Growth pattern and distribution of biomass of Calluna vulgaris on an ombrotrophic peat bog

The distribution pattern of Calluna vulgaris on the ombrotrophic peat bog Åkhultmyren, S. Sweden, was investigated.
Calluna occurs primarily on hummocks, with its maximum biomass (ca 250 g m⁻² above ground, and ca 300 g m⁻² below ground) concentrated on hummock tops. Biomass decreased gradually along the hummock-hollow gradient to a level of ca 5 cm above the water level. This decreasing biomass was correlated with a decrease in the predominant age of the above ground shoots from 6–8 yr to 3–4 yr old shoots.
Calluna is characterized by extremely slow diameter growth and biomass increment. There was, however, a poor relation between height above water level and stem thickness, assimilating biomass and total shoot weight, respectively.     

Primary productivity and biomass of epiphytes on Phragmites australis in a eutrophic Danish lake

A field incubator based on a closed flow system was applied for primary productivity measurements in situ. The seasonal development of epiphytes showed a pronounced productivity maximum in May (610 mg C m⁻² Phragmites stand d⁻¹) and a maximum chlorophyll a content of 414 mg m⁻² Phragmites stand. Substratum limitation was indicated during the spring maximum. Primary productivity and biomass decreased to low values in late summer, mainly due to shading from the aerial shoots. Significant quantitative heterogeneities in epiphyte biomass occurred over a few decimeter of Phragmites stem. Productivity and biomass were higher on old stems than on new ones throughout the growth period. The annual epiphyte production (23,7 g C m⁻² Phragmites stand) was mainly a result of the spring maximum. The fact that 64% was produced on old stems emphasizes the importance of the highly variable degree to which these may be destroyed. The host plant phenology appears from this investigation to be a key factor affecting epiphyte growth in the emergent vegetation determined by (1) the amount of available substratum and (2) the light penetration through the canopy.     

Biomass and oxygen dynamics of the epiphyte community in a Danish lowland stream

SUMMARY. 1. We examined the abundance and oxygen metabolism of epiphytic organisms on the dominant macrophyte, Potamogeton pectinatus , in headwaters of the eutrophic River Suså. Microbenthic algae were abundant in the stream during spring and macrophytes during summer.
2. The low macrophyte biomass in spring supported a dense epiphyte cover whereas the high macrophyte biomass during summer had a thin epiphyte cover of 10–100-fold lower abundance per unit area of macrophyte surface. The epiphyte community was dominated by microalgae in spring and by heterotrophs, probably bacteria, during summer. This seasonal shift was shown by pronounced reductions of the chlorophyll a content (from 2–3% to 0.1–0.7% of organic DW), the gross photosynthetic rate (from 20–85 to 3–15 mg O₂, g-¹ organic DW h⁻¹) and the ratio of gross photosynthesis to dark respiration in the epiphyte community (from 5–18 to 1). The reduced contributions of epiphytic microalgae correlated with reduced light availability during summer.
3. Both the density and the photosynthetic activity of epiphytic algae were low on a stream area basis relative to those of microbenthic algae and macrophytes. Rapid variations in water velocity and extensive light attenuation in water and macrophyte stands probably constrained the development of epiphytic algae. The epiphyte community was more important in overall stream respiration, contributing c. 10% to total summer respiration and c. 20% to summer respiration within the predominantly heterotrophic microbial communities on sediments and macrophyte surfaces.     

Production and litter processing by crayfish in an Appalachian mountain stream

SUMMARY 1. Mean annual density and biomass () of Cambarus bartonii in an Appalachian mountain stream (U.S.A.) was 12 individuals m⁻² and 1669 mg (ash-free dry weight) m⁻².
2. Annual production ( P ) of C bartonii was 961 mg AFDW m⁻². Despite high biomass, low growth rates resulted in low production and a low P/ ratio of 0.58.
3. While C bartonii constituted 61% of the total macroinvertebrate biomass, it contributed only 13% of annual community secondary production.
4. Litter processing was positively related to temperature and crayfish size. Cambariis bartotnii was estimated to comminute 36 g m⁻² y⁻¹ of leaf litter (>1 mm²) to 24 g m−^>2 y⁻¹ fine particulate material (<1 mm²). The annual pattern of litter comminution by crayfish was regulated by temperature. As a result, >5()% of shredding activity by crayfish occurred from June to September which was also the period of lowest litter standing crops and activity of other shredding macroinvertebrates.
5. We speculate that during summer crayfish play an important role in temperate woodland streams by converting slowly processed leaf litter species (e.g. Rhododendron ) to fine particles which are then available to collector-gatherers (e.g. Chironomidae, Oligochaeta).     

The life-cycle and productivity of Tibifex tubifex (Oligochaeta; Tibificidae) in the Moat-Feeder Stream, Cardiff, South Wales

A population of Tubifex tubifex in an organically rich stream was found to have an annual life-cycle with a prolonged period of reproductive activity throughout the winter and spring. Cocoons were produced mainly during the late winter and early spring. No cocoons were found during August and September, and there were few mature worms at this time.
The population density ranged between 5420 m⁻² in mid-September and 613000 m ⁻² in mid-May. The maximum population biomass (Bmax) recorded was 106 g dry wt m⁻² (March) and the minimum was 10 g dry wt m⁻² (September). Total annual production (P) was 139 g dry wt m⁻² and the average annual biomass ( B ) was 46 g dry wt m⁻² giving an annual P/ B ratio of 3.0, and a P/Bmax ratio of 1.3.     

Vertical distribution and abundance of invertebrates within the sandy substrate of a low-gradient headwater stream

SUMMARY. 1 The vertical distribution of invertebrates (>0.053 mm) was studied in a sandy-bottomed, first-order stream on the Coastal Plain of Virginia, U.S.A. Invertebrate species composition, abundance and bio-mass were determined monthly over one year at sediment depth intervals of 0–1, 1–5, 5–15,15–30 and 30–40 cm.
2. The subsurface community was numerically dominated by species of Chironomidae, Nematoda and Crustacea, while much of the biomass was due to early instars of several species of Trichoptera.
3. Invertebrate density and biomass decreased significantly with depth in the substrate (ANOVA; P <0.05). Annual mean density decreased from 1,346,844 individuals m⁻³ at the surface to 13,578 individuals m⁻³ at 15–30 cm. Annual mean biomass decreased from 66.30 g m⁻³ at the surface to 0.44 g m⁻³ at 15–30 cm.
4. Dissolved oxygen decreased markedly from the surface to the 5 cm depth in the substrate, anaerobic conditions often occurring below 10 cm. Density and biomass both showed a significant positive relationship with dissolved oxygen concentration (Linear regression; P <0.05).
5. Physical forces were important in structuring the subsurface invertebrate community. Besides low dissolved oxygen concentration, sediment scouring resulting from storm discharge dramatically reduced density and biomass     

Biomass and production estimates of a fish community in a small South African estuary

The fish community of the small (17·5 ha) intermittently open East Kleinemonde estuary was sampled between 1994 and 1997 to estimate population size, standing stock, growth and productivity. The estuarine-spawning species were numerically more abundant ( n c . 750 000) but due to their small size contributed only 11·7% to the total biomass. The total annual productivity of all fishes in the estuary ( n c . 890 000), with a standing stock of 28·44 g m ⁻², was calculated at 55·89 g m⁻² year⁻¹. The small sparid Rhabdosargus holubi with a production estimate of 41·35 g m⁻² year⁻¹ accounted for <74% of the total fish production in this estuary.     

Biomass, productivity and relative rate of photosynthesis of Sphagnum at different water levels on a South Swedish peat bog

The distribution pattern of Sphagnum species on bogs follows a hummock-hollow gradient. S . Sect. Acutifolia (that is in this study S. fuscum and S. rubellum combined) dominates hummock tops, ca 20 cm above the maximum water level with a green biomass of 50 g m⁻², S. magellancium dominates at a lower level, about 5 cm above the water level with a green biomass of 75 g m⁻² and S. cuspidatum dominates in the wettest hollows with a green biomass of about 50 g m⁻².
In situ measurements of length growth of S . Sect. Acutifolia and S. magellanicum using a ¹⁴CO₂-labelling technique during three consecutive years, revealed an unexpectedly high between-year variation in length growth of 7-23 mm yr⁻¹, and 16-22 mm yr⁻¹, respectively. Consequently the dominating producer in the transition between hummock and hollow changes from year to year, probably depending on climatic conditions.
In vitro experiments on the effects of different water levels of 2, 5, 10 and 20 cm below the moss surface, on photosynthetic activity of S . Sect. Acutifolia and S. magellanicum , measured by a second ¹⁴CO₂-technique, indicate optimal conditions for S. magellanicum at 10 cm above water level, and for S . Sect, Acutifolia at 20 cm above water level.
Differences in capillary water transport capability between the species are more important than the sensitivity of photosynthesis to water stress in explaining field patterns of productivity and distribution.     

Very high secondary production at a lake outlet

SUMMARY. 1. Larvae and pupae of Simulium noelleri Fried, coated the concrete of parts of an artificial lake outlet in southern England.
2. In the first two (of three) summer generations, development was synchronous and this allowed the calculation of their secondary production by the instantaneous growth method. The production of the two summer generations was, respectively, 229.1 g C m⁻² (7.4 g C m⁻²day⁻¹) and 185.5 g C m⁻² (8.8 g C m⁻² day⁻¹) The contribution of the third summer generation, and the overwintering generation, to annual production would be less than that of the first two summer generations. Nevertheless, annual production will have exceeded 500 g C m⁻² at this site.
3. Larvae are suspension feeders and they captured the rich supply of particulate and dissolved organic material which passed over them after export from the lake. As food is brought to the larvae they only require space for attachment and can thus build up very high population densities (which exceeded 1 × 10⁶ m⁻² on some occasions during the summer). The high population densities result in a high biomass and hence in the high levels of production.     

Population dynamics and feeding of mayfly larvae in some acid and alkaline New Zealand streams

SUMMARY. 1. Population dynamics (density, biomass, annual production), gut contents and feeding rates of mayflies ( Deleatidium spp.; Leptophlebiidae) were compared in two naturally acid (mean pH≃4.8). brownwater streams and two alkaline (mean pH 7.5), clearwater streams in South Westland, New Zealand.
2. Mean densities of larvae (range 234–2318 m⁻²) were higher in alkaline streams on most of the six bimonthly sampling dates. Mean biomass (range 0.020–0.376 g larval dry weight (LDW) m⁻²) was always highest at the stable, spring-fed, alkaline site and was lower at the acid sites and another alkaline site where the population was always dominated by small larvae.
3. Annual production was high at the more stable, alkaline site (10.35 gLDW m⁻²) but much lower at the other sites (2.49–3.77 g m⁻²).
4. Gut contents of larvae were dominated by fine (45–75 μm widest diameter) paniculate matter (69–99%), diatoms (up to 21%) and. at one site, filamentous algae (8–13%).
5. Grazing rates of mayflies on epilithon were significantly higher on stones taken from acid than alkaline streams and material grazed from the former contained a higher proportion of inorganic material (87–93% and 61–83% inorganics, respectively).
6. Higher grazing rates may reflect lower quality of epilithic food in acid, brownwater streams, a factor that could contribute to the lower productivity of Deleatidium populations at these sites.     

Seasonal biomass and diversity of estuarine fishes coupled with tropical habitat heterogeneity (southern Gulf of Mexico)

Nekton dynamics were studied in two contrasting habitats in Terminos Lagoon, Mexico. Over an annual cycle, a total of 83 fish species used the high-salinity fringing mangrove/ Thalassia testudinum habitat and biomass ranged from 0.43 to 3.43 g m⁻². The highest biomass occurred during the dry season when aquatic primary production was highest (i.e. 333 g C m⁻² year⁻¹). By contrast, 65 species used the freshwater and low-salinity riverine mangrove/Crassostrea virginica/Vallisneria habitat and biomass ranged from 0.57 to 1.48 g m⁻² with the highest biomass occurring during the wet season, the time of highest primary production in this habitat (i.e. 219 g C m⁻² year⁻¹). The high- and low-salinity habitats serve as ecological bridges between freshwater areas and the sea. Fish life histories have evolved to utilize these habitats for spawning, feeding and nursery grounds in a manner which generally leads to the use of different habitats during the periods of highest primary productivity.     

Life-history and production of the amphipod Gammarus pulex in a Dorset chalk stream

SUMMARY. The seasonal variation in population density of Gammarus pulex was studied in a Dorset chalk stream. The numbers increased markedly in June and July and reached a maximum of c. 10000m⁻² in September whilst the most rapid decline in density occurred in October-November and reached a minimum of 820 m⁻² in February. The animals occurred in greater densities in habitats containing Ranunculus or Callitriche than in those devoid of vegetation. The population structure was determined monthly and was split into juveniles (length <4mm), immature males, immature females, mature males and ovigerous females. The percentage of juveniles (39–76) was always the highest of any of the categories. Ovigerous females were found at all times of the year. The sex ratio varied with the time of year both for immatures and matures, although there was approximately a 1:1 ratio for the mature individuals. Seasonal variation in biomass showed a maximum of 7.l g dry wt m⁻² in September and a minimum of 1.4 g dry wt m⁻² in March. Production was calculated by two methods giving values of 12.9 g dry wt m⁻² year⁻¹ and 12.8 g dry wt m⁻² year⁻¹.     

Continuous growth of the giant grass Zizaniopsis bonariensis in subtropical wetlands

1.  Zizaniopsis bonariensis (giant grass) is an emergent macrophyte species endemic to subtropical wetlands in Brazil, Argentina, Paraguay and Uruguay. In this study, we show the effects of its continuous clonal reproduction and its 'phalanx' growth strategy in the Taim Wetland (southern Brazil).
2. The continuous clonal growth of this 3-m high grass gave rise to the emergence of 11.7 new shoots m⁻² per month and a high total above ground production (2870 g dry weight m⁻² year⁻¹). The biomass of the new shoots emerging every month formed a wave of growth, moderated by only weak seasonal variation.
3. We show its phalanx growth strategy by analysing the variations in population density and shoot height within a transect through the stand canopy. The inverse relation between density and height from the border to the interior indicates self-regulation of biomass.
4. The plants modified their environment, enhancing resistance to drought within the stand and thus facilitating their dominance. This positive feedback suggests that the dominance of the plant might constitute an alternative state in subtropical wetlands.     

Growth and production of some important species of fish in a Mexican coastal lagoon system

In terms of biomass, the three dominant fish species in the Huizache-Caimanero lagoon system during 1975–76 were the mullet Mugil curema , the anchovy, Anchoa panamensis and the catfish, Galeichthys caerulescens . Peaks in the abundance of the secondary predators occurred at the end of the wet season (September-October), while pelagic forms and members of the centropomid-gerreid association (Warburton 1968a ) were most common during November-February and December-February respectively. Twelve species, including the ten having the highest overall mean biomass, were selected for growth and production studies. Lagoon-specific differences in the patterns of growth and recruitment of several species were observed. The total estimated annual fish production in Caimanero lagoon was 34·48 g m⁻² y⁻¹, with M. curema contributing 9·36 g m⁻², A. panamensis 9·24 g m⁻² and G. caerulescens 6·15 g m⁻² (maximum estimate). Mean turnover ratios (annual production: mean biomass) were 3·25 (demersal species), 8·44 (pelagic species) and 4·48 (all species). Implications for possible fishery and aquacultural expansion are discussed.     

Population dynamics and production of Daphnia galeata (Crustacea, Cladocera) in Lake Esrom

The population dynamics and production of D. galeata Sars were investigated from April 1974 to April 1975. The population density and biomass was maximum in June. Population dynamics indicated that food supply was better in spring and early summer than mid-summer. Net production was calculated by method of daily addition of biomass for eight size groups. The total net production of biomass for the year of investigation was 26.5 g dw m⁻². The P/B yr⁻¹ was 35 8.     

Oxygen and nitrate respiration in a reed swamp sediment from a eutrophic lake

Seasonal measurements of the oxygen and nitrate uptake by a reed swamp sediment were carried out in a shallow, eutrophic Danish lake, Arreskov Sø. The oxidation of organic carbon in the sediment by aerobic and nitrate respiration was 290 and 188 g C m⁻² yr⁻¹ respectively. During winter, nitrate respiration amounted to 94% of the total carbon oxidation, whereas it was zero during summer. On an annual basis nitrate respiration constituted 39% of total respiration. Sediment nitrate uptake was correlated to nitrate concentration. In consequence of this the nitrate uptake rates varied during the year from zero in summer to 55 mg N m⁻² d⁻¹ in spring.
Oxygen uptake rates varied from 30 to 250 mg O₂ m⁻² h⁻¹ during the year, with a maximum uptake in August. The oxygen uptake per year was calculated to 860 g O₂ m⁻². The oxygen uptake rate was correlated to lake temperature and Kjeldahl nitrogen content of the sediment. The oxygen uptake rate, however, showed no correlation with loss on ignition of the sediment. A Q₁₀-value of 2.2 was found for lake measurements in the temperature interval of 5–15°C. The corresponding O₁₀-value in the laboratory was 2.6. A high microbial biomass indicated by the maximum content of Kjeldahl nitrogen and the lowest ratio of loss on ignition on Kjeldahl nitrogen appeared in late August, when the maximum oxygen uptake occurred. The oxygen uptake rate increased during the time interval from sampling to the start of the experiments.     

Life history and production of Paranephrops zealandicus in a forest stream, with comments about the sustainable harvest of a freshwater crayfish

1. Life history and production were assessed for the crayfish Paranephrops zealandicus in three reaches of a headwater stream with a catchment of regenerating coniferous-broadleaf forest in the south-east of the South Island of New Zealand.
2. Crayfish density ranged from 3 to 4 m⁻² in riffles and 4–12 m⁻² in pools, depending on reach. Crayfish biomass (4–33 g AFDW m⁻²) and annual production (2–11 g AFDW m⁻²) were high compared with values reported elsewhere, while P:B ratio was low (0.33–0.43). This substantial production was dependent primarily upon high biomass rather than high growth rate.
3. The crayfish of this population rank amongst the longest lived and slowest growing ever recorded. Individuals estimated to be 16+ year of age were not uncommon. Females became reproductively active at 6+ year. Fewer than 4% of females carried eggs, and young remained attached to females for at least 15 months.
4. We propose that characteristics of this population are the consequence of a cool thermal regime (mean daily stream temperature = 7.0 °C, range 1.8–11.9 °C), and that low biomass turnover and poor reproductive rate precludes any sustainable commercial harvest of crayfish from streams in New Zealand with similar thermal regimes.     

The loss of submerged plants with eutrophication II. Relationships between fish and zooplankton in a set of experimental ponds, and conclusions

SUMMARY. 1. In 1982 and 1983 sets of experimental ponds were left with their submerged plant communities intact (plant ponds) or were cleared manually of them (cleared ponds). The ponds were all fertilized with ammonium nitrate and with variable amounts of phosphate. In 1982 fish were removed from the ponds. Zooplankton communities were dominated by large Cladocera with Daphnia prominent in the cleared ponds and Simocephalus in the plant ponds. There was no detectable effect of differential phosphorus additions on zooplankton communities or populations.
2. In 1983 zooplanktivorous fish (mainly roach) were stocked in the ponds. In the plant ponds the fish did not survive, probably through severe deoxygenation and the zooplankton community again included large-bodied Simocephalus. Fish survival was variable in the cleared ponds. Where fish stocks were absent or low (0.5–1 g m⁻²) a Daphnia- dominated community persisted; at intermediate fish stocks (18.1 g m⁻²) Eudiaptomus gracilis was predominant and where fish stock was high (22.8–29.1 g m⁻²) Bosmina longirostris , and cyclopoid copepods dominated the communities. Mean biomass of the zooplankton community declined with increase in fish stock to between 5.1 and 18.1 g m⁻² then increased.
3. On the basis of results from the experimental ponds and elsewhere, a new hypothesis is put forward to account for the switch from aquatic plant to phytoplankton dominance in eutrophicated shallow lakes. It envisages dominance by either group to be possible as alternative states over a wide range of high nutrient loadings. It suggests that each state is buffered against increased loading by mechanisms involving plant and algal physiology and zooplankton grazer populations. The nature of the buffers and the reasons by which one state may be switched to the other are, discussed.     

Modelling black fly production dynamics in blackwater streams

SUMMARY. 1. Two predictive models were employed along with intensive field sampling to estimate production of black flies ( Simulium spp.) on snags (submerged wood) in three blackwater streams on the Georgia Coastal Plain of the southeastern U.S.A. One model predicts daily growth rate from temperature and hydrograph pattern; the other predicts habitat abundance (of snags) from river height.
2. In the sixth order Ogeechee River, annual production was twice as high in 1982 (7.1 g dry mass [=DM] m⁻² of snag surface) as in 1983 (3.6 g DM m⁻²). When converted to production per m² of river bottom, values were 35–40% of the snag surface estimates. Annual production was much lower in fourth order Black Creek (1982, 1.3 g DM m⁻² of snag surface) and much higher in the sixth order Satilla River (1975, 15.6–40.0 g DM m⁻²).
3. There was a distinct bimodal pattern of black fly production in the Ogeechee River in both years, with peaks occurring in winter and summer. Similar bimodal patterns of production were found in Black Creek and in the Satilla River. Although there appears to be an intrinsic component to the bimodal pattern, production peaks (growth rate and biomass) appear to be associated with initial stages of flooding.
4. Annual production/biomass ratios (37–85) are the highest reported for black fly populations. The variation of annual P/B ratios among sites was more strongly dependent on the temporal distribution of standing stock biomass than on differences in growth rates. Variation in production among sites appears to be due to differences in current velocity, hydro-graph variability, and abundance of coexisting consumers.     

Phytoplankton ecology in an Antarctic lake

SUMMARY. The ecology of the phytoplankton of Heywood Lake, Signy Island, South Orkney Islands, Antarctica was investigated during 1969–72. The lake, which is ice-covered for 8–10 months per year, is moderately eutrophic due to enrichment by seal excreta.
The annual cycle of the phytoplankton is described. During the winter (approximately May-September), very few algal cells could be detected in the water column and ¹⁴C fixation was below measurable limits. In spring (October-November), a rapidly-growing population of algae caused a large increase in the chlorophyll- a concentration (maximum value 170 mg m⁻²) but carbon fixation remained low, with values <500 mg C m⁻² day⁻¹. The algae contributing to this peak were mainly small chlorophytes and chrysophytes. The summer open-water period (December-March) was characterized by a different phytoplankton population dominated by cryptophytes. Chlorophyll levels were lower ( c . 40 mg m⁻²) but ¹⁴C fixation rates >3 g C m⁻² day⁻¹ were measured on bright days. Values for Assimilation Number were very high (maximum value 10.5 mg C h⁻¹ mg⁻¹ (chlorophyll- a ) in January (1971) though temperatures never exceeded 8°C. In autumn, the phytoplankton regressed to winter levels. Both spring and summer algal populations probably overwinter as resting stages.