Life Cycle And Production Of Hydrobia Ventrosa And H .
Vol. 7 : 75-82, 1982lMARINE ECOLOGY - PROGRESS SERIESMar. Ecol. Prog. Ser.IPublished January 1Life Cycle and Production of Hydrobia ventrosaand H. neglecta (Mollusca: Prosobranchia)Hans Redlef SiegismundInstitute of Ecology and Genetics, University of Aarhus. DK-8000 Aarhus C, DenmarkABSTRACT: Life cycle, growth, and production of the mud snails Hydrobia ventrosa (Montagu)and H.neglecta Muus were studied in the Kysing Fjord estuary, Denmark. Recruitment of Age class 0 insummer revealed 2 maxima: July-August and September.The first recruited group reached a length of2.3 mm in H. neglecta and 2.5 mm in H. ventrosa in November. After September, no growth was foundin the last recruited group of both species; their mean length remained 1.3 mm. Both species have a lifespan of approximately 18 months. The annual production of H. ventrosa and H, neglecta was 8.40 and5.86 g ash-free dry weight m-2,respectively.INTRODUCTIONMATERIALS AND METHODSThe hydrobiid species Hydrobia ventrosa (Montagu),H. neglecta Muus, H. ulvae (Pennant),and Potamopyrgus jenkinsi (Smith) are important members of theshallow-water fauna in Denmark. They are found atmost lenitic localities, except where the sediment consists of mud. The salinity preference varies among thespecies (Hylleberg, 1975), resulting in some differential habitat selection. However, their distributionsalong salinity gradients often show considerable overlap, leading to the CO-existenceof 2 or 3 of the species(Fenchel, 1975). The hydrobiids are deposit feederswith diatoms as their main food source (Fenchel andKofoed, 1976; Jensen and Siegismund, 1980). Theingested diatoms are assimilated with a high efficiency(Kofoed, 1975a).Where abundant, the population densities of thespecies are often in the range of 20 000 to 40 000 m-2.Such high densities make the snail an important linkin the estuarine food web, e.g. as a food resource forwaders and ducks (Olney, 1965; Evans et al., 1979).However, an estimate of the annual production isneeded in order to obtain a quantitative measure of themud snails as consumers of the microflora and as a foodresource for predators. This paper studies the production in populations of Hydrobia ventrosa and H. neglecta in the Kysing Fjord estuary. Life cycles of the 2species are described and production is estimated fromthe knowledge of the age structure and densitythrough time.Study AreaO Inter-Research/Printed in F. R. GermanyThe study was carried out in Kysing Fjord, a smallestuary on the east coast of Jutland, Denmark (Fig. 1).The estuary is shallow with a mean depth of 0.6 m, onethird of the water mass is exchanged during each tide(Muus, 1967).An average salinity gradient from 12%0Sat the innermost part to 20%0 S at the mouth of theestuary was observed during the study period.All 3 Hydrobia species are present in the estuary.with H. ventrosa and H. neglecta being the dominantspecies and H. ulvae only of minor importance. H.neglecta dominates at the mouth of the estuary; itspopulation density decreases inwards, where H. ventrosa dominates in the middle part of the estuary. Thezone of overlap between the 2 species extends throughmost of the estuary. In addition to the Hydrobia speciesmentioned, the hydrobiid Potamopyrgus jenkinsi isfound in the innermost part of the estuary, where itdominates during summer.While Hydrobia ventrosa and H, neglecta werestudied at several stations in the estuary, this papertreats only a single station (Fig. 1);here the 2 speciesCO-existedand reached high densities, allowing bothof them to b e studied in the same area. The distance ofthe station from the shoreline was about 50 m; theS during the studysalinity varied from 10.5 to 22.5Y period with a mean of l6%0S.
Mar Ecol. Prog. Ser. 7: 75-82, 198276Fig, I. Kysing Fjord estuary showing sampling station (encircledcross)SamplingSnails were collected from April 21, 1978 to February21, 1979. Samples of the sediment were taken withPlexiglas tubes (inner diameter 2.6 cm). The sedimentwas sieved through a 0.5 mm sieve and the snails weresubsequently removed from the remaining sedimentmaterial with a dissecting microscope. Snail lengthwas measured from apex to anterior margin of theaperture with an ocular micrometer at 12 X magnification.Age classes were separated according to Harding(1949), assuming that size-frequency distributions ofthe age classes were normally distributed. The proportion of each age class, average length, and standarddeviation were estimated from a plot of the size-frequency distribution on probability paper. The densityof an age class was calculated as the product of totaldensity and proportion of the given age class.Length-Weight RelationshipThe average weight (W) of individuals from a givenage class was estimated from the average length (L) ofthe age class, usingThe parameters a and b were estimated by a regressionof the logarithm of the ash-free dry weight on tbelogarithm of length. The ash-free dry weight was measured as weight loss after 8 h of incineration at 550 "Cof snails dried at 105 ' C for 24 h.Production MeasurementThe different age classes of both species wereregarded as separate cohorts, and production was calculated separately for each of these cohorts. Theproduction of a cohort which declines in density fromtime t to time t A t can be calculated as where N (t) and W (t) are density of the cohort andaverage weight at time t, respectively (Crisp, 1971),The expression { N(t) N ( t A t ) ) / 2approximates themean density of the cohort that occurs during the timeinterval At, and W ( t At) - W (t) measures the weightgain during this period. Total production of the cohortis calculated as sum of the production increments overall time intervals.According to Crisp (1971), this method can also beapplied to an age class with a prolonged period ofrecruitment in which the density increases until therecruitment is finished. Crisp's method, however,seems to underestimate the production of the cohortduring periods of increasing density. The survivors of acohort at time t A t would have a production of N( t At) X { W ( t At) - W (t)} which is larger than (N(t)N ( t A t ) ) / 2 { W ( t A t ) - W ( t ) } because N( t At) N (t). A better approximation of the production of the cohort during a period of increasing densitywould, therefore, be simply to measure the differencebetween biomass at the time of highest density andinitial biomass. In the present paper, the biomass ofhatched larvae was ignored.The modification of Crisp's method still underestimates production, as it neglects the production of individuals recruited during the period of increasingdensity, and eliminated before observation at the endof the period. However, this estimate is closer to theactual production than an estimate following Crisp'smethod. From the time when density decreases, theproduction can be measured by Crisp's method.For comparison, production of the snails was measured by both Crisp's method and by its modificationdescribed.
77Siegisniund: Life cycle and production of HydrobiaRESULTSGrowth and Life CycleIn both Hydrobia ventrosa and H. neglecta, the initial Age class I consisted of large individuals with anunimodal size distribution in July when the recruitment of Age class 0 started (Fig. 2). Therefore, offspring classes could easily b e distinguished at thebeginning of the recruitment. In both species Age class0 was recruited in separate groups during summer.Age class 0 of the Hydrobia ventrosa population wasrecruited twice during summer: in July (0-1 group)and in September (0-2 group) (Fig. 2). The firstrecruited group attained a size of 2.50 mm inNovember when growth ceased. The second group didnot grow after it had been observed in September, andmean length did not exceed 1.50 mm (Fig. 3 ) .Age classI of the H. ventrosa population started to grow in AprilJ,A1978,,MJ,J,A,S,O,N,O,J1979,FFig. 3 . Hydrobia ventrosa. Growth of Age classes I, 0-1, and0-2L ngthh lH ventrosoLength (mmlH neglect0Fig. 2. Hydrobia ventrosa and Hydrobia neglecta. Lengthfrequency distribution from April 1978 to February 1979.Sums of fitted normal distributions drawn from June onF i g . 4 . Hydrobia neglecta. Growth of Age classes I, 0-2, and0-3
Mar. Ecol. Prog. Ser. 7: 75-82, 198278a n d reached a length of 3.6 mm in November rightbefore it vanished.Age class 0 in the Hydrobia neglecta population wasrecruited in 3 groups. The first recruitment group (0-1)w a s observed in July at a low density. It reachedmaximum density of 1600 m-2 in August; from September on, it could not be distinguished from Group Iand the second recruited group. Age class 0-2 was thefirst larger recruitment in the H. neglecta population(Fig. 2). It was observed in August and attained alength of 2.3 m m in November when it ceased to grow(Fig. 4).The third recruited group, 0-3, was observedin September. Its mean length (1.3 mm) did not changeduring the observation period. Age class I in the H.neglecta population started to grow from May andattained a size of 3.4 mm in November. This age classsurvived the winter, but its density decreased from7700 m-2 in November to 2800 m-' in February(Table 1).Length-Weight RelationshipAsh-free dry weight (pg) as a function of length (mm)in Hydrobia ventrosa and H. neglecta is illustrated inFigs. 5 a n d 6. The functions are:H. ventrosa:W 0.0417L' ' (3 0.93,n 57)H. neglecta:W 0.0290L'. ' (3 0.97,n 53)ProductionIn the Hydrobia ventrosa population the major production took place in Age class 0.In this a g e class, aproduction of 5.21 g ash-free dry weight m-' of a totalof 6.34 g ash-free dry weight m-' was achieved by thefirst recruited group (Table 2). Production of the 0group mainly occurred before November, when growthTable 1. Hydrobia neglecta. Production of different age classes of the population studied from April 1978 to February 1979SamplingdateAge classDensity(1000 m-')Mean length Mean ash-free(mm)dry weight (mg)Biomass(g m-')Production'(g m-7Production.( g m-2)Total production of Age class I"Total product onof Age class 0-10.170.28Total production of Age class 0-21.201.66Total production of Age class 0-30.090.70Calculated according to Crisp (1971)Calculated according to a modification of Crisp's method (see text)
79S egismund:Life cycle and production of HydrobiaTable 2. Hydrobia ventrosa. Production of different age classes of the population studied from April 1978 to February 1/2787878787878787879Age Mean length Mean ash-free(mm)dry weight (mg)Biomass(g 030 tion'(g m-2)0.830.62-0.500.170.510 .3370.337-0.572.204.315.063.441.38Total production of Age class 20.222.062.061.411.000.90004.310.90003.315.210.15- 0 060.09Total production of Age class 0-2"0.830.620.500.170.510 43-Total production of Age class I15/724/826/96/1112/1221/2Production.(g m-')0.180.950.150.060.091.13Calculated according to Crisp (1971)Calculated according to a modification of Crisp's method (see text)ceased. During winter, production was zero in the 0-1group and partly negative in the 0-2 group (Table 2).Production of Age class I amounted to 2.06 g ash-freedry weight m-' (Table 2). During summer, negativeproduction was found from June to July in this ageclass due to decline in length from 3.26 to 2.98 mm.Total production from April 1978 to February 1979 inthe Hydrobia ventrosa population amounted to 8.40 gash-free dry weight m-' (Table 3). An estimate according to Crisp's method, 5.55 g ash-free dry weight m-',is 34 % lower.The major production in the Hydrobia neglectapopulation took place in Age class I. The production ofthis age class amounted 3.22 g ash-free dry weight m-'.As in the H. ventrosa population, a negative production was observed in this age class from April to May.During winter, production of Age class I declined andwas approximately zero from November 1978 to February 1979. The production of Group 0 amounted to2.64 g ash-free dry weight m-2, of which the major partwas caused by the production of the 0-2 group (1.66 gash-free dry weight m-2). As in Group I, the productionof Group 0 was negligible during winter. Total production of the H. neglecta population amounted to 5.86 gash-free dry weight mT2(Table 3). Calculation according to Crisp's method yields 4.68 g ash-free dry weight,i. e. a 20 % smaller value.The total production of Hydrobia ventrosa and H.neglecta from April 1978 to February 1979 yielded14.26 g ash-free dry weight m-' at this locality.Table 3. Hydrobia ventrosa and the Hydrobia neglecta. Production of populations studied from April 1978 to February1979Production'weight m-2)Production' '( g ash-free dryweight m-')5.554.688.405.86(g ash-free dryH. ventrosaH. neglecla''Calculated according to Crisp (1971)Calculated according to a modification of Crisp'smethod (see text)
Mar Ecol. Prog. Ser 7: 75-82, 198280Length lmmlLengthlmmlFig. 5. Hydrobia ventrosa. Regression of ash-free dry weighton body lengthFig. 6. Hydrobia neglecta. Regression of ash-free dry weighton body lengthDISCUSSIONreproduction throughout the summer usually with asingle peak in the recruitment. These variations inrecruitments are probably caused by climatic changes.The differences in size distributions in April 1978 andFebruary 1979 (Fig. 2) suggest that the recruitment in1977 might have had a single peak in the H. ventrosapopulation because of unimodal size distribution inApril 1978, while the recruitment of the H. neglectapopulation might have had a small second peak in1977, as its size distribution in April 1978 is skewed tothe left.In late autumn, the first recruited group of Hydrobiaventrosa (0-1) and the first major recruitment of H.neglecta (0-2) had grown from a size of 0.2 mm athatching (Muus, 1967) to a size of 2.5 and 2.3 mm,respectively. The last recruited groups (0-3 in H. neglecta and 0-2 in H. ventrosa) did not show any growthafter they had been observed in September. This absence of growth may be d u e to high intra- and interspecific competition for food. The 2 groups had approximately the same size (1.3 mm), hence they areexpected to have a n almost complete overlap in theirLife CycleAge class 0 of the Hydrobia ventrosa population wasrecruited from 2 groups, whereas recruitment of thisage class was observed 3 times in H. neglecta (the firstone being of minor importance). The first majorrecruitment in H. neglecta was displaced 1 mo compared with the first recruitment in H. ventrosa. Thisdisplacement was found only at the reference station inKysing Fjord. At other stations where the 2 species coexisted, t h e recruitment was simultaneous (unpubl.own results).Two maxima of reproduction were also reported byFenchel (1975b) for Hydrobia ventrosa and H. ulvaepopulations in the Limfjord, Denmark, and by Fish andFish (1974) for H. ulvae populations in the DoveyEstuary, Great Britain. In both cases, e g g depositionoccurred in spring and late summer. However, Muus(1967) a n d Lassen and Clark (1979) observed in severalpopulations of the 3 Hydrobia species continuous
Siegismund: Life cycle and production of Hydrobiaresource niche (Fenchel, 1975b). Furthermore, the sumof their densities was high, 26700 m-', and the primaryproduction of their main food, diatoms, decreased during that period (Grontved, 1960).The parental a g e classes, I, were about 1 yr old attheir first reproduction. In Hydrobia ventrosa this ageclass disappeared in autumn, whereas in H, neglecta asmall number of this age class survived the winter. Theresulting life span of about 18 mo in both species is inagreement with Muus (1967).The observed body sizes of both species is in linewith the ranges previously reported (Muus, 1967; Fenchel, 1976; Hylleberg, 1978).ProductionThe average weight of a n individual of a given a g eclass was calculated from the average length of the a g eclass aswhere p, is the frequency of the size group with amedian length of Liwithin the a g e class. This causes aminor underestimation of weight (and therefore of production) d u e to the convexity of the function W aLbwhen b is larger than 1. The average weight ought to b ecalculated as the average of the weights of the sizegroups in the age class,W Z pi (aL,?.1Calculations indicate that the average underestimateis about 3 % with the size frequencies in the presentpopulations.The production calculated by Crisp's (1971) methodunderestimates the production in Hydrobia ventrosaby 34 % and in H. neglecta by 20 % . Crisp's methodhas been used by serveral workers; this may haveresulted in similarly low estimates. From the works ofBuchanan and Warwick (1974) a n d Warwick a n d Price(1975) the production of a g e classes with a prolongedrecruitment was calculated with the modified methodand compared with their own estimates based onCrisp's method. Buchanan a n d Warwick (1974). investigating a population of the polychaete Heteromastusfiliformis, underestimated the production of the Yearclass 0 by 53 % ; Warwick a n d Price (1975), investigating the polychaete Nephtys hombergi, underestimatedthe production of the Year class 0 by 10 %. The suggested modification still underestimates the actualproduction during a period of increasing density,because the calculated production ignores the production of individuals being recruited a n d eliminatedwithin the period of observation. The modified method81still appears to provide a better estimate of the actualproduction.The total production of Hydrobia ventrosa a n d H.neglecta from April 1978 to February 1979 amounted to14.26 g ash-free dry weight m-2. Although determinedfor only 10 mo, this probably approximates the totalannual production d u e to the negligible growth inearly spring. The sum of the production of both speciesis similar to that reported by Wolff and d e Wolf (1977)for allopatric H. ulvae populations on tidal flats in theGrevelingen estuary, The Netherlands.The importance of hydrobiid snails in the estuarinefood chain can be evaluated by comparing their production with the production of their food resource,benthic diatoms. Grsntved (1960) measured the annualbenthic primary production to b e 116 g C m-2, a n avera g e value for some Danish fjords. In the form of glucosethis would correspond to 4.539 MJ m-'. The calorificvalue of aquatic invertebrates has a mean of 23.44 kJg-' ash-free dry weight (Winberg, 1971), rendering theproduction of Hydrobia ventrosa and H. neglecta 334.3kJ m-2 yr-l. This value neither includes the productionof gametes nor excreted organic matter. The latter maybe significant at least for H. ventrosa (Kofoed, 1975b).Kofoed (1975b) showed that about 2 0 % of the consumption of a relatively protein-rich diet were used forproduction. With this value the total consumption of H.ventrosa and H. neglecta amounts to 1.672 MJ m-2 yr-l,i.e. these snails would consume about 4O0/0 of theannual primary production of the benthic microflora.This evaluation is crude, but it suggests the Hydrobiaspecies studied to be most important consumers ofbenthic microalgae.Acknowledgement. I would like to express my gratitude toDr. Jsrgen Hylleberg for numerous stimulating discussionsregarding the biology of Hydrobia.LITERATURE CITEDBuchanan, J. B., Warwick, R. M. (1974). An estimate ofbenthic macrofaunal production in the offshore mud of theNorthumberland coast. J. mar. biol. Ass. U. K. 54: 197-222Crisp. D. J. (1971). Energy flow measurements. In: Holme,N. A., McIntyre, A. D. (eds.) Methods for the study ofmarine benthos. Blackwell, Oxford, pp. 197-279Evans. P. R., Herdson, D. M., Knights, P. J., Pienkowski,M. W. (1979). Short-term effects of reclamation of part ofSeal Sands, Teesmouth, on wintering waders and shelduck. Oecologia (Berl.) 41: 183-206Fenchel, T. (1975a).Factors determining the distribution patterns of mud snails (Hydrobiidae). Oecologia (Berl.) 20:1-17Fenchel. T. (1975b). Character displacement and coexistencein mud snails (Hydrobiidae). Oecologia (Berl.) 20: 19-32Fenchel, T., Kofoed, L. H. (1976). Evidence for exploitativeinterspecific competition in mud snails (Hydrobiidae).Oikos 27: 367-376
82Mar. Ecol. Prog. Ser. 7 . 75-82, 1982Fish, J. D., Fish, S. (1974). The breeding cycle and growth ofHydrobia ulvae in the Dovey estuary. J. mar. biol. Ass.U.K. 54: 685-697Crontved, J. (1960). O n the productivity of microbenthos andphytoplankton in some Danish fjords. Medd. Danm. Fisk.Havunders. N. S. 3: 1-17Harding, J. P. (1949). The use of probability paper for thegraphical analysis of polymodal frequency distributions.J. mar. biol. Ass. U. K. 28: 141-153Hylleberg, J. (1975).The effect of salinity and temperature onegestion in mud snails (Gastropoda: Hydrobiidae).Oecologia (Berl.) 21: 279-289Hylleberg, J. (1978). Mud snails o n h a n d 11: a study ofpotential competition in term of snail sizes and spacialsegregation. (Swedish; Engl. summary). Huso biol. stat.Medd. 20: 31-49Jensen, K. T., Siegismund, H. R. (1980). The importance ofdiatoms and bacteria in the diet of Hydrobia-species.Ophelia 1 (Suppl.): 193-199Kofoed, L. H. (1975a). The feeding biology of Hydrobia ventrosa (Montagu). I. The assimilation of different components of the food. J. exp, mar. Biol. Ecol. 19: 233-241Kofoed. L. H. (1975b). The feeding biology of Hydrobia venrrosa (Montagu). 11. Allocation of the components of thecarbon-budget and the significance of the secretion ofdissolved organic matter J. exp. mar. Biol. Ecol. 19:243-256Lassen, H. H., Clark, M. E. (1979). Comparative fecundity inthree Danish mudsnails (Hydrobiidae). Ophelia 18:171-178Muus. B. J. (1967).The fauna of Danish estuaries and lagoons.Medd. Danm. Fisk. Havunders. N. S. 5: 1-316Olney, P. J. S. (1965).The food and feeding habits of shelduckTadorna tadorna. Ibis 107: 527-532Warwick. R. M. and Price, R. (1975). Macrofauna productionin an estuarine mud-flat. J. mar. biol. Ass. U. K. 55: 1-18Winberg, G . G. (1971). Methods for the estimation of production of aquatic animals, Academic Press. London, NewYorkWolff, W. J., de Wolf, L. (1977). Biomass and production ofzoobenthos in the Grevelingen estuary, The Netherlands.Estuar coast. mar. Sci. 5: 1-24This paper was presented by Professor T. Fenchel; it was accepted for printing on October 15, 1981
Vol. 7: 75-82, 1982 l MARINE ECOLOGY - PROGRESS SERIES I Published January 1 Mar. Ecol. Prog. Ser. Life Cycle and Production of Hydrobia ventrosa and H. neglecta (Mollusca: Prosobranchia) Hans Redlef Siegismund Institute of Ecology and Genetics, University of Aarhus. DK-8000 Aarhus C, Denmark ABSTRACT: Life cycle, growth, and production of the mud snails Hydrobia ventrosa
2.1 Life cycle techniques in life cycle sustainability assessment 5 2.2 (Environmental) life cycle assessment 6 2.3 Life cycle costing 14 2.4 Social life cycle assessment 22 3 Life Cycle Sustainability Assessment in Practice 34 3.1 Conducting a step-by-step life cycle sustainability assessment 34 3.2 Additional LCSA issues 41 4 A Way Forward 46
life cycles. Table of Contents Apple Chain Apple Story Chicken Life Cycle Cotton Life Cycle Life Cycle of a Pea Pumpkin Life Cycle Tomato Life Cycle Totally Tomatoes Watermelon Life Cycle . The Apple Chain . Standards of Learning . Science: K.7, K.9, 2.4, 3.4, 3.8, 4.4 .
4.UNEP/SETAC (2011). Global Guidance Principles for Life Cycle Assessment Databases. UNEP/SETAC Life-Cycle Initiative. ISBN: 978-92-807-3021-. 5.UNEP (2003). Evaluation of environmental impacts in Life Cycle Assessment, Division of Technology, Industry and Economics (DTIE), Production and Consumption Unit, Paris. 6.ISO 14040 (2006).
Insect Life Cycle Level L 5 6 These animals have a different kind of life cycle. A life cycle is the series of changes an animal goes through during its life. Insects have fascinating life cycles. Some insects have a four-stage life cycle. The insect lives as an egg, larva (LAR-vuh), pupa (PYOO-puh), and an adult. Others have a three-stage life
Life Cycle Impact Assessment—phase of life cycle assessment aimed at understanding and evaluating the magnitude and significance of the potential environmental impacts for a product system throughout the life cycle of the product. Life Cycle Interpretation—phase of life cycle assessment in which the findings of either the
Life Cycle Impact Assessment (LCIA) "Phase of life cycle assessment aimed at understanding and evaluating the magnitude and significance of the potential environmental impacts for a product system throughout the life cycle of the product" (ISO 14040:2006, section 3.4) Life Cycle Interpretation "Phase of life cycle assessment in which the .
2.0 Life Cycle Assessment (LCA) 5 2.1 Life Cycle Inventory (LCI) 7 2.2 Life Cycle Impact Assessment (LCIA) 11 2.3 Framework 13 2.4 System Boundaries 16 2.5 Limitation and Problems 19 3.0 Life Cycle Cost Assessment (LCCA) 20 3.1 Life Cycle Cost (LCC) 20 3.2 Levelized Cost of Energy (LCOE) 22 3.3 Financial Supplementary Measures 23
3.1 life cycle 3.2 life cycle assessment 3.3 life cycle inventory analysis 3.4 life cycle impact assessment 3.5 life cycle interpretation 3.6 comparative assertion 3.7 transparency 3.8 environmental aspect 3.9 product 3.10 co-product 3.11 process 3.12 elementary flow 3.13 energy flow 3.14 feedstock energy 3.15 raw material LCA MODULE A1 18
