Primary productivity of papyrus (Cyperus papyrus) in a tropical swamp; Lake Naivasha,Kenya

Papyrus (Cyperus papyrus) standing biomass and the primary productivity of undisturbed and previously harvested areas of papyrus was measured in Lake Naivasha swamp, Kenya. Papyrus culm density in undisturbed swamp was estimated to be 13·1±1·9 culms m⁻² and aerial biomass was 3602 g m⁻². In undisturbed swamp the aerial productivity was 14·1 g m⁻² day⁻¹ while the previously harvested swamp reached a peak of 21·0 g m⁻² after 6 months. The annual aerial production rate of papyrus in Lake Naivasha was estimated to be 5150 g m⁻² year⁻¹. To sustain yields of regularly harvested papyrus swamps, the harvest intervals should exceed 1 year.     

Population Dynamics,Growth and Productivity of Abra ovata (Mollusca,Bivalvia) in the Evros Delta (North Aegean Sea)

Monthly samples of Abra ovata were collected during February 1983-January 1984 in the Evros Delta (N. Aegean Sea). Population density (mean annual value = 2407.5 ind · m⁻²) was characterized by seasonal variation. An analysis of the length frequency distributions shows that one annual recruitment of juveniles (> 2 mm) occurred in October-January; and also that, throughout the year, two age groups existed in the population. One growth ring was formed on the shells of the oldest age group during July-August. Mean growth in shell length can be described by Bertalanffy function. A positive correlation existed between shell length and decalcified dry weight. Secondary production in A. ovata, calculated by the instantaneous growth method, showed a mean biomass of 29.221 g dry weight m⁻²yr⁻¹, a productivity of 17.086 g dry weight m⁻²yr⁻¹ and an annual turnover ratio of 0.59.     

Interactions between gnathiid isopods,cleaner fish and other fishes on Lizard Island,Great Barrier Reef

The rate of emergence of micropredatory gnathiid isopods from the benthos, the proportion of emerging gnathiids potentially eaten by Labroides dimidiatus, and the volume of blood that gnathiids potentially remove from fishes (using gnathiid gut volume) were determined. The abundance (mean ±s.e .) of emerging gnathiids was 41·7 ± 6·9 m^?2 day^?1 and 4552 ± 2632 reef^?1 day^?1 (reefs 91–125 m²). The abundance of emerging gnathiids per fish on the reef was 4·9 ± 0·8 day^?1; but excluding the rarely infested pomacentrid fishes, it was 20·9 ± 3·8 day^?1. The abundance of emerging gnathiids per patch reef was 66 ± 17% of the number of gnathiids that all adult L. dimidiatus per reef eat daily while engaged in cleaning behaviour. If all infesting gnathiids subsequently fed on fish blood, their total gut volume per reef area would be 17·4 ± 5·6 mm³ m^?2 day^?1; and per fish on the reefs, it would be 2·3 ± 0·5 mm^?3 fish^?1 day^?1 and 10·3 ± 3·1 mm³ fish^?1 day^?1 (excluding pomacentrids). The total gut volume of gnathiids infesting caged (137 mm standard length, L_S) and removed from wild (100–150 mm L_S) Hemigymnus melapterus by L. dimidiatus was 26·4 ± 24·6 mm³ day^?1 and 53·0 ± 9·6 mm³ day^?1, respectively. Using H. melapterus (137 mm L_S, 83 g) as a model, gnathiids had the potential to remove, 0·07, 0·32, 0·82 and 1·63% of the total blood volume per day of each fish, excluding pomacentrids, caged H. melapterus and wild H. melapterus, respectively. In contrast, emerging gnathiids had the potential of removing 155% of the total blood volume of Acanthochromis polyacanthus (10·7 mm L_S, 0·038 g) juveniles. That L. dimidiatus eat more gnathiids per reef daily than were sampled with emergence traps suggests that cleaner fishes are an important source of mortality for gnathiids. Although the proportion of the total blood volume of fishes potentially removed by blood‐feeding gnathiids on a daily basis appeared to be low for fishes weighing 83 g, the cumulative effects of repeated infections on the health of such fish remains unknown; attacks on small juvenile fishes, may result in possibly lethal levels of blood loss.     

High rates of net primary production and turnover of floating grasses on the Amazon floodplain: implications for aquatic respiration and regional CO2 flux

We investigated whether rates of net primary production (NPP) and biomass turnover of floating grasses in a central Amazon floodplain lake (Lake Calado) are consistent with published evidence that CO₂ emissions from Amazon rivers and floodplains are largely supplied by carbon from C4 plants. Ground‐based measurements of species composition, plant growth rates, plant densities, and areal biomass were combined with low altitude videography to estimate community NPP and compare expected versus observed biomass at monthly intervals during the aquatic growth phase (January–August). Principal species at the site were Oryza perennis (a C3 grass), Echinochloa polystachya, and Paspalum repens (both C4 grasses). Monthly mean daily NPP of the mixed species community varied from 50 to 96 g dry mass m^?2 day^?1, with a seasonal average (±1SD) of 64±12 g dry mass m^?2 day^?1. Mean daily NPP (±1SE) for P. repens and E. polystachya was 77±3 and 34±2 g dry mass m^?2 day^?1, respectively. Monthly loss rates of combined above‐ and below‐water biomass ranged from 31% to 75%, and averaged 49%. Organic carbon losses from aquatic grasses ranged from 30 to 34 g C m^?2 day^?1 from February to August. A regional extrapolation indicated that respiration of this carbon potentially accounts for about half (46%) of annual CO₂ emissions from surface waters in the central Amazon, or about 44% of gaseous carbon emissions, if methane flux is included.     

Composition and Productivity of the Benthic Macroinvertebrate Community of a Subtropical Reservoir

Physical-chemical conditions, phytoplankton productivity, community structure and productivity of the macroinvertebrate benthic community were determined during 1976–77 in a subtropical reservoir. Physical-chemical results revealed high nitrate and phosphate concentrations with highest values in the riverine segment. Large phytoplankton populations were present during most of the year. Phytoplankton productivity was high, producing an annual mean of 87 mg C · m⁻³ · h⁻¹ (12 hours light day). High turbidity in the riverine segment limited phytoplankton productivity during winter and spring. Macrobenthos was dominated by chironomids (Chironomus, Procladius, Coelotanypus and Tanypus) and oligochaetes (Limnodrilus). The annual mean benthic population was estimated at 1,626 · m⁻² with a mean dry weight of 0.66 g · m⁻². Mean benthic species diversity was 1.80. A lacustrine-riverine community gradient was revealed. Benthic productivity was 6.8 g · m⁻² · yr⁻¹ (dry weight) with a P: B ratio of 10. A low correlation was observed between benthic and phytoplankton productivity, and between phytoplankton standing crop and benthic macroinvertebrate numbers throughout the reservoir. Algal food supplies had little impact on the benthic community which was composed predominately of species which fed mostly on organic detritus. Stressful conditions caused by low dissolved oxygen concentrations probably inhibited development of the benthic community throughout the reservoir during summer months, while high sedimentation rates limited development in the head waters.     

Modeling algal productivity in large outdoor cultures and waste treatment systems

A deterministic mathematical model was used to describe the production of green microalgae (Scenedesmus obliquus and Coelastrum sphaericum) in outdoor mass cultures. The model was calibrated against 16 months of temperature and irradiance measurements, during which time productivity measurements were made in up to five ponds with surface areas of up to 263 m². During this period rates of algal dry matter production varied between 1·7 and 16·92 g m⁻² day⁻¹. The model predicted productivity to within 4·2% of the observed rates, for the same period. Negative productivity values (loss of biomass) were calculated for the months from November to January. It was concluded that appreciable amounts of biomass could be produced for 7 months per year in temperate areas.Several assumptions were made during the construction of the model, especially with regard to loss factors, such as: respiration, release of exuded organic carbon and photo-inhibition. The latter was included as a separate factor in the model and is merely conceptual. Several applications of the model are discussed, one of which concerns the relation between areal density and productivity, where the optimal areal density for maximal productivity was calculated to be 38–41 g (dry wt) m⁻². A distinction was also made between cultures which were mainly autotrophic and waste systems. It was shown that the presence of gilvin and/or tripton would adversely influence productivities and that the contribution of these factors to vertical light attenuation would have to be measured in waste systems.     

Feeding Rate of Brachionus plicatilis O. F. Müller on Two Types of Food Depending on Ambient Temperature and Salinity

Feeding rates of Brachionus plicatilis were studied for two types of food — algae Monochrysis lutheri and baker's yeast Saccharomyces cerevisae. The main regularities of changes in filtration rate and ration were studied in small culture volumes (1 ml) for adult amictic females depending on food concentration (1, 2, 4, 8 and 16 · 10⁶ cells · ml⁻¹), ambient temperature (16 and 26 °C), and salinity (5, 10, 15, 20, 25 and 30 ppt). B. plicatilis ration did not depend on the salinity, but was largely determined by temperature and food concentration. It was found that at 16 and 26 °C the dependence of the ingestion rate (ration) on food concentration differed greatly. A hypothesis was suggested to explain this phenomenon. A critical concentration of both types of food at which the increase in the rotifer ration ceased is 4 · 10⁶ cells · ml^−1. This is the minimum “background” food concentration for B. plicatilis mass cultivation. The average rations measured at the concentration of M. lutheri and S. cerevisae of 4 · 10⁶ cells · ml⁻¹ where 1.3 ± 0.1 and 4.8 ± 1.3 μg dry weight. · ind⁻¹ · day⁻¹ at 26 °C and 0.54 ± 0.1 and 1.9 μg d. w. · ind⁻¹ · day⁻¹ at 16 °C, respectively. The rations obtained in the laboratory were corrected for the conditions of rotifer commercial production in the open field in summer time. The correct values were 0.86 and 0.72 μg d. w. · ind⁻¹ · day⁻¹ for algae and yeast, respectively.     

Productivity of theEcklonia cava community in a bay of Izu Peninsula on the Pacific Coast of Japan

Net production of theEcklonia cava community was monitored on a monthly basis for a year, and annual net production was estimated. Growth rate of blades reached a maximum of about 13 g dry wt·m^?2·day^?1 in spring and a minimum of about 2 g dry wt·m^?2·day^?1 in late summer. Annual production of blades was calculated to be 2.84 kg dry wt·m^?2·year^?1. If the growth of stipes is taken into account, annual net production is estimated to be about 2.9 kg dry wt·m^?2·year^?1. Standing crop was monitored monthly for two and a half years, and a close negative correlation was found between seasonal change in standing crop and net production. Standing crop reached a maximum of about 3 kg dry wt·m^?2 in summer and a minimum of about 1 kg dry wt·m^?2 in winter. Low productivity in summer at a period of maximum biomass may be explained by the dense canopy and the large area of reproductive portion occupying a blade, which diminish net assimilation.     

Grazing behavior of rangeland beef cows differing in milk production

Differences in grazing behavior among Hereford (HH), 50% Angus-50% Hereford (AH), 50% Simmental-50% Hereford (1S1H) and 75% Simmental-25% Hereford (3S1H) lactating cows grazing foothill range were measured using vibracorders and pedometers to estimate daily grazing hours and distance traveled, respectively. There were four 10-day grazing periods during July and August. Cow weight, calf weight and milk production estimates were taken prior to Periods 1 and 4. During Periods 1, 2 and 4, the 48 cows were located on a daily basis between 06.00 and 09.00 h, and each animal location was recorded on gridded aerial photo maps. Pasture use was defined as the amount of total area utilized for grazing for the four periods.The overall mean for daily grazing hours was 9.4 h day⁻¹ (633 observations) and no significant breed type differences were found. Daily grazing hours increased from 8.0 to 10.0 h day⁻¹ during the 40-day observation period. Milk production and calf age significantly influenced daily grazing hours and the partial regression coefficients were 0.05 h·day⁻¹·kg·day⁻¹ and −0.02 h·day⁻¹·day⁻¹, respectively. The overall mean distance traveled was 4.7 km day⁻¹ (82 observations) and followed the same trend as daily grazing hours. For each kilometer of travel, 2h were spent grazing during the four grazing periods. The 1S1H cows traveled less (P < 0.05) than HH, AH and 3S1H cows. Breed type means were 5.0, 4.8, 4.1 and 4.8 km day⁻¹ for HH, AH, 1S1H and 3S1H cows, respectively. The overall mean for pasture use was 103 ha per cow (47 observations) and breed type was not significant in explaining variation in pasture use. For each kilogram increase in calf weight (adjusted for cow condition), pasture use increased by 0.5 ha (P < 0.05). Thus, the grazing behavior of different breed types under rangeland conditions was similar.     

Lipid and biomass production by the halotolerant microalga Nannochloropsis salina

The effect of environmental factors on cell-lipid content, on the growth rate and on the overall productivity of Nannochloropsis salina was tested in the laboratory and in outdoor cultures. Under optimum conditions in the laboratory, the maximum growth rate (μ_max) was 0·030 h⁻¹, which corresponds to a doubling time of 23 h. Cellular lipid content was affected by the phase of growth and the temperature, but not by nitrogen starvation, pH or the source of sea water. The most important factor affecting the output rate of biomass was the cell concentration. The maximum biomass productivity obtained in outdoor ponds was 24·5 g·m⁻²·day⁻¹, and the lipid production rate was 4·0 g m⁻²·day⁻¹.     

Granulation in anaerobic sludge bed reactors treating food industry wastes

Three parallel laboratory reactors, R1, R2 and R3, received food industry wastewater: R1 unadulterated; R2 supplemented with calcium and phosphate; R3 supplemented with ferric chloride and traces of nickel and cobalt. Reactors were packed with active granular sludge from a large scale pilot reactor treating the same wastewater. Addition of calcium and phosphate was found to be detrimental to the granule formation at naturally established reactor pH = 6·9–7·4 in R2 while iron promoted granulation in R3. Conditions of upflow velocities of 1·5–6 m h⁻¹, rapid increase of loads up to 15 kg COD m⁻³ day⁻¹ and ratios of recycle to raw waste feed of 20:1–80:1 were imposed on all reactors. The granules in R1 and R2 disintegrated, from 70–100 g liter⁻¹ VSS to a flocculant sludge at 1·5–3 g liter⁻¹. In spite of such severe washout, reactors R1 and R2 were able to maintain a steady COD removal of over 90% at a load of 10kg m⁻³ day⁻¹. R3 retained a VSS concentration around 100 g liter⁻¹ and maintained COD removal at over 95%. R3 exhibited a more stable performance and was less vulnerable to the shock treatment to which all reactors were subjected.     

Fate of leaf litter in restored Kandelia obovata (S. L.) mangrove forests with different ages in Jiulong River Estuary,China

Ecological processing of leaf litter plays important roles in carbon dynamics of mangrove forests. Fate of leaf litter, that is, removal by crabs, microbial decomposition, and tidal export was quantified in two restored Kandelia obovata forests with ages of 24 years and 48 years, respectively, from December 2009 to November 2010. Crab abundance was also investigated to test the role of crabs in leaf litter processing. Daily leaf litter production was 1.064 ± 0.108 g C m^?2 day^?1 at the 24‐year forest and was 0.689 ± 0.040 g C m^?2 day^?1 at the 48‐year forest. Annual mean removal of leaf litter by crabs was lower at the 24‐year forest than at the 48‐year forest (0.177 ± 0.046 g C m^?2 day^?1 vs. 0.220 ± 0.050 g C m^?2 day^?1), due to a higher crab abundance at the older forest. Microbial decomposition and change in standing stock of leaf litter on the forest floor made a negligible contribution to the annual leaf litter production. Tidal exports of leaf litter were estimated as 0.875 ± 0.090 g C m^?2 day^?1 and 0.458 ± 0.086 g C m^?2 day^?1 at the 24‐year and 48‐year forests, respectively, accounting for 82.2% and 66.5% of their daily leaf litter production. Turnover rate of leaf litter was higher at the younger forest (1.7 ± 0.4 day^?1) than the older forest (1.2 ± 0.3 day^?1). Removal of leaf litter by crabs was higher in warm months while tidal export of leaf litter showed a much less apparent seasonal pattern. Spatial variations of crab removal and tidal export of leaf litter with forest zones were observed within each forest, while microbial decomposition of leaf litter was comparable among the different zones. These indicated that the ecosystem functions of restored mangrove forest could not reach a level equivalent to those of a mature forest even 24 years after restoration.     

Biomass yield and nutrient removal by water hyacinth (Eichhornia crassipes) as influenced by harvesting frequency

The effects of harvesting frequency on productivity, nutrient storage and uptake, and detritus accumulation by water hyacinth (Eichhornia crassipes /Mart/ Solms) cultured outdoors in nutrient-enriched waters were evaluated for a period of 13 months. Significant differences in hyacinth standing crop and productivity were measured with harvesting regimes of 1, 3 (harvest at maximum density) and 21 harvests over a 13-month period. The average plant standing crop decreased from 65 to 20 kg (fresh wt) m⁻² for systems with 1 and 21 harvests, respectively. Total harvested plant biomass was 67 kg (fresh wt) m⁻², 110 kg (fresh wt) m⁻² and 162 kg (fresh wt) m⁻² for 1, 3 and 21 harvests, respectively. The mean net productivity increased from 7·7 to 16·5 and 24·5 g (dry wt) m⁻² day⁻¹ for 1, 3 and 21 harvests, respectively. Nutrient storage in water hyacinth biomass (live, dead and detrital) at the end of the study decreased from 93 to 46 and 30 g N m⁻², and from 20 to 12 and 5 g P m⁻², for 1, 3 and 21 harvests, respectively. For the system with one harvest, 46% of the stored N and 25% of the stored P were recovered in dedrital tissue at the bottom of the tank. For the systtem with 21 harvests, only 11% of the stored N and 15% of the stored P were recovered in detrital tissue at the bottom of the tank. Ammonium-N and soluble reactive P concentrations in the water column were significantly higher for the treatment with one harvest compared to the treatments with 3 and 21 harvests.     

Effects of feeding propylene glycol to mid-lactating dairy cows

Propylene glycol (PG) is a gluconeogenic precursor widely used to prevent and treat ketosis postpartum. The study has investigated the effects of PG administration to dairy cows at mid stage of lactation. According to a 3 × 3 latin square design, three Italian Brown lactating cows (125 ± 7 days in milk) fitted with rumen cannula were fed a corn silage based diet (CP 14.7%, NDF 41.1% DM) with 0, 200 or 400 g day⁻¹ PG added. Dry matter intake was increased by feeding PG with a significant quadratic component per dose (16.2, 17.2 and 16.5 kg day⁻¹ for 0, 200 and 400 g PG day⁻¹, respectively). Milk yield was not affected by PG, averaging 17.1 kg day⁻¹. Average daily gain increased from 64 to 206 and 302 g day⁻¹ when cows received 200 and 400 g day⁻¹ of PG (linear component per dose P < 0.05). Digestibility of the diet did not differ among treatments, whereas repeated rumen fluid samples, taken 0, 2, 4, 6 and 8 h after the meal, showed a consistently lower acetate to propionate ratio when feeding PG. Blood insulin was not affected by PG administration. Except for therapeutic treatments, PG administration to dairy cows at mid stage of lactation should be advised against. Despite the positive effect on intake, administration of the additive, increasing the molar percentage of rumen propionate, contributes to shift the energy partition from milk production to liveweight gain.     

Key parameters for outdoor biomass production of Scenedesmus obliquus in solar tracked photobioreactors

The biomass productivity of Scenedesmus obliquus was investigated outdoors during all seasons in solar tracked flat panel photobioreactors (PBR) to evaluate key parameters for process optimization. CO₂ was supplied by flue gas from an attached combined block heat and power plant. Waste heat from the power plant was used to heat the culture during winter. The parameters pH, CO₂, and inorganic salt concentrations were automatically adjusted to nonlimiting levels. The optimum biomass concentration increased directly with the photosynthetic active radiation (PAR) from 3 to 5 g dry weight (DW)?L^?1 for a low PAR of 10 mol photons m^?2 day^?1 and high PAR of 40–60 mol photons m^?2 day^?1, respectively. The annual average biomass yield (photosynthetic efficiency) was 0.4?±?0.5 g DW mol^?1 photons. However, biomass yields of 1.5 g DW mol^?1 photons close to the theoretical maximum were obtained at low PAR. The productivity (including the night biomass losses) ranged during all seasons from ?5 up to 30 g DW m^?2 day^?1 with a mean productivity of 9?±?7 g DW m^?2 day^?1. Low night temperatures of the culture medium and elevated day temperatures to the species-specific optimum increased the productivity. Thus, continuous regulation of the biomass concentration and the culture temperature with regard to the fluctuating weather conditions is essential for process optimization of outdoor microalgal production systems in temperate climates.     

Seasonal growth and biomass ofTrapa japonica Flerov in Ojaga-Ike Pond,Chiba, Japan

In order to determine the seasonal growth and biomass ofTrapa japonica Flerov, field observations were carried out at Ojaga-ike Pond, Chiba, Japan, during 1979 and 1980. In spring, the plant showed exponential growth (c. 0.080 g g⁻¹ day⁻¹) and shoot elongation was as rapid as 10 cm day⁻¹. The plant attained its maximum biomass (380.5±35.1 g m⁻²) in late August, and about 50% of this was concentrated in the topmost 30-cm stratum (645.7±33.1 g m⁻³); maximum total stem length exceeded 6m. The plant produced large (500–800 mg per fruit), but small numbers of nut-like fruit (maximum, 5 fruits per rosette). Defoliation occurred almost linearly with time at a rate of 30.6 leaves m⁻² day⁻¹; annual net leaf production was estimated to be about twice as large as the seasonal maximum leaf biomass. While the number of leaves per rosette showed moderate seasonal change, rosette density, rosette area and leaf dry weight changed considerably during the year. From the negative log-log correlation between mean total leaf dry weight per rosette and rosette density, density-dependent rosette growth was assumed. The cause of the wide spread of this species in aquatic habitats is briefly discussed in terms of its seed size and morphology.     

Effects of diurnal fluctuations in light intensity on the efficiency of growth of Skeletonema costatum (Grev.) Cleve (Bacillariophyceae) in a cyclostat

The effects of diurnal variations in light intensity on the biomass characteristics and the efficiency of daily growth of Skeletonema costatum (Grev.) Cleve were evaluated. The relative importance of changes in carbon specific rates of respiration and organic release to the efficiency of growth was determined. Light intensity was either constant at 130 μE · m^?2 · s^?1 during the light period or fluctuated throughout the light period from 500 to 10 μE · m^?2 · s^?1 at rates of either 1 or 12 cycles · day^?1. Total daily light was equivalent for all light regimes at 5.6 E · m^?2 · day^?1.Daily rates of growth remained comparable at ≈ 1 · day^?1 under constant and fluctuating light regimes. Cell size as daily mean carbon · cell^?1, nitrogen · cell^?1 and cellular volume was decreased under diurnally varying light whereas daily mean chlorophyll a · cell^?1 was unaffected.Rates of respiration, organic release and gross production were elevated several fold under diurnally varying light in comparison to constant light. Net growth efficiency decreased from 0.69 under constant light to values of 0.50 and 0.38 under 1 and 12 cycles · day^?1, respectively. Decreased efficiency of growth under diurnally fluctuating light resulted mostly from greater respiratory activity while organic release remained < 10% of gross production. Increased rates of gross production reflected enhancement in the efficiency of carbon fixation with fluctuating light.     

The distribution,growth, and reproduction of the Antarctic limpet Nacella (Patinigera) concinna (Strebel, 1908)

Twenty-one monthly collections of the Antarctic limpet Nacella (Patinigera) concinna (Strebel, 1908) were obtained by divers at Signy Island, South Orkney Islands. A mean monthly population density of 123.7 ± 21.2 · m^?2, mean biomass of 13.7 ± 2.7 g dry tissue wt · m^?2, and annual production of 2.9 g · m^?2 were recorded in the depth range 2–12 m below mean low water.Shell growth was slow with a maximum growth rate, in the first 3–5 yr of life, of 3 4 mm per year. Maturity was attained at 7–8 yr (21 mm length), and maximum size (41 mm length) at about 21 yr. Unique spawning behaviour was observed in two Austral springs, and data relating spawning to the spring increase in sea temperature were obtained.     

Littoral benthos of the Northern Baltic Sea. IV. Pattern and dynamics of macrobenthos in a sandy-bottom Zostera marina community in Tvärminne

The composition and abundance of the macroscopic biota of a sandy-bottom Zostera marina community at a depth of 3–5 m were studied in Tvärminne, S Finland, in 1968–1971. Zostera occurred contagiously and very sparsely, 6 ± 2 shoots · m⁻², ash-free dry weight (AFDW) 2 ± 1 g · m⁻² (95% confidence interval). Totals of 45 plant and 70 animal taxa were found. Fucus vesiculosus (80%) and Zostera marina (11%) dominated the plant biomass, 16.5 ± 17.8 g · m⁻² in June 1971. At this time animal density was 8540 ± 830 ind. · m⁻² (0.6-mm mesh) and AFDW 17.3 ± 5.0 g · m⁻², 80–90% of the latter consisting of Macoma baltica, Mya arenaria, Corophium volutator, Nereis diversicolor and Hydrobia spp. The same percentage of animal density was made up by Hydrobia spp., M. baltica, C. volutator and Pygospio elegans. Normal analysis by classification of the samples suggested that the community was spatially rather homogeneous in 1971. Inverse analysis, based on interspecific correlations, revealed three distributional groups of species. These groups corresponded to the compositional subdivisions suggested by normal analysis. The community was subdivided into strata characterized by (D) deposit feeders, (Z) Zostera marina and (F) Fucus vesiculosus. The periodicity of the biota in the Zostera-characterized stratum was investigated. The principal dominants, especially Fucus, Zostera and Macoma, showed no distinct seasonal or interannual differences in 1968–1971, which made the community seem very stable. Yet, the species diversity of plants varied with the abundance of filamentous algae. Animal species diversity and mean animal density reached their seasonal minima in late summer, when the parental stocks of many invertebrates were dying and the summer's offspring were often still too small to be obtained by our methods. The recruitment of many important animal species failed in 1968 as compared with the other years.     

KINETICS OF GROWTH AND DEATH IN ANABAENA FLOS-AQUAE (CYANOBACTERIA) UNDER LIGHT LIMITATION AND SUPERSATURATION

The kinetics of population growth and death were investigated in Anabaena flos-aquae (Lyngb.) Bréb grown at light intensities ranging from limitation to photoinhibition (5 W·m⁻² to 160 W·m⁻²) in a nutrient-replete turbidostat. Steady-state growth rate (μ, or dilution rate, D) increased with light intensity from 0.44·day⁻¹ at a light intensity of 5 W·m⁻² to 0.99·day⁻¹ at 20 W·m⁻² and started to decrease above about 22 W·m⁻², reaching 0.56·day⁻¹ at 160 W·m⁻². The Haldane function of enzyme inhibition fit the growth data poorly, largely because of the unusually narrow range of saturation intensity. However, it produced a good fit (P < 0.001) for growth under photoinhibition. Anabaena flos-aquae died at different specific death rates (γ) below and above the saturation intensity. When calculated as the slope of a v_x⁻¹ and D⁻¹ plot, where v_x and D are cell viability (or live cell fraction) and dilution rate, respectively; γ was 0.047·day⁻¹ in the range of light limitation and 0.103·day⁻¹ under photoinhibition. Live vegetative cells and heterocysts, either in numbers or as a percentage of the total cells, showed a peak at the saturation intensity and decreased at lower and higher intensities. The ratio of live heterocysts to live vegetative cells increased with intensity when light was limiting but decreased when light was supersaturating. In cells growing at the same growth rate, the ratio was significantly lower under light inhibition than under subsaturation and the cell N:C ratio was also lower under inhibition. The steady-state rate of dissolved organic carbon (DOC) production increased with light intensity. However, its production as a percentage of the total C fixation was lowest at the optimum intensity and increased as the irradiance decreased or increased. The rate and percentage was significantly higher under photoinhibition than limitation in cells growing at the same growth rate. About 22% of the total fixed carbon was released as DOC at the highest light intensity. No correlation was found between the number of dead cells and DOC.