Central Arctic Ocean paleoceanographic interpretations based on Late Cenozoic calcareous dinoflagellates

Four calcareous dinoflagellate morphotypes, interpreted to represent a single species, Thoracosphaera arctica n. sp., occur in upper Miocene to Holocene sediments of the central Arctic Ocean. The calcareous fossils generally are rare except during one interval, that of the latest Pliocene to late Pleistocene. During this interval the fossil dinoflagellates were alternately abundant and rare in approximate coordination with greater and lesser times of foraminifera productivity. Dinoflagellates and foraminifera generally are rare during times of accumulation of abundant coarse textured ice-rafted sediment during this interval.The life cycle of the dinoflagellate that produces the Arctic Ocean calcareous fossil is unknown but the fossils probably are either resting cysts, motile vegetative cells or hypnozygotes. A vegetative cell origin better explains the co-occurrence of foraminifera as well as the negative correlation with ice-rafting. This tentative interpretation leads to the conclusion that during the interval 2.0 to 0.7 m.y. b.p., the Arctic Ocean had relatively productive surface waters with very thin or even periodic absence of pack-ice alternating with conditions more like that of the present. During periods before 2.0 m.y. and since 0.7 m.y., the Arctic Ocean probably was ice-covered, with oceanographic conditions similar to that of the modern ocean. These conclusions differ from previous interpretations that the Arctic was continually ice-covered, had no surface productivity or was covered by a giant, Antarctic-like ice-cap.     

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.     

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.     

Calcareous dinoflagellate cysts in South and equatorial Atlantic surface sediments: diversity,distribution, ecology and potential for palaeoenvironmental reconstruction

Several marine, peridiniphycidean dinoflagellate species produce calcareous cysts during their life cycle, which are relatively resistant to chemical and physical degradation and are therefore often found in large quantities in oceanic bottom sediments. Although the use of these calcareous cysts as proxies for palaeoenvironmental and palaeoclimatic reconstructions has seen many advances over the last decade, until now only relatively patchy and regional information was available on their recent distribution patterns and ecology, especially at the species level. In this paper, comprehensive calcareous cyst diversity and distribution data have been compiled from published and unpublished work for 167 South and equatorial Atlantic Ocean surface sediments, ranging from 20°N to 50°S, and 30°E to 65°W. The main aim has been to focus on the complex, often non-linear, relationships between individual species’ distributions and the physicochemical and trophic conditions of the overlying (sub)surface waters through the use of x–y graphs of cyst abundance vs. (sub)surface water environmental parameters, and detrended correspondence analyses. Ten cyst species and the calcareous vegetative coccoid species Thoracosphaera heimii were observed in the bottom sediments, each species showing its own characteristic distribution pattern in relation to the environmental conditions of the upper water masses above them (e.g. sea surface temperature, productivity, stratification). The sensitive reactions of various species to unique combinations of environmental parameters shows that each species has its own specific ecological traits, thus rejecting the bundled use of ‘calcareous cyst accumulation’ as a general proxy for oligotrophy or stratification in future palaeoenvironmental analyses. The acquired ‘reference’ data set of this study is large and diverse enough to allow its future application in quantitative palaeoenvironmental reconstruction models, and shows that there is still an enormous reconstruction potential concealed in many fossil calcareous dinoflagellate cyst assemblages.     

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.     

Late Albian dinoflagellate cyst paleobiogeography as indicator of asymmetric sea surface temperature gradient on both hemispheres with southern high latitudes warmer than northern ones

Late Albian temperature sensitive dinoflagellate cysts are characterized in order to better understand mid-Cretaceous sea surface temperature gradients. Distribution maps of thirty-seven species recovered from one hundred fifty outcrops and deep sea drilling holes (ODP, DSDP) Sites located from low and high paleolatitudes over the two hemispheres (75°N–70°S) are encountered. Fifty years of published data available in eighty-seven articles have been considered and synthesized using a database coupled with a Geographical Information System (GIS). The continuous and disjoint biogeographic patterns of dinocyst species along latitudes define seven climatic belts, four in the northern hemisphere (high, mid-high, mid-low, low latitude belts) and three in the southern hemisphere (low, mid-low, mid-high latitude belts). Dinocysts restricted along latitudes are temperature sensitive species. Limit ranges of temperature sensitive dinocysts of mid-low and mid-high latitude belts reveal mixing belts, located at 40–45°N and 50°–70°S. They represent major palaeofrontal systems as paleosubtropical fronts with strongly mixed water column. The northern frontal system (40–45°N) was located as in the modern ocean. The large southern frontal system (50°S–70°S) was 10°–20° poleward to Antarctica. Semi-quantitative temperature range limits for mid-Cretaceous dinoflagellates and SST gradients in the two hemispheres are suggested by setting dinocyst climatic belts against estimated δ¹⁸O temperature curve from fish teeth. A paleoecological classification is suggested. Latitudinal distribution of extant temperature sensitive dinoflagellate cysts follows the asymmetric modern temperature gradient. Asymmetric latitudinal ranges of Late Albian dinocyst species of mid-low latitude belts restricted between 45°N and 70°S demonstrate asymmetric temperature gradients with southern high latitudes being warmer than northern high latitudes.     

Cyst formation,sedimentation, and preservation: Factors affecting dinoflagellate assemblages in recent sediments from trondheimsfjord,Norway

Plankton records and 25 samples of Recent sediment from Trondheimsfjord and the adjoining shelf were studied to investigate production, sedimentation, and preservation of cysts, as factors which influence the eventual composition of dinoflagellate cyst assembleges. All sediment samples were examined for dinoflagellate cysts using routine semiquantitative palynological procedures. In addition, fjord sediments were subjected to a limited sediment analysis, and, for three samples, results from preparations both with and without acid treatments were compared. For the first time, cyst assembleges from Recent sediments were directly compared with extensive plankton records from overlying waters. Results indicate that approximately 20% of the 55 locally recorded dinoflagellate species contribute cysts to bottom sediments. Once formed, cysts behave as fine silt particles in the sedimentary regime, increasing in abundance as the percentage abundance of finer sediment increases, usually with increased water depth. Cyst-forming species are almost entirely restricted to a few genera, particularly Gonyaulax and Peridinium, within the order Peridiniales. For some groups, reasonably good correspondence was found between percentage abundances of dinoflagellates in plankton and their cysts in sediment, though plankton records covering at least five years were required to establish this. Gonyaulax grindleyi Reinecke (Von Stosch 1969) appeared to be consistently overrepresented by cysts in sediment relative to available plankton evidence; possible explanations are suggested. At least 30% of the cyst species present, including most Peridinium species, were eliminated, or rendered unreliable for semiquantitative palynology, by application of routine palynological preparation treatments. Such cysts may provide useful, non-quantitative, palynological information from Recent and possibly Quaternary sediments, but their persistence would seem unlikely. Thus, factors of preservation probably further restrict the dinoflagellate fossil record. Cyst assemblages from Trondheimsfjord are comparable with those previously recorded from the northeastern coast of U.S.A., and from Scotland and northeastern England. Fjord assemblages are dominated by small, simple, spinose cysts which would be regarded as acritarchs if culture experiments had not proved that they are dinoflagellate cysts. Much potential biogeographic and palaeoenvironmental information was included within the less abundant species.Attention is drawn to the role which future culture experiments may be expected to play in helping to resolve taxonomic difficulties currently affecting dinoflagellate studies. Palynological significance of results from the present study is discussed especially with reference to recent work by Von Stosch which strongly suggests that cysts may be hypnozygotes formed routinely in sexual cycles of dinoflagellates.     

The (palaeo) environmental significance of modern calcareous dinoflagellate cysts: a review

Increased interest in the environmental applicability of calcareous dinoflagellate cysts for palaeo-environmental studies arose in the last two decades, when it was discovered that they constitute a widespread and abundant group within the calcareous phytoplankton. As primary producers they are directly influenced by environmental Parameters of the surrounding water masses, and therefore extremely suitable for detailed palaeo-environmental and -oceanographical reconstructions. During the last years, detailed investigations on their distribution in surface sediments of the South Atlantic Ocean, the Mediterranean Sea and the Arabian Sea were carried out, in order to reveal which environmental parameters influence their distribution. This, in turn, formed the base for palaeo-environmental and -oceanographical reconstructions. The compilation of the available data on calcareous dinoflagellate ecology, morphology, taxonomy and palaeo-environmental application presented here demonstrates their ample application potential as palaeo-environmental tools.      

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.     

Allochthonous inputs of riverine picocyanobacteria to coastal waters in the Arctic Ocean

The observed onset of climate change at high northern latitudes has highlighted the need to establish current baseline conditions in the Arctic Ocean, and has raised concern about the potential for the invasion and growth of biota that have warm temperature optima, such as cyanobacteria. In this study, we used 16S rRNA gene sequences as a molecular marker to evaluate the hypothesis that Arctic rivers provide a major inoculum of cyanobacteria into the coastal Arctic Ocean. Surface samples were collected along a transect extending from the Mackenzie River (Northwest Territories, Canada), across its estuary, to 200 km offshore at the edge of the perennial Arctic pack ice (Beaufort Sea). The highest picocyanobacteria concentrations occurred in the river, with concentrations an order of magnitude lower at offshore marine stations. The 16S rRNA gene clone libraries of five surface samples and five strains along this gradient showed that the cyanobacterial sequences were divided into eight operational taxonomic units (OTUs), six OTUs closely related to freshwater and brackish Synechococcus and two OTUs of filamentous cyanobacteria. No typically marine Synechococcus sequences and no Prochlorococcus sequences were recovered. These results are consistent with the hypothesis of an allochthonous origin of picocyanobacteria in the coastal Arctic Ocean, and imply survival but little net growth of picocyanobacteria under the present conditions in northern high-latitude seas.     

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.     

The Effects of Temperature, Nitrogen, and Phosphorus on the Encystment of Peridinium cinctum, Stein (Dinophyta)

For avoiding the unfavorable environmental conditions several aquatic microorganisms are capable of forming specialized resistance cells like akinets, hypnospores, statospores, etc. Recognition of the important role of cysts in the life cycles of dinoflagellates increased the need to study their role in the ecology of phytoplanktons, and this, combined with the knowledge of chemical and biological characteristics of the water, may lead to a better understanding of the spatial and temporal dynamics of dinoflagellates. This paper reports on the effects of temperature, nitrogen, and phosphorus on the percentage of encystment of the dinoflagellate Peridinum cinctum Stein. The phosphorus content of the medium affected encystment only at the highest temperature applied (22 °C). Nitrogen content and temperature were the most important factors controlling the encystment.     

有害甲藻孢囊的分类鉴定研究进展

有害甲藻孢囊主要是指能产生毒素和(或)能引起有害藻华发生并对水生态系统产生各种危害效应的甲藻孢囊。我国沿海共记录了10属18种,占全球有害甲藻孢囊的3/4。这些有害甲藻孢囊广泛分布于我国沿海,会对水产养殖业造成严重的经济损失,甚至会威胁人类的身体健康。因此,有害甲藻孢囊的多样性及分布越来越受到人们的关注。对有害甲藻孢囊的准确判断不仅对研究其多样性及分布至关重要,而且有助于水产品的安全检验和有害藻华的早期预警。对有害甲藻孢囊的分类主要存在鉴定困难、鉴定不准确等问题。本文综述了有害甲藻孢囊的危害、中国沿海有害甲藻孢囊的种类和分布,以及有害甲藻孢囊的鉴定等3个方面的研究进展,并提出利用孢囊及营养细胞的形态学特征、分子生物学、毒理学等多学科研究手段准确鉴定有害甲藻孢囊的建议。     

The potential of organic-walled dinoflagellate cysts for the reconstruction of past sea-surface conditions in the Southern Ocean

In this study we investigate the potential of organic-walled dinoflagellate cysts (dinocysts) as tools for quantifying past sea-surface temperatures (SST) in the Southern Ocean. For this purpose, a dinocyst reference dataset has been formed, based on 138 surface sediment samples from different circum-Antarctic environments. The dinocyst assemblages of these samples are composed of phototrophic (gonyaulacoid) and heterotrophic (protoperidinioid) species that provide a broad spectrum of palaeoenvironmental information. The relationship between the environmental parameters in the upper water column and the dinocyst distribution patterns of individual species has been established using the statistical method of Canonical Correspondence Analysis (CCA). Among the variables tested, summer SST appeared to correspond to the maximum variance represented in the dataset.To establish quantitative summer SST reconstructions, a Modern Analogue Technique (MAT) has been performed on data from three Late Quaternary dinocyst records recovered from locations adjacent to prominent oceanic fronts in the Atlantic sector of the Southern Ocean. These dinocyst time series exhibit periodic changes in the dinocyst assemblage during the last two glacial/interglacial-cycles. During glacial conditions the relative abundance of protoperidinioid cysts was highest, whereas interglacial conditions are characterised by generally lower cyst concentrations and increased relative abundance of gonyaulacoid cysts. The MAT palaeotemperature estimates show trends in summer SST changes following the global oxygen isotope signal and a strong correlation with past temperatures of the last 140 000 years based on other proxies. However, by comparing the dinocyst results to quantitative estimates of summer SSTs based on diatoms, radiolarians and foraminifer-derived stable isotope records it can be shown that in several core intervals the dinocyst-based summer SSTs appeared to be extremely high. In these intervals the dinocyst record seems to be highly influenced by selective degradation, leading to unusual temperature ranges and to unrealistic palaeotemperatures. We used the selective degradation index (kt-index) to determine those intervals that have been biased by selective degradation in order to correct the palaeotemperature estimates. We show that after correction the dinocyst based SSTs correspond reasonably well with other palaeotemperature estimates for this region, supporting the great potential of dinoflagellate cysts as a basis for quantitative palaeoenvironmental studies.     

The potential of organic-walled dinoflagellate cysts for the reconstruction of past sea-surface conditions in the Southern Ocean

In this study we investigate the potential of organic-walled dinoflagellate cysts (dinocysts) as tools for quantifying past sea-surface temperatures (SST) in the Southern Ocean. For this purpose, a dinocyst reference dataset has been formed, based on 138 surface sediment samples from different circum-Antarctic environments. The dinocyst assemblages of these samples are composed of phototrophic (gonyaulacoid) and heterotrophic (protoperidinioid) species that provide a broad spectrum of palaeoenvironmental information. The relationship between the environmental parameters in the upper water column and the dinocyst distribution patterns of individual species has been established using the statistical method of Canonical Correspondence Analysis (CCA). Among the variables tested, summer SST appeared to correspond to the maximum variance represented in the dataset.To establish quantitative summer SST reconstructions, a Modern Analogue Technique (MAT) has been performed on data from three Late Quaternary dinocyst records recovered from locations adjacent to prominent oceanic fronts in the Atlantic sector of the Southern Ocean. These dinocyst time series exhibit periodic changes in the dinocyst assemblage during the last two glacial/interglacial-cycles. During glacial conditions the relative abundance of protoperidinioid cysts was highest, whereas interglacial conditions are characterised by generally lower cyst concentrations and increased relative abundance of gonyaulacoid cysts. The MAT palaeotemperature estimates show trends in summer SST changes following the global oxygen isotope signal and a strong correlation with past temperatures of the last 140 000 years based on other proxies. However, by comparing the dinocyst results to quantitative estimates of summer SSTs based on diatoms, radiolarians and foraminifer-derived stable isotope records it can be shown that in several core intervals the dinocyst-based summer SSTs appeared to be extremely high. In these intervals the dinocyst record seems to be highly influenced by selective degradation, leading to unusual temperature ranges and to unrealistic palaeotemperatures. We used the selective degradation index (kt-index) to determine those intervals that have been biased by selective degradation in order to correct the palaeotemperature estimates. We show that after correction the dinocyst based SSTs correspond reasonably well with other palaeotemperature estimates for this region, supporting the great potential of dinoflagellate cysts as a basis for quantitative palaeoenvironmental studies.     

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.     

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...     

Marine dinoflagellates show induced life-history shifts to escape parasite infection in response to water-borne signals

Many dinoflagellate species form dormant resting cysts as a part of their life cycle, and in some freshwater species, hatching of these cysts can be delayed by the presence of water-borne signals from grazing zooplankton. Some marine dinoflagellates can form temporary cysts, which may function to resist unfavourable short-term environmental conditions. We investigated whether the marine dinoflagellate Alexandrium ostenfeldii is able to induce an increased resistance to the parasitic flagellate Parvilucifera infectans by forming temporary cysts. We performed several laboratory experiments where dinoflagellates were exposed either to direct contact with parasites or to filtered water from cultures of parasite-infected conspecifics (parasite-derived signals). Infection by P. infectans is lethal to motile A. ostenfeldii cells, but temporary cysts were more resistant to parasite infection. Furthermore, A. ostenfeldii induced a shift in life-history stage (from motile cells to temporary cysts) when exposed to parasite-derived water-borne signals. The response was relaxed within a couple of hours, indicating that A. ostenfeldii may use this behaviour as a short-term escape mechanism to avoid parasite infection. The results suggest that intraspecies chemical communication evoked by biotic interactions can be an important mechanism controlling life-history shifts in marine dinoflagellates, which may have implications for the development of toxic algal blooms.     

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.     

Long‐standing environmental conditions,geographic isolation and host–symbiont specificity influence the relative ecological dominance and genetic diversification of coral endosymbionts in the genus Symbiodinium

Aim This study examines the importance of geographic proximity, host life history and regional and local differences in environment (temperature and water clarity) in driving the ecological and evolutionary processes underpinning the global patterns of diversity and distribution of symbiotic dinoflagellates. By comparing and contrasting coral–algal symbioses from isolated regions with differing environmental conditions, we may assess the potential of coral communities to respond to significant changes in climate. Location Indian Ocean. Methods Community assemblages of obligate symbiotic invertebrates were sampled at numerous sites from two regions, the north‐eastern Indian Ocean (Andaman Sea, western Thailand) and the western Indian Ocean (Zanzibar, Tanzania). Molecular genetic methods, including denaturing gradient gel electrophoresis analysis of the ribosomal internal transcribed spacers, DNA sequencing and microsatellite genotyping, were used to characterize the ‘species’ diversity and evolutionary relationships of symbiotic dinoflagellates (genus Symbiodinium). Host–symbiont specificity, geographic isolation and local and regional environmental factors were evaluated in terms of their importance in governing the distribution and prevalence of certain symbiont taxa. Results Host‐generalist symbionts (C3u and D1‐4, formerly D1a now designated Symbiodinium trenchi) frequently occurred alone and sometimes together in hosts with horizontal modes of symbiont acquisition. However, the majority of Symbiodinium diversity consisted of apparently host‐specific ‘species’. Clade C Symbiodinium were diverse and dominated host assemblages from sites sampled in the western Indian Ocean, a pattern analogous to symbiont communities on the Great Barrier Reef with similar environmental conditions. Clade D Symbiodinium were diverse and occurred frequently in hosts from the north‐eastern Indian Ocean, especially at inshore locations, where temperatures are warmer, water turbidity is high and large tidal exchanges commonly expose coral populations to aerial desiccation. Main conclusions Regional and local differences in cnidarian–algal combinations indicate that these symbioses are ecologically and evolutionarily responsive and can thrive under various environmental conditions. The high temperatures and turbid conditions of the north‐eastern Indian Ocean partly explain the ecological success of Clade D Symbiodinium relative to Clade C. Phylogenetic, ecological and population genetic data further indicate that Clade D has undergone an adaptive radiation, especially in regions around Southeast Asia, during the Pleistocene.