Life cycles and growth rates of Baetis spp. (Ephemeroptera: Baetidae) in the laboratory and in two stony streams in Austria

SUMMARY. Larvae of Baetis alpinus, B. lutheri and B. rhodani were reared in a stream channel (water temperature range 4.2–11.4°C) in the laboratory. The larval growth was exponential and the mean specific growth rate varied from 1.93 to 2.24% day^?1 for B. alpinus, 1.49 to 3.41% day^?1 for B. lutheri and 0.79 to 3.11% day^?1 for B. rhodani. These variations in growth rate were related to variations in mean temperature and this was the major factor affecting growth in the laboratory. Non-quantitative samples of the benthos in the Seebach and Unterseebach, two stony streams near Lunz, Austria, were taken at approximately monthly intervals from November 1965 to May 1968. In each year, there were two winter and three summer cohorts for B. alpinus from Seebach and two or three winter and one to three summer cohorts for B. lutheri and B. rhodani from Unterseebach. Over the study period of 30 months, eleven cohorts were recorded for B. alpinus and B. lutheri, and ten cohorts for B. rhodani. The life cycle of a cohort varied from 3 to 8 months in B. alpinus, from 2.5 to 9 months in B. lutheri and from 2.5 to 8 months in B. rhodani. Mean specific growth rate in length varied from 0.82 to 2.97% day^?1 for B. alpinus, 0.96 to 3.33% day^?1 for B. lutheri and 0.65 to 3.01% day^?1 for B. rhodani. The percentage of the variability in growth rate accounted for by variations in mean temperature was 63% for B. alpinus, 91% for B. lutheri and 82% for B. rhodani. Therefore mean temperature was clearly the major factor affecting the growth rates in the field. An agreement was found between the growth rates of B. alpinus in the field and the laboratory. The growth rates of B. lutheri and B. rhodani were slower in the field than in the laboratory at higher temperatures. The possible reasons for this latter discrepancy are discussed, and the growth rates of the three Baetis spp. are compared with those of other species of Ephemeroptera.     

Feeding and growth of Asellus aquaticus (Isopoda) on food items from the littoral of Windermere, including green leaves of Elodea canadensis

SUMMARY. In the laboratory, Asellus aquaticus devoured intact green leaves from growing shoots of the aquatic macrophyte Elodea canadensis. In four collections of A. aquaticus on Elodea in a lake (Windermere), c. 20% of the specimens contained in their guts fragments of green Elodea leaves; this material and pieces of oak (Quercus) were identified from characteristic leaf hairs. Some specimens had also eaten the filamentous alga Oedogonium. Fluorescence microscopy is a useful aid for screening invertebrates that may have eaten living plant tissues. Immature A. aquaticus, with an initial mean body length of c. 3 mm, wet weight c. 1 mg, were grown through sexual maturity over a 49-day period at 15°C in a series of twenty-two experiments (six to twelve isolated specimens in each experiment) comparing growth rates on different foods, including instances where no food was given. Animals were fed on a variety of items collected from the littoral of Windermere, plus some laboratory cultures of algae and bacteria. The highest mean specific growth rate (5.8% day^?1) was obtained on young Elodea leaves mechanically shaken to remove epiphytes. Other diets yielding fast growth rates (3.7–5.3% day^?1) were young growing leaves of Elodea with few epiphytes and older green and brown living leaves covered with a thick growth of epiphytic algae, epiphytic algae removed from Elodea, plastic imitation Elodea immersed in the lake until covered with attached algae, epilithic algae on stones, Oedogonium, and decaying oak leaves. Slower growth (1.3–2.2% day^?1) and poorer survival was obtained on the following: a pure culture of the bacterium Sphaerotilus natans; cultured bacteria from lakewater; the filamentous algae Cladophora and Stigeoclonium both with and without epiphytes; faecal matter from Asellus; freshly killed Asellus; lake sediment. Some growth (mean = 0.7% day^?1) and 50% survival for 21 days occurred in ‘starved’ animals kept in filtered, sterilized lakewater. Better survival and slightly faster growth (1.0–1.5% day^?1) occurred in ‘starved’ animals kept in filtered and unfiltered lakewater. Growth of A. aquaticus was also experimentally determined from birth in animals fed on young green Elodea leaves and on decaying oak leaves. On both diets, growth was curvilinear and approximately exponential from birth to sexual maturity reached at c. 2mg wet weight in 46–60 days at 15°C. In older specimens the relative growth rate gradually fell over a period of 50 days, representing a more linear phase of growth during sexual maturity.     

Growth of migrating and non-migrating cryptophytes in thermally and chemically stratified experimental columns

• 1 Growth rates of migrating and non-migrating populations of two strains of freshwater cryptophytes, CCAP 979/67 and 979/62, under different light and nutrient regimes were calculated from experiments conducted in laboratory columns which were thermally stratified. During the experiments, cellular carbon, nitrogen, phosphorus, carbohydrate and protein were also analysed. The intention was that the populations would become either phosphorus- or nitrogen-depleted following a period of growth.
• 2 In all experiments, populations of cryptophytes grew but growth appeared of short duration. In a phosphorus depletion experiment with Cryptomonas 979/67, there was a period of rapid growth starting on day 2 and finishing on day 8, during which the estimated growth rate was c. 0.9 div. day^-1. In a nitrogen depletion experiment, the period of rapid growth of C. 979/67 lasted only for 2–3 days with a growth rate of c. 0.85 div. day^-1.
• 3 In a phosphorus depletion experiment with C. 979/62, the onset of a period of rapid growth coincided with the commencement of diel vertical migration. The highest growth rate was estimated as c. 1.0 div. day^-1. In a nitrogen depletion experiment, C. 979/62 did not migrate and attained a growth rate of only 0.28 div. day^-1.
• 4 For C. 979/67 the highest observed growth rate was lower than the maximum potential growth rate of 1.38 div. day^-1 estimated in batch culture. For C. 979/62 the maximum growth rate in the column was similar to the maximum potential growth rate of 0.87 div. day^-1 in batch culture experiments.
• 5 The results suggest that some migrating cryptophytes under favourable conditions in stratified water columns can attain high growth rates supporting the hypothesis of Raven & Richardson (1984) that, based on cost-benefit analysis, diel vertical migrations could increase the growth rate of flagellates. Such growth appears of short duration and its ecological importance still requires further verification.

     

Effects of diet, body size, age and temperature on growth rates in the amphipod Gammarus pulex

SUMMARY. Increase in body wet weight of Gammarus pulex fed on decaying elm leaves was followed to senescence and death. Growth in juveniles was approximately exponential; from birth to death it conformed to a logistic growth curve, with maximum absolute increments in weight about half-way through a life span of 350–450 days at 15°C. Some individuals lived longer, for up to 640–700 days. The instantaneous or specific growth rate was maximal near birth, at c. 5–6% wet wt day^?1, and declined exponentially with increasing size and age. Over the range 4.7–14.8°C there was a log-log relationship between temperature and specific growth rate. Growth was maximal at 20°C in newborn animals and at 15°C in 6–9-mg animals. The specific growth rate of young individuals was fastest on decaying leaves of elm with a well developed flora of fungi and other microorganisms. Leached elm leaves without this flora supported growth at a lower rate. The latter diet was sufficient for survival and growth of newborn individuals; detritus, faeces or other food items were not needed. Isolated specimens grew as fast as those kept in groups. Growth was generally slower on leached leaves of oak and sycamore. In newborn animals fed on the fine roots of aquatic plants (Veronica, Rorippa and Glyceria), growth was as fast as on decaying elm leaves; growth on the green living leaves of the plants was slower, as on detritus from two streams and on a pure culture of an aquatic fungus. Consumption of leached elm leaves was related to leaf thickness. In a full gut the wet weight (1.34–1.37 mg) and volume (3.8–4.1 mm³) (for 20-mg animals) was independent of leaf thickness but dependent on animal size, increasing 4-fold over the range 2–50 mg body wt. Daily consumption (dry wt) was approximately equivalent to 50% body dry wt at 5 mg and 20% at 50 mg body wet wt. Individuals fed on thick leaves ingested 50% more dry weight per day and absorbed more in the gut than when fed on thin leaves, but the relative efficiency of absorption was the same at 36–59% for 10–20-mg animals. Weight-specific absorption in the gut was highest in juveniles and decreased with increasing body weight; relative efficiency of absorption was generally lower in the larger individuals. Assuming an energy value of 5 cal mg^?1 dry wt for elm leaves, daily mean energy intake by absorption in thegutof G. pu/ex was2.2 cal mg^?1 animaldry wt (9.2 J mg^?1) in individuals of 0.4 mgdry wt (2 mg wet wt), decreasing to 0.3 cal mg^?1 (1.3 J mg^?1) at 10 mg dry wt (50 mg wet wt). Growth in Gammarus is briefly reviewed in the hght of work on other animals and it is emphasized that all aspects of feeding, growth and metabol-ism should be specifically related to size and age of the individuals, using well defined diets.     

The use of the chemostat to study the relationship between cell growth rate, viability, and the effect of interferon on L 1210 cells

Mouse leukemia L 1210 cells were cultivated in the chemostat at growth rates ranging from 0.1 day⁻¹ (population doubling time (T_d) 166.3 h) to 2.0 day⁻¹ (T_d 8.3 h). At growth rates of 1.0 day⁻¹ and above, the viability of the steady-state culture was greater than 99%. However, below 1.0 day⁻¹ there was a progressive decrease in the viability of the culture with decreasing growth rate until a minimum growth rate (0.1 day⁻¹) was reached below which steady-state cultures of L 1210 cells could not be established. Interferon treatment had no effect on the viability (>99%) of L 1210 cells cultivated at fast growth rates in the chemostat, whereas at slow growth rates (0.35 day⁻¹) interferon treatment markedly reduced the viability of the culture, even though the percentage increase in the doubling time of interferon-treated cultures was the same for cells cultivated at both fast and slow growth rates. Thus, although interferon is not directly cytotoxic, it can cause cell death by reducing the rate of cell multiplication below the minimum value compatible with viability.     

Growth Kinetics of Microbacterium lacticum and Nitrate-Dependent Degradation of Ethylbenzene under Anaerobic Conditions

A pure strain of Microbacterium lacticum DJ-1 capable of anaer-obic biodegradation of ethylbenzene was isolated from soil contaminated with gasoline. Growth of the strain and biodegradation of ethylbenzene in batch cultures led to stoichiometric reduction of nitrate. M. lacticum DJ-1 could degrade 100 mg L^?1 of ethylbenzene completely, with a maximum degradation rate of 15.02 ± 1.14 mg L^?1 day^?1. Increasing the initial concentration of ethy-lbenzene resulted in decreased degradative ability. The cell-specific growth rates on ethylbenzene conformed to the Haldane–Andrew model in the substrate level range of 10–150 mg L^?1. Kinetic parameters were determined by nonlinear regression on specific growth rates and various initial substrate concentrat-ions, and the values of the maximum specific growth rate, half saturation constant, and inhibition constant were 0.71 day^?1, 34.3 mg L^?1, and 183.5 mg L^?1, respectively. This is the first report of ethylbenzene biodegradation by a bacterium of Microbacterium lacticum under nitrate-reducing conditions.     

Fish as sources and sinks of nutrients in lakes

1. The release of total phosphorus (TP) and nitrogen (N in ammonium) was measured for the five most abundant fish species (>85% of biomass) in Mouse and Ranger Lakes, two biomanipulated, oligotrophic lakes in Ontario. 2. The specific release rate of both nutrients was significantly related to fish mass; log₁₀ TP release rate (μg h^?1) = 0.793 (±0.109) [log₁₀ wet mass (g)] + 0.7817 (±0.145), and log₁₀ N release rate (μg h^?1) = 0.6946 (±0.079) [log₁₀wet mass (g)] + 1.7481 (±0.108). 3. When fish nutrient release was standardized for abundance (all populations, 1993–95) and epilimnetic volume, fish were estimated to contribute 0.083 (±0.061) μg TP L^?1 day^?1, and 0.41 (±0.17) μg N L^?1 day^?1 in Mouse L., and 0.062 (±0.020) μg TP L^?1 day^?1 and 0.31 (±0.08) μg N L^?1 day^?1 in Ranger L. 4. In comparison, concurrent rates of total planktonic P regeneration were 1.02 (±0.45) μg L^?1 day^?1 (Mouse L.) and 0.85 (±0.19) μg L^?1 day^?1 (Ranger L.). Fish represented 8% of planktonic P release in Mouse L. and 7% in Ranger L. 5. Fish dry mass had mean elemental body compositions of 39.3% carbon, 10.9% nitrogen, and 4.0% phosphorus (all fish combined), with a mean molar C : N : P ratio of 27 : 6 : 1. This comprised about 55% and 23% of the total epilimnetic particulate P and N respectively. 6. Turnover times of P and N in fish were approximately 103 and 48 days respectively. In comparison, planktonic turnover times of particulate P in Mouse and Ranger Lakes were 4.3 and 4.4 days respectively. Given their high P content and low turnover rates, fish appear to be important P sinks in lakes.     

Kinetics of growth, oxygen uptake, and substrate utilization of wild type and genetically engineeredBurkholderia sp

The gene (vgb) encoding the hemoglobin (VHb) ofVitreoscilla sp. was cloned intoBurkholderia sp. and the effect of VHb on the growth characteristics of genetically engineeredBurkholderia (YV1) were compared with wild typeBurkholderia (R34) using continuous flow reactors (chemostat) at various dilution rates under aerobic conditions. Batch oxygen uptake rate showed that YV1 has much higher oxygen uptake rate than R34 (i.e. 0.63 mg O₂/g biomass/min vs. 1.43 mg O₂/g biomass/min for R34 and YV1 respectively at a dilution rate of 1.2 day⁻¹). Monod parameters, maximum growth rate (μ_max) and half saturation coefficient (K_s) were found to be 7.03 day⁻¹ and 691 mg/L for R34 respectively, compared to 5.49 day⁻¹ and 404 mg/L for YV1 respectively. At low dilution rates (<2.5 day⁻¹), when the substrate is present in low concentrations, the growth yield was much higher in YV1 (0.52) than in R34 (0.37). Although substrate utilization rates were similar between R34 and YV1, the latter showed much higher oxygen uptake rate than did R34 at all dilution rates. When the stability of VHb was tested on agar plates containing 40 μg/L of kanamycin and 100 μg/L of ampicillin,vgb gene containing VHb plasmid in YV1 was stable over 82 days. When survivability under oxygen limited conditions was tested, R34 survived only for 11 days whereas YV1 survived over 25 days in liquid media; in agar plate experiments, R34 did not survive more than 40 days whereas more than 75% of YV1 survived over 110 days.     

Development,Reproduction and Growth Pattern of two Coexisting,Pond Dwelling Cladocerans

Laboratory investigations on life history parameters of 2 coexisting cladocerans (Daphnia obtusa. Moina brachiata) from a nearly temporary pond in South Germany revealed that the species have different temperature tolerances and temperature optima. D. obtusa experienced the highest reproductive success at 15 and 20 °C and was able to survive and to reproduce at 2 °C but died at 30 °C. The reproductive success of M. brachiata was highest at 25 and 30 °C and the species could not withstand temperatures <15 °C and ≥35 °C. At temperatures between approximately 20 and 25 °C, where both cladocerans coexisted in nature, M. brachiata showed a faster population growth due to its approximately twofold higher egg production rates (10–12 eggs female⁻¹ day⁻¹ compared to approximately 5 eggs female⁻¹ day⁻¹ in D. obtusa) and its shorter juvenile development (3.3 and 2.4 days compared to 6.3 and 5.3 days in D. obtusa); M. brachiata needs generally only 3 molts to reach maturity while D. obtusa requires 5–6 molts.     

AUTOLYSIS KINETICS OF THE MARINE DIATOM DITYLUM BRIGHTWELLII (BACILLARIOPHYCEAE) UNDER NITROGEN AND PHOSPHORUS LIMITATION AND STARVATION1

Autolysis kinetics in axenic cultures of the diatom Ditylum brightwellii (West) Grunow were studied under nutrient limitation in continuous cultures and under nutrient starvation in batch-mode cultures obtained by switching off nutrient supply in the continuous cultures. Under N limitation, the specific algal autolysis rates (δ, day^?1) were found constant at 0.014 ± 0.002 day^?1over a broad range of specific dilution rates (D, day^?1) (0.09–0.56 day^?1), implying an intrinsic death factor independent of the physiologzc state of the algal cells. Under P limitation, 8 was inversely related to D and ranged between 0.067 and 0.005 day^?1 at D = 0.17–0.44 day^?1. Under conditions of nutrient stamation, the degree of algal nutrient deficiency prior to stamation affected autolysis rates (δ_b, day^?1) and subsequently survival of the algal cultures. Nitrogen-starved D. brightwellii showed highest δ_b (maximum, 0.10 day^?1) when precultured at the higher growth rates. Phosphorus stamation led to highest δ_b (maximum, 0.21 day^?1) in the cultures preconditioned at the lower steady state growth rates. The lower death rates for D. brightwellii under limitation and starvation of N compared to P suggest that D. brightwellii was better equipped to handle N than P deficiency. The present results showed that cell lysis induced by nutrient stress was a significant cause of mortality in D. brightwellii and provided more insight into the field distribution of this neritic diatom.     

N- and P-addition inhibits growth of rich fen bryophytes

A greenhouse experiment was set up to investigate if infrequently and frequently occurring species respond differently to simulated habitat changes. Two frequently occurring (Bryum pseudotriquetrum and Calliergonella cuspidata) and two infrequently occurring (Hamatocaulis vernicosus and Paludella squarrosa) rich fen bryophytes were grown in mixed culture and subjected to rainwater or groundwater and three levels of N, ammonium nitrate (0, 1 and 3?mg?N?L^–1) and P, potassium phosphate (0, 0.05 and 0.1?mg?P/L). All species responded negatively to higher N-levels and three of the four species responded negatively to rainwater and higher P-levels. C. cuspidata had highest relative growth rate (RGR) in all treatments, and the infrequently occurring species had lower RGR and were more negatively affected by high levels of N than the frequently occurring species. A negative effect of rainwater seemed to be caused by higher background levels of N in rainwater compared to groundwater. We found a negative effect of high initial bryophyte density in three of the four species indicating density-dependent inhibition between species. We suggest that maintenance of oligotrophic conditions by recharge of nutrient-poor groundwater is vital for conservation of infrequently as well as frequently occurring rich fen bryophytes.     

Structure and grazing impact of the protozooplankton community in the waters surrounding the Prince Edward Islands (Southern Ocean)

Fish <1 year old were sampled during 1 year using nets inshore at South Georgia. Some fish were kept in aquaria. Growth rates were estimated using the exponential model. During June to October 1980, field growth rates of Parachaenichthys georgianus and Champsocephalus gunnari were 0.33 and 0.48% SL day⁻¹, respectively. Gobionotothen marionensis (1979 cohort) grew at 0.40% SL day⁻¹ during June to November in the field, and 0.34% SL day⁻¹ in the laboratory from September to March. Notothenia coriiceps grew at 0.28% SL day⁻¹ in the laboratory during September to March. During November to December, Artedidraco mirus grew at 0.82% SL day⁻¹ in the field. The 1980 cohort of G. marionensis grew at 1.39% SL day⁻¹ during November to January in the field. During January, the field growth rate of G. gibberifrons was 1.39% SL day⁻¹. Growth rates increased three-fold from winter to summer. Temperature can only explain one-half of this range in growth rates, whereas all of this range can be explained by food availability. Therefore, seasonal food resource limitation has a major effect on Antarctic fish growth. Received: 30 June 1997 / Accepted: 7 September 1997     

Food consumption and growth of larvae and juveniles of three cyprinid species at different food levels

Synopsis The relationships between food availability, consumption and growth were analyzed from the onset of feeding to an age of 90 days in three cyprinid species. Fish were held at 20 ± 0.5° C and given two (three) constant rations of approximately 30, (40) or 100% dry body weight (dbw) ind^-1 day^-1. Food consisted of living zooplankton, the size of which correlated with fish size. At high food densities consumption rates decreased rapidly with fish size in all three species. At reduced rations, fish consumed most of the food offered until they were larger than 10 mg dbw. In all species and at each feeding level daily rations consumed increased allometrically with body size. Respiration rate, expressed as routine metabolic rate differed insignificantly between the three species. At high ration levels, growth rates of small bleak, Alburnus alburnus, were distinctly lower than those of roach, Rutilus rutilus, and blue bream, Abramis ballerus. At low food supply all three species grew at similar rates. Assimilation efficiency at low food conditions was approximately twice that of the well-fed groups. If the caloric equivalents of oxygen consumption as measured in well-fed fish are applied to fish fed at low rations their energy budgets do not balance. This indicates the limitations of fish larvae in the partitioning of energy for growth or activity at such conditions.     

Light effects on leaf development and photosynthetic capacity of Hydrocotyle bonariensis Lam.

Rates of net CO₂ uptake were examined in developing leaves of Hydrocotyle bonariensis. Leaves that developed under high photosynthetically active radiation (48 mol m^-2 day^-1 PAR) were smaller, thicker, and reached maximum size sooner than did leaves that developed under low PAR (4.8 mol m^-2 day^-1). Maximum net CO₂ uptake rates were reached after 5 to 6 days expansion for both the low and the high PAR leaves. Leaves grown at high PAR had higher maximum photosynthetic rates and a higher PAR required for light saturation but showed a more rapid decline in rate with age than did low PAR leaves. To assess the basis for the difference observed in photosynthetic rates, CO₂ diffusion conductances and the mesophyll surface available for CO₂ absorption were examined for mature leaves. Stomatal conductance was the largest conductance in all treatments and did not vary appreciably with growth PAR. Mesophyll conductance progressively increased with growth PAR (up to 48 mol m^-2 day^-1) as did the mesophyll surface area per unit leaf area, but the cellular conductance exhibited most of its increase at low PAR (up to 4.8 mol m^-2 day^-1).     

Development and application of a nutrient-diffusing bioassay for large rivers

1. Laboratory and field experiments were performed to develop and then apply a nutrient-diffusing substratum (NDS) design suitable for use in large, fast-flowing rivers. 2. Initial laboratory experiments quantified diffusion of PO₄ and NO₃ from new and previously used clay pots, which were soaked in deionized distilled water. Mean release rates initially exceeded 2.4 and 725 μmol l^–1 day^–1 P and 0.22 and 18 μmol l^–1 day^–1 N from new and used pots, respectively, but declined rapidly with increasing time spent in deionized distilled water and were below detectable levels after about 18 and 29 days, respectively. 3. A phosphorus (P) dose–response experiment in a P-limited reach of the Athabasca River, Alberta, Canada showed that epilithic biomass and macroinvertebrate density on NDS increased with increasing concentrations of KH₂PO₄ up to about 0.5 m . Beyond this threshold, biomasses and densities were unaffected by initial KH₂PO₄ concentration. Coefficients of variation of epilithic biomass estimates declined with increasing KH₂PO₄ whereas invertebrate density appeared to be unaffected by KH₂PO₄ levels. 4. Release rates of both P and N from NDS filled with 0.5 m KH₂PO₄ or 0.5 m NaNO₃ declined at a log-negative rate from about 5000 μmol N-NO₃ l^–1 day^–1 and 3500 μmol P-PO₄ l^–1 day^–1 on day 2, to 200 μmol l^–1 day^–1 for both N and P on day 32. 5. After development, we used the diffusing substrata to identify spatial patterns in nutrient limitation at seven sites along a 120 km reach in the Athabasca River, that receives two known point-source nutrient inputs. NDS consisting of N, P, N + P and unenriched controls were attached to the river bottom for 22–23 days and then retrieved and sampled for epilithic chlorophyll a. Physicochemical parameters and epilithic biomasses on upper stone surfaces were also quantified when NDS were deployed and retrieved from each site. 6. Sites located immediately downstream of the two point source inputs had higher water column concentrations of PO₄ and epilithic biomasses than the site immediately upstream; epilithic biomass was positively related to PO₄ in the late autumn (r²⁼ 0.58) but not in early autumn. Sites located immediately below nutrient inputs were not nutrient-limited, whereas upstream reference sites were P-limited.     

Growth and loss of mariculture kelp Saccharina japonica in Sungo Bay, China

The aim of this study was to understand the growth dynamics of Saccharina japonica (previously known as Laminaria japonica), particularly the portion lost during its growth cycle and the key factors that control loss rate in Sungo Bay, China. Growth and loss of S. japonica were investigated between January and July 2010 in Sungo Bay. Losses of the seaweed are typically the result of three factors: removal of the entire individual from mariculture ropes (falloff), breakage in sections of the thalli (breakoff), and erosion of distal tissue. Results showed that individual growth rates in wet weight ranged between 2.4 and 32.7 g day^?1. The total falloff rate was approximately 16% and took place during January and February. Breakoff rate showed a significant positive correlation with kelp length and took place during June and July. The erosion rate increased significantly from January to the end of April, reaching a maximum value of 20.4 g day^?1 on 25 April, and maintained a relatively higher value following the peak value (approximately 10–15 g day^?1). Erosion rates were positively correlated with temperature (r?=?0.787, n?=?23, p?<?0.01) before May; however, they were not significantly correlated with temperature from May to July (p?=?>0.05). There was no significant relationship between erosion and transparency. At the end of this experiment, the ratio of total loss of carbon and nitrogen to gross production was 61% and 54%, respectively. Loss from distal erosion, falloff, and breakoff in carbon was 91.5, 4.2, and 4.3%, respectively. In Sungo Bay, the annual gross production and total loss in carbon and nitrogen were estimated to be 58,652 t C and 3,506 t N, and 36,150 t C and 1,920 t N. This is expected to have a significant impact on the detritus available in the food chain.     

PATTERNS OF RELATIVE GROWTH IN NEREOCYSTIS LUETKEANA (PHAEOPHYTA)1

Plants of Nereocystis luetkeana (Mert.) Post. et Rupr. of different sizes were held on a raft at the surface of the sea off the Friday Harbor Laboratories, San Juan Island, Washington for 5 day periods for observation of detailed relative growth of different parts. Each stipe was marked at intervals with injected Indian ink and each blade was punched with a series of holes. Measurements of diameter, length, width and thickness were made before and after the 5 day periods. Blades showed a very similar pattern of relative growth rate (R) over an 18-fold range of sizes. The maximum local R in length was about 0.2 day⁻¹ and occurred at 6.5% of the distance from the bulb to the tip, declining to 0.01 at half way. Half the linear growth occurred in the proximal one tenth of the blade and 95% within the proximal half. The relative growth rate of the whole blade declined only slightly with increased size and lay between 0.0.3 and 0.06 day⁻¹ (approx. 3–6% day⁻¹). The linear growth rate therefore increased with blade size, the maximum observed being 14 cm day⁻¹. The maximum relative growth rate in blade width was slower, and sited more distally than that in length. Unless fertile tissue was involved all blade tissue, except that closely adjoining the bulb, became thinner during growth. R in volume reached 0.3 day⁻¹. Presumably because the plants were held near the sea surface stipes grew slowly, with a maximum linear rate of 9 mm day⁻¹. The maximum R in length decreased with stipe length. Bulb R in volume also decreased as size increased, from a maximum of 0.3 day⁻¹.     

ACTIVE GROWTH OF THE OCEANIC DINOFLAGELLATE CERATIUM TERES IN THE CARIBBEAN AND SARGASSO SEAS ESTIMATED BY CELL CYCLE ANALYSIS1

The growth rate of an oceanic dinoflagellate, Ceratium teres Kofoid, was investigated in the Sargasso and Caribbean Seas from September 1989 to July 1990 using the cell cycle analysis method. Estimated growth rates ranged from 0.29 to 0.58 day^?1 and were 1.5–7.2 times higher than generally accepted rates for oceanic dinoflagellates. The higher rates in this report were mainly due to an improvement in techniques that determine the duration of a terminal cell cycle phase in situ. The day-to-day variation in growth rates was surprisingly small, but, from long-term measurements, a weak correlation was found among temperature, daily irradiance, and seasonal growth rate. The calculated species-specific primary production ranged from 0.5 to 1.8 mg C·m^?2·day^?1, about 1% of the estimated total production. Ceratium teres may be an important carbon source at the base of the grazing food chain.     

How<Emphasis Type="Italic"> Daphnia</Emphasis> copes with excess carbon in its food

Animals that maintain near homeostatic elemental ratios may get rid of excess ingested elements from their food in different ways. C regulation was studied in juveniles of Daphnia magna feeding on two Selenastrum capricornutum cultures contrasting in P content (400 and 80 C:P atomic ratios). Both cultures were labelled with ¹⁴C in order to measure Daphnia ingestion and assimilation rates. No significant difference in ingestion rates was observed between P-low and P-rich food, whereas the net assimilation of ¹⁴C was higher in the treatment with P-rich algae. Some Daphnia were also homogeneously labelled over 5 days on radioactive algae to estimate respiration rates and excretion rates of dissolved organic C (DOC). The respiration rate for Daphnia fed with high C:P algae (38.7% of body C day^-1) was significantly higher than for those feeding on low C:P algae (25.3% of body C day^-1). The DOC excretion rate was also higher when animals were fed on P-low algae (13.4% of body C day^-1) than on P-rich algae (5.7% of body C day^-1) . When corrected for respiratory losses, total assimilation of C did not differ significantly between treatments (around 60% of body C day^-1). Judging from these experiments, D. magna can maintain its stoichiometric balance when feeding on unbalanced diets (high C:P) primarily by disposing of excess dietary C via respiration and excretion of DOC.