Amphipods, isopods and surface currents: a case for passive dispersal in the Bay of Fundy, Canada

Six species of isopods and 18 species of amphipods were collectedin the neuston of the Bay of Fundy and adjacent waters. Collectionswere made over a grid of stations covering 2.4x10⁴ km² duringthree spring, three summer and two autumn surveys. No isopodsand only five species of amphipods were found in spring surveys.Isopods and amphipods were diverse and plentiful in the neustonin summer and autumn. Dominant isopods were Idotea baltica andI.metallica, and dominant amphipods were Calliopius laeviusculusand Parathemisto gaudichaudi. Amphipods and isopods reach theneuston of the Bay of Fundy in three ways. Idotea metallica,the only euneustonic species present, was probably advectedinto the Bay of Fundy from southern waters in summer, and didnot appear to overwinter in the Bay. Most species, includingI.baltica, were collected with drifting littoral vegetation,and we suggest that transport by surface currents is an importantfactor in dispersal of some shoreline crustaceans. Midwaterplankton, such as Parathemisto gaudichaudi, reached the neustoneither by advection in upwelling waters or by an extension oftheir normal diel vertical distribution.     

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.     

Annual cycle of tintinnids in Admiralty Bay with an emphasis on seasonal variability in Cymatocylis affinis/convallaria lorica morphology

In water samples collected from the middle of Admiralty Bay(King George Island 62°08'S 58°25'W) between February1990 and January 1991, 17 Tintinnina species were noted. TotalTintinnina numbers in summer were very high (up to 5000 cellsm^–3), but species diversity was low, consisting mainlyof Cymatocylis affnislconvallaria, forma convallaria. Duringaustral winter, cell numbers were very low, but species compositionwas diverse. Cymatocylis affnislconvallaria, forma affinis,and C.affmis/convallaria, forma convallaria, the polymorphicforms of one species C.affinis/convallaria, appear to be interchangeableduring the year. The transition from one form to the other occursin the spring and autumn. The typical Tintinnina polymorphismcan be attributed to the prevailing environmental conditions.     

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.     

Seasonal dynamics in the abundance of Micromonas pusilla (Prasinophyceae) and its viruses in the Gulf of Naples (Mediterranean Sea)

To assess the role of viruses in the bloom dynamics of Micromonaspusilla in the Gulf of Naples (Mediterranean Sea), variationsof host and virus abundance were followed over one annual cycleand in late winter–spring of three consecutive years.Micromonas pusilla was recorded from autumn to spring, withpeak values up to 6.6 x 10³ cells ml^–1, but was undetectablein summer. Free M.pusilla viruses were detectable in all seasons,with concentrations from 0.02 viruses ml^–1 to 1.9 x 10³viruses ml^–1, exceeding host abundances only in one case.We found a great intraspecific variability in host susceptibilityto viruses present in natural samples, with viral titres rangingover one or two orders of magnitude for the same samples incubatedon different M.pusilla strains. Over the winter–springperiods, a highly dynamic situation was evident, with wide fluctuationsfor both host and virus abundances from one week to another.In some cases, peak host concentrations were accompanied byan increase in viral numbers, whereas in other cases the respectivefluctuations were uncoupled. Although fluctuations of M.pusillaabundance could be influenced by viral infection, there wasno evidence that viruses were able to terminate host blooms.The summer decline of M.pusilla populations did not appear tobe related to the impact of viral infection.     

Successional dynamics of the phytoplankton in the lower part of the river Ebro

The temporal and spatial dynamics of phytoplankton have beenstudied in four sites located along the last 60 km of the riverEbro, over a period of 1 year. Diatoms and green algae werethe most abundant groups; blue-green algae were frequent onlyin autumn. Asterionella formosa dominated the winter phytoplanktonassemblages. In autumn, spring and early summer centric diatomswere dominant: Aulacoseira granulata (Ehr.) Simonsen in autunm;Cyclotella sp. p1., Skeletonema potamos (Weber) Hasle and StephanodisciLssp. p1. in spring. A great abundance of green algae was observedduring the summer, mainly in the lower sites. In the sites closerto the mouth, the spring maximum of centric diatoms extendedto the summer. Mainly in the downstream sites, a remarkablegrowth of Acrinocyclus normanii f. subsalsa (Juhl.-Daunf.) Hustedtand Stephanodiscus hantzschii f tenuis (Hust.) Hak. & Stoerm.was added to green algae in the late summer. As has been investigatedthrough a principal component analysis, the phytoplankton temporalsuccession and longitudinal differences between the sites maybe affected by the variations in flow and the increase of waterconductivity downstream; both factors seem to act together.The river is rather homogeneous with respect to the phytoplanktonassemblages during the winter and spring months, and from latespring to the following autumn, differences greatly increaseboth in time and downstream.     

The Effects of Nitrogen Fertilization and the Growing Season on Carbon Partitioning in a Sward of Tall Fescue (Festuca arundinacea Schreb)

The effect of N fertilization on the relative carbon partitioningto the roots of tall fescue (Festuca arundinacea Schreb ), grownunder field conditions, was studied with a ¹⁴C-labelling techniqueon three regrowths representing contrasting growing seasonsUnder non-limiting N growing conditions, the relative carbonpartitioning to the roots averaged 17.0, 15 8, and 11 1% inthe summer, autumn, and spring regrowths, respectively The relativecarbon partitioning to the roots increased during the summerand autumn regrowths but decreased during the spring regrowthIn the absence of N fertilization, the relative carbon partitioningto the roots averaged 31 3, 26 5, and 26 7 in the summer, autumn,and spring regrowths, respectively The results were interpretedin terms of a functional equilibrium between the shoots andthe roots It was concluded that, for a dense canopy of a perennialgrass growing under fluctuating conditions of solar radiationand temperature, the relative growth of the roots compared tothe relative growth of the total biomass is primarily a functionof the shoot biomass Festuca arundinacea Schreb, carbon, partitioning, nitrogen, root growth, fertilization, grass     

Macrozooplankton studies in Kuwait Bay (Arabian Gulf). II. Distribution and composition of planktonic penaeidea

Six penaeideans were identified during a 12-month investigationof macrozooplankton in Kuwait Bay. The numerically dominantspecies included two sergestids, Lucifer hanseni and Acetesjaponicus. Of the two, L.hanseni appears to spawn in the bayduring summer months while, A.japonicus may concentrate itsspawning in coastal waters during late spring through fall.The most abundant penaeids were Parapenaeopsis stylifera andMetapenaeus spp., although Kuwait Bay may not be a major spawningarea for these species. However, the Khor al Sabiya, a river-likechannel northeast of Kuwait Bay, may serve as a nursery forat least two of the penaeids (Metapenaeus spp. and Penaeus semisulcatus)as well as for A.japonicus. Both P.stylifera and Metapenaeusspp. larvae were most abundant during late spring. Penaeus semisulcatuslarvae exhibited fall and spring-summer maxima but were neverlocally abundant.     

Feeding of Sagitta enflata and vertical distribution of chaetognaths in relation to low oxygen concentrations

Zooplankton samples were collected in Mejillones Bay, northernChile (23°00'15'S, 70°26'43'W ). Sampling was conductedat 4 h intervals, for 24 h during three seasons, austral spring(October 2000), summer ( January 2001) and winter (August 2001)at three different strata (0–25, 25–50 and 50–100m). Five species of chaetognaths were collected. Sagitta enflatawas the most abundant species, representing up to 65% of allchaetognaths in total numbers, followed by Sagitta bierii, makingup 34% of the total abundance of chaetognaths. S. enflata wasdistributed mainly above the Oxygen Minimum Zone, while S. bieriiremained below this zone. Feeding rates were relatively constantwithin the upper layer (0–25 m depth), for each samplingdate, averaging 1.2 prey S. enflata day^–1, and decreasingwith depth. Gut content analyses demonstrated that predationwas principally focused on small copepods (<1500 µm),with greatest feeding activity occurring at night. The dailypredation impact on the total standing stock of small copepodsvaried seasonally between 6% in spring and 0.4% in winter. Thispercentage may represent a negligible impact on the entire copepodcommunity, but it is relevant at the species or genus level,since S. enflata removed more than 20% of the standing stockof Centropages brachiatus and Corycaeus sp. Thus, during someperiods of the year, chaetognaths may strongly influence theabundance and size distribution of copepods in coastal upwellingecosystems.     

莱州湾及黄河口水域鱼类群落结构的季节变化

根据2011年5月—2012年4月对莱州湾及黄河口水域9个航次的渔业底拖网调查数据,对该水域鱼类群落结构特征及其季节变化进行了初步研究。结果表明:莱州湾及黄河口水域共捕获鱼类62种,隶属于11目、34科、53属,主要由暖水种和暖温种组成,其中鲈形目种类最多(37种),其次是鲉形目(7种)和鲽形目(6种)。春季优势种包括矛尾鰕虎鱼(Chaeturichthys stigmatias)、鲱衔(Callionymus beniteguri)、短吻红舌鳎(Cynoglossus joyneri)、矛尾复鰕虎鱼(Synechogobius hasta)和方氏云鳚(Enedrias fangi),其渔获量占总渔获量的70.8%;夏季包括矛尾鰕虎鱼、斑鰶(Konosirus punctatus)、鲱衔和短吻红舌鳎,占总渔获量的68.1%;秋季包括矛尾鰕虎鱼、赤鼻棱鳀(Thrissa kammalensis)、鳀(Engraulis japonicus)、青鳞小沙丁鱼(Sardinella zunasi)、斑鰶、小黄鱼(Larimichthys polyactis)和矛尾复鰕虎鱼,占总渔获量的87.1%。平均单位时间渔获量存在显著季节变化,以秋季最高(22.63kg/h),其次是夏季(16.75kg/h),春季最低(1.29kg/h)。春季(5月)平均单位时间渔获量为0.69kg/h,为1959年、2003年、2006年和2008年春季(5月)的0.3%、0.3%、1.7%和541.2%,鱼类资源量虽有所回升,但总体呈大幅下降的趋势。鱼类种类数、丰富度指数和多样性指数夏季较高,秋季次之,春季最低,但是以渔获尾数计算的均匀度指数,夏季最大,春季最小,以渔获量计算的均匀度指数则相反,且丰富度指数和多样性指数与表层温度呈极显著相关(P0.01),丰富度指数和均匀度指数与表层盐度呈极显著相关(P0.01)。     

Size and species-specific primary productivity and community structure of phytoplankton in Tokyo Bay

Combined methods of size fractionation and single-cell isolationwere used to investigate the seasonal variation of phytoplanktondynamics in Tokyo Bay with an emphasis on primary productivity.Red tides occurred in Tokyo Bay from spring to autumn; a diatom,Skeletonema costatum, and a raphidophycean, Heterosigma akashiwo,were the most important primary producers. Small diatoms andflagellates, including these species, were dominant and showedrapid changes of phytoplankton community structure within severaldays in summer. The nanoplankton (3–20 µm) fractioncontributed most to chlorophyll a concentration and primaryproductivity during spring to autumn, whereas the microplankton(>20 µm) contribution was remarkable in winter. Picoplankton(<3 µm phytoplankton) remained relatively constantthroughout the year. A significant reverse relationship wasobtained between assimilation rate and chlorophyll a contentfor the total and nanoplankton population; the assimilationrate was high at the initial phase of the bloom, then decreasedto a minimum level at the peak of the bloom. Factors controllingthe reduction of assimilation rates at the peak, and changesin phytoplankton community structure, are discussed.     

Life cycle strategies and seasonal variations in distribution and population structure of four dominant calanoid copepod species in the eastern Weddell Sea, Antarctica

The dominant Antarctic copepod species Calanoides acutus, Calanuspropinquus, Rhincalanus gigas and Metridia gerlachei were investigatedwith respect to their abundance, vertical distribution, developmentalstage composition, dry weight and lipid content. The specimenswere sampled during three expeditions to the eastern WeddellSea in summer (January/February 1985), late winter/early spring(October/November 1986) and autumn (April/May 1992) between0 and 1000 m depth to follow the seasonal development of thepopulations. Three species were most abundant in April, onlyC.propinquus reached highest concentrations in February. A seasonalmigration pattern was evident in all four species, but was mostpronounced in C.acutus. In October/November, they inhabiteddeeper water layers, their ascent started by mid-November andin mid-February the species concentrated in the upper 50 m,except for M.gerlachei (50–100 m). Their descent was observedin April/May. The stage composition changed dramatically withseason, the older developmental stages (CIII–CVI) dominatedthe populations in late winter/early spring, whereas youngerstages (CI and CII) prevailed during summer (C.acutus, C.propinquus)or autumn (R.gigas, M.gerlachei). Only C.acutus ceased feedingin autumn and diapaused at depth. Strong differences betweenseasons were also detected in dry weight and lipid levels, withminima in late winter/early spring and maxima in summer (C.acutus,R.gigas) or autumn (C.propinquus, M.gerlachei). Lipid reservesseem to be most important for the older stages of C.acutus andC.propinquus. Based on these seasonal data, different life cyclestrategies are suggested for the four species.     

LIFE HISTORY AND POPULATION DYNAMICS OF COCHLICELLA ACUTA (MuLLER) (GASTROPODA: HELICIDAE) IN A PASTURECEREAL ROTATION

The conical snail Cochlicella acuta was sampled over a 3-yearperiod in a pasture-cereal rotation and a nearby roadside wastelandat Hardwicke Bay, South Australia. The life cycle of C. acuta was primarily biennial in the agriculturalfields, with offspring being produced in large numbers in thepasture phase but not the cereal phase of the rotation. Thebreeding season lasted from autumn to spring. Snails were mostabundant in spring and summer, especially near the edges offields. During summer, snails aggregated on robust weeds suchas Reseda lutea. Many snails were killed by burning pasturesin autumn, prior to sowing crops. Snails were more abundantand smaller in size in the roadside wasteland than in the agriculturalfields. Strategies for the control of C. acuta in pasture-cereal rotationsare discussed. (Received 9 April 1990; accepted 10 August 1990)     

Observations on Alexandrium tamarense (Lebour) Balech and Other Dinoflagellate Populations in Golfo Nuevo, Patagonia (Argentina)

The toxic dinoflagellate Alexandrium tamarense and other dinoflagellatespecies were studied, along with water temperature and nutrientconcentrations, from September 1995 to December 1998 in theGolfo Nuevo, Chubut, Argentina. Nutrient concentrations werelow, showing a peak of high concentration in winter and a phaseof depletion in late spring and summer. Dinoflagellates tendedto be abundant during spring and summer, when Prorocentrum micanswas the most important species. Other dinoflagellates were Pyrophacushorologium and Dinophysis acuminata. Ceratium tripos, C. fususand C. horridum were present during the autumn, and a C. tripospeak up to 5.9 x 10³ cell l^–1 was observed in May 1997.Alexandrium tamarense showed strong interannual variation, thehighest concentration being found in spring (September–October)1995, with densities up to 15 x 10³ cells l^–1. The secondA.tamarense peak was observed during October–November1998 with maximal densities up to 5 x 10³ cells l^–1. Moderatelyhigh A. tamarense cyst densities, up to 300 cysts cm^–3of sediment, were found in the deep zone of the Golfo Nuevobasin. Among meteorolog-ical variables, increased late winterrain and higher solar radiation during spring may have influencedA. tamarense blooms.     

Seasonal variability of phytoplankton populations in the middle Adriatic sub-basin

The seasonal variability of phytoplankton assemblages in themiddle Adriatic sub-basin is described. The investigated areacrossed the middle Adriatic from the Italian to the Croatiancoasts. Hydrographic data, chlorophyll (Chl) a and phytoplanktonwere collected on a seasonal basis from May 1995 to February1996. Highest phytoplankton densities (up to 6 x 10⁶ cells dm^–3)were observed in spring and autumn in the western side, withinthe diluted waters. The vertical distribution of Chl a exhibiteda pronounced subsurface maximum associated, in coastal waters,with micro-planktonic diatoms. Phytoplankton assemblages weredominated by phytoflagellates in all the periods investigated.Diatom maxima were observed in spring and autumn: their verticaldistribution generally reflected the Chl a pattern and in thewestern coastal area peaks are due to large diatom species (Pseudo-nitzschiaspp.). In offshore waters, dinoflagellates strongly prevailover diatoms and provide a relevant contribution to the totalbiomass, especially in highly stratified conditions. Coccolithophoridswere mostly encountered in surface layers and their highestcontribution to the total biomass was observed in the LevantineIntermediate Water.     

Copepod abundance in the western Irish Sea: relationship to physical regime, phytoplankton production and standing stock

The distinct patterns of stratification in the North Channeland stratified region of the western Irish Sea influence theseasonal abundance of phytoplankton. The 3–4 month productionseason in the stratified region was characterized by productionand biomass peaks in the spring (up to 2378 mg C m² day^–1and 178.4 mg chlorophyll m^–2) and autumn (up to 1280 mgC m^–2 day^–1 and 101.9 mg chlorophyll m^–2).Phytoplankton in the North Channel exhibited a short, late productionseason with a single summer (June/July) peak in production (4483mg Cm^–2 day^–1) and biomass (–160.6 mg chlorophyllm^–2). These differences have little influence on copepoddynamics. Both regions supported recurrent annual cycles ofcopepod abundance with similar seasonal maxima (182.8–241.810³ind. m^–2) and dominant species (Pseudocalanus elongatusand Acartia clausi). Specific rates of population increase inthe spring were 0.071 and 0.048 day¹ for the North Channel andstratified region, respectively. Increased copepod abundancein the stratified region coincided with the spring bloom, andwas significantly correlated with chlorophyll standing stock.Increased copepod abundance preceded the summer production peakin the North Channel. This increase was not correlated withchlorophyll standing crop, suggesting that a food resource otherthan phytoplankton may be responsible for the onset of copepodproduction prior to the spring bloom. Hetero-trophic microplanktonas an alternative food source, and advection of copepods fromthe stratified region, are proposed as possible explanationsfor copepod abundance increasing in advance of the summer peakin primary production.     

Horizontal distribution and dominant species of heteropods in the East China Sea

This article discusses the horizontal distribution and dominantspecies of heteropods in the East China Sea. The ecologicalcharacteristics of heteropods and their adaptability to theenvironments were also considered. Oceanographic census wascarried out in the East China Sea (23°30 '33° N and118°30'128° E) in four seasons from 1997 to 2000. Itwas found that the total abundance showed obvious seasonal variations.It peaked in autumn with a mean value of 21.03 ind. (100 m³)^–1,followed by summer (4.89 ind. (100 m³)^–1). The lowestabundance occurred in winter and spring. As to the horizontaldistribution, abundance in summer and autumn was higher in thenearshore than in the offshore of the East China Sea. In winterand spring, heteropods were barely found in the northern nearshore.Three dominant species were observed in four investigated seasons,in which only Atlanta rosea dominated in winter, spring andsummer while Atlanta peroni and Atlanta lesueuri mainly dominatedin autumn. These two dominant species observed in autumn exhibiteda rather higher occurrence frequency than A. rosea. Temperaturewas found to be a major influencing factor whereas salinitywas a minor one. Comparing their adaptability, A. rosea cansurvive in a wider temperature range (1628°C), which enablesit to dominate in four seasons, while A. peroni survives ina relatively narrow temperature range (1928°CC) and therange for A. lesueuri was even more narrow (2128°CC). Moreover,A. rosea was also adapted to a wider range of salinity. However,the abundance of A. rosea in autumn was lower than those ofA. peroni and A. lesueuri. It can be thereby inferred that themultiplication speed of A. rosea was lower than the other twospecies within the same favorable temperature range. Due totheir adaptability to high salinity, the distribution of heteropodswas closely related to the domain of the Taiwan Warm Currentand Kuroshio. Especially for A. peroni and A. lesueuri, theirhigh abundance areas are always indicative of the lasting existenceof strong warm currents. The negative values of aggregationindices indicated relatively even distribution of heteropodsin the East China Sea. The high abundance area (31°00' N,126°00' E) of heteropods in autumn is on the migration pathwayof the mackerel (Scomber japonicus Houttuyn). Thus, there isalso a fishing ground of the mackerel. This suggested that thehigh abundance area of heteropods in autumn is important tothe fisheries in the East China Sea. Comparing with the historicalrecords, the abundance of heteropods appeared to increase inthe past 40 years. This may be a result of strengthened warmcurrents due to global warming.     

The productive and optical status of the oligotrophic waters of the Southern Aegean Sea (Cretan Sea), Eastern Mediterranean

Primary production, pigment concentrations and spectral measurementsof downwelling irradiance were made at four stations in fourseasons (spring, summer, autumn, winter) during 1994 in thewaters of the South Aegean Sea (Cretan Sea), Eastern Mediterranean.Rates of production were determined using in Situ incubationtechniques and included measurements at the surface microlayer.Depth-integrated values averaged over season were 5.66 mg Cm^–2 h^–1 for primary production and the correspondingchlorophyll (Ch1) a and phaeophytin (Phaeo) a values had meansof 4.87 and 1.21 mg m^–3 respectively. The assimilationratio remained very low (mean over season: 1.19 mg C mg^–2Chl a h^–1 as did the Phaeo a/Chl a ratio (mean over season:0.24). The annual production for the area was estimated to yield24.79 g C m^–2 year^–1. Primary production and Chla estimates showed statistically significant seasonal, spatialand depth variations. The spectral values of the attenuationcoefficient Kd (     

FOOD PREFERENCES AND DIETARY OVERLAP BY TERRESTRIAL SNAILS IN LOGOS AREA (EDESSA, MACEDONIA, NORTHERN GREECE)

Among the five coexisting species of snail in Edessa (N. Greece),Bradybaena fruticum and Helix lucorum dominated in density andbiomass in comparison with Xeropicta arenosa, Monacha cartusianaand Cepaea vindobonensis. Resting places of each species inrelation to plant cover and diet preferences are examined seasonallyand throughout a year. Discriminant analysis for the annualdata showed that 83% of the snail group species could be differentiatedby the plants on which they were attached. Each snail specieswas usually found sitting on one of the most abundant plants.Cepaea preferred to sit on and eat senescent material even inspring time and Bradybaena green material. In spring, the snailsdid not consume plant material in proportion to the occurrenceof those plants but they usually did so in summer and in autumn.Hedera helix was not consumed even when it was abundant. Inspring and autumn the snails had consumed plants to which theywere found attached, but in summer they did not. (Received 9 August 1993; accepted 14 February 1994)     

Distribution and species-specific egg production of Pseudocalanus in the Gulf of Alaska

Pseudocalanus species are important contributors to the secondaryproduction of the northern hemisphere mid- to high-latitudeoceans. In the coastal Gulf of Alaska, Pseudocalanus are presentyear round and are represented by three species. In 2001, Pseudocalanusmimus was the dominant Pseudocalanus species on the shelf duringspring and summer, comprising 30–100% of the total, whilePseudocalanus newmani dominated in Prince William Sound (10–90%).Pseudocalanus minutus were only abundant in Prince William Soundduring early spring. Egg production (by number and volume) wasa function of female prosome length and decreased from springto summer; however, significant variability was attributableto regional influences that were independent of size. For thesame sized female, P. newmani produced more eggs per clutchthan P. mimus. Pseudocalanus mimus, however, tended to havea larger mean egg size than P. newmani. Consequently, clutchvolumes of the two species were indistinguishable. Pseudocalanusegg production rates (EPRs) (eggs female^–1 day^–1)were lower in July and August (ca. 2–4) than April andMay (ca. 1–9), but total egg production by the population(eggs day^–1) was nearly equivalent for the two time periodsdue to higher female concentrations in summer.