Records of upwelling, seasonality and growth in stable-isotope profiles of Pliocene mollusk shells from Florida

Oxygen and carbon isotopic profiles across the shells of well-preserved bivalves and gastropods from the Pliocene Pinecrest Beds near Sarasota, Florida, provide detailed records of the paleoen-vironmental and paleoclimatic conditions under which these high-density shell beds accumulated, as well as offer insight into shell-growth rates and longevity. Eight turritellid gastropods were analyzed from within and surrounding two Turritella-rich beds, an upper bed within unit 2(2.5-2.0 Ma) and a lower bed situated near the top of the main shell bed, unit 6/7(3.5-2.5 Ma). Three bivalves plus another turritellid specimen from a lower horizon (middle of unit 6/7), considered to represent offshore, normal-marine conditions, were also analyzed. The isotopic profiles of all shells reflect year-round shell growth in a seasonal, subtropical to warm-temperate paleoenvironment. Cyclical patterns in δ¹⁸O reflect annual variations in water temperature which on average ranged from 15 to 24d?C; minimum paleoseasonality contrasts varied from 7 to 9d?C. Summer paleo-temperatures compare favorably with those detemined from ostracodes, whereas winter temperatures appear slightly cooler. Except for one pectinid specimen, temperature differences between horizons and specimens are small. Annual δ¹⁸O cycles indicate: Turritella apicalis lived longer and grew slightly faster than Turritella gladeensis; and, shell growth rates and increment formation in Mercenaria campechiensis are comparable to modern Florida populations. Coincident episodes of heavy δ¹⁸O and light δ¹⁸C in both turritellids and bivalves suggest a pattern of seasonal upwelling. This cool, nutrient-rich, upwelled water may be partially responsible for the great abundance of Pinecrest fossils. □Stable isotopes, Pliocene, Pinecrest Beds, Florida, upwelling, paleotemperature, mollusk, Turritella.      

Winter Climate Limits Subantarctic Low Forest Growth and Establishment

Campbell Island, an isolated island 600 km south of New Zealand mainland (52°S, 169°E) is oceanic (Conrad Index of Continentality  = −5) with small differences between mean summer and winter temperatures. Previous work established the unexpected result that a mean annual climate warming of c. 0.6°C since the 1940''s has not led to upward movement of the forest limit. Here we explore the relative importance of summer and winter climatic conditions on growth and age-class structure of the treeline forming species, Dracophyllum longifolium and Dracophyllum scoparium over the second half of the 20^th century. The relationship between climate and growth and establishment were evaluated using standard dendroecological methods and local climate data from a meteorological station on the island. Growth and establishment were correlated against climate variables and further evaluated within hierarchical regression models to take into account the effect of plot level variables. Winter climatic conditions exerted a greater effect on growth and establishment than summer climatic conditions. Establishment is maximized under warm (mean winter temperatures >7 °C), dry winters (total winter precipitation <400 mm). Growth, on the other hand, is adversely affected by wide winter temperature ranges and increased rainfall. The contrasting effect of winter warmth on growth and establishment suggests that winter temperature affects growth and establishment through differing mechanisms. We propose that milder winters enhance survival of seedlings and, therefore, recruitment, but increases metabolic stress on established plants, resulting in lower growth rates. Future winter warming may therefore have complex effects on plant growth and establishment globally.     

Population Biology and Growth of Ozark Cavefish in Logan Cave National Wildlife Refuge, Arkansas

Ozark cavefish, Amblyopsis rosae, is a threatened species endemic to the Springfield Plateau of the Ozark Highlands in Arkansas, Missouri, and Oklahoma. One of the largest known Ozark cavefish populations, located in Logan Cave, Arkansas, was surveyed 25 times over a two-year period between 1993 and 1995. During the study, 147 Ozark cavefish > 30 mm (TL) were marked with visual implant tags and 140 Ozark cavefish were available for recapture; 68 were recaptured 189 times and the rest (72) were never recaptured. Individual Ozark cavefish persisted in Logan Cave for a relatively short time. Only 14% of 80 fish tagged during a previous study in 1992 were recaptured during this study, and half of all recaptured fish disappeared within three months. However, if a fish persisted for at least seven months in the cave, its probability of being recaptured over an additional year was high. Maximum persistence of a tagged fish was 28 months, suggesting these fish have a maximum life-span of 4–5 years. Growth averaged 0.6 mm per month, with maximum recorded growth of 6 mm per month and a maximum size of 65 mm TL. Smaller fish grew faster than larger fish but growth rates were sporadic, with several mid-sized fish (45–49 mm) showing little growth (0–3 mm year^-1) while some fish > 50 mm grew up to 12 mm year^-1. Most fish gained in length during April–October, the same period a maternity colony of gray bats occupied the cave. Gross Ozark cavefish movement over the study period ranged up to 1002 m, with a mean movement of 1.2 m day^-1; movement was positively correlated with Ozark cavefish total length. Death seemed the most likely explanation for loss of tagged Ozark cavefish, including fish that emigrated out of the cave. Little up-stream movement was recorded between reaches and did not account for loss of tagged fish. Reproduction within the cave and immigration from the aquifer accounted for persistence of Ozark cavefish in Logan Cave.     

Dynamics of a bloom of halophilic archaea in the Dead Sea

After a period of more than ten years in which bacterial and algal community sizes were extremely small, a dense bloom of halophilic archaea developed in the upper 5–10 m of the Dead Sea water column in the summer of 1992. The development of this bloom followed a dilution of the upper water layer by winter rainfloods, which enabled the development of a short-lived dense bloom of the unicellular green alga Dunaliella parva. The dense archaeal community (up to 3.5 × 10⁷ cells m1^–1 in June 1992) imparted a red coloration to the Dead Sea, due to its high content of bacterioruberin. Bacteriorhodopsin was not detected. High levels of potential heterotrophic activity were associated with the bloom, as measured by the incorporation of labeled organic substrates. After the decline of the algal bloom, archaeal numbers in the lake decreased only little, and most of the community was still present at the end of 1993. The amount of carotenoid pigment per cell, however, decreased 2–3-fold between June 1992 and August 1993. No new algal and archaeal blooms developed after the winter floods of 1992–1993, in spite of the fact that salinity values in the surface layer were sufficiently low to support a new algal bloom. A remnant of the 1992 Dunaliella bloom maintained itself at the lower end of the pycnocline at depths between 7 and 13 m (September 1992–August 1993). Its photosynthetic activity was small, and very little stimulation of archaeal growth and activity was associated with this algal community.     

Population structure and growth of the Japanese littleneck clam <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> in Amursky Bay,Sea of Japan

This paper deals with the size, age, and sex structure of population and growth of the Japanese littleneck clam Ruditapes philippinarum in Amursky Bay (Peter the Great Bay, Sea of Japan). One-year-olds and individuals with a shell length less than 19.8 mm were not found in the population under study. The population consisted mostly of 3-4-year-old clams (72.4%) with a shell length of 35–45 mm (67.8%). The maximum recorded age of R. philippinarum was 7 years, and maximum shell length was 52.7 mm. The male to female ratio was approximately 2: 1. Hermaphroditism (2.1%) and parasitic castration (1.4%) were observed. Linear growth rates of clams were found to increase until the age of three years old (11.6 ± 0.6 mm/year). Mollusks reach a commercial size of over 35 mm in shell length in the fourth year of life. The parameters of the von Bertalanffy equation describing group linear growth were L _∞ = 56.6 mm, k = 0.302 year^?1, and t ₀ = 0.468 year. The relationship between the shell length and the wet body weight is described by the equation W = 0.000253L^2.954.     

Impact of Engineered Zinc Oxide Nanoparticles on the Individual Performance of Mytilus galloprovincialis

The increased use of engineered nanoparticles (ENPs) in consumer products raises the concern of environmental release and subsequent impacts in natural communities. We tested for physiological and demographic impacts of ZnO, a prevalent metal oxide ENP, on the mussel Mytilus galloprovincialis. We exposed mussels of two size classes, <4.5 and ≥4.5 cm shell length, to 0.1–2 mg l⁻¹ ZnO ENPs in seawater for 12 wk, and measured the effect on mussel respiration, accumulation of Zn, growth, and survival. After 12 wk of exposure to ZnO ENPs, respiration rates of mussels increased with ZnO concentration. Mussels had up to three fold more Zn in tissues than control groups after 12 wk of exposure, but patterns of Zn accumulation varied with mussel size and Zn concentrations. Small mussels accumulated Zn 10 times faster than large mussels at 0.5 mg l⁻¹, while large mussels accumulated Zn four times faster than small mussels at 2 mg l⁻¹. Mussels exposed to 2 mg l⁻¹ ZnO grew 40% less than mussels in our control group for both size classes. Survival significantly decreased only in groups exposed to the highest ZnO concentration (2 mg l⁻¹) and was lower for small mussels than large. Our results indicate that ZnO ENPs are toxic to mussels but at levels unlikely to be reached in natural marine waters.     

Parental size and environmental conditions affect egg capsule production by Nassarius reticulatus (Linnaeus 1758) (Gastropoda: Nassariidae)

In shallow coastal habitats scavenging netted whelks Nassarius reticulatus attached egg capsules to the stipes of red algae Chondrus crispus and occasionally on Furcellaria lumbricalis and Plumaria plumose. In the laboratory egg capsules were laid on aquaria sides and lids by individuals ≥ 21 mm shell length. Larger size classes produced more egg capsules and spawned over a longer period and in doing so partitioned less energy into shell growth. Large netted whelks (25-28.9 mm) produced larger capsules which contained significantly more and larger eggs than those produced by smaller individuals (21-24.9 mm). Egg capsule production continued throughout the year by regularly fed N. reticulatus held at ambient seawater temperatures. Egg production increased in the spring and summer with peak production during June (15 °C), decreased between August and October and resumed again during the winter (November to February at ∼ 7 °C). During the summer (15-16 °C) egg capsules were smaller and contained smaller eggs than those deposited during the winter (7-10 °C), although the number of eggs · capsule⁻¹ was similar. Enforced food limitation reduced the number and size of the egg capsules, the number and size of eggs produced · female⁻¹ and the duration of the breeding period. Hatching success of N. reticulatus egg capsules was high (95%) even at winter seawater temperatures (11-8.5 °C) and the duration of embryonic development was fastest between 15 and 17.5 °C.     

Shell form,behaviour, and tolerance to water movement in the limpet Patina pellucida (L.) (Gastropoda: Prosobranchia)

The diotocardian gastropod Patina pellucida (L.) is a macro-herbivore common upon the fronds of laminarian algae. Considerations of shell shape, adhesive tenacity, and current tolerance, together with calculations of expected hydrodynamic drag, indicate that this limpet is effectively streamlined. Smaller individuals are relatively more resistant to dislodgement than are larger ones. Experimental animals of 6.0–13.5 mm shell length resisted constant flows of up to 0.9-1.3 m s^?1. An orientation, in which the longitudinal axis of a limpet is aligned parallel to the direction of the prevailing flow, is induced by currents faster than ≈ 0.5 m s^?1, and is an adaptation to conditions of directional water streaming. P. pellucida appears to show a seasonal change in orientatory preference, individuals tending to point distally with respect to the algal lamina in spring and proximally in autumn: this change may be associated with the annual growth cycle of the host plant.     

Size and age composition of populations and growth of Mytilus trossulus (Bivalvia: Mytilidae) in the subtidal area of western Kamchatka

Fairly large Mytilus trossulus beds were found in the subtidal zone at depths to 40 m off the western coast of Kamchatka. The size and age composition of local populations and growth rates of M. trossulus in this region and at Atlasova Island were studied. Significant variability of the shell shape of mollusks was found. In the western Kamchatka subtidal, M. trossulus grew faster than in the northern Kuril Islands and eastern Kamchatka. Mussels attained commercial size (50 mm in shell length) in the fourth year of life in the former case and in the fifth-sixth year in other cases. Mollusks of different ages, from 1 to 8–9 year olds, were present in western Kamchatka populations; i.e., juvenile recruitment takes place regularly, while growth rates vary. Growth and population structure of M. trossulus are discussed in relation to the habitat conditions on the western Kamchatka shelf.     

Calculation of Cell Production from [3H]Thymidine Incorporation with Freshwater Bacteria

The conversion factor for the calculation of bacterial production from rates of [³H]thymidine incorporation was examined with diluted batch cultures of freshwater bacteria. Natural bacterial assemblages were grown in aged, normal, and enriched media at 10 to 20°C. The generation time during 101 growth cycles covered a range from 4 to >200 h. The average conversion factor was 2.15 × 10¹⁸ cells mol^-1 of thymidine incorporated into the trichloroacetic acid (TCA) precipitate (standard error = 0.29 × 10¹⁸; n = 54), when the generation time exceeded 20 h. At generation times of <20 h, the average conversion factor was 11.8 × 10¹⁸ cells mol^-1 of thymidine incorporated into TCA precipitate (standard error = 1.72 × 10¹⁸; n = 47). The amount of radioactivity in purified DNA increased with decreasing generation time and increasing conversion factor (calculated from the TCA precipitate), corresponding to a decrease in the percentage in protein. The conversion factors calculated from purified DNA or from the TCA precipitate gave the same variability. Conversion factors did not change significantly with the medium, but were significantly higher at 20°C than at 15 and 10°C. A detailed examination of the [³H]thymidine concentrations that were needed to achieve maximum labeling in DNA was carried out 6 times during a complete growth cycle. During periods with low generation times and high conversion factors, 15 nM [³H]thymidine was enough for the maximum labeling of the TCA precipitate. This suggests that incorporation of [³H]thymidine into DNA is probably limited by uptake during periods with generation times of <20 h and that freshwater bacterioplankton cell production sometimes is underestimated when a conversion factor of 2.15 × 10¹⁸ cells mol^-1 of thymidine incorporated is used.     

Population dynamics,growth and reproductive rates of Littorina nigrolineata Gray from a moderately sheltered locality in North Wales

The population dynamics of Littorina nigrolineata Gray on a moderately sheltered boulder shore was characterized by an almost constant mortality rate of post-juvenile snails both within and between years. Cohorts of post-juvenile snails had a “half life” of about 5 months. Juvenile snails had higher mortality rates than post-juveniles. Mortality rate was independent of size in post-juveniles. The population of post-juvenile snails fluctuated only about two-fold during the 3 yr of study. Maxima of population size occurred each September as a result of an autumnal pulse of recruitment into the post-juvenile size classes. These recruits originated from eggs laid in the summer of the previous year. The size-frequency structure of the population lacked well defined modes except during the spring and summer when the pulse of recruits formed a distinct mode, which later disappeared due to growth and mortality of the recruits. Oviposition continued throughout the year with a pulse in summer. Newly laid eggs took 4–7 wk to hatch. The hatchlings had a mean shell height of 0.5 mm and were estimated to take 6–9 months to grow to a shell height of about 4 mm. Growth increments over periods of 3 months. estimated from tagged cohorts of snails ranging from 3 to 16 mm, released on a stone jetty, revealed seasonal and size-specific changes in growth rate. Growth rate was significantly lower between December and March than at other times of the year. Seasonal differences in growth rate did not, however, significantly affect the yearly size increments of snails hatching in summer or winter. Growth increments did not decline linearly with increasing body size, as is assumed by the von Bertalanffy growth model, but increased to a maximum at about 6–7 mm shell height. Beyond the maximum, the growth increments decreased linearly with increasing shell height. This non-linearity caused an inflexion in the growth curve, so that the shell height. This non-linearity caused an inflexion in the and 12.4 mm by the von Bertalanffy growth curve. The deviation from the von Bertalanffy growth model was possibly due to departures from the assumptions that the assimilation rate is proportional to the square of a linear size dimension and that the metabolic rate is proportional to the cube of the same dimension. A von Bertalanffy growth curve, fitted to growth increments measured from “growth checks” on tagged snails on the boulder shore, predicted slightly faster growth rates than the von Bertalanffy growth curve fitted to increments of mean cohort size on the stone jetty. The closeness of the two curves, however, suggested that both methods of measuring growth increments were tolerably accurate.     

Prawn Shell Chitosan Has Anti-Obesogenic Properties,Influencing Both Nutrient Digestibility and Microbial Populations in a Pig Model

The potential of natural products to prevent obesity have been investigated, with evidence to suggest that chitosan has anti-obesity effects. The current experiment investigated the anti-obesity potential of prawn shell derived chitosan on a range of variables relevant to obesity in a pig model. The two dietary treatment groups included in this 63 day study were: T1) basal diet and T2) basal diet plus 1000 ppm chitosan (n = 20 gilts per group (70 ± 0.90 kg). The parameter categories which were assessed included: performance, nutrient digestibility, serum leptin concentrations, nutrient transporter and digestive enzyme gene expression and gut microbial populations. Pigs offered chitosan had reduced feed intake and final body weight (P< 0.001), lower ileal digestibility of dry matter (DM), gross energy (GE) (P< 0.05) and reduced coefficient of apparent total tract digestibility (CATTD) of gross energy and nitrogen (P<0.05) when compared to the basal group. Fatty acid binding protein 2 (FABP2) gene expression was down-regulated in pigs offered chitosan (P = 0.05) relative to the basal diet. Serum leptin concentrations increased (P< 0.05) in animals offered the chitosan diet compared to pigs offered the basal diet. Fatness traits, back-fat depth (mm), fat content (kg), were significantly reduced while lean meat (%) was increased (P<0.05) in chitosan supplemented pigs. Pigs offered chitosan had decreased numbers of Firmicutes in the colon (P <0.05), and Lactobacillus spp. in both the caecum (P <0.05) and colon (P <0.001). Bifidobacteria populations were increased in the caecum of animals offered the chitosan diet (P <0.05). In conclusion, these findings suggest that prawn shell chitosan has potent anti-obesity/body weight control effects which are mediated through multiple biological systems in vivo.     

Performance of Chlorella sorokiniana under simulated extreme winter conditions

High annual microalgae productivities can only be achieved if solar light is efficiently used through the different seasons. During winter the productivity is low because of the light and temperature conditions. The productivity and photosynthetic efficiency of Chlorella sorokiniana were assessed under the worst-case scenario found during winter time in Huelva, south of Spain. The maximum light intensity (800?μmol photons m^-2 s^-1) and temperature (20°C) during winter were simulated in a lab-scale photobioreactor with a short light-path of 14?mm. Chemostat conditions were applied and the results were compared with a temperature-controlled situation at 38°C (optimal growth temperature for C. sorokiniana). When temperature was optimal the highest productivity was found at a dilution rate of 0.18 h^-1 (P _v?=?0.28?g Kg^-1 h^-1), and the biomass yield on light energy was high (Y _x,E?=?1.2?g?mol^-1 photons supplied). However, at suboptimal temperature, the specific growth rate of C. sorokiniana was surprisingly low, not being able to support continuous operation at a dilution rate higher than 0.02 h^-1. The slow metabolism under suboptimal temperature resulted in a decline of the light energy requirements of the cells. Consequently, the maximum winter irradiance was experienced as excessive, leading to a low photosynthetic efficiency and productivity (Y _x,E?=?0.5?g mol^-1 photons supplied, P _v?=?0.1?g Kg^-1 h^-1). At suboptimal temperature a higher carotenoid-to-chlorophyll ratio was observed indicating the activation of light-dissipating processes. We conclude that temperature control and/or light dilution during winter time will enhance the productivity.     

Substrate activation of rat trypsins 1 and 2

Qualitative differences in the active center of rat trypsins 1 and 2 resulted in different ratios of K_cat for N¹-tosyl-l-arginine methyl ester vs K_cat for N¹-benzoyl-l-arginine ethyl ester. These ratios were 2.5 for trypsin 1 and 1.2 for trypsin 2.Substrate activation with N¹-tosyl-l-arginine methyl ester enhanced the catalytic rate constant of rat trypsin 1 2.5-fold and that of rat trypsin 2 only 1.5-fold. The increase in the catalytic rate constant found with N¹-benzoyl-l-arginine ethyl ester was the same (1.5-fold) for both trypsins. Consequently, at 20 mm substrate concentration, trypsin 1 catalyzed the esterolysis of N¹-tosyl-l-arginine methyl ester 4.5 times faster than that of N¹-benzoyl-l-arginine ethyl ester, while trypsin 2 was only 1.3 times more efficient with the first substrate.Furthermore, the activation of both rat enzymes by N-acetyl-l-tyrosine ethyl ester was even more effective than that obtained with the two cationic esters; the maximum rates of hydrolysis of this neutral substrate by trypsins 1 and 2 were enhanced 120- and 50-fold, respectively, by high concentrations of N-acetyl-l-tyrosine ethyl ester.     

Rearing tench (Tinca tinca L.) larvae on live feed (Artemia) and on two transition schedules from live to dry diets

Two 60‐day experiments were carried out on tench (Tinca tinca L.) from day 5 post‐hatch. Density was 20 larvae L^?1 and temperature 24 ± 0.5°C. In experiment 1, Artemia nauplii were the sole food, testing nauplii amounts and feeding frequency. High survival rates (between 79.5% and 95.5%) were obtained. Growth was faster as nauplii amounts were greater; the highest growth rate (11.00), weight (265.5 mg) and Fulton’s coefficient (1.40) were obtained when fish were fed in excess once a day, without significant differences from the growth obtained by feeding in excess of eight times a day. In experiment 2, a dry diet for marine fish was tested as a replacement for Artemia nauplii, following two transition protocols, one faster than the other; high survival rates (between 77.7% and 87.1%) were again obtained. The slower transition allowed a growth rate of 10.14, length of 23.1 mm, weight of 158.3 mg and a Fulton’s coefficient of 1.28, without significant differences from the faster transition. At all stages, growth values were significantly higher from feeding nauplii in excess as the sole food, but the required nauplii quantity was six times higher than the amount supplied to the animals fed the dry diet.     

Life in the Supralittoral Fringe: Microhabitat Choice, Mobility and Growth in the Tropical Perwinkle Cenchritis (=Tectarius) muricatus (Linneaus, 1758)

The littorinid snail, Cenchritis muricatus, inhabits supralittoral vertical rocky walls along Caribbean shores, at times surpassing 14 meters above mean sea level. As the sole macrofaunal representative of this habitat, this marine gastropod presumably experiences extraordinary conditions of thermal load and desiccation. In order to understand the effect of behavioral choices on periwinkle survivorship and growth, snail distribution, microhabitat utilization, and crawling speed were documented in St John (US Virgin Islands). In general, snails rarely inhabited open surfaces; instead, periwinkles were commonly observed in microhabitats that may reduce water and heat stresses (e.g., > 75% in crevices and depressions). Snails found on occasional buttonwood trees (Conocarpus erectus) were larger than elsewhere. Although typically found in repose, C. muricatus crawling speed on moist, shaded, and smooth substrata averaged more than 3 cm^.min^- 1, but did not vary with slope. Repeated mark-recapture of tagged periwinkles exhibited high recovery rates (ca. 35% after 4 yr), absence of mortality, and a projected cessation of growth at 16.5 mm (shell height). Nearly 10% of marked individuals were recaptured every year. Dead, tagged snails were never noted; indeed, seven individuals were only recovered once, a full 4 yrs after release. Site-specific growth rates were absent. Projections using von Bertalanffy growth functions (VBGF) suggest that periwinkles will require 15+ years to achieve the maximum shell height. These VBGF models cannot address extraordinary individuals reaching 22 mm. C. muricatus's remarkable supralittoral distribution may be explained by physiological tolerance, selection of microhabitats, lack of predators and long lifespan.     

Regulation of stable RNA synthesis and ppGpp levels in growing cells of Escherichia coli

Under the balanced condition of growth of E. coli cells, no distinct difference is observed in stable RNA and protein synthesis between CP78 (rel⁺) and CP79 (rel⁻), whereas a considerable difference is present in RNA accumulation between NF161 (rel⁺) and NF162 (rel⁻), where NF161 < NF162. The RNA content of NF161 is lower than that of NF162 in four different cultures with different growth rates. These two sets of isogenic pairs of rel⁺ and rel⁻ strains are commonly used in the study of rel gene function; however, NF161 is a mutant in the spoT gene whose product may be responsible for the degradation of ppGpp. The basal levels of ppGpp in these four strains growing with three different growth rates were examined: NF161 (rel⁺spoT⁻) has a much higher content of ppGpp than do other strains. Furthermore, the contents of ppGpp tend to be lower when the above four strains are growing at a faster rate. Thus a close correlation seems to exist between the content of RNA and the basal level of ppGpp under the condition of balanced growth.     

Regulation of hyphal growth rate ofHypoxylon mammatum by amino acids: Stimulation by proline

Variation among isolates ofHypoxylon mammatum caused by amino acids added as sole nitrogen sources demonstrated genetic heterogeneity among the population in the mechanisms regulating hyphal growth rates. Isolates were obtained by a random sample consisting of 22 single ascospore isolates from a local population of hypoxylon cankers onP. tremuloides. Hyphal growth rates were determined from colony diameter measurements on defined media containing either alanine, asparagine, glycine, leucine, lysine, or proline. All isolates but two grew faster on proline than the other amino acids tested. The mean growth rate of the population sample was 3.9 mm day⁻¹ on proline compared to 1.96 mm day⁻¹ on asparagine, the second fastest mean growth rate. Growth rates of the 22 isolates on these six amino acids were largely uncorrelated, indicating independent mechanisms of regulation. Only asparagine gave significant correlations with more than two other amino acids. A more detailed examination of selected isolates representing a range of growth rates on proline showed that the rapid growth rates were also dependent on other materials present in Difco Bacto-Agar. Growth of the proline stimulated isolates was considerably slower on media gelled with Noble agar. Other nitrogen sources, especially glutamate, added with proline stimulated the growth of these isolates. Isolate dependent variation in the stimulatory effect of the N source added with proline was demonstrated. Stimulation of growth rate by proline may be related to drought stress-enhanced canker elongationin vivo, since drought stress caused proline accumulation in the host,Populus tremuloides.     

Growth and tissue mass cycles in the infaunal bivalve Yoldia eightsi at Signy Island, Antarctica

Shell growth in Yoldia eightsi was measured over an austral summer and winter in 1992. In specimens < 12 mm length, growth was not significantly different between summer and winter periods, and the fastest recorded rate, 6.3 μm day⁻¹ was for 5-mm individuals during the winter. In summer, specimens of all lengths grew significantly, but in winter bivalves > 27 mm length did not increase in length. Tissue dry and ash-free dry mass (AFDM) cycles were assessed at monthly intervals between December 1988 and January 1991. ANCOVA indicated significant interannual and seasonal effects on this cycle. Tissue mass increased in the summer, coinciding with the phytoplankton bloom and the period of maximum sedimentation of organic material from the water column. A standard 20-mm-length animal reached a maximum AFDM of 114 mg in February 1990. The minimum value (68 mg AFDM) throughout the 2 years of measurements was in early December 1988, at the end of the austral winter. Periods of tissue mass increase were, therefore, decoupled from shell growth, at least in juveniles. Tissue mass was significantly higher in 1990 than 1989, which was mainly due to high organic contents in the summer (January to May). This was not consistent with the pattern of organic content in the sediments at the study site, but was in phase with the cycle in sediment chlorophyll a content. Tissue mass increase depended on major resource input during the summer, but Y. eightsi was capable of maintaining winter condition from stocks of benthic microalgae in years of poor ice cover. Tissue mass declined between April and July each year. This was accompanied by large falls in tissue ash content, and coincided with the spawning period in early June. These are the first monthly tissue mass data collected over a 2-year period for an Antarctic mollusc. They are the first such data indicating seasonal variation in tissue mass and showing a decoupling of shell and tissue growth in a polar bivalve. The P/B ratio calculated from these data was 0.106, which is slightly lower than previous values found for this species, but is in line with general values for Antarctic marine benthos. Accepted: 6 December 1999     

Growth history and ecology of the Atlantic surf clam,Spisula solidissima (Dillwyn), as revealed by stable isotopes and annual shell increments

The shells of the Atlantic surf clam, Spisula solidissima (Dillwyn), contain a record of both life history and environmental changes. These shell records were investigated using oxygen and carbon stable isotopic analyses (δ¹⁸O, δ¹³C) and shell growth increment analyses. δ¹⁸O variations across annual shell increments reflect the yearly cycle of sea-water temperatures off the New Jersey coast, further documenting the proposed annual periodicity of the major shell increments. The 11-yr shell record analyzed here confirms that shell growth is most rapid in spring-early summer, slow in late summer-fall, and extremely slow or non-existent in winter. Shell growth appears to occur in isotopic equilibrium with sea water and measured δ¹⁸O values are used to refine the aragonite-water temperature scale. Variations in the timing of annual growth increment formation are noted as well as ontogenetic effects upon the range of isotopic values recorded in shell carbonate. Both the δ¹⁸O and δ¹³C profiles are influenced by changes in the sea-water temperature regime over the 11-yr period studied (1965–1976) and record these effects in the shell. The combination of stable isotope and growth increment analyses provides a powerful tool for interpreting the shell records of both modern and fossil molluscs.