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1.
Copepod abundance in the western Irish Sea: relationship to physical regime, phytoplankton production and standing stock 总被引:1,自引:0,他引:1
Gowen R.J.; McCullough G.; Dickey-Collas M.; Kleppel G.S. 《Journal of plankton research》1998,20(2):315-330
The distinct patterns of stratification in the North Channeland stratified region of the western Irish Sea influence theseasonal abundance of phytoplankton. The 34 month productionseason in the stratified region was characterized by productionand biomass peaks in the spring (up to 2378 mg C m2 day1and 178.4 mg chlorophyll m2) and autumn (up to 1280 mgC m2 day1 and 101.9 mg chlorophyll m2).Phytoplankton in the North Channel exhibited a short, late productionseason with a single summer (June/July) peak in production (4483mg Cm2 day1) and biomass (160.6 mg chlorophyllm2). These differences have little influence on copepoddynamics. Both regions supported recurrent annual cycles ofcopepod abundance with similar seasonal maxima (182.8241.8103ind. m2) and dominant species (Pseudocalanus elongatusand Acartia clausi). Specific rates of population increase inthe spring were 0.071 and 0.048 day1 for the North Channel andstratified region, respectively. Increased copepod abundancein the stratified region coincided with the spring bloom, andwas significantly correlated with chlorophyll standing stock.Increased copepod abundance preceded the summer production peakin the North Channel. This increase was not correlated withchlorophyll standing crop, suggesting that a food resource otherthan phytoplankton may be responsible for the onset of copepodproduction prior to the spring bloom. Hetero-trophic microplanktonas an alternative food source, and advection of copepods fromthe stratified region, are proposed as possible explanationsfor copepod abundance increasing in advance of the summer peakin primary production. 相似文献
2.
The relative importance of food and temperature to copepod egg production and somatic growth in the southern Benguela upwelling system 总被引:2,自引:0,他引:2
The fecundity and somatic growth rates of Calanus agulhensisand Calanoides carinatus, the dominant large calanoid copepodsin the southern Benguela upwelling system, as well as the fecundityof several other common copepods, were measured between Septemberand March of 1993/94 and 1994/95. Mean egg production of mostcopepods was low at >30 eggs female-1 day-1 {Calanoides carinatus23.7, Calanus agulhensis 19.0, Neocalanus tonsus 16.1 and Rhincalanusnasutus 26.1), whereas the mean fecundity of Centropages brachiatuswas significantly greater (83.6 eggs female1 day-1).This study also presents the first comprehensive field estimatesof the fecundity of Nanno-calanus minor (mean: 26.1 eggs female1day1, range: 0.096.2 eggs female1 day1)and of somatic growth of N6 and all copepodite stages of Calanoidescarinatus (decreasing from 0.58 day1 for N6 to 0.04 day1for C5). Somatic growth rates of Calanus agulhensis also declinedwith age: from 0.57 day1 for N6 to 0.09 day1 for C5. Data ongrowth rates were used to assess the relative importance offood [as measured by total chlorophyll (Chi) a concentration],phytoplankton cell size (proportion of cells >10 µm)and temperature to the growth of copepods. Multiple regressionresults suggested that fecundity and somatic growth rates werepositively related to both Chi a concentration and phytoplanktoncell size, but not to temperature. Although it was not possibleto separate the effects of Chi a concentration and phytoplanktoncell size, data from previous laboratory experiments suggestthat copepod growth is not limited by small cells per se, butby the low Chi a concentrations that are associated with theseparticles in the field. Despite growth not being directly relatedto temperature, a dome-shaped relationship was evident in somespecies, with slower growth rates at cool (<13°C) andwarm (>18°C) temperatures. The shape of this relationshipmirrors that of Chi a versus temperature, where poor Chi a concentrationsare associated with cool and warm temperatures. It is concludedthat the effect of food limitation on growth of copepods outweighsthat of temperature in the southern Benguela region. Sourcesof variability in relationships between growth and Chi a concentrationare discussed. 相似文献
3.
The in situ predation rate of the siphonophore Sphaeronectesgracilis was estimated from gut content analysis of hand-collectedsiphonophores and from laboratory data on digestion rates ofprey organisms. At daytime prey densities of 0.25 copepods 11,S. gracilis was estimated to consume 8.1 15.4 prey day1siphonophore1. From data on abundances of siphonophoresand copepods, S. gracilis was estimated to consume 24%of the copepods daily. In laboratory experiments, ingestionrates averaged 13.8 prey day1 siphonophore1 atprey densities of 5 copepods 11 and 36.9 at 20 copeods11. This was equivalent to a specific ingestion rate(for both carbon and nitrogen) of 17% day1 and45% day1, respectively, while specific ingestion in situwas only 2% day1. Ammonium excretion averaged 0.095 µg-atsiphonophore1 day1 at 5 prey 11, and 0.162at 20 prey 11. The specific respiration (carbon) andspecific excretion (nitrogen as ammonium) were calculated tobe 3% day1 at the lower experimental food level, and5% day1 at the higher food level.
1Contribution from the Catalina Marine Science Center No. 66.
2Present address: Dept. of Biology, University of Victoria,Victoria, B.C., Canada V8W 2Y2. 相似文献
4.
Histiobalantium sp. was found regularly in the pelagic zoneof Lake Constance, FRG, over five annual cycles. Maxima of upto 6400 cells l1 were recorded in late summer, with similarnumbers in the 08 and 820 m depth intervals. Onan annual average, the population accounted for 1017%of the total biomass of planktonic ciliates. In the laboratory,Histiobalantium grew well on a diet of the cryptophyte Rhodomonassp. Maximum growth rates obtained in batch cultures were 0.21and 0.33 day11 at 9 and 18°C, respectively. In situexperiments using diffusion chambers yielded positive growthrates in autumn and winter. The highest values recorded at theambient temperatures 5, 14 and 17°C were 0.17, 0.32 and0.40 day1, respectively. Comparing these results withthe different seasonal distributions and higher measured growthrates of other ciliates from Lake Constance, we conclude thatHistiobalantium is a superior competitor at relatively low algalfood concentrations.
2Present address: Fisheries & Oceans Canada, 4160 MarineDrive, West Vancouver, BC, V7V 1N6, Canada 相似文献
5.
Two planktonic cyclopoid copepods (Tropocyclops prasinus andMesocyclops longisetus) were raised in the laboratory to obtainlife history information (duration of embryonic and post-embryonicdevelopment, reproductive performance, longevity, and stage-specificlength and weight values). Animals were maintained at 20 and25°C, and fed ad libitum. Development times were temperaturedependent when food was not limiting, with shorter periods ofembryonic and post-embryonic development and decreased longevityat 25°C. Laboratory data on the duration of developmentand biomass, together with population dynamics data obtainedin the field, were used to estimate summer and winter biomassand production of these species in a shallow reservoir, LagoaDourada, Brazil. The maximum production rate of T. prasinus,attained during summer, was 2.8 mg dry weight (DW) m3day1 and the highest daily production:biomass (P:B) ratiowas 0.29, whereas for M. longisetus the maximum production ratewas 1.4 mg DW m3 day1 and the highest daily P:Bratio was 0.39, in the winter. Over short time intervals (everyother day), there was great variability of the species productionrates. Species production rates were low compared to valuesreported in the literature for the same or other species ofequivalent sized copepods from both tropical and subtropicalregions. 相似文献
6.
The growth of heterotrophic nanoflagellates (HNF) in mesotrophicLake Constance was measured in situ during a 13 month period.Experiments were conducted with 10 µm pre-filtered lakewater incubated in diffusion chambers at 3 m water depth atthe sampling location for 24 h. Growth rates were calculatedfrom changes in cell numbers occurring during the period ofincubation. Growth rates of all dominant taxa showed pronouncedseasonal variation (0.13 to 1.76 day1 and weregenerally highest in summer at high water temperatures. In situgrowth rates were well below maximum growth rates known forthe respective and similar species from laboratory experiments.While water temperature was a key parameter positively relatedto the growth of all HNF species, the effect of various potentialfood items was taxon specific and less clear. Bacterial abundancewas equally important as temperature for growth in the smallbactenvorous Spumella sp., but was insignificant for growthrates of the larger omnivorous Kathablepharis sp. In Spuniellasp., 84% of the observed seasonal variation of its growth ratecould be explained by temperature and bacterial food supply.Based on these results, a multiple linear regression equationwith temperature and bacterial concentration as dependent variableswas calculated for the growth rate of Spumella. Taxon-specificproduction rates were derived from growth rates and averagebiomass of these two species, and compared to total HNF productionestimated from previously measured community growth rates andbiomass in Lake Constance. Production peaks of Spumella sp.and Kathablepharis sp. alternated seasonally. Total HINF productionranged from 0.01 to 10 mg C m3 day1. Theaverage seasonal production varied between 1.4 and 33 mg C m3day1 over 6 consecutive years. These small protozoa thuscontribute a substantial amount to total zooplankton productionin Lake Constance. 相似文献
7.
Primary and bacterial production compared to growth and food requirements of Daphnia longispina in Lake Kvernavatnet, west Norway 总被引:1,自引:0,他引:1
B{phi}rsheim Knut YUngve; Andersen Sissel; Hele Johnsen Geir; Eva {phi} Kambestad; Norland Svein 《Journal of plankton research》1988,10(5):921-939
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 m2day1 and bacterial production averaged 163 mg C m2day1. 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 m2day1 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. 相似文献
8.
Centropages abdominalis is a neritic, omnivorous, temporallyabundant copepod present throughout the subarctic Pacific andits marginal seas. The two main objectives of this study wereto determine how temperature influences the development of C.abdominalis and whether growth rates of in situ populationsmay be limited by available food. At 6.9°C, median developmenttime from eggs laid to 50% adults was 42 days and the averageweight-specific somatic growth rate was 0.17 day1. At4.6°C, median development time to adult was 59 days (projected)and growth rate averaged 0.08 day1, suggesting that 4.6°Cmay be approaching the lower temperature for development andgrowth in this species. The functional relationship betweendevelopment time and temperature was established over the temperaturerange in which this species occurs. The in situ adult growthrates between 10 and 13°C averaged 0.14 day1 andwere generally lower than the laboratory-reared juvenile growthrates, which may indicate that adult C. abdominalis are foodlimited in the field during summer and autumn. 相似文献
9.
In situ growth and development of Neocalanus flemingeri/plumchrusstage C1C4 copepodites were estimated by both the artificial-cohortand the single-stage incubation methods in March, April andMay of 20012005 at 56°C. Results from thesetwo methods were comparable and consistent. In the field, C1C4stage durations ranged from 7 to >100 days, dependent ontemperature and chlorophyll a (Chl a) concentration. Averagestage durations were 12.414.1 days, yielding an averageof 56 days to reach C5, but under optimal conditions stage durationswere closer to 10 days, shortening the time to reach C5 (fromC1) to 46 days. Generally, growth rates decreased with increasingstage, ranging from 0.28 day1 to close to zero but weretypically between 0.20 and 0.05 day1, averaging 0.110± 0.006 day1 (mean ± SE) for single-stageand 0.107 ± 0.005 day1 (mean ± SE) forartificial-cohort methods. Growth was well described by equationsof MichaelisMenten form, with maximum growth rates (Gmax)of 0.170.18 day1 and half saturation Chl a concentrations(Kchl) of 0.450.46 mg m3 for combined C13,while Gmax dropped to 0.080.09 day1 but Kchl remainedat 0.380.93 mg m3 for C4. In this study, in situgrowth of N. flemingeri/plumchrus was frequently food limitedto some degree, particularly during March. A comparison withglobal models of copepod growth rates suggests that these modelsstill require considerable refinement. We suggest that the artificial-cohortmethod is the most practical approach to generating the multispeciesdata required to address these deficiencies. 相似文献
10.
Biomass, feeding and production of Noctiluca scintillans in the Seto Inland Sea, Japan 总被引:1,自引:0,他引:1
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 1345 cells 11(temporalaverage = 93 cell11) and 0.149.6 µg C l1(temporalaverage = 13.8 µg C l1; 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 >0.15.2 µg C l1 day1(temporalaverage = 1.4 µg C l1 day1; 64% of the productionof calanoid copepods during the same period). Diatom clearancerates by N.scintillans were in the range 0.100.35 mlcell1 day1, and the phytoplankton population clearanceby N.scintillans was >12% day1. 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. 相似文献
11.
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 (28 µn), this copepodactively fed on >10 µm particles, including autotrophic/heterotrophic(dino)flagel-lates and ciliates, with clearance rates of 0.030.38ml animal1 h1. 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 animal1 h1. Daily carbon ration fromthe combination of these food items averaged 148 ng C animal1day1 (41% of body C day1), with ciliates and heterotrophicdino-flagellates being the main food source ({small tilde}69%of total carbon ration). Respiration rates were 0200.23µl O2 animal1 day1. Assuming a respiratoryquotient of 0.8 and digestion efficiency of 0.7, the carbonrequirement for respiration was calculated to be 125143ng C animal1 day1, 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. 相似文献
12.
The growth of juvenile Bithynia tentaculata (Proso-branchia,Bithyniidae) was measured under controlled laboratory conditionsover 18 months. The animals were fed with different concentrationsof suspended food (Chlamydomonas reinhardii at 2, 000 cells.ml1and at 10, 000 cells.ml1), solid food (lettuce) and combinationsof both (lettuce with 2, 000 cells.ml1 and with 10, 000cells.ml1 Chlamydomonas). The growth of all animals wasmeasured weekly, and after 1 years final shell sizes, shelldry weights and ash-free dry weights, as well as soft body dryweights and ash-free dry weights were determined. Survival rateof the animals increased from 20% when fed with 2, 000 algalcells.ml1 to 75% with lettuce and 10, 000 cells.ml1as food. Final shell sizes and shell weights were not influencedby food, but soft body dry weights were significantly reducedwhen animals were fed on suspended food only. Reproduction (i.e.egg laying) was observed at the end of the second summer whenlettuce (with or without algal addition) was given as food.The ecological consequences of these results are discussed. (Received 7 April 1993; accepted 9 August 1994) 相似文献
13.
Egg production, growth and development rates of Oithona similiswere measured in the laboratory as a function of food concentrationand composition. On an optimum diet, development is isochronaland growth is near exponential. The maximum juvenile growthrate at 15C (0.2 day1) is similar to juvenile growthin calanoid copepods. The maximum weight-specific egg productionrate (0.1 day1), on the other hand, is substantiallyless than in free-spawning calanoids, but similar to that inegg-carrying calanoids. In the Kattegat, Oithona spp. egg productionis strongly limited by food during summer and controlled bytemperature during winter. The seasonal signal in fecundityand population biomass is much weaker than in the co-occurringfree-spawning calanoid genera, where fecundity and populationbiomass undergo dramatic seasonal viaration.
1Present address: Instituto Nacional de Investigacin y DesarrolloPesquero, INIDEP, CC 175, Playa Grande, Mar del Plata, Argentina 相似文献
14.
Napp Jeffrey M.; Hopcroft Russell R.; Baier Christine T.; Clarke Cheryl 《Journal of plankton research》2005,27(5):415-426
Pseudocalanus species are important contributors to the secondaryproduction of the northern hemisphere mid- to high-latitudeoceans. In the coastal Gulf of Alaska, Pseudocalanus are presentyear round and are represented by three species. In 2001, Pseudocalanusmimus was the dominant Pseudocalanus species on the shelf duringspring and summer, comprising 30100% of the total, whilePseudocalanus newmani dominated in Prince William Sound (1090%).Pseudocalanus minutus were only abundant in Prince William Soundduring early spring. Egg production (by number and volume) wasa function of female prosome length and decreased from springto summer; however, significant variability was attributableto regional influences that were independent of size. For thesame sized female, P. newmani produced more eggs per clutchthan P. mimus. Pseudocalanus mimus, however, tended to havea larger mean egg size than P. newmani. Consequently, clutchvolumes of the two species were indistinguishable. Pseudocalanusegg production rates (EPRs) (eggs female1 day1)were lower in July and August (ca. 24) than April andMay (ca. 19), but total egg production by the population(eggs day1) was nearly equivalent for the two time periodsdue to higher female concentrations in summer. 相似文献
15.
Microplanktonic respiration rates were estimated in waters offthe coast of northern Chile (Antofagasta, 23°S) during ElNiño and pre-El Niño conditions. Three cruiseswere conducted during pre-El Niño summer (January/February1997), El Niño winter (July 1997) and El Niñosummer (January 1998). Oxygen consumption was estimated by theWinkler method using a semi-automatic photometric end-pointdetector. The ranges of microplanktonic respiration rates foundwere 0.1121.15, 0.036.25 and 0.069.01 µmolO2 l1 day1 during pre-El Niño summer, ElNiño winter and El Niño summer, respectively.Significant differences were found between winter and summerrespiration rates (non-integrated and integrated). The meanintegrated respiration (mixed layer) for pre-El Niñosummer, El Niño winter and El Niño summer was95 ± 51 (SD) mmol O2 m2 day1, 50 ±23 (SD) mmol O2 m2 day1 and 63 ± 32 (SD)mmol O2 m2 day1, respectively. The strong seasonalsignal detected in microplanktonic integrated respiration inthe area seems to be characteristic of the pre-El Niño/ElNiño 199798 period. The integrated respirationrates found off Antofagasta are similar to reported values forthe upwelling area off Peru despite methodological differences.A positive significant correlation was found between respirationand water temperature (r = 0.76, P 相似文献
16.
Microzooplankton herbivory and bacterivory in Newfoundland coastal waters during spring, summer and winter 总被引:8,自引:0,他引:8
Grazing by microzooplankton on autotrophic and heterotrophicpicoplankton as well as >0.7 µm phytoplankton (as measuredby chlorophyll a) was quantified during July, August, October,January and April in the surface layer of Logy Bay, Newfoundland(47°38'14'N, 52°39'36'W). Rates of growth and grazingmortality of bacteria, Synechococcus and >0.7 µm phytoplanktonwere measured using the sea water dilution technique. Microzooplanktoningested 83184, 96366 and 64118% of bacterial,Synechococcus and >0.7 µm phytoplankton daily potentialproduction, respectively and 34111, 2530 and 16131%of bacterial, Synechococcus and >0.7 µm phytoplanktonstanding stocks, respectively. The trends in prey net growthrates followed the seasonal cycles of prey biomass, suggestingthat microzooplankton are important grazers in Newfoundlandcoastal waters. Ingestion was lowest during January and October(~2 µg C l1 day1) and highest in August(~20 µg C l1 day1). Aside from April when>0.7 µm phytoplankton represented the majority (~80%)of carbon ingested, bacterioplankton and <1 µm phytoplanktonrepresented most of the carbon ingested (~40100%). Althoughmicrozooplankton have here-to-fore been unrecognized as an importantgrazer population in Newfoundland coastal waters, these resultssuggest that they play an important role in carbon flow withinthe pelagic food web, even at low temperatures in Logy Bay. 相似文献
17.
Community structure, biomass and productivity of size-fractionated summer phytoplankton populations in lower Narragansett Bay, Rhode Island 总被引:1,自引:0,他引:1
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 108µm 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 a1 h1; 0.9day1)and<5 µm(1.7 g C g Chl a1h1; 0.5day1)size fractions were consistently lower than those of the totalpopulation (4.8 g C g Chl a1 h1; 1.3 day1)and the <10 µm size fraction (5.8 g C g Chl a1h1; 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. 相似文献
18.
Pseudobalanion plancioracum was the most abundant ciliate speciesin the pelagic zone of Lake Constance, FRG, over a 3 year period.Annual averages accounted for 30, 35 and 43% of total ciliatenumbers in the uppermost 20 m of the water column in 1987, 1988and 1989 respectively. Highest cell numbers were observed inearly spring, simultaneously with the first phytoplankton maximum.The small ciliate (mean length 15 µm, mean cell volume1300 µm3) is a raptorial feeder and predominantly consumesphytoplankton. In laboratory cultures, P planctonicum grew wellon a diet of Rhodomonas sp. (Cryptophyceae). Maximum growthrates increased from 0.46 day1 at 5 5°C to 1.52 day1at 18.5° C, while temperatures above 21°C were lethal.Depending on food concentration, 0.24.4 Rhodomonas cellswere ingested per ciliate and hour. 相似文献
19.
The contribution of ammonia excreted by zooplankton to phytoplankton production in Narragansett Bay 总被引:1,自引:0,他引:1
Ammonia excreted by mixed zooplankton populations over an annual(19721973) cycle in Narragansett Bay varied from 0.04to 3.21 µg at NH3-N dry wt1 day1, exclusiveof two exceptional rates measured one year apart: 11.74 and18.39 µg at NH3-N mg dry wt1 day1. Grossphytoplankton production integrated over the year (19721973)averaged 151 mg C m3 day1 for an 8 m water column;peaks of 332 and 905 mg C m3 day1 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 m2)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. 相似文献
20.
Water exchange, temperature tolerance and oxygen consumptionof the snail, Trigonephrus sp., from the southern Namib desertof Namibia were examined and related to activity. At 25°Cand 15% R.H. mean water loss and food and water uptake were5.95 mg. day1 and 630 mg.day1, respectively. Bodytemperature tracked sand temperature. Snails tolerated sandtemperatures as high as 45°C. Mean ± S.D. oxygenconsumption rates were 32.0 ± 2.94 µlO2.g totalbody mass1.h1 at 15°C, when the snails wereactive, and 11.27 µlO2.g total body mass1.h1at 25°C, when the snails were inactive. These values are2-6 times lower than those recorded for the similarly sizedmesic snail, Helix aspersa. Activity experiments indicated thatlow ambient temperatures and high humidities were favoured bythe snails. This, together with the burying behaviour of thesesnails during high temperatures, suggests that they limit stressby restricting activity to physiologically-favourable periods,even though more-extreme conditions may be tolerated. (Received 7 June 1990; accepted 20 November 1990) 相似文献