Life cycle strategies and seasonal variations in distribution and population structure of four dominant calanoid copepod species in the eastern Weddell Sea, Antarctica

The dominant Antarctic copepod species Calanoides acutus, Calanuspropinquus, Rhincalanus gigas and Metridia gerlachei were investigatedwith respect to their abundance, vertical distribution, developmentalstage composition, dry weight and lipid content. The specimenswere sampled during three expeditions to the eastern WeddellSea in summer (January/February 1985), late winter/early spring(October/November 1986) and autumn (April/May 1992) between0 and 1000 m depth to follow the seasonal development of thepopulations. Three species were most abundant in April, onlyC.propinquus reached highest concentrations in February. A seasonalmigration pattern was evident in all four species, but was mostpronounced in C.acutus. In October/November, they inhabiteddeeper water layers, their ascent started by mid-November andin mid-February the species concentrated in the upper 50 m,except for M.gerlachei (50–100 m). Their descent was observedin April/May. The stage composition changed dramatically withseason, the older developmental stages (CIII–CVI) dominatedthe populations in late winter/early spring, whereas youngerstages (CI and CII) prevailed during summer (C.acutus, C.propinquus)or autumn (R.gigas, M.gerlachei). Only C.acutus ceased feedingin autumn and diapaused at depth. Strong differences betweenseasons were also detected in dry weight and lipid levels, withminima in late winter/early spring and maxima in summer (C.acutus,R.gigas) or autumn (C.propinquus, M.gerlachei). Lipid reservesseem to be most important for the older stages of C.acutus andC.propinquus. Based on these seasonal data, different life cyclestrategies are suggested for the four species.     

Seasonal variations in energy levels and metabolic processes of two dominant Acropora species (A. spicifera and A. digitifera) at Ningaloo Reef

Seasonal variations in coral health indices reflecting autotrophic activity (chlorophyll a and zooxanthellae density), metabolic rates (RNA/DNA ratio and protein) and energy storage (ratio of storage: structural lipids or lipid ratios) were examined for two dominant Acropora species [Acropora digitifera (AD) and Acropora spicifera (AS)] at Ningaloo Reef (north-western Australia). Such detailed investigation of metabolic processes is important background, with regard to understanding the vulnerability of corals to environmental change. Health indices in AD and AS were measured before and after spawning in austral autumn and winter 2010, and austral summer 2011 at six stations. Health indices showed seasonal and species-specific differences but negligible spatial differences across a reef section. For AD, autotrophic indices were negatively correlated with lipid ratios and metabolic indices. Metabolic indices were significantly higher in AS than AD. No correlation was observed between RNA/DNA ratios and lipid ratios with any autotrophic indices for AS. Lipid ratios were stable throughout the year for AS while they changed significantly for AD. For both species, indices of metabolic activity were highest during autumn, while autotrophic indices were highest in winter and summer. Results suggest that the impact of the broadcast spawning event on coral health indices at Ningaloo Reef occurred only as a backdrop to massive seasonal changes in coral physiology. The La Niña summer pattern resulted in high autotrophic indices and low metabolic indices and energy stores. Our results imply different metabolic processes in A. digitifera and A. spicifera as well as a strong impact of extreme events on coral physiology.     

Annual cycle of tintinnids in Admiralty Bay with an emphasis on seasonal variability in Cymatocylis affinis/convallaria lorica morphology

In water samples collected from the middle of Admiralty Bay(King George Island 62°08'S 58°25'W) between February1990 and January 1991, 17 Tintinnina species were noted. TotalTintinnina numbers in summer were very high (up to 5000 cellsm^–3), but species diversity was low, consisting mainlyof Cymatocylis affnislconvallaria, forma convallaria. Duringaustral winter, cell numbers were very low, but species compositionwas diverse. Cymatocylis affnislconvallaria, forma affinis,and C.affmis/convallaria, forma convallaria, the polymorphicforms of one species C.affinis/convallaria, appear to be interchangeableduring the year. The transition from one form to the other occursin the spring and autumn. The typical Tintinnina polymorphismcan be attributed to the prevailing environmental conditions.     

Dinoflagellate cyst production at a coastal Mediterranean site

To assess the diversity and seasonality of dinoflagellate cystproduction, surface sediment and trap samples were studied inthe Gulf of Naples (Mediterranean Sea). A total of 59 differentcyst morphotypes were recorded. At the stations within the 70m isobath, sediment assemblages were dominated by calcareousPeridiniales (66–79%), while at the deepest stations non-calcareousPeri-diniales attained the highest percentages (40–49%).The sediment trap sampling, carried out fortnightly over twoannual cycles, revealed high production rates (up to 1.7 x 10⁶cysts m^–2 day^–1) from spring to late autumn of bothyears, with a distinct seasonal production pattern. Althoughrather similar in species composition, the total cyst flux differedmarkedly between the 2 years (1.26 and 0.55 x 108 cysts m^–2year^–1, respectively). Species-specific production patternswere observed: some species formed cysts over several months,others in restricted periods of the year. Cyst-forming speciesconstituted a small part of the planktonic dinoflagellate populationsrecorded in the area. A coupling between the trap material andsurface water plankton was observed for calcareous Peridiniales.This sampling approach allowed the detection of some speciesnever recorded before in the gulf, including two potentiallytoxic species: Alexandrium andersoni and Gymnodinium catenatum-likespecies.     

Size and species-specific primary productivity and community structure of phytoplankton in Tokyo Bay

Combined methods of size fractionation and single-cell isolationwere used to investigate the seasonal variation of phytoplanktondynamics in Tokyo Bay with an emphasis on primary productivity.Red tides occurred in Tokyo Bay from spring to autumn; a diatom,Skeletonema costatum, and a raphidophycean, Heterosigma akashiwo,were the most important primary producers. Small diatoms andflagellates, including these species, were dominant and showedrapid changes of phytoplankton community structure within severaldays in summer. The nanoplankton (3–20 µm) fractioncontributed most to chlorophyll a concentration and primaryproductivity during spring to autumn, whereas the microplankton(>20 µm) contribution was remarkable in winter. Picoplankton(<3 µm phytoplankton) remained relatively constantthroughout the year. A significant reverse relationship wasobtained between assimilation rate and chlorophyll a contentfor the total and nanoplankton population; the assimilationrate was high at the initial phase of the bloom, then decreasedto a minimum level at the peak of the bloom. Factors controllingthe reduction of assimilation rates at the peak, and changesin phytoplankton community structure, are discussed.     

Successional dynamics of the phytoplankton in the lower part of the river Ebro

The temporal and spatial dynamics of phytoplankton have beenstudied in four sites located along the last 60 km of the riverEbro, over a period of 1 year. Diatoms and green algae werethe most abundant groups; blue-green algae were frequent onlyin autumn. Asterionella formosa dominated the winter phytoplanktonassemblages. In autumn, spring and early summer centric diatomswere dominant: Aulacoseira granulata (Ehr.) Simonsen in autunm;Cyclotella sp. p1., Skeletonema potamos (Weber) Hasle and StephanodisciLssp. p1. in spring. A great abundance of green algae was observedduring the summer, mainly in the lower sites. In the sites closerto the mouth, the spring maximum of centric diatoms extendedto the summer. Mainly in the downstream sites, a remarkablegrowth of Acrinocyclus normanii f. subsalsa (Juhl.-Daunf.) Hustedtand Stephanodiscus hantzschii f tenuis (Hust.) Hak. & Stoerm.was added to green algae in the late summer. As has been investigatedthrough a principal component analysis, the phytoplankton temporalsuccession and longitudinal differences between the sites maybe affected by the variations in flow and the increase of waterconductivity downstream; both factors seem to act together.The river is rather homogeneous with respect to the phytoplanktonassemblages during the winter and spring months, and from latespring to the following autumn, differences greatly increaseboth in time and downstream.     

Annual cycle of zooplankton community in the Abra Harbour (Bay of Biscay): abundance, composition and size spectra

The annual cycle of the zooplankton community in a coastal embaymentof the Bay of Biscay was studied from data on zooplankton fractionslarger than 45 and 250 µm Smaller zooplankton and chlorophyllmaxima coincided in summer, while larger zooplankton reachedthe maximum in spring. Copepods dominated in both fractionsmost of the year, being copepod nauplii and postnaupliar stagesof Oithona nana and Paracalanus parvus the main constituentsof the microzooplankton maxima, and older copepodites and adultsof Acartw clausi of the meso-macrozooplankton maxima. Secondarypeaks of abundance due to protozoan blooms of Steno-semellanivalu, in early spring, and Noctiluca santillans, in summer,were also observed in smaller and larger fractions respectively.The collapse of phytoplankton biomass in early autumn was followedby a strong decrease of zooplankton in mid autumn. From thisperiod to winter, chlorophyll and zooplankton abundance showedsmall variations, but noticeable changes in the compositionand size spectra of zooplankton were observed. In winter, valuesof chlorophyll and zooplankton abundance reached minima, A.clausidominated the copepod assemblage and carnivorous zooplankterswere absent or negligible The annual development of the mainpredator populations (Sagitta frideria, Luiopc tetraphylla andanchovies) were found to be synchronized with the variationsin abundance and size spectra of zooplankton in the study area.     

Distribution, dynamics and in situ seeding potential of Scrippsiella hangoei (Dinophyceae) cyst populations from the Baltic Sea

The distribution and seasonal dynamics of cyst populations ofthe spring bloom dinoflagellate Scrippsiella hangoei were studiedin surface sediments on the southwest coast of Finland, BalticSea. In situ germination was assessed by monitoring the fractionof empty cysts and chlorophyll a fluorescence in cyst populationsat different coastal sites throughout the annual cycle. Scrippsiellahangoei resting cysts were widely distributed in the study areaand occurred in exceptionally large numbers (magnitudes of 10⁴–10⁶cysts cm^–3) at all sampling locations between the innermostparts of the coastal archipelago and the open Gulf of Finland.The decreases in cyst number in winter and the increases occurringin late spring reflected the dynamics of germination and encystmentof the species. Chlorophyll fluorescence appeared in mid-winterin ~40% of cysts from well-aerated basins and 6–15% ofcysts from temporarily anoxic sediments. A generally low increasein the proportion of empty cysts indicated that only a partof the potentially germinable cysts actually germinates. Giventhe high cyst concentrations in the sediments, the potentialfor germination is considerable, despite the environmentallyand physiologically determined losses. In contrast, the sizeof the vegetative inoculum is very low, indicating that thesurvival of germlings is problematic under harsh winter conditions.This is an unusual life cycle strategy; however, the early releaseof cells into the water column provides a high probability forsuccessful bloom initiation under the unpredictable meteorologicalconditions in winter and early spring, which often lead to thesudden onset of favourable growth conditions.     

Biological observations on small cyclopoid copepods in the Red Sea

The breeding activity, sex ratio and variation in body lengthof a number of cyclopoid copepod species from the upper 450mof the Red Sea were analyzed. In most species the body lengthof adult specimens was in the lower range or less than thosereported from other pelagic regions. In the central Red Seamost species had some individuals actively breeding, duringboth autumn and winter. To the north, breeding was observedin fewer species. Only two species, Paroithona sp. and Agetuslimbatus, however, seemed to find conditions for reproductionbetter in the north than in the central area. The sex ratioswere quite consistent for all species within the families Sapphirinidaeand Corycaeidae (high percentage of males) and Oithonidae (lowpercentage of males). Within the Oncaeidae, the percentage ofmales varied from a few percent to >60% of adults. Thereappears to be a relationship between sex ratio and size. Populationsof the very small Oncaea species, O.ivlevi, O.prendeli and O.zernovi,include far fewer males than those of their larger congeners.The available information on the biology of Oncaea is summarized.Peculiarities in their life histories and reproduction are discussed.     

Cladistic Approaches in the Study of Soil and Plant Parasitic Nematodes

Cladistic analysis of free-living soil nematodes of the Leptonchoidea(Nematoda: Dorylaimida) resulted in groupings different fromthose obtained by traditional methods. We can interpret distributionsof species groups obtained by phyletic analysis in relationto plate tectonic events. Similar techniques are applicableto plant parasitic nematodes. Grouping on the basis of synapomorphiesproduced a cladogram of genera of the family Heteroderidae (Nematoda:Tylenchida) in which Meloidodera and Cryphodera appear to bethe most ancestral genera and the cyst forming genera the mostderived. A cladogram of groups of species in Heterodera sensulato showed a major division, with the round cyst nematodesand the Cacli group in one grouping and the rest of the Heteroderaspecies in the second. I interpret present-day distributionsby a strict vicariance view and suggest potential falsifiers;and also discuss ancient dispersal routes as alternative waysof thinking about nematode distribution.     

Relationships Between Climate and Flowering of Eight Herbs in a Swedish Deciduous Forest

Effects of annual variation in rainfall, temperature and humidityon flowering abundance of eight temperate woodland plants (Anemonenemorosa, Cardamine bulbifera, Lamiastrum galeobdolon,Oxalisacetosella , Ranunculus ficaria, Stellaria holostea, Viola reichenbachianaand Viola riviniana) were studied during 12 consecutive years(1989–2000) in a hornbeam (Carpinus betulus) forest insoutheast Sweden. Above-average rainfall/humidity in late summerto early autumn of the preceding year increased flowering abundancein L. galeobdolon, O. acetosella, V. reichenbachiana, V. rivinianaand, especially, in R. ficaria, but not in S. holostea and A.nemorosa. Moreover, flowering of R. ficaria and O. acetosellawas positively related to rainfall/humidity during several partsof, or the entire, preceding year. On the contrary, floweringof S. holostea and A. nemorosa was closely related to low valuesof rainfall/humidity in autumn and/or winter of the precedingyear and also to low humidity in the current year in A. nemorosa.Two long periods (3–4 years) of increasing rainfall deficitcoincided with decreasing flowering abundance in most of thespecies, but not with decreasing vegetative development. Temperaturevariability was less consistently related to flowering. A coolperiod during the preceding summer or autumn seemed importantfor flowering in L. galeobdolon, O. acetosella and the Violaspecies, although these relations were, at least partly, causedby interactions with rainfall/humidity. No significant (P <0.05) correlations were found between flowering and the conditionsprevailing in April to May—the main flowering season—ofthe current year. Copyright 2001 Annals of Botany Company Climate, flowering, rainfall, temperature, Anemone nemorosa, Cardamine bulbifera, Lamiastrum galeobdolon, Oxalis acetosella, Ranunculus ficaria, Stellaria holostea, Viola reichenbachiana, Viola riviniana     

Overwintering of Microcystis aeruginosa Kutz. in a shallow lake

The standing crop and photosynthetic activity of Microcystisaeruginosa Kütz. in both the plankton and sediment wereinvestigated from November 1979 to May 1982 in Lake Kasumigaura,Japan. The number of planktonic colonies of this species decreasedfrom early autumn to early spring, but increased in the sedimentduring late summer and autumn. The overwintering colonies inthe sediment were –100–1000 times greater per unitarea than those in lake water. No photoinhibition of photosynthesiscould be observed in overwintering Microcystis. The values ofthe initial slopes of photosynthesis-light (P-I) curves weresimilar to those of the summer population, although the maximumphotosynthetic rate (P_max) measured at 20°C was lower thanthat of the summer planktonic population. In winter the valuesof initial slope of the P-I curve, and the ratio of phycobilinto chlorophyll a sorted from sediment were higher than in coloniesfrom the plankton.     

Seasonal Changes in Abscission Responses to Auxin in Debladed Petioles

The abscission of debladed petioles of various ages in Ervatamiaand Coleus has been followed throughout the year. In general,the retention times for the two species were found to be maximalin the summer and minimal in the winter months. In both speciesolder petioles tended to abscise earlier. The occurrences ofan auxin-inhibitable stage-I and an auxin-promotable stage-IIwere clearly established. The sensitivity to auxin in both stagesdeclined with increase in age, particularly in the two-nodeand three-node twigs of Ervatamia and in the four-node twigsof Coleus. The durations of stage-I and stage-II were foundto be characteristically different in different seasons. Ingeneral, stage-I lasted longer both in younger petioles andduring the summer months. Auxin sensitivity in both stages wasgreater in summer than in winter. Intermediate results wereobtained in the other two seasons. In both the species the auxin-promotablestage-II weakened with time, as shown by a smaller promotionwith delayed auxin application.     

Can season interfere with diatom ecological quality assessment?

To understand whether seasons influence the ecological quality assessment of streams on the basis of diatoms, a study was undertaken in two lowland water courses located in northwest Portugal, between autumn 2008 and summer 2009. Temporal variation in the chemical pollution of these streams was small as revealed by a number of physical and chemical parameters analyzed. PERMANOVA global test revealed significant variation in water temperature among seasons. The diatom communities also showed a temporal variation although not all the seasons were statistically different. The multidimensional scaling analysis showed that the main differences in the diatom communities were between two groups of seasons: autumn/winter and spring/summer. Species such as Cocconeis pseudolineata, Gomphonema parvulum var. exilissimum, Fragilaria vaucheriae, Encyonema minutum, and Nitzschia recta were more abundant in spring/summer, while species such as Mayamaea atomus and Nitzschia pusilla were more abundant in autumn/winter. The BIOENV routine confirmed that the biological and temperature patterns are highly correlated. Despite the effects observed on diatom communities, these differences were buffered by the EQR (IPS) values which do not reflect seasonal differences. Therefore, the use of the index IPS seems to allow the monitoring of the streams’ ecological quality throughout the year without the interference of the natural temporal variability of diatom communities.     

Post-embryonic development of cyclopoid copepods in various seasons at Lake Balaton (Hungary)

The development, generation number and diapausing state of threeCyclops species dominant in the open water of Lake Balaton werestudied by means of vials placed back into the lake, in naturalfeeding conditions. The males of all three species turned intoadults earlier than the females. The copepodite V stage wasof the longest duration. Three generations of Cyclops vicinusdeveloped yearly; in spring, autumn and winter. About 50% ofthe copepodite stage IV of the spring generation entered activediapause at the end of May, beginning of June, then entereddormancy between the middle of June and middle of July. Consideringthe literary data as well, it seems that the generation numberof the species is the function of temperature and of the water'strophic state. The Acanthocydops robustus f. limnetica is fondof warm water (> 14°C). Seven generations of this speciesdeveloped completely yearly, during an average of 2-week intervalsbetween May and September. The eightli generation died in thenaupliar stage. The generation number of A. robustus f. limneticadepends on the average temperature of the lake. Inactive diapausecould not be observed for this species. Only one generationof Mesocyclops latckarti developed in autumn. The copepoditeV of the winter generation entered active diapause below a watertemperature of 10°C, and inactive diapause from the endof January, which state ended in March.     

FOOD PREFERENCES AND DIETARY OVERLAP BY TERRESTRIAL SNAILS IN LOGOS AREA (EDESSA, MACEDONIA, NORTHERN GREECE)

Among the five coexisting species of snail in Edessa (N. Greece),Bradybaena fruticum and Helix lucorum dominated in density andbiomass in comparison with Xeropicta arenosa, Monacha cartusianaand Cepaea vindobonensis. Resting places of each species inrelation to plant cover and diet preferences are examined seasonallyand throughout a year. Discriminant analysis for the annualdata showed that 83% of the snail group species could be differentiatedby the plants on which they were attached. Each snail specieswas usually found sitting on one of the most abundant plants.Cepaea preferred to sit on and eat senescent material even inspring time and Bradybaena green material. In spring, the snailsdid not consume plant material in proportion to the occurrenceof those plants but they usually did so in summer and in autumn.Hedera helix was not consumed even when it was abundant. Inspring and autumn the snails had consumed plants to which theywere found attached, but in summer they did not. (Received 9 August 1993; accepted 14 February 1994)     

Horizontal dinoflage11ate cyst distribution, sediment characteristics and benthic flux in Manila Bay, Philippines

The lateral variation of sediment properties and associated cyst content of sediment in Manila Bay were determined and their possible role/s in the occurrences of Pyrodinium bahamense Plate var. compressum (Bohm) Steidinger, Tester et Taylor toxic blooms were assessed. Manila Bay's surface sediment was determined to be silt dominated. Clay generally increased towards the coast, probably as a result of flocculation and rapid deposition upon entry of sediments from the rivers. High sand content characterized the southeastern part of the bay attributed to the greater sand inputs and relatively strong currents in this area. Bulk densities were lower in the eastern side of the bay from dilution by high organic load from sewage and urban areas. Benthic flux calculations, particularly NH3, suggest more than 50% nutrient contribution comes from sediments. In general, dinoflagellate cyst density increased from the center of the bay towards the coast, except in Pampanga Bay where it deceased near the coasts. A maximum of 23 dinoflagellate species were identified: 5 were autotrophic (Lingulodinium polyedrum (Stein) Dodge, Gonyaulax spp., Pyrophacus steinii (Schiller) Wall et Dale, Protoceratium reticulatum (Claparede et Lachmann) Butschli, and Pyrodinium bahamense var. compressum), and the rest were predominantly composed of Protoperidinium spp. and Diplopsalis spp. Heterotrophs comprised about 70% of the total cyst counts. Pyrodinium counts increased towards the northwestern part of the bay where it was the dominant autotroph species. Negative correlations were observed for live Pyrodinium cyst density and N flux, P flux, ratio of N to P and total organic carbon (TOC) content. However, areas with high N:P ratio contain abundant Pyrodinium live cysts.     

Picoplankton community structure along the northern Iberian continental margin in late winter-early spring

The surface distribution of autotrophic and heterotrophic picoplanktonwas assessed in 24 transects perpendicular to the coast alongthe N and NW Iberian peninsula shelf in late winter and earlyspring 2002. Community structure was analyzed by flow cytometry(FC) and found to be strongly influenced by hydrography. Typicallate winter conditions were found during the survey, characterizedby the presence of the poleward Portugal coastal counter current(PCCC) in the west and an increasing stratification eastwards.Cyanobacteria (mostly Synechococcus) dominated at low chlorophylla (Chl a) concentration whereas both the total and relativeabundance of picoeukaryotes generally increased with total phytoplanktonbiomass. Differences in the cell size of most FC-defined picoplanktonicgroups were also observed along the longitudinal and coastal–offshoregradients. The presence of Prochlorococcus (<10³ cells mL^–1)coincided with the core of the PCCC and its significant correlationwith salinity suggests its possible use as a tracer of thiscurrent. Two groups of heterotrophic bacteria were distinguishedaccording to their relative DNA content. High DNA bacteria dominatedthe community (60 ± 1% SE of total numbers), reachingmaximum values in areas under riverine influence with presumedhigher inputs of organic matter. Picoplankton biomass was dominatedby heterotrophic bacteria in the western region (58 ±3%) while autotrophic groups contributed on average 66 ±2% in the southern Bay of Biscay. The heterotrophic bacteriato phytoplankton biomass ratio decreased significantly alongthe measured range. Yet showing regional differences, the estimatedcontribution of picophytoplankton to total algal biomass washigh (mean 59 ± 4%), indicating the important role ofsmall cells at the onset of the spring bloom in these temperateshelf waters.     

A 5-year study of the influence of the northeast and southwest monsoons on copepod assemblages in the boundary coastal waters between the East China Sea and the Taiwan Strait

Danshuei River in the northwestern tip of Taiwan dischargesinto the boundary coastal waters between the East China Seaand the Taiwan Strait. We conducted a 5-year study between October1998 and September 2003 to assess the influence of the northeast(NE) and the southwest (SW) monsoons on copepod assemblagesin the area. A total of 110 copepod species were identified.Temora turbinata, Paracalanus aculeatus, Acrocalanus gibber,Parvocalanus crassirostris and Oithona rigida comprised 80%of the copepod assemblages that consisted of coastal speciesfrom the East China Sea and species associated with the KuroshioBranch Current. The effect of the NE monsoon was observed duringa short period of each winter when species such as Calanus sinicuswere transported into the study area by the China Coastal Current.In summer, species such as A. gibber, Acrocalanus gracilis andCanthocalanus pauper may be transported into the study areafrom Southern Taiwan by the combined effect of the SW monsoonand the Kuroshio Current. Influence of the NE monsoon on thecopepod assemblages in terms of introduction of species fromthe Yellow Sea and the East China Sea during winter was observedevery year but was unlikely to represent an important carbonsource into the region due to its short-term nature. Local speciessuch as T. turbinata, P. crassirostris and O. rigida form amajor component of the copepod assemblage. The high copepoddiversity in the area was caused by the year-round presenceof many local species and the aggregation of different speciesfrom subtropical, tropical, and temperate water masses. Monsoon-drivenwater currents and the Kuroshio Branch Current appeared to maskthe effect of river discharge in the region.     

A COMPARISON OF THE LIFE CYCLES OF THE SLUGS DEROCERAS RETICULATUM (MULLER) AND ARION INTERMEDIUS NORMAND ON PERMANENT PASTURE

Life cycles of the slugs Deroceras reticulatum and Arion intermediuswere compared over a four-year period on permanent pasture nearOvingham, Northumberland. Both species were semelparous, theirlife cycles taking about one year. D. reticulatum, unlike A.intermedius and other species, had two overlapping generationsthat laid their eggs in late spring and autumn respectivelyand also had one instead of two immature phases in its lifecycle. The pattern and rates of growth for the immature phasesin the life cycle of A. intermedius differed markedly from thosedescribed under laboratory conditions. Growth in the infantilephase was delayed in the field by low winter temperatures whilesecond stage growth was usually delayed in late spring by dryconditions. The life cycle of A. intermedius appears to be synchronisedby seasonal changes in photoperiod, unlike that of D. reticulatum.Growth in D. reticulatum continued throughout the winter monthsexcept under exceptionally cold conditions and was not usuallydelayed by dry conditions in spring. The size of hermaphroditegland relative to body weight in D. reticulatum reached a maximumin mature-unmated slugs and then became progressively smalleras the slug approached the post-reproductive stage which wasrelatively brief. Exceptionally dry conditions in 1962 delayedthe development of the hermaphrodite gland, the maximum sizereached was significantly reduced and fewer eggs were laid. (Received 17 September 1987; accepted 2 January 1988)