Transport of diatom and dinoflagellate resting spores in ships' ballast water: implications for plankton biogeography and aquaculture

Diatom and dinoflagellate species that are not endemic to aregion can be inadvertently introduced when their resistantresting stages are discharged with the ballast-tank waters andsediments of bulk cargo vessels. A survey of 343 cargo vesselsentering 18 Australian ports showed that 65% of ships were carryingsignificant amounts of sediment on the bottom of their ballasttanks. All of these samples contained diatoms, including speciesthat are not endemic to Australian waters. Diatom resting spores,especially of Chaetoceros, were also detected. Dinoflagellateresting spores (cysts) were present in 50% of the sediment samples.Of the 53 cyst species identified, 20 (including Diplopelta,Diplopsalopsis, Gonyaulax, Polykrikos, Protoperidinium, Scrippsiellaand Zygabikodinium spp.) were successfully germinated to produceviable cultures. Such diversity of diatom and dinoflagellatespecies in ships' ballast water suggests that the apparent cosmopolitanismof many coastal phytoplankton species may be due partly to theglobal transport of seawater ballast. Of considerable concernwas the detection in 16 ships of cysts of the toxic dinoflagellatesAlexandrium catenella, Alexandrium tamarense and Gymnodiniumcatenatum. One single ballast tank was estimated to contain>300 million viable A.tamarense cysts, some of which weresuccessfully germinated in the laboratory to produce toxic cultures.These toxic dinoflagellate species, which can contaminate shellfishwith paralytic shellfish poisons, pose a serious threat to humanhealth and the aquaculture industry. Ballast-water quarantinemeasures recently introduced in Australia are discussed. Mid-oceanexchange of ballast water is only partially effective in removingdinoflagellate cysts which have settled to the bottom of ballasttanks. The present work indicates that the most effective measureto prevent the spreading of toxic dinoflagellate cysts via ships'ballast water would be to avoid taking on ballast water duringdinoflagellate blooms in the water column of the world's ports.     

Dinoflagellate cyst production at a coastal Mediterranean site

To assess the diversity and seasonality of dinoflagellate cystproduction, surface sediment and trap samples were studied inthe Gulf of Naples (Mediterranean Sea). A total of 59 differentcyst morphotypes were recorded. At the stations within the 70m isobath, sediment assemblages were dominated by calcareousPeridiniales (66–79%), while at the deepest stations non-calcareousPeri-diniales attained the highest percentages (40–49%).The sediment trap sampling, carried out fortnightly over twoannual cycles, revealed high production rates (up to 1.7 x 10⁶cysts m^–2 day^–1) from spring to late autumn of bothyears, with a distinct seasonal production pattern. Althoughrather similar in species composition, the total cyst flux differedmarkedly between the 2 years (1.26 and 0.55 x 108 cysts m^–2year^–1, respectively). Species-specific production patternswere observed: some species formed cysts over several months,others in restricted periods of the year. Cyst-forming speciesconstituted a small part of the planktonic dinoflagellate populationsrecorded in the area. A coupling between the trap material andsurface water plankton was observed for calcareous Peridiniales.This sampling approach allowed the detection of some speciesnever recorded before in the gulf, including two potentiallytoxic species: Alexandrium andersoni and Gymnodinium catenatum-likespecies.     

A survey for body scales in dinoflagellates and a revision of Cachonina and Heterocapsa (Pyrrhophyta)

Small organic scales 0.2 to 0.4 µm in diameter have beenobserved to form a layer on the surface of three species ofmarine dinoflagellates. Two of the species were originally describedas members of the genus Cachonina; the third is Heterocapsapygmaea Loeblich et al., 1981. The body scales are very similarto those previously described covering cells of Heterocapsatriquetra (Ehrenberg) Stein, 1883. These scales are freely shedfrom the cells of the above four species and can be found inthe culture medium; no scales were observed in the culture mediumof 35 other dinoflagellate species representing 18 genera and11 families. The complete thecal plate pattern of H. triquetra,type species of Heterocapsa, has been determined, and on thebasis of similarities in body scale morphology and thecal platetabulation, the genus Cachonina is placed in the synonomy ofHeterocapsa. Cachonina illdefina and C. niei are transferredto Heterocapsa.     

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

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

A new ketocarotenoid from the heterotrophic dinoflagellate Protoperidinium depressum (Bayley) Balech, 1974

Pigments from a dinoflagellate population, in which Protoperidiniundepressum was the dominant species, were studied. This investigationrevealed the presence of a conjugated ketocarotenoid not previouslyreported for dinoflagellates.     

Spatial and temporal aspects of Gyrodinium galatheanum in Chesapeake Bay: distribution and mixotrophy

Gyrodinium galatheanum (Braarud) Taylor 1995 is a common bloom-forming,potentially toxic photosynthetic dinoflagellate in ChesapeakeBay, USA. Abundance of this dinoflagellate achieved densities>4 x 10³ cells ml^–1 in the mid- and upper Bay duringlate spring and early summer of 1995 and 1996. Ingestion ofcryptophytes by this dinoflagellate was detected in most samplescollected from the Bay. During late spring and early summer,mean number of ingested cryptophytes per G.galatheanum was ashigh as 0.46 for dinoflagellate populations located in surfacewaters of the mid- and upper Bay where dissolved inorganic phosphoruswas low. Observations on the distribution of G.galatheanum inChesapeake Bay show that populations of this dinoflagellatewere usually restricted to waters with salinities ranging from7 to 18 psu, seasonally progressed up the estuary, and usuallyco-occurred with cryptophytes. Correlation analysis indicatesthat abundance of G.galatheanum and incidence of feeding wasnegatively correlated with dissolved inorganic phosphorus, andthat incidence of feeding was positively correlated with abundanceof cryptophyte prey. These results indicate that G.galatheanumis an important component of the Chesapeake Bay phytoplanktonduring the spring and summer. Our results suggest that the phagotrophiccapability possessed by this phototrophic dinoflagellate maycontribute to its success in a varying-resource environmentlike Chesapeake Bay.     

PCR detection of dinoflagellate cysts in field sediment samples from tropic and temperate environments

Species-specific primers were constructed for Scrippsiella trochoidea, Protoceratium reticulatum and Lingulodinium polyedrum, which all are common cosmopolitan cyst forming dinoflagellates. The designed primers amplified a product of expected size from cultured planktonic cells of the three species, and did not yield any product with a wide range of other algal species used as negative controls. The PCR method for detection and identification of dinoflagellate cysts from the three species was applied on field samples. Undisturbed surface sediment was collected along the southwest coast of India and the west coast of Sweden. DNA extract from sediment including DNA from dinoflagellate cysts could be obtained after repeated grinding with mortar and pestle under liquid nitrogen followed by microwave boiling. All sediment samples that contained any of the target species as confirmed by microscopy, were also positive for PCR. Field samples negative for any of the target species by microscopy, were also negative by PCR. Restriction enzyme digestion and/or DNA sequencing confirmed the specificity of all the PCR products from field samples. The yield of DNA from sediment extraction was low, and therefore nested PCR was necessary for accurate species-specific detection of the three species in most of the field samples.     

Short-term changes in the mesozooplanktonic community in theSeine ROFI (Region of Freshwater Influence)(eastern English Channel)

Discrete-depth, hourly mesozooplankton samples were collectedover a 92 h period in May 1992 at an anchor station within theSeine Region of Freshwater Influence (ROFI) (English Channel).The mesozooplankton community defined as a euryhaline marineassemblage was dominated by the calanoid copepods Acartia spp.,Temora longicornis and Centropages hamatus, the cladoceran Evadnenordmanni and the appendicularian Oikopleura dioica. The semi-diurnaltidal current was the dominant factor in determining the short-termtemporal changes in the community in terms of density and speciescomposition so that zooplankton patches displayed oscillatingmotion in relation to tidal advection. Although a few species(e.g. Pleurobrachia pileus) exhibited higher densities aroundlow tide, maximum densities were observed for most species (e.g.T.longicornis and E.nordmanni) around high tide, according tosalinity variations. Diurnal changes were only reported forcyclopoid copepods (i.e. Halicyclops sp. and Cyclopina sp.)which wer$$$ mainly endobenthic during the day and moved intothe water column at night. Besides temporal changes in depth-averageddensities, most species exhibited vertical migrations at dieland/or tidal periods. Tidal vertical migrations were reportedonly for a few taxa and could be the result of passive mechanisms(e.g. vertical mixing) rather than of active behaviour. Dielvertical migrations were observed in most of the abundant taxa.While this migration pattern did not appear to be an adaptationto predator avoidance within the Seine ROFI, it could regulatehorizontal transport of organisms and promote their retention.The consequences of the short-term mesozooplankton fluctuationsfor sampling designs are discussed.     

Phased cell division in a natural population of Dinophysis sacculus and the in situ measurement of potential growth rate

A method for the in situ estimation of the potential growthrate of the dinoflagellate Dinophysis sacculus based on thepattern of cell division and the duration of the cell cyclephases according to the model of McDuff and Chisholm (Limnol.Oceanogr., 27, 783–788, 1982) is proposed. In order toobserve the cell cycle and measure the in situ growth rate ofD.sacculus, water samples were taken from Alfacs Bay in theEbro River Delta, Spain, in May and June 1994, and kept in thelaboratory under a light-dark cycle similar to that in the field.The pattern of cell division in the D.sacculus population wasestablished by intensive sampling over 24 h periods. The maximumfrequency of cells undergoing cytokinesis was observed at dawnand that of recently divided cells 2 h later. Based on the patternof cell division and the duration of the various cell cyclephases, a generation time between 2 and 5 days was estimated.Subsequently, in situ estimates of the growth rate for D.sacculuswere carried out in St Carles de la Ràpita harbour duringOctober 1995. A mean generation time of 7 days was estimated.     

Occurrence and Inheritance of 2 n Pollen in Musa

Sexual polyploidization explains the formation of most polyploidcrop species and provides means for their genetic improvement.This paper reports the occurrence and inheritance of 2n pollenin diploid and polyploidMusa . Pollen samples of male fertileaccessions available in the field gene bank of the InternationalInstitute of Tropical Agriculture were microscopically examinedthroughout a calendar year. Based on pollen diameter 2n pollenproducers were identified. The presence of 2n pollen in diploidspecies suggests that unilateral sexual polyploidization (2nxn) could have been involved in the origin of triploidMusa species.Segregation data suggests that at least one dominant gene controls2n pollen production inMusa . Further introgression of desirablealleles from diploid species to polyploids could be achievedeither through unilateral or bilateral (2nx2n ) sexual polyploidizationinMusa . Musa spp.; Musa hybrids; 2n gametes; evolution; ploidy manipulations; sexual polyploidization     

HPLC analysis of phytoplankton pigments from Lake Kinneret with special reference to the bloom-forming dinoflagellate Peridinium gatunense (Dinophyceae) and chlorophyll degradatio products

Photosynthetic pigments extracted from the paniculate materialof the water column of Lake Kinneret were studied throughoutthe periods of May 1988-June 1989, and November 1993-November1994, by means of HPLC. The temporal and vertical variationof the pigment suite found agreed with the microscopically determinedphytoplankton record. The regression calculations of taxon-specificbiomass with the corresponding signature pigments suggest thatpigment analysis may be a useful tool for the monitoring ofbloom-forming species, e.g. the dinoflagellate Peridinium gatunenseNygaard. The HPLC pigment analysis permitted the identificationand quantification of chlorophyll degradation products, providingfor the first time information about their composition in LakeKinneret. Chlorophyllide a was the major detectable degradationproduct of chlorophyll a, varying between 1 and 9% of the chlorophylla concentration. Other chlorophyll a derivatives appeared mostlyin minor quantities. Pheophytin a was virtually lacking in allthe samples. Removal rates of pigments, measured by sedimentationtraps, indicated that the degradation of chlorophyll a via chlorophyllidea is a dynamic process that continues during the sedimentationof the phytoplankton particles.     

Interactions between red tide microalgae and herbivorous zooplankton: the noxious effects of Gyrodinium corsicum (Dinophyceae) on Acartia grani (Copepoda: Calanoida)

Gyrodinium corsicum is a dinoflagellate responsible for recurrentwater discolourations during winter in Alfacs Bay (Ebre Riverdelta, NW Mediterranean). Since first detected in 1994, episodicmortality of mussels and fish was attributed to this organism,although no direct evidence was obtained. In order to establishthe direct role of the dinoflagellate in the mortality of marinefauna, we have studied the effects of G.corsicum on a potentialpredator, the co-occurring planktonic copepod Acartia grani.Female A.grani were exposed to different concentrations of intactcells, and <5 µm and <0.2 µm filtrates ofthe dinoflagellate. At concentrations of     

Production of dissolved organic carbon in phyloplankton cultures as measured by high-temperature catalytic oxidation and ultraviolet photo-oxidation methods

The production of dissolved organic carbon (DOC) in culturesof the diatoms Chaetoceros gracilis and Phaeodactylum tricornutum,the flagellate Isochrysis galbana, the dinoflagellate Alexandriumtamarense and a natural algal assemblage from the NorthwestArm, Halifax, Nova Scotia, Canada, was followed using a high-temperaturecatalytic oxidation (HTCO) and a UV photo-oxidation method.Molecular weight fractionation of the DOC was performed fortwo cultures: C.gracilis and I.galbana. While the DOC in theculture medium increased significantly during log-phase growthfor all organisms except the dinoflagellate, this increase wasproportional to the increase in cell numbers; the increase inDOC per cell was either small or zero. In all cultures, maximumrelease took place during stationary and senescent phases, usuallyafter cell numbers had started to decrease. In both C.gracilisand I.galbana, a major portion (>65%) of the organic matterreleased to the medium during log-phase growth had mol. wtsof <10 000 Da. The increase in DOC in the I.galbana culturein stationary and senescent phases was due to the release ofhigh-molecular-weight materials. The differences in extracellularrelease of DOC between species and between different growthstages in the same species suggest that both the species compositionand physiological state of phytoplankton populations must beknown before interpretations and predictions based on fielddata can be made. In order to determine whether the differencesin DOC values found by the HTCO and UV oxidation methods arecaused by the resistance to UV oxidation of some compounds producedby phytoplankton, rather than by less than optimum efficiencyof the UV unit used, standards must be based on naturally occurringcompounds, rather than the pure compounds normally used.     

Dessication-induced Changes in the Protein Complement of Soluble Extracts from Leaves of Resurrection Plants and Related Desiccation-sensitive Species

Polyacrylamide gel electrophoresis studies were conducted onthe soluble proteins of angiosperm plants whose leaf protoplasmcan revive from complete dehydration (Xerophyta viscosa, Talbotiaelegans, Sporobolus stapfianus, Myrothamnus flabellifolia, Boryanitida) and of desiccation sensitive plants (Sporobolus pyramidalis,Eragrostis tenuifolia, Selaginella kraussiana). Changes in thesoluble protein composition were found in all species afterdehydration, and were extensive in most species, both resurrectionand non-resurrection. Both groups showed loss of protein bands,but there was no consistent pattern of compositional changewithin either type of plant. Net hydrolysis of high molecularweight protein could be deduced, and the possibility of disulphide-mediatedaggregation arose in some species. Induction of tolerance todesiccation in Borya nitida appeared to be associated with retentionor restoration of the control pattern of protein bands in contrastto loss of very low and very high mol. wt protein (loss wasextreme in desiccation-killed leaves). There was evidence of a disproportionately great synthesis ofvery low mol. wt protein during the midphase of rehydrationin X. viscosa. These results point to the possibility of an important roleof protein synthesis for survival of dehydration. Resurrection plants, desiccation-sensitive plants, protein complement, polyacrylamide gel electrophoresis     

OLIGONUCLEOTIDE PRIMERS FOR THE DETECTION OF BIOLUMINESCENT DINOFLAGELLATES REVEAL NOVEL LUCIFERASE SEQUENCES AND INFORMATION ON THE MOLECULAR EVOLUTION OF THIS GENE1

Bioluminescence is reported in members of 18 dinoflagellate genera. Species of dinoflagellates are known to have different bioluminescent signatures, making it difficult to assess the presence of particular species in the water column using optical tools, particularly when bioluminescent populations are in nonbloom conditions. A “universal” oligonucleotide primer set, along with species and genus‐specific primers specific to the luciferase gene were developed for the detection of bioluminescent dinoflagellates. These primers amplified luciferase sequences from bioluminescent dinoflagellate cultures and from environmental samples containing bioluminescent dinoflagellate populations. Novel luciferase sequences were obtained for strains of Alexandrium cf. catenella (Whedon et Kof.) Balech and Alexandrium fundyense Balech, and also from a strain of Gonyaulax spinifera (Clap. et Whitting) Diesing, which produces bioluminescence undetectable to the naked eye. The phylogeny of partial luciferase sequences revealed five significant clades of the dinoflagellate luciferase gene, suggesting divergence among some species and providing clues on their molecular evolution. We propose that the primers developed in this study will allow further detection of low‐light‐emitting bioluminescent dinoflagellate species and will have applications as robust indicators of dinoflagellate bioluminescence in natural water samples.     

Durinskia baltica (Dinophyceae), a newly recorded species and genus from China, and its systematics

A freshwater dinoflagellate was identified as Durinskia baltica (Levander) Carty & Cox by morphological characteristics,with the plate formula:Po,x,4',2a,6',5c,4s,5',2'.Durinskia was a newly recorded dinoflagellate genus for China with two anterior intercalary plates and six characteristic precingular plates.Partial sequences of the small and large subunit ribosomal DNA and internal transcribed spacer sequences for the dinoflagellate cells were obtained from field samples.Molecular phylogenetic results indicated Durinskia species could cluster into a monophyletic group,which were distinct from Peridinium species.According to morphological and molecular evidence,it was agreed that the genus Durinskia was separated from the genus Peridinium,which could be a polyphyletic group.In addition,D.baltica was an infrequent diatom-harboring dinoflagellate which was known to possess an endosymbiotic diatom or diatom-like alga.The phylogenetic analyses indicated that D.baltica had a close affinity with Peridiniopsis penardii and P.niei,common freshwater bloom-forming species in China.     

Evolution of group size in the dolphins and porpoises: interspecific consistency of intraspecific patterns

I investigated group size variability in dolphins and porpoisesusing intraspecific comparisons. Explanatory factors consideredin the analysis were variables of the physical environment,the diet, and the life history of the species. Open habitatand small body size were viewed as increasing predation risk.This pattern was apparent in Risso's dolphins (Grampus griseus) and weakly apparent in bottlenose dolphins (Tursiops spp.).Group size was negatively correlated with body size in pilotwhales (Globicephala spp.) and positively correlated with theopenness of habitat in killer whales (Orcinus orca), stripeddolphins (Stenella coeruleoalba), and common dolphins (Delphinus spp.). No such relationship was found for harbor and Dall'sporpoises (Phocoena phocoena, P. dalli). Group size also seemedto vary depending on other physical measures of the habitat,which may indirectly reflect diet; group size showed U-shapedpatterns if related to temperature. The predictive power ofvariables comprising detailed prey information on group sizewas variable. For example, pilot whales had smaller group sizes when they fed more on mesopelagic fish and less on mesopelagiccephalopods, and common dolphins had larger groups if theyfed on varying types of fish. In most Delphinoidea species,group size could be described by the variables considered inthis study. But each species showed its own pattern of correlationsbetween group size and a specific set of explanatory variables. Thus, no general and consistent relation between group sizeand the other variables was found. It remains unknown whetherthese species-specific patterns result from a historical processor whether they are specialized adaptations.     

Armoured dinoflagellates in the NE Atlantic during the BOFS cruises, 1988-90

The armoured dinoulagellates present in 90 plankton samplescollected by the use of an Apatein closing net were enumerated.The samples were collected from various stations around the20W meridian and between 44 and 60N during the 1988, 1989and 1990 Biogeochemical Ocean Flux Study (BOFS) cruises. Atmost stations, samples were obtained from various depths, althoughin 1990 only the surface zone was sampled. A total of 126 specieswere identified, of which 49 have chloroplasts and are thoughtto be autotrophic, 47 are assumed to be heterotrophic and thenutritional type of the remainder is unknown. The samples collectedduring July 1988 were dominated by large numbers of the twophotosynthetic species Gonyaulax polygramma and Protoceratiunreticulatum (=Gonyaulax grindleyi). The much more intensivesampling of 1989 revealed several Ceratiun species, C.fusus,C.furca and C.lineazum, together with Gonyaulax polygramma,as the most common dinoflagellates. In 1990 the samples, whichwere taken during a Lagrangian survey in May-June, were alsodominated by Ceratium species. This time C.azoricwn was a majorcomponent and Protoceratium reticulatum was again present inhigh numbers as in 1988. A number of analyses were carried outon the data collected. It was found that the majority of themore frequent species were autotrophs and most were membersof the genus Ceraziwn. The effects of depth were shown to resultin reduced numbers of cells and species, but no clear associationwas found between species and depth. After the application ofDetrended Correspondence Analysis (DECORANA) to all surfacesamples, there was found to be a clear association between thespecies composition and both time of year and latitude. Watercolumn stability is also probably an important factor in speciescomposition and cell numbers. Seasonal changes in the frequencyof the main species were also noted with some, such as C.lineatum,being more important early in the summer and others, such asProtoceratium reticulatum and particularly G.polygramma, becomingdominant later. The use of Two-way Indicator Analysis (TWINSPAN)revealed some potential species associations.     

GROWTH AND REPRODUCTION IN THE AEOLID NUDIBRANCH AEOLIDIA PAPILLOSA (L.)

The growth and reproductive (spawn) output was followed in thelaboratory for 48 Aeolidia papillosa (L.). Groups of these nudibranchswere maintained on different anemone diets throughout the entireexperimental period from collection from the field, just aftersettlement and metamorphosis, in October 1982, until death inJuly 1983. Extreme between-individual variations prevented the detectionof any diet-related effects on the growth-rate or final sizeof the molluscs. In addition, there was no evidence of any statisticallysignificant differences in reproductive effort that could berelated to anemone diet. Nevertheless, specific growth-ratesamong individuals which spawned (irrespective of diet) weresignificantly higher than those for animals which failed toreproduce. The 21 A. papillosa which spawned all showed an increasingrate of spawn production over their reproductive periods. Furthermore,in contrast to the pattern observed for other reported nudibranchspecies, A. papillosa continued to grow during most of thistime. This pattern may possibly be related to advantages ofmaintaining a larger body size to enhance success of predationon anemone species: this in itself could lead to increased individualfecundity. (Received 20 January 1986;     

Vertical distribution and feeding pattern of Euphausiacea (Crustacea) in the eastern Banda Sea (Indonesia) during the SE and NW monsoons

The vertical distribution of Euphausiacea (Crustacea) in theeastern Banda Sea (Indonesia) during the SE and NW monsoon seasonswas studied. In August 1984 and February/ March 1985, stratifiedday and night sampling was carried out between 0 and 500 m atfour stations. A total of 31 species was found, of which mostwere present in both monsoon seasons. Species with a high presencein samples and performing diurnal vertical migration in bothmonsoon seasons were Euphausia diomedeae, Euphausia pseudogibba,Thysanopoda monacantha, Thysanopoda iricus-pidaia and Nematoscelismicrops. Species with a high presence in samples showing nodiurnal vertical migration in both monsoon seasons were Euphausiasimilis, Nematobrachion boopis. Nematoscelis tenella, Stylocheironmaximum and Thysanopoda orientalis. The density of Euphausiaceaat the sampled stations was higher, but more heterogeneous,in the nutrient-enriched SE monsoon period than in the relativelynutrient-poor NW monsoon season, when densities were lower andmore similar. The vertical distributions and diurnal verticalmigration of species did not show a unanimous and strong responseto seasonal hydrographic differences. The day–night depthdistribution pattern of the Euphausiacea population in the upper500 m is largely the same in both seasons, with comparable migrationranges. Some species showed a somewhat upward shifted depthdistribution in the nutrient-enriched period. For mesopelagicand bathypelagic species especially, food resources were thenfavourable in the upper layers, as indicated by rare recordsof Thysanopoda crisiata. Analyses of stomach contents snowedmainly a nocturnal feeding pattern for the diurnal verticalmigrating species and a continuous feeding pattern for the non-migratingspecies.