A recurrent and localized dinoflagellate bloom in a Mediterranean beach

A recurrent, prolonged and singular bloom of Alexandrium tayloriBalech in an open beach (La Fosca, Spain, NW Mediterranean)is described. Alexandrium taylori appears at several placesalong a wide area of the NW Mediterranean (Costa Brava) duringthe summer, reaching concentrations up to 10⁵ cells l^–1,but it only proliferates persistently, massively (densities>10⁶ cells l^–1) and recurrently during August in LaFosca beach. The A.taylori bloom can be considered a manifestationof large-scale proliferation in a restricted area, where couplingbetween resting cysts in the sediment and bloom outbreak isnot a major factor compared to the interaction of local environmentalconditions with the planktonic organism's life history. Fromobservations of environmental conditions (the environmentalwindow) and the multiscale spatio-temporal distributions andlife history of A.taylori, we describe the bloom dynamics andanswer some critical questions about the different phases ofthe bloom. Some of these answers are: (i) the source of theA.taylori population is widespread offshore and is not locateddirectly at the beach; (ii) high cell densities are reachedand maintained with a moderate in situ growth and low loss rates;(iii) temporary cysts act as a reserve of the population.     

Distribution, dynamics and in situ seeding potential of Scrippsiella hangoei (Dinophyceae) cyst populations from the Baltic Sea

The distribution and seasonal dynamics of cyst populations ofthe spring bloom dinoflagellate Scrippsiella hangoei were studiedin surface sediments on the southwest coast of Finland, BalticSea. In situ germination was assessed by monitoring the fractionof empty cysts and chlorophyll a fluorescence in cyst populationsat different coastal sites throughout the annual cycle. Scrippsiellahangoei resting cysts were widely distributed in the study areaand occurred in exceptionally large numbers (magnitudes of 10⁴–10⁶cysts cm^–3) at all sampling locations between the innermostparts of the coastal archipelago and the open Gulf of Finland.The decreases in cyst number in winter and the increases occurringin late spring reflected the dynamics of germination and encystmentof the species. Chlorophyll fluorescence appeared in mid-winterin ~40% of cysts from well-aerated basins and 6–15% ofcysts from temporarily anoxic sediments. A generally low increasein the proportion of empty cysts indicated that only a partof the potentially germinable cysts actually germinates. Giventhe high cyst concentrations in the sediments, the potentialfor germination is considerable, despite the environmentallyand physiologically determined losses. In contrast, the sizeof the vegetative inoculum is very low, indicating that thesurvival of germlings is problematic under harsh winter conditions.This is an unusual life cycle strategy; however, the early releaseof cells into the water column provides a high probability forsuccessful bloom initiation under the unpredictable meteorologicalconditions in winter and early spring, which often lead to thesudden onset of favourable growth conditions.     

Relationship between vegetative cells and cyst production during Alexandrium minutum bloom in Arenys de Mar harbour (NW Mediterranean)

A recurrent Alexandrium minutum bloom in the Arenys de Mar harbour(Catalan coast, North Western Mediterranean) was monitored inorder to establish the relationship between vegetative cellsand cyst production. The bloom lasted from January 21 to February24, 2002 and reached cell concentrations of up to 47 x 10⁶ cellL^–1. Two aspects related to the resting cysts depositionwere studied: (i) production of resting cysts during the bloomperiod (by means of sediment traps) and (ii) distribution ofresting cysts in the sediment after the bloom (May 2002). Cystformation in Arenys clearly started in a period with high vegetativecell densities in the water column. Once production was initiatedencystment fluxes remained constant for two weeks, and coveringthe periods of maintenance and decline of the bloom. High cystfluxes (up to 6000 cysts cm^–2 day^–1) were quantifiedas a result of the high vegetative cell concentration. Moreover,encystment occurring in less than 1% of the total populationindicates that most of the cells are not involved in restingcysts formation. A comparison of the resting cyst flux valuesobtained from the sediment traps and the resting cyst concentrationsin surface sediment (628–3270 cysts cm^–3) threemonths later, revealed that the number of cysts in the sedimentdecreased during that time. The studies of excystment showeda high germination percentage (91%) and germling viability (100%).These data, together with the resting cyst distribution in thesediment, are important in assessing the role of resting cystsin the bloom dynamics of A. minutum in confined waters.     

Coupling planktonic and benthic shifts during a bloom of Alexandrium catenella in southern Chile: Implications for bloom dynamics and recurrence

Cell abundances and distributions of Alexandrium catenella resting cysts in recent sediments were studied along time at two locations in the Chilean Inland Sea exposed to different oceanographic conditions: Low Bay, which is much more open to the ocean than the more interior and protected Ovalada Island. The bloom began in interior areas but maximum cyst concentrations were recorded in locations more open to the ocean, at the end of the Moraleda channel. Our results showed a time lapse of around 3 months from the bloom peak (planktonic population) until the number of resting cysts in the sediments reached a maximum. Three months later, less than 10% of the A. catenella cysts remained in the sediments. Maximum cyst numbers in the water column occurred one month after the planktonic peak, when no cells were present. The dinoflagellate assemblage at both study sites was dominated by heterotrophic cysts, except during the A. catenella bloom. CCA analyses of species composition and environmental factors indicated that the frequency of A. catenella blooms was associated with low temperatures, but not with salinity, chlorophyll a concentration, and predator presence (measured as clam biomass). However, resting cyst distribution was only related to cell abundance and location. The occurrence of A. catenella cysts was also associated with that of cysts from the toxic species Protoceratium reticulatum. By shedding light on the ecological requirements of A. catenella blooms, our observations support the relevance of encystment as a mechanism of bloom termination and show a very fast depletion of cysts from the sediments (<3 months), which suggest a small role for resting cyst deposits in the recurrence of A. catenella blooms in this area.     

Plankton distribution across a slope current-induced front in the southern Bay of Biscay

Relatively warm (12.50–12.75°C) and high-salinity[<35.640 practical salinity units (PSU)] water flowing eastwardwas detected at the shelf-break during a cruise carried Outin the southern Bay of Biscay in Spring 1987. The slope currentinduced the formation of a convergent front separating well-mixedoceanic waters from haline-stratified coastal waters. Very highconcentrations of dissolved oxygen (295 µmol kg^–1)and chlorophyll a(>4.5 mg m^–3) were found at the outeredge of the frontal boundary. Small autotrophic flagellatesdominated the phytoplankton community. Primary production peakedat the boundary region. Estimated phytoplankton growth ratesindicated that active growth was taking place, with lower turnovertimes integrated over the water column at the frontal station(2.5–5 days) than at coastal (1.5–2.8 days) or oceanic(1.5–3.5 days) stations. The lowest doubling times (1–2days) were calculated for surface frontal populations. Accumulationof zooplankton was also observed associated with the convergentphysical structure, although this relationship was less markedthan for phytoplankton. Copepods, mainly Paracalanus parvus,Acartia clausi and Oithona helgolandica, formed the bulk ofthe mesozooplankton biomass. Compatibility between the sizeof phytoplankton cells and copepod size spectra indicate highfood availability for these animals, particularly in the vicinityof the front. The distribution of fish eggs and fish larvaewas also coupled with the slope current-induced front. Sardinelarvae were more abundant at the coastal side of the front,whereas larval stages of blue whiting reached the highest densitiesat off-shelf stations. Larvae of lamellibranch molluscs andbryozoa were restricted to nearshore waters, as the frontalboundary prevented larval dispersion to the open ocean. Theresults presented in this paper suggest that the Iberian slopecurrent and its associated shelf-break frontal structure werecrucial in controlling phytoplankton primary production, activityof grazers, distribution of larvae of fishes and benthic invertebrates,and ultimately in determining the structure of the pelagic foodweb in the southern Bay of Biscay during the seasonal periodof vertical mixing.     

The effects of temperature, growth medium and darkness on excystment and growth of the toxic dinoflagellate Gymnodinium catenatum from northwest Spain

The chain-forming dinoflagellate Gynmodinium catenatum Grahamcauses recurrent outbreaks of paralytic shellfish poisoning(PSP) in the Galician Rias Bajas (northwest Spain). A sedimentsurvey in Ria de Vigo in April 1986 indicated that the highestconcentrations of cysts of this species were located in themiddle sections of the ria, with maximum abundance of 310 cystscm^–3. The effects of temperature, growth medium compositionand irradiance on the germination of laboratory-produced restingcysts were investigated. Newly formed cysts required very littletime for maturation, as excystment was possible within 2 weeksof encystment. Growth media did not affect germination success.In contrast, the excystment rate was retarded signifiantly indarkness. Germination was also strongly affected by temperature,with {small tilde}75% excystment success at 22–28°Cand little or no germination below 11°C after 1 month ofincubation. In culture, the optimum growth rate of vegetativecells was between 22 and 28°C, the highest rate being 0.53divisions day^–1 at 24°C. Growth did not occur at temperatures< 11°C or >30°C. These results are important withrespect to the different hypotheses proposed to explain theinitiation of G.catenatum blooms in the Galician Rias Bajasand Northern Portugal. The pattern of G.catenatum bloom developmentalong this coast has been related to seasonal upwelling in thearea, with major blooms occurring during the autumn as warmeroffshore surface water is transported towards the coast whenupwelling relaxes. The landward transport of established offshorepopulations of G.catenatum with the warm surface layer remainsa viable explanation for the observed blooms within the rias,but alternatively, our data suggest that cysts within the riascan provide the inoculum population at times conducive to growthand bloom formation. Even though newly formed G.catenatum cystshave a very short maturation time and can germinate in darknessacross a wide temperature range, bloom development will be significantonly during the late summer and early autumn, since in othermonths light levels at the sediment surface and temperaturesthroughout the water column are too low for significant germinationor growth.     

Productivity, photosynthetic pigments and hydrology in the coastal front of the Eastern English Channel

In the French area of the Eastern English Channel, the coastalwaters 3 or 4 miles wide are separated from offshore watersby a coastal front. The phytoplanktonic biomass (B) and production(P) are higher in coastal waters, and an increase of biomasshas been observed at the interface. This frontal biomass, lessproductive, resulted from hydrodynamic accumulation, not dueto local growth. The productivity (P/B) deficit (50%) spreadsover the external area of the front, probably because the biomassis partly constituted of exported inactive coastal phytoplankton.The productivity is higher again in offshore waters. The variationof the pigment pool indicates a stress on phytoplankton in thefront and this ergocline was not productive at the time of thetwo cruises.     

Species diversity and abundance of dinoflagellate resting cysts seven months after a bloom of Alexandrium catenella in two contrasting coastal systems of the Chilean Inland Sea

In Chile, 90% of the fish farms and major natural shellfish beds are located in the region surrounding the Inland Sea, where over the last few decades harmful phytoplankton blooms have often been observed. The onset and recurrence of bloom events are often related to the resuspension and germination of resting cysts that have accumulated in the sediments. The degree of cyst settling, accumulation and germination is highly variable between areas and depends on physical and environmental factors. To learn how differences in oceanographic exposure, amount of river runoff and bathymetry affect dinoflagellate cyst deposition, we examined the diversity and abundance of dinoflagellate resting cysts from two hydrographically contrasting coastal areas (oceanic Guaitecas Archipelago and estuarine Pitipalena Fjord) of the Chilean Inland Sea in September 2006, seven months after a bloom of Alexandrium catenella, a producer of paralytic shellfish toxin. Cyst species diversity consisted of 18 taxa, including A. catenella and the noxious species Protoceratium reticulatum, both of which have caused blooms in the study area. Our results revealed significant differences between the two study sites in terms of the abundance and diversity of resting cysts, suggesting that in the specific case of A. catenella, only Guaitecas stations have potential for cyst accumulation and successful growth of cells. However, there was no evidence of long-term resting cyst beds of A. catenella at either study site.     

Factors regulating germination of resting cysts of the spring bloom dinoflagellate Scrippsiella hangoei from the northern Baltic Sea

The role of cyst germination as a factor in bloom initiationwas investigated for the dinoflagellate Scrippsiella hangoei(Schiller) Larsen from the northern Baltic Sea. This speciesblooms in very cold, often ice-covered waters, and is responsiblefor a significant fraction of the production in that region.Dormancy, temperature, oxygen and light were studied as factorspotentially controlling the germination of S.hangoei restingcysts. Laboratory-stored and field-collected cysts began togerminate in December following a mandatory dormancy periodlasting 6 months. Germination after this maturation intervalwas maximal when temperatures were within a 0–9°C‘window’. Mandatory dormancy is therefore the primaryfactor regulating the timing of germination in this species,as temperatures in the natural environment normally fall withinthis range at the time when S.hangoei cysts deposited the precedingyear have matured. Non-optimal temperatures, darkness and lowoxygen conditions all maintain a state of quiescence in thecysts. Cysts could germinate in darkness, but the rate of excystmentwas significantly higher in the light. Likewise, excystmentwas completely inhibited in anoxic conditions and was reducedunder severe hypoxia, with normal germination under moderatehypoxic concentrations. Temporary exposure to high sulfide concentrationspermanently reduced germination potential, indicating that S.hangoeicysts have low resistance to oxygen deficiency. Prolonged periodsof anoxia at the sediment surface, as frequently occurs in thestudy area, might reduce the size of the viable cyst pool andthus, alter the magnitude of the inoculum for S.hangoei bloominitiation. Together, these internal and external regulatoryfactors play important roles in the bloom dynamics of this importantdinoflagellate.     

Dynamics of Alexandrium fundyense blooms and shellfish toxicity in the Nauset Marsh System of Cape Cod (Massachusetts,USA)

Paralytic Shellfish Poisoning (PSP) toxins are annually recurrent along the Massachusetts coastline (USA), which includes many small embayments and salt ponds. Among these is the Nauset Marsh System (NMS), which has a long history of PSP toxicity. Little is known, however, about the bloom dynamics of the causative organism Alexandrium fundyense within that economically and socially important system. The overall goal of this work was to characterize the distribution and dynamics of A. fundyense blooms within the NMS and adjacent coastal waters by documenting the distribution and abundance of resting cysts and vegetative cells. Cysts were found predominantly in three drowned kettle holes or salt ponds at the distal ends of the NMS – Salt Pond, Mill Pond, and Town Cove. The central region of the NMS had a much lower concentration of cysts. Two types of A. fundyense blooms were observed. One originated entirely within the estuary, seeded by cysts in the three seedbeds. These blooms developed independently of each other and of the A. fundyense population observed in adjacent coastal waters outside the NMS. The temporal development of the blooms was different in the three salt ponds, with initiation differing by as much as 30 days. These differences do not appear to reflect the initial cyst abundances in these locations, and may simply result from higher cell retention and higher nutrient concentrations in Mill Pond, the first site to bloom. Germination of cysts accounted for a small percentage of the peak cell densities in the ponds, so population size was influenced more by the factors affecting growth than by cyst abundance. Subsurface cell aggregation (surface avoidance) limited advection of the vegetative A. fundyense cells out of the salt ponds through the shallow inlet channels. Thus, the upper reaches of the NMS are at the greatest risk for PSP since the highest cyst abundances and cell concentrations were found there. After these localized blooms in the salt ponds peaked and declined, a second, late season bloom occurred within the central portions of the NMS. The timing of this second bloom relative to those within the salt ponds and the coastal circulation patterns at that time strongly suggest that those cells originated from a regional A. fundyense bloom in the Gulf of Maine, delivered to the central marsh from coastal waters outside the NMS through Nauset Inlet. These results will guide policy decisions about water quality as well as shellfish monitoring and utilization within the NMS and highlight the potential for “surgical” closures of shellfish during PSP events, leaving some areas open for harvesting while others are closed.     

Gymnodinium catenatum Graham (Dinophyceae)in Europe: a growing problem?

The microreticulate resting cyst of the potentially toxic, chain-forming,unarmoured neritic dinoflagellate Gymnodinium catenalum Graham1943. the planktonic stage of which is not known from NorthEuropean waters, is reported for the first time from recentGerman coastal sediments of the North Sea and Baltic Sea. Insandy mud sediments of the German Bight, a maximum of 8 5 livingcysts cm^–3 were found. In Kiel Bight sediments G.catenalumwas found in maximum concentrations of 17.0 living cysts cm^–3.In surface waters of the German Bight resuspended G catenatumcysts were observed at concentrations of up to 3.6 cysts l^–1.Successful germination experiments conducted with natural seawatershow that the occurrence of a vegetative form of G.catenatumin northern Europe is very likely. The present study highlightsthat cyst surveys provide an important tool for the evaluationof areas with potential toxicity problems, as they may indicatethe presence of hitherto overlooked species in the water column.     

Zooplankton diversity and the predatory impact by larval and small juvenile fish at the Fisher Banks in the North Sea

The biomass and diversity of the mesozooplankton and fish larvaecommunity were investigated across a frontal zone in the centralNorth Sea in the early summer, to investigate whether larvalfish predation is a regulator of mesozooplankton production.Pronounced changes in the mesozooplankton community were observedacross the front off the Jutlandic coast. The biomass and thediversity of copepods changed across the front as the populationof Calanus finmarchicus became abundant in the deeper water.The crustaceans (Acartia spp. and Evadne spp.) and polychaetelarvae dominated the mesozooplankton in the coastal water. Thebiomass of fish larvae was dominated by gadoid larvae. As inthe copepods, a shift in fish diversity was observed in thefrontal zone. On the coastal side of the front, whiting (Merlangiusmerlangus) dominated the biomass, while offshore from the frontwhiting were absent and cod (Gadus morhua) was the dominantlarval fish species on the deeper stations. The present investigationdemonstrates two different trophic pathways related to hydrographyin the central North Sea. First, in the shallow coastal water,the abundant small neritic copepods are predominately predatedby whiting, while in the offshore region the larger oceaniccopepods are predated by cod larvae. However, the predationpressure by the fish larvae was in general low (<10%) relativeto copepod production per day. Consequently, in the early summer,the copepod production potentially results in a build-up ofcopepod biomass on both sides of the front.     

Picoplankton community structure at a coastal front region in the northern part of the South China Sea

Abundances of picoplankton groups were determined by flow cytometryin the Northern South China Sea (SCS) in winter 2004 to studythe dynamics of picoplankton at a coastal front region. Prochlorococcusis more abundant in relatively high temperature and salinitywaters than in nearshore area. Heterotrophic bacteria dominatein total picoplanktonic biomass but keep rather stable in biomassand surface/bottom biomass ratio on both sides of the front.Increases of picophytoplanktonic biomass and their surface/bottombiomass ratio are remarkable mainly owing to the contributionof Synechococcus on the offshore open SCS waters. Temperatureis found to limit the growth of Synechococcus and Prochlorococcus.Picoeukaryotes and heterotrophic bacteria are less sensitiveto the change in hydrographic conditions across the front. Theautotrophic/heterotrophic biomass ratio of picoplankton is lowerin eutrophic coastal waters on the nearshore side relative tothe offshore and oligotrophic open SCS.     

Life history,excystment features,and growth characteristics of the Mediterranean harmful dinoflagellate Alexandrium pseudogonyaulax

Studies considering the biology and ecology of the toxic bloom‐forming species, Alexandrium pseudogonyaulax, are rare. Our results highlight five features not described before in A. pseudogonyaulax life cycle: (i) A. pseudogonyaulax gametes showed two modes of conjugation, anisogamy and isogamy, (ii) sexual conjugation occurs either in the dark or in the light phase by engulfment or a fusion process, (iii) the presence of planozygote and newly formed cysts in monoclonal culture suggests homothallism, (iv) newly formed cysts have very dark vesicular content and are mostly unparatabulated when observed under light microscope and (v) natural resting cysts are able to give either a planomeiocyte or two vegetative cells. Cyst viability was enhanced after 5 months of cold storage (4°C), with excystment rate reaching 97% after 3 d of incubation. Excystment rate was highest (43%–79%) in Enriched Natural Sea Water diluted culture medium, whereas few germling cells were able to survive without the culture medium (0%–13%). Salinity‐irradiance experiments revealed that the highest cell concentrations occur at high irradiances for all the tested salinities. Vegetative growth rates generally increased with increasing irradiance, and were less dependent on salinity variations. The relatively low growth rate, low cell densities in the laboratory, and the notable capacity of producing cysts along growth phases of A. pseudogonyaulax could explain the occurrence of high resting cysts densities in the sediment of Bizerte lagoon and the relatively low abundances of vegetative cells in the water column.     

Development of the diatom-Phaeocystis spring bloom in the Dutch coastal zone of the North Sea: the silicon depletion versus the daily irradiance threshold hypothesis

The Dutch coastal zone of the North Sea is characterized byhigh nutrient inputs and low water column irradiance due tohigh concentrations of suspended matter. The vernal phytoplanktonblooms are dominated by diatoms and the flagellate Phaeocystis(Haptophyta). Two hypotheses that predict the timing of thePhaeocystzs bloom were tested with field data collected in 1992.The first one, stating that the Phaeocystis bloom starts whensilicon has been depleted by a preceding diatom bloom, couldnot be bracketed with observations. The second hypothesis, predictingthat Phaeocysus blooms under nitrogen- and phosphorus-repleteconditions after a daily irradiance threshold has been passedcould be supported by field observations. Furthermore, it isshown that the Dutch coastal zone is not continuously homogeneouslymixed. It is argued that this is an important factor in thelife cycle of Phaeocystis and in foam formation on nearby shores.Grazing by the ciliate Strombidium sulcatum and heterotrophicgymnodinoid flagellates accounted for 92% of Phaeocystis cellloss after the bloom.     

Effects of dinoflagellate bioluminescence on the ingestion rates of herbivorous zooplankton

Ingestion rates of Acartiatonsa (Dana) on highly luminescent cultures of Gonyaulax excavata (Braarud) Balech are reduced by 50–75% relative to cultures with low capacity for luminescence. The effect is particularly noticeable at high cell concentrations. It is suggested that the dense array of flashes surrounding an animal disrupts its swimming and/or feeding patterns. The activity of Acartia clausi at a density of 1 animal/3 ml stimulates 1.1% of the cells' capacity for luminescence each minute. Pseudocalanus minutus stimulates only 0.03% per min, except in rare cases where the animals appear to be much more active. Cirripede and copepod nauplii never stimulate any emission. Favorable conditions for bioluminescence may arise before or during a bloom, and the consequent reduction in grazing may contribute to maintenance of the bloom. Natural concentrations of zooplanktonic organisms cannot exhaust the bioluminescence of healthy Gonyaulax excavata cells.     

Growth and decline of a diatom spring bloom phytoplankton species composition, formation of marine snow and the role of heterotrophic dinoflagellates

During the spring of 1994, we determined the factors responsiblefor the decline of the seasonal diatom bloom in the Gullmarfjord, on the west coast of Sweden. Four species constituted>75% of the biomass—Detonula confervacea, Chaetocerosdiadema, Skeletonema costatum and Thalassiosira nordenskioeldii—reachingconcentrations of 4900, 350, 8200 and 270 cells ml^–1,respectively. Growth of phytoplankton was exponential (growthrate = 0.12 day^–1) from 3 to 21 March, after which a galewith winds >15 m s^–1 caused massive aggregation. Amaximum of 130 p.p.m. (v/v) of marine snow aggregates was observedby in situ video at the peak of the bloom. Critical concentrations(Jackson, Deep-Sea Res., 37, 1197–1211, 1990) were similarto observed showing that coagulation theory could explain thesudden decline of the bloom. The heterotrophic dinoflagellateGyrodinium cf. spirale increased exponentially after the peakof the bloom with maximum (temperature-adjusted) growth rates.After the rapid aggregation and sedimentation of the bloom,they were able to control any further growth of diatoms. Nitrateand silicate were never depleted, but phosphate may have beenlimiting by the end of the study period. We conclude that massaggregation during a gale marked the end of the bloom, and thatintense grazing by heterotrophic dinoflagellates prevented anysubsequent increase of diatoms.     

Aphanizomenon ovalisporum (Forti) in Lake Kinneret, Israel

The filamentous cyanobacterium Aphanizomenon ovalisporum wasobserved for the first time in Lake Kinneret in August 1994and formed a prominent bloom from September through October.Aphanizomenon ovalisporum reappeared in diminished amounts inthe summer and fall of 1995. These events are the first recordof significant quantities of a potentially toxic nitrogen-fixingcyanobacterium in this lake. No definite provenance of inoculumhas been identified, although A.ovalisporum was also observedin a newly reflooded area (Lake Agmon) in the catchment. Unusuallyhigh water temperatures and low wind inputs were observed priorto and during the A.ovalisporum bloom period. These, togetherwith possibly enhanced availability of phosphorus or other growthfactors, may have contributed to the cyanobacterium growth in1994. Phosphorus limi tation, as indicated by high cellularalkaline phosphatase activity, the onset of stormy conditionsand a fall in water temperatures led to the demise of the 1994bloom. Although the A. ovalisporum bloom in 1994 had no seriousdirect impact on water quality, the continued presence of apotentially toxic cyanobacterium in Lake Kinneret, a major nationalwater supply source, is a cause for serious concern.     

Presence of Gymnodinium catenatum (Dinophyceae) in a coastal Mediterranean lagoon

The occurrence and abundance of the toxic, chain-forming dinoflagellateGymnodinium catenatum in a Tyrrhenian coastal lagoon, the Fusaro,during an annual sampling cycle are reported. Peak abundanceswere observed from late spring until early autumn Although veryhigh cell numbers were recorded, up to 1 5 x 10⁶ cells l^–1,no monospecific bloom of this species occurred. The first observationof G.catenatum in the Mediterranean occurred in the Fusaro andthe appearance of this species in a traditional shellfish farmingarea, where no shellfish intoxication has been reported to date,is discussed in relation to human interventions in the basin.In particular, intensive dredging in recent years with resuspensionof bottom sediments may have seeded the water body with cysts.A Gymnodinium n d species, illustrated using scanning electronmicroscopy, caused a monospecific bloom in concomitance withmaximum abundances of G.catenatum, apparently outcompeting thislatter species     

Spatial heterogeneity and dynamics of vernal phytoplankton species in the Baltic Sea in April-May 1986

The mesoscale phytoplankton distribution was studied as partof an international joint Baltic Sea Patchiness Experiment (PEX'86)during April–May 1986 in the open Baltic Proper. The studyperiod covered the peak phase of the phytoplankton spring bloom.The spatio-temporal dynamics of four dominating phytoplanktonspecies, Achnanthes taeniata, Chaetoceros spp., Skeletonemacostatum and Thalassiosira levanderi were studied within anarea of 20x40 nmi with grids of 2 and 4 nmi spatial resolution.The results showed highly varying spatial distributions forall species, and the variability was accentuated on the synopticspace scale before the development of the seasonal thermocline.The maxima of Chaetoceros spp. and Thalassiosira levanderi coincidedwith the anticyclonic and cyclonic eddies prevailing in thearea. Skeletonema costatum was found in high abundances onlywithin a warmer water mass of higher salinity advecting intothe area. The results pointed out that different successionalstages can simultaneously be found even in adjacent water massesand both the phytoplankton growth and composition during thebloom peak phase in the Central Baltic depend on complex factors,mainly those connected with mesoscale hydrodynamic features(eddies, frontal zones, jet currents).