Predation, production and the organization of an estuarine copepod community

The copepod community of the estuaries near Beaufort, NC underwenta consistent seasonal succession from a spring assemblage dominatedby the medium-sized copepod Acartia tonsa (1 mm) to a summer—fallassemblage dominated by the small-bodied copepods Parvocalanuscrizsrirostris and Oithona colcarva (both 0.5 mm). However,in enclosure experiments during this period, A. tonsa dominatedthe community, due to higher growth rates and its predationon the nauplii of other species. Nutrient additions enhancedthe dominance by A. tonsa. The decline in abundance of A. tonsain the estuary was associated with increased abundance of planktivorousanchovies and silversides. In other enclosure experiments, planktivorousfish eliminated A. tonsa and other large copepods, althoughthey persisted in enclosures lacking fish. I conclude that predationby size-selective planktivorous fish prevents dominance by A.tonsa during summer—fall. ¹Present address: Institute of Marine Sciences, University ofNorth Carolina, 3407 Arendell Street, Morehead City, NC 28557,USA     

Diet changes in the carbon and nitrogen content of the copepod Metridia lucens

Diel changes in the near-surface (0–50 m) abundance, prosomelength, and carbon and nitrogen content of the copepod Metridialucens were measured in Deep Cove, Doubtful Sound, New Zealand(45°27'S, 167°9'E) between 3 and 6 September 1996. Metridialucens showed maximal abundance a night, suggesting a patternof normal diel vertical migration (DVM). The change in abundancesuggested that the descent of the population occurred –1h prior to dawn and the ascent –1 h after dusk. However,a proportion of the population remained near the surface duringthe day. Although there was no diel pattern in the prosome lengthof M.lucens collected near the surface, there was a marked dielcycle in the measured carbon and nitrogen contents, with maximalvalues being measured towards the end of the night prior tothe downward migration. We suggest that this diet cycle in themeasured elemental content was caused by DVM occurring morestrongly in those animals which had a better body condition,i.e. a higher elemental content per unit length.     

Surface hydrography and phytoplankton of the Brazil-Malvinas currents confluence

Results are presented on the phytoplankton species compositionand abundance from bottle samples collected in September 1989near the confluence of the Brazil and Malvinas currents offArgentina. The phytoplankton assemblages were dominated by diatomsand dinoflagellates. A surface diatom bloom was found alongthe west side of the Brazil Current, and was dominated by Thalassiosiradelicatula Ostenfeld emend. Hasle (cell numbers up to 5.5 x10⁵ cells 1^–1) The bloom was associated with strong temperaturegradients separating Brazil and Malvinas waters, and with thepresence of a cyclonic eddy near the confluence of the currents.These features were detected in satellite imagery coincidentwith the in situ sampling dates.     

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.     

Relationship between the bloom of Noctiluca scintillans and environmental factors in the coastal waters of Sagami Bay, Japan

In order to study the mechanism of the bloom formation of Noctilucascintillans, the relationship between the variation in the abundanceof N. scintillans and environmental factors was examined inthe coastal waters of Sagami Bay, Japan. Hydrographic (temperature,salinity, water stability), biological (chlorophyll a concentration,zooplankton biomass) and meteorological (rainfall, wind velocity,wind direction) factors were investigated from 1997 to 2004.For all years, the abundance of N. scintillans started to increasefrom March and reached a maximum in spring between April andMay. The abundance in 1997 and 2000 was relatively high comparedto the other years while the abundance in 1998 and 2004 wasrelatively low. A stepwise multiple linear regression analysisshowed that the wind direction and rainfall were significantlycorrelated with the variation in the abundance of N. scintillans.Our results suggest that bloom formation can be separated intoa three-step process: (i) initial increase in the abundanceof N. scintillans attributed to an increase in optimum hydrographicand biological factors, (ii) N. scintillans is then accumulatedby convergence of seawater by the factors of low rainfall andwind and (iii) swarmer-effects suggested enhanced bloom formation.Accumulation is considered to be a key trigger in this processof the formation of large-scale blooms. This paper was presented at Plankton Symposium III, held atFiguera da Foz, Portugal between 17 and 20 March 2005, underthe auspices of the University of Coimbra and the Universityof Aveiro, and coordinated by Mário Jorge Pereira andUlisses M. Azeiteiro.     

Planktonic predators and copepod abundance near the Dutch coast

Hypotheses that planktonic predators are responsible for thespring-summer decrease in copepod abundance and that the dominantpredator, Pleurobrachia pileus, is associated with high concentrationsof copepods were investigated at a station near the Dutch coast.Neither hypothesis was supported. Predators and copepods weresampled together with a 156 L ‘water box’ from lateApril through early July, including the season of P.pileus abundance.Using predators and copepods from the same box samples, hencefrom the same water parcel, feeding rates on copepod naupliiand copepodites + adults were measured onboard ship. Less than6% of the copepods, the sensitivity of the method, were removedper day. In additional shipboard feeding experiments net-caughtP.pileus were added to ambient copepod densities. By combiningwater volume cleared of copepods with ambient P.pileus densityin the sea, the predicted impact was 0–1.6% of copepodseaten per day from late April to early July. The hypothesisthat P.pileus associates with copepod concentrations was testedby comparing abundances of both groups from the same box samples.The correlations were not significant for any sample series.The ways measurement methods have restricted progress in understandingthe predatory impact of Pleurobrachia sp. are also considered.     

The demography of Calanus finmarchicus (Copepoda: Calanoida) in the Middle Atlantic Bight, USA, 1977-2001

The spatial distribution and annual cycle of abundance for thelate-stage copepodites of the calanoid copepod Calanus finmarchicusare described for the shelf and slope waters of the Middle AtlanticBight (MAB), a subregion of the US Northeast large marine ecosystem.Samples were collected with bongo nets from 1977 to 2001 onbroad-scale surveys of the region and from a continuous planktonrecorder (CPR) towed at 10-m depth along a route that traversedthe area. The copepod’s abundance in shelf waters increasedrapidly in early spring and reached maximum levels in May–June.It declined slowly thereafter, until a minor secondary pulseoccurred in late autumn, which was followed by the annual winterlow. Slope water abundance of C. finmarchicus peaked in Apriland was virtually absent there at 10-m depth from July throughthe following February. The two samplers, both portrayed similarhigh interannual abundance variability with no long-term trendevident for the 25-year period. Cluster analysis pinpointedthree shelf areas with similar abundance patterns, one of whichwas a region of high density located in the northeastern offshorewaters. Evidence is presented that indicates the source of thishigh abundance is likely from the populations that overwinterin deep water basins of the Gulf of Maine (GOM). The copepod’sinterannual abundance variability was found to be negativelycorrelated with water temperature and unrelated to fluctuationsof the North Atlantic oscillation (NAO) index.     

Temporal variability in the night-time distribution of epipelagic siphonophores in the North Atlantic Ocean at Bermuda

The temporal variability of siphonophores was compared on night-to-night,month-to-month and year-to-year scales in open-net collectionsmade at or near the Bermuda Atlantic Time Series (BATS) site.These collections were made as oblique tows to 100 m on (i)one summer night in each of 1986, 1989 and 1991, (ii) one nightper month on 13 cruises between April 1991 and August 1992,and (iii) three consecutive summer nights of 1992. The meanwet displacement volume (WDV) of sipho nophores in the thesecollections was 1.4 ± 0.6 ml per 100 m³ or 20 ±10% of the total catch biovolume. The most common species belongedto the Calycophorae families Diphyidae and Abylidae: the combinednumerical abundance of Chelophyes appendiculala, Eudoxoidesmitra, Lensia subtilis. Eudox-oides spiralis, Bassia bassensisand Abytopsis eschscholtzi averaged 300–400 per 100 m³.Combined numbers of these common species varied little whensampled hour by hour at the same location during consecutivesummer nights or at different night-time sampling locations10¹–10² km apart when these were sampled within 3–5h. In contrast, most of these six species exhibited 2- to 3-folddifferences in night-time abundance between summers of differentyears and between seasons. Three seasonal groups were detected,with a winter group being the most distinct from the others.Changes in the abundance of several species were correlatedwith seasonal changes in the depth of the mixed layer.     

Vertical structure of small metazoan plankton, especially noncalanoid copepods. I. Deep Arabian Sea

The abundance and vertical distribution of micro-metazoans sampledwith fine nets of 0.05 mm mesh size were studied at three stationsin the Arabian Sea during the intermonsoon period (April/May1987) and down to 1850 m depth. In the epipelagic zone (0–100m). values of biomass and metazoan abundance tended to be higherthan those reported for other tropical oceanic areas. In themesopelagic zone, which is characterized by an extreme oxygendeficiency between 100 and 1000 m depth, the abundance of metazoantaxa and species numbers of non-calanoid copepods were largelyreduced. However, intermediate abundance maxima occurred withinthis zone, which were dominated by specific metazoan taxa (copepods.appendicularians) and species of non-calanoids (Oncaea sp. C).In the bathypelagic zone below 1050 m, the species diversityof the dominant copepod family Oncaeidae increased substantially.Two-thirds of a total of 69 oncaeid species recovered were confinedto this layer. As most of them were small in size and occurredin low abundance only, the increase in total oncaeid densityand/or plankton biomass was less conspicuous. Dominant Oncaeaspecies in the bathypelagic zone were O.longipes and O.brodskii.The results are compared with published data from the ArabianSea and other tropical oceanic areas with and without an extrememesopelagic oxygen minimum zone Possible causes of the intermediateabundance maxima within the oxygen deficiency zone are discussed.     

Erratum

Journal of Plankton Research 12, 1295–1314, 1990 The abstract was incorrectly printed. The correct version isgiven below. The fine- to coarse-scale distribution patterns of tuna larvaein the east Indian Ocean were investigated by a combinationof continuous transect sampling using surface tows and randomsampling using double oblique tows. Thunnus maccoyii was themost abundant species, reaching densities near patch centresof 22 m^–3 in surface tows, which is 25 times greater thanthe highest previous records for tuna larvae. Patches of T maccoyiilarvae in areas of high abundance appeared to be 5–15km in diameter. Smaller patches in areas of low abundance wereusually composed of older larvae Lloyd's index of patchinesswas consistently high for all tuna species, ranging from 3.0to 5.2 for T.maccoyii. There was no change in the index whentow distance was doubled to 1200 m, which suggests that thedominant patch size was somewhat larger than the larger samplinginterval. Sampling larvae at the same site 4 days apart resultedin estimates of abundance that differed by an order of magnitude.Abundance estimated from a single station would depend largelyon what day the station was occupied and where the sample wastaken in relation to a patch.     

DISTRIBUTION AND ABUNDANCE OF GYMNOSOMATA (GASTROPODA: OPISTHOBRANCHIA) IN THE SOUTHWEST ATLANTIC

The distribution and abundance of gymnosome gastropods in theArgentine Sea and Brazil—Malvinas Confluence during 1978–1979and 1988 were studied. The collections analyzed included 768quantitative samples obtained between 48°W and the coast,and from 35°S to 55°S. Two species were found. Spongiobranchaeaaustralis was the most frequent and abundant (up to 730 per1000 m3); its presence in the area was associated with the coreof the Malvinas Current. Clione antarctica was less abundant(maximum abundance: 230 per 1000 m³) and was also associatedwith the Malvinas Current. The geographic ranges of both speciesin the area are wider than previously described. Since the rangeof S. australis in the area extends far from the range of itsprey Clio, it is not clear whether S. australis can feed onthe thecosomatous pteropod Limacina (and not only on Clio, asdescribed in the bibliography) or it starves in that area. Duringthe 1978–1979 annual cycle, the abundance of both speciesfollowed neither the abundance patterns of their prey nor ofthe total zooplankton, and differed from each other. The residencetime of swarms of both gymnosomes were shorter than one month.As a general pattern, the aggregates are rapidly transportednorthward by the Malvinas Current and also penetrate the outershelf water, but they remain there only during a short periodand cannot preclude the final expatriation. So, the abundanceof gymnosomes in the area depends on passive migration morethan intrinsic population factors. (Received 9 July 1997; accepted 15 December 1997)     

THE FINE STRUCTURE AND FUNCTION OF THE ANAL GLAND OF THE MURICID NUCELLA LAPILLUS (NEOGASTROPODA) (AND A COMPARISON WITH THAT OF THE TROCHID GIBBULA CINERARIA)

The fine structure of the anal gland of Nucella lapillus isdescribed, and compared with that of Gibbula cineraria. It isconcluded that the glands are not analogous in function andare unlikely to be homologous. The anal gland of Gibbula isa small rectal diverticu-lum near the anal papilla, lined bymucus-secreting cells. The evidence suggests that the largeanal gland of Nucella extracts macromolecules and cations fromthe blood, metabolizes or sequesters them in lyso-somes andultimately expels the resultant residual bodies by apocrinesecretion. It has large reserves of lipid and glycogen, andthe abundance of melanin indicates that it is a major site oftyrosine degradation. The invariable presence of bacteria inthe lumen, and of pits in the epithelium to house them, impliesa symbiotic relationship in which the bacteria metabolize anddegrade the cell debris, some of which is resorbed. The lossof the anal gland in bucci-nids and nassariids is accompaniedby great reduction in size and importance of the rectal sinus,and increase in complexity of the kidney. (Received 31 December 1991; accepted 23 January 1992)     

Interannual variability in the distribution of the phytoplankton standing stock across the seasonal sea-ice zone west of the Antarctic Peninsula

The spatial distribution of phytoplankton cell abundance, carbon(C) biomass and chlorophyll a (Chl a) concentration was analysedduring three summers (1996, 1997 and 1999) in a seasonal sea-icearea, west of the Antarctic Peninsula. The objective of thestudy was to assess interannual variability in phytoplanktonspatial distribution and the mechanisms that regulate phytoplanktonaccumulation in the water column. Phytoplankton C biomass andChl a distributions were consistent from year to year, exhibitinga negative on/offshore gradient. The variations in C concentrationhad a close and non-linear relationship with the upper mixedlayer depth, suggesting that the vertical mixing of the watercolumn is the main factor regulating phytoplankton stock. Themagnitude of C gradients was 5-fold higher during 1996 thanduring 1997 and 1999. This was ascribed to interannual variationsin the concentration of diatom blooms in the region influencedby sea-ice melting. Vertical distribution of the phytoplankton,as estimated from Chl a profiles, also varied along an on/offshoregradient: Chl a was distributed homogeneously in the upper mixedlayer in coastal and mid-shelf stations and concentrated inthe deep layer (40–100 m) occupied by the winter waters(WW, remnants of the Antarctic surface waters during summer)in more offshore stations. The region with a deep Chl a maximumlayer (DCM layer) was dominated by a phytoplankton assemblagecharacterized by a relatively high concentration of diatoms.The extent of this region varied from year to year: it was restrictedto pelagic waters during 1996, extended to the shelf slope during1997 and occupied a major portion of the area during 1999. Itis hypothesized that iron depletion in near surface waters dueto phytoplankton consumption, and a higher concentration inWW, regulated this vertical phytoplankton distribution pattern.Furthermore, we postulate that year-to-year variations in thespatial distribution of the DCM layer were related to interannualvariations in the timing of the sea-ice retreat. The similaritybetween our results and those reported in literature for otherareas of the Southern Ocean allows us to suggest that the mechanismsproposed here as regulating phytoplankton stock in our areamay be applicable elsewhere.     

Trophic interactions in a high arctic snow goose colony

We examined the role of trophic interactions in structuringa high arctic tundra community characterized by a large breedingcolony of greater snow geese (Chen caerulescens atlantica).According to the exploitation ecosystem hypothesis of Oksanenet al. (1981), food chains are controlled by top-down interactions.However, because the arctic primary productivity is low, herbivorepopulations are too small to support functional predator populationsand these communities should thus be dominated by the plant/herbivore trophic-level interaction. Since 1990, we have beenmonitoring annual abundance and productivity of geese, the impactof goose grazing, predator abundance (mostly arctic foxes, Alopexlagopus) and the abundance of lemmings, the other significantherbivore in this community, on Bylot Island, Nunavut, Canada.Goose grazing consistently removed a significant proportionof the standing crop (     

Temporal patterns and variations in phytoplankton community organization and abundance in Narragansett Bay during 1959-1980

Incident irradiance, surface water temperature and phytoplanktonspecies abundances were measured at weekly intervals in NarragansettBay from 1959 through 1980. Stepwise discriminant analyses (SDA)of this 22-year data set indicate that fundamental ecosystemchanges occurred between the 1960s and 1970s, with 1969 beingthe key transitional year in these decadal shifts in phyto planktontaxonomic structure and seasonal abundance. This decadal shiftwas accompanied by the increased summer abundance of small Thalassiosiraspp., which first appeared in 1966 and by 1969 became the sixthmost important phytoplankton component in this bay. Decadaltrends in phyto plankton community organization and abundancewere also accompanied by distinct long-term climatological gradientsof temperature and light. The 1960s were generally colder andbrighter than the 1970s. Prior to 1969, the annual phytoplanktonmaximum occurred most commonly during winter; in the 1970s,the annual maximum generally shifted to a summer event. Three5-year phytoplankton cycles occurred between 1959 and 1974.During each pentade, the phytoplankton community returned toa similar taxonomic organization and abundance cycle after divergingin the intervening years. Pentade cycles did not occur after1974; the phytoplankton community thereafter diverged significantlyfrom each preceding year. Five species [Skeletonema costatum,Detonula confervacea, Asterionellopsis glacialis, Hererosigmaakashiwo (= Olisthodiscus lureus) and Thalassiosira nordenskioeldii]dominated the phytoplankton over the 22-year period. SDA revealeda high degree of similarity and constancy in the annual occurrencepatterns of these taxa. The decadal shifts revealed by SDA weremore directly related to the considerable interannual variabilitythat characterized the abundance and seasonality of the lessabundant species.     

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.     

Determining relative abundance of specific DNA sequences in flow cytometrically sorted maize nuclei

A wide breadth of DNA content variation has been reported amongmaize lines. While the extent of this variation has been welldocumented, few studies have focused on its cause. Some of thenuclear DNA content variation has been explained by the presenceof B chromosomes or knobs. However, variation in these two structuresdoes not account for all of the observed variation. In orderto identify other fluctuating DNA sequences, a rapid and reliablemethod of estimating relative abundance of DNA sequences neededto be developed. The potential of flow cytometry in conjunctionwith spot hybridization for determining relative abundance ofspecific DNA sequences in maize was studied. Different numbersof G1 phase nuclei were sorted on nitrocellulose filters andnon-radioactive hybridization and signal detection performed.Results from these experiments revealed a significant, positivelinear correlation between the amount of target sequence andsignal density using both knob (R = 0.98) and ribosomal spacer(R =0.99) DNA sequences. In addition, G1 phase nuclei of eightinbred lines differing in the amount of knob heterochromatin,were sorted on to filters and the non-radioactive hybridizationand signal detection performed. A significant, positive linearcorrelation between C-band number and signal density (R =0.83;P = 0.0051) as well as between per cent heterochromatin andsignal density (R=0.96;P = 0.0002) was observed. These resultsindicate the usefulness of flow cytometry for spot hybridizationin determining the relative abundance of DNA sequences in themaize genome. Key words: Flow cytometry, copy number, non-isotope labelling, spot hybridization, flow sorting, Zea mays L.     

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.     

Zooplankton biomass distribution patterns along the western Antarctic Peninsula (December 2002)

The phytoplankton [chlorophyll a (Chl a)], microzooplankton,mesozooplankton and macrozooplankton biomass and distributionwere studied as part of a multidisciplinary project (Tempano)along the Antarctic Peninsula during December 2002. Even thoughthe summer phytoplankton bloom was not yet developed in thearea, autotrophs dominated the plankton biomass. Phytoplanktonvertical distribution was, in general, homogeneous in the upper40–50 m of the water column, further decreasing with depth.Protozoans showed low biomass; their contribution to the totalplankton being one order of magnitude lower than that of autotrophs.The vertical distribution of protozoans was variable among stationswith marked peaks at depths ranging from 30 to 80 m. Mesozooplankton-integratedbiomass was generally low, although there was a notable increasesouthward near the ice marginal zone. Macrozooplankton distributionwas more variable without any clear zonal distribution pattern.The vertical distribution of meso- and macrozooplankton (>4mm) biomass showed clear peaks of abundance comprising differentspecies depending on the geographical area. Our biomass distributiondata suggest a food-web scenario in which macrozooplankton arepreying on mesozooplankton populations only in the northernerstations, and mesozooplankton are, in their turn, shaping theabundance of the emerging populations of microzooplankton. Phytoplankton,on the other hand, seem to be hardly controlled by grazing activity.     

Distribution of common octopus and common squid paralarvae in a wind-driven upwelling area (Ria of Vigo, northwestern Spain)

The variation of paralarval abundance in a region subjectedto wind-driven upwelling (Ria of Vigo, northwestern Spain) wasstudied. Research cruises were undertaken during the favourableupwelling season (May to October) in 2000 and 2001. Each cruiseincluded biological and hydrographic sampling and consistedof five stations in waters located to the east and west of theCies Islands. A total of 221 paralarvae of Octopodidae and Loliginidaewere collected over the 12-month study period. During 2000,higher abundance of paralarvae was observed in July, Septemberand October for Loligo vulgaris and Octopus vulgaris. In 2001,abundance of both species was higher in May and also in Septemberfor O. vulgaris. The mantle length of the paralarvae variedfrom 1.25 to 2.25 mm and from 1.00 to 4.90 mm within the O.vulgaris and L. vulgaris individuals, respectively. The presence/absenceof upwelling modulates the abundance and spatial distributionof loliginid and octopod paralarvae. The relationship betweenthe distribution and movement of these paralarvae in the Riaof Vigo seems to follow the circulation system defined for thisarea; when the upwelling extends its influence inside the Ria,the paralarvae are transported to the inner part in a west—eastdirection.