Effects of suspended clay on Daphnia body growth and fitness

1. Suspended sediments often reduce the abundance, fitness, and feeding rates of planktonic cladocerans. This paper examines the effect of suspended clay particles on the body growth and life-history parameters of Daphnia ambigua. Cohorts were exposed to zero or 50mgl^?1 suspended clay (particle size <2μm). Individuals exposed to clay had significantly lower body lengths at a given age than individuals in the control cohort. Parameters for the von Bertalanffy body growth equation were calculated for each individual; the asymptotic maximum body length (l_max) was reduced, but the growth rate constant (k) was unaffected, by the presence of suspended clay. Body length at reproductive maturity was lower in the presence of suspended clay; this may be an adaptive response and is similar to the response of cladocerans to limiting food concentrations. 2. Age-specific survivorship and fecundity were both reduced, and the ages of maturity and first reproduction were both increased, in the presence of suspended clay. The overall effect of these demographic changes was a 70% decline in the net reproductive rate (R_o), a measure of fitness. 3. Suspended clay affected the relationship between body length and fecundity. Animals of a given length produced fewer eggs in the presence of suspended clay. In addition, there was a significant interaction in the effects of body length and clay on brood size: the slope of the regression line of brood size as a function of body length was lower in the presence of clay. This interaction has also been observed in limiting food concentrations, and may be caused by reductions in body length at maturity in low food or high clay environments. 4. The similarity between the effects of limiting food concentrations and suspended clay on Daphnia body growth, survivorship, fecundity, and brood size makes sense, given previous observations showing that suspended clay reduces the feeding rate of D. ambigua by up to 70% due to mechanical interference with feeding behaviours.     

Susceptibilities of different-sized ciliates to direct suppression by small and large cladocerans

• 1 Laboratory experiments compared the susceptibilities of six ciliates and the rotifer Keratella cochlearis to predation and interference from Daphnia pulex and Bosmina longirostris.
• 2 Susceptibilities of the ciliates to D. pulex were similar to or less than that of the rotifer, and decreased with increasing ciliate size. Most ciliates were just as susceptible to B. longirostris as to the much larger D. pulex. The jumping response of the oligotrich Strobilidium gyrans appeared to be an effective defence against B. longirostris.
• 3 Clearance rates of B. longirostris and D. pulex on different ciliate species at a density of 1,3 ciliates ml^?1 ranged from 1–30 to 5–24ml ind.^?1 day^?1, respectively. In natural plankton communities, cladocerans could impose high mortality rates on ciliates and shift the size structure of ciliate assemblages towards larger and less susceptible species.

     

Predation on ciliates by freshwater calanoid copepods: rates of predation and relative vulnerabilities of prey

• 1 The susceptibility of ciliates in a mesotrophic lake to predation by Epischura lacustris, Diaptomus minutus and D. pygmaeus was assessed during summer. Oligotrichs, particularly Strobilidium velox (c. 43 μm), were removed efficiently by adult copepods and contributed substantially to the diet of female D. minutus. The presence of approximately 1,6 adult Epischura 1-^?1, or sixteen adult female Diaptomus 1-^?1, could halt the growth of S. vechx populations in summer.
• 2 Factors affecting the rate at which copepods prey on ciliates were examined in experiments with D. pygmaeus and cultured ciliates. Rate of predation on S. velox, the preferred species, became saturated at 5 S. velox ml^?1 (45ngCml^?1) and did not change with a 10-fold increase in alternative algal food.
• 3 Behavioural differences among ciliates, and the presence of other ciliates, contributed to differences in ciliate susceptibility to predation and suggest reasons why rates of removal of ciliates are not related to ciliate size.
• 4 By feeding selectively, at high rates, calanoids may suppress populations of some ciliates and thereby influence microzooplankton community structure.

     

Optimum body size in aphids

Abstract.

• 1 Smallness in British plant-sucking bugs is associated with feeding on the contents of individual plant cells, especially phloem.
• 2 The sizes of species of aphids living in similar habitats and the rates of water loss from those that have and lack a filter chamber do not support the contention that small size in aphids is a means of maximizing the loss of water by cuticular transpiration.
• 3 An optimum energy partitioning model, previously developed for aphids, was used to predict the interspecifie relation between adult weight and birth weight that would maximize the population growth rate, r_m. Using the observed r_m/IRGR ratio (0.8–0.9) and that the gonads are smaller than the soma at birth the predicted relation between the logarithm of the adult weight and the logarithm of the birth weight is linear and has a slope of 1.
• 4 The relation between the logarithm of the adult weight and the logarithm of the birth weight for eighteen species of aphids is linear and has a slope of 1.
• 5 Birth size differs between species of aphids and in each species is assumed to be the minimum size necessary for feeding. Accepting this constraint then the optimum adult size for maximizing r_m is approximately 15 times the birth size.

     

Effects of copper on production of periphyton, nitrogen fixation and processing of leaf litter in a Sierra Nevada, California, stream

SUMMARY.

• 1 Production of periphyton, nitrogen fixation and processing of leaf litter were examined in an oligotrophic Sierra Nevada stream and the responses of these processes to copper (2.5, 5 and 10μg 1^-1 Cu_T [total filtrable copper]; approximately 12, 25 and 50 ng 1^-1 Cu²⁺) were determined.
• 2 Autotrophic and total production were estimated from 3-week accumulations of biomass on artificial substrates. Mean autotrophic production in the control ranged from 0.22 to 0.58 mg C m^-2 h^-1 in summer-autumn 1979, but declined to 0.08–0.28 mg C m ² h^-1 after peak discharge in summer 1980, apparently due to phosphorus-limited growth. Total production in the control ranged from 0.30 to 0.82 mg C m^-2 h ^-1 in summer-autumn 1979 and from 0.16 to 0,68 mg C m ^-2 h ^-1 in 1980. Mean autotrophic productivity, estimated by ^l4C-bicarbonate uptake in daylight, ranged from 0.30 to 2.8 mg C m^-2 h^-1.
• 3 Autotrophic productivity was reduced by 57–81% at 2.5μg 1^-1 Cu_T, 55–96% at 5μg 1^-1 Cu_T, and 81–100% at 10μg 1^-1 CU_T, Heterotrophic productivity (based on dark ³⁵S-sulphate uptake) was inhibited to a lesser extent (28–63% at 2.5μg 1^-1 Cu_T, 24–84% at 5μg 1^-1 Cu_T, and 67–92% at 10μg 1^-1 Cu_T), The inhibition of autotrophic and heterotrophic productivity persisted through the year of exposure. Production in stream sections previously exposed to 2.5 and 5μg 1^-1Cu_T increased to control levels within 4 weeks after dosing, but remained depressed for more than 7 weeks after exposure to 10μg 1^-1 Cu_T.
• 4 The specific rate of photosynthesis (mg C mg chlorophyll a^-1 h^-1) of mature periphyton communities declined at all test concentrations of copper, but the rate for periphyton on newly-colonized surfaces did not change. The species composition of benthic algae shifted during exposure to an assemblage more tolerant of copper. Achrtanthes minutissima and Fragilaria crotonensis were the primary replacement species on newly-colonized surfaces.
• 5 The nitrogenase activity of blue-green algae was low. with controls ranging from 2.4 to 12 nmol C₂H₂ m^-2 h^-1. Nitrogenase activity was inhibited during the initial weeks of exposure by 5 and 10μg 1^-1 Cu_T. However, after 9 months of exposure, control and copper-treated sections did not differ.
• 6 The rate of processing of leaf litter, estimated by microbial respiration and nutrient quality of litter of resident riparian woodland taxa, was inhibited at all test concentrations of copper.

     

Suspended clay reduces Daphnia feeding rate

SUMMARY. 1. Suspended sediments often reduce cladoceran abundance in the field, and reduce the algal feeding rates of cladocerans in the laboratory. This paper explores the behavioural mechanisms by which suspended clay reduces Daphnia feeding rates. Feeding experiments using radiolabelled Cryptomonas cells showed that 50–200 mg 1-^?1 coarse suspended clay (particle size<2 μm) reduced the algal ingestion rate of Daphnia ambigua by 29–87%, but fine suspended clay (<1 μm) had no effect. Suspended clay decreased feeding rate by 60–70% at low algal concentrations (≤5×10³ cells ml^?1), but by only 27% at high algal concentrations (20×10³ cells ml^?1). Thus, the inhibitory effects of suspended clay are greater at low algal concentrations. The sudden addition (or removal) of suspended clay caused immediate reductions (or increases) in algal ingestion rate. 2. Observations of the feeding behaviour of tethered D.pulex showed that the frequency of postabdominal rejections increased greatly in the presence of suspended clay. The rejected boluses contained both algae and clay. Thoracic feeding appendage beat frequency decreased in the presence of suspended clay, decreasing the volume of water searched for food particles. 3. These behavioural responses indicate that clay reduces cladoceran feeding rate by mechanically interfering with both the collection and ingestion of algal cells. Both inhibitory effects are caused because cladocerans collect and ingest suspended clay particles. The behavioural mechanisms by which cladocerans regulate their feeding rate in very high concentrations of algal cells (rejection of excess food and reduction in thoracic limb pumping movements) are the same mechanisms responsible for the inhibition of algal ingestion rate in the presence of high concentrations of suspended clay particles.     

Previous infestation with Psammotettix alienus on spring wheat seedlings decreased the fitness of Sitobion avenae in a subsequent infestation

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A statistical model of the reproduction of aphids

1. The logistic function has been generally used to describe the reproductive process of a “population” of animal. However, this model can not give us any information about the reproductive process of “individuals” in the population. In this study a statistical model on the basis of the reproduction of individuals of barley aphid is presented to find the proportion of the mature individuals, the heterogeneity in reproductive ability of the aphids, etc.
2. The model is constructed as follows:
3. The probability that j insects are found on a plant at time t₀ is represented as Q(j).
4. The probability that h individuals of j have reproductive ability, say, mature individuals, in the period t₀ to t₁ is represented as B(h/j)=_jC_hw^h(1−w)^j−h, where w is the proportion of mature individuals.
5. In a population with a homogeneous reproductive ability, the probability that each parent lays i offspring in the period t₀ to t₁ is represented as P(i/m)=e^−mmⁱ/i!, where m is mean. And, in a population, m changes according to the gamma distribution. Hence the probability that a parent lays i offspring between t₀ and t₁ is represented as , where p and k are parameters of negative binomial distribution. The probability that h parents on a plant lays s offspring is represented as .
6. From the assumptions mentioned above, the probability that s offspring are to be found at time t₁ on a plant with the original j individuals at time t₀ is represented by
7. The experimental populations were demonstrated to fit well to the model.

     

Cyclopoids feed selectively on free-living stages of parasites

1. Many aquatic organisms can consume parasite larvae, thus hampering parasite transmission; however, information about feeding on them in the presence of an alternative prey remains scarce. When having a food choice, predators may decrease parasite consumption, therefore, it is important to assess the role of parasites in the diet of predators in natural communities with different types of prey available. Our study aims to test whether common freshwater cyclopoids feed on trematode free-living stages (cercariae) when an alternative food source is present.
2. We experimentally studied ingestion rates of cyclopoids Macrocyclops distinctus fed with cercariae of trematode Diplostomum pseudospathaceum, a common and harmful parasite of freshwater fishes, and ciliates Paramecium caudatum (an alternative prey, known as suitable food for copepods). First, the feeding response of cyclopoids to different densities of each prey was studied. Then, feeding selectivity in the mixtures of cercariae and ciliates was tested.
3. Feeding rates of cyclopoids increased with prey densities (both ciliates and cercariae) but almost stopped growing at high prey densities, which indicated saturation (Holling type II functional response). In most cases, cyclopoids consumed cercariae at higher rates than ciliates. Maximum ingestion rates estimated from the obtained curves were 37 cercariae ind⁻¹ hr⁻¹ and 17 ciliate ind⁻¹ hr⁻¹.
4. When exposed to prey mixtures, cyclopoids fed on cercariae selectively. When cercariae were offered to cyclopoids at concentrations exceeding the saturation level, the ingestion of ciliates remained constantly low at all ciliate densities. In contrast, the ingestion of cercariae increased with rising cercariae densities even when ciliates were presented ad libitum, decreasing only at very high prey densities. Possible reasons of such feeding preferences are discussed.
5. Our study demonstrated that cyclopoids may prefer to feed on cercariae when there is an alternative food choice and can ingest cercariae at high rates. These experimental results could be extended to natural communities, suggesting that cyclopoids can reduce the transmission of parasites and contribute to the incorporation of parasite production in food webs of lentic ecosystems.

     

Leaf‐cutting ants as ecosystem engineers: topsoil and litter perturbations around Atta cephalotes nests reduce nutrient availability

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DYNAMICS OF ARBUSCULE DEVELOPMENT AND DEGENERATION IN A ZEA MAYS MYCORRHIZA

A quantitative light and electron microscope study of developing and degenerating mycorrhizal arbuscules of Glomus fasciculatum in Zea mays was carried out in order to estimate three parameters during the colonization cycle. These were: 1) V_v(f,c), the fraction of the host cell volume occupied by a volume of fungus; 2) V_v(cy,c), the fraction of the host cell volume occupied by host cytoplasm; 3) S_v(pr,c), the surface-area-to-volume ratio of the host protoplast to the whole host cell. Uninfected cortical cells had an S_v(pr,c) of 0.13 μm²/μm³. As the fungus penetrates the cell wall, the protoplast invaginates, causing a decrease in protoplast volume and an increase in protoplast S_v. The S_v(pr,c) of a cell containing a mature arbuscule is 1.275 μm²/μm³. Because of the shrinkage of the protoplast, the S_v of the protoplast to its own volume rather than the original cell volume is 2.55 μm²/μm³, or almost a 20-fold increase. Total cell size is unaffected. When the arbuscule is mature, the fungus occupies 42% of the cell, with 24% as 1-μm-diam branches, and 18% as trunk. Arbuscular branch formation progresses at a linear rate and is the most important factor in causing the increased host S_v. The correlation coefficient for V_v(br,c) the volume fraction for arbuscular branches, vs. Sv(pr,c) is r = 0.932 (P < 0.001). Degeneration of the arbuscule is marked by a rapid decrease in branches, host S_v, and host cytoplasm. The trunk develops and degenerates at a slower rate than the branches.     

Biogeochemistry of billabong sediments. I. The effect of macrophytes

SUMMARY.

• 1 We examined the effects of an emergent macrophyte (Eleocharis sphacelata R. Br., Cyperaceae) and a submerged macrophyte (Vallisneria gigantea Graeb., Hydrocharitaceae) on the biogeochemistry of the sediments of a billabong in south-eastern Australia.
• 2 Sediments from an E. sphacelata bed had significantly lower concentrations of exchangeable phosphorus than did sediments from a nearby bare area or a V. gigantea bed, but neither macrophyte had a measureable effect on their sediment's exchangeable ammonium content.
• 3 The redox potential in the upper 10cm of E. sphacelata sediments was about 100 mV higher than that of bare sediments, or of sediments colonized by V. gigantea.
• 4 There were few consistent differences between vegetated and bare sediments in terms of the activity of extracellular enzymes, such as α-amylase, protease, β-d glucosidase, lipase or alkaline phosphatase. Rates of alkaline phosphatase activity (235–306μmol (g dry wt)^?1 day^?1) were markedly higher than those commonly reported for sediments or soils.
• 5 Rates of gas release were higher from bare sediments (21–93 ml m^?2 h^?1) than from E. sphacelata or V. gigantea sediments (17–23 and 21-24ml m^?2 h^?1, respectively). Gas bubbles consisted mainly of methane (26–66%) and nitrogen (15–68%). Rates of methane ebullition varied from 5 to 60ml m^?2 h^?1.
• 6 In-vitro methanogenesis was most rapid in samples of the upper flocculent sediment. Methanogenesis was slower in V. gigantea sediments than in bare area or E. sphacelata sediments, but was markedly accelerated by additions of acetate and/or H₂/CO₂ in all sites.
• 7 Profiles of total extractable fatty acids and phospholipid fatty acids demonstrated that material derived from higher plants dominated the sediment organic matter in all sites. Bacteria were also a significant component of sediment organic matter, as fatty acids for which bacteria can be assumed the sole source accounted for 18–30% of total fatty acid content. Biomarkers for sulphate-reducing bacteria (Desulfobacter spp.) were detected, and for type II methanotrophic bacteria.

     

Short communication. Influence of light intensity on the ingestion rate of a marine ciliate, Lohmanniella sp

Using fluorescently labeled algae (FLA) as food particles, the ingestion rate of an oligotrichous ciliate, Lohmanniella sp., was 0.4 FLA ciliate^-1 min^-1 in the dark, but decreased to 0.07 FLA ciliate^-1 min^-1 when illuminated at 115 s^-1 m^-2. When the light was abruptly switched on or off, changes in ingestion rate were immediate with no delay. These results suggest that the effect of light may have to be considered in the experimental design when measuring ciliate feeding rates in marine environments.      

Invasive submerged freshwater macrophytes are more plastic in their response to light intensity than to the availability of free CO2 in air‐equilibrated water

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Phosphorus and nitrogen relationships of Cladophora glomerata in two lake basins of different trophic status

• 1 Cladophora has increased in abundance and cover in the South Basin of Windermere, English Lake District, in recent years. During the growing seasons of 1992 and 1993, the maximum biomass of Cladophora in the South Basin, at nearly 200 g dry weight m^-2, was nearly six times greater and the percentage cover, at 95%, was nearly ten times greater than in the North Basin.
• 2 Nutrient analysis showed that Cladophora from the South Basin had significantly higher average contents of N than that from the North Basin. The suggested rate-limiting tissue N content, 1.3% of dry weight, was never reached in the South Basin but was reached in 20% of samples from the North Basin. In contrast, the average P content was not significantly different, at about 0.24% in both basins. The suggested rate-limiting P content, 0.16% of dry weight, was reached in 31% of the samples from the South Basin and 37% from the North Basin.
• 3 On average, the standing stock of P in the South Basin was 0.12 g m^-2, twelvefold that in the North Basin at 0.01 g m^-2 and the standing stock of N in the South Basin was 1.81 g m^-2, elevenfold that in the North Basin at 0.16 g m^-2. Maximum standing stocks of P were 0.38 g m^-2 in the South and 0.05 g m^-2 in the North Basin. Maximum standing stocks of N were 5.02 g m^-2 in the South and 0.60 g m^-2 in the North Basin.
• 4 The maximal rate of PO₄–P uptake ranged between 298 and 2949 μg P g^-1 DW h^-1 and the specific affinity varied between 2.9 and 24.3 μg P g^-1 DW h^-1 (mg PO₄–P m^-3)^-1. The higher values of both characteristics are within the range which is believed to indicate severe P limitation.
• 5 Using the nutrient uptake characteristics, rates of uptake at pelagic and littoral concentrations of PO₄–P were calculated to be between 0.1 and 1.7% of the maximal rates apart from one site where rates were up to 5.6% of V_maxi and 40% of V_maxi based on pelagic and littoral concentrations of PO₄–P, respectively. Despite these generally low rates of uptake, calculations suggest they were just sufficient to account for the measured rate of increase of P standing stock, assuming no biomass loss. Similar calculations suggested that pelagic concentrations of NO₃–N could support between 21 and 30% of maximal rates and these were between four and six times (North Basin) and twenty-five times (South Basin) the observed rates of increase in N standing stock. Littoral concentrations of NO₃–N were similar and so would have allowed similar rates.
• 6 Evidence from nutrient tissue contents, standing stocks and rates of uptake suggests that the growth of Cladophora, in both basins of Windermere, is controlled primarily by the availability of P.

     

醉马草水浸液对豌豆蚜触杀活性及种群增长的影响

为探讨醉马草水浸液对豌豆蚜触杀活性及种群增长的影响,采用带虫浸叶法比较不同生育期醉马草带菌（E+）和不带菌（E-）水浸液对豌豆蚜触杀活性及种群生命表,测定了豌豆蚜的死亡率及触杀后对其生殖期,平均繁殖力,繁殖率及生命表参数的影响。结果表明,不同生育期醉马草带菌（E+）水浸液触杀豌豆蚜后对其各项指标均有显著影响。在苗期时,E+水浸液触杀豌豆蚜后校正死亡率最高,繁殖力最低,内禀增长率（r_m=0.145 d^-1）和净生殖率（R₀=4.802头）均为最小值。在成熟期时,E+水浸液触杀豌豆蚜24 h、48 h和72 h后校正死亡率分别为26.15%,19.01%,9.07%;繁殖期（3.87 d）,平均繁殖力（8.80头）,繁殖率（1.40%）,内禀增长率（r_m=0.208 d^-1）和净生殖率（R₀=8.820头）。在枯黄期时,E+水浸液触杀豌豆蚜后校正死亡率最低,繁殖力最强,内禀增长率（r_m=0.247 d^-1）和净生殖率（R₀=13.647头）均为最大值。不同生育期醉马草E-水浸液触杀豌豆蚜后对其种群繁殖无显著影响,与对照差异不显著（P>0.05）。综上,苗期醉马草E+水浸液对豌豆蚜有较好的触杀效果,校正死亡率高,且触杀后当代繁殖力减弱,种群扩建时间延长,不利于其种群繁殖和增长;故苗期醉马草E+水浸液具有很好的杀虫潜力,所采用水浸液方法制备简单,成本低,可为新型植物源农药研发提供重要理论依据。     

The genetic consequence of differing ecological demands of a generalist and a specialist butterfly species

Many studies aim at testing the impact of recent fragmentation on the genetic diversity and connectivity of populations, while some species do exist naturally in fragmented landscapes because of their habitat requirements. Therefore, it is important to look at the genetic signatures of species occurring in naturally fragmented landscapes in order to disentangle the effect of fragmentation from the effect of habitat requirements. We selected two Nymphalid butterflies for this purpose. While Melanargia galathea is a common butterfly in flower-rich meadows, Melitaea aurelia is closely connected to calcareous grasslands, thus being historically fragmented due to its ecological demands. For the analysis of the genetic response on these opposed patterns, we analysed 18 allozyme loci for 789 individuals (399 individuals of M. galathea and 390 individuals of M. aurelia) in a western German study region with adjacent areas in Luxemburg and northeastern France. Both species showed similarly low genetic differentiations among local populations (M. galathea: F _ST 3.3%; M. aurelia: F _ST 3.6%), both combined with a moderate level of inbreeding. Isolation-by-distance analysis revealed a significant correlation for both species with similar amounts of explained variances (M. galathea: r ² = 27.8%; M. aurelia: r ² = 28.5%). Most parameters of genetic diversity were higher in M. galathea than in M. aurelia, but the latter species had a considerably higher amount of rare or locally restricted genes; the differing ecological demands are thus reflected in these differences. Both species thus seem to be genetically well suited to their respective ecological requirements. In the light of conservation genetics, we deduce that highly fragmented populations are not necessarily prone to extinction. The extinction risk might be linked to the life history of an organism and its population genetic structure.     

An investigation of allelopathic effects of Daphnia

• 1 The hypothesis is tested that large daphnids are able to suppress their own and other species' feeding and reproduction by means of excreting an inhibitory chemical (or chemicals).
• 2 In laboratory experiments with an Australian species, Daphnia carinata, water preconditioned with 3–67 daphnids 1-^?1 for 30 h had the effect of reducing feeding rates of D. carinata and D. lumholtzi provided with Selenastrum capricornutum.
• 3 For the two Daphnia species, there were highly significant negative correlations between feeding rate and the preconditioning density of D. carinata.
• 4 Water preconditioned with 20–30 daphnids 1-^?1 for 1–2 weeks reduced the grazing rates of Daphnia, Moina, and Diaphanosoma 2–3-fold.
• 5 Moina kept in such water for 2 days stopped feeding. Conditioned water kept for 3 days without animals still inhibited grazing by Moina. Hearing to 100°C removed the inhibitory effect.
• 6 Given excess food, and in non-renewed water, a gradient of D. carinata densities developed a strong negative correlation between clutch size and daphnid density after a 6-day time lag. This result may help explain the direct density-dependent regulation of cladoceran reproduction observed earlier in a subtropical lake.

     

Benthic secondary production and biomass of insects emerging from a northern German temperate stream

• 1 Secondary production and emergence of aquatic insects were examined in the outlet of Lake Belau, Northern Germany, by means of benthic samples and emergence traps.
• 2 At three stream sections annual larval secondary production varied between 4.9 and 10.8 gDM (dry mass) m^‐2 year^‐1. Insects contributed with 3.4, 8.9, and 8.7% to the total macroinvertebrate production that varied between 56.5 and 215.1 gDM m^‐2 year^‐1. Emerged biomass was between 1.0 and 2.0 gDM m^‐2 year^‐1. At all three stream sections Diptera dominated with a larval production of 3.0–l6.1 gDM m^‐2 year^‐1, followed by Trichoptera with 1.0–2.1 and Ephemeroptera with up to 0.9 gDM m^‐2 year^‐1.
• 3 Average larval production amounted to 9.0 gDM m^‐2 year^‐1 and emerged biomass to 1.7 gDM m^‐2 year^‐1. Larvae of insects amounted to 7.0% of total macroinvertebrate production.
• 4 The ratio of annual emerged biomass to secondary production (E/P) varied among individual taxa. At the stream sections the ratio ranged from 15.9% to 20.1% with an average of 18.3% for the stream.
• 5 Relative constancy of the E/P ratio suggests that the determination of emerged biomass can be used as a method for estimating the secondary production of aquatic insects. The composition of functional feeding groups clearly differs between emerged biomass and total macroinvertebrate production. Therefore, the method does not allow conclusions on the level of production of the whole benthic community. However, composition of functional feeding groups at emergence roughly reflects composition of these groups in the benthic insect community.

     

Biological response to lake remediation by phosphate stripping: control of Cladophora

• 1 The North and South Basins of Windermere, Cumbria, have experienced a large increase in concentrations of nutrients, particularly phosphate, since 1945 when detailed measurements began. Over‐winter concentrations have increased from 1 to 3 mg PO₄‐P m^‐3 in the 1940s, up to 30 mg PO₄‐P m^‐3 in the South Basin of Windermere in the early 1990s where nutrient enrichment has been most marked. A visible manifestation of this ‘eutrophication’ in recent years has been the production of a large biomass by the green filamentous macroalga, Cladophora.
• 2 Since April 1992, tertiary chemical stripping of phosphate at the two sewage treatment plants on Windermere has reduced direct sources of phosphate to both basins. In the South Basin, over‐winter concentrations of phosphate have fallen to values similar to those in the early 1970s.
• 3 The biomass of Cladophora has declined markedly in response to the reduced phosphate availability. Significant relationships were found between the annual maximum biomass of Cladophora and two measures of phosphate availability: the over‐winter concentration and, more strongly, the day of year when the concentration fell below 1 mg m^‐3.
• 4 The annual biomass maxima of Cladophora since 1945, estimated from the regressions, showed a gradual increased potential for biomass production after 1965 as phosphate concentrations increased, followed by a striking and rapid biological response to lake remediation by phosphate stripping.