Influence of the Agulhas Current on the distribution of lanternfish larvae off the southeast coast of Africa

Spatial and temporal distribution patterns of lanternfish larvaealong the southeast coast of Africa were analysed in relationto oceanographic conditions. Investigations werebased on theplankton collections made during winter, spring and summer monthsof 1990–1991. The warm southward-flowing Agulhas Currentis the dominant large-scale oceanographic feature in the area.The number of species of myctophid larvae collected per cruiseranged from 35 to 38. The most abundant species differed fromone season to the other.Afew species showed marked seasonalityin their occurrence, e.g. Scopelopsis multipunclatiis only appearedin winter and Hygophum hygomii showed the highest abundancesin winter. The majority of species occurred in relatively lowconcentrations during all three periods. Relatively large concentrationsof lanternfish larvae of most species sometimes occurred veryclose inshore (especially in the north of thestudy area) inwater depths of 50–100 m. This was related to shorewardintrusions ofAgulhas Current surface water. Low numbers of larvaeof few species appeared on the inshore shelf of the southernsector of the study area, where cold central Indian Ocean wateris forced onto the shelf by kinematic upwelling.     

Seasonal and tidal abundance patterns of decapod crustacean larvae in a shallow inlet (SW Spain)

Planktonic larvae of decapod crustaceans were collected monthlyfrom July 1991 to June 1992 by pumping during nocturnal floodand ebb tides to establish seasonal larval abundance patternsin an inlet of the Bay of Cdiz. Additional 24 h series of sampleswere collected seasonally (July 1991, October 1991, January1992 and May/June 1992) during spring and neap tides to analyselarval abundance in relation to the main environmental cycles(diel, tidal and lunar phases) and vertical position in thewater column. First zoeae were the most abundant stage for mostspecies, representing 97.6% of all individuals collected. ZoeaI abundance was higher in spring and swmner and, on most samplingoccasions, there was a net output from the inlet to the bay.Five species (Liocarcinus arcuatus and Liocarcinus vernalis,Uca tangeri, Diogenes pugilator and Panopeus africanus) represented60% of total individuals caught. The seasonal occurrence offirst zoeae of the most abundant species indicated two differentreproductive patterns: species with a short reproductive periodand species spawning year round. Zoea I of several species (Panopeusafricanus, Uca tangeri, Pachygrap sus marmoratus, Processa spp.)were significantly more abundant during ebb tides and theirlater larval stages were scarcely collected, suggesting thatthese larvae are released in the inlet and exported to the bay.Conversely, a net input of first zoeae was observed for otherspecies (D.pugilator and Pinnotheres pinnotheres), but theirlater larval stages were also scarcely collected. Such importationcould be a larval rhythm artifact due to release of larvae inthe bay that drifted into the inlet by tidal currents. The crabIlia nucleus, whose later larval stages were collected frequently,was the only species that seemed to complete its life cyclewithin the bay. These results suggest that the studied inletwas primarily used by decapods as an adult habitat and spawningground, while larval development occurred in open sea. Sincevertical migration was not observed for exported larvae, thetidal synchronization of female release seemed to be the mostprobable mechanism of larval exportation. There were no significantdifferences between larval release during spring and neap tides.     

Atlantis II Cruise: uniformity of deep copepod assemblages in the Mediterranean Sea

Studies of the community structure and biomass of deep copepodsbelow 500 m from R/V Atlantis II cruises AII49 and AII59 inMay–June 1969 and September–October 1970 denoteuniformity in deep assemblages among all major Mediterraneansubregions. Of the 65 copepod species recorded from 600–2500m, 45 were common for both Western and Eastern basins Eightof these species were dominant for all deep Mediterranean waters,comprising 77% of the deep plankton population The uniformityof deep copepod assemblages was confirmed by the Mantel testapplied to a simulated sampling procedure Only in terms of biomassdid Western and Eastern basins show appreciable regional differenceswith highest values for density and volume characterizing Westernstations ¹Died tragically at sea during the course of a cruise on December15, 1988     

Seasonal abundance and distribution of Caridea larvae in Isafjord-deep, north-west Iceland

The abundance and distribution of Candea larvae was studiedin Ísafjord-deep, north-west Iceland, at approximatelymonthly intervals from February 1987 to February 1988 Zooplanktonsampling was made at nine stations along the length of the fjord,while temperature and chlorophyll a measurements from one ofthe stations are also presented Larvae of six species occurredin the samples, Eualus pusiolus and Pandalus borealis were mostnumerous, constituting 62 8 and 25 9% of the larvae respectively.The other species were, in declining order of abundance, Pandalusmontagui, Spirontocaris spp. (S spinus and s lilljeborgii) andSabinea septemcarinata. Eualus pusiolus was of highest abundancein the outer and middle parts of the fjord, while P.borealiswas most common in the middle and inner parts The onset of hatchingof all species in April–May appeared closely linked tothe phytoplankton spring bloom, while the temperature in thefjord was by then near the annual low (2–3°C). Exceptfor E pusiolus, of which a small part of the population produceda second brood during the summer, most of the larvae had disappearedfrom the plankton by the middle of August The monthly carapacegrowth of P.borealis larvae during the summer months was estimatedto be 1.0 mm.     

Larval and early post-larval stages in the abbreviated development of Heterosquilla tricarinata (Claus, 1871) (Crustacea, Stomatopoda)

Heterosquilla tricarinata was laboratory-cultured through itscomplete larval development and found to have one propelagicand two pelagic larval stages prior to metamorphosis to thejuvenile. These larval stages, the first juvenile, and relevantportions of the second juvenile stage, are described and figured.Individual larvae do not change in size during intermoult periods.Larvae occurring in the plankton show a progressive decreasein mean size between early (September) and late (November) springtime.Reasons for this are suggested. The first pelagic stage of H.tricarinata is anatomically very advanced in development, andthe number of pelagic stages very few, in comparison with otherknown stomatopod life-histories. Ecological implications ofthis are discussed in relation to the high-latitude distributionof the species. Comparison is made between the final pelagicstage of H. tricarinata and that of its congenor H. brazieri. ^*Permanent address: Zoology Department, University of Queensland,Brisbane, Australia     

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.     

Trophodynamics of the plankton community at Dogger Bank: predatory impact by larval fish

The trophodynamics of a coastal plankton community were studied,focusing on fish larvae and their copepod prey. The major objectiveswere to describe distributional overlap and evaluate the predatoryimpact by larval fish. The study was carried out across DoggerBank in the North Sea, August-September 1991. Sampling transectscrossed tidal fronts off the Bank and plankton at all trophiclevels showed peak abundance within frontal zones. Also Verticallythere was a significant overlap in distributional patterns ofthe plankton. Seven species of fish larvae were abundant, ofthese sprat (Sprattus sprattus) dominated. The abundance ofone group of fish larvae peaked in the shallow water close tothe Bank, whereas other species, including sprat, were foundin deeper water. Prey preference and predation pressure of fishlarvae were assessed using information on prey sizes and growthrates of larvae and the copepod prey. We estimated larval removalof preferred prey sizes to 3–4% day^–1, counterbalancedby a 3–7% day^–1' replenishment from copepod productionand growth. Additional predation pressure on copepods by aninvertebrate predator was estimated to 1–3%day^–1.In conclusion, the dynamics of fish larvae and other zooplankterswere closely linked. At peak abundances of fish larvae (>35mg dry weight m^–2), the accumulated predation on specificsize ranges of copepods, exerted by larvae and other predators,could exceed the ability of copepod replenishment and intra-/interspecificcompetition among predators might take place.     

Midsummer succession of rotifer plankton in a shallow eutrophic pond

Temporal changes in the density of rotifer plankton were examinedin a shallow eutrophic pond during July to September 1990, whenabiotic environmental variables were relatively stable. In earlyJuly when Daphnia similis was abundant, rotifer populationsremained at a low density. This is probably due to interferenceby the large cladoceran, because possible food was abundantand the rotifers showed high egg ratio. After late July, whenthe large cladoceran disappeared, a striking succession wasfound in the rotifer plankton. In late July, when Filinia longisetaand Conochilus dossuarius dominated, and in mid- to late Septemberwhen F.opoliensis and Brachionus falcatus dominated, there wasa causal relationship between the density and egg ratio, suggestingthat temporal changes in rotifer density were regulated mainlyby food abundance. However, in August, changes in the densityof most rotifers were not necessarily related with those inthe egg ratio. Brachionus angularis, B.forficula and Keratellaspp. decreased or remained at a low density regardless of theegg ratio, when the population of Asplanchna brightwelli wasdeveloped. However, Polyarthra vulgaris, B.calyciflorus andH.intermedia increased or maintained a high density at thistime. Stomach contents of A.brightwelli revealed that B.angularis,B.forficula and Keratella spp. were the preferred prey, whereasP.vulgaris, B.calyciflorus and H.intermedia were not. Theseresults provide strong evidence that the structure of rotiferplankton can change strikingly within a season due to species-specificdifferences not only in diet, but also in the ability to escapepredation, even if abiotic environmental variables are stable.     

Development of specific rRNA probes to distinguish between geographic clades of the Alexandrium tamarense species complex

The globally occurring Alexandrium tamarense/fundyense/catenellaspecies complex consists of toxic and non-toxic strains thatare morphologically difficult to distinguish. We developed fourspecific ribosomal RNA probes that can identify the entire speciescomplex, the strains of the toxic North American clade and thestrains of the two non-toxic clades from Western Europe andthe Mediterranean Sea by DNA dot blot and fluorescence in situhybridization. These probes are a first step for the developmentof an early warning system for the presence of A. tamarense.     

The dynamics of sponge larvae assemblages from northwestern Mediterranean nearshore bottoms

In this study, we show for the first time the dynamics of spongelarvae assemblages from nearshore meroplankton. Plankton wascollected by SCUBA diving once or twice a week during a 2-yearperiod over a rocky artificial reef in the NW Mediterranean.Data on larval abundance were cross correlated with the valuesof environmental parameters (i.e. seawater temperature, solarradiation, wind speed and atmospheric pressure). In the laboratory,we recorded external features and main behaviors of larvae.We collected larvae belonging to 20 different taxa of sponges,which are among the most common in the sublittoral hard bottomcommunities of the NW Mediterranean and other temperate areas.There was a positive correlation between maximum abundance oflarvae and highest water temperatures. Maximum solar radiationpreceded the maximum of larval abundance. Wind speed showedno clear seasonal patterns and atmospheric pressure was overallthe lowest when larvae were most abundant. Two main patternsin the larval release periods were observed. One was shown byspecies releasing larvae in summer, right before the maximumwater temperatures (orders Dictyoceratida and Dendroceratida)and another by the species whose larvae release from the endof summer till autumn, when temperatures decrease (order Poecilosclerida).The larvae of Phorbas tenacior, Raphidoflus jolicoueri, Mycalerotalis, Tedania anhelans, Pleraplysilla spinifera, Aplysillasulfurea var. rosea and Chelonaplysilla noevus are describedfor the first time. The larvae collected mainly belonged tothe parenchymella type (except for the species Oscarella sp.and probably Cliona viridis) and showed different features andbehaviors: from the elongated parenchymellae of Scopalina lophyropoda(order Halichondrida), which show simple swimming behavior andno response to light, to the parenchymellae of Poeciloscleridaand Dictyoceratida orders with variable morphologies as adaptationsto complex swimming behaviors. Our database will hopefully contributeto the present knowledge of larval types in sponges and definitivelyhighlight the importance of this group in the dynamics of meroplanktonfrom nearshore bottoms.     

Bulk-phase viscoelastic properties of seawater relationship with plankton components

The viscous and elastic moduli at different shear rates, togetherwith various biological oceanographic properties, were determinedin seawater from different hydrological layers in the southernNorth Sea in June. The biological oceanographic parameters includedPhaeocystis and Noctiluca abundances, chlorophyll a level (Chl),bacteria. HNAN and aggregate volume fraction. The plankton wasjointly dominated by Phaeocyslis sp. and Noctiluca scinullans.Noctiluca abundance showed no correlation with any other biologicalor viscoelastic parameter, but Phaeocystis abundance correlatedstrongly. The other biological parameters correlated with Phaeocystisand with each other positively and mostly significantly. Overall,viscoelasticity correlated more strongly with Chl than withany other biological parameter. For non-microlayer samples,the excess complex (viscoelastic) modulus (µ.Pa) G^*_E =2.0 x Ch1^1–3 (Chl in mg m^–3). Viscous and elasticmoduli also correlated closely with each other. For a givenvalue of Chl. the microlayer samples were 6.5 or 14 times (dependingon the estimation method) more viscoelastic than in bulk-phasesamples. Viscoelasticity in samples of settled benthic ‘fluff’were lower even than bulk-phase samples, but this differencewas not significant. Comparison with Mediterranean data on viscoelasticity(Jenkinson. Oceanol. Acta, 16, 317–334, 1993), using publishedvalues for phytoplankton biomass (Wiadnyana, J. Rech. Océanogr.,17, 1–6, 1992), suggests that the relationship betweenChl (or phytoplankton biomass) and viscoelasticity might begeneral. This apparent biomodification of the viscosity andelasticity of seawater is discussed in relation to its likelyimpact on turbulence and plankton ecology.     

EASTERN MEDITERRANEAN OPISTHOBRANCHIA: OXYNOIDAE, POLYBRANCHHDAE, STILIGERIDAE (SACOGLOSSA)

An account is given of the ceratiform sacoglossans collectedon diving expeditions to the Mediterranean shores of Yugoslaviaand Greece during the period 1978–86. Six species aredescribed, two of which, Cyerce graeca and Hermaea (Placida)saronica, are new to science; four of the six represent additionsor new records for the eastern Mediterranean (Received 20 July 1987;     

First record of the calanoid copepod Acartia omorii (Copepoda: Calanoida: Acartiidae) in the southern bight of the North Sea

The occurrence of the calanoid copepod, Acartia omorii, is reportedfor the first time in the coastal waters of the Southern bightof the North Sea, off Calais harbour. Acartia omorii males andfemales were consistently found in four plankton samples. Thecollected specimens were compared with A. omorii individualscollected from the type locality (Tokyo Bay, Japan). The captureof A. omorii, a species native to Japanese coastal waters, isin agreement with the recent observation of the Japanese macroalgaeUndaria pinnatifida within Calais harbor and the hypothesisof passive transport in ship’s ballast water.     

Larval fishes and zooplankton in a cyclonic eddy in Hawaiian waters

A cold-core eddy occurred off the Kona coast of the island ofHawaii in July 1982. It remained in that area for {small tilde}70days, sufficient time for many reef fish species to completetheir planktonic larval phase. The deployment of eight currentdrogues in the eddy showed how entrainment of plankton fromthe reef and adjacent offshore waters can occur and that passivedrift can return drifters from the deep sea to shore. Larvalfishes may be swept past the island every 7–8 days ina weak eddy and 3.5–5 days in a strong eddy. Planktoncollections were made at night near the surface and at the samedepth as the current drogues. Zooplankton were most concentratedat the eddy center. Taxonomic analysis of the plankton showedthat the dominant animals were calanoid copepods, malacostracans,hyperud amphipods, gastropod and bivalve larvae and chaetognaths.The densities of zooplankton and larval fishes in the eddy werehigher than in the same area before the arrival of an eddy.Larval fishes were most abundant in the periphery and amongthese, midwater fish larvae (gonostomatids and myctophids) werethe most numerous. Other numerous fish larvae in the eddy includedscombrids, particularly Thunnus albacares. carangids and thereef fish, Abudefduf abdominalis is (Pomacentridae).     

Description of Rhynchoteuthion larvae of Illex argentinus from the summer spawning subpopulation

The Rhynchoteuthion larvae of Illex argentinus resulting fromsummer spawning in North Patagonic shelf waters, its distributionand abundance, are described in this paper. The material wascollected in the Argentine Sea (35–55°S) by meansof plankton nets. The research cruises were made by the R/VShinkai Maru and the R/V Walther Herwig during the period April1978 to April 1979. The most important spawning ground of thesummer spawning subpopulation is found in continental-shelfwaters (between 43 and 46°S) during the period December-February.This area was established on the basis of both ripe (December)and spent females (February). The larvae which were caught duringthe same period, especially in March, confirmed the spawningarea of this demographic unit. The larvae showed the lengthof the mantle (ML) to be from 1.2 to 6.5 mm. Tentacles weresplitting in specimens from 5.0 to 6.5 mm ML (transition stage).When 7.0 mm ML or more, all specimens were juveniles and hadtheir tentacles completely separated. Larvae were characterizedas type C, following the proposal of Sato (1973) and Sato andSawada (1974) in the Bulletin of the Shizuoka Prefectural FisheriesExperimental Station.     

DISTRIBUTION AND PRODUCTION OF THREE HYDROBIA SPECIES (GASTROPODA: HYDROBIIDAE) IN A SHALLOW COASTAL LAGOON IN THE BAY OF CADIZ, SPAIN

The abundance, life span, growth and production of the mud snailsHydrobia minoricensis, H. ulvae and H. ventrosa in a semi-naturallagoon system were studied by taking monthly samples at threesites during 1991 and 1992. The most abundant species, H. minoricensisoccurred at mean densities of 12834 to 26264 snails m^–2(10.7 to 25.8g dry weigh m^–2), depending on the site.The least abundant species, H. ulvae, occurred at mean densitiesof 185 to 353 snails m^–2 (3.2 to 2.2g dry weight m^–2).The numerical abundance and biomass of the three Hydrobia specieswere positively related to the biomass of benthic macroalgae(P<0.01). Although H. ulvae egg capsules were recorded throughoutthe year, newly hatched snailsof this species were not observed,in contrast to the other two species. The early spring and summercohorts of H. minoricensis and H. ventrosa seemed to be themost numerous. The average life spans of these two species wereestimated to be about 18 and 13 months respectively. Annualproduction estimates for the whole lagoon system were 29.0 (6.3),5.5 (0.8) and 5.2 (1.0)g dry weight (ash-free dry weight) m^–2yr^–1 for H. minoricensis, H. ulvae and H. ventrosa respectively.The annual P/B ratio was about 2 for H. minoricensis and H.ventrosa. (Received 5 July 1994; accepted 5 October 1994)     

The seasonal dynamics and distribution of burrowing shrimp larvae of the infraorders Gebiidea and Axiidea in Amursky and Ussuriysky Bays,the Sea of Japan

The species composition, period of occurrence, density, and distribution of the larvae of burrowing shrimp of the infraorders Gebiidea and Axiidea in Amursky and Ussuriysky bays (Sea of Japan) were studied in May–October 2008. Larvae of eight species of this group were found in plankton samples. The period of occurrence of larvae in the bays was longest in Upogebia major and Nihonotrypaea petalura (4 and 3 months, respectively). Zoeae of the rest of the species occurred in the plankton for no more than 2 months, indicating a single larval hatching during the reproductive season. The average density of gebiidean and axiidean larvae was low and reached the highest values (4 ind./m³) in June in Amursky Bay and in July in Ussuriysky Bay; their contribution to the total density of decapod larvae was not above 18%. In general, larvae of the family Upogebiidae dominated in Amursky Bay and larvae of the Callianassidae were predominant in Ussuriysky Bay. The zoeae of U. major (up to 37 ind./m³) and Nihonotrypaea makarovi (up to 46 ind./m³) were most numerous. Larvae of the family Axiidae were recorded only in very low numbers in both bays.     

The Diatom Genus Tabellaria: II. Taxonomy and Morphology of the Plankton Varieties

Plankton samples of Tabellaria from all the lakes of the EnglishLake District have been examined and evidence of morphologicallydistinct populations has been found in samples from (a) a singlelake at one time, (b) different lakes, and (c) a single lakeat different times. Clone cultures have been used to study thenature of these differences. Fifteen characters have been foundto show quantitative or qualitative variation in plankton populationsof Tabellaria, and the morphological diversity of differentpopulations is largely due to different combinations of thesecharacters. All known plankton populations of Tabellaria arereferred to the species T. flocculosa.