Structure and dynamics of zooplankton communities maintained in closed systems, with special reference to the algal food supply

Seasonal changes in the structure of the zooplankton communitiesof two large (18 500 m³) experimental enclosures (‘LundTubes’) are reviewed. The diets of the two most prominentcrustaceans, Daphnia hyalina and Diaptomus gracilis, were investigatedby direct analyses of gut contents and in a series of shortterm experimental manipulations of communities isolated in 6m³ bags, placed in one of the enclosures. The relative abundanceof Daphnia hyalina generally coincided with warmer water temperaturesbetween late spring and late summer, but its numbers fluctuatedwithin that period, apparently in response to the availabilityof smaller algae (<10⁴ µm³ unit volume: chiefly cryptomonads,chlorellids and Ankyra). Daphnia numbers declined steadily throughthe summer in the enclosure overwhelmingly dominated by Microcystis,although it did feed on smaller colonies (< 10⁵ µm³in volume). Diaptomus gracilis and most rotifers were also prominentin the first half of the year, but peak abundances of Keratellaquadrata followed the presence of large populations of small(<10³ µm³) algae. Under conditions of limiting foodavailability, mortality was greatest amongst the smaller speciesand the juvenile instars of the large Crustacea. ¹Present address: Anglian Water Authority, North Street, Oundle,Peterborough, UK     

Predation impact of Cyclops vicinus on the rotifer community in Lake Constance in spring

The predation impact of Cyclops vicinus on rotifers was studiedunder near-natural conditions in small enclosures to evaluatewhether copepod predation is responsible for the decline ofrotifers in Lake Constance in spring. Cyclops vicinus fed selectivelyon Synchaeta spp.; Keratella and Polyarthra spp. were not selectedfor. Predation rates increased with prey density up to a maximumof 37 Synchueta day^–1 at a density of 1.6 x 10⁶ Synchaetam^–2, i.e. at -1200 Synchaeta l^–1. Calculation ofcropping rates suggests that Cyclops alone can control the abundanceof Synchaeta in spring, i.e. that mainly Cyclops is responsiblefor the decline of Synchaeta species in Lake Constance in May.     

Response of ciliates and Cryptomonas to the spring cohort of a cyclopoid copepod in a shallow hypereutrophic lake

The impact of a cyclopoid copepod population on the protozoacommunity (two ciliate categories and Cryptomonas) was assessedweekly during the spring cohort of Cyclops vicinus (one monthduration) in hypereutrophic Lake Søbygård by insitu gradient experiments with manipulation of ambient zooplanktonabundance. As C.vicinus always made up >92% of the zooplanktonbiomass, the response of protozoa is assumed to be a resultof predation by the copepod. Significant effects of copepodbiomass on protozoa net population growth rates were obtainedin the four experiments. Copepod clearance rates were significantlyhigher on oligotrichs than on prostomatids and Cryptomonas butdeclined for all three protozoa categories during the firstthree weeks of the copepod cohort, probably because of the changein developmental instar composition of the copepod population.Grazing impact on protozoa at ambient copepod abundance wasconsiderable (range, 0.05–0.87 day^–1) and could,together with the estimated reproductive potential of protozoans(range, –0.20–0.87 day^–1), account for thedecline in abundance and biomass of protozoa during the cohortdevelopment. Carbon flow from the protozoa to C.vicinus (range,2.8–23.5 µg C l^–1 day^–1) documents thepresence of a trophic link between protozoa and the spring cohortof C.vicinus in Lake Søbygård.     

Resting egg production and oviducal cycling in two sympatric species of alpine diaptomids (Copepoda: Calanoida) in relation to temperature and food availability

Resting egg production and oviducal cycling were investigatedfor the calanoid copepods Arctodiaptomus alpinus and Acanthodiaptomusdenticornis both in the laboratory and in a small karstic alpinelake by making a census of the number of eggs produced and theproportion of females in each of four morphologically distinguishedreproductive conditions each day in the laboratory or duringa 2–3 week period in lake enclosures. In the laboratory,individuals were maintained on a mixed diet of natural phytoplanktonat constant temperatures of 4, 10, 15 and 20C, respectively.Both species differed considerably in their temperature requirementsfor reproduction. Lifetime fecundity was highest at 10C in A.alpinusand at 20C in A.denticornis, with up to 327 eggs ^–1 spawnedin the former and up to 582 eggs ^–1 in the latter species.Unfavorable temperatures were further reflected in an increasein egg mortality and the allocation of time spent in a post-reproductivephase, as well as in a decrease of longevity. Increasing temperaturesenhanced egg production rates due to decreasing clutch productionperiods, although clutch size was negatively correlated withtemperature. Maximum rates reached 5.88 and 7.98 eggs ^–1day^–1 in the laboratory, and 0.73 and 0.55 eggs ^–1day^–1 in enclosures in A.alpinus and A.denticornis, respectively.Egg production rates and clutch size were clearly governed bynutritional conditions in the lake, but were less affected byfood supply in the laboratory. Here, rates of egg productionwere adapted to improving food supply by increasing the frequencyof spawning events, rather than the number of eggs per clutch.No correlation was found between female body size and reproductiveparameters in the laboratory. A very low proportion of totalclutch production resulted in clutches composed of subitaneouseggs, i.e. 0.14% in A.denticornis and 1.20% in A.alpinus. Oviducalphase duration allocations indicate that there exists a temperatureoptimum for gamete maturation.     

In situ bacterial production and growth yield measured by thymidine, leucine and fractionated dark oxygen uptake

In situ bacterial net production and growth yield were measuredusing thymidine, leucine incorporation and dark oxygen consumptiontechniques in marine enclosures and in the Bay of Aarhus, Denmark.Bacterial respiration was significantly correlated with thymidine(r² = 0.42, P < 0.01, y = 0.l2x + 0.054) and leucine (r²= 0.45, P < 0.01, y = 0.09x + 0.043). The range of bacterialgrowth yield, calculated from the relationship net production/netproduction + respiration, was 0.07–0.77 with 74% of theobservations lying in the 0.15–0.45 growth yield interval.Substrate was an important determinant of growth yields. A significantdifference was found between growth yields obtained from anenclosure with added glycine (mean 0.32±0.096) and onewith added inorganic nutrients (mean 0.16±0.051) (P <0.01, t-test). Growth yield showed a weak but significant negativecorrelation with temperature (r² = 0.0.35, P < 0.001, y =–0.017 + 0.52). No correlation between chlorophyll a andgrowth yield was found (r² = 0.25, P > 0.05). The resultssuggest that thymidine and leucine techniques reflect the levelsof bacterial production to better than an order of magnitude.The variations found in the growth yield support the notionthat relying on fixed growth yields reduces the accuracy ofestimating gross bacterial production.     

In situ filtration responses of Daphnia galeata to changes in food quality

In the stoichiometric study of phyto–zooplankton interactions,a controversy exists about how Daphnia species regulate theirfeeding rate when submitted to low-quality food (i.e. high dietarycarbon:phosphorus [C:P] ratio). In this study, we gathered dataover 3 years on in situ clearance rates of a Daphnia galeatapopulation, by conducting grazing experiments from April 1998to October 2000 in the Esch-sur-Sûre reservoir (Grand-Duchyof Luxembourg). Observed clearance rates (2.5–13.5 mLindividual^–1 day^–1, mean 7.0 mL individual^–1day^–1) were correlated with population and environmentalvariables. Mean body size of Daphnia individuals was the bestpredictor of clearance rate (r² = 0.639), followed by watertemperature (r² = 0.262) and P concentration in the seston (r²     

Distribution pattern of decapod larvae off the north-western Iberian Peninsula coast (NE Atlantic)

In October 1977 the model of general circulation of the watermasses off the coast of Galicia, and the presence of a coastalupwelling, led to a high primary productivity. This high productivityin turn favoured the development of a rich population of decapodlarvae. The abundance and distribution pattern of these organismswere closely linked (i) to the abundant presence of the correspondingadult species in the area, (ii) with the spatial distributionof phytoplanktonic populations concurrently studied by Estrada[J. Plankton Res ., 6, 417–434 (1984)] and (iii) withthe hydrodynamic pattern in the area. Fifty-two decapod larvaetaxa were identified and Solenocera membranacea, Pisidia longicornis,Pilumnushirtellus and Goneplax rhomboides were the most representativespecies It was observed that the greatest concentrations oflarvae (3387 larvae 10^–2 m^–3) were to be found nearthe mouth of the Rfas Baixas (situated in the south-west ofthe coastal area) and in some zones further out to sea (863larvae 10^–2 m^–3) (due to a process of hydrodynamictransport)     

The Effects of Temperature, Photoperiod and Light Integral on the Time to Flowering of Pansy cv. Universal Violet (ViolaxwittrockianaGams.)

The effects of temperature, photoperiod and light integral onthe time to first flowering of pansy (ViolaxwittrockianaGams)were investigated. Plants were grown at six temperatures (meansbetween 14.8 and 26.1 °C), combined with four photoperiods(8, 11, 14 and 17 h). The rate of progress to flowering increasedlinearly with temperature (up to an optimum of 21.7 °C)and with increase in photoperiod (r²=0.91, 19 d.f.), the latterindicating that pansies are quantitative long day plants (LDPs).In a second experiment, plants were sown on five dates betweenJuly and December 1992 and grown in glasshouse compartmentsunder natural day lengths at six temperatures (means between9.4 and 26.3 °C). The optimum temperature for time to floweringdecreased linearly (from 21.3 °C) with declining light integralfrom 3.4 MJ m^-2d^-1(total solar radiation). Data from both experimentswere used to construct a photo-thermal model of flowering inpansy. This assumed that the rate of progress to flowering increasedas an additive linear function of light integral, temperatureand photoperiod. Independent data from plants sown on threedates, and grown at five temperatures (means between 9.8 and23.6 °C) were used to validate this model which gave a goodfit to the data (r²=0.88, 15 d.f.). Possible confounding ofthe effects of photoperiod and light integral are discussed. Pansy;Violaxwittrockiana; flowering; photo-thermal model; temperature; photoperiod; light integral     

Biomass, feeding and production of Noctiluca scintillans in the Seto Inland Sea, Japan

The abundance and biomass of the large heterotrophic dinoflagellateNoctiluca scintillans, together with the changes in its potentialprey items, were monitored in the Seto Inland Sea, Japan, duringsummer 1997 (17 July-11 August). Growth and grazing rates ofNscintillans fed natural plankton populations were also measuredeight and seven times, respectively, during the survey period.The abundance and biomass of N scintillans averaged over thewater column (19 m) were in the range 1–345 cells 1^–1(temporalaverage = 93 cell1^–1) and 0.1–49.6 µg C l^–1(temporalaverage = 13.8 µg C l^–1; three times higher thanthat of calanoid copepods during the same period). Noctilucascintillans populations followed the changes in phytoplankton:N.scintillans biomass was increasing during the period of diatomblooms and was at a plateau or decreasing during periods oflow chlorophyll a. The growth rates of N.scintillans (µ)were also consistent with the wax and wane of the N.scintillanspopulation: N.scintillans showed highest growth rates duringdiatom blooms. A simple relationship between µ and chlorophylla concentration was established, and the production of N.scintillanswas estimated using this relationship and the measured biomass.The estimated production averaged over the water column wasin the range >0.1–5.2 µg C l^–1 day^–1(temporalaverage = 1.4 µg C l^–1 day^–1; 64% of the productionof calanoid copepods during the same period). Diatom clearancerates by N.scintillans were in the range 0.10–0.35 mlcell^–1 day^–1, and the phytoplankton population clearanceby N.scintillans was >12% day^–1. Thus, although thefeeding pressure of N.scintillans on phytoplankton standingstock was low, N.scintillans was an important member of themesozooplank-ton in terms of biomass and production in the SetoInland Sea during summer.     

Sink Activity Estimation by Sink Size and Dry Matter Increase During the Ripening Stage of Barley (Hordeum vu/gare) and Rice (Oryza sativa)

During the ripening stage of barley and rice, the sink activitywas defined as the dry matter increase per units sink size,leaf area and time, as follows: NAR = A.SinkW+NAR', where NAR is the net assimilation rate (g d.wt dm^–2d^–1);A is the sink activity [g d.wt g^–1d.wt (ear) dm^–2d^–1]; Sink W is ear wt per plant at heading (g d.wt);and NAR' is net assimilation rate excluding the assimilate ofsink organ (g d.wt dm^–2 d^–1). Plant material with 16 combinations of mutually different sink(ear) and source (leaf) size were produced at heading for eachcrop: parts of each leaf and ear were removed to produce fourgrades in barley, and also a part of each leaf was removed producingfour grades for four rice varieties showing different ear size.NAR and NAR' were determined during 26 and 21 d in barley andrice after heading, respectively. Sink activity (A), representedas the assimilation rate induced by the sink organ, was estimatedfrom the relationship between SinkW and NAR using the previousequation. The sink activity was significantly higher in ricewith a value of 0–0.028 g d.wt g^–1 d.wt (ear) dm^–2d^–1 vs. 0–0.0017 in barley, suggesting that therelative role of leaves for grain filling is considerably higherin rice than in barley. The sink activity obtained in the studymight be introduced into a model to predict the yields of barleyand rice. Hordeum vulgare L, barley, Oryza saliva L, rice, dry matter, NAR, sink, source, sink activity, model     

Distinct roles of PMCA isoforms in Ca2+ homeostasis of bladder smooth muscle: evidence from PMCA gene-ablated mice

We previously showed that plasma membrane Ca²⁺-ATPase (PMCA) activity accounted for 25–30% of relaxation in bladder smooth muscle (8). Among the four PMCA isoforms only PMCA1 and PMCA4 are expressed in smooth muscle. To address the role of these isoforms, we measured cytosolic Ca²⁺ ([Ca²⁺]_i) using fura-PE3 and simultaneously measured contractility in bladder smooth muscle from wild-type (WT), Pmca1^+/–, Pmca4^+/–, Pmca4^–/–, and Pmca1^+/–Pmca4^–/– mice. There were no differences in basal [Ca²⁺]_i values between bladder preparations. KCl (80 mM) elicited both larger forces (150–190%) and increases in [Ca²⁺]_i (130–180%) in smooth muscle from Pmca1^+/– and Pmca1^+/–Pmca4^–/– bladders than those in WT or Pmca4^–/–. The responses to carbachol (CCh: 10 µM) were also greater in Pmca1^+/– (120–150%) than in WT bladders. In contrast, the responses in Pmca4^–/– and Pmca1^+/–Pmca4^–/– bladders to CCh were significantly smaller (40–50%) than WT. The rise in half-times of force and [Ca²⁺]_i increases in response to KCl and CCh, and the concomitant half-times of their decrease upon washout of agonist were prolonged in Pmca4^–/– (130–190%) and Pmca1^+/–Pmca4^–/– (120–250%) bladders, but not in Pmca1^+/– bladders with respect to WT. Our evidence indicates distinct isoform functions with the PMCA1 isoform involved in overall Ca²⁺ clearance, while PMCA4 is essential for the [Ca²⁺]_i increase and contractile response to the CCh receptor-mediated signal transduction pathway. PMCA; bladder smooth muscle; gene-altered mice     

An Analysis of Seed Development in Pisum sativum: IV. COTYLEDON CELL POPULATIONS IN VIVO AND IN VITRO

A method for quantifying changes in the cell population of Pisumsativum cotyledons during development is described. The methodis based on determining the frequency distribution for cellarea following the random sampling of a single-cell suspensionof cotyledon cells. The population profile of these cells changedprogressively and systematically from a single population, similarin size to meristematic cells, found in embryos less than 3.0mg in fresh weight, to a bimodal population in embryos greaterthan 100 mg fresh weight. This method was used to compare embryosof similar size from two genotypes near-isogenic except forgenes at the r locus. No significant differences were foundbetween the cell population profiles of embryos up to 30 mgfresh weight. However, a significant difference was found betweenembryos with fresh weights of 100 mg, the wrinkled (rr) linehaving a higher mean and maximum cell area (2 951 µm²and 9 240 µm² respectively) than the round (RR) line (2591µm²and 6470 µm²respectively). Comparisons were alsomade between cotyledon cell populations from round (RR) embryosgrown in vivo and in vitro. The most obvious differences werethe higher mean and maximum cell size of the large cell populationof in vitro grown embryos which were twice those found in vivo.Embryos grown to either 30 mg or 100 mg fresh weight in vitrohad a much greater proportion of large cells in the populationwith a corresponding reduction in total cotyledon cell number,compared with similar sized embryos grown in vivo. These data suggest that comparisons between different genotypes,or, between cultured and in vivoembryos, based on morphologicalsimilarities between embryos, may be invalid and subject tomisinterpretation. Key words: Pea, seed development, cell population     

THE BIOLOGY OF THE NORTHEASTERN PACIFIC TURRIDAE II. OENOPOTA

The habitat, diet, some reproductive and mortality factors forseveral shallow-water species of the boreal turrid genus Oenopotafrom the Puget Sound region were determined. All fed exclusivelyon tubicolous polychaetes. Oenopota fidicula was a dietary andhabitat generalise Oenopota elegans eats Schistocomus hiltoniand lives in areas of shell fragments. Oenopota excunata eatsTharyx multifilis and is a habitat generalist. Oenopota tabulataappears to be a dietary generalist, but lives only on or nearrocks. The widely-distributed species, O. levidensis, eats spionidpolychaetes, primarily Polydora species, or Owenia fusiformis,and is a habitat generalist. Feeding frequencies are low asare population densities; although O. levidensis sometimes exceeds15 animals m^–2. Crabs are major predators upon turridsin some areas, but mortality causes are generally obscure. Spawningwas observed in four species, but only O. elegans and O. levidensishad viable larvae. Development takes 13–15 weeks, 6–7weeks in a capsule and 6–7 weeks as planktonic veligers.There are no nurse eggs. Settling was not observed. ^*Present mailing address: Bamfield Marine Station Bamfield,B.C. VOR 1B0 CANADA (Received 30 May 1982;     

Seasonal variability in the relationship between body length and individual dry weight as related to food abundance and clutch size in two coexisting Daphnia species

Dry weights of individual Daphnia galeata and D. hyalina, whichcoexist in Lake Constance, were determined weekly during a twoyear investigation. From each sample and each species a length–weightrelationship (LWR) was calculated resulting in 54 (65) regressionequations based on N=2466 (3032) in D. galeata (D. hyalina).The constants (Ln(A)) and (B) of the LWRs showed a marked seasonalvariability, ranging from Ln(A)=1.0784–2.4740(1.0152–2.3860)and B=2.14–4.20 (2.11–4.15). The seasonal variabilityof the LWR was estimated with four different models. Condensingthe 54 (65) equations into one seasonal cycle resulted in amodel with an explained variance of r²=0.873 (0.869). Threemore models were established by calculating multiple regressionswith take stratification, average fecundity (E), and food concentrationas determining variates. Differences in LWRs of the two Daphniaspecies were significant (p <0.001). As the most useful approximationduring the period of stratification, LWRs are recommended forD. galeata: Ln(W)=(1.5674+0.0287^*(E))+Ln(L)^*(3.3611+0.0111^*(E)) as a generalized LWR for an epilimnetic daphnid, and for D.hyalina: Ln(W)=(1.5593+0.0613^*(E))+Ln(L)^*(3.2709+0.0017^*(E)) as LWR for a daphnid which migrates diurnally between epi andhypolimnion. The explained variance of this model is r²=0.843(0.826). The influence of food concentration in the epilimnionon LWRs was found to be significant on Ln(A) but not on (B). ^*This research project was supported by the Deutsche Forschungsgemeinschaft     

CHLOROPHYLL AMOUNT AS AN INDICATOR OF MATTER PRODUCTIVITY IN BIO-COMMUNITIES

The data of chlorophyll amounts in diverse bio-communities arecompiled and discussed with reference to matter production. The chlorophyll amount in euphotic zone of lakes and oceanswas less than 1 g/m², mostly less than 0.1 g/m². In phytoplanktonblooms it was ca. 0.1–1 g/m². Large values of 5–20g/m² were obtained in the outdoor mass cultures of Chlorella,in which the high population density and chlorophyll contentof the alga were observed. In terrestrial higher plant communitiesthe chlorophyll amount (ca. 1–10 g/m²) was usually higherthan in aquatic phytoplankton communities. The largest (13.3g/m²) was obtained with an evergreen gallery forest in Thailand.The chlorophyll amount of desert bio-community could be expectedto be as high as that in water blooms. The maximum chlorophyll amount in bio-communities seems to attainup to 20 g/m² when the conditions are favorable. ¹ Dedicated to Prof. H. TAMIYA on the occasion of his 60th birthday. (Received December 25, 1962; )     

The seasonal population changes and carbon budget of the calanoid copepod Boeckella minuta Sars in a newly formed sub-tropical reservoir

The population carbon budget and seasonality of Boeckella minutain a newly formed subtropical reservoir were examined 3 yearsafter the reservoir filled. Average daily biomass was 26.4 mgC m^–3 and the annual population carbon budget was: consumption2470, egestion 1482, assimilation 988, production 493 and respiration495, mg C m^–3 year^–1, and the average P/B and P/Aratios were 0.08 and 0.5 respectively. Clutch size and reproductiveeffort (egg production/assimilation) were low, and the proportionof males decreased throughout the population cycle. The seasonalabundance pattern changed from perennial (pre-filling years)to a 7 month cycle. It is suggested that eutrophication andthe spring bloom of cyanobacteria may have accentuated a seasonaldecrease in reproductive effort and survival, leading to anabsence of planktonic stages during summer, and that restingeggs facilitated population survival during the summer periodof stratification.     

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     

Changes in the growth rates of saline-lake diatoms in response to variation in salinity, brine type and nitrogen form

The growth rates of four saline-lake diatom taxa were measuredunder varying conditions of salinity (5, 8 and 11), brine type(sulfate- versus bicarbonate-dominated) and nitrogen form (NH₄⁺versus NO₃^–), using a full factorial design. With NO₃^–as the nitrogen source, Cyclotella quillensis, Cymbella pusillaand Anomoeoneis costata exhibited lower growth rates in thesulfate versus bicarbonate media. The strain of Chaetoceroselmorei used in these experiments, isolated from a sulfate-dominatedlake, was unable to grow on NO₃^– alone. In the NH₄⁺ treatments,neither salinity nor brine type affected the growth rates ofC.quillensis or C.elmorei. When supplied with NH₄⁺, C.pusillaand A.costata had higher growth rates in the bicarbonate versussulfate media, although for C.pusilla the difference on NH₄⁺was not as great as on NO₃^–. The impact of brine typeon NO₃^– use is consistent with the theory that sulfateinhibits molybdate uptake, as molybdenum is required for NO₃^–use but not NH₄⁺. Cymbella pusilla was the only taxon affectedby changes in salinity. The four taxa used in these experimentsare frequently found in saline lakes and saline-lake sediments,hence they are used in paleoclimate reconstructions; the resultspresented here provide additional information that may enhancethese diatom-based reconstructions.     

Predation and respiration by the small cyclopoid copepod Oithona similisr: How important is feeding on ciliates and heterotrophic flagellates?

Feeding on natural plankton populations and respiration of thesmall cyclopoid copepod Oithona similis were measured duringthe warm season in Buzzards Bay, Massachusetts, USA. AlthoughO.similis did not significantly ingest small autotrophic andheterotrophic flagellates (2–8 µn), this copepodactively fed on >10 µm particles, including autotrophic/heterotrophic(dino)flagel-lates and ciliates, with clearance rates of 0.03–0.38ml animal^–1 h^–1. The clearance rates increased withthe prey size. O.similis also fed on copepod nauplii (mainlycomposed of the N1 stage of Acartia tonsa with a clearance rateof 0.16 ml animal^–1 h^–1. Daily carbon ration fromthe combination of these food items averaged 148 ng C animal^–1day^–1 (41% of body C day^–1), with ciliates and heterotrophicdino-flagellates being the main food source ({small tilde}69%of total carbon ration). Respiration rates were 020–0.23µl O₂ animal^–1 day^–1. Assuming a respiratoryquotient of 0.8 and digestion efficiency of 0.7, the carbonrequirement for respiration was calculated to be 125–143ng C animal^–1 day^–1, close to the daily carbon rationestimated above. We conclude that predation on ciliates andheterotrophic dinoflagellates was important for O.similis tosustain its population in our study area during the warm season.     

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 (