Nitrogen fixation in subarctic streams influenced by beaver (Castor canadensis)

Nitrogen fixation was measured in four subarctic streams substantially modified by beaver (Castor canadensis) in Quebec. Acetylene-ethylene (C₂H₂ C₂H₄) reduction techniques were used during the 1982 ice-free period (May–October) to estimate nitrogen fixation by microorganisms colonizing wood and sediment. Mean seasonal fixation rates were low and patchy, ranging from zero to 2.3 × 10^–3 µmol C₂H₄ · cm^–2 · h^–1 for wood, and from zero to 7.0 × 10^–3 µmol C₂H₄ · g AFDM^–1 · h^–1 for sediment; 77% of all wood and 63% of all sediment measurements showed no C₂H₂ reduction. Nonparametric statistical tests were unable to show a significant difference (p > 0.05) in C₂H₂ reduction rates between or within sites for wood species or by sediment depth.Nitrogen contributed by microorganisms colonizing wood in riffles of beaver influenced watersheds was small (e.g., 0.207 g N · m^–2 · y^–1) but greater than that for wood in beaver ponds (e.g., 0.008 g N · m^–2 · y^–1) or for streams without beaver (e.g., 0.003 g N · m^–2 · y^–1). Although mass specific nitrogen fixation rates did not change significantly as beaver transform riffles into ponds, the nitrogen fixed by organisms colonizing sediment in pond areas (e.g., 5.1 g N · m^–2 · y^–1) was greater than that in riffles (e.g., 0.42 g N · m^–2 · y^–1). The annual nitrogen contribution is proportional to the amount of sediment available for microbial colonization. We estimate that total nitrogen accumulation in sediment, per unit area, is enhanced 9 to 44 fold by beaver damming a section of stream.     

The impacts of a watershed CaCO3 treatment on stream and wetland biogeochemistry in the Adirondack Mountains

Temporal and longitudinal variations in the chemistry of two tributary streams of Woods Lake in the Adirondack Mountains of New York were monitored before and after a watershed CaCO₃ application. One subcatchment of the lake had a large beaver pond and wetland at its headwaters, while the second was free-flowing. Treatment of both subcatchments with CaCO₃ resulted in an immediate increase in acid neutralizing capacity (ANC) associated with Ca²⁺ release. The extent and duration of the response to the treatment were greater in the wetland-impacted stream. Aluminum was retained and complexed with organic solutes generated within the beaver-pond. In the free-flowing stream, NO ₃ ^– concentration increased significantly after the manipulation; this pattern was not evident in the wetland-impacted stream. Net retention of SOkinf4/sup2– was evident in the beaver pond prior to and following treatment, and this response was enhanced after the watershed liming. Comparisons of beaver pond inlet/outlet concentrations, mass balance calculations, and in-pond profiles of chemical parameters revealed patterns of retention of SO ₄ ^2– , NO ₃ ^– and Al, and release of Fe²⁺, dissolved organic carbon (DOC) and NH ₄ ⁺ in the wetland during the summer before CaCO₃ treatment. Post-treatment releases of Ca²⁺ from the near-sediment zone in the beaver pond corresponded to anoxic periods in mid- to late-summer and under ice in winter. These findings demonstrate the importance of increased microbial processing of organic matter, along with high partial pressure Of CO₂ (Pco₂) in facilitating the dissolution of the applied CaCO₃. Dissolved silica (H₄SiO₄) was retained in the wetland during the summer prior to treatment but was released after the manipulation. This phenomenon may reflect the dissolution of diatom frustules or silicate minerals in the wetland at higher pH and DOC concentrations. Within two years of the CaCO₃ treatment 60% of the CaCO₃ applied to the beaver pond and surrounding wetland was dissolved and transported from the pond, in contrast to only 2.2% of the CaCO₃ applied to the upland subcatchment draining into the wetland. These results, coupled with high quantities of exchangeable Ca²⁺ found in sediments and onSphagnums mosses in the pond, demonstrate the importance of hydrologic source areas and wetlands in facilitating the dissolution of added CaCO₃ and in regulating the production of chemical species important in ANC generation.     

Short-term effects of a catastrophic beaver dam collapse on a stream fish community

Synopsis We examined the short-term effects of the natural catastrophic collapse of a beaver dam on downstream benthic insect density and fish community structure in a headwater tributary of the Mississippi River. The catastrophic collapse of the dam and ensuing flash flood resulted in a dramatic (< 90%) decrease in benthic insect density in riffle and pool habitats. Sixty days after collapse of the dam, insect densities in riffles were 62% of pre-collapse densities. Insect recolonization of pools was slower than for riffles; 60 days after collapse of the dam insect densities in pools were 8% of pre-collapse levels. Collapse of the beaver dam altered the structure of the downstream fish community by causing a short-term (2–4 days) influx of pond species, resulting in a brief increase in species richness and abundance. Fish species richness and abundance then decreased for 4–60 days to levels below those prior to the collapse.     

Activity of beavers as an ecological factor that affects the benthos of small rivers - a case study in the Żylica River (Poland)

The Eurasian beaver (Castor fiber) has a greater impact on local ecosystems than other herbivores, and the affected area exceeds the range of its presence. Its activity may change or create new habitats by modifying the availability of the biotic and abiotic resources available not only to beavers, but also to other groups of animals. Our aim was to study how beaver activity affects the benthos composition in a small river and in a beaver pond. The way in which beavers function in the case of small rivers has received little attention. The study showed a lower density of benthos above the dam (beaver pond - 1467 ind./m²) compared to the river (3147 ind./m²). Below the dam, the diversity of Trichoptera and Coleoptera was greater, while Diptera were more abundant in the beaver pond. Betidae were a constant component in the benthos assemblages and were most abundant in the beaver pond. Collectors-gatherers and predators were the most numerous in the beaver pond. Decreasing percentages of collectors-gatherers were observed with an increased abundance of collectors-filterers and shredders in the river. All of the ratio values except the P/T FFG (Predators to total of all other groups) were lower in the beaver pond compared to the river. The % EPT (Ephemeroptera Plecoptera and Trichoptera) was also greater in the beaver pond. Small differences in the physicochemical properties of the water and organic matter content in the bottom sediments were found both above and below the beaver dam.     

The effect of fertilization regime on juvenile walleye growth and prey utilization in rearing ponds

Synopsis The effect of two contrasting fertilization regimes on juvenile walleye growth, survival and harvest was tested in six identical rearing ponds treated with fermented soybean meal at either a constant (36 g m^–3week^–1) or a progressively reduced (32 to 0 g m^–3week^–1) rate. Walleye length, percent survival and biomass harvest in constant fertilization ponds were 32, 83 and 294% greater, respectively, than those of reduced fertilization ponds. Chironomid larvae and pupae were the dominant prey (in terms of biomass) in juvenile walleye larger than 22 mm TL. Mean chironomid biomass was significantly higher in the constant fertilization ponds (5.1 vs. 1.7 g dry wt m^–2), particularly after peak emergence around week 4. Zooplankton were less important prey after week 2, and mean zooplankton density was not significantly different between treatments. From these data we conclude that better walleye performance in the constant fertilization ponds was due to higher chironomid density during the last half of the experiment. Our findings are reviewed in light of current knowledge of juvenile walleye feeding ecology and contemporary pond culture procedures.     

Beaver population fluctuations and tropospheric methane emissions in boreal wetlands

Measurements of net methane flux were made during the 1988 ice-free season (May–October) at a beaver-meadow complex in northern Minnesota, USA. The site included upland boreal forest, sedge meadow, submerged aquatic plants, and the open water of a beaver pond. Annual fluxes were 8–11 g C/m² in the permanently wetted zones and 0.2–0.4 g C/m² at the occasionally inundated meadow and forest sites. These data, when coupled with long-term (46 yr) data on beaver (Castor canadensis) population size and habitat alteration, suggest that about 1% of the recent rise in atmospheric methane may be attributable to pond creation by beaver in North America.     

The effects of predation on the survival and size-distribution of estuarine fishes: an experimental approach

Synopsis The effect of southern flounder,Paralichthys lethostigma, predation on the survival and size-distribution of spot,Leiostomus xanthurus, was investigated using feeding experiments in outdoor tanks and estuarine ponds. In the outdoor tank experiments, southern flounder, 143 mm average standard length (SL), fed for 48 h on spot (25–30 mm SL), over a range of densities (4–20 m^–2). In these trials, flounder showed a Type II functional response to spot density. In the estuarine pond experiment, flounder density (2 or 4 flounders 70 m^–2) contributed significantly to spot mortality relative to predator-free controls. The effect of flounder density on spot mortality was non-linear; in the 4-flounder treatment the daily instantaneous mortality due to flounder (0.0177) was 3.5 times that in the 2-flounder treatment (0.0051). The total spot mortality rate in the 4-flounder treatment (0.028) was similar to that observed from published field observations. Flounder also altered the size distribution of spot relative to predator-free controls. Predation by flounder resulted in fewer intermediate-sized spot at the end of the experiment when compared to predator-free controls. Flounder also significantly reduced survival and mean length of two killifishes,Cyprinodon variegatus andFundulus heteroclitus, that invaded the pond. Flounder predation was a significant size-structuring force on the prey fish assemblage in the pond. Results from both the outdoor tank experiment and the pond experiment indicate that flounder may represent a significant source of mortality for juvenile estuarine fishes.     

Towards an understanding of human impact upon the hydrology of Lake Naivasha,Kenya

The growth of a strain of Moina macrocopa (Straus 1820) isolated from an experimental stabilization pond in Marrakesh, was examined at seven concentrations of algae (6.25–6.25 × 10⁵ cells ml^–1 and at 5 different temperatures (15–30 °C)). Feeding conditions influenced the growth rate as well as the maximum size that reached 1.8 mm at 25 °C and at the highest algal concentration (6.25 × 10⁵ cell ml^–1). The life span and number of moltings reached a maximum (17.4 days and 13 moltings) at average nutrient concentrations (6.25 × 10⁵ cell ml^–1). Juvenile stages varied from 1 to 3 and adult ones from 6 to 8. In the temperature interval tested, growth rate increased with temperature while longevity decreased. Temperature had less effect on maximal size than nutrient availability. Population density (but not crowding) influenced longevity and survival but had no effect on growth.     

Emergence of Chironomidae from the shallow eutrophic Lake Kasumigaura,Japan

Seasonal chironomid emergence was monitored in the shallow eutrophic Lake Kasumigaura and 18 species were collected with a battery-operated light trap fixed on a floating stage and with surface emergence traps. During October–December, samples in the light trap comprised exclusively Tokunagayusurika akamusi (Tokunaga) and small numbers of one or two other species. T. akamusi, Procladuis (Holotanypus) culiciformis (L.), and Chironomus plumosus (L.) constituted 91.6% of the annual catch of chironomid adults. The predominance of T. akamusi (75.3 % of chironomid catch) and the high ratio (13) of T. akamusi to C. plumosus was more marked in this lake than other Japanese eutrophic lakes. Glyptotendipes tokunagai Sasa and Dicrotendipes pelochloris (Kieffer) were also caught abundantly with the light trap, but not with surface traps, indicating these were littoral species. The dry weight of emerging adults during May–December 1982 was 2.87 g m^–2, of which 1.92 gm^–2 (67%) was T. akamusi and 0.67 gm^–2 (23%) C. plumosus and 0.23 g m^–2 (8%) Clinotanypus sugiyamai Tokunaga and 0.03 gm^–2 (1%) P. (H.) culiciformis. The weight of emerging Tanypodinae was much higher than the annual mean larval biomass or estimated larval production, which have been due to underestimating the population density using an Ekman-Birge dredge. High numbers of individuals and species of chironomids were caught during April–July, presumably as a result of the high food supply for chironomid communities.     

Phosphorus and nitrogen retention in five Precambrian shield wetlands

Phosphorus and nitrogen mass balances of five wetlands (two beaver ponds, two conifer-Sphagnum swamps and one sedge fen) situated in three catchments in central Ontario, Canada, were measured. Monthly and annual input-output budgets of total phosphorus (TP), total nitrogen (TN), total organic nitrogen (TON), total inorganic nitrogen (TIN), ammonium ion (NH₄ ⁺ -N), nitrate (NO ₃ ^– -N) and dissolved organic carbon (DOC) were estimated for the five wetlands during the 1982–83 and 1983–84 water years. Except for the deepest beaver pond (3.2 m) which had annual TP retention of –44% (–0.030 ± 0.015 g m^–2 yr^–1), the wetlands retained < 0.001 to 0.015 g M^–2 yr^–1 ; however, this wasless than 20% of the inputs and the estimated budget uncertainties were equal to or greater than the retention rates. Annual TN retentions ranged from –0.44 to 0.56 g m^–2 yr^–1 (–12 to 4%) but were not significantly different from zero. The wetlands transformed nitrogen by retaining TIN (16 to 80% RT) and exporting an equivalent amount as TON (–7 to 102% RT). The beaver ponds, however, retained NO ₃ ^– while NH ₄ ⁺ was passed through or the outputs exceeded the inputs. In contrast, the conifer swamps retained both NH ₄ ⁺ and NO ₃ ^– . DOC fluxes into and out of the beaver ponds were equal (–18 and 4% RT) but output from the conifer swamps exceeded input by > 90%. Marked seasonal trends in nutrient retention were observed. Nutrient retention coincided with low stream flow, increased evapotranspiration and biotic uptake during the summer. Net nutrient export occurred during the winter and spring when stream flows were highest and biotic uptake was low.     

Microbial treatment of a synthetic sour brine

Summary The ability of the chemoautotroph and facultative anaerobeThiobacillus denitrificans to deodorize and detoxify an oil-field-produced water containing sulphides was evaluated under simulated field conditions. A sulphide-tolerant strain ofT. denitrificans was used to remove inorganic sulphide from a synthetic sour brine containing 4000 mg L^–1 total dissolved solids (TDS) and 100 mg L^–1 sulphide. The sour brine was treated continuously in a rectangular plugflow reactor which approximated the scaled dimensions of an existing field detention pond. The head space of the reactor was purged with N₂ in order to capture H₂S off-gases in a zinc acetate trap. Brine was fed to the reactor continuously for 90 days at rates corresponding to residence times of 0.17–6 days. Temperature and pH ranged from 22 to 40.5°C and 7.5 to 8.8, respectively. The start-up biomass concentration was approximately 100 mg L^–1 (by dry weight). No. additionalT. denitrificans biomass was added to the reactor after start-up. At residence times of 0.3 days and greater inorganic sulphide was undetectable in the effuent. No H₂S was detected in the outlet gas or the zinc acetate trap. Approximately 80% of the sulphide feed was oxidized to sulphate and removed from the reactor in the liquid effluent. The remainder was partially oxidized to elemental sulphur which was retained in the reactor. It is suggested that oxidation of inorganic sulphides byT. denitrificans represents a viable process concept for the treatment of sour water co-produced with oil and gas.     

Larval abundance of Chironomus circumdatus in relation to biotic and abiotic factors

Larval abundance of Chironomus circumdatus in sewage canal and pond systems was studied during 1988–1990. Monthly changes in the morphometric features of the pond revealed that both total and littoral areas progressively decreased from 1063 and 107 m² in December 1988 to 151 and 43 m² in May '89; the decrease during the year 1989–1990 was from 1116 and 92 m² in October to 109 and 31 m² in May. A significant negative correlation (r= – 0.52) was obtained for the relation between littoral area and larval density in the pond. Larval density and biomass depended generally on the nature of the substrate and quantity of organic matter. Larval density of Ch. circumdatus was positively correlated with O₂, bacterial count and organic matter content, but negatively correlated with CO₂ level. Daily removal of organic matter by the larvae ranged from 20 to 31 % of the available organic matter in the sewage canal and from 3 to 11 % in the pond.     

Effect of whole catchment liming on the episodic acidification of two adirondack streams

During the fall of 1989 7.7Mg/ha of calcium carbonate was applied on two tributary catchments (40 ha and 60 ha) to Woods Lake, a small (25 ha) acidic headwater lake in the western Adirondack region of New York. Stream-water chemistry in both catchment tributaries responded immediately. Acid-neutralizing capacity (ANC) increased by more than 200 eq/L in one of the streams and more than 1000 eq/L in the other, from pre-liming values which ranged from –25 to +40 eq/L. The increase in ANC was primarily due to increases in dissolved Ca²⁺ concentrations. Most of the initial response of the streams was due to the dissolution of calcite that fell directly into the stream channels and adjacent wetlands. A small beaver impoundment and associated wetlands were probably responsible for the greater response observed in one of the streams.After the liming of subcatchmentIV (60 ha), Ca²⁺ concentrations increased with increasing stream discharge in the stream during fall rain events, suggesting a contribution from calcite dissolved within the soil and transported to the stream by surface runoff or shallow interflow. Concentrations of other ions not associated with the calcite (e.g. Na⁺) decreased during fall rain events, presumably due to mixing of solute-rich base flow with more dilute shallow interflow. The strong relation between changes in Ca²⁺ and changes in NO ₃ ^– concentrations during spring snowmelt, (r² = 0.93, slope = 0.96, on an equivalent basis) suggests that both solutes had a common source in the organic horizon of the soil. Increases in NO ₃ ^– concentrations during snowmelt were balanced by increases in Ca²⁺ that was released either directly from the calcite or from exchange sites, mitigating episodic acidification of the stream. However, high ambient NO ₃ ^– concentrations and relatively low ambient Ca²⁺ concentrations in the stream during the spring caused the stream to become acidic despite the CaCO₃ treatment.In stream WO2 (40ha), Ca²⁺ concentrations were much higher than in stream WO4 because of the dissolution of calcite which fell directly into the upstream beaver pond and its associated wetlands. Calcium concentrations decreased as both NO ₃ ^– concentrations and stream discharge increased, due to the dilution of Ca-enriched beaver pond water by shallow interflow. Despite this dilution, Ca²⁺ concentrations were high enough to more than balance strong acid anion (SO ₄ ^– , NO ₃ ^– , Cl^–) concentrations, resulting in a positive ANC in this stream throughout the year. These data indicate that liming of wetlands and beaver ponds is more effective than whole catchment liming in neutralizing acidic surface waters.     

Cultivation and carrageenan yield and quality ofKappaphycus alvarezii in the waters of Vietnam

The carrageenan-producing red algaKappaphycus alvarezii (Doty) Doty was brought to Vietnam from Japan in 1993. Branch fragments of this species were cultivated in a pond, lagoon, inlet and offshore in Vietnam for the first time. The best daily growth rate (DGR) of plants grown in the lagoon area attained 9–11 % day^–1 in May to June (cold season). The water temperature and salinity in this area ranged from 27.2–32.4 °C and 31.4–33.7 °C, respectively. DGR of plants grown in the inlet ranged from 7 to 9% day^–1 in June. Grazing by fish has been observed to occur in this area. The DGR of plants grown in the pond ranged from 5–6% in January–July, but decreased to less than 4% day^–1 in August (hot season). K. alvarezii in Vietnam showed a carrageenan yield of 18.8–24.6% and gel strength of 1566–1712 g cm^–2. These values are similar ones obtained fromK. alvarezii cultivated in the Philippines and Indonesia.     

A study of the freshwater rotifer Brachionus calyciflorus in Pekanbaru, Riau, Indonesia

Brachionus calyciflorus is one of freshwaterrotifers found in fish ponds in Pekanbaru, Riau,Indonesia. Its density varied depending on that ofphytoplankton. Maximum of 2.5 ×10³ ind. l^–1 was found in ponds fertilised with animal wastes.The fecundity and population growth of B.calyciflorus was studied. Results indicated that the fecundity of amictic females was higher thanthat of unfertilized mictic females. During their life span, amictic and mictic females produced29.7 and 12.5 eggs per female, respectively. In the mass culture of 500 ml media, the highestdensity of female and male rotifers was 975.8 and 9.6 ind. ml^–1, respectively. During 8 days cultureperiod, they also produced eggs as many as 124.2 ml^–1.Human and animal wastespromoted the growth of phytoplankton as food forrotifers in the pond. A laboratory study confirms this. The best growth of B. calyciflorus at a density of 109 ind. ml^–1 was found at 0.5 g l^–1 of humanexcreta. A high density of B. calyciflorus (542ind. ml^–1) was also found in semi-continuous culturewith chicken excreta.     

Influence of gizzard shad on phytoplankton size and primary productivity in mesocosms and earthen ponds in the southeastern U.S.

Gizzard shad (Dorosoma cepedianum), a filter feeding omnivore, can consume phytoplankton, zooplankton and detritus and is a common prey fish in U.S. water bodies. Because of their feeding habits and abundance, shad have the potential to affect primary productivity (and hence water quality) directly through phytoplankton grazing and indirectly through zooplankton grazing and nutrient recycling. To test the ability of shad to influence primary productivity, we conducted a 16-day enclosure study (in 2.36-m³ mesocosms) and a 3-year whole-pond manipulation in 2–5 ha earthen ponds. In the mesocosm experiment, shad reduced zooplankton density and indirectly enhanced chlorophyll a concentration, primary productivity, and photosynthetic efficiency (assimilation number). While shad did not affect total phytoplankton density in the mesocosms, the density of large phytoplankton was directly reduced with shad. Results from the pond study were not consistent as predicted. There were few changes in the zooplankton and phytoplankton communities in ponds with versus ponds without gizzard shad. One apparent difference from systems in which previous work had been conducted was the presence of high densities of a potential competitor (i.e., larval bluegill) in our ponds. We suggest that the presence of these extremely high larval bluegill densities (20–350 larval bluegill m^–3; 3–700 times higher density than that of larval gizzard shad) led to the lack of differences between ponds with versus ponds without gizzard shad. That is, the influence of gizzard shad on zooplankton or phytoplankton was less than the influence of abundant bluegill larvae. Differences in systems across regions must be incorporated into our understanding of factors affecting trophic interactions in aquatic systems if we are to be able to manage these systems for both water quality and fisheries.     

Ecological problems of Lake Ladoga: causes and solutions

We studied the outcome of competition between a large (Brachionus calyciflorus) and a small (Anuraeopsis fissa) rotifer species at five algal (Scenedesmus acutus) concentrations (0.5 × 10⁶ to 40.5 × 10⁶ cells ml^–1) and with varying initial densities in mixed populations (100 to 0% of B. calcyciflorus or A. fissa), the combined initial biomass being 0.2 µg ml^–1 in all test jars. Experiments were conducted at 28 ± 1 °C.Regardless of food concentration, B. calcyciflorus showed a greater increase in biomass than A. fissa, peak densities (mean ± standard error) at the lowest food concentration in the controls being 1.34 ± 0.31 µg dry weight ml^–1 and 0.82 ± 0.08 dry weight ml^–1, respectively. At the lower food concentrations, A. fissa displaced B. calyciflorus and vice versa at the higher food concentrations. At the intermediate food concentrations of 4.5 × 10⁶ cells ml^–1, B. calyciflorus outcompeted A. fissa only if its initial population density was three times higher. The rates of population growth in controls varied from 0.792 ± 0.06 d^–1 to 1.492 ± 0.13 d^–1 for B. calyciflorus and 0.445 ± 0.04 to 0.885 ± 0.01 for A. fissa depending on food level. When both species were introduced together, low food levels favoured higher abundance of A. fissa than B. calyciflorus, suggesting, in nature, it is likely that small Anuraeopsis colonize oligotrophic water bodies more successfully than larger Brachionus. The results also suggest that the outcome of competition depends not only on the size of the competing species and food availability but also on their colonizing density.     

Characteristics of mixotrophic growth of Synechocystis sp. in an enclosed photobioreactor

Synechocystis sp. PCC 6803 was grown in a 2.5 l enclosed photobioreactor on medium with or without glucose. The incident light intensities ranged from 1.5 klux to 7 klux. The highest average specific growth rates of mixotrophic culture and photoautotrophic culture were, respectively, 1.3 h^–1 at a light intensity of 7 klux on 3.2 g l^–1 glucose and 0.3 h^–1 at both light intensities of 5 klux and 7 klux. The highest cell density 2.5 g l ^–1 was obtained at both of light intensities 5 klux and 7 klux on 3.2 g glucose l^–1. Glucose consumption decreased with decreasing light intensity. The energy yields of mixotrophic cultures were 4 to 6 times higher than that of photoautotrophic cultures. Light favored mixotrophic growth of Synechocystis sp. PCC 6803, especially at higher light intensities (5–7 klux).     

Aquacultural characteristics of <Emphasis Type="Italic">Rhizoclonium</Emphasis><Emphasis Type="Italic">riparium</Emphasis> and an evaluation of its biomass growth potential

A study was made of environmental factors affecting the growth of Rhizoclonium riparium in order to evaluate its suitability for large-scale culturing. The results indicate that under the natural conditions prevailing at Taishi, Taiwan, this species can grow year-round, with a monthly biomass production (oven-dried) of 945–1540 kg ha⁻¹ pond surface (assuming a pond depth of 1 m). The specific growth rate ranged from –2.1 to 10.4% per day. Salinity and temperature, both influenced the rate significantly, with optimal values at 20% and 25 °C, respectively. Short (2-mm) lengths of filaments had a higher specific growth rate than longer (20 mm) filaments. Under rotational culturing conditions, the specific growth rate was reduced when flow was increased.     

Comparative bioenergetics of permanent and temporary pond populations of the freshwater clam,Musculium partumeium (Say)

The population energetics of a temporary and a permanent pond population of Musculium partumeium in Southwest Ohio were studied. In the permanent pond (surface area = 396 m², maximum depth = 0.7 m) the population was bivoltine and iteroparous whereas in the temporary pond (surface area = 1042 m², maximum depth = 0.9 m) the population was usually univoltine and semelparous.Growth and biomass were assessed as total organic carbon and total nitrogen to provide estimates of productivity and seasonal changes in C:N for each generation. Productivity (non-respired assimilation = growth + reproduction; N-R.A. = G + R) was 6939 mgC·m^–2·a^–1 (3858 and 3353 mgC·m^–2·a^–1 for each generation) and 1661 mgC·m^–2·a^–1 for the permanent and temporary pond populations respectively. The average standing crop biomass (B) was 606.8 mgC·m^–2 (357.5 and 249.3 mgC·m^–2 for each generation) and 231.9 mgC·m^–2 with overall productivity: biomass ratios of 11.4 and 7.2 for the permanent pond and temporary pond populations respectively.Respiration rates were converted to carbon equivalents (respired assimilation = R.A.) and used to evaluate the components of total assimilation (T.A. = R.A. + N-R.A.) and the efficiency of partitioning this energy to N-R.A. for G and R. When expressed as a percentage, the production efficiencies (100 × N-R.A.:T.A.) were 50.4 and 62%, and the reproductive efficiencies (100 × R:N-R.A.) were 26.4 and 18% for the permanent and temporary pond populations respectively. The reproductive efficiencies for populations of these viviparous clams are greater than those for most oviparous molluscs.The comparative information on the energetics of these populations does not completely fit any theoretical consideration of reproductive effort or life-history strategy. These data are discussed in relation to selection for population success in temporary ponds.Funded in part by grants to Albert J. Burky from the Ohio Biological Survey and the University of Dayton Research CouncilFunded in part by grants to Albert J. Burky from the Ohio Biological Survey and the University of Dayton Research Council