Net Growth Efficiency Research Articles

Growth, filtration and respiration in the mussel Mytilus edulis:no evidence for physiological regulation of the filter-pump to nutritional needs

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 141:37-45 (1996) - doi:10.3354/meps141037 Growth, filtration and respiration in the mussel Mytilus edulis: no evidence for physiological regulation of the filter-pump to nutritional needs Clausen I, Riisgård HU The specific growth rate of blue mussels Mytilus edulis fed Rhodomonas sp. algal cells in laboratory experiments increased with increasing food concentration to obtain a maximum value of about 9.5% d-1, irrespective of a relatively high concentration of silt (5 mg l-1) added to the water. Likewise, the net growth efficiency increased with the specific growth rate to a maximum value of about 75%. Measurements of the relationship between respiration and growth showed that the energy cost of growth constituted 12% of the growth. The filtration rate of a 100 mg dry wt 'standard' mussel was high and constant (about 30 ml min-1) at algal concentrations below about 6000 cells ml-1 when measured in both short-time (5 h) and long-time (9 to 14 d) experiments. High algal concentrations of 1.3 to 2.4 x 104 cells ml-1 reduced the filtration rate by about 40%. The estimated growth, presuming maximum filtration rate, satisfactorily described the actual growth at algal concentrations <5000 cells ml-1, and the concentration necessary for maximum growth was estimated at 4500 cells ml-1 (corresponding to 5.6 µg chlorophyll a l-1). The mean specific growth rate in M. edulis transferred in net bags to a fjord system (Kertinge Nor/Kerteminde Fjord, Denmark) was about 6% d-1. The results show that there is no physiological regulation of the filtration rate to nutritional needs, and that food uptake in nature (median concentration in Danish waters = 5.1 µg chlorophyll a l-1) is characterized by the full exploitation of the capacity of the bivalve filter-pump. Actual and estimated growth · Feeding and effects of silt · Costs of growth · Net growth efficiency · Regulation of filtration rate Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 141. Publication date: October 03, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Nitrogen Flow in a Chemostat Culture of the Rotifer &lt;i&gt;Brachionus plicatilis&lt;/i&gt;

Nitrogen flow in a chemostat culture of the rotifer Brachionus plicatilis was measured. It was found that a chemostat could keep the rotifer in a stable condition and were suitable for studying the effect of algal density. The rotifer egested 70-80% of the ingested nitrogen as particulate organic nitrogen (PON) and about 80% of the remaining assimilated nitrogen was utilized for reproduction. Low net growth efficiency (K2) at high algal densities proved “superfluous feeding”. 20% of PON egested was incorporated in the rotifer again by bacteriovory, and 13% of that was remineralized to NH+4 by bacteria. The PON was accumulated as a suspended or attached form in the culture vessel, which might cause an unstable environment. For a safety culture of the rotifer, removal of PON is an effective counter plan.

Multiple-locus heterozygosity, physiology and growth at two different stages in the life cycle of the Chilean oyster Ostrea chilensis

A random sample of 150 individuals of a laboratory-produced cohort of Ostrea chilensis Philippi, 1845 was taken at 10 and 36 mo of age to estimate physiological variables and individual heterozygosity using 4 loci (Lap, Pgi, Pgm and Ca). Juveniles of 10 mo of age showed a mean D value of 0.134 (p > 0.05) and a positive correlation between oyster size and multiple-locus heterozygosity (MLH) (p 0.05), oxygen consumption rate (p < 0.05) and MLH was found. The K2 value (standardized net growth efficiency) was positively correlated (p < 0.05) with MLH. At 36 mo a heterozygote deficiency was present with a mean value D = -0.431 (p < 0.05). No relationship between standard dry weight and MLH and also a negative correlation between the scope for growth and MLH were found. The oxygen consumption and excretion rates also showed an increase in large size individuals. The slopes for filtration and excretion rates against MLH were negative and not statistically significant. However, ingestion and absorption rates showed significant (p < 0.05) decrease with an increase in heterozygosity. The results seem to indicate that within sexually immature individuals of O. chilensis, a positive correlation between growth rate and MLH can be found, while in adults the higher energy allocation for reproduction precludes the detection of this relationship.

Physiological energetics of the zebra musselDreissena polymorpha in lakes III. Metabolism and net growth efficiency

Oxygen consumption and ammonia excretion of the zebra musselDreissena polymorpha from 3 sites in lakes were estimated regularly over the course of 1 1/2 years at ambient temperature. They showed a pronounced annual cycle, when expressed in absolute terms (at standard shell length) and in weight specific terms (at standard tissue weight). The atomic ratio of oxygen consumed to ammonia-N released (O/N ratio) was lowest in late summer at all sites (10 to 20) and highest during winter and spring (50 to > 100). The mean body weight exponent pooled from these sites was 0.78 (95% confidence interval±0.07) for the oxygen consumption rate and 0.80 (confidence interval±0.10) for the ammonia excretion rate. Both oxygen consumption and ammonia excretion were significantly correlated with the water temperature at the 2 shallow water sites, where temperature variation was most pronounced. Correlation with seston content or gonad volume were insignificant at these sites. The quotient of filtration capacity to oxygen consumption rate was about 3 times higher at the site with the poorest food conditions compared to the other sites. Net growth efficiency was highly variable; its annual average was 35 to 40 per cent and independent of locality and animal size.

Growth and energetics of the sponge Halichondria panicea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 128:239-246 (1995) - doi:10.3354/meps128239 Growth and energetics of the sponge Halichondria panicea Thomassen S, Riisgård HU The filtration rate (F, ml min-1 measured as clearance of algal cells) and maintenance respiration rate (Rm, ml O2 h-1 measured as starvation respiration rate) as a function of Halichondria panicea colony size (dry weight DW, g) were described by: F = 28.35DW0.914 and Rm = 0.632DW0.927, respectively. At the maximum specific growth rate of 4% d-1 the net growth efficiency was about 30%. The specific respiration rate (Rs) as a function of the specific growth rate (mu) was described by the equation: Rs = n mu + a where n is the energy cost per unit of growth and a is Rs at zero growth rate. It was found that the energy cost of growth constituted 139% of the biomass increase. This showed that sponges apparently have a higher energy demand for growth than other invertebrates. When sponge colonies were transferred to filtered sea water, a near linear decrease of chlorophyll a (chl a) was seen during the first 24 h. A similar decrease was observed in sponges transferred directly from the field to filtered sea water. The reduction constants (r) in the 2 cases were 3.3 and 2.8% h-1, respectively. The estimated filtration rates, using the equation Fest = (r x S)/chl a, where S is the steady-state chl a content, were almost identical to filtration rates measured as clearance. It is stressed that sponges have a low water pumping capacity compared with other filter-feeding invertebrates, but compensate for this by a high retention efficiency for small particles &GT0.1 um. Filtration rate . Respiration rate . Energy cost of growth . Net growth efficiency . Suspension feeding Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 128. Publication date: November 23, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Growth and energetics in the ascidian Ciona intestinalis

Rates of growth, filtration and respiration of the ascidian Ciona intestinalis (L.) were measured in the laboratory in the presence of food (flagellate Rhodomonas sp.) concentrations ranging from 0 to 12000 cells ml-' (0 to 500 pg C I-'). Weight-specific growth rate (dry weight of body parts not including the tunic) increased sigrnoidally with increasing algal cell concentration to 7.7 % d-' Maximum specific growth rate was related to age rather than size. A condition index (C1 = DWw@Wrotal) reflected level of growth. Specdic filtration rate decreased logarithmically with increased algal cell concentration. Weight-specific respiration rate showed a relation to algal cell concentration similar to that shown by weight-specific growth rate. All rates were transformed into units of carbon, and a carbon budget was established for 2 size groups. Assimilation efficiency (AE) was approximately 50% but decreased at the highest carbon concentrations. The amount of carbon assimilated per body unit that was needed to maintain body (not including the tunic) or total (including the tunic) carbon was independent of initial size and amounted to 10 or 16 pg C mg C' d' , respectively. Gross growth efficiency (GGE) and net growth efficiency (NGE) varied with food concentration and approached a level of 0.23 or 0.78, respectively, in terms of body carbon. In terms of total carbon, GGE was found to be 0.27 to 0.28 and NGE to be 0.79. Costs of maintenance were greater in the largest ascidians, while costs of body growth were equal in the 2 size groups (0.21 to 0.23).

Growth, metabolism and growth efficiency of a euphausiid crustacean Euphausia pacifica in the southern Japan Sea, as influenced by temperature

Growth (assessed from intermolt period and molt increment) and metabolism (oxygen con- sumption) of the post-larva of Euphausia pacifica from the southern Japan Sea were determined at seven graded temperatures ranging from 1 to 25°C. The intermolt period shortened progressively as temperature increased from 1 to 20°C, but an effect of temperature on molt-to-molt growth increment was not seen. Oxygen consumption rates were accelerated by the increase in temperature up to 20°C. Beyond 20°C, E.pacifica exhibited reduced oxygen consumption and died within 1 day without molting. After removing the effect of body size, the relationships between growth rate and temperature, and between oxygen consumption rate and temperature, were established. The carbon budget was calcu- lated as a function of temperature. Because of differential effects of temperature on growth and metab- olism, the net growth efficiency (K{. growth x 100/(growth + metabolism)) changed with temperature. The optimum temperature at which E.pacifica attained the maximum K2 was 11.4°C, which was derived from calculation of cumulative carbon invested in growth and metabolism in this animal. In an alterna- tive method, the optimum temperature was obtained mathematically by solving a set of differential equations. The biological and ecological significance of the optimum temperature which leads to the

Feeding, growth and respiration in the polychaetes Nereis diversicolor (facultative filter-feeder) and N. virens (omnivorous)-a comparative study

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 125:149-158 (1995) - doi:10.3354/meps125149 Feeding, growth and respiration in the polychaetes Nereis diversicolor (facultative filter-feeder) and N. virens (omnivorous)-a comparative study Nielsen AM, Eriksen NT, Iversen JJL, Riisgård HU The polychaetes Nereis diversicolor and N. virens were fed various amounts of shrimp meat in laboratory experiments and linear relationships between specific growth rate and specific respiration rates were found. From this relation the energy cost of growth ('specific dynamic action', SDA) was found to be 20 to 26% of the growth. The starvation respiration rate (maintenance) (Rm, ul O2 h-1 ind.-1) as a function of body mass (W, g dry wt) was: Rm = 1306W1.2 and Rm = 704W1.0 for N. diversicolor and N. virens, respectively. For worms fed shrimp meat the maximum specific growth rate was 7% d-1 in N. diversicolor and 5.9% d-1 in N. virens. In filter-feeding N. diversicolor fed algal cells (6.2 um diameter Rhodomonas sp.) there was a strong correlation between ingestion rate and growth rate, the maximum specific growth rate being 3% d-1. No functional response was seen even at the highest algal concentration of 2 x 104 cells ml-1. It is possible that filter-feeding in N. diversicolor is a relatively recent adaptation which has resulted in a broader fundamental niche compared to that of the closely related N. virens. This filter-feeding adaptation may possibly explain the coexistence of the 2 polychaetes in certain brackish water areas. Feeding . Growth . Respiration . Costs of growth . Specific dynamic action (SDA) . Net growth efficiency . Filter-feeding Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 125. Publication date: September 14, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

The physiology and biochemistry of diploid and triploid Manila clam ( Tapes philippinarum Adams & Reeve) larvae and juveniles

Triploidy was induced in fertilised eggs of the Manila clam [ Tapes philippinarum (Adams and Reeve)] at meiosis II. Growth rate, survival, food consumption, respiration rate and biochemical content of separate ploidy classes containing diploid or mainly (> 60%) triploid larvae and juveniles reared in the hatchery were compared and found to be similar. Newly formed D-larvae were 88–95 μm in length and became pediveligers after 15–17 days, when they had grown to 200–220 μm. Juveniles grew from 0.03 mg (mean dry weight) to 15 mg in 7 wk. Larval food consumption was described by the equation C= 0.577 × LW 0.587 (where C = organic weight of food cells consumed (μg·d −1) and LW = organic weight of larvae (μg). Juveniles consumed 0.76 μg·d −1 of food per μg organic weight. Lipid and carbohydrate reserves increased during larval growth to 17.5 and 7.5% of organic content, respectively. Lipid reserves were utilised during metamorphosis. In the juveniles, reserves remained constant at about 11% (lipid) and 7% (carbohydrate). The relationship between dry weight (W, mg) and oxygen consumption ( R, μg· d −1) of individual clams was described by R = 15.07 × W 0.638. Energy budgets for larval and juvenile Manila clams were calculated. Assimilation efficiency was high in the larvae (> 80%), and net growth efficiency increased with size and declining activity of the clams. The physiological and biochemical attributes of the clams were similar to those reported for other bivalve mollusc species. The results are discussed in relation to the apparent absence of recruitment of Manila clams in UK coastal waters.

Determination of optimal thermal conditions for growth of clam ( Venerupis pullastra) seed

The energy budget of Venerupis pullastra clam seed (3 mm) fed the microalga, Isochrysis galbana T-ISO, was calculated after acclimation at 10, 15, 20 and 25°C. Physiological measurements included ingestion rate, absorption efficiency, oxygen consumption and ammonia excretion. The effect of temperature on these rates was described. Ingestion rate was directly related to temperature up to a maximum at 20°C. Further temperature increase caused a slight decrease in ingestion. Absorption efficiency was not significantly influenced by the temperature, although maximum mean values were also found at 20°C. Both respiration and ammonia excretion rates were directly related to temperature over the whole experimental range, reaching their maxima at 25°C. For all the physiological rates measured the higher slopes in the rate/temperature lines occurred in the medium range of temperatures (15–20°C). The scope for growth (SFG) was positive at all temperatures and maximum at 20°C, chiefly as a consequence of the enhanced ingestion rate which offset the concomitant elevation in metabolic rates. Both gross and net growth efficiencies are also expected to be maximum at 20°C, which is, therefore, the thermal optimum for this species under the experimental conditions applied in our study. An acclimation strategy for this low-shore species within the range of thermal variation in its natural environment (10–20°C), maximizing SFG at high temperatures by enhancing ingestion rate, despite increased metabolic costs, is proposed.

Comparison of the scope for growth with the growth performance of Ostrea edulis seed reared at different food concentrations in an open-flow system

Oyster (Ostrea edulis L.) seed was reared on five rations of Isochrysis galbana Parke: 10, 30, 100, 200 and 300 cells μl-1, in an open-flow system. Physiological parameters such as clearance, ingestion, absorption and respiration rates were measured, and the scope for growth (SFG) calculated from these parameters was compared with actual growth over 20 d. Actual growth was negligible at 10 cells μl-1 (daily maintenance ration=2.5% organic wt) and maximum (growth rate=13.64 d-1) at 200 cells μl-1 (daily ration=43% organic wt), which also supported the maximum gross and net growth efficiencies (K1=50%, K2=85%). Ingestion rate was directly correlated to cell concentration up to maximum of ∼100 cells μl-1, but further increases failed to support higher ingestions. Absorption efficiency decreased with increasing algal concentration from 95% down to 60%. Due to the costs of growth, respiration rate significantly increased when food was added above maintenance levels; however, metabolic costs associated with feeding activity were undetectable. The scope for growth calculated from these physiological parameters agreed with the long-term growth performance, validating the physiological energetics method as a valuable tool for predicting long-term growth performance under constant environmental conditions.

Variations in larval growth and metabolism of an estuarine shrimp Palaemonetes pugio during toxicosis by an insect growth regulator

1. Exposure of the estuarine shrimp, Palaemonetes pugio, to a juvenile hormone analogue (⩾8 μg methoprene 1 −1) throughout larval development inhibited successful completion of metamorphosis. 2. Methoprene exposure retarded growth in early larval stages and postlarvae, but enhanced growth in premetamorphic larvae. 3. Respiration rates of early larvae were elevated by methoprene exposure, but not so older larvae or post larvae. 4. Lower net growth efficiency ( K 2 values) in methoprene-exposed early larvae suggests that increased metabolic demands reduced assimilated energy available for growth. 5. Modifications in O:N ratios of premetamorphic larvae and postlarvae suggest that methoprene altered substrate utilization patterns during metamorphosis.

Determinants of diet quality: the effects of diet pH, buffer concentration and buffering capacity on growth and food utilization by larvae of Manduca sexta (Lepidoptera: Sphingidae)

The growth of fourth-instar Manduca sexta larvae on nutrient-rich artificial diets is significantly affected by the characteristics of the buffer system present in the diet. An increase in diet buffer concentration or buffering capacity can cause decreases in total larval weight gain, relative growth rate, net growth efficiency and larval lipid content, and increases in the length of the instar, respiration rate, and the amount of assimilated food allocated to energy metabolism. We conclude that there is a significant metabolic cost associated with processing a diet with a high buffer concentration or buffering capacity. Within the pH range examined in this study (4.4–5.5), pH has a less pronounced effect on herbivore growth parameters, and presumably also on fitness, than do buffer concentration and buffering capacity. These results demonstrate that foliar buffer systems are potentially important determinants of the nutritional value of foliage to insect herbivores.

Diet‐switching by gypsy moth: effects of diet nitrogen history vs. switching on growth, consumption, and food utilization

AbstractGypsy moth (Lymantria dispar (L.) (Lepidoptera: Lymantriidae)) larvae were reared from hatch on 1.25% N or 3.5% N artificial diet (previous diet) and switched reciprocally to the other diet (current diet) after molting into the second, third, fourth, or fifth instar. The nitrogen concentration of food consumed during previous instars had a strong residual effect on the growth rate in subsequent instars when a diet switch was made during instars two through four, but did not affect growth rate of fifth‐instar larvae despite effects on food consumption and utilization. In early instars, larvae reared on 1.25% N artificial diet and then switched to 3.75% N diet had lower mass‐adjusted growth rates than larvae continuously reared on 3.75% N diet. Conversely, larvae reared on 3.75% N diet and switched to 1.25% N had higher mass‐adjusted growth rates than larvae reared continuously on 1.25% N diet. Relative to larvae previously reared on 1.25% N diet, fifth‐instar male larvae previously reared on 3.75% N diet had slightly lower consumption rates, higher net growth efficiency (ECD), and higher gross growth efficiency (ECI). Larvae previously reared on 3.75% N diet tended to have lower food assimilation efficiency (AD) and lower nitrogen assimilation efficiency (AD(N)). Although both previous and current diet nitrogen concentration strongly affected larval growth and food utilization, the interaction term between these was not significant for any response variables except ECD and ECI. Because the interaction term reflects the effect of switching per se, the results indicate that there was a metabolic cost associated with switching, but no inherent net cost or benefit of diet‐switching to growth.

The effect of dietary nicotine on the allocation of assimilated food to energy metabolism and growth in fourth-instar larvae of the southern armyworm, Spodoptera eridania (Lepidoptera: Noctuidae).

Dietary nicotine (0.5%), which is a substrate of the PSMO (polysubstrate monooxygenase) detoxification system in the southern armyworm Spodoptera eridania, has significant negative effects on the weight of food ingested, weight gained, relative growth rate (RGR), and efficiency of conversion of digested food (ECD) by fourthinstar S. eridania larvae on a nutrient-rich artificial diet. It has a significant positive effect on the weight of food respired by the larvae. Thus, the detoxification of nicotine by the PSMO system exacts a fitness cost and imposes a metabolic cost on S. eridania larvae. In contrast, dietary α-(+)-pinene, an inducer of the PSMO system, neither exacts a fitness cost nor imposes a metabolic cost on the larvae. We believe this to be the first study to demonstrate unequivocally that the negative effect of a dietary toxin on net growth efficiency (ECD) in an insect herbivore is due to an increase in the allocation of assimilated food to energy metabolism and not to a decrease in the amount of food assimilated. This study, therefore, supports the hypothesis that detoxification can impose a significant metabolic load on an insect herbivore. Implications of a corroboration of the metabolic load hypothesis are discussed.

Growth patterns, chemical composition and oxygen consumption in early juvenileHyas araneus (Decapoda: Majidae) reared in the laboratory

Early (instar I and II) juveniles of the spider crabHyas araneus were reared under constant conditions (12 °C, 32‰S) in the laboratory, and their growth, biochemical composition, and respiration were studied. Every second day, dry weight (W), ash-free dry weight (AFW), and contents of ash, organic and inorganic carbon (C), nitrogen (N), hydrogen (H), protein, chitin, lipid, and carbohydrates were measured, as well as oxygen consumption. Changes in the absolute amounts of W. AFW, and C, N, and H during the moulting cycle are described with various regression equations as functions of age within a given instar. These patterns of growth differ in part from those that have been observed during previous studies in larval stages of the same and some other decapod species, possibly indicating different growth strategies in larvae and juveniles. There were clear periodic changes in ash (% of W) and inorganic C (as % of total C), with initially very low and then steeply increasing values in postmoult, a maximum in intermoult, and decreasing figures during the premoult phase of each moulting cycle. Similar patterns were observed in the chitin fraction, reaching a maximum of 16% of W (31% of AFW). Ash, inorganic C, and chitin represent the major components of the exoskeleton and hence, changes in their amounts are associated with the formation and loss of cuticle material. Consequently, a high percentage of mineral matter was lost with the exuvia (76% of the late premoult [LPM] ash content, 74% of inorganic C), but relatively small fractions of LPM organic matter (15% of AFW, 11% of organic C, 5–6% of N and H). These cyclic changes in the cuticle caused an inverse pattern of variation in the percentage values (% of W) of AFW, organic C, N, H, and biochemical constituents other than chitin. When these measures of living biomass were related to, exclusively, the organic body fraction (AFM), much less variation was found during individual moulting cycles, with values of about 43–52% in organic C, 9–10% in N, 6–9% H, 31–49% of AFW in protein, 3–10% in lipid, and <1% in carbohydrates. All these constituents showed, on the average, a decreasing tendency during the first two crab instars, whereas N remained fairly constant. It cannot be explained at present, what other elements and biochemical compounds, respectively, might replace these decreasing components of AFW. Decreasing tendencies during juvenile growth were observed also in the organic C/N and in the lipid/protein weight ratios, both indicating that the proportion of lipid decreased at a higher rate than that of protein. Changes were observed also in the composition of inorganic matter, with significantly lower inorganic C in early postmoult (2–4% of ash) than in later stages of the moult cycle (about 9%). This reflected probably an increase in the degree of calcification, i.e. in the calcium carbonate content of the exoskeleton. As a fraction of total C, inorganic C reached maximum values of 17 and 20% in the crab I and II instars, respectively. The energy content of juvenile spider crabs was estimated independently from organic C and biochemical constituents, with a significant correlation between these values. However, the former estimates of energy were, on the average, significantly lower than the latter (slope of the regression ≠1). Since organic C should be a reliable integrator of organic substances, but the sum of protein, lipid, chitin, and carbohydrates amounted to only 60–91% of AFW, it is concluded that the observed discrepancy between these two estimates of energy was caused by energy from biochemical constituents that had not been determined in our analyses. Thus, energy values obtained from these biochemical fractions alone may underestimate the actual amount of organic matter and energy. Respiration per individual in juvenile spider crabs was higher than that in larval stages of the same species (previous studies), but their W-specific values of oxygen consumption (QO2) were lower than in conspecific larvae (0.6–2μg O2·[mg W]−1). QO2 showed a consistent periodic pattern in relation to the moult cycle: maximum values in early postmoult, followed by a rapid decrease, and constant values in the intermoult and premoult phases. This variation is interpreted as an effect mainly of cyclic changes in the amounts of cuticle materials which are metabolically inactive. From growth and respiration values (both expressed in units of organic C), net growth efficiency, K2, values may be calculated. In contrast to previous findings in larval stages, K2 showed an increasing trend during growth of the first two juvenile instars ofH. araneus.

Aboveground production and canopy dynamics in sugar maple and red oak trees in southwestern Wisconsin

Aboveground net primary production, canopy allometry, growth efficiency, and sapwood volume were compared for early- to mid-successional red oak (Quercusrubra L.) and late-successional sugar maple (Acersaccharum Marsh.) co-occurring in young and mature natural stands in southwestern Wisconsin. For similar-diameter trees, shade-tolerant sugar maple supported a significantly greater (p &lt; 0.05) stem, branch, and foliage biomass and leaf area than mid-tolerant red oak. Red oak and sugar maple had similar stem net primary production rates over a 5-year period (1984–1988), but sugar maple had a significantly greater total aboveground net primary production than similar-diameter red oak. However, red oak had a significantly greater (p &lt; 0.0001) growth efficiency (stem net primary production per unit of leaf area) than sugar maple. The significantly greater sapwood volume, but equal stem volume, of sugar maple versus red oak suggests that annual stem maintenance respiration costs may be greater for sugar maple than for red oak. Possible causes for differences in stem net primary production and growth efficiency between early- and late-successional tree species are discussed.

Energetics of growth and reproduction in cockles (Cerastoderma edule): Seasonal and age-dependent variations

Seasonal patterns of growth were compared interannually between 1983 and 1985 for different ageclasses of an intertidal population of cockles,Cerastoderma edule L., in the Mundaka Estuary (Basque Country, North Spain). Growth data and simultaneous determinations of respiratory metabolism were integrated over defined periods of time in order to compute assimilation and net growth efficiency. Consistent differences between the exponents that scale both assimilation and metabolism to body size led to growth efficiency values that were a decreasing function of age. Total growth was partitioned into three components: somatic growth, reproductive output and reserve storage, and the corresponding effort indexes were calculated. Despite important differences in total growth, reproductive output was constant between years, indicating a higher reproductive effort under poorer growth conditions. Increased costs of reproduction that appeared to be associated with this higher reproductive effort did not affect somatic maintenance, since previously stored carbohydrate reserves were primarily used to fuel gametogenesis.

Photosynthetic responses and daily carbon balance ofColpomenia peregrina: Seasonal variations and differences between intertidal and subtidal populations

The seasonal photosynthetic responses and daily carbon gain of upper intertidal, low intertidal and subtidal (3 to 4 m depth) populations ofColpomenia peregrina were examined over a 2 yr period (1986–1988) in Santa Catalina Island, California, USA. The populations showed significant differences in their photosynthetic responses, daily carbon balance and carbon-specific growth rates when normalized to tissue area or to chlorophyll content. The substantial plasticity with respect to photosynthetic responses shown byC. peregrina is considered to be an important factor in facilitating the colonization of both intertidal and subtidal habitats. This species appears to have a cellular carbon metabolism influenced by responses to season and tidal elevation. Highest net daily carbon balance, predicted carbonspecific growth rates and net growth efficiency were achieved in upper intertidal habitats during summer. These parameters decreased in winter and progressively declined with increasing depth as plants become increasingly exposed to low-light regimes. The diminishing net daily carbon balance and predicted carbon-specific field growth rates found during winter suggest that standing stock and lower subtidal limits of distribution ofC. peregrina are at least partly controlled by these two factors.

Energy flux in a natural population of the land snail Eobania vermiculata (Müller) (Gastropoda: Pulmonata: Stylommatophora) in Greece

Survivorship, production, mortality rate, consumption rate, assimilation, and growth and ecological efficiencies were studied in a natural population of the land snail Eobania vermiculata in Greece. Eobania vermiculata may take 5 years or more to reach maximum size (33 mm). Mortality rate and life expectancy decreased with age. Net reproductive rate was 3.4 and per capita rate of increase was 1.0. Energy flux in E. vermiculata was studied using Urtica dioica and Lactuca sativa as food. The highest daily consumption and assimilation rates (weight specific) were observed in newly hatched animals and the lowest in adults. Assimilation efficiency, mean monthly production, and gross growth and ecological or net growth efficiencies fluctuated with the season and the physiology of the snails. Snails fed U. dioica showed higher assimilation, gross growth, and net growth efficiencies than those fed L. sativa. Energy flow through the E. vermiculata population was 78.9 cal∙m−2∙year−1 (1 cal = 4.1868 J), mean assimilation efficiency was 52% if the snails were fed U. dioica only, and the ingestion rate was 19.5%. When E. vermiculata was fed U. dioica during its lifetime, 4.26% of the total assimilated energy was used for egg production, 10.2% for growth, and 87.8% for metabolic energy. Annual secondary production gave a mean adult density of 4.1 individuals/m2, a mean annual standing crop (biomass) of 6.8 g∙m−2, and an annual production of 13.9 ± 1.8 g∙m−2 or 2859.5 mg C∙m−2. The annual turnover ratio, or productivity rate constant, was 2.0.