Observations on the vertical distribution of zooplankton, including post-larval teleosts, off Plymouth in the presence of a thermocline and a chlorophyll-dense layer

During 1973 – 1977, when Sagitta elegans was returningto dominance over S. setosa in Plymouth waters, there was often,in summer in stratified conditions, a community characterizedby S. setosa in the warm water above the thermocline, and atypical S. elegans community in the colder layer below the thermocline.This vertical separation persisted at night even though somespecies from the S. elegans community migrated up into the warmlayer. Such vertical migration was not stopped by a temperaturediscontinuity of from 3° to 6°C, but fewer individuals,or a lesser proportion of species, took part at the higher temperaturedifference. Only a small part of the zooplankton, comprisingsmall individuals of Limacina retroversa, the appendicularians,and, possibly, post-larvae of Arnoglossus laterna, showed signsof aggregation at the thermocline or the chlorophyll maximumclose to it.     

Population structure, vertical distribution and diel migration of Sagitta setosa (Chaetognatha) in the south-western part of the Black Sea

The population structure of Sagitta setosa from the south-westernpart of the Black Sea was examined between May 1994 and December1996. In addition, the vertical distribution and diel verticalmigration of S.setosa were studied for juveniles (     

The role of thermal stratification on the population dynamics of Sagitta elegans Verrill in the western Irish Sea

Temperature and prey availability have a marked effect on thedevelopment and growth of Sagitta elegans. This study addressesthe effects of thermal stratification on the growth and sizeof adult S.elegans in the western Irish Sea. It shows that instratified waters, bottom water temperature had a greater effecton the development of mature adults than surface water temperature.Whilst the length of mature individuals caught in 1992 and 1994decreased with increasing temperature, they did not conformto the models of McLaren (1963) and Sameoto (1971), as the animalswere larger than predicted. The long breeding period found inthe stratified region, suggests that previous reports of oneor two generations per year in the western Irish Sea do notaccount for the likely mix of generations that occur from Februarythrough to September.     

Vertical distribution of pelagic chaetognaths and feeding of Sagitta enflata in the Central Equatorial Pacific

The vertical distribution and feeding of pelagic chaetognathsat 5°S, 160°W in the Central Equatorial Pacific wereinvestigated using a series of 0–500 m vertical haulswith a VMPS net over a 24 h period between 6 and 7 October 1990.The total number of individuals per haul was between 370 and688. Fourteen species in four genera were found at this station.The most abundant species was Sagitta enflata which comprised32.4–61.1% of the individuals collected from the 0–500m layer. Mesopelagic species made up 9.3–15.1% of thetotal number of individuals. Sagitta enflata and Pterosagittadraco were found in the upper part of the thermocline both byday and at night. The fraction of the population containingfood items (FCF) of S.enflata in the 0–50 m layer variedbetween 4.8 and 12.5% (mean 10.8%) and feeding activity washighest between sunrise and noon. The percentages of Copepoda,Foraminifera, crustacean larvae, Chaetognatha, Pteropoda, Ostracoda,fish and unidentified material in the gut of S.enflata were51.9,6.7,3.8,2.9,1.9,1.9 and 30.9%, respectively. Sagitta enflataconsumed food organisms which were mainly between 0.5 and 1.0mm in length. The daily feeding rate of S.enflata was 1.81 preyper individual, which was equivalent to 8.06 mg C m^–2day^–1. This corresponded to     

Composition, spatial and temporal variations of Chaetognatha in Guanabara Bay, Brazil

This paper presents the specific composition and distributionof adult chaetognaths in Guanabara Bay, Brazil. A comparisonhas been made between chaetognath and copepod distribution patterns.Three areas were distinguished within Guanabara Bay: an externalarea, influenced by oceanic waters; an internal area, influencedby fluvial waters; and a transitional area between the two.Monthly samples were collected by horizontal surface hauls usinga conical net with 200µm mesh. Three species were identified:Sagitta friderici, S.enflata and S.hispida. Sagitta fridericiwas the dominant species and occurred throughout the year atthe three areas. Sagitta enflata and S.hispida were limitedto the more saline waters. Generally, greater densities of chaetognathswere observed following copepod peakden sities. Temperatureand salinity associated with copepod abundance were the mostimportant factors affecting the distribution pattern and theabundance of chaetognath species in Guanabara Bay.     

Notes on feeding of Chaetognatha in Guanabara Bay, Brazil

A preliminary analysis, by means of the gut content, of thediet of Sagitta friderici and Sagitta enflata occurring in GuanabaraBay was carried out. The samples were collected at differenttimes over a 4day period in September 1995, during verticaltows with a conical net of 200 µm mesh size at a fixedstation (30 m depth). In total, 1000 individuals were examined.Copepoda were the numerically dominant group of prey of S.fridericiand S.enflata (67.2 and 74.6%, respectively); both species behaveas opportunistic carnivores, feeding mainly on the more abundantcopepod species throughout the water column. Adult individualsof S.fnderici and S.enflata (stages III and IV) seem to havefood requirements different from juveniles: adults fed on otheritems (chaetognaths, crus tacean larvae, hydromedusae and luciferidae),and the food containing ratio (FCR) was higher in indi vidualsof stage Ill. In general, only one prey per gut was registered.Chaetognaths may have chosen their prey in relation to theirsize, since the size of the prey was proportional to the sizeof their predators. Feeding intensity (NPC) was higher in individualscollected during the night periods.     

Polarisationsoptische Untersuchungen an Sagitta setosa und Sagitta hexaptera

Zusammenfassung Die doppelbrechenden Lipoide in der Körperwand der Sagitta setosa werden an Aufnahmen in polarisiertem Licht nach dem lebenden Objekt vorgeführt, und zwar sowohl die Lipoidstreifen und die Lipoidspindeln der Hauptmuskulatur als auch die nur polarisationsoptisch nachweisbaren Lipoideinlagerungen in den Fasern der lateralen Muskelfelder. Weiter wird die Lokalisation der Lipoide an Quer- und Längsschnitten durch die Körperwand der Sagitta hexaptera dargelegt.     

Seasonal variation and life history of the pelagic chaetognatha, Sagitta elegans Verrill, in Toyama Bay, southern Japan Sea

The seasonal variation and life history of the pelagic chaetognatha,Sagitta elegans Verrill, in Toyama Bay, southern Japan Sea,were investigated using a time series of 0–500 m verticalhauls with a Norpac net from 1 February 1990 to 30 January 1991.Nine species of one genus occurred in Toyama Bay throughoutthe year, including the cold-water species S.elegans. Therewas no remarkable variation in abundance throughout the year,although many individuals were collected in August. Juvenilesoccurred mostly in spring and summer, from late March to August.Adults (Stage 3) occurred in all seasons, except summer. Thebody length of adults ranged from 26 to 30 mm. There were twoprincipal spawning periods. One was in March-May and the otherwas in August. Life spans of both cohorts were 10–12 months.Copepods were major prey of S.elegans inhabiting Toyama Bay.The annual mean food-containing ratio (FRC) was 6.1%, but values>10% occurred in February, April, May, July and September.     

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.     

DISTRIBUTION AND POPULATION DYNAMICS OF THREE POPULATIONS OF SIPHONARIA ON ROCKY INTERTIDAL SHORES IN HONG KONG

The pulmonate limpets Siphonaria japonica and Siphonana siriusoccur over a wide range of local habitat types in terms of exposureto wave action and salinity. This is a study of these two specieson three different shore types in Hong Kong, ranging from anextremely exposed, high salinity (32–35) shore at Caped'Aguilar to a sheltered, low salinity (16–33) shore atTai Lam Chung. Both species are restricted to the low shore,year round. S. japonica is a winter breeder and recruitmentoccurred between October and January. The recruitment of S.sirius could not be recognised from the size-frequency histograms.The algal standing crop at Tai Lam Chung was higher than atWu Kwai Sha during the winter period, i.e., between Octoberand April. Seasonal fluctuations in growth rate were recordedfor both Siphonaria species with the time of fastest growthoccurring in winter. S. japonica grew faster at Tai Lam Chungthan at Wu Kwai Sha. Food availability is thought to be an importantfactor affecting growth. (Received 17 September 1993; accepted 16 June 1994)     

Ecological investigations of the zooplankton community of Balsfjorden,northern Norway: Population structure and breeding biology of the chaetognath Sagitta elegans Verrill

The population dynamics of the chaetognath Sagitta elegans Verrill has been followed in Balsfjorden in 1976 and 1977. Seasonal variation in abundance, length-frequency distribution, growth in total length, and maturity stages are presented and discussed in relation to changes in hydrography.An annual generation of S. elegans was found, with a protracted and more or less continuous breeding season from May until October during 1977. The 1976 year-class consisted of two distinct length groups, both of which participated in the 1977 spawning. This spawning gave rise to possibly four sub-populations during 1977. The variation in numbers of sub-populations produced during the spawning season in 1976 and 1977 is discussed in relation to the hydrographical conditions in Balsfjorden. From November 1976 to March 1977 the abundance of S. elegans varied between 1 and 8 ind. · m^?3. The lowest value was recorded in May (0.9 ind. · m^?3). From September to December 1977 the population abundance was ≈2 ind. · m^?3.     

The life history and vertical distribution of the chaetognath, Sagitta elegans, in Dabob Bay, Washington

Seasonal changes in the population structure and patterns ofvertical distribution and migration of the dominant chaetognath,Sagitta elegans, in a fjord off Puget Sound were determinedwith samples collected at approximately semi-monthly intervalsfrom November 1972 to November 1973. S. elegans bred continuouslyfrom March through August, with major recruitment in June andJuly. Seasonal changes in the vertical distribution of the populationand in the proportion of the population that vertically migratedreflected the stage of maturity and size of the individuals.Small chaetognaths were non-migratory and distributed in thetop 100 m. Stage II individuals were dispersed throughout thewater column; some did migration was evident. Breeding stageswere restricted to a layer between SO and 100 m during the dayand migrated to the surface layer at night, enhancing the probabilityof successful reproduction.     

Interannual variability in a predator-prey interaction: climate, chaetognaths and copepods in the southeastern Bering Sea

The interaction of the chaetognath Sagitta elegans with thecopepod community of the southeast Bering Sea middle shelf wasexamined in relation to environmental conditions during 1995–1999.Predation impact was estimated for 2 years, 1995 and 1997, usinggut content analysis, experimentally derived digestion time(DT) and abundances of chaetognaths and prey. Pseudocalanusconcentrations correlated with water temperature and Calanusmarshallae with sea ice extent. Sagitta elegans were less abundantbut individuals were larger in 1995, when C. marshallae predominated,compared to 1997, when Pseudocalanus and Acartia were the primaryprey. Predation by S. elegans removed <1% standing stockday^–1 of Pseudocalanus or C. marshallae in 1995 and 1.7to 2.3% of Pseudocalanus in 1997. The percent of the copepodcommunity biomass required by chaetognaths was estimated tobe <1% in 1995 compared with 8–12% in 1997. Calanusmarshallae may be more vulnerable than Pseudocalanus to cumulativepredation effects because of its reproductive strategy. Theeffect of chaetognath predation on the copepod community dependson which copepod species is predominant and its susceptibilityto cumulative predation effects, as well as on daily predationimpact, both of which varied between years with different climaticconditions.     

Sur quelques zooplanctontes abondants dans l'upwelling de Cabo Frio (Bresil)

On some zooplankters common in the Cabo Frio (Brazil) upwelling.In the waters off Cabo Frio zooplankton maxima are observedbetween February and April, which is the period of upwellingoccurrence. Copepods are highly diversified; we identified 96species at a single collecting station during one year. In summerCalanoides carinatus, Paracalanus parvus and Oncea media areabundant, whereas we observed dominance of Temora stylifera,Clausocalanus furcatus, C. arcuicomis, Oithona plumifera andgreat quantity of Creseis acicula during winter. Chaetognatha(Sagitta enflata), Appendicularia (Oikopleura longicauda), Ostracoda(Conchoecia spp.) and Pteropoda (Limacina sp.) are permanentthroughout the year, and maximum in summer. The vertical distributionof zooplankton depends on the hydrological structure, i.e. natureof the water mass and degree of mixing between different waters.Brazil current water, with low quantity of organisms and dominanceof copepods (Clausocalanus furcatus, Mecynocera clausi, Corycaeidae,Oithonidae, Oncaeidae) accompanied by Evadne spinifera and Lucifertypicus. South Atlantic Central Water (upwelling water) characterizedby rare deep copepods and abundance of Calanoides carinatusand Ctenocalanus vanus which are excellent indicator speciesfor upwelling occurrence. Coastal water, with low salinity,where some species with brackish affinity are observed, likeOithona ovalis and Podon polyphemoides.     

THE ECOLOGY OF THE HONG KONG LIMPETS CELLANA GRATA (GOULD 1859) AND PATELLOIDA PYGMAEA (DUNKER 1860): REPRODUCTIVE BIOLOGY

Cellana grata is large, relatively long lived (3 years), withone winter breeding season each year which can be correlatedwith major seasonal climatic and hydro-logical events, e.g.,winter reduction in temperature and higher seas. C. grata ischaracterised by a relatively low value of mean annual reproductiveeffort (males: 23%; females: 18%). Patelloida pygmaea is small,short lived (1 year), with one spring breeding season each yearand devotes a large proportion of metabolic energy for reproduction.P. pygmaea showed a higher value of mean annual reproductiveeffort (males: 46%; females: 31%) than C. grata. Mature gonads of Cellana grata first appeared in June and itreached a peak maturity (100%) in September, remaining so untilDecember, i.e., the maturation of the gonads coincided withincreasing water temperatures, with spawning associated witha decrease in water temperature. Gonadal development by Patelloidapygmaea began in either July or August and reached a peak inDecember, remaining so until a major peak in spawning took placebetween April and May, i.e., gonad maturation coincided witha decline in water temperature, with spawning following thesubsequent increase. Limpet gonadal cycles are likely gearedto temperature and food supply. Spawning occurred between Novemberand December, when wave heights are typically 1 m higher thanin summer. (Received 1 December 1992; accepted 25 June 1993)     

Subantarctic krill, Euphausia vallentini Stebbing, preyed upon by penguins around Crozet Islands (Southern Indian Ocean): population structure and annual cycle

Dietary studies performed on three planktivorous penguins, Eudypteschrysolophus, E.chrysocome and Pygoscelis papua, provided alarge collection of well-preserved Euphausia vallentiru at differentperiods of the year. The change of carapace-length distributions,gut fullness and sexual maturity stages of E.vallentini aredescnbed. and a scheme for the life history of this speciesis proposed from this set of data. Its main characteristicsare as follows: mating peak in October-November; recruitmentof post-larval individuals from December-January onwards; fastgrowth until May; zero winter growth between June and mid-Augustdue to a minimum feeding activity Feeding activity reaches itshighest level from August to early October and is coincidentwith maturation, growth recovery, enhancement of sexual dimorphismand beginning of breeding season. Assuming that juveniles are1 year old when they begin to be recruited in penguin stomachs,E.vallentini is supposed to have a 2-year-life span in Crozetwaters. Two-year-old individuals are supposed to die in summeror autumn Juveniles can reach sexual maturity as early as November-Decemberwhen they are 1 year old and 16 mm body length: however, theyare unlikely to mate in significant numbers at this age. Inspite of specific limitations, the present sampling method iswell suited to routine surveys of local euphausiid populations.     

PRIMARY MOULT,WEIGHT AND BREEDING CYCLES OF THE ROCK PIGEON ON DASSEN ISLAND

Cooper, J. 1975. Primary moult, weight and breeding cycles of the Rock Pigeon on Dassen Island. Ostrich 46:154-156.

The primary moult season of the adult Rock Pigeon Columba guinea on Dassen Island is spread over at least nine months. Individual duration is estimated at eight months. Adult birds were heaviest in the winter months outside the breeding season. Overlap between the breeding and moulting seasons occurred and evidence was obtained of incubating birds with active primary moult. Juveniles were lighter than adults. Adults fed on the mainland and probably made daily flights there.     

Annual cycle of zooplankton community in the Abra Harbour (Bay of Biscay): abundance, composition and size spectra

The annual cycle of the zooplankton community in a coastal embaymentof the Bay of Biscay was studied from data on zooplankton fractionslarger than 45 and 250 µm Smaller zooplankton and chlorophyllmaxima coincided in summer, while larger zooplankton reachedthe maximum in spring. Copepods dominated in both fractionsmost of the year, being copepod nauplii and postnaupliar stagesof Oithona nana and Paracalanus parvus the main constituentsof the microzooplankton maxima, and older copepodites and adultsof Acartw clausi of the meso-macrozooplankton maxima. Secondarypeaks of abundance due to protozoan blooms of Steno-semellanivalu, in early spring, and Noctiluca santillans, in summer,were also observed in smaller and larger fractions respectively.The collapse of phytoplankton biomass in early autumn was followedby a strong decrease of zooplankton in mid autumn. From thisperiod to winter, chlorophyll and zooplankton abundance showedsmall variations, but noticeable changes in the compositionand size spectra of zooplankton were observed. In winter, valuesof chlorophyll and zooplankton abundance reached minima, A.clausidominated the copepod assemblage and carnivorous zooplankterswere absent or negligible The annual development of the mainpredator populations (Sagitta frideria, Luiopc tetraphylla andanchovies) were found to be synchronized with the variationsin abundance and size spectra of zooplankton in the study area.     

Reproduction of the greater bushbaby (Galago crassicaudatus panganiensis) under laboratory conditions

A breeding colony of Galago crassicaudatus panganiensis was maintained under laboratory conditions for four years, August 1971 to July 1975. The estrous cycle and the gestation period averaged 39 and 132 days in length, respectively. Twinning occurred in 14.5% of the pregnancies. No postpartum estrus was observed, although 1.2 conceptions per female per year were recorded. Breeding occurred throughout the year. Puberty occurred between ten and 18 months of age, the first conception occurred between 15 and 18 months of age, and reproductive capability decreased rapidly between ten and 12 years of age.     

Seasonal species composition of barnacle larvae (Cirripedia: Thoracica) in Rhode Island waters, 1977-1978

Cirripede larvae can occur year-round in temperate and tropicalwaters, often in significant numbers, yet the species compositionof the ‘Balanus sp.’ component is rardy studied.Weekly plankton samples were analyzed qualitatively for larvalcirripede species and stage over a year (1977–1978) attwo Rhode Island stations. Six species of larvae were foundin Lower Narragansett Bay (30° salinity). Semibalanus balanoidesand Balanus balanus have a single winter brood. S. balanoidesis the predominant winter breeder with a minor release of naupliiin early December and major release in March followed by cypridsin mid-April.B. balanus populations release all larvae in Marchwith cyprids in mid-April. Balanus crenatus is mainly a winterbreeder, but has multiple broods; it does not breed in July-Septemberwhen the water temperature is above 18°C. Balanus venustusis the predominant summer breeder, and larvae were observedfrom May through December (water >8°C). Larvae of Chthamalusfragilis and Balanus eburneus occur in low numbers from May-October.At the Pettaquamscutt River site (12 salinity), Balanus improvisuslarvae predominate and early stage nauplii (I-II) occur in samplesyear round (0–27°C). Two peaks of later stage naupliiand cyprids occur in late spring (May) and early winter (Nov.-Jan.).Continued temperatures bdow 5°C or above 20°C appearto inhibit larval development. Comparison of results with existing literature reveals severalsignificant findings. The bimodal rdease of S. balanoides larvaeis unusual and may be in response to the phytoplankton dynamicsof the year; however, the existence of distinct races of S.balanoides may also be a factor. Larvae of B. venustus predominatein the lower bay during the summer, yet this species is unreportedin past studies. B. improvisus nauplii are more cold tolerantthan previously reported. Comparison of findings with reportedbreeding patterns in Florida indicate significant differencesin temperature responses between northern and southern populations. ¹Contribution No. 188 from EPA Environmental Research Laboratory,South Ferry Rd., Narragansett, RI 02882