Anguilla rostrata glass eel migration and recruitment in the estuary and Gulf of St Lawrence

This study describes catches of Anguilla rostrata glass eels and associated oceanographic conditions in the St Lawrence Estuary and Gulf. Ichthyoplankton survey data suggest that they enter the Gulf primarily in May, migrate at the surface at night, and disperse broadly once they have passed Cabot Strait. They arrive in estuaries beginning at about mid-June and through the month of July. Migration extends west up to Québec City, in the freshwater zone of the St Lawrence Estuary, 1000 km west of Cabot Strait. Anguilla rostrata glass eels travel between Cabot Strait and receiving estuaries at a straight-line ground speed of c. 10–15 km day⁻¹. Catches of fish per unit effort in estuaries in the St Lawrence system are much lower than those reported for the Atlantic coast of Canada. Low abundance of A. rostrata glass eels in the St Lawrence system may be due to cold surface temperatures during the migration period which decrease swimming capacity, long distances from the spawning ground to Cabot Strait and from Cabot Strait to the destination waters (especially the St Lawrence River), complex circulation patterns, and hypoxic conditions in bottom waters of the Laurentian Channel and the St Lawrence Estuary.     

'St Martin's Summer': the case of an autumn phytoplankton bloom in the Gulf of Naples (Mediterranean Sea)

Phytopiankton abundance. species composition and primary productionof the Gulf of Naples were investigated during an autumn bloomin November 1985. Hydrographic data and surface phytoplanktonsamples were collected during a 3 day cruise, whereas investigationson in situ primary production and phytoplankton vertical distributionwere conducted from a second boat on three different dates.A coast-offshore gradient was recorded for most of the chemicaland biological parameters analysed. At stations closer to thecoast, which were affected by land run-off, phytoplankton populationsattained concentrations of 2.5 10⁶ cells l^–1 with amarked dominance of diatoms belonging to the genera Thalassiosiraand Chaetoceros. The most striking character of the system wasa remarkably high carbon assimilation rate (up to 1.04 g C m^–2day^–2) at stations closer to the coast. The causativemechanism for this bloom appeared to be land-derived nutrientenrichment, possibly enhanced by autumn rains, followed by aperiod of favourable meteorological conditions, which occursrecurrently in the region for a brief period around November,known locally as ‘St Martin's Summer’. We hypothesizethat a similar mechanism can stimulate phytoplankton growthmore than once every year. since high-stability penods followingmeteoro logical perturbations can occur several times in temperateregions of the northern hemisphere in autumn.     

Green mass aggregations of Gyrodinium cf. aureolum Hulburt in the Ria of Pontevedra (north-west Spain)

In this paper we report a bloom of Gyrodinium cf. aureolum occurringin an estuary of the north-west coast of Spain. It was sampledin late August 1989, in shallow waters 2 m deep in the Ria ofPontevedra. Its temperature was 19.5°C and salinity 35     

An unusual bloom of Gyrodinium cf. aureolum in the Argentine sea: community structure and conditioning factors

In October 1988 a bloom of Gyrodinium cf. aureolum was recordedalong a transect across the continental shelf reaching celldensities of 1300 ml^–1 and chlorophyll a concentrationsup to 16 µg 1^–1. The bloom was restricted to a nutrient-richthin surface layer of 10 m depth at the beginning of seasonalpycnocline. Hydrological conditions showed a particular salinitydistribution. The phytoplankton community was dominated by G.cf. aureolum but the coexisting flora presented a great diversity.UV-absorbing pigments were recorded in the community.     

Temperature and salinity effect on growth and chemical composition of Gyrodinium aureolum Hulburt in culture

A factorial experiment shows highly significant effects of temperature(12 5–22.5°C) and salinity (17.8–34 S) on thegrowth rate of Gyrodinium aureolum, with a significant temperature-salinityinteraction. The maximum growth rate of G aureolum is measuredto 0.61 div. day^–1 at 20°C and 22.3 S. Gyrodiniumaureolum does not grow at temperatures :10 °C or 25°Cand at salinities 12 S. The cellular content of carbon (C) andnitrogen (N) and the elemental ratios N/C, P/C and N/P are significantlyaffected by the temperature The cellular content of phosphorus(P) and the elemental ratios P/C and N/P vary significantlywith salinity Significant temperature-salinity interactionsare found for the cellular content of carbon, nitrogen and phosphorus.Variations in the N/P ratio indicate that G.aureolum has a largestorage capacity for phosphorus It is suggested that temperatureis one important limiting factor in the initiation of bloomsof G.aureolum in north European waters.     

Immuno-flow cytometric identification and enumeration of the ichthyotoxic dinoflagellate Gyrodinium aureolum Hulburt in artificially mixed algal populations

Flow cytometric identification and enumeration of Gyrodiniumaureolum Hulburt (Dinophyceae) were performed in artiticiallymixed algal populations using direct immunofluorescence. Calibrationof the flow cytometer, performed with a mixed algal populationspiked with immuno-fluorescently labelled G.aureolum cells,showed that selection of target cells after analysis on greenand orange fluorescence can be done with a recovery of 91.8%[coefficient of variation (CV) = 0.09]. Other selection methodswere less good, with 67.4% (CV = 0.16) and 58.4% (CV = 0.43)recovery based on green and red fluorescence or green fluorescenceand perpendicular light scattering. For mixed algal populationsspiked with unlabelled G.aureolum cells, the quantificationof target cells was quite good (recovery of 76.7%; CV = 0.20).The percentage of total cell loss was high (58.0–92.0%),but this was caused mostly by loss of species smaller in sizethan G.aureolum. Estimates of the relative contribution of G.aureolumin labelled samples were therefore often far too high, but detectionand quantification were not affected. The methodological underestimation(23.3%) was partly caused by gating on green and orange fluorescence(inaccuracy 8.2%).     

Size-fractionated primary production studies in the vicinity of the Subtropical Front and an adjacent warm-core eddy south of Africa in austral winter

Results are presented of size-fractionated primary productionstudies conducted in the vicinity of the Subtropical Front (STF),an adjacent warm-core eddy, and in Sub-antarctic waters duringthe third South African Antarctic Marine Ecosystem Study (SAAMESIII) in austral winter (June/July) 1993. Throughout the investigation,total chlorophyll (Chl a) biomass and production were dominatedby small nano- and picophytoplankton. No distinct patterns intotal Chl a were evident. At stations (n = 7) occupied in thevicinity of the STF, total integrated biomass values rangedfrom 31 to 53 mg Chl a m^–2. In the vicinity of the eddy,integrated biomass at the eddy edge (n = 3) ranged from 24 to54 mg Chl a m^–2 and from 32 to 43 mg Chl a m^–2 inthe eddy (n = 2). At the station occupied in the Sub-antarcticwaters, total integrated biomass was 43 mg Chl a m^–2.Total daily integrated production was highest at stations occupiedin the vicinity of the STF and at the eddy edge. Here, totalintegrated production ranged from 150 to 423 mg C m^–2day^–1 and from 244 to 326mg C m^–2 day^–1, respectively.In the eddy centre, total integrated production varied between134 and 156 mg C m^–2 day^–1. At the station occupiedin the Sub-antarctic waters, the lowest integrated production(141 mg C m^–2 day^–1) during the entire survey wasrecorded. Availability of macronutrients did not appear to limittotal production. However, the low silicate concentrations duringthe survey may account for the predominance of small nano- andpicophytoplankton. Differences in production rates between theeddy edge and eddy core were related to water column stability.In contrast, at stations occupied in the vicinity of the STF,the control of phytoplankton production appears to be relatedto several processes, including water column stability and,possibly, iron availability.     

Copepod egg production, moulting and growth rates, and secondary production, in the Skagerrak in August 1988

Measurements of hydrography, chlorophyll, moulting rates ofjuvenile copepods and egg production rates of adult female copepodswere made at eight stations along a transect across the Skagerrak.The goals of the study were to determine (i) if there were correlationsbetween spatial variations in hydrography, phytoplankton andcopepod production rates, (ii) if copepod egg production rateswere correlated with juvenile growth rates, and (iii) if therewas evidence of food-niche separation among co-occumng femalecopepods The 200 km wide Skagerrak had a stratified water columnin the center and a mixed water column along the margins. Suchspatial variations should lead to a dominance of small phytoplanktoncells in the center and large cells along the margins; however,during our study blooms of Gyrodinium aureolum and Ceratium(three species) masked any locally driven differences in cellsize: 50% of chla was >11 µm, 5% in the 11–50µm fraction and 45% <50 µm. averaged for allstations. Chlorophyll ranged from 0.2 to 2.5 µg l^–1at most depths and stations. Specific growth rates of copepodsaveraged 0.10 day^–1 for adult females and 0.27 day^–1for juveniles The latter is similar to maximum rates known fromlaboratory studies, thus were probably not food-limited. Eggproduction rates were food-limited with the degree of limitationvarying among species: 75% of maximum for Centropages typicus, 50% for Calanus finmarchicus, 30% for Paracalanus parvus and 15% for Acartia longiremis and Temora longicornis. Thedegree of limitation was unrelated to female body size suggestingfood-niche separation among adults. Copepod production, summedover all species, ranged from 3 to 8 mg carbon m^–3day^–1and averaged 4.6 mg carbon m^–1 day^–1. Egg productionaccounted for 25% of the total.     

Spatial and temporal distribution of mesozooplankton in the Gulf of Aqaba and the northern Red Sea in February/March 1999

The distribution pattern, taxonomic composition and communitystructure of mesozooplankton was studied along a transect with10 positions between the Gulf of Aqaba and the northern RedSea. Five positions were resampled two or three times duringa cruise of RV ‘Meteor’ in February/March 1999.In spite of clear differences in the density stratificationbetween the Gulf of Aqaba and the northern Red Sea, the mesozooplanktoncomposition was very similar: Copepods were by far the mostabundant taxon, contributing 76–95% to the total community.The remainder was composed largely of ostracods, chaetognaths,appendicularians and molluscs. The mesozooplankton of the deeplymixed stations was homogeneously distributed, at all other stationsthe bulk of the mesozooplankton (>70%) was concentrated inthe mixed surface layer with peaks of calanoids, cyclopoidsand appendicularians in the vicinity of the chlorophyll a (Chla) maximum layer. Ostracods and poecilostomatoids dominatedthe layers below. Standing stocks within the total water column(550–1200 m) varied between 93 and 431 x 10³ individualsm^–2 for copepods and 5–76 x 10³ individuals m^–2for other mesozooplankton with highest numbers in the northernGulf of Aqaba, where vertical mixing was deep (400–500m) and Chl a and mesozooplankton distributions homogeneous throughoutthe water column. Towards the south, the mixed depth decreasedfrom 300 m in the central Gulf of Aqaba to 50 m in the Red Sea.Cluster analysis separated three distinct groups of stations,compounding the observed differences between the northern Gulfof Aqaba (Position I) and the other positions. The analysisalso revealed temporal differences between the February andMarch sections of the cruise, indicating the winter–springtransition. The stations sampled in March are characterisedby a higher total abundance and by a higher percentage of appendiculariansand ostracods than the stations sampled in February     

Species-specific phytoplankton sedimentation in relation to primary production along an inshore--offshore gradient in the Baltic Sea

The temporal and spatial variability in the quality and quantityof settling phytoplankton material in relation to concurrentprimary production was studied using sediment traps at threecoastal stations from a semi-enclosed bay (Pojo Bay) throughthe outer archipelago to the open Gulf of Finland. The fluxof settling phytoplankton was high (9.3 g C m^–2period^–1)in Pojo Bay, especially in spring, and lower in the archipelago(8.1 g C m^–2 period^–1) and open-sea area (5.2 gC m"2 period"1), although the primary production followed theopposite pattern. A large influx of allochthonous material intoPojo Bay in spring brought allochthonous phytoplankton cellsinto the traps, but limited primary production. Diatoms werethe most abundant settled phytoplankton at all stations, butthe species composition varied between Pojo Bay (Aulacoseiraspp., Rhizosolenia minima) and the outer stations (Skeletonemacostatum, Chaetoceros spp.)At the outer stations, migratingdinoflagellates (Peridiniella catenate) comprised part of thesettling material in spring. The high settling flux of the cyanophyteAphanizomenon flos-aquae is discussed. The species compositionof the phytoplankton assemblage influenced the proportion ofthe total organic carbon sedimentation that consisted of phytoplanktoncarbon.     

Photomovement and Photobleaching In Two Gyrodinium Species

The phototactic orientation in Gyrodinium dorsum and G. aureolumhas been analyzed. Both species show only positive phototaxiswith an optimum at about 300 W-m^–2. The mechanism of photoorientationdoes not seem to be based on a dichroic orientation of the photoreceptorpigments as in the flagellate Euglena gracilis. Photobleachingexperiments have shown a far higher resistance toward continuousirradiation at even high fluence rates than in other flagellateswhich is in good agreement with the exclusive behavior of positivephototaxis. (Received August 7, 1987; Accepted July 14, 1988)     

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.     

Observations on pigments and morphology of Gyrodinium aureolum Hulburt, a marine dinoflagellate containing 19' -hexanoyloxyfucoxanthin as the main carotenoid

Gyrodinium aureolum, a common "red tide" dinoflagellate in Europeanwaters often associated with fish mortality, was isolated fromthe Oslofjord, Norway, and analysed for chlorophylls and carotenoids.Besides chlorophyll a and c the following carotenoids were characterizedby thin-layer chromatography, visible light spectrophotometryand mass spectrometry: ß,-carotene, ß,ß-carotene,djatoxanthin, diadinoxanthin, 19'-hexanoyloxyfucoxanthin and3 xanthophylls which could not be correlated with hitherto structurallyknown carotenoids from dinoflagellates. G. aureolum deviatesfrom most dinoflagellates by the lack of peridinin, but showsaffinity with Gyrodinium sp.-A by the possession of 19'-hexanoyloxyfucoxanthin. Preliminary light microscopical observations on the internalstructure indicate that G. aureolum is uni-nucleate with a typicaldinokaryotic nucleus containing continually condensed chromosomes.The chloroplasts seem to possess an internal pyrenoid like someother dinoflagellates with deviating carotenoid pigmentation.The similarity in carotenoid pigmentation and chloroplast structureof Emiliania huxleyi (Prymnesiophyceae) and Gyrodinium sp.-Aand G.aureolum (Dinophyceae) is pointed out. The potential chemotaxonomicvalue of the carotenoid composition in establishing identitywith morphologically similar and ichthyotoxic dinoflagellatesis briefly discussed.     

Thalassiosira scotia, sp. nov.: observations on a phytoplankton increase in Early Austral Spring North of the Scotia Ridge

The dominant species in an early spring phytoplankton increasein characteristically antarctic waters north of South GeorgiaIsland is described as Thalassiosira scotia G. Fryx. et Hobanand compared to related species in the South Atlantic, suchas T. antarctica Comber and T. austratis Peragallo. Found ona cooperative US-Argentine cruise of the ISLAS ORCADAS 17–78,T. scotia dominated the phytoplankton in the well-mixed watercolumns of two stations more than 100 km apart. The maximumabu dance of the new species recorded in a discrete water samplewas about 315,000 cells/liter, with up to 18.4 x 10⁹ cells undera m² in the top 100 m, in spite of the fact that there was nowell-marked thennocline to aid in maintaining one water massand thus netaining the population in the euphotic zone. A fewresting spores were noted in one station. The water temperaturein the area was about 1°C, and the salinity 33.9 o/oo.     

Abundance and productivity of heterotrophic nanoplankton in Georgia coastal waters

The population abundances and rates of biomass production ofheterotrophic nanoplankton (HNAN) in Georgia coastal waterswere evaluated by epifluorescence microscopy. HNAN populations(mostly non-pigmented microflagellates <10 µm in diameter)ranged from 0.3 x 10³ cells ml^–1 in shelf waters 15 kmoffshore to 6.3 x 10³ cells ml^–1 in waters 0.25 km fromthe coast. There was a strong correlation (r = 0.83) betweenHNAN and free bacterioplankton population abundances, but noapparent relation (r = 0.38) between HNAN and phototrophic nanopLankton(PNAN) abundances. HNAN biomass production in estuarine andnearshore shelf waters, as estimated from increases in HNANpopulations during laboratory incubations of natural water samples,ranged from 0.10 to 0.79 mg C m^–3 h^–3, with populationgeneration times of 9.7 to 26.5 h. There was a significant linearrelation (r = 0.95) between HNAN biomass and HNAN productivity.We calculated that HNAN may graze at least 30% to 50% of dailybacterioplankton production in Georgia coastal waters.     

Diel variations in gut pigment content, diel vertical migration and estimates of grazing impact for copepods in the southern Benguela upwelling region in October 1987

The gut fluorescence technique was used to estimate ingestionand filtration rates of the adult female copepods Paracalanusparvus, Cenlropages brachiatus and Calanus austrails, and copepoditestages 3, 4 and 5 of C.australis in the southern Benguela upwellingregion. During the study period chlorophyll concentrations withinthe upper 20 m of the water column were high, 5 µg I^–1in mid-shelf waters and 15–30 µg I^–1 in innershelf waters. Copepod gut pigment content was low and constantduring the day then increased sharply during the first 2 h aftersunset. Gut pigment content was 2–6 times higher duringthe night compared with daytime values. Small non-migratingcopepods (Paracalanus parvus) showed the smallest diel differencein gut pigment content and large migrating copepods (Centropagesbrachiatus and Calanus australis) the largest difference. Eggproduction rates were 20 and 50% of maximum at the mid-shelfand inner shelf stations respectively, suggesting food-limitation.Comparison of ingestion rates calculated from egg productiondata with ingestion rates calculated from gut pigment data suggestedthat the copepods were feeding omnivorously at the inner shelfstations but herbivorously at the mid-shelf stations. Assumingthat all of the phytoplankton was available as food, the nearshorecopepod assemblage grazed {small tilde}1% of the standing cropeach day, and the mid-shelf assemblage grazed 5% day^–1.Because of errors and uncertainties associated with the gutfluorescence technique, the feeding impact could be underestimatedby 2–4-fold. We discuss several approaches which couldlead to more precise estimates of feeding rates. ³Present address: Marine Sciences, SUNY, Stony Brook, NY, 11794-5000,USA     

An immunofluorescent survey of the brown tide chrysophyte Aureococcus anophagefferens along the northeast coast of the United States

Surveys were conducted along the northeast coast of the USA.between Portsmouth, NH, and the Chesapeake Bay in 1988 and 1990,to determine the population distribution of Aureococcus anophagefferens,the chrysophyte responsible for massive and destructive ‘browntides’ in Long Island and Narragansett Bay beginning in1985. A species-specific immunofluorescent technique was usedto screen water samples, with positive identification possibleat cell concentrations as low as 10–20 cells ml^–1.Both years.A.anophagefferens was detected at numerous stationsin and around Long Island and Barnegat Bay, NJ, typically athigh cell concentrations. To the north and south of thus ‘center’,nearly half of the remaining stations were positive for A.anophagefferens,but the cells were always at very low cell concentrations. Manyof the positive identifications in areas distant from Long Islandwere in waters with no known history of harmful brown tides.The species was present in both open coastal and estuanne locations,in salinities between 18 and 32 practical salinity units (PSU).The observed population distributions apparently still reflectthe massive 1985 outbreak when this species first bloomed, giventhe number of positive locations and high abundance of A.anophagefferensin the immediate vicinity of Long Island. However, the frequentoccurrence of this species in waters far from this population‘center’ is disturbing. Aureococcus anophagefferensis more widely distributed than was previously thought. Numerousareas thus have the potential for destructive brown tides suchas those associated with the sudden appearance of the speciesin 1985.     

Temporal and spatial variation of plankton abundance in the Gulf of Carpentaria, Australia 1975-1977

The Gulf of Carpentaria is a large (ca. 3.7 x 10⁵ km²) shallow(<70 m) embayment in tropical northern Australia lying between11 and 17.5°S latitude. Although it contains a multi-speciespenaeid prawn fishery which is Australia's largest and mostvaluable fishery its hydrology and planktology are largely unknown.As a background to a study of the larval ecology of penaeidstocks, ten Gulf-wide survey cruises, sampling the planktonand hydrography, were undertaken over a twenty month periodfrom August 1975 to May 1977. Though comparisons with otherstudies are difficult because of variations in sampling techniquesand biomass estimation methods, the plankton biomass in theGulf of Carpentaria appears to be high by comparison with otherareas around Australia. The mean estimate over all stationsand all cruises of 77 mg/m³ dry weight (1880 mg/m²) compareswith the very high abundances found only in seasonal upwellingareas south of Java and off the northwest shelf of Australia.Further, the Gulf of Carpentaria standing stocks of planktoncompare with other coastal areas supporting important fisheriesoff the west coast of North America, the eastern North AtlanticOcean and some European waters. Because of its depth, relativelyhigh temperature and primary production rates, secondary productionrates are assumed to be high as well but as yet are unmeasured. ^*Microfiche of station list available upon request. CSIRO MarineLaboratories Reprint No. 1280     

Gene flow patterns of the euphausiid, Meganyctiphanes norvegica, in the NW Atlantic based on mtDNA sequences for cytochrome b and cytochrome oxidase I

Population genetic structure and patterns of gene flow are describedfor the euphausiid, Meganyctiphanes norvegica, in the NW AtlanticOcean based on DNA sequence variation of two regions of mitochondrialDNA (mtDNA). DNA sequences were determined for portions of cytochromeoxidase I (COI; 400 base pairs; 76 individuals) and cytochromeb (CYB; 300 base pairs; 101 individuals) for euphausiids collectedfrom the Gulf of Maine in 1991, the Gulf of St Lawrence in 1993and 1994, the Scotian Shelf in 1994, and Georges Bank in 1994.For comparison, M.norvegica collected from the fjords of westernNorway in 1992 were sequenced for COI (20 individuals) and CYB(18 individuals). COI was less variable than CYB, based on bothhaplotype (h=0.6847 for COI; 0.9077 for CYB) and nucleotidediversities (