in sedimentary records, is a promising approach to reconstruct the diversity of past planktonic communities. This provides information about past ecological and environmental changes. A major advantage of this approach is that individual species, including those that did not leave other characteristic markers, can be identified. In this study, we determined which dinoflagellate marker (i.e. 18S rDNA, dinosterol or dinocysts) provided the most detailed information about the late-Holocene succession of dinoflagellates in an Antarctic Fjord (Ellis Fjord, Vestfold Hills). The preserved rDNA revealed two intervals in the 2750-year-old sediment record. The dinoflagellate diversity was the highest until ∼1850 cal yr bp and included phylotypes related to known dinosterol producers. A lower concentration of dinosterol in sediments <1850 cal yr bp coincided with a community shift towards a predominance of the autotrophic sea-ice dinoflagellate Polarella glacialis , which is not a source of dinosterol. Remarkably, cultures of P. glacialis are known to produce other diagnostic sterols, but these were not recovered here. In addition, conspicuous resting cysts of P. glacialis were not preserved in the analyzed sediments. Overall, dinocysts were rare and the paleoenvironmental genomics approach revealed the highest diversity of dinoflagellates in Ellis Fjord, and was the only approach that recorded a shift in dinoflagellate composition at ∼1850 cal yr bp indicative of a colder climate with more extensive ice cover – this timing coincides with a period of changing climate reported for this region.     

九龙江西陂库区沉积物甲藻孢囊的分布

孢囊在甲藻的生活史中发挥重要作用,福建省九龙江从2009年起,暴发多次拟多甲藻水华事件。采用显微镜观察和单细胞PCR技术,对九龙江西陂库区2012—2013年不同月份沉积物中的甲藻孢囊进行种属判定,并对甲藻孢囊的分布及其影响因素进行分析。结果表明,西陂库区沉积物中的甲藻孢囊主要为拟多甲藻属,约占80%,其次为裸甲藻属,发现了2009年水华的优势种佩式拟多甲藻(Peridiniopsis penardii)孢囊。库区沉积物中甲藻孢囊的丰度在(13.7±1.2)—(105.2±8.3)个/g干重之间。多元相关分析结果显示甲藻孢囊的丰度与含水率呈现显著正相关性(P0.05),反映了甲藻孢囊沿水流方向逐渐积累。本研究结果填补了国内水库甲藻孢囊鉴定和萌发的研究空白,为九龙江甲藻水华的防治提供科学参考。     

Relationship between planktonic dinoflagellate abundance, cysts recovered in sediment traps and environmental factors in the Gullmar Fjord, Sweden

In order to study the relationship between planktonic dinoflagellates,cyst production and environmental factors, a sediment trap studywas conducted in the Gullmar Fjord, Swedish west coast, during21 days in May–June 1998. Five locations for sedimenttraps were randomly selected every third day. The traps weremoored at the five locations and moved to new locations after3 days. At every location, a CTD depth profile was obtainedand water samples were collected for plankton, chlorophyll aand nutrient analysis. Meteorological and hydrographic datafor the period were obtained from continuous monitoring. Threedinoflagellate species, which have not previously been recordedfrom the Kattegat or the Skagerrak (Scrippsiella crystallina,Scrippsiella lachrymosa and Scrippsiella trifida), were encounteredduring the analysis of cysts from the sediment traps. The abundanceof the different species in the motile form encountered in thewater column and cyst form encountered in the sediment trapsvaried greatly. The discrepancy between the number and speciesencountered in traps and water samples is discussed. No density-dependentrelationship between the abundance of planktonic cyst-formingdinoflagellates and the number of cysts recovered could be observed.A multiple regression showed that the variation in cyst yieldfrom the traps for the most abundant species was correlatedwith water surface temperature, ambient light radiation andthe depth of the halocline. The nutrient concentrations (NH₄⁺,NO₂^–, NO₃^– and PO₄^3–), which are known toplay a crucial role in induction of sexuality and cyst formationunder laboratory conditions, correlated poorly with the numberof dinoflagellate cysts encountered in the traps.     

ISLANDINIUM BREVISPINOSUM SP. NOV. (DINOFLAGELLATA), A NEW ORGANIC‐WALLED DINOFLAGELLATE CYST FROM MODERN ESTUARINE SEDIMENTS OF NEW ENGLAND (USA)1

Modern estuarine environments remain underexplored for dinoflagellate cysts, despite a rapidly increasing knowledge of cyst distributions in open marine sediments. A study of modern estuarine sediments in New England has revealed the presence of Islandinium brevispinosum sp. nov., a new organic‐walled dinoflagellate cyst that is locally common and probably of heterotrophic affinity. Resistance of this cyst to standard palynological processing indicates its geological preservability, although fossils are not yet known. Previously assigned species of the genus Islandinium are characteristic of polar and subpolar environments today and cold paleoenvironments in the Quaternary. The present record of I. brevispinosum extends the ecological and geographical range of this genus into the warm temperate zone, where I. brevispinosum occupies specific environments with reduced salinities and elevated nutrient levels.     

Biodiversity and Association of Dinoflagellates in Coral Reef Rubble,Carrie Bow Cay,Belize

The species diversity and distribution of benthic dinoflagellates are illustrated from the back reef sand habitats at Carrie Bow Cay. Sand appears an ideal environment for nurturing a variety of species. Sand supported blooms of toxic, nontoxic, and parasitic assemblages of dinoflagellates. Morphology of dinoflagellates is illustrated in SEM and LM pictures; including the life cycle of a parasitic dinoflagellate's vegetative stage, sporogenetic stages, and the morphology of the feeding organelle. The feeding organelle of the primary dinoflagellate cysts is a hold fast and a peduncle‐like infestation tube, a ‘sucker organelle’, that inserts itself into copepod eggs. The parasitic dinoflagellate continues feeding on crustacean eggs since it is the only food source during vegetative cell division within the cyst. This is the first observation of the presence of parasitic dinoflagellates in shallow coral reef water. The study attempts to provide new knowledge on dinoflagellate associations and morphology of sand‐welling species in the microscopic food web of shallow warm tropical waters. Even, sand‐inhabiting invertebrates are not exempt from parasitic dinoflagellates.     

Alexandrium and Scrippsiella cyst viability and cytoplasmic fullness in a 60-cm sediment core from Sequim Bay,WA

Many marine protists produce a benthic resting stage during their life history. This non-motile cyst stage can either germinate near the sediment surface to provide the inoculum for subsequent blooms or, be buried by sediment deposits over time and entrained into the sedimentary record. Buried cysts can be resuspended into the water column by mixing events (e.g., storms) or other disturbances (e.g., dredging). It is not clear how long cysts can survive while buried in the sediments and still be capable of germinating given favorable conditions. Here, the germination success of cysts produced by the potentially toxic dinoflagellate genus Alexandrium and the non-toxic dinoflagellate genus Scrippsiella is reported from a 60-cm sediment core collected in Sequim Bay, WA, in December 2011. Cysts of Alexandrium spp. and Scrippsiella spp. were isolated from 2-cm sections of the core, placed in individual wells of a 96-well plate with growth medium, imaged, incubated at favorable conditions and monitored for germination. An image analysis program, DinoCyst, was used to quantitatively measure the amount of granular storage products, presumed energy stores, inside the cytoplasm to test the hypothesis that older cysts located deeper in the sediment core will have fewer energy stores available and will be less likely to germinate. An index of the area of the cytoplasm occupied with granular storage products relative to cyst size, termed ‘cytoplasmic fullness’, and age, based on ²¹⁰Pb dating of surrounding sediments, was compared with germination success or failure. This research indicates that cysts of Alexandrium spp. and Scrippsiella spp. can remain viable in sediments for 60 years or longer, show little visual evidence of cytoplasmic deterioration over this timescale (as measured by cytoplasmic fullness), and that germination success is statistically similar for cysts isolated from 0–60 cm deep in the sediment core. These results suggest that a cyst's cytoplasmic fullness is not indicative of viability and that cysts located as deep as 60 cm in the sediments are as likely to germinate as surface cysts given favorable conditions.     

First report of fossilized cysts produced by the benthic Bysmatrum subsalsum (Dinophyceae) from a shallow Mexican lagoon in the Gulf of Mexico

Cysts belonging to the benthic dinoflagellate Bysmatrum subsalsum were recovered from palynologically treated sediments collected in the Alvarado Lagoon (southwestern Gulf of Mexico). The cysts are proximate, reflecting the features of the parent thecal stage, and their autofluorescence implies a dinosporin composition similar to the cyst walls of phototrophic species. This finding is important for our understanding of B. subsalsum life cycle transitions and ecology. Encystment may play an important role in the bloom dynamics of this species as it can enable the formation of a sediment cyst bank that allows reinoculation of the water column when conditions become favorable. This is the first report of a fossilized cyst produced by a benthic dinoflagellate recovered from sub‐recent sediments.