Morphologic variability of the coccolithophorid Calcidiscus leptoporus in the plankton, surface sediments and from the Early Pleistocene

On a global scale, morphological variability of the extant coccolithophorid Calcidiscus leptoporus (Murray and Blackman, 1898) Loeblich and Tappan was investigated in surface sediments and plankton samples and from an Early Pleistocene time-slice (1.8 Ma to 1.6 Ma). In the bivariate space coccolith diameter versus number of rays in the distal shield, Holocene samples follow a single, unimodal morphocline. Sample means of coccolith size and number of elements group in three clusters, I, II and III, which are of biogeographic significance. Clusters II and III coccoliths (mean coccolith size of 5.0 μm and 20.9 elements, and 6.6 μm and 25.6 elements, respectively) are found in a tropical belt extending from 11 °N to 17 °S with an annual minimum sea-surface temperature above 23.5 °C. Cluster I coccoliths (5.8 μm, 20.7 elements) are found in samples outside that belt. The distribution of coccoliths in the surface sediments is tentatively interpreted to be a result of mixing to a varying degree of at least three different morphotypes (‘small’, ‘intermediate’ and ‘large’), which were identified in the living plankton, and which are separated from each other at 5 μm and 8 μm mean coccolith diameter, respectively. A comparison of the surface sediments with the Early Pleistocene assemblages revealed that between 1.6 Ma and 1.8 Ma two morphoclines A and B existed, the first of which persisted until the Holocene in the form of C. leptoporus, while the second comprises only extinct morphotypes including Calcidiscus macintyrei as one end-member. During the Early Pleistocene morphocline A was more homogeneous and no clusters were evident.Morphocline B shows a clear bimodality with a separation of morphotypes at 9.5 μm. Our observations suggest that morphoclines are subsets within the total stratigraphical range of a single species, and represent the global variability of that species in a particular time interval. Morphotypes, which belong to a morphocline, represent the infra-specific variability of that species within the biogeographic and stratigraphic limits of that species.     

Morphometry,biogeography and ecology of Calcidiscus and Umbilicosphaera in the South Atlantic

Here we present morphometrical evaluation, biogeographical distribution patterns and ecological information for five coccolithophore taxa (Calcidiscus leptoporus, C. leptoporus small, C. quadriperforatus, Umbilicosphaera foliosa and U. sibogae). This information is based on data obtained from surface sediments from the South Atlantic. The three Calcidiscus taxa can easily been distinguished by a combination of size and qualitative characters of their distal shields. Mostly encountered in the temperate to sub-polar regions C. leptoporus is the most abundant taxon and exhibits a negative correlation to temperature and salinity. Both, C. leptoporus small and C. quadriperforatus reach their maximum abundances also at higher latitudes and in the SW-African upwelling area. Their distributions therefore suggest preference for nutrient-enriched waters, which is also indicated by CCA. The two circular Umbilicosphaera species exhibit significant differences in coccolith morphology and show little overlap in size. Highest abundances are encountered in sub-tropical latitudes and are mainly derived from U. sibogae. In contrast, U. foliosa is present in very low abundances. Both species exhibit a preference for warm and oligotrophic conditions. However, U. foliosa increases in relative proportion to U. sibogae at the southernmost locations and in the Benguela upwelling. This could be interpreted as an affinity for slightly cooler and nutrient-enriched environments.     

Communities of arbuscular mycorrhizal fungi in grassland: Seasonal variability and effects of environment and host plants

The seasonal dynamics of a community of endomycorrhizal fungal morphotypes in the roots of three grassland species (Achillea millefolium, Poa angustifolia, Plantago lanceolata) was evaluated, together with the effects of experimental treatment (mowing and phosphorus application) and the host plant properties. Strong seasonal variability was found in the fungal community, where clear seasonal patterns can be distinguished for several fungal morphotypes. The sampling date explained 20 to 30% of the total compositional variability for all three host species. ThePlantago roots host the highest number of arbuscular mycorrhizal (AM) fungal populations. There are two co-dominant fungal morphotypes inAchillea roots (assigned to the generaScutellospora andGlomus) and only one strongly dominant morphotype (assigned toGlomus), in thePoa roots. All three host species have a comparable pattern of richness of AM morphotypes with a single peak in the summer, possibly aligned with the flowering time of the host.     

A Critical Comparison of Two Long-term Zooplankton Time Series from the Central-west North Sea

Long-term changes in relative and absolute zooplankton abundanceand species composition were compared between the Dove MarineLaboratory and Continuous Plankton Recorder (CPR) time seriesin the central-western North Sea. The two time series employdifferent sampling mechanisms, with the Dove series beng obtainedby net sampling at a fixed station off the Northumberland coast,while the CPR series utilizes a network of fixed towed routes. It was found that there was a significant correlation (r =0.64, P < 0.001) between the relative year-to-year fluctuations of the two series and a significant agreement in the pattern of year-to-year variations in species composition of the dominant taxa (P = 0.01) over the majority of the time period. However, examination of absolute zooplankton abundances found large differences between the two time series. Differences in mesh size and in the sample processing methodologies were not wholly responsible for these. Model-derived catching efficiencies for the two sampling devices suggested that differences in absolute abundances may have been mainly due in some taxa to a greater degree of active avoidance of the CPR sampling device by zooplankton, although it is likely that passive avoidance as a result of hydrodynamic factors has a role.>     

Seasonal variations in the morphology of the coccolithophore Calcidiscus leptoporus off Bermuda (N. Atlantic)

Calcidiscus leptoporus is a cosmopolitan coccolithophore specieswith one of the longest fossil records. A previous morphometricstudy on coccoliths of C. leptoporus, carried out on a globalset of Holocene sediment samples, indicated that temperaturemight be a significant factor influencing the size distributionof C. leptoporus. In the present study, C. leptoporus morphologicalvariations and dynamics are studied in samples from HydrostationS time series, near Bermuda, over a 3 year interval (1991 to1994) with monthly sampling. Calcidiscus leptoporus was presentall year round in very low abundances but displayed strong variationsthrough the time-series, both in absolute abundances (maximum551 cells/l and minimum <10 cells/l) and in morphology. Nosignificant correlation between environmental parameters andC. leptoporus abundances was found. The seasonal dynamics ofC. leptoporus, therefore, appears to be the consequence of planktoncommunity interactions and, possibly, of life-cyle. The morphologicalstudy of C. leptoporus shows a sharp decrease in size and variabilityoccurring during the spring–summer transition at the onsetof water stratification. Our results give no conclusive evidenceas to whether C. leptoporus at Hydrostation S consists of anassemblage of different species or ecophenotypes. However, weprovide evidence for significant morphological plasticity linkedto seasonality and possibly temperature. More importantly, ourresults show a trend between temperature and morphology oppositeto the study of Knappertsbusch et al. (Knappertsbusch et al.,1997) based on Holocene sediments. These results emphasize thenecessity of plankton studies in order to interpret patternsobserved in sediments.     

Seasonal changes and population dynamics of the ctenophore Mnemiopsis leidyi after its first year of invasion in the Kiel Fjord, Western Baltic Sea

We analyzed the seasonal variations of the ctenophore Mnemiopsis leidyi weekly collected since its first record in the western Baltic Sea in October 2006. The distribution pattern together with the seasonal dynamics and population outbreaks in late summer 2007 indicate recent successfully establishment of M. leidyi in this area. Seasonal changes showed two periods of high reproductive activity characterized by a population structure dominated by small size classes, followed by an increase of larger ones. These results further revealed that the bulk of the population remains in deep layers during the periods of low population density, whereas it appeared situated in upper layers during the proliferation of the species. We further emphasized the strength of the population outbreaks, which can reach abundances >10-fold higher in time periods shorter than a week. The predatory impact this species may have in pelagic ecosystems warns on the importance of its recent range of expansion.     

Vertical and lateral variations in coccolithophore community structure across the subtropical frontal zone in the South Atlantic Ocean

In this study the coccolithophore compositions of 11 plankton depth stations along a N–S transect from the South Atlantic Subtropical Gyre to the Subantarctic Zone were examined qualitatively and quantitatively. The lateral and vertical distribution patterns of not only the most abundant taxa but also of the morphotypes of distinct species complexes, such as Calcidiscus leptoporus, Emiliania huxleyi, and Umbellosphaera tenuis were the focus. Geographic variation among morphotypes mirrors different ecological affinities of the members of a species complex. Multivariate statistics were used to infer the relationship between a set of known environmental data and species concentrations. The results of the detrended Canonical Correspondence Analysis (CCA) revealed the presence of distinct species assemblages. The Subtropical Gyre assemblage within the upper 50 m of the photic zone is mainly composed of Umbellosphaera irregularis, U. tenuis types III and IV, Discosphaera tubifera, Rhabdosphaera clavigera, S. pulchra and E. huxleyi var. corona, adapted to warm and oligotrophic conditions. In the deeper photic zone abundant Florisphaera profunda, Gephyrocapsa ericsonii and Oolithotus spp. are encountered, benefiting from higher nutrient concentrations in the vicinity of the nutricline. A well-defined Subtropical Frontal Zone (STFZ) association is clearly dominated by E. huxleyi types A and C throughout the upper 100 m of the water column. Secondary contributors in the upper photic zone are Syracosphaera spp. (mainly S. histrica, S. molischii), Michaelsarsia elegans, Ophiaster spp. and U. tenuis type II. This assemblage is associated with cooler, nutrient-rich waters. E. huxleyi type B is found deeper in the water column. Here it is accompanied by Algirosphaera robusta, G. muellerae, and S. anthos indicating a tolerance of lower light availability in environments with elevated productivity. C. leptoporus spp. leptoporus shows relatively high cell numbers in all sampled water levels throughout the STFZ. Interestingly, its coccoliths are often smaller 5 μm in lith diameter. The mean coccolithophore assemblages of a station were compared to the underlying surface sediment assemblages. For the most part, the distribution of the morphotypes is reflected in the sedimentary archive, thus proving their potential as paleoecological proxies.     

Chironomid assemblages from seabird-affected High Arctic ponds

Seabirds can shunt nutrients and contaminants from marine to terrestrial ecosystems by forming dense breeding colonies and releasing wastes to these sites. A large colony of seabirds at Cape Vera (Devon Island, High Arctic Canada) has resulted in eutrophic conditions and potentially toxic concentrations of sedimentary metals in several freshwater ponds that drain their nesting sites. Here, we investigated the effects of elevated nutrient and sedimentary metal concentrations on the distribution of subfossil chironomids in surface sediments from 21 ponds that span a gradient of seabird influence. Although many ponds registered high nutrient concentrations (e.g., mean TP = 45 μg l ⁻¹), eutrophic taxa typical of temperate waters were not common, with most assemblages being dominated by morphotypes of Psectrocladius and Tanytarsina, as well as Corynoneura arctica-type, and Metriocnemus hygropetricus-type. Although the ponds within and outside the area influenced by seabirds contained largely similar taxa, variations did exist in the relative abundances of the different species. Lakewater pH was the only measured environmental variable that explained statistically significant amounts of variation in the chironomid assemblages. Although direct effects of pH on chironomids cannot be ruled out, pH is likely tracking production-related changes driven by limnetic dissolved inorganic carbon dynamics. Sediment cores collected from seabird-affected and seabird-free ponds showed a greater number of chironomid taxa and higher head capsule abundances in the pond receiving seabird inputs. Chironomid assemblages in both cores recorded increased abundances in recent decades, likely in response to warmer conditions and lengthened growing seasons.     

Habitats, abundance patterns and isotopic signals of morphotypes of the planktonic foraminifer Globigerinoides ruber (d'Orbigny) in the eastern Mediterranean Sea since the Marine Isotopic Stage 12

The chemical composition of shells of the planktonic foraminifer Globigerinoides ruber (white) is frequently used to determine past sea surface conditions. Recently, it has been shown that arbitrarily defined morphotypes within this species exhibit different chemical and isotopic signatures. Here, we investigate the occurrence through time and in space of morphological types of G. ruber (white) in late Quaternary and Holocene sediments of the central and the eastern Mediterranean Sea. In 115 samples representing two distinct time intervals (MIS 1–2 and MIS 9–12) at ODP Site 964 and the piston core GeoTü-SL96, we have defined three morphological types within this species and determined their relative abundances and stable isotopic composition. A quantitative analysis of morphological variation within G. ruber (white) in four samples revealed that the subjectively defined morphotypes occupy separate segments of a continuous and homogenous morphospace. We further show that the abundance of the morphotypes changes significantly between glacials and interglacials and that the three morphotypes of G. ruber show significant offsets in their stable isotopic composition. These offsets are consistent within glacial and interglacial stages but their sign is systematically reversed between the two Sites. Since the isotopic shifts among the three G. ruber morphotypes are systematic and often exceed 1‰, their understanding is essential for the interpretation of all G. ruber-based proxy records for the paleoceanographic development of the Mediterranean during the late Quaternary.     

Postsettlement growth of two estuarine crab species, Chasmagnathus granulata and Cyrtograpsus angulatus (Crustacea, Decapoda, Grapsidae): laboratory and field investigations

The estuarine grapsid crabs Chasmagnathus granulata and Cyrtograpsus angulatus belong to the most typical and dominant inhabitants of brackish coastal lagoons in southeastern South America. In a combined laboratory and field investigation of juvenile growth, we measured the increase in body size in these species under controlled conditions as well as in field experiments (in Mar Chiquita lagoon, Argentina), seasonal changes in size frequency distribution of a natural population, and growth related changes in selected morphometric traits of male and female juveniles (relations between carapace width, carapace length, propodus height and length of the cheliped, and pleon width). At 24°C, Cy. angulatus grew faster than Ch. granulata; it reached the crab-9 instar (C9; 13 mm carapace width) after 92 days, while Ch. granulata required 107 days to reach the C8 instar (7.4 mm). At 12°C, growth ceased in both species. The pleon begins to show sexual differences in the C5 (Cy. angulatus) and C8 instar (Ch. granulata), respectively, while the chelae differentiate earlier in Ch. granulata than in Cy. angulatus (in C4 vs C6). In the field, growth was maximal in summer, and was generally faster than in laboratory cultures. However, there is great individual variability in size (about 25% even in the first crab instar) and in size increments at ecdysis, increasing throughout juvenile growth. Our data indicate that, in the field, small-scale and short-term variations in feeding conditions, temperature, and salinity account for an extremely high degree of variability in the absolute and relative rates of growth as well as in the time to sexual differentiation. Received in revised form: 20 September 2001 Electronic Publication     

Morphology of the nematocysts of the medusae of two scyphozoans, Catostylus mosaicus and Phyllorhiza punctata (Rhizostomeae): implications for capture of prey

Abstract. We examined the cnidomes (total complement of nematocysts) of medusae of the zooxanthellate and azooxanthellate jellyfishes Phyllorhiza punctata and Catostylus mosaicus (Rhizostomeae, Scyphozoa), and compared the assemblage of zooplankton captured on the oral arms of each species to determine whether differences in the types or amount of zooplankton captured were consistent with possible differences in the cnidomes. Cnidomes were described using light and scanning electron microscopy. Each species had a distinct cnidome and, in general, specimens of P. punctata appeared to have far fewer nematocysts than those of C. mosaicus. Four types of nematocysts were identified in medusae of C. mosaicus; 2 types of holotrichous isorhizae, rhopaloids, and birhopaloids. In C. mosaicus, the oral arms and bell margins possessed all of these types, but the cnidomes of the 2 regions differed in relative abundances and sizes of isorhizae and rhopaloids. Five types of nematocysts were identified in medusae of P. punctata, although not all types were found in all specimens. Round holotrichous isorhizae were found only in the bell, while oval holotrichous isorhizae, rhopaloids of 2 distinct size ranges, and birhopaloids were found in the bell and oral arms. Cnidomes of the bell and oral arms in specimens of P. punctata also differed in the relative abundance and sizes of oval isorhizae and rhopaloids. Although there were clear differences in the overall cnidomes and absolute abundances of nematocysts in each species, the oral arms (feeding appendages) of specimens of both C. mosaicus and P. punctata had similar types and relative abundances of nematocysts. Zooplankton sampled from the oral arms of each species showed that both species preyed predominantly on copepod nauplii and larvae of gastropods and bivalves. Medusae of C. mosaicus captured ～10 × more gastropod larvae and 5 × more bivalve larvae than those of P. punctata. Specimens of P. punctata captured approximately twice as many copepod nauplii as those of C. mosaicus. Differences in the relative abundance of types of zooplankton captured by each species could not be adequately explained by differences in the cnidomes of the oral arms.     

Temperature-mediated changes in zooplankton body size: large scale temporal and spatial analysis

Climate warming has been linked with changes in the spatiotemporal distribution of species and the body size structure of ecological communities. Body size is a master trait underlying a host of physiological, ecological and evolutionary processes. However, the relative importance of environmental drivers and life history strategies on community body size structure across large spatial and temporal scales is poorly understood. We used detailed data of 83 copepod species, monitored over a 57-year period across the North Atlantic, to test how sea surface temperature, thermal and day length seasonality relate to observed latitudinal-size clines of the zooplankton community. The genus Calanus includes dominant taxa in the North Atlantic that overwinter at ocean depth. Thus we compared the copepod community size structure with and without Calanus species, to partition the influence of this life history strategy. The mean community body size of copepods was positively associated with latitude and negatively associated with temperature, suggesting that these communities follow Bergmann's rule. Including Calanus species strengthens these relationships due to their larger than average body sizes and high seasonal abundances, indicating that the latitudinal-size cline may be adaptive. We suggest that seasonal food availability prevents high abundance of smaller-sized copepods at higher latitudes, and that active vertical migration of dominant pelagic species can increase their survival rate over the resource-poor seasons. These findings improve our understanding of the impacts that climate warming has on ecological communities, with potential consequences for trophic interactions and biogeochemical processes that are well known to be size dependent.     

Seasonal and geographic climate variabilities during the Last Glacial Maximum in North America: Applying isotopic analysis and macrophysical climate models

Climate models provide estimates of climatic change over periods of time in the ancient past. Macrophysical climate models (MCM) differ from the more widely used general circulation models (GCM), in that MCMs provide temporally high-resolution (~ 100 years) and site-specific estimations of monthly values of climate variables such as temperature and precipitation. In this paper, seasonal changes in climate variables are modeled for six ¹⁴C-dated fossil localities in North America. Five of these localities represent the time of maximum extent of ice during the most recent glacial episode, the Full Glacial (25 + –15 ka), including one at the peak of the Last Glacial Maximum (17–15 ka). The other locality represents the time as the ice began to recede, the Late Glacial (15–11 ka). Seasonal variations in temperature and precipitation modeled by MCM are herein compared with interpretations of seasonal variation based upon oxygen isotopes from serially sampled hypsodont teeth (mostly Equus and Bison) collected from each of these localities. Additionally, the MCM-modeled seasonal variations are used to predict the expected abundances of different plant functional groups (PFG) during those times, especially C3 and C4 functional groups, using modern relationships. These predictions are compared with carbon isotopic values from the same teeth. The importance of atmospheric pCO² for the relative abundance of plants utilizing the C4 metabolic pathway is discussed, given that glacial episodes are known to have been times of lower atmospheric pCO². Interpretations of seasonal variability and the relative abundance of C3 versus C4 vegetation based upon isotopes from tooth enamel are in broad agreement with predictions using the MCM and the modern distribution of PFGs with climate variables. The influence of pCO² on the distribution of C4 vegetation during glacial times appears to be negligible.     

Mediterranean marine copepods: basin-scale trends of the calanoid Centropages typicus

The Mediterranean Sea is located in a crossroad of mid-latitude and subtropical climatic modes that enhance contrasting environmental conditions over both latitudinal and longitudinal ranges. Here, we show that the large-scale environmental forcing is reflected in the basin scale trends of the adult population of the calanoid copepod Centropages typicus. The species is distributed over the whole Mediterranean basin, and maximal abundances were found in the north-western basin associated to oceanic fronts, and in the Adriatic Sea associated to shallow and semi enclosed waters. The peak of main abundances of C. typicus correlates with the latitudinal temperature gradient and the highest seasonal abundances occurred in spring within the 14–18°C temperature window. Such thermal cline may define the latitudinal geographic region where C. typicus seasonally dominates the >200 μm-sized spring copepod community in the Mediterranean Sea. The approach used here is generally applicable to investigate the large-scale spatial patterns of other planktonic organisms and to identify favourable environmental windows for population development.     

Subtropical Front fluctuations south of Australia (45°09′S, 146°17′E) for the last 130 ka years based on calcareous nannoplankton

Calcareous nannoplankton assemblages from a Late Quaternary deep-sea core (GC07; 46°09′S, 146°17′E) south of Australia provide information on regional palaeoceanography and palaeoclimate changes in the Southern Ocean, in particular the movement of the Subtropical Front for the past 130 ka years. Marine Isotope Stages 1–5 are identified through changes in calcareous nannoplankton assemblages, supported by ¹⁴C dates, and oxygen isotope and %CaCO data.Two distinct assemblages are recognised: a warm water assemblage with higher abundances of Calcidiscus leptoporus, Emiliania huxleyi, Helicosphaera.carteri, Syracosphaera pulchra, Gephyrocapsa caribbeanica and Gephyrocapsa oceanica; and, a cold water assemblage with higher abundances of Gephyrocapsa muellerae and Coccolithus pelagicus. Alternation between these two assemblages downcore in GC07 reflect movement of the Subtropical Front across the location and can be correlated to Marine Isotope Stages (MIS) 1–5. Sediments with a cold water assemblage indicate the position of the Subtropical Front equatorward of the site when transitional to sub-antarctic waters were overlying the site. Conversely sediments with a warm water assemblage indicate the Subtropical Front was poleward of GC07 when warmer, subtropical waters were over the site. MIS 1 and 5 are interpreted as warmer than MIS 3 (based on species composition) with the Subtropical Front more poleward than for MIS 3. During MIS 3 the Subtropical Front is interpreted as adjacent to or immediately poleward of GC07. Some species including C. leptoporus and C. pelagicus show negative covariance and are considered to be reliable species in identifying glacial and interglacial intervals in this region.Comparison with established biostratigraphy based on calcareous nannoplankton showed the datum event for the reversal between E. huxleyi and G. muellerae of 73 ka in transitional waters is not applicable in this region. The reversal between these two species occurs between 48 and 30 cm downcore in GC07 with a ¹⁴C date of 11 020 year BP at 49–48 cm, i.e. the reversal event is younger than this date.     

Differing contributions of density dependence and climate to the population dynamics of three eruptive herbivores

1. Although both endogenous and exogenous processes regulate populations, the current understanding of the contributions from density dependence and climate to the population dynamics of eruptive herbivores remains limited. 2. Using a 17‐year time series of three cereal aphid species [Rhopalosiphum padi L., Metopolophium dirhodum (Walker), and Diuraphis noxia (Kurdumov)] compiled from a trapping network spanning the northwestern U.S.A., temporal and spatial patterns associated with population fluctuations, and modelled density dependence in aphid abundances were tested. These models were used to analyse correlations between climate and aphid abundances in the presence and absence of residual variance as a result of density‐dependent effects. 3. The temporal dynamics of aphid population fluctuations indicated periodicity, with no clear evidence for a spatial pattern underlying population fluctuations. 4. Aphid abundances oscillated in a manner consistent with delayed density dependence for all three aphid species, although the strength of these feedbacks differed among species. 5. Diuraphis noxia abundances were negatively correlated with increasing temperatures in the absence of density‐dependent effects, whereas M. dirhodum abundances were positively correlated with increasing cumulative precipitation in the presence of density‐dependent effects; yet, R. padi abundances were unrelated to climate variables irrespective of population feedbacks. 6. Our analysis suggests that endogenous feedbacks differentially regulate aphid populations in the northwestern U.S.A., and these feedbacks may operate at an expansive spatial scale. It is concluded that the contributions of density dependence and climate to aphid population dynamics are species‐specific in spite of similar ecological niches, with implications for assessing species responses to climate variability.     

Reproductive trade-off of the copepod Acartia tonsa in a hypersaline estuary of the Southwestern Atlantic. Temporal variations in the morphology of eggs

The purpose of the present work was to study the seasonal variations in egg production, morphology and hatching success in the cryptic species Acartia tonsa, taking into account variations in female size, population abundance and environmental factors in a turbid and hypersaline estuary. Sampling was performed during the austral warm (18–23°C and 32–36 salinity) and cold seasons (5–7°C; 32–38) in Bahía Blanca Estuary (BBE), Argentina, during 2007 and 2009. Field-collected females were incubated in the laboratory simulating in situ environmental conditions, and specimens from fixed samples were measured using optical and scanning electronic microscopy. Acartia tonsa’s marked seasonality in its reproductive traits was found to ensure its permanence in the water column all over the year. During the warm season, small-sized females were observed to invest their energy in the production of subitaneous eggs with high hatching success and smooth appearance (12.95?±?2.38 eggs f^?1 day^?1 and specific egg production rate (SEP) of 16.57%C f^?1 day^?1). During the cold season, females invested C in body mass as well as in the production of resting eggs of three different morphotypes (6.56?±?3.2 eggs f^?1 day^?1 and SEP of 7.37%C f^?1 day^?1). Although these morphotypes were found to show differences in surface ornamentation, they exhibited the same delayed hatching behaviour. The eggs with shorter spines were found to integrate the resting egg bank in BBE. Our findings confirming a delayed egg hatching behaviour and a great tolerance to low temperatures and high salinities in the A. tonsa population in BBE suggest that this possible strain is a valuable phenotype for aquaculture.     

Spatiotemporal variations in the abundances of the prokaryotic rRNA genes, <Emphasis Type="Italic">pmoA</Emphasis>, and <Emphasis Type="Italic">mcrA</Emphasis> in the deep layers of a peat bog in Sarobetsu-genya wetland,Japan

Spatiotemporal variations in microbial gene abundances were investigated to identify potential zones of methanotroph and methanogen biomass in a peat bog in Sarobetsu-genya wetland. The abundances of the bacterial and archaeal 16S rRNA genes, pmoA, and mcrA were 10⁷–10⁹, 10⁷–10⁸, 10⁴–10⁶, and 10⁴–10⁷ copies g⁻¹ dry peat, respectively. Correlation analysis based on microbial gene abundances and environmental factors showed that the spatiotemporal distributions of the abundances of the four microbial genes in peat layers were similar. The mcrA abundance showed a significant negative correlation with the dissolved organic carbon content and a significant positive correlation with the peat temperature. The pmoA abundance was not detectable during the spring thaw when the lowest peat temperature at a depth of 50 cm was recorded. At a depth of 200 cm, the peat temperature exceeded 6°C throughout the year, and the mcrA abundance exceeded 10⁴ copies g⁻¹ dry peat. These results indicate that the seasonal microbial activity related to methane should be evaluated in not only the shallow but also the deep peat layers in order to elucidate the methane dynamics in boreal wetlands.     

Respiratory metabolism in pacifastacus leniusculus (Dana) (crustacea: decapoda) as related to its ecology

Summary Respiratory metabolism in the high-altitude crayfish, Pacifastacus leniusculus from Lake Tahoe (California-Nevada, U.S.A.) was investigated in a series of laboratory experiments. In general, oxygen consumption was found to be directly proportional to size when expressed per individual, and inversely proportional to size when expressed per ash-free gram dry weight per unit time. No significant variations in respiratory rates were observed between males and females. There was little variation in uptake over a temperature range of 5°C to 12.5°C, while the lowest and highest uptake values were observed at 0°C and 15°C respectively. An increase in temperature above 15°C, however, resulted in a decrease in respiratory activity. These results closely correlate with patterns of ventilatory activity, oxygen extraction efficiency, and seasonal feeding and reproductive activity in Pacifastacus as related to the annual temperature profile for their Lake Tahoe habitat. These results, as well as the extremely low tolerance of this species for low oxygen levels, suggest temperature as the possible critical environmental factor in the determination of the nature of seasonal metabolic cycles. It is concluded that Pacifastacus shows little tolerance for fluctuations in environmental oxygen and temperature and is well adapted to the narrow range of condition present in its Lake Tahoe habitat.