首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 546 毫秒
1.
The growth of C. consobrina of the White Nile near Khartoum was studied during March–December, 1977 from material collected from fish guts every two months. It was found that the growth season extends from February to July in correlation with the rise in temperature. Food was abundant and the concentration of the dissolved calcium in the river water was also increasing.During the flood season from July to October, the clams entered a resting state as a result of the annual siltation and consequently growth was arrested. Growth rings were found to be formed as a result of the siltation-induced resting state.There is evidence that little growth occurred during the cooler months from October to December. The development of the false rings on the shells is possibly a result of the changes in the water levels.Analysis of the growth of the adult clams showed that there is a clear size-time relation; there was close agreement between the calculated maximum sizes and the actual data collected from the field.Other examples from Sudanese inland waters were also discussed. The role of the annual hydrological cycles in regulating the populations activities and hence the growth of the individuals was found to be important.  相似文献   

2.
Age composition and growth rates of the squid Loligo vulgaris(Lamark, 1797) were studied by examination of growth incrementswithin statohths of 419 specimens (mantle length, ML, rangingfrom 32 to 400 mm). The squid were obtained by monthly samplingfrom the catches of commercial trawls off southern Portugalbetween March and September, 1993 The total number of growthincrements in the mounted and ground statohths was counted usinga semi-automatic image analysis system. ML was significantlycorrelated with both the statolith length, TSL and the numberof increments, NI. The female statolith was slightly largerthan the male statolith for the same mantle size. Growth ratesof individuals showed high variability with an average estimatedat 34.6 mm month–1 for males and 33.5 mm month–1for females. Growth in length between 70 and 280 days was bestdescribed by a power function for both sexes. The growth indexof the statolith (TSL/NI) decreased with individual growth.This result may be related with the onset of sexual maturation.L. vulgaris hatched throughout the year with two distinct peaks,in spring which is the mam breeding period, and in autumn. Thelife cycle of the L. vulgaris population on the south Portugueseshelf was completed in one year *Present address for correspondence: Instituto de InvestigacionMariflas. Eduardo Cabello. 6 - 36208 VIGO. Spain (Received 28 November 1995; accepted 7 February 1996)  相似文献   

3.
Pseudanodonta complanata is listed as ‘Near Threatened’on the IUCN Red List (IUCN, 2006) and is a species of conservationpriority on the UK Biodiversity Action Plan. The UK is hostto some of the largest populations of this species, but littleis known about their reproductive biology. Two populations werestudied in the Great Ouse catchment and the Waveney and Yarecatchment, East Anglia, UK. Both populations are reproductivelyactive, producing viable glochidia. Small mussels (<30 mmlength) in both catchments indicate that recruitment is occurring.A short non-gravid period in May is followed by three monthsof glochidial formation in June, July and August; by Septembermussels contain mature glochidia ready for release the followingApril. Females brood between 5,000 and 50,000 glochidia, andthis scales with mussel length L (mm) as: nglochL2.1. The sexratio is skewed towards females (2.5 females:1 male), and malesare larger than females. No hermaphrodites were found duringthe histological examination of the gonads of 24 mussels. Thein vivo examination of demibranchs is shown to be an effectivenonsacrificial means of determining sex and gravidity. Conservationrecommendations include: minimizing management operations inriver stretches containing large populations; avoiding formsof management which preferentially remove large mussels (i.e.males and the most fecund females); performing management duringthe non-gravid period to avoid causing the premature releaseof glochidia; leaving sufficient time between management operationsfor populations to recover; and temporarily translocating musselsto refugia during management operations. (Received 9 February 2005; accepted 2 May 2007)  相似文献   

4.
The aim of this study was to document and model the populationdynamics of zebra mussels Dreissena polymorpha (Pallas, 1771)in Pool 8 of the Upper Mississippi River (UMR), USA, for fiveconsecutive years (1992–1996) following their initialdiscovery in September 1991. Artificial substrates (concreteblocks, 0.49 m2 surface area) were deployed on or aroundthe first of May at two sites within each of two habitat types(main channel border and contiguous backwater). Blocks wereremoved monthly (30 ± 10 d) from the end ofMay to the end of October to obtain density and growth information.Some blocks deployed in May 1995 were retrieved in April 1996to obtain information about over-winter growth and survival.The annual density of zebra mussels in Pool 8 of the UMR increasedfrom 3.5/m2 in 1992 to 14,956/m2 in 1996. The average May–Octobergrowth rate of newly recruited individuals, based on a von Bertalanffygrowth model fitted to monthly shell-length composition data,was 0.11 mm/d. Model estimates of the average survivalrate varied from 21 to 100% per month. Estimated recruitmentvaried substantially among months, with highest levels occurringin September–October of 1994 and 1996, and in July of1995. Recruitment and density in both habitat types increasedby two orders of magnitude in 1996. Follow-up studies will benecessary to assess the long-term stability of zebra musselpopulations in the UMR; this study provides the critical baselineinformation needed for those future comparisons. (Received 5 November 2004; accepted 30 September 2005)  相似文献   

5.
This paper examines the biology and ecology of Helix lucorumL. which lives in mainland Greece, as well as its growth andsecondary production. A demographic study revealed that (a)3 cohorts exist at any time during the year (when adults ofall generations belong to the same cohort) (b) egg-laying andhatching occur during the months of July and August respectively,(c) the most rapid growth takes place during spring. Study ofH. lucorum genitalia in relation to age showed that the snailsaxe sexually mature 3 years after hatching, when the largestdiameter of their shell (D) is equal to or greater than 35 mm Von Bertallanffy's method suggests that Helix lucorum may liveup to 14 years or more in order to reach its possible maximumsize (48.80 mm) The study of relative growth of D in relation to Ps (peristomesurface) of Helix lucorum shows that D grows faster than Pswhen D12.50 mm; juveniles change their growth rate when theirD arrives at 22.05 mm, and growth becomes slower when adultsarrive at 36.27 mm Annual secondary production calculated by the size frequencymethod gave a mean annual density of 3.39 individuals per m2,a mean annual crop (biomass) of 4.04 g-m–2 and an annualproduction (P) of 5.02 g · m–2. The annual turnoverratio (P//b) is equal to 1.24 (Received 23 June 1987;  相似文献   

6.
Freshwater mussels of the genus Diplodon (Unionida) are commoninhabitants of lakes and rivers in South America, and have slowgrowth and long life spans. We established the annual periodicityof incremental shell growth in Diplodon chilensis patagonicus(d'Orbigny, 1835) and calculated growth rates at different ages,using internal ring counting supported by dyeing methods and18O isotope analyses, in two Patagonian populations (Lago Steffenand its effluent Río Manso Inferior, Argentina). Longevitiesof ca. 90 years (Lago Steffen) significantly extend the lifespans reported in the past. Growth rates for old individuals(>30 years) from both lake and river populations average0.16 mm per year along the axis of minimal growth. We evaluatedthe seasonal periodicity of minor and trace elements (Mn, Mg,Sr, Ba, Na, S) in situ by Laser Ablation ICP-MS and ElectronProbe Microanalyser analyses. Line-scans in a valve from LagoSteffen show that Mn, Sr and Ba are preferentially accumulatedduring the summer, while higher concentrations of Mg are foundin the winter bands. Metal/Ca ratios may serve as long-termarchives of environmental variables, e.g. metal concentrationsin water, water temperature and primary productivity. Diplodonchilensis patagonicus valves exhibit excellent characteristicsto construct an accurate chronological archive with time windowsof up to around a century, resolving the environmental signalannually and even seasonally. (Received 6 May 2008; accepted 3 November 2008)  相似文献   

7.
Coexisting populations of the mussels, Perna perna and Mytilusgalloprovincialis, were monitored at two sites on the NorthAfrican coast, east of Algiers, over a five year period (1985–1989).While spatfalls were observed throughout the year, only themajor spring-summer recruitment, which occurred during favourableweather conditions, contributed to the renewal of both musselspecies at both sites. Very high densities (>10, 000 ind.m–2) were observed at both sites, but the mussel bedswere composed principally of young and small specimens due toharvesting of the largest animals for use as bait and for humanconsumption. The maximal length observed was 75 mm in P. pernaand 49 mm in M. galloprovincialis. The life span of the specieswas low, 12–24 months in P. perna and 11–28 monthsin M. galloprovincialis. This survey showed that M. galloprovincialisbecame dominant in both mussel beds due to its resistance todisturbance by human activities. (Received 5 January 1995; accepted 18 April 1995)  相似文献   

8.
Two populations of Anadara senilis were sampled periodicallyin a lagoon of Senegal. Spatfall occurs in summer during therainy season. Population density decreases from about 50, 000.m–2,two months after spatfall, down to 6, 750 one year later and750 after 28 months. The average growth, measured on the surfaceof the shell, following the umbo rim axis is 0.8 mm per month.The main reduction in growth rate occurs in winter and endsby the deposition of a growth ring. A second growth reductiontakes place during the rainy season and sometimes ends by aweak growth ring. The microgrowth increments are conspicuousand widest during spring equinox. They are not directly relatedto the tidal cycle, but it was impossible to determine if theyhave a tidal or a daily periodicity. (Received 11 February 1990; accepted 16 July 1993)  相似文献   

9.
The life cycle, population dynamics, growth and secondary productionof the pulmonate land snail Bradybaena fruticum were studiedin northern Greece. The demographic analysis of the populationsof B. fruticum revealed that a) two cohorts exist in the fieldthroughout the year b) the reproductive period started in thebeginning of summer and c) growth was increased during springand autumn. According to von Bertallanffy' method B. fruticum needs 5 yearsto attain its maximum size in the field of 25.40 mm. Mortalityrate increases and life expectancy decreases with increasingage. Net reproductive rate (Ro) was equal to 3. 15 and per capitarate of increase (rc) was equal to 1. Annual secondary production, calculated by Hynes' size frequencymethod, revealed a mean annual density of 5.9 individuals/m2,a mean standing crop (B) of 8.09 g/m2/year and an annual production(P) of 1.92 ± 0.11g/m2/year. Annual turnover ratio (P/B)was equal to 2.37. (Received 25 May 1989; accepted 17 March 1989)  相似文献   

10.
The seasonal abundance of copepod eggs in bottom sediments ofMalaga harbour was documented during an annual cycle betweenJune 1989 and June 1990. The concentration noted ranged from6.6.106 to 0.19106 m–2. The number of adults in thewater column and eggs recovered from the bottom sediments fluctuatedmarkedly with season. The highest egg abundance in sedimentswas found coincidentally with the early population growth season,although the values remained high until the adults disappearedfrom the water column. During the winter, the number of eggsdecreased until the development of the next copepod population.When bottom sediments were incubated in the laboratory, a largenumber of Acartia nauplii hatched, which showed that eggs laidin the autumn remain viable at the bottom until late spring,thus providing a large pool of potential recruits for the planktonicpopulation. 1Present address: Departamento de Biologa Animal, Vegetal yEcologa, Facultad de Ciencias Experimentales, Universidad deMan Paraje Las Lagunillas s/n, 23071 Man, Spain  相似文献   

11.
ABSTRACT

We investigated the annual gametogenic phenology of the freshwater pearl mussel, Lamellidens marginalis (Lamarck, 1819), collected from a lentic habitat at Mymensingh, Bangladesh, using biometry and histology through monthly sampling from August 2015 to July 2016. After biometric measurements, thin slices of dorso-ventral sections were cut from the middle of the mussels for histology to determine sex and level of gonadal maturation. The condition index (CI) ranged from 0.64 (March) to 0.99 (January) over the study period. The CI peaked three times (January, April and July) indicating that the mussels were ripe during these months and subsequent decreases in CI indicated spawning, which was consistent with histology. Both males and females exhibited similar patterns in terms of gonadal development, maturation and spawning activity. It was confirmed that natural populations of L. marginalis spawn throughout the year with remarkable temporal variations, except during December when the surface water temperature reaches annual minima (16.5°C). Highest spawning activity of L. marginalis was noted during February–March, May and July–November. The data obtained in the present study could be useful for the conservation managers of this commercial species by allowing harvesting of better quality mussels to be timed without interrupting major spawning activity.  相似文献   

12.
Two mussels, Choromytilus meridionalis (Krauss) and Aulacomyaater, (Molina) were used as indicators of biotic factors thatapparently result in radically different sublittoral communitiesat two closely situated islands on the South African west coast.Specimens of both species were attached to submerged plates,which were either unprotected or protected from predation bycages. C. meridionalis grew faster and tolerated silting andsmothering better than A. ater. At Malgas Island adults of C.meridionalis are completely absent and those of A. ater scarcedue to intense predation by rock-lobsters. When protected againstpredation, growth of both species was significantly faster andsurvivership higher at Malgas than at Marcus Island, where C.meridionalis is abundant but A. ater absent. When the musselswere unprotected at Malgas, they were eaten in a few hours.At Marcus Island where rock-lobsters are virtually absent, cagedmussels grow faster than unprotected individuals and survivedlonger. Drilling whelks (mostly Nucella squamosa (Lamarck))were major predators at Marcus. Relative intensity of rock-lobsterpredation and competition between the mussels appear to controlthe structure and diversity of the sublittoral communities atthese sites, rather than physical factors. Growth rate, shellthickness and tolerance of smothering by other species determinewhich species of mussel predominates. (Received 5 April 1988; accepted 11 July 1988)  相似文献   

13.
Philine orientalis occurs on Hong Kong's beaches for {smalltilde}2 months each year, in May and June when it breeds, laysegg capsules and dies. It is believed to have a life span ofone year. Hoi Sing Wan, a sandy beach in the New Territoriesof Hong Kong is dominated at lower levels by the venerid bivalveTapes philippinarum, the population of which in May and June,following spring recruitment, mostly comprises juveniles. P.orientalis, occurring at a density of {small tilde} 1.m–2,feeds voraciously upon these juveniles consuming, in laboratoryexperiments, a mean of 25.day–1. At Hoi Sing Wan, P. orientalisappears to be highly prey specific. It is, however, known tofeed on other prey items and probably has a catholic diet, duringits annual migration from deeper to shallower sediments, accordingto the prevailing fauna. In terms of wet weight, P. orientalis consumes a mean of {smalltilde}4.4% (2.2–6.7%) of its body weight day–1.In terms of dry weight, however, this figure increases to amean of 35.5% and one figure of 208% has been recorded. Althoughthis is because of the large body fluid content of this, essentiallyshell-less, gastropod, using a hydrostatic skeleton to achieveburrowing, such figures further attest to the voracity of thebreeding adults. This study joins others in questioning ourpresent understanding of the scale of energy budgets on suchshores, i.e., are our estimates of loss to predation grosslyunderestimated? *Present address: Department of Biology, Baptist College, WaterlooRoad, Kowloon, Hong Kong. (Received 20 May 1989; accepted 3 July 1989)  相似文献   

14.
Crevice-dwelling land snails emerge only infrequently to theexposed surface, and very little is known about their naturalhistory. Here we report on the biology, life cycle, populationdynamics and longevity of one such species, Cristataria genezarethana,which we studied over a period of three years. C. genezarethana spends 95–98% of its lifetime withinrock crevices. In winter the crevice serves as an egg layingsite, and as a retreat during periods of inactivity. Throughoutsummer it serves for aestivation adults aestivate near CTeviceopenings, young apparently deeper inside. The surface of the rock serves mainly as a lichen-feeding andcopulating site, to which the snails emerge during brief periodsof activity. Both for the onset and for the continuation ofits activity season, C. genezarethana is absolutely dependentupon rain. However, activity ends before the end of the rainyseason, suggesting that aestivation is not merely a direct responseto dry climate. Though the population as a whole was active on each rainy day,no more than 15%–20% of the population were active simultaneously.An individual snail was active, on average, for only 6–12days per year. Population size of the study-rock reached 2000–2900individuals, and mean density was 150–200 snails m2. Thissnail carrying capacity of the rock is broadly similar to thatof densely populated bushy habitats (when snail weight is considered).In these dense populations, low mating frequencies and growthinhibition may regulate population size. In all three seasons, the population consisted of two main large,well defined age groups: adults and young. As compared to theadults, the young were active on different parts of the rockand at different times. Although a third, intermediate groupof sub adults was found, it was always very small. A fourthgroup, of juveniles, appeared during winter; later, most ofthem disappeared. We did not observe any shift from the young to the adult sizegroup. This suggests a broadly stable population, with virtuallyno recruitment, in which final growth to adulthood is inhibitedby the adults. Growth was very slow, suggesting that maturityin nature is reached in about 11 years, and that individualslive sixteen years at least. Mortality occurred in all age groups,and about 5% of the population died each year. There was noevidence for heavy predation. Crevices might be a suitable habitat for land snails in whichthe hatching period, and period of juvenile growth, are verylong. (Received 1 February 1993; accepted 27 March 1993)  相似文献   

15.
Growth and nitrate reductase activity (NRA) of Atropa belladonnacells were studied in medium supplemented with NaNO3, NH4NO3,and amino acid precursors to tropane alkaloids. Growth and NRAwere stimulated by NH4+ and by proline, by proline plus ornithine,but not by glutamate, in NO3-containing medium. Testedamino acids inhibited neither utilization of inorganic nitrogennor growth. (Received September 30, 1988; Accepted August 28, 1989)  相似文献   

16.
The influence of cell size on the growth rate of Thalassiosira weissflogii   总被引:1,自引:0,他引:1  
Growth rate and average cell volume were measured throughoutauxospore formation in two populations of Thalassiosira weissflogii(Hustedt). In both cases, the entire population shifted fromrelatively small (800 µm3) to large cells (2800 µm3)over a 5 day interval. This shift was accompanied by a dramaticincrease in the average growth rate of the populations from1.6 to 3.4 doublings/day.  相似文献   

17.
Experimental studies into the feeding biology of rotifers in brackish water   总被引:1,自引:0,他引:1  
Mass developments of rotifers of the genus Brachionus, and especiallyof B.quadridentatus, occur regularly in the largely hypertrophicchain of shallow waters (‘boddens’) south of theDarss-Zingst peninsula (Southern Baltic). Interest in the autecologyof the species is, therefore, considerable. Various food sourceswere used in laboratory experiments to ascertain the food requirementsof B.quadridentatus, determine its filtration and ingestionrates, and assess its food particle size-selection ability.Growth experiments showed that the chlorophyceans Nannochlorissp. and Chlorella vulgaris possess considerable nutritionalvalue for the species, whereas abundances declined when Microcystisfirma, detritus from Enteromorpha sp. and only bacteria (Pseudomonas),respectively, were provided as food sources. Filtration ratesvaried between 0.02 and 1.73 µl ind.–1 h–1,and ingestion rates between 121 and 5560 cells ind.–1h–1, depending on the filtration rate and algal concentration.Investigations into food particle size selection using fluorescentlatex particles revealed that particle size influences foodparticle intake. When particles of different sizes were mixed,the animals showed a preference for the larger particles andingested the smaller ones with a diameter of 1–2 µmless efficiently. The brackish water species Brachionus plicatiliswas studied besides B.quadridentatus in all experiments. Theformer species proved to be superior both in its range of utilizableparticle sizes and its growth rate. The experiments with laboratorycultures were backed up by studies performed with various rotiferspecies taken from natural populations.  相似文献   

18.
Populations of the sea hare, Aplysia oculifera (Adams &Reeve, 1850) (Gastropoda: Opistho-branchia), were studied inthe northern coast of the Gulf of Eilat (Aqaba) between April1988 and March 1992. Recruitment occurred from December to February,synchronized with the blooming of green algae (Enteromorphaintestinalis and Ulva sp.). A single recruitment event occurredeach year, while a secondary recruitment was rarely, observedand was related to acute catastrophic disturbance of the habitat.Adult sea hares inhabited the inter- and subtidal zones fromDecember-January to April-June, feeding on E. intestinalis andUlva sp. Populations disappeared in April-June which coincidedwith disappearance of these green algae. Mean maximum body livemass of adult sea hares (MMBLM, that is the highest mean bodymass recorded at specific site within the season) ranged from0.77 to 33 g MMBLM, varied significantly among populations inhabitingthe various study sites, and was significantly and inverselycorrelated with water movement intensity. Abundance of sea haresvaried among sites and among years and was related to the amountof green algae during the recruitment season. 2Present address: Department of Biology, University of Haifaat Oranim, Tivon 36006, Israel. E-mail: plaut{at}research.haifa.ac.il (Received 29 April 1997; accepted 26 July 1997)  相似文献   

19.
The effects of a population of the boring gastropod Natica tectaon the bivalve Choromytilus meridionalis were investigated atBailey's Cottage, False Bay, South Africa. In July 1979 theN. tecta density on the mussel bed averaged 69 m–2 andthe population consisted mainly of reproductively mature individualsbetween 20–33 mm shell width. Laboratory experiments on N. tecta showed that prey size selectionis an increasing function of predator size. The prey size rangetaken by large N. tecta is also greater than that taken by smallindividuals. The position of the borehole on the mussel shellis a function of the way in which the shell is held by the footduring the boring process. Consumption rates measured in thelaboratory showed an increase from approximately 1 kJ per weekin 18 mm N. tecta to 4.5 kJ per week in 28 mm individuals. Populationconsumption in the field was calculated as 663 kJ m–2month–1. It was estimated that at this rate the standingcrop of mussels in the pool would be eliminated within 10 months.Field measurements showed significant depletion after 6 months. New spat settlement of mussels occur every 4–6 years.The growth curve shows that after one year the population meansize exceeds 30 mm shell length, which is beyond the prey selectionsize range of small N. tecta. It was concluded that at the timeof a new mussel settlement a niche is provided for the simultaneoussettlement and growth of juvenile N. tecta in high densities.However, within one year the increase in prey size, togetherwith depletion due to over-exploitation, limits population growthand density in N. tecta. (Received 14 March 1980;  相似文献   

20.
A radiochemical method has been developed to measure the growthrate of aquatic Crustacea, based on the rate of incorporationof [14C]NAG, from [14C)UDP-NAG, into the chitinous exoskeleton.Daphnia was used as the test organism. The specific activity(d.p.m. nmol–1) of the [14C]UDP-NAG precursor pool increasedlinearly with time, as did the rate of [14C]NAG incorporationinto exoskeletons. Growth rates were calculated in a manneranalogous to that used in the 14C ‘primary production’technique. Comparison of growth rates derived from the [14C]chitinsynthesis method to those obtained by independent conventionalmeans showed agreement to within 5%. This is the first radiochemicalmethod to accurately measure the growth rate in a metazoan.It can potentially be applied to field populations of any organismswhich synthesize chitin.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号