Μg Dry Wt Research Articles

Particulate matter ingestion and associated nitrogen uptake by four species of scleractinian corals

The ingestion of two size classes of natural particulate matter (PM) and the uptake of the associated nitrogen by four species of scleractinian corals was measured using the stable isotopic tracer 15N. PM collected in sediment traps was split into 105 µm size fractions and labeled with (15N-NH4)2SO4. Siderastrea radians, Montastrea franksi, Diploria strigosa, and Madracis mirabilis were incubated in flow chambers with the labeled PM in suspension ( 105 µm). Ingestion was detected for all four species (98–600 µg Dry wt. cm–2 h–1), but only for D. strigosa was any difference detected between suspended and deposited PM. Only the three mounding species, S. radians, M. franksi, and D. strigosa showed uptake of suspended and deposited particulate nitrogen (PN); whereas, the branched coral M. mirabilis had no measurable PN uptake. Only coral host tissues were enriched with 15N, with no tracer detected in the symbiotic zooxanthellae. Uptake rates ranged from as low as 0.80 µg PN cm–2 h–1 in S. radians to as high as 13 µg PN cm–2 h–1 in M. franksi. M. franksi had significantly higher uptake rates than S. radians (ANOVA, p<0.05), while D. strigosa had a statistically similar uptake rate compared to both species. These results are the first to compare scleractinian ingestion of nitrogen associated with suspended and deposited particulate matter, and demonstrate that the use of PM as a nitrogen source varies with species and colony morphology.

Role of nutrients and zooplankton grazing on phytoplankton growth in a temperate reservoir in New South Wales, Australia

The role of nitrogen (N) and phosphorus (P) and zooplankton grazing on the growth of a phytoplankton community was investigated at different times in the Ben Chifley reservoir. In situ nutrient enrichment bioassays (n�= 12) indicated that phytoplankton growth was limited by P in 33% of experiments, by both N and P in 25% of experiments and no limitation was found in 42%. The hypothesis that N or P limitation occurred when ambient N : P ratios were different from the Redfield ratio was supported in 33% of bioassay experiments, suggesting that ambient N : P ratios do not always correctly indicate if N or P is limiting. Grazing rates of the reservoir zooplankton (&gt;150�μm in size) ranged from 0.023–0.199 day–1 (mean: 0.078 day–1, n = 8). The grazing efficiency, as measured by a weight-specific clearance rate, ranged from 0.049–0.743 mL μg dry wt–1 day–1, and was positively correlated with the relative biomass of Daphnia in the community. The nutrient-stimulated growth of phytoplankton ranged from 0.085–1.031 day–1 (mean: 0.461 day–1, n = 10). The effect of nutrient enrichment exceeded that of zooplankton grazing in 62% of experiments. Further study is necessary to understand a qualitative effect of nutrients and zooplankton grazing on the phytoplankton community structure in the Ben Chifley reservoir.

Process-based models of feeding and prey selection in larval fish

Feeding success is essential to larval fish survival. We present detailed mechanistic models of the foraging processes (prey encounter, approach, pursuit, and capture) in larval fish, where all parameters have explicit physical or biological meaning. The model is a unification of the processes believed to be important to prey selectivity and environmental regulation of feeding in fish. We include the sensitivity of prey to the hydrodynamic signal generated by approaching larval fish and a simple model of the potential loss of prey due to turbulence whereby prey is lost if it leaves the perceptive field during pursuit time. We parameterise the model for larval cod Gadus morhua L., a species for which data from numerous experimental and field studies are available. Model predic- tions are compared to observations of feeding rates under various conditions and appear to match estimated ingestion rates and prey selection in larval cod. Observed pursuit times of larvae are long and approach velocity slow enough to avoid an escape response from prey, but too short to avoid loss of prey at high turbulence levels. The pause-travel search mode is predicted to promote ingestion of larger prey than a cruising search mode. We use these models to evaluate temporal and spatial (ver- tical) diel feeding rates of larval cod across Georges Bank. Contrary to previous models, our model suggests that larval cod are food-limited only in deep waters along a 160 km transect of the bank at a prey concentration of 20 µg dry wt l -1 . The spatio-temporal fluctuation of turbulence (tidal cycle) and light (sun height) over the bank generates complex structure in the patterns of food intake of larval fish, with different patterns emerging for small and large larvae.

An Assay Method for Nitric Oxide Synthase in Crude Samples by Determining Product NADP +

An assay method for nitric oxide synthase (NOS) was developed based on fluorometric or enzymatic determination of NADP +. An aliquot (≤ 2 μ1) of crude enzyme sample, homogenate or supernatant of rat cerebellum, was added to a reaction mixture containing arginine, NADPH, and O 2 and incubated at 25°C for 30 min. A strongly fluorescent substance was formed from a product, NADP +, and measured (fluorometric assay). When rat cerebellar layers were assayed, freeze-dried sections of layers (0.2 to 2 μg dry wt) were added directly into 1.24 μl of NOS reaction mixture and the total NADP + formed in picomole amounts was specifically amplified up to 4000-fold and determined, using an enzymatic NADP cycling amplification reaction (enzymatic-cycling assay). NOS activity was calculated as the difference in NADP +-forming activity in the absence and presence in the reaction mixture of N G-nitro-L-arginine, a specific inhibitor of NOS. Enzymatic activity was analyzed in rat cerebellar supernatants by two procedures. With supernatants (and purified macrophage NOS), the ratio between the specific activities on a protein basis using the present NADP + formation assay and using [ 3H]citrulline formation from [ 3H]arginine as substrate was 2. The distribution of NOS activity was shown between the particulate and supernatant fractions of rat cerebellum. The molecular and granular layers of rat cerebellum contained similar NOS activities, while the activity in the white matter was negligibly low. NOS distribution is also reported among rat organs.

Zooplankton Grazing During the Zebra Mussel (Dreissena polymorpha) Colonization of Saginaw Bay, Lake Huron

Weight-specific zooplankton filtering rates were determined at three sites in Saginaw Bay during the period of maximum zooplankton abundance prior to and after the establishment of zebra mussel colonies (June 1991 and June 1992). Biomass-specific filtering rates were similar in both years (inner bay: 0.24–0.33 mL μg dry wt.−1 d−1; outer bay: 1.27–1.83 mL μg dry wt.−1 d−1), but large decreases in zooplankton biomass resulted in a decrease, on average, of 58% in community filtering rates between years. As part of a large-scale monitoring program, zooplankton abundance and biomass estimates were also recorded at 13 sites during May-August of both years. Mean biomass in the inner bay was 40% lower in 1992 than in 1991, and in the outer bay, mean biomass was 70% lower in 1992 than in 1991. Zooplankton community composition was the same in both years. We estimated the time required to clear the water volume of the inner bay during the May–June period to be 17 days in 1991 and 37 days in 1992. For these two periods, decreased zooplankton numbers and community filtering rates indicate that grazing by zooplankton was likely not responsible for noted declines in phytoplankton abundance and productivity.

Delivery of dietary components to larval shrimp (Penaeus vannamei) by means of complex microcapsules

Efficient delivery of nutrients is necessary for the successful study of aquatic larval nutrition. Conventional artificial food particles for larval shrimp (Penaeus vannamei) have poor water stability and poor nutrient retention or both. We developed a novel food particle type that retained low-molecular weight, water-soluble nutrients (vitamins and glucose) within lipid-wall microcapsules embedded with dietary ingredients in particles of gelled alginate-gelatin. The combination of lipid-wall microcapsules (LWMs) embedded in gelled food particles was termed complex microcapsules (CXMs). Eighty-five percent of 14C-activity associated with encapsulated 14C-glucose was retained by CXMs (after 18 h of suspension in seawater). Bioavailability of CXM-encapsulated molecules was demonstrated by release of encapsulated dye marker into the gut lumen of larval shrimp, and by uptake of 14C from encapsulated 14C-glucose. Minimum ingestion rates, calculated from 14C-uptake for larval shrimp (Mysis-1 through Postlarva-2) fed CXMs, ranged from 48 to 99 μg dry wt larva-1 d-1, and were similar to literature values reported for ingestion of live rotifers by penaeid larvae. Complex microcapsules described in this study will be a valuable new tool for studying nutrition of suspension-feeders in that both micro-and macronutrients can be delivered to these animals by one particle type.

The influence of freshwater and material export on sedimentary facies and benthic processes within the Fly Delta and adjacent Gulf of Papua (Papua New Guinea)

Large volumes of freshwater and suspended material debouch from the Fly River in southwestern Papua New Guinea into the Gulf of Papua, greatly influencing the hydrography and sedimentary processes within the river delta and adjacent shelf region. Sedimentary facies within the subtidal regions of the Fly Delta are composed mainly of compacted and eroded very fine black sand, and highly laminated, muddy sand and sandy mud, progressing to prodelta mud with intermixed primary and biogenic structures in the inner Gulf of Papua. These prodelta muds grade further to mixed terrigenous-carbonate deposits southwards into the northern Great Barrier Reef and Torres Strait, and to well-bioturbated, fluid mud northwards into the Gulf of Papua. The transition from physically-dominated, estuarine conditions within the delta to more quiescent, marine conditions on the shelf leads to concomitant changes in sediment chemistry, microbial activity and infaunal and epifaunal communities. Particulate (C, N, P) and dissolved inorganic and organic nutrient concentrations were a function of sediment type (higher in finer deposits) rather than location (delta vs gulf). C: N: P ratios of solid-phase nutrients varied greatly, but were usually less than those predicted by the Redfield ratio. Mean interstitial concentrations of dissolved inorganic nutrients were low (μM range), but dissolved organic carbon, nitrogen and phosphorus levels were equivalent to those found in higher latitude systems. Fluxes of dissolved inorganic nutrients were generally low (μmol m −2 day −1). Flux rates were mostly negative (into the sediment) in the delta suggesting that these deposits are a sink for nutrients. In the offshore deposits, dissolved inorganic fluxes were higher and mostly positive indicating that they are a source for dissolved nutrients. Standing crops of bacteria (range: below detection limits— 2.5 × 10 10 cells g −1 dry wt), meiofauna (range: 5–750 individuals 10 cm −2; 9–1006 μg dry wt 10 cm −2) and infauna (range: 86–5555 individuals m −2; 0.10-5.85 g AFDW m −2) were generally lower in the delta than in the gulf. The infauna was dominated by nematodes, copepods, foraminifera and small, tube-building, deposit- and suspension-feeding polychaetes and amphipods. Rates of bacterial productivity were very erratic with sediment depth across stations, ranging from 0–2108 mg C m −2 day −1 (DNA synthesis) and from 0–228 mg C m −2 day −1 (protein synthesis), respectively. Rates of benthic respiration and DOC flux across the sediment-water interface were generally high, ranging from 63–780 mg C m −2 day −1 and from −797 to 514 mg C m −2 day −1, respectively. Epibenthos were more diverse (at the phyletic level) at the mid-shelf than inshore, composed mainly of sponges, crabs, crinoids, echinoids, bivalves, hydroids and asteroids. Demersal nekton abundance was low, dominated by the leatherjacket, Paramonacanthus filicauda, the pony fish, Leiognathus splendens and the grunter, Pomadasys argyreus, suggesting limited transfer of infaunal biomass to higher trophic levels. The response of the benthic regime to the export of freshwater and material from the Fly River generally conforms to the Rhoads et al. [(1985) Continental Shelf Research, 4, 189–213] model of benthic response to effluent derived from the Changjiang River in the East China Sea and is similar to infaunal and sedimentary patterns off the Amazon. Nutrient release from the delta sediments contributes little to water-column production, but in the gulf, nutrient efflux from the benthos contributes, on average, 38 and 61% of the annual N and P requirements of phytoplankton production, reflecting closer benthic-pelagic coupling and enrichment of biological productivity in the Gulf of Papua due to nutrient export from the Fly River.

The importance of zooplankton‐protozoan trophic couplings in Lake Michigan

The importance of the zooplankton‐protozoan trophic coupling was determined experimentally by measured changes in protozoan growth rates with increasing zooplankton biomass. In five of six experiments conducted in Lake Michigan, a significant inverse relationship between protozoan growth and zooplankton biomass was observed (avg r2 = 70%). Zooplankton clearance rates on protozoan assemblages [range, 1.0–6.2 ml (µg dry wt)‒1 d‒1] were comparable to those previously measured for phytoplankton which suggested that protozoa are important prey for zooplankton. Clearance rates on individual protozoan taxa [0–15.6 ml (µg dry wt)‒1 d‒1] were size‐dependent. Rates were greatest for taxa &lt;20 µm in size (mainly nanoflagellates and small ciliates). In contrast to findings for phytoplankton, no evidence emerged for grazer resistance nor growth enhancement by planktonic protozoa in response to grazing. The high flux rates for macrozooplankton on heterotrophic nanoflagellates observed in all experiments (0.2–6.0 µg C liter‒1 d‒1) provided evidence that a large fraction of picoplankton C may be directly transferred to higher trophic levels via a picoplankton‐flagellate‐zooplankton coupling.

Mycolytic activity and the development of microflora in soils of different mechanical structure

The mycolytic activity of four soils differing in mechanical structure was determined by the Lloyd-Lockwood method. Also investigated was the interdependence between this activity and the number of mycolytic microorganisms (Carter-Lockwood method), the number of bacteria growing on agar with soil extract, the number and biomass of whole bacterial communities as well as the fungal biomass (direct methods). Mycolytic activity and development of the microorganisms listed above were also studied in soil treated with carbon and mineral nitrogen. Mycolytic activity differed significantly depending on soil type and was positively correlated with silt and clay content. Addition of C and mineral-N did not affect its intensity to a significant degree. The number of mycolytic microorganisms ranged from 56 × 10 3 to 160 × 10 3 g − dry wt of soil. The number of microorganisms growing on agar plates with soil extract ranged from 5 × 10 6 to 18 × 10 6 g − dry wt of soil and that of whole bacterial communities from 3 × to 8 × 10 6 10 9g −1 dry wt of soil. The number of all investigated groups of bacteria differed significantly depending on soil type and was positively correlated with silt and clay content. When C and N were added a greater rise in the number of these organisms was observed in heavier than lighter soils. Small numbers of mycolytic bacteria, in comparison with the numbers of other bacterial groups, point to their limited role in determining the intensity of mycolytic soil activity. Bacterial biomass averaged 395 and 180 μg dry wt g − dry wt of heavier and lighter soils respectively and was highly positively correlated with the silt and clay content of the soil. Fungal biomass ranged from 300 to 440 μg dry wt g − dry wt of investigated samples and was highly significantly but negatively correlated with the content of fine fractions in the soil. A negative correlation with this soil fraction was also determined for the F:B coefficient (ratio of the fungal to the bacterial biomass). The F:B coefficient for balanced control samples averaged 0.5 for heavier and 2.0 for lighter soils. Apart from soil type, the sampling date and treatment also significantly differentiated the value of the F:B coefficient. The addition of C and N resulted in a more than two-fold increase of fungal domination in lighter soils and in an equalization of the fungal and bacterial biomass in heavier soils. No statistically significant correlation was determined between examined bacteria and fungi, although the heavier soils, with their greater mycolytic activity, were more favourable for the development of bacteria, whereas the lighter soils, less active mycolytically, were dominated by fungi.

Partitioning of oxygen consumption between “maintenance” and “growth” in developing herring Clupea harengus (L.) embryos

Growth and oxygen consumption was measured in developing herring Clupea harengus (L.) embryos. By considering the variations in oxygen consumption with embryonic size and growth rate, an attempt was made to partition oxygen consumption between growth related and growth unrelated (i.e., “maintenance”) processes. The metabolic cost of growth was estimated as ≈ 150 ng O 2 · μg dry wt tissue formed −1. This estimate compares favourably with the biochemical estimate of the costs of transport and net biosynthesis. The “maintenance” component was proportional to embryonic mass (77 ng O 2 · μg −1· d −1). Over the entire embryonic period, growth processes were responsible for ≈ 25% of the cumulated oxygen consumption.

Recent Growth, Biochemical Composition and Prey Field of Larval Haddock (Melanogrammus aeglefinus) and Atlantic Cod (Gadus morhua) on Georges Bank

A transect across southern Georges Bank in May 1983 showed higher levels of available prey for haddock (Melanogrammus aeglefinus) and cod (Gadus morhua) larvae at two stratified sites than at a well-mixed site. At the stratified sites, prey biomass was high (30–300 μg dry wt∙L−1) near the surface above the thermocline; values were lower and more uniform with depth (10–30 μg dry wt∙L−1) at the well-mixed site. Larval population centers generally coincided with prey biomass vertically. Recent growth in dry weight of haddock larvae as estimated by RNA–DNA ratio analysis was higher at the stratified sites (8–13%∙d−1) than at the well-mixed site (7%∙d−1). Larvae appeared to be in excellent condition at the stratified sites, but up to 50% of haddock larvae from the well-mixed site had RNA–DNA ratios in the range observed for starved larvae in the laboratory. Cod collected at the same site were in better condition and growing faster than haddock. The data support the hypotheses that (1) stratified conditions in the spring favor good growth and survival of haddock larvae and (2) cod larvae are better adapted to grow and survive in well-mixed waters at lower levels of available food than haddock larvae.

Food limitation in naupliar and adult Diaptomus pallidus1

The relationships between survivorship and fecundity of Diaptomus pallidus and algal food concentrations (Cryptomonas reflexa) were examined with a flow‐through system that prevents the depletion and settling of algal cells. Egg production in adult females increased with increasing food concentration up to a maximum at 600 µg dry wt liter−1. Under starvation conditions, egg production stopped and survival decreased, whereas at 60 µg dry wt liter−1 production was halted and survival was high. Adults survived longer under conditions of starvation than did nauplii. Adult survival was high at all food concentrations; naupliar survival was highest at 60 µg dry wt liter−1, slightly lower at 600 µg dry wt liter−1, and much lower at 6,000 µg dry wt liter−1. Naupliar development was faster at 600 and 6,000 µg dry wt liter−1 than at 60 µg dry wt liter−1.

Seasonal dynamics of rotifer and crustacean zooplankton populations in a eutrophic, monomictic lake with a note on rotifer sampling techniques

The abundances, biomass, and seasonal succession of rotifer and crustacean zooplankton were examined in a man-made, eutrophic lake, Lake Oglethorpe, over a 13 month period. There was an inverse correlation between the abundance of rotifers and crustaceans. Rotifers were most abundant and dominated (>69%) the rotifer-crustacean biomass during summer months (June–September) while crustacean zooplankton dominated during the remainder of the year (>89%). Peak biomasses of crustaceans were observed in the fall (151 µg dry wt l−1 in October) and spring (89.66 µg dry wt l−1 in May). Mean annual biomass levels were 46.99 µg dry wt l−1 for crustaceans and 19.26 µg dry wt l−1 for rotifers. Trichocerca rousseleti, Polyarthra sp., Keratella cochlearis and Kellicottia bostoniensis were the most abundant rotifers in the lake. Diaptomus siciloides and Daphnia parvula were the most abundant crustaceans. Lake Oglethorpe is distinct in having an unusually high abundance of rotifers (range 217–7980 l−1). These high densities can be attributed not only to the eutrophic conditions of the lake but also to the detailed sampling methods employed in this study.

Phosphatase activity ofPenicillium citrinum submerged batch cultures and its relationship to fungal activity

Acid and alkaline phosphatase activities were evaluated using batch fermenter cultues ofPenicillium citrinum, an organism used in studies of fungal functioning in soil. Fungal activity was assessed by monitoring rates of O2 utilization, glucose utilization, dry weight changes over time, and lengths of FDA-stained hyphae. At low growth rates (7 μg dry wt increases·h−1·ml−1) and low culture activity, phosphatase activity at both pH 8.5 and 5.5 tended to decrease with culture age, with the exception that phosphatase activity at pH 8.5 peaked during early stationary phase. At higher growth rates (25 μg dry wt increase·h−1·ml−1) and high culture activity, phosphatase activity tended to remain constant throughout the course of the experiment. The relationship between phosphatase activity and other measures of fungal activity was consistent only at low growth rates for acid phosphatase. These results suggest that phosphatase measurements will be of limited utility in assessing activity, except at low growth rates.

The effect of food composition on ingestion, development, and survival of a harpacticoid copepod, Tisbe cucumariae Humes

Feeding experiments were carried out on the benthic harpacticoid copepod Tisbe cucumariae Humes, using seven different diets of various dried and ground macroalgae and marsh grass, algal Aufwuchs, diatoms, polychaete meat, and cereal. In short-term experiments (1 h), 14C-labelled foods were used to measure ingestion rate of non-ovigerous adult females (individual dry wt = 5.57 ± 2.49 μg). No significant difference was found among the rates at which all foods, except polychaete meat, were ingested (12.7 to 17.3 × 10 −2 μg dry wt· ind −1· h −1). Polychaete meat was consumed faster (23.9 × 10 −2 μg dry wt·ind −1· h −1). The nutritional value of the foods was estimated in long-term experiments (22 days) by measuring development time and survival of T. cucumariae. Both these variables were significantly correlated with the nitrogen, protein content, and C:N ratio of the foods. No relation was found, however, with the amount of carbon, calories and available calories in the diets. Thus, nitrogen (protein) content of the food was the factor limiting secondary production of the copepods.

Food limitation of production by adult Acartia tonsa in Narragansett Bay, Rhode Island1

Egg production, dry weight, cephalothorax length, and condition factor were measured for adult Acartia tonsa females collected twice weekly from Narragansett Bay, R.I., during summer 1979 and incubated in ambient bay water and in ambient bay water enriched with laboratory‐cultured algae. Egg production, dry weight, and condition factor of copepods in the ambient bay water fluctuated considerably (ranges 1.6–51.6 eggs·female‒1·d‒1, 7.37–16.60 µg dry wt, and 1.09–2.37 condition factor) and closely followed the seasonal trends in Chl a and particulate carbon and nitrogen. Cephalothorax length remained fairly constant during the study. The overall mean egg production rate, dry weight, and cephalothorax length of the copepods after incubation for 48 h in the algae‐enriched water were significantly greater than for copepods incubated in ambient bay water (mean values 45.9 vs. 25.3 eggs·female‒1·d‒1, 13.2 vs. 11.8 µg dry wt, and 901.7 vs. 891.8 µm long). Since body size and egg production in adult A. tonsa responded rapidly to a change in food availability, the copepods must have been continuously food limited in Narragansett Bay during summer.

The respiration of five brackish-water harpacticoid copepod species

The dependency of respiration rate on body weight at 20 °C was determined for five meiobenthic copepods from a brackish-water habitat. The respiration rate of the four smaller species was generally high, ≈ 10–14 nl O 2 · h −1 · μg dry wt −1, but was much lower for a larger species, Canuella perplexa T & A. Scott 1893 (2–3nl O 2 · h −1 · μg −1). This pattern is discussed in terms of the adaptive behaviour of the populations. The significance of respiration rates in the evolution of populations is illustrated by differences between the respiration rates of a Belgian Tachidius discipes Giesbrecht 1882 population, and that of T. discipes from the Lynher estuary, U.K. It is hypothesized that respiration rates will be lower when species are in competition for relatively stable food sources.

Control of microbial growth on eelgrass (Zostera marina L.: Spermatophyta) by leaf-derived metabolites

The role of minor components of the leaves ofZostera marina L. in altering the activity of micro-organisms directly and indirectly by affecting amphipod grazers was investigated in laboratory experiments. Water-soluble extracts of eelgrass leaves inhibited the growth of many marine bacteria and a micro-alga (Platymonas sp.) at concentrations equivalent to as little as 10 μg dry wt. of leaf.ml−1. The potency of leaf extracts was higher in young, actively metabolizing tissue than in older leaves, and was higher in leaves collected in summer during rapid growth than in winter. Water-soluble inhibitors may explain the low biomass of epiphytes on actively growing leaves. Phenolic acids, previously identified in eelgrass leaves, may account for part of the antimicrobial activity. Three free phenolic acids inhibited the test micro-organisms at concentrations as low as 2 μM; caffeic acid was more potent than either protocatechuic or gentisic acid. Extracts of young leaves also inhibited grazing by amphipods on dead leaves. The time required for leaching of soluble inhibitors may account for the delay observed between the loss of leaves from the plants and the onset of grazing. Thus, interactions among the biotic components of the detritus ecosystem may be significantly modified by minor components of the macrophyte tissue.

Gramine in Barley Forage ‐ Effects of Genotype and Environment1

Consumption of reed canarygrass (Phalaris arundinacea L.) containing about 2,000 μg dry wt or more of the indole alkaloid gramine can adversely affect ruminant performance. Because gramine occurs in barley (Hordeum vulgare L.) leaves, 20 cultivars of barley and four races of Hordeum spontaneum Koch were analyzed for gramine and related alkaloids after growth in controlled environments (21/16 C, day/night) to the fourleaf stage. Shoot gramine levels ranged from &lt;30 to &gt;10,000 μg/dry wt; 10 ‘high‐gramme’ genotypes (six H. vulgare, four H. spontaneum) contained at least 2,000 μg/g. Other indole alkaloids were absent or present only in trace amounts.Beginning at the two‐leaf stage, the high‐gramine barley cultivars ‘Arimar’ and ‘Maraini’ were grown for 2 weeks at 21/16 C and 30/25 C, with either adequate or limited water supply. Growth of both cultivars at the higher temperatures approximately doubled their gramine concentrations (to about 4,000 μg/g). Cyclic wilting, which resulted from limiting irrigation, did not greatly affect gramine concentrations. In a cool, spring, field planting at a loamy, non‐irrigated site, the gramine concentration in Arimar shoots was 1,700 μg/g at the three‐to‐four‐leaf stage, but fell to 200 μg/g at the six leaf stage. In a warm, summer, field planting at a sandy irrigated site, the gramine concentrations at both three‐to‐four and six‐leaf stages were ≥2,700 μg/g in Arimar and ≥4,500 μg/g in Maraini.Gramine merits attention as a potential anti‐quality factor in breeding programs for barley suited to grazing or other forage uses.

Growth and energetics inSpisula subtruncata(da Costa) and the effect of suspended bottom material

Abstract The influence of suspended bottom material (0–25 mg · l−1) in addition to algal cells (Phaeodactylum tricornutum) (0–500 µg dry org wt · l−1) on clearance, growth and energetics in Spisula subtruncata (da Costa) has been studied. Clearance and respiration rate were independent of concentrations of algae and suspended bottom material. Algal ingestion rate was proportional to algal concentration, and independent of the concentration of suspended bottom material. Growth rate increased with algal concentration, and was further increased by 10 to 110 % by the addition of suspended bottom material. The positive effect of suspended bottom material on growth is due to a higher efficiency of assimilation of the ingested algae and/or to the utilization of organic matter in the suspended bottom material. The efficiency of algal assimilation decreased from 76 % at a low (150 µg dry org wt · 1−1) to 33 % at a high (500 µg) algal concentration in specimens fed pure suspensions of algae. The water processing po...