Experimental evaluation of herbivory in the ctenophore Mnemiopsis leidyi relevant to ctenophore-zooplankton-phytoplankton interactions in Narragansett Bay, Rhode Island, USA

Herbivory of Mnemiopsis leidyi and its interactions with phytoplanktonand non-gelatinous zooplankton were examined in small-scalemicrocosm experiments. Clearance rates for M. leidyi incubatedwith phytoplankton were generally negative, but ranged up to4.5 1 ctenophore^–1 day^–1 when the large (80 µmø) diatom Ditylum brightwelli was offered as a food source.These highest ingestion rates would provide Mnemiopsis withonly 21 % of its daily carbon requirements for respiration.Mean shrinkage of M. leidyi was 8.2–51% when incubatedwith phytoplankton. Although M. leidyi neither fed activelyon phytoplankton, nor satisfied its nutritional needs on sucha diet, the chain-forming diatom Skeletonema costatum becameentangled in mucus strands and balls produced by M. leidyi inthe absence of zooplankton. Attachment onto mucus occurred atphytoplankton concentrations commonly observed in NarragansettBay and may be important in the formation of "marine snow" duringsummer M. leidyi pulses; phytoplankton sinking rate and the"package size" available to herbivores would also be affected.The experiments support our previous hypothesis based on fieldobservations in Narragansett Bay that M. leidyi indirectly regulatesphytoplankton abundance there during the summer bloom as a consequenceof predation on zooplankton. The extent to which M. leidyi influencedphytoplankton dynamics in the microcosms was dependent on therelative abundance and physiological state of the three trophiclevels. A food web diagram for M. leidyi is presented.     

Growth and feeding rates of the newly hatched larval ctenophore Mnemiopsis leidyi A. Agassiz (Ctenophora, Lobata)

Mnemiopsis leidyi: larvae depend on microplankton (<200 µm) prey duringthe first few days following hatching until larvae are >0.5mm in length and can successfully capture and consume mesozooplanktonprey. Feeding and growth rates of newly hatched M. leidyi larvaewere measured in controlled laboratory experiments. When fednatural microplankton assemblages, newly hatched larvae consumedsignificant quantities of both autotrophic and heterotrophicprey, including diatoms, phototrophic, heterotrophic and mixotrophicdinoflagellates, euglenoid flagellates, aloricate and tintinnidciliates, and rotifers. Average per capita clearance rates were1.99–7.59 mL individual^–1 h^–1 ( = 4.01 mL individual^–1 h^–1; SD = 1.95)and total per capita ingestion was 0.01–4.70 µgC individual^–1 day^–1 x 10² ( = 0.83 µg C individual^–1 day^–1 x 10²; SD =1.89). Larval growth rates were –0.13 to 0.56 mm individual^–1day^–1 (equivalent to –1.72 to 4.33 µg C individual^–1day^–1) over a range of larval sizes from 0.5 (<0.5µg C) to 5 mm (85 µg C). A diet consisting entirelyof microplankton prey supported larval growth for >2 weeks,and growth rate decreased when larvae reached 4–5 mm inlength, corresponding to the beginning of their morphologicaltransition from tentaculate to lobate feeding mode. The grossgrowth efficiency of larvae fed natural microplankton assemblageswas 3%.     

Growth and ingestion rates of larval fish populations in the coastal waters of Israel

Clupeoid larvae were collected on eight cruises between February1984 and February 1985 in the coastal waters of Israel. Fromanalysis of daily growth increments of otoliths, growth ratesof the abundant clupeoids, Engraulis encrasicolus, Sardina pilchardusand Sardinella aurita were found to be 0.55 mm day^–1,0.67 mm day^–1 and 0.60 mm day^–1, respectively, duringthe first month after hatching. Ingestion rates were estimatedusing an equation from the literature relating ingestion andgrowth of larval fish. Ingestion calculated for populationsof fish larvae in pelagic waters ranged from 0 to >23 mgC m^–2 day^–1 with maximum rates observed in April.Annual ingestion by larval fish at a pelagic station near Haifawas calculated to be 2.2 g C m^–2 year^–1, 10–20%of annual primary production estimated from ¹⁴C uptake.     

The contribution of ammonia excreted by zooplankton to phytoplankton production in Narragansett Bay

Ammonia excreted by mixed zooplankton populations over an annual(1972–1973) cycle in Narragansett Bay varied from 0.04to 3.21 µg at NH₃-N dry wt^–1 day^–1, exclusiveof two exceptional rates measured one year apart: 11.74 and18.39 µg at NH³-N mg dry wt^–1 day^–1. Grossphytoplankton production integrated over the year (1972–1973)averaged 151 mg C m^–3 day^–1 for an 8 m water column;peaks of 332 and 905 mg C m^–3 day^–1 occurred duringthe winter-spring and summer blooms, respectively. Excretedammonia, integrated seasonally and annually, contributed only0.2% and 4.9% of the nitrogen required for observed gross productionduring the winter-spring and summer blooms, respectively, and4.4% annually. However, excreted ammonia may be an importantsource of the nitrogen required by Skeletonema costatum, thedominant diatom in Narragansett Bay, during the post-bloom periodwhen 186% of the nitrogen required for its net production wasmet by ammonia excretion. A combination of zooplankton ammoniaexcretion and benthic ammonia flux contributed 22% of the nitrogenrequired for the annual gross production (440 g C m^–2)while 51% of the nitrogen required for the net production ofSkeletonema was accounted for by regenerated nitrogen. ¹This research was supported by NSF grant GA 31319X awardedto Dr.T.J.Smayda.     

Microzooplankton, vertical mixing and advection in a larval fish patch

A large ({small tilde}30 ? 75 km) patch of larval walleye pollock,Theragra chalcogramma, was located south of the Alaska Peninsuladuring May 1986. A drifter deployed in this patch followed ananticyclonic path consistent with dynamic topography. Changesin community composition and vertical distribution of microzooplankton>40 µm were sampled for 4 days alongside this drifterto examine feeding conditions for larvae. Biological and physicalchanges during the first 2 calm days revealed substantial small-scalevariability within the larger circulation pattern. Changes duringthe last 2 days were dominated by vertical mixing due to strongwinds. Despite mixing, prey concentrations remained adequatefor feeding by larval pollock as determined by laboratory studies.A satellite-tracked drifter replaced the first drifter and wasstill located within the patch 6 days later. Overall distributionsof larvae and movements of the drifters show a net translationof 7.8 km day^–1 south-westward, but details of the studyreveal complex interactions between coastal waters and a coastalcurrent. During the 10-day period there was an increase in standardlength of the larval fish population of 0.13 mm day^–1and a decline in abundance of {small tilde}7.6% day^–1.Both calculated rates must be underestimates due to continuingrecruitment of small larvae from hatching eggs.     

Pigment-specific rates of phytoplankton growth and microzooplankton grazing in a subtropical lagoon

Phytoplankton growth and microzooplankton grazing rates wereevaluated in one station in Bahía Concepción,located in the middle region of the Gulf of California, México.We used high-performance liquid chromatography (HPLC) estimationsof phytoplankton pigment signatures to evaluate the annual variationof taxon-specific grazing and growth rates obtained with thedilution technique. Chlorophyll-a (Chl-a) concentrations variedwidely (0.34–3.32 µg L^–1) and showed two maxima,during late spring and autumn, associated with the transitionbetween mixed and stratified conditions. Phytoplankton growthrates varied seasonally with the lowest rates during summer(range: 0.01–2.55 day^–1 for Chl-a; 0.00–3.84day^–1 for Chl-b; 0.26–3.29 day^–1 for fucoxanthin;0.00–6.27 day^–1 for peridinin; 0.00–4.35 day^–1for zeaxanthin). Microzooplankton grazing was an important lossprocess (range: 0.0–1.89 day^–1 for Chl-a; 0.00–3.12day^–1 for Chl-b; 0.26–3.29 day^–1 for fucoxanthin;0.00–2.03 day^–1 for peridinin; 0.00–3.51 day^–1for zeaxanthin). Average grazing rates accounted 68–89%of estimated average phytoplankton pigment-specific growth rates.The analysis of pigment signatures indicates that diatoms anddinoflagellates were the dominant groups, and contrary to expectationfor typical subtropical lagoons, the specific growth rates inBahía Concepción showed a pronounced seasonalvariability, linked to transitional hydrographic conditions.Our results indicate a close coupling between the communitymicrozooplankton grazing and phytoplankton growth rates, withoutselective feeding behavior. These results suggest that microzooplanktonplay a critical role and may significantly modify the availabilityand efficiency of transfer of energy to higher trophic levels.     

Trophodynamics of the scyphomedusae Aurelia aurita. Predation rate in relation to abundance, size and type of prey organism

Ephyra larvae and small medusae (1.7–95 mm diameter, 0.01–350mg ash-free dry wt, AFDW) of the scyphozoan jellyfish Aureliaaurita were used in predation experiments with phytoplankton(the flagellate Isochrysis galbana, 4 µm diameter, {smalltilde}6 x 10^–6 µg AFDW cell^–1), ciliates (theoligotrich Strombidium sulcatum, 28 µm diameter, {smalltilde}2 x 10^–3 µg AFDW), rotifers (Synchaeta sp.,0.5 µg AFDW individual^–1) and mixed zooplankton(mainly copepods and cladocerans, 2.1–3.1 µg AFDWindividual^–1). Phytoplankton in natural concentrations(50–200 µg C I^–1) were not utilized by largemedusae (44–95 mm diameter). Ciliates in concentrationsfrom 0.5 to 50 individuals ml^"1 were consumed by ephyra larvaeand small medusae (3–14 mm diameter) at a maximum predationrate of 171 prey day^–1, corresponding to a daily rationof 0.42%. The rotifer Synchaeta sp., offered in concentrationsof 100–600 prey I^–1, resulted in daily rations ofephyra larvae (2–5 mm diameter) between 1 and 13%. Mixedzooplankton allowed the highest daily rations, usually in therange 5–40%. Large medusae (>45 mm diameter) consumedbetween 2000 and 3500 prey organisms day^"1 in prey concentrationsexceeding 100 I^–1. Predation rate and daily ration werepositively correlated with prey abundance. Seen over a broadsize spectrum, the daily ration decreased with increased medusasize. The daily rations observed in high abundance of mixedzooplankton suggest a potential ‘scope for growth’that exceeds the growth rate observed in field populations,and this, in turn, suggests that the natural populations areusually food limited. The predicted predation rate at averageprey concentrations that are characteristic of neritic environmentscannot explain the maximum growth rates observed in field populations.It is therefore suggested that exploitation of patches of preyin high abundance is an important component in the trophodynamicsof this species. ¹Present address: University of Bergen, Department of MarineBiology, N-5065 Blomsterdalen, Norway     

Primary and bacterial production compared to growth and food requirements of Daphnia longispina in Lake Kvernavatnet, west Norway

Primary production, and bacterial production as measured byincorporation of [³H-methyl]thymidineinto ice cold TCA insolublematerial were investigated during 1984 in Lake Kvernavatnet,west Norway. Primary production averaged 222 mg C m^–2day^–1 and bacterial production averaged 163 mg C m^–2day^–1. The bacterial production in the euphotic pelagiczonecontributed -60% of the total pelagic bacterial production.The zooplankton was dominated byDaphnia longispina. From growthexperiments with animals fed only natural food in coarse filteredlake water, the population daily growth increments were calculated.The average production of D.longispina was 151 mg C m^–2day^–1 during the period investigated. The estimated primaryproduction was too low to sustain both the bacterial productionand the zooplankton food requirements. These results imply thatthe carbon cycle of the lake is dependent on the supply of allochtonousmaterial, or that the current methods for measuring productionrates in aquatic environments are systematical erratic.     

Noctiluca scintillans MACARTNEY in the Northern Adriatic Sea: long-term dynamics, relationships with temperature and eutrophication, and role in the food web

The first ‘bloom’ of Noctiluca scintillans in theNorthern Adriatic Sea was recorded in 1977. The organism causedseveral red tides in the whole basin during the late 1970s,a period characterized by increasing nutrient loads. Duringthe 1980s and early 1990s, there was no ‘red tide’,but the species was an almost constant summer presence, associatedwith high temperatures. Noctiluca scintillans was almost completelyabsent from 1994 until May 1997, concurrent with a general planktondecrease. From summer 1997, N. scintillans was recorded againin the whole basin, although there was no other signal of increasingeutrophication. In contrast to all previous observations, duringwinter 2002–2003, N. scintillans was continuously sampledin the Gulf of Trieste. We estimated experimentally growth andgrazing rates of the dinoflagellate at 9–10°C in cultureand consuming the natural assemblage. Noctiluca scintillanswas able to reproduce actively at low temperatures, showingsimilar growth rates in both experiments (k = 0.2 day^–1).The values found were close to those reported in the literaturefor higher temperatures. The natural diet was mainly composedof phytoplankton (ingestion = 0.008 µg C Noctiluca ^–1day^–1), microzooplankton (ingestion = 0.008 µg CNoctiluca ^–1 day^–1) and bacteria (ingestion = 0.005µg C Noctiluca ^–1 day^–1) with an average carboncontent of 0.138 ± 0.020 µg C Noctiluca cell^–1.     

Influence of cladoceran grazing activity on dissolved organic matter, enzymatic hydrolysis and bacterial growth

To assess the influence of grazing by cladocerans on dissolvedorganic matter (DOM), glycolytic and proteolytic activitiesand bacterial growth were measured by in situ incubation oflake water from the epilimnion of an oligotrophic reservoirin three different treatments: in absence of zooplankton, andin presence of zooplankton (natural abundance and concentratedfour-fold). These experiments were conducted at two periodsin the succession of plankton populations (May and June 1998),that differed in the quality of the prey ingested (Eudorinasp. compared to Cryptomonas sp. and Rhodomonas sp.) and theirgrazing intensity (31.8 ± 2.2 µg C l^–1 day^–1compared to 10.2 ± 0.5 µg C l^–1 day^–1).A systematic increase in bacterial biomass was measured in thetreatments containing the highest zooplankton concentrations.The DOM concentrations produced in situ showed few significantdifferences between the three treatments, but the assimilationof DOM was higher in the presence of zooplankton than in theirabsence. These results show that the influence of cladoceranson the DOM was more of a qualitative than a quantitative nature.The protein compounds derived from the grazing activities ofmetazoans seem to be a major nutrient source for growth forbacteria (r = 0.81, P <0.05). In this study, the highesthydrolytic activities were recorded in the presence of highconcentrations of metazoan zooplankton. However, the processesthat regulated these activities differed between the two experimentaldates (repression compared to enzyme stimulation). Grazing activitiescould lead to an increase in phytoplanktonic excretion duringthe growth phase, and therefore the production of low molecularweight compounds that are easily assimilated by the bacterialplankton.     

Trophic links in the lowland River Meuse (Belgium): assessing the role of bacteria and protozoans in planktonic food webs

Trophic interactions within the plankton of the lowland RiverMeuse (Belgium) were measured in spring and summer 2001. Consumptionof bacteria by protozoa was measured by monitoring the disappearanceof ³H-thymidine-labelled bacteria. Metazooplankton bacterivorywas assessed using 0.5-µm fluorescent microparticles (FMPs),and predation of metazooplankton on ciliates was measured usingnatural ciliate assemblages labelled with FMPs as tracer food.Grazing of metazooplankton on flagellates was determined throughin situ incubations with manipulated metazooplankton densities.Protozooplankton bacterivory varied between 6.08 and 53.90 mgC m^–3 day^–1 (i.e. from 0.12 to 0.86 g C^–1bacteria g C^–1 protozoa day^–1). Metazooplankton,essentially rotifers, grazing on bacteria was negligible comparedwith grazing by protozoa (1000 times lower). Predation of rotiferson heterotrophic flagellates (HFs) was generally low (on average1.77 mg C m^–3 day^–1, i.e. 0.084 g C^–1 flagellatesg C^–1 rotifers day^–1), the higher contribution ofHF in the diet of rotifers being observed when Keratella cochleariswas the dominant metazooplankter. Predation of rotifers on ciliateswas low in spring samples (0.56 mg C m^–3 day^–1,i.e. 0.014 g C^–1 ciliates g C^–1 rotifers day^–1)in contrast to measurements performed in July (8.72 mg C m^–3day^–1, i.e. 0.242 g C^–1 ciliates g C^–1 rotifersday^–1). The proportion of protozoa in the diet of rotiferswas low compared with that of phytoplankton (<30% of totalcarbon ingestion) except when phytoplankton biomass decreasedbelow the incipient limiting level (ILL) of the main metazooplantonicspecies. In such conditions, protozoa (mainly ciliates) constituted50% of total rotifer diet. These results give evidence thatmicrobial organisms play a significant role within the planktonicfood web of a eutrophic lowland river, ciliates providing analternative food for metazooplankton when phytoplankton becomesscarce.     

Photosynthetic algal production, accumulation and release of phytoplankton storage carbohydrates and bacterial production in a gradient in daily nutrient supply

In a mesocosm experiment providing a gradient of semi-continuousaddition of mineral nutrient, production rates and mortalityof phytoplankton were estimated. Heterotrophic bacterial biomassand production rates and their responses to the mineral nutrientsadditions were also estimated. The purpose of the experimentwas to establish responses of the major biological factors asa function of nutrient amendments. Initial primary productionwas 0.47 µg C L^–1 day^–1. In the most fertilizedmesocosm, phytoplankton biomass increased at a specific rateof 0.4 day^–1 during the first week of the experiment,and on day 9 primary production reached a peak at 1027 µgC L^–1 day^–1. The responses in the other fertilizedmesocosms were intermediate, and in an unfertilized controlthe variables measured stayed almost constant throughout theexperiment. The termination of the blooms in the fertilizedmesocosms was a consequence of nitrogen limitation, and nitrogenlimitation subsequently induced storage of intracellular organicmaterial in the phytoplankton. In the mesocosm receiving thehighest daily dose of nutrients, strong post-bloom nutrientlimitation resulted in high phytoplankton mortality, and releaseof organic material from the algae supported the gradient’shighest heterotrophic bacterial production.     

Summer coastal zooplankton biomass and copepod community structure near the Italian Terra Nova Base (Terra Nova Bay, Ross Sea, Antarctica)

The structure of the zooplankton biotic community and of copepodpopulation in the coastal area of Terra Nova Bay (Ross Sea,Antarctica) was investigated during the 10th Italian AntarcticExpedition (1994/1995). Zooplankton biotic community consistedmainly of pteropods (Limacina helicina and Clione antarctica),Cyclopoid (Oithona similis), Poecilostomatoid (Oncaea curvata)and Calanoid (Ctenocalanus vanus, Paraeuchaeta antarctica, Metridiagerlachei and Stephos longipes) copepods, ostracods, larvalpolychaetes and larval euphausiids. Zooplankton abundance rangedfrom 48.1 ind m^–3 to 5968.9 ind m^–3, and copepodabundance ranged from 45.2 ind m^–3 to 3965.3 ind m^–3.The highest peak of zooplankton abundance was observed between25 m and the surface and was mainly due to the contributionof O. similis, O. curvata and C. vanus. Zooplankton biomassranged from 5.28 mg m^–3 to 13.04 mg m^–3 dry weight;the maximum value was observed between 25 m and the surface.Total lipid content varied from 216.44 to 460.73 mg g^–1dry weight.     

Abundance and diversity of surface zooplankton in the Gulf of Aqaba, Red Sea, Egypt

Surface zooplankton were studied in Egyptian coastal watersof the Gulf of Aqaba, from bimonthly samples from July 1994to May 1995. Species diversity, numerical abundance and dynamicswere analysed for each taxon, at six sites, inside three Protectorates.A total of 62 taxa and species were identified. At all sites,copepods were predominant in the standing crop with an averageof 1945 ind. M^–3 and formed {small tilde}75.5%, numerically,of the total zooplankton community. The meroplanktonic larvaeoccupied the second rank and they constituted {small tilde}19.7%of the total zooplankton. Seasonally, the main peak of zooplanktonabundance was recorded in winter (January) with an average of3510 ind. M^–3 while September was characterized by thelowest density (1906 ind. m^–3 The relatively higher diversityvalues were recorded at Ras Mohammed Protectorate and a progressivedecline in diversity was observed northward.     

Larval age, growth and mortality in the oceanic squid Sthenoteuthis pteropus (Cephalopoda, Ommastrephidae) from the eastern tropical Atlantic

An investigation was carried out on larvae of the oceanic tropicalsquid Sthenoteuthis pteropus in the equatorial Atlantic (230'N–7S;12W–830'E) The age of the larvae was calculated from thestatolith microstructure of 20 larvae; mortality was estimatedfrom the size structure of 1128 larvae. The larval stage lasts32–38 days. At ages ranging from 14 to 38 days. the dailyrelative growth rates of mantle length decrease from 7.5 to2.8% day^–1 and from 14–16 to 5.8% of body weightday^–1 At age 12–24 days, mortality rates were estimatedusing both raw catch data and corrected data accounting fornet avoidance. The mean value of raw mortality rates was 0.189,the corrected value was 0.158. During the proboscis division(transformation of the larva into juvenile) at age 25–35days, a sharp decrease in larval growth rates and a simultaneousincrease in mortality rates (raw 0.443, corrected 0.379) wereobserved.     

Seasonal population dynamics and production of Microsetella norvegica, a widely distributed but little-studied marine planktonic harpacticoid copepod

Microsetella norvegica is a widely distributed marine planktonicharpacticoid copepod, which is poorly known from the biologicalpoint of view. We investigated the seasonal population dynamicsandproduction of M. norvegica in the central part of the InlandSea of Japan. It occurred throughout the year, whilst its reproductionwas confined to the warm season between May and November. Theproportion of ovigerous females, which carry a single egg sac,was low (mean: 23.1%) in August and September, and high (53.6%)in October. Their brood size attained a maximum (mean: 15.8eggs per sac) in July and August and declined gradually to 6.2eggs in November. Duration time from egg laying to moultingto adulthood was temperature-dependent; it was 31.9 and 14.3days at 20 and 27°C, respectively, under excess food conditionsin the laboratory. An enormously high population abundance (7.32x 10⁴ individuals m^-3), which accounted for 86.5% of the totalcopepods, and biomass (69.6 mg C m^-3) gave an annual maximumproduction rate of 4.90 mg C m^-3 day^-1) in October. Naupliiand copepodites disappeared in December, and the overwinteringpopulation was represented by adults, mainly large females.Associations of M. norvegica with marine snow aggregates, whichhave often been found in oligotrophic waters, were not observedin the food-rich environment of the Inland Sea of Japan.     

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.     

Growth and development of Metridia pacifica (Copepoda: Calanoida) in the northern Gulf of Alaska

Juvenile growth and development rates for Metridia pacifica,one of the dominant larger copepods in the subarctic Pacific,were investigated from March through October of 2001–2004in the northern Gulf of Alaska. The relationship between prosomelength (PL, µm) and dry weight (DW, µg) was determined:log₁₀ DW = 3.29 x log₁₀ PL – 8.75. The stage durationsof copepodites ranged from 3 to 52.5 days but were 8–15days under optimal condition. Seasonally, growth rates increasedfrom March to October and typically ranged between 0.004 and0.285 day^–1, averaging 0.114 ± 0.007 day^–1(mean ± SE). After standardization to 5°C (Q₁₀ of2.7), growth rates averaged 0.083 ± 0.005 day^–1and were significantly correlated to chlorophyll a, with saturatedgrowth rates of 0.149 day^–1 for C1–C3, 0.102 day^–1for C4–C5 and 0.136 day^–1 for all stages combined.Measured juvenile growth rates were comparable with specificegg production rates in this species. The comparisons of ourrates in this study with those predicted by the global modelsof copepod growth rates suggested that further refinement ofthese models is required.     

Production of Penilia avirostris in Kingston Harbour, Jamaica

The cladoceran Penilia avirostris is one of the more abundantand widespread members of the crustacean zooplankton in nearshoretropical and subtropical waters. Its abundance, biomass, fecundity,development rate and production were estimated in Kingston Harbour,Jamaica, during an 18 month period. Mean annual abundance ofPenilia was 1821 m^–3, while biomass (excluding eggs/embryos)was 2.87 mg ash-free dry-weight (AFDW) m^–3 (43.1 mg AFDWm^–2), accounting for 13% of the copepod community biomass.Fecundity increased with body size. There was no clear seasonalpattern of abundance, size or fecundity, nor were physical orbiological variables correlated to these variations. Developmenttime averaged 20.5 h for juveniles and 41.4 h for adult femalesduring incubations; there was no clear evidence of a diel patternto molting. Growth rate appeared to be exponential, with correspondingsomatic growth rates, averaging 0.27 day^–1 for juveniles,and 0.34 day^–1 for somatic plus reproductive growth inadult females. Annual production was estimated as 173 kJ m^–2year^–1,     

Community structure, biomass and productivity of size-fractionated summer phytoplankton populations in lower Narragansett Bay, Rhode Island

Seventeen size-fractionation experiments were carried out duringthe summer of 1979 to compare biomass and productivity in the< 10, <8 and <5 µm size fractions with that ofthe total phytoplankton community in surface waters of NarragansettBay. Flagellates and non-motile ultra-plankton passing 8 µmpolycarbonate filters dominated early summer phytoplankton populations,while diatoms and dinoflagellates retained by 10 µm nylonnetting dominated during the late summer. A significant numberof small diatoms and dinoflagellates were found in the 10–8µm size fraction. The > 10 µm size fraction accountedfor 50% of the chlorophyll a standing crop and 38% of surfaceproduction. The <8 µm fraction accounted for 39 and18% of the surface biomass and production. Production by the< 8 µm fraction exceeded half of the total communityproduction only during a mid-summer bloom of microflagellates.Mean assimilation numbers and calculated carbon doubling ratesin the <8 µm (2.8 g C g Chl a^–1 h^–1; 0.9day^–1)and<5 µm(1.7 g C g Chl a^–1h^–1; 0.5day^–1)size fractions were consistently lower than those of the totalpopulation (4.8 g C g Chl a^–1 h^–1; 1.3 day^–1)and the <10 µm size fraction (5.8 g C g Chl a^–1h^–1; 1.4 day ^–1). The results indicate that smalldiatoms and dinoflagellates in fractionated phytoplankton populationscan influence productivity out of proportion to their numbersor biomass. ¹Present address: Australian Institute of Marine Science, P.M.B.No. 3, Townsville M.S.O., Qld. 4810, Australia.