Population dynamics and production of Daphnia hyalina in a eutrophic reservoir

The population dynamics and production of Daphnia hyaiina^ the dominant cladoceran i n Eglwys Nynydd, a shallow eutrophic reservoir in South Wales, were studied for 2 years against a background of limnological measurements. The appearance and development of successive generations from egg to adult could be followed from changing numbers in arbitrarily defined size classes. Seasonal variations in mean length, mean brood-size and proportion of gravid adults were recorded and mean brood-size was related to changing food and temperature conditions. Egg-development times for D. hyaiina were determined in culture and the population parameters finite birth (S), instantaneous birth (b′), instantaneous population change (r′), instantaneous death (d′) and finite death rates (D) were estimated from field data. Turnover and production estimates were calculated from finite death rates and biomass. The calculated potential rate of increase (b′) was nearly always greater than the observed rate of increase (r′): seasonal changes in death rate (d′) generally parallel changes in birth rate (b′) but remain somewhat out of phase. Population oscillations are probably due t o a delay in the expression of the effects of population density upon birth and death rates. The mean biomass of Daphnia in 1970 was 0-57 mg dry wt/l (0-88 g C/m²) and in 1971 0-32 mg dry wt/l (0.49 g C/m²). Annual production for Daphnia was 11-8 mg dry wt/l (18-2 g C/m²) in 1970 and 8-30 mg dry wt/l (12 8 g C/m²) in 1971. Information available on primary production in the reservoir suggests that the production of Daphnia accounts for less than 2% of gross primary production. However, the pattern of population growth of Daphnia in Eglwys Nynydd almost certainly reflects a food limited system. In summer, blue-green algae may be abundant but serve as a poor food source: throughout the blue-green bloom egg production remains low, at times remaining below 0-5 eggs/adult.     

Habitat and substrate influences on population and production dynamics of a stream caddisfly, Ceraclea ancylus (Leptoceridae)

SUMMARY. Population and production dynamics of Ceraclea ancylus (Vorhies), a leptocerid caddisfly with a univoltine life cycle, five larval instars, and a single cohort population, were examined in Brashears Creek, Kentucky. A systematic sampling approach that included analysis in riffle, pool, and waterwillow bed habitats was used and fourteen sampling transects were taken across Brashears Creek between May 1971 and July 1972. For each of the 70 m² samples taken along a transect, the depth, habitat, and substrate type were recorded. The number of C. ancylus cases and numbers and dry weights of each larval instar were determined. The majority of the C. ancylus population was in the second larval instar in July, the third larval instar in August, the fourth larval instar in September, and the fifth larval instar from October through May. The spring population was 30% of the early instar maximum estimated the previous August. The spatial distribution of C. ancylus reflects a logarithmic pattern with early instar larvae more highly clumped than the late larval instar and pupal populations. Initial standing stock estimates were less than 1% of the standing stock biomass. A production estimate of 9.9 mg/m²·year (dry weight) was determined using the instantaneous growth method, Allen's Curve method, and the Hynes method of estimating secondary production. Turnover ratios (7.0 annual TR, 5.7 cohort TR) were higher than estimates reported as typical for benthic macroinvertebrates because of the low initial to final mean individual weight of the C. ancylus larvae (0.4%). Production estimates calculated for C. ancylus populations in waterwillow bed (4.4 mg/m²·year) and pool (13.7 mg/m²·year) habitats were less than calculated for the riffle population (19.9 mg/m²·year). The annual turnover ratio (10.2) was higher in the pool population than in other habitats because of spring larval migration into the pool from other habitats. A trend of higher production estimates with larger sized substrate particles and increased numbers of particles may reflect the increase in available food sources or attachment sites. The accuracy of production estimates and their applicability to water resource management may be limited by a failure to consider the spatial distributions of the population being sampled and the tendency for sampling procedures to be confined to single habitats.     

Primary production and biomass on a Dutch salt marsh: emphasis on the below-ground component

The primary production and below-ground biomass of angiosperms were measured in four almost monospecific vegetation stands situated on a salt marsh along the Oosterschelde estuary, The Netherlands. Maximum below-ground biomass values found for Spartina anglica, Elymus pycnanthus, Halimione portulacoides and Triglochin maritima, were very high relative to values reported from other European salt marshes: 12 586, 9 717, 17 737 and 16 121 g m^-2 respectively. These relatively high values may be due to the fineness of the sieve used, compared to other studies. The actual values are likely to be even higher because the sample treatment has probably caused loss of fine root material. Below-ground production estimates, based on the difference between maximum and minimum biomass, yielded: 6 044 g m^-2 yr^-1 for Spartina, 4 421 g m^-2 yr^-1 for Elymus, 7 799 g m^-2 yr^-1 for Halimione and 3 475 g m^-2 yr^-1 for Triglochin. This high production is mainly concentrated in the deeper layers of the root environment (20–60 cm). Although these production figures are considerably higher than those generally reported for comparable species or vegetation types in Europe, statistical evidence suggests that, for the first three species, they are real values rather than figures caused by random fluctuations.     

The Oldest,Slowest Rainforests in the World? Massive Biomass and Slow Carbon Dynamics of Fitzroya cupressoides Temperate Forests in Southern Chile

Old-growth temperate rainforests are, per unit area, the largest and most long-lived stores of carbon in the terrestrial biosphere, but their carbon dynamics have rarely been described. The endangered Fitzroya cupressoides forests of southern South America include stands that are probably the oldest dense forest stands in the world, with long-lived trees and high standing biomass. We assess and compare aboveground biomass, and provide the first estimates of net primary productivity (NPP), carbon allocation and mean wood residence time in medium-age stands in the Alerce Costero National Park (AC) in the Coastal Range and in old-growth forests in the Alerce Andino National Park (AA) in the Andean Cordillera. Aboveground live biomass was 113–114 Mg C ha^-1 and 448–517 Mg C ha^-1 in AC and AA, respectively. Aboveground productivity was 3.35–3.36 Mg C ha^-1 year^-1 in AC and 2.22–2.54 Mg C ha^-1 year^-1 in AA, values generally lower than others reported for temperate wet forests worldwide, mainly due to the low woody growth of Fitzroya. NPP was 4.21–4.24 and 3.78–4.10 Mg C ha^-1 year^-1 in AC and AA, respectively. Estimated mean wood residence time was a minimum of 539–640 years for the whole forest in the Andes and 1368–1393 years for only Fitzroya in this site. Our biomass estimates for the Andes place these ecosystems among the most massive forests in the world. Differences in biomass production between sites seem mostly apparent as differences in allocation rather than productivity. Residence time estimates for Fitzroya are the highest reported for any species and carbon dynamics in these forests are the slowest reported for wet forests worldwide. Although primary productivity is low in Fitzroya forests, they probably act as ongoing biomass carbon sinks on long-term timescales due to their low mortality rates and exceptionally long residence times that allow biomass to be accumulated for millennia.     

Comparison of Rates of Flagellate Bacterivory and Bacterial Production in a Marine Coastal System

Protozoan predation on bacteria and bacterioplankton secondary production were simultaneously determined in La Salvaje Beach water during 1990. Protozoan grazing on bacterioplankton was measured from fluorescently labeled bacterium uptake rates; estimates of bacterial secondary production were obtained from [³H]thymidine incorporation rates. Two different conversion factors were used to transform thymidine incorporation rates into bacterial production rates; both of them were specific for La Salvaje Beach and were calculated by using empirical and semitheoretical approaches. The average flagellate predation rate was 14.0 bacteria flagellate^-1 h^-1; the average population predation rate was 7.35 x 10⁶ bacteria liter^-1 h^-1. The estimates of bacterial production differed greatly depending on the conversion factor used, and so did the percentages of bacterial production consumed by flagellated protozoa (4.6% when the empirical conversion factor for La Salvaje Beach was used and 113% when the semitheoretical conversion factor specific for this system was used). The ecological implications of each of these values are discussed.     

Snail numbers,biomass and respiratory metabolism in a beech woodland — Wytham Woods,Oxford

Summary Two methods of extraction were used in the estimation of snail population densities in woodland litter. The time-consuming-Vágvölgyi technique proved to be 6.25 times more efficient than infra-red heat extraction but it was shown that the results obtained by the latter method could be easily corrected to conform with those of the former.Snail density varied with season (Winter, 1,000–1,250 m^-2, Summer, 50–600 m^-2), the annual mean density being 645 m^-2. The annual mean ash-free dry weight biomass was 176 mg m^-2 while annual population metabolism equalled 0.8941 O₂ (=17.84 kJ m^-2 yr^-1).Two independent estimates of the energy equivalent of food consumption gave rise to values of 25.37 and 57.98 kJ m^-2 yr^-1, these respectively account for 0.54 and 1.23% of the known ground litter disappearance of 4,716.58 kJ (=235 g dry wt. m^-2 yr^-1).     

Chitin production by arthropods in the hydrosphere

Chitin is widely distributed in nature and its annual production is thought to be huge. However, the chitin production has been rarely estimated in aquatic ecosystems, despite the growing economic interest in this polymer. Arthropods are one of the main chitin producers in the hydrosphere and a correct evaluation of the chitin production by these organisms in the different marine and freshwater ecosystems is of prime interest to understand their importance in the biogeochemical cycles of carbon and nitrogen. Such evaluation is also worth considering to achieve a rational exploitation of crustaceans which are currently the major source of chitin for the industry. Annual chitin production of crustaceans and insects in aquatic ecosystems was estimated on the basis of annual tissue production estimates and body chitin content measurements. About 800 annual tissue production estimates were collected from the literature. Estimates mainly concerned continental fresh waters and neritic ecosystems. Data were almost inexistent for athalassohaline and oceanic ecosystems. On the whole, 60% of the production estimates fell between 0.1 and 10.0 g dry weight m^–2 yr^–1. Published chitin levels in crustaceans and insects ranged from 3 to 16% of the whole body dry weight. Data were, however, lacking for some major groups such as trichopterans or amphipods. Aquatic insects and crustaceans were therefore collected and assayed for chitin using a highly specific enzymatic method. The chitin content of the collected insects (Coleoptera, Diptera, Ephemeroptera, Odonata, Plecoptera, Trichoptera) varied from 3 to 10% of the whole body dry weight; that of the collected crustaceans (Amphipoda, Branchiopoda, Copepoda) from 2.5 to 8.5% of the whole body dry weight. Total annual chitin production by arthropods had been estimated to 28 × 10⁶ T chitin yr^–1 for the freshwater ecosystems, to 6 × 10⁶ T chitin yr^–1 for athalassohaline ecosystems and to 1328 × 10⁶ T chitin yr^–1 for marine ecosystems. The importance of the chitin production corresponding to the formation of exuviae and peritrophic membranes in arthropods and the chitin production by non-arthropod organisms in the chitin budget of aquatic ecosystems was highlighted and discussed.     

Zygote-derived seedling production of Sargassum thunbergii: focus on two frequently experienced constraints in tank culture of seaweed

Mass collection of germlings and growth of fouling algae are two main constraints for the seedling production of Sargassum thunbergii. In this study, 65% and 40% of reproductive output (allocation of biomass to sexual reproductive tissue) for farmed and natural populations respectively, were recorded during peak reproduction. In terms of germlings per kilogram wet weight of plants, the farmed population gave a higher yield than the natural population (3.2?×?10⁵ and 1.2?×?10⁵ germlings kg^-1, respectively). These results indicate that farmed populations could be used as parental plants for germling collection in seedling production. During the experiment, fouling was controlled by jet washing and high-density seeding. A germling detachment of less than 10% was observed when, after 48?h of attachment, collectors were jet-washed with an intensity of 1?kg cm^-2. High-density seeding had adverse effects on length mean, size equality, and occurrence of branches of germlings. However, 30–50 individuals cm^-2 are thought to be usable in the seedling production of S. thunbergii because of less density effects. Seedlings of?>?0.5?cm length could be achieved after 1?month of tank culture.     

Production of Cricotopus ornatus (Meigen) (Diptera: Chironomidae) in Waldsea Lake,Saskatchewan

Cricotopus ornatus was the predominant chironomid in meromictic, saline Waldsea Lake. Annual production of C. ornatus larvae in the mixolimnion was estimated to be 107 mg m^-2 (dry weight) in 1974, 66.5 mg m^-2 in 1975 and 69.5 mg m^-2 in 1976. These estimates are similar to those for chironomids in Canadian arctic lakes and deep-water areas of the Great Lakes. Annual P/B ratios were 5.4 in 1974, 6.8 in 1975 and 6.8 in 1976. These ratios are in the middle of the range reported for chironomids. The major factors limiting chironomid production in Waldsea Lake appear to be: (1) restriction of the habitable zone because of meromixis with accompanying loss of mobile first and second instars that are swept out of the mixolimnion (2) the relatively narrow zone of good C. ornatus habitat, i.e. areas of dense macrophyte or benthic algal growth and (3) predation by nine-spine stickleback and damselfly naiads.     

Studies on some aspects of peroxidase from submaxillary gland

A peroxidase has been purified 25- to 30-fold over crude homogenate from goat submaxillary gland, which shows a single band of protein on polyacrylamide gel electrophoresis at four different pH values (4.6–10.0). A molecular weight (M_r) of approximately 2 × 10⁴ per heme binding site has been found. The molecular weight of the enzyme determined by Sephadex-gel filtration method, appeared to be 4 × 10⁴. The sedimentation pattern of the purified enzyme shows a symmetrical peak, although there was evidence of some small heterogenous material near the meniscus. The sedimentation coefficient of the enzyme (s^o 20^wat 0.4% of the enzyme concentration) was found to be 4.18, which indicates the molecular weight of the enzyme to be approximately 6 × 10⁴.     

Studies on production and food consumption by the larval simuliidae (Diptera) of a chalk stream

Summary Large populations of S. ornatum and S. equinum inhabit Ranunculus plants in the Bere Stream at Bere Heath. A weekly sampling programme obtained both larvae and pupae. The results of weekly sampling indicated four annual generations of S. ornatum and three of S. equinum. Quantitative samples of larvae, obtained at least three times in each generation gave estimates of production ranging from 0.26 g to 2.75 g dry weight m-² per generation of larvae of S. equinum and 0.15 g to 1.19 g dry weight m-² per generation of larvae of S. ornatum.Retention times of food by larvae, under field conditions were in the order of twenty to thirty minutes. Following determination of the weight of the gut contents for each size class of larvae, the activity of feeding larvae was calculated to achieve complete theoretical clearance of suspended material in a distance of 0.6 km, at peak population densities in the summer months.Dept. of Applied Biology, Bath University of Technology     

The production of five genera of Chironomidae (Diptera) in Lake Norman,a North Carolina reservoir

The production of five genera of chironomids collected at 4- and 8-m depths at four stations in Lake Norman, North Carolina, was estimated using the size-frequency method. To correct for multivoltinism, the estimates were adjusted by multiplying by 365/Cohort Production Interval. Ranges of production estimates (P) in milligrams dry mass m^-2 yr^-1 and production/mean annual biomass ratios (P/B ratios) for each genus over both depths were: Tanytarsus, P = 744 to 8788, P/BB = 66 to 176; Cladotanytarsus, P = 74 to 2387, P/B = 69 to 100; Stempellina, P = 19 to 412, P/ B = 74 to 132; Chironomus, P = 166 to 7293, P/ B = 50 to 70; Cryptochironomus, P = 92 to 398, P/ B = 71 to 221. These estimates are among the highest reported for chironomids, due primarily to the rapid larval development times estimated for these genera.     

The “deduction” approach: A non-invasive method for estimating secondary production of earthworm communities

Secondary production is an important parameter for the study of population dynamics and energy flow through animal communities. Secondary production of earthworm communities has been determined with the size-frequency and instantaneous growth rate methods, whereby earthworm populations are repeatedly sampled at regular intervals and the change in biomass of cohorts or individuals between sampling dates is determined. The major disadvantage of repeated sampling is that it disturbs the soil and permanently removes earthworms from the study area. The “deduction” approach is a theoretical model that partitions individuals into defined pools and makes assumptions about the growth, recruitment and mortality of each pool. In 2004 and 2005, earthworms were added to undisturbed field enclosures and the “deduction” approach was used to estimate secondary production of the indigenous and added earthworm populations during the crop growing period (17–18 weeks) in each year. Secondary production estimates made by the “deduction” approach were similar to estimates from direct earthworm sampling in temperate agroecosystems. The “deduction” approach is an indirect method that estimates population dynamics and secondary production, and is appropriate for manipulation experiments where removal of organisms and physical disturbance of the habitat by repeated sampling could bias results.     

Dynamics and Distribution of Cyanophages and Their Effect on Marine Synechococcus spp.

Cyanophages infecting marine Synechococcus cells were frequently very abundant and were found in every seawater sample along a transect in the western Gulf of Mexico and during a 28-month period in Aransas Pass, Tex. In Aransas Pass their abundance varied seasonally, with the lowest concentrations coincident with cooler water and lower salinity. Along the transect, viruses infecting Synechococcus strains DC2 and SYN48 ranged in concentration from a few hundred per milliliter at 97 m deep and 83 km offshore to ca. 4 × 10⁵ ml^-1 near the surface at stations within 18 km of the coast. The highest concentrations occurred at the surface, where salinity decreased from ca. 35.5 to 34 ppt and Synechococcus concentrations were greatest. Viruses infecting strains SNC1, SNC2, and 838BG were distributed in a similar manner but were much less abundant (<10 to >5 × 10³ ml^-1). When Synechococcus concentrations exceeded ca. 10³ ml^-1, cyanophage concentrations increased markedly (ca. 10² to > 10⁵ ml^-1), suggesting that a minimum host density was required for efficient viral propagation. Data on the decay rate of viral infectivity d (per day), as a function of solar irradiance I (millimoles of quanta per square meter per second), were used to develop a relationship (d = 0.2610I - 0.00718; r² = 0.69) for conservatively estimating the destruction of infectious viruses in the mixed layer of two offshore stations. Assuming that virus production balances losses and that the burst size is 250, ca. 5 to 7% of Synechococcus cells would be infected daily by viruses. Calculations based on contact rates between Synechococcus cells and infectious viruses produce similar results (5 to 14%). Moreover, balancing estimates of viral production with contact rates for the farthest offshore station required that most Synechococcus cells be susceptible to infection, that most contacts result in infection, and that the burst size be about 324 viruses per lytic event. In contrast, in nearshore waters, where ca. 80% of Synechococcus cells would be contacted daily by infectious cyanophages, only ca. 1% of the contacts would have to result in infection to balance the estimated virus removal rates. These results indicate that cyanophages are an abundant and dynamic component of marine planktonic communities and are probably responsible for lysing a small but significant portion of the Synechococcus population on a daily basis.     

Dynamics of bacterioplankton in a mesotrophic French reservoir (Pareloup)

Bacterioplankton abundance, biomass and production were studied at a central station (35 m depth) from April 1987 to September 1988 in a mesotrophic reservoir. Bacterial production was calculated by the (³H) thymidine method.For the water column, integrated estimates of bacterioplankton abundance ranged from 2.3 10⁹ to 4.6 10⁹ cells l^–1, and carbon biomass from 0.037 to 0.068 mg C l^–1; the thymidine incorporation rates ranged from 0.8 to 17.2 picomoles l^–1 h^–1, leading to net bacterial production estimates of less than 0.7 µg C l^–1 d^–1 in winter to 18 µg C l^–1 d^–1 in summer. About 55% of the production occurred in the euphotic layers.Over the year, the bacterial carbon requirement represented 90% of the autotrophic production for the whole lake. It was five times lower than autotrophic production in spring, but twice as high in summer. This important temporal lack of balance suggests that not all the spring primary production products are consumed immediately and/or that other carbon sources probably support bacterial growth in summer.     

In situ estimates of annual net nitrogen mineralization and nitrification in a subarctic watershed

Summary Annual estimates of surface soil nitrogen transformations were determined using an in situ method in four different subarctic vegetation types within a watershed in southwestern Alaska. The net nitrogen mineralization estimates were 22.5, 0.5, 4.7, and 2.7 kg-N ha^-1 yr^-1 for the alder, dry tundra, moist tundra, and white spruce sites, respectively. Only the soil from the alder site showed net nitrification (about 10 kg-N ha^-1 yr^-1). Annual inogranic nitrogen flux from the overlying organic layer to the mineral soil was almost seven times greater than net N production in the surface mineral soil in the alder site, indicating that the alder forest floor is potentially a substantial source for plant-available N. Rates of mobilization of N from the surface organic layers of the other sites were similar to net N production rates in surface mineral soils. In situ rates of N transformations showed a similar trend among sites as did laboratory estimates conducted in a previous study, suggesting a strong substrate control of N transformations in these soils.     

Calorific values of the soft parts of the tellinid bivalve Macoma balthica (L.) as determined by two methods

Calorific values of the ash-free dried soft parts of Macoma balthica (L.), sampled monthly during 1 year at a tidal flat station in the Dutch Wadden Sea, have been estimated by two methods. The indirect method started from an analysis of the biochemical composition and used conversion factors for the various components to calculate the calorific value of the total tissue. The direct method employed a micro-bomb calorimeter and a furnace for separate ash determinations.The indirect method yielded estimates that were consistently higher than those from the direct one. Two sources, explaining most of the difference, could be traced, viz. incomplete drying of the samples used in the calorimeter and a too high conversion factor for weight to calories applied conventionally for lipids. This conversion factor was found to depend on the method of extraction of the lipids. but was always significantly below the commonly used 9.3 to 9.7 cal · mg^?1.The best estimates for the annual mean of the calorific value at complete combustion of the ash-free and well-dried soft parts of Macoma were 5.47 for the direct and 5.59 cal·mg^?1 ash-free dry wt for the indirect method. Both values are higher than estimates for Macoma published earlier by various authors. Calorific values at physiological oxidation amount to only about 4.6 cal·mg^?1 or less, due to incomplete protein oxidation.For this reason, it is concluded that biologically significant calorimetry cannot dispense with biochemical analysis. On the other hand, calculation of calorific values from biochemical composition should be accompanied by some calorimetry, as the conversion factor for the lipid fraction, at least, may deviate significantly from commonly applied values.     

Calibration of a burrow count index for the Indian desert jird, Meriones hurrianae

Population estimates, often difficult to acquire, warrantee the use of an index as an economical substitute for rapid assessments of populations. We estimated population size of the little known social, semi-fossorial Indian desert jird (Meriones hurrianae) in Kachchh, Gujarat, India under closed population capture-mark-recapture (CMR) framework to calibrate a burrow count index for the species. A total of 147 individuals were trapped in 16 colonies using baited Sherman traps and the number of burrow entrances at each colony was recorded. Data from colonies with low number of captures were pooled to estimate capture probability using Huggins heterogeneity models with gender, site, body weight and age category as covariates in Program MARK. Colony sizes ranged from 2 to 46 individuals. The number of burrow entrances was calibrated against CMR-based population estimates using least squares regression (n = 16, adjusted R ² = 0.96, t = 18.18, P < 0.001). The index was further validated using Jackknife (JK) analysis where JK-predicted population estimates strongly correlated with CMR estimates (r = 0.96, P < 0.001). In habitats and climatic conditions similar to Kachchh and within the range of colony sizes sampled, our calibrated index can be a valuable and effective tool for large scale surveys of the desert jird, which occupies a keystone trophic level in the semi-arid ecosystem.     

Estimating Arundo donax shoot biomass

We developed an equation for estimating Arundo donax shoot dry weight from shoot length. The equation, shoot dry weight (g) = 14.254 (standard error = ±0.275) × shoot height² (m), was as effective at explaining a high proportion of total variation in shoot dry weight (R² = 0.90) as more complicated equations containing additional morphometric parameters. Tested against two independent datasets, the equation provided accurate estimates of dry weight for shoots ranging from 0.3 to 7.06 m height (dataset 1, P < 0.0001, R² = 0.87, N = 29; dataset 2, P < 0.0001, R² = 0.82, N = 192). The equation provides aboveground biomass estimates from stem counts and heights more rapidly than harvest methods.     

Studies on Chironomidae in experimental recirculating stream systems. II. The growth, development and production of a spring generation of Orthocladius (Euorthodadius) calvus Pinder

SUMMARY.

• 1 Orthodadius (Euorthodadius) calvus Pinder. similar to Orthocladius (Euorthodadius) thienemanni Kieffer. colonized a new gravel substratum in two recirculating stream channels. A maximum population density of 68.621 m^-2 was attained after only 16 days. This had fallen to a negligible density by the thirty-third day.
• 2 Some recruitment occurred over most of the study period (April-May 1981) and no single sharply defined cohort was evident. There was a large range of body lengths within each instar. and considerable overlap between instars. The population density estimates for instars I and II were low compared with instars III and IV.
• 3 The relationship between instantaneous growth rate (g) and geometric mean length indicated that growth was best described by a Gompertz curve. Growth rate decreased with increasing length from a value of about 40% length day^-1 at 2 mm body length to about 5% length day^-1 at 9 mm.
• 4 Growth rates for individual larvae, kept in culture, were very variable with maximum rates close to the values determined from the field data. Mean duration of larval life was 16 days.
• 5 Estimates of production for the study period ranged from 13.5 g dry wt m^-2 (Channel III, size-frequency method) to 34.2 g dry wt m^-2 (Channel II, Allen's graphical method, values corrected for non-linear growth).
• 6 Gut contents were estimated to represent about 55% of the total weight therefore production values should be reduced by this amount.