Combined effects of heavy metal (Hg) concentration and algal (Chlorella vulgaris) food density on the population growth of Brachionus calyciflorus (Rotifera: Brachionidae)

The combined effects of two food levels (0.5 x 10(6) and 1.5 x 10(6) cells ml(-1) of Chlorella vulgaris) and five concentrations (0, 0.000625, 0.00125, 0.0025, 0.005 mg l(-1) of HgCl2) of mercury on the population growth of the rotifer Brachionus calyciflorus was evaluated. The growth experiments were conducted for 18 days at 23+/-1 degrees C under continuous fluorescent illumination. For each food level - heavy metal combination, we maintained 3 replicates. Our data showed that regardless of food level, increase in the heavy metal concentration in the medium resulted in decreased population growth of B. calyciflorus. At any given heavy metal concentration, B. calyciflorus grown under higher food levels had higher population abundance. The rate of population increase was significantly influenced by both the heavy metal concentration and the algal level. The highest population growth rate (0.435+/-0.003 per day) was observed in controls at 1.5 x 10(6) cells ml(-1). The results of this study were discussed in relation to the protective role of algal density against heavy metal toxicity.     

Population dynamics of the tropical cladoceran Ceriodaphnia rigaudi Richard, 1894 (Crustacea: Anomopoda). Effect of food type and temperature

The knowledge of population effects of food on tropical, filter-feeding cladocerans is scarce because a reduced number of species has been extensively studied. Ceriodaphnia rigaudi Richard 1894, a small-sized cladoceran distributed mainly in tropical and subtropical regions of the world, was studied. The aim of this study was to contribute to the knowledge of the reproductive biology of a poor-known Cladoceran; for this we assessed the effect of feeding and temperature on the reproduction and life cycle of this species. Three microalga species (Pseudokirchneriella subcapitata, Ankistrodesmus falcatus, and Chlorella vulgaris) were supplied as food each at a concentration of 12 mg l(-1) (dry weight, equivalent to 1.3 x 10(6), 0.4 x 10(6) and 1.35 x 10(6) cell m1(-1), respectively, and equivalent to 7.8 microg C ml(-1), at two temperatures (20 and 25 degrees C). We evaluated, among other responses, longevity, total progeny, survival, life expectancy at birth and fecundity. Organisms fed with the microalgae A. falcatus and P subcapitata presented both higher longevity (30.7 +/- 5.91, 26.6 +/- 3.59 days, respectively) and total progeny (45 +/- 13.80, 40.7 +/- 0.66 neonates female (-1) values than those organisms fed C. vulgaris (13.5 +/- 4.63 days and 17.6 +/- 6.19 neonates female (-1), respectively). On the other hand, temperature affected significantly the population parameters of C. rigaudi, recording maximal longevity values (56.1 +/- 9.41 days) at 20 degrees C in organisms fed A. falcatus; however, age at first reproduction and total progeny were negatively affected by this temperature: sexual maturation of the females was delayed until the age of 16 days and the number of neonates produced was smaller (9.8 +/- 3.45 with C. vulgaris; 24.7 +/- 6.01 with P subcapitata, and 35.5 +/- 8.59 neonates female(-1) with A. falcatus). The best reproductive responses for C. rigaudi in this study were obtained with A. falcatus at degrees 25 degrees C.     

Life table demography of Ceriodaphnia dubia (Cladocera) exposed to copper at different levels and periods

We studied the demographic responses of Ceriodaphnia dubia exposed to copper at 3 different levels (0.1, 0.2 and 0.4 mg l(-1)) and at 4 exposure periods (3, 6, 12 and 24 hr) in addition to controls (without the heavy metal). The tested levels of Cu concentration and the chosen periods of exposure affected some demographic variables (average lifespan, gross and net reproductive rates and generation time). Depending on the heavy metal concentration and the period of exposure, the average lifespan of C. dubia varied from 18 to 24 day Net reproductive rates (NRR) ranged from 50 to 80 offspring per female per lifespan, while the rate of population increase (r) varied from 0.30 to 0.34 per day Though gross reproductive rates (especially at low and intermediate copper levels and shorter duration of exposure) showed significantly higher values than controls, both NRR and r were either unaffected or decreased. It is therefore necessary to regulate the release of untreated industrial effluents containing copper into freshwater ecosystems. Our study thus highlights the importance of including, not only toxicant concentrations but also exposure time, in ecotoxicological evaluations.     

Effects of algal and larval densities on development and survival of asteroid larvae

Effects of larval and algal culture density and diet composition on development and survival of temperate asteroid larvae were studied in the laboratory at Santa Cruz, California, USA, during summer and fall of 1990. Larvae of Asterina miniata were reared at two densities, 0.5 or 1.0 ml^-1, and fed one or two species of cultured phytoflagellates — Dunaliella tertiolecta alone or mixed with Rhodomonas sp. — at three concentrations of 5x10², 5x10³, and 5x10⁴ total cells ml^-1. Algal concentration strongly influenced larval development; however, larval density also had a marked effect. Development progressed further with increasing algal concentration. Larval growth and differentiation were sometimes uncoupled; i.e., growth measures were directly related to food level, while differentiation indicators were less so. At the lowest food level, growth was negative and differentiation was arrested at early precompetent stages; these larvae never formed juvenile rudiments or brachiolar attachment structures. Development times of larvae given more food ranged from 26 to 50 d and depended directly on food availability. Development time to metamorphosis at the highest food concentration was similar for siblings fed D. tertiolecta alone or mixed with Rhodomonas sp. In contrast, when food level was an order of magnitude lower, larvae fed the algal mixture metamorphosed significantly earlier than larvae fed the unialgal diet. This suggests interactive effects of food quantity and food quality. Survival was little affected by larval or food density, except at the lowest ration. Feeding experiments in well-controlled laboratory conditions are useful to predict and compare the physiological or developmental scope of response of larvae to defined environmental factors; however, results from such studies should not be extrapolated to predict rates and processes of larval development in nature.     

Studies on comparative population growth of some species of the rotifer Lecane (Rotifera)

We compared the population growth patterns of 5 species of the rotifer genus Lecane [(L. quadridentata (Ehrenberg, 1830), L. comuta (Muller, 1786), L. papuana (Murray, 1913), L. unguitata (Fadeev, 1925) and L. pyriformis (Daday, 1905)] ranging in adult average body size from 30 to 140 microm. All species were cultured under laboratory conditions for 25-30 days using the green alga Scenedesmus acutus as the exclusive diet, at a density of 1.0 x 10(6) cells ml(-1) at 24 degrees C. Regardless of the species, lecanids reached their peak population densities after 4 weeks. Peak population densities ranged from 15 to 320 ind. ml(-1), depending on body size. There was an inverse curvilinear relation between body lengths and peak population abundances (densities) of the Lecane species. Egg ratios (eggs per female) for the tested species were < 0.6 during the exponential phase but declined to 0.1 (or lower) as the population density increased. The rates of population increase for the lecanids were in general lower(0.10 to 0.21 day (-1)) than other well-studied rotifer species including members of Brachionidae.     

Influence of algal concentration and temperature on the filtration rate of Mytilus edulis

The filtration rates of Mytilus edilis (=galloprovincialis; 40 mm) were determined in relation to food concentration and temperature, using pure suspensions of the unicellular alga Platymonas suecica in concentrations ranging from 3x10⁵ cells/l to 1.5x10⁸ cells/l. The rate of filtration (ml/h/mussel) generally decreased as cell concentrations increased, and dropped to low values when concentrations above 5x10⁷ cells/l were supplied. The amount of water swept clear varied continuously, and noticeable differences in the filtration activity of M. edulis were observed over short time intervals (5 min). Fluctuations of filtered volumes per unit time were greater with lower than with higher concentrations of algae. The influence of temperature on filtration activity was highest between 5°–15°C and 25°–30°C. A temperature increase from 15° to 25°C resulted in only a slight increase in filtration rate. At 5° and 30°C, filtration dropped to very low values, namely 350 and 100 ml/h, respectively. The temperature coefficients for the filtration rates of M. edulis were determined as: Q₁₀ (5° to 15°C)=4.96; Q₁₀ (10° to 20°C)=1.22. The amount of algae cells ingested per mussel per hour is directly related to food concentration. The maximum number of cells filtered/mussel/h in an algal suspension of 70x10⁶ cells/l was 21.5x10⁵ cells/h. Cell concentrations of up to 40x10⁶ cells/l were swept clear without producing pseudofaeces. The critical cell density for M. edulis was reached at algal concentrations of 70 to 80x10⁶ cells/l. Above these concentrations no normal filtration activity was observed.     

Combined effects of temperature and salinity on the complete development ofEurytemora velox (Crustacea: Calanoidea)

The calanoid copepodEurytemora velox was collected from rock pools at Castletown, Isle of Man, UK. Its optimum environmental requirements, particularly temperature and salinity, were determined, with a view to its possible future use as living food in intensive fish and shellfish farming. The species was cultured in 21 different temperature and salinity combinations. Investigations covered a period of two years from December 1983 to December 1985. Complete development from hatching to adult stage was followed in 21 temperature and salinity combinations. Nauplii suffered relatively high mortalities, indicating the sensitivity of this development stage to variations in temperature and salinity. Highest nauplii survival was observed in the combinations 15°C with 25 and 20 S and 20°C with 20 S, the highest copepodite survival at 10°C and 20 S. Lower salinities were tolerated better at higher temperatures and higher salinities at lower temperatures. Development time varied with the temperature and salinity combinations. Lower salinities at the lower temperatures of 10° and 15°C and both lower and higher salinities at 20°C prolonged development, particularly of the naupliar stage. Highest Q₅ values (i.e., rate of change of development with a 5 C° increase in temperature) were recorded for the naupliar stage. Statistical analysis indicated that salinity influences the survival of both nauplii and copepodites; however, this effect is not linear.     

全氟辛烷磺酸盐(PFOS)替代品对4种本土水生生物的生态毒性

本文选择了紫背浮萍、四尾栅藻、蚤状溞和稀有鮈鲫4种本土水生生物,开展了阳离子表面活性剂、织物三防整理剂、C4三防整理剂和C6三防整理剂4种全氟辛烷磺酸盐(PFOS)替代品的安全性评估,为筛选理想PFOS化学替代品提供科学依据。急性毒性结果发现阳离子表面活性剂对4种水生生物均未显示出急性毒性;织物三防整理剂、C4三防整理剂和C6三防整理剂对蚤状溞的LC50值分别为17.97、64.61和85.58 mg·L-1,显示出低的急性毒性。另外,织物三防整理剂对四尾栅藻的半数抑制浓度(EC50)值为88.32 mg·L-1,而对稀有鮈鲫半致死浓度(LC50)值为14.79 mg·L-1,均存在急性毒性。短期生长抑制试验结果发现阳离子表面活性剂、织物三防整理剂、C4三防整理剂和C6三防整理剂对稀有鮈鲫生长抑制最低可见效应浓度(LOEC)值分别为20、1.5、100和50 mg·L-1,表明4种PFOS替代品均显示低慢性毒性。急慢性综合分析可知C4和C6三防整理剂相对较安全,可能成为理想的PFOS替代品。     

Effect of temperature on growth and reproduction of the epigeic earthworm,Eudrilus Eugeniae (Kinberg)

Influence of temperature on growth and reproduction of Eudrilus eugeniae has been investigated by laboratory culturing at regulated 25.0 degrees C, 30.0 degrees C, 37.5 degrees C and 40.0 degrees C and in fluctuating (22.7-27.3 degrees C) room temperature of prevailing (winter) season over 16 weeks. All worms died during first and tenth week at 40.0 degrees C and 37.5 degrees C respectively. Weight (biomass) and growth of worms cultured at different temperature varied significantly (P<0.01). The mean growth (mg/g live weight/day) at 25.0 degrees C., 30.0 degrees C, 35.0 degrees C, 37.5 degrees C and in fluctuating temperatures was 1,074.04 +/- 6.07, 1,554.01 degrees 192.37, 148.1 +/- 15.28, 192.83 +/- 25.8 and 1450.4 +/- 162.1 respectively. Growth declined after maturity drastically with coccon production. At 25.0 degrees C though worms are sexually mature, they failed to produce cocoons within 16 weeks whereas, at 35.0 degrees C and 37.5 degrees C they did not sexually mature. Worms attained sexual maturity at a mean weight of about 1000 mg/worm. The mean per cent maturity was higher and earlier in fluctuating temperatures and at 30.0 degrees C than at 25.0 degrees C. Cocoon production was observed only at 30.0 degrees C and in fluctuating temperatures with a mean of 0.9 and 1.5 cocoons/ wom/week and the cumulative cocoon number of 10.8 and 14.7/worm over 16th week respectively. The fluctuating temperature of uncontrolled room environment and 30.0 degrees C were favorable for various life activities of the worms. Eudrilus eugeniae appears to have range of temperature optima more than 25.0 degrees C and less than 28 degrees C. The climatic conditions prevailing in whole of the peninsular India during winter season are favourable for employing this worm in intensive field scale vermiculturing practices.     

Effect of temperature fluctuations and food supply on the growth and metabolism of juvenile sea scallops (Placopecten magellanicus)

On the eastern shore of Nova Scotia late summer atmospheric systems cause upwelling of shelf water; the associated temperature variations of 10 °C with a 6 to 8 d period are comparable in magnitude to the seasonal variation. A laboratory study was undertaken to assess the effects of these temperature fluctuations on sea scallop (Placopecten magellanicus) growth and metabolism. In a factorial design, scallops were subjected to constant (10 °C) or a variable (6 to 15 °C) 8 d temperature cycle, and either a low (seston in filtered seawater) or high (seston supplemented with cultured phytoplankton) food diet. During the 48 d experiment scallop mortality was low and growth positive in all treatments. Shell and total tissue growth rate did not differ between temperature treatments, but growth in the high food treatments was 40 to 50% higher than in the low food treatments. However, soft tissue (excluding adductor) growth did show a temperature treatment effect; growth rates were significantly higher in the fluctuating temperature treatment, due in part to greater gonad development. Weight-standardized rates of scallop oxygen consumption (V _sO₂ , μmol O₂ g⁻¹ h⁻¹) were 20 to 25% higher in high food than in low food treatments, consistent with the expected increase in respiration due to the higher growth rates. Scallop metabolism did not acclimate to the fluctuating temperature cycle; V _sO₂ and ammonium excretion (V _sNH⁺ ₄, μmol O₂ g⁻¹ h⁻¹) remained dependent on ambient temperature throughout the experiment. V _sNH⁺ ₄ Q₁₀ (2.77) was higher than V _sO₂ Q₁₀ (2.01) which was reflected in a decrease in the O:N ratio at 15 °C, indicating a shift toward increased protein catabolism and a stressed state. At 10 °C, V _sO₂ and V _sNH⁺ ₄ in the variable temperature treatments were 15 to 18% lower than in the constant temperature treatments, a difference that was not detected in growth measurements. Results demonstrate that the metabolism of Placopecten magellanicus, unlike some bivalve species, is tightly coupled to fluctuations in ambient temperature. Although an absence of compensatory acclimation had a minimal effect on growth in this study, if high temperatures were combined with low food conditions a reduction in scallop production could result. Received: 23 June 1998 / Accepted: 8 February 1999     

A comparative seasonal study of two populations of Hypnea musciformis from the East and West Coasts of Florida,USA II. Photosynthetic and respiratory rates

Respiration rates of Hypnea musciformis (Wulfen) Lamouroux in Florida, USA, generally increased with increased temperature. Gulf coast H. musciformis respired at significantly higher rates than the Atlantic coast population, which exhibited a region of temperature independence between 24°–32°C. Respiration rates were highest in the fall and winter, during the periods of rapid growth. Respiration rates were lowest in the summer indicating a period of storage and low metabolism. Photosynthetic responses to various levels of light and temperature indicated that the Gulf coast population was more tolerant to high light intensities than the Atlantic coast population. Maximum photosynthetic responses for both populations occurred between 24° and 32°C which corresponds to the shallow slope region of the respiration-temperature curves. The results indicate that water temperature rather than light intensity is a significant factor in modifying seasonal photosynthetic capacities. The greatest seasonal variation in photosynthetic responses occurred at the light-temperature levels of highest responses while little seasonal variation was demonstrated at tolerance limits.     

Combined effects of temperature and salinity on embryos and larvae of the northern bay scallop Argopecten irradians irradians

The combined effects of temperature and salinity on embryonic development and on larval survival and growth to setting size of the northerm bay scallop Argopecten irradians irradians (Lamarck) were studied in the laboratory. A 6x6 complete factorial design was used; temperatures ranged from 10° to 35°C, at 5C° intervals, and salinities ranged from 10 to 35S, at 5S intervals. Response-surface contour diagrams were generated to provide estimates of conditions for optimal responses. Normal development of embryos occurred over a very narrow range of temperature and salinity. Survival of larvae occurred over a wider range of temperature and salinity than did embryonic development or growth of larvae. Satisfactory growth (>70% of the maximum observed value) occurred only at high temperature-high salinity conditions; optimal conditions for survival occurred at similar salinities, but at slightly lower temperatures. Temperatures of 35°C or greater and/or salinities of 10S or less were lethal for all life stages studied. Both salinity and temperature exerted significant effects on development and survival, but temperature was clearly the dominant factor influencing growth. It is suggested that northern bay scallop embryos and larvae be reared at their respective optimal temperature-salinity levels so as to increase efficiency of aquaculture operations.This paper is adapted from a thesis submitted to the College of Fisheries, University of Washington, in partial fulfillment of the requirements for the MS degree. This study was conducted at the NMFS Laboratory in Milford, Connecticut, USA     

Resting eggs of zooplankton (Copepoda and Cladocera) from the Kiel Bay and adjacent waters (southwestern Baltic)

Resting eggs of four species of calanoid copepods and three species of cladocerans were collected from sediments up to 5cm depth from the Kiel Bay and adjacent waters in the southwestern Baltic Sea during April–May 1994. All but one species of cladoceran was successfully hatched/reared in the laboratory. In the Kiel Bay, egg abundances varied from 1.8x10⁵ to 7.4x10⁵ m^-2. Hatching success of copepod eggs collected from all depths was high (49 to 94%), but was 0 to 79% for cladoceran eggs. Darkness did not seem to affect hatching. Eggs found in the 4 to 5 cm layer of sediment were estimated to be about 15 yr old, showing the presence of an egg bank in the Baltic. Formation of resting eggs may be a genetic trait acquired during the ice ages.     

Effect of temperature,salinity and food level on sexual and asexual reproduction in Brachionus plicatilis (Rotifera)

The reproductive response of sexual and asexual female Brachionus plicatilis (Muller) was examined over temperatures ranging from 20° to 40°C, salinities from 5 to 40 S, and food levels from 0.25 to 20 g Chlorella vulgaris dry-weight per ml. Reduced food levels, as well as temperature and salinity extremes, reduced reproduction of both sexual and asexual females, but did so differentially. Reproduction by sexual females was reduced to a greater extent at environmental extremes than asexual females. The broad, flat reproductive response curve of asexual females extended beyond the limits of the narrower, more sharply peaked curve of sexual females. Thus zones of exclusively asexual reproduction exist at environmental extremes where sexual reproduction is physiologically restricted. These results are corroborated by a comparison of the lifetime fecundity of individual sexual and asexual females over a 20°C temperature range. No differences in lifetime fecundity occurred between sexual and asexual females at 18° and 28°C. At 38°C, however, asexual female fecundity reached its highest level, while sexual female fecundity declined 15%. The appearance of sexual females in rotifer populations in the result of both inducible and repressible factors.     

Analysis of phytoplankton pigments by HPLC before,during and after mass occurrence of the microflagellate Corymbellus aureus during the spring bloom in the open northern North Sea in 1983

Daily observations in April and May 1983 near a subsurface drifter launched in the Fladen Grounds area of the North Sea revealed that a large crop of the microflagellate Corymbellus aureus Green, producing up to 3 g C m^-2 d^-1, succeeded the diatoms dominating during the earlier phase of the spring bloom. The concentration of fucoxanthin was highest during the first half of May, while pigment fingerprints of high-performance liquid chromatograms of suspended matter sampled during the second half of May were dominated by 19-hexanoyloxyfucoxanthin, the main carotenoid of C. aureus (0.8x10^-9 mg cell^-1). This colonial Prymnesiophycean was described for the first time less than 10 years ago and has nerver been reported to be present in the North Sea. After 16 May the C. aureus population rapidly lost its growth potential, but the peak of the bloom in terms of cell number was found several days later (up to 9x10⁶ cells per dm³ on 19 May). The population then started to decline; senescence was associated with decreasing pigment contents of cells. The low growth rate of copepods registered during the second half of May was probably related to the poor quality of C. aureus as copepod food: the concentration of a phaeophorbide a typically found in copepod fecal pellets was highest during the diatom phase of the spring bloom preceding the C. aureus bloom.     

Riparian shading and groundwater enhance growth potential for smallmouth bass in Ozark streams.

Moderation of stream temperatures by riparian shading and groundwater are known to promote growth and survival of salmonid fishes, but effects of riparian shade and groundwater on to be growth of warmwater stream fishes are poorly understood or assumed to be negligible. We used stream temperature models to relate shading from riparian vegetation and groundwater inflow to summer water temperatures in Missouri Ozark streams and evaluated effects of summer water temperatures on smallmouth bass, Micropterus dolomieu, growth using a bioenergetics model. Bioenergetics model simulations revealed that adult smallmouth bass in non-spring-fed streams have lower growth potential during summer than fish in spring-fed streams, are subject to mass loss when stream temperatures exceed 27 degrees C, and will likely exhibit greater interannual variation in growth during summer if all growth-influencing factors, other than temperature, are identical between the two stream types. Temperature models indicated that increased riparian shading will expand the longitudinal extent of thermal habitat capable of supporting adult smallmouth bass growth in spring-fed stream reaches when mean daily air temperatures exceed 27 degrees C. Optimum growth temperature (22 degrees C) will be present only in spring-fed streams under these conditions. Potential for increasing shade through riparian restoration is greatest for streams <5 m wide and along north-south reaches of larger streams. However, temperature models also indicated that restoring riparian shading to maximum levels throughout a watershed would increase the total stream mileage capable of supporting positive growth of adult smallmouth bass by only 1-6% when air temperatures are at or near average summer maxima; increases in suitable thermal habitat would be greatest in watersheds with higher spring densities. Riparian management for maintenance or restoration of the thermal habitat of adult smallmouth bass during summer should be focused in areas strongly influenced by groundwater. Restoring riparian shading along spring-fed warmwater streams will likely benefit adult smallmouth bass growth and may ultimately influence population sizes.     

The interplay between environmental conditions and allee effects during the recovery of stressed zooplankton communities

Many important ecological phenomena depend on the success or failure of small introduced populations. Several factors are thought to influence the fate of small populations, including resource and habitat availability, dispersal levels, interspecific interactions, mate limitation, and demographic stochasticity. Recent field studies suggest that Allee effects resulting from mate limitation can prevent the reestablishment of sexual zooplankton species following a disturbance. In this study, we explore the interplay between Allee effects and local environmental conditions in determining the population growth and establishment of two acid-sensitive zooplankton species that have been impacted by regional anthropogenic acidification. We conducted a factorial design field experiment to test the impact of pH and initial organism densities on the per capita population growth (r) of the sexual copepod Epischura lacustris and the seasonally parthenogenetic cladoceran Daphnia mendotae. In addition, we conducted computer simulations using r values obtained from our experiments to determine the probability of extinction for small populations of acid-sensitive colonists that are in the process of colonizing recovering lakes. The results of our field experiment demonstrated that local environmental conditions can moderate the impacts of Allee effects for E. lacustris: Populations introduced at low densities had a significantly lower r at pH 6 than at pH 7. In contrast, r did not differ between pH 6 and 7 environments when E. lacustris populations were introduced at high densities. D. mendotae was affected by pH levels, but not by initial organism densities. Results from our population growth simulations indicated that E. lacustris populations introduced at low densities to pH 6 conditions had a higher probability of extinction than those introduced at low densities to a pH 7 environment. Our study indicates that environmental conditions and mate limitation can interact to determine the fate of small populations of sexually reproducing zooplankton species. If a more rapid recovery of acid-damaged zooplankton communities is desired, augmentation of dispersal levels may be needed during the early phases of pH recovery in order to increase the probability of establishment for mate-limited zooplankton species.     

Autecology and clonal variability of the marine centric diatom Thalassiosira rotula (Bacillariophyceae) in response to light,temperature and salinity

The influence of 49 combinations of salinity (10–40 S, at 5 S intervals) and temperature (0°–30°C, at 5C° intervals) on the maximum daily division rate (K) and 18 combinations of light intensity (six levels) and temperature (5°, 15°, and 25°C) on photosynthesis, cell division, and chlorophyll a was examined using two clones of Thalassiosira rotula Meunier isolated from the upwelling area of Baja California (clone C8) and from Narragansett Bay, Rhode Islands (clone A8). Physiological differences appear to characterize these to clones with regard to their temperature tolerance (C8 5°–30°C, A8 0°–25°C), maximum growth rate (C8 K=2.9, A8 K=2.4), chlorophyll a content, and in the rates of growth and photosynthesis in response to light intensity and temperature. Optimum salinity for both clones (25–30 S) was generally independent of temperature, while chlorophyll a content decreased with temperature. T. rotula is a cosmopolitan paractic species; experimental studies indicate that it is eurythermal and moderately euryhaline. Comparison of five additional Narragansett Bay isolates of T. rotula reveal minimal spacial or temporal variability in genetically determined physiological characteristics within this local population.     

Extracellular amylase(s) production by fungi Botryodiplodia theobromae and Rhizopus oryzae grown on cassava starch residue

The fungi Botryodiplodia theobromae and Rhizopus oryzae produce extracellular amylase when grown on a liquid medium containing 2% (WN) soluble starch or cassava starch residue(CSR) (as starch equivalent), a waste generated after extraction of starch from cassava, as the sole carbon source. Using CSR as the sole carbon source, the highest amylase activity of 3.25 and 3.8 units (mg, glucose released x ml(-1) x h(-1)) were obtained in shake flask cultures during the late stationary phase of growth of B. theobromae and R. oryzae, respectively. These values were slightly lower than the values obtained using soluble starch as the carbon source. Maximum enzyme synthesis in CSR incorporated medium occurred at the growth temperature of 30 degrees C and pH 6.0. Presence of inorganic NH4+ salts like ammonium acetate and ammonium nitrate in culture medium yielded more amylase than the other nitrogen sources. Amylase(s) production in the controlled environment of a Table-Top glass Jar Fermenter (2-L capacity) was 4.8 and 5.1 units for B. theobromae and R. oryzae, respectively using CSR as the carbon substrate. It is concluded that CSR, a cheap agricultural waste obtained after starch extraction from cassava could replace soluble starch as carbon substrate for commercial production of fungal amylase(s).     

Ingestion rate,assimilation efficiency and energy balance in Mytilus chilensis in relation to body size and different algal concentrations

Basing on a quantification of filtration, ingestion, assimilation, biodeposition, excretion and respiration rate, energy budgets were established in Mytilus chilensis Hupé in relation to body size and three different food concentrations of the unicellular green alga Dunaliella marina. The present quantifications revealed that in M. chilensis the ingestion rate only increases slightly with an increase in food concentration which, however, is counterbalanced by a significant decrease in assimilation efficiency in such a way that assimilation rate finally is nearly constant and independent of the food concentrations tested. The quantifications of these results are given by the a-values of the general allometric growth equation P=aW^b relating the energy disposable for growth and reproduction (P; cal d^-1 to body size (W; dry-tissue wt, g). The best energy budget was obtained at the lowest food concentration tested (0.8 mg algal dry wt l^-1; at 12°C and 30 S) with an a-value of 58.8, while the energy budget at the highest food concentration (2.14 mg l^-1) was only slightly lower with an a-value of 49.8; the b-values were 0.49 and 0.51, respectively. The net growth efficiencies (K₂) decreased with increasing body size (from 20 mg to 3 000 mg drytissue wt) from 76.7 to 47.9% at the lowest food level and from 72.6 to 44.0% at the highest food level tested. These relatively high net growth efficiencies seem to reflect optimal experimental conditions. Furthermore, by a comparison of estimated growth (calculated on the basis of the best energy budget) with growth actually quantified in culture raft mussels in the south of Chile during the highest production period of the year, it is obvious that the energy budgets established really reflect the conditions experienced by the mussels in their natural environment.This research was supported by grants S-80-3 and C-80-1 of the D.I.D.-UACH, by CONICYT, Found. Volkswagenwerk, Found. Fritz-Thyssen, by the GTZ, DFG and by the DAAD