The life cycles of Leptophlebia vespertina (L.) and L. marginata (L.) (Ephemeroptera) in Llyn Dinas, North Wales

Data is presented on the life cycles of Leptopblehia vespertina (L.) and L. marginata (L.) in Llyn Dinas, an oligotrophic North Wales lake. Both species are univoltine and growth continues throughout the winter although somewhat retarded. Except during July and August there is a clear size separation of the two species, L. marginata being larger and emerging earlier. The egg incubation period was determined directly from laboratory studies. The results are discussed in relation to previous research in the English Lake District.     

Experimental studies on nymphal growth in Leptophlebia vespertina (L.) (Ephemeroptera)

The mayfly, Leptophlebia vespertina (L.) was reared at field temperatures in the laboratory. The egg incubation period was 21–26 days. There were seventeen to nineteen nymphal instars. Growth was generally rapid during the first 3½ months and slow thereafter. This change occurred at the same time in both the laboratory and the field population. Temperature is considered to be the major factor regulating this and other changes in growth rate.     

The distribution,life cycle and production of Leptophlebia vespertina (L.) (Ephemeroptera) in a lowland lake

Oak Mere, the water body studied, is a moderately productive base-poor lowland lake. It has zones of submerged marginal vegetation growing on sand at the south-west end and on peat at the north-east end. The distributions of L. vespertina and other macroinvertebrates are described in relation to these two distinct areas. Laboratory experiments on behaviour and survival are described in an attempt to explain the patterns of distribution. The seasonal distribution, variations in population density, spatial distribution variance in relation to mean density, life cycle, length-weight relationship, growth and biomass of L. vespertina are then described during two years at the sandy south-west end. The data are used to estimate annual production. Distribution, life cycle, growth and production are compared with populations in water bodies of lower conductivity in the British Isles and Scandinavia.     

Effects of subacute doses of iron (Fe) on Leptophlebia marginata (Insecta: Ephemeroptera)

1. The objective of this paper was to reveal the toxicity of Fe³⁺ and Fe²⁴ at pH 4.5 and 7 on larvae of the mayfly Leptophlebia marginata, by examining survival, motility, gill ventilation, moulting and feeding in experiments. 2. Fe²⁺ was the dominant metal species at pH 4.5, and Fe³⁺ at pH 7. Precipitation of Fe occurred only at pH 4.5, where Fe-precipitarions were observed on the thorax and the gills of the larvae. 3. Both feeding activity and motility of the animals decreased at pH 4.5 and 10, 20 or 50mg1-^?1 Fe_tot. After a short period of normal feeding, the animals stopped feeding for approximately 2 weeks and did not start to feed again until the end of the experiment. They were constipated. Survival was >95% in all treatments, except at pH 4.5 and 50 mg Fe_tot. In this group, about 20% of the animals died after having been constipated for 2 weeks.     

Joint and single toxicity of Cd and Fe related to metal uptake in the mayfly Leptophlebia marginata (L.) (Insecta)

The toxic effects of Cd and Fe on the mayfly Leptophlebia marginata were tested during single and joint exposure to the metals. Data on uptake and localization of the metals were related to the following biological parameters: survival, food consumption (% gut contents) and activity (escape from prodding).The uptake of Cd by L. marginata was significantly reduced by the presence of Fe (p<0.0005).Fe²⁺- and Fe³⁺-crusts on the gills, body surface and on the gut membrane precipitated when the mayflies were exposed to either Fe alone or to Fe and Cd. This caused decreased food consumption by the mayflies.In the pigments of the eyes and the cuticle Fe²⁺ was found.Exposure to Cd led to disturbances in Cl^– and K⁺ ion balance, which were ameliorated by additional Fe-exposure due to co-precipitation processes.Exposure to Cd caused an increase in the concentrations of S and P in the mayflies.Whereas Fe caused sublethal effects (food consumption) without being taken up into the organism. Cd caused lethal effects (inactivity, death) due to disturbances of the ion balance at the membranes.     

Short term toxicity of iron (Fe) and lead (Pb) to the mayfly Leptophlebia marginata (L.) (Insecta) in relation to freshwater acidification

The mayfly Leptophlebia marginata was exposed to different concentrations of Fe²⁺ or Pb²⁺ at pH 4.5 and pH 7.0. The effects of the metals on escape behavior and survival of the mayflies were investigated during an exposure of 120 hours.

1. Whole-body metal loads (Fe; Pb) of the mayflies increased in a dose-dependent way at both pH levels. A significant effect of pH on metal concentration in the mayflies was only found for Pb (p < 0.001).
2. In terms of mortality, both metals were more toxic at pH 4.5 than at pH 7. The 96 h-LC₅₀ values for Fe were 106.3 mg Fe l^-1 at pH 7 and 89.5 mg Fe l^-1 at pH 4.5. Those for Pb were > 5 mg Pb l^-1 at pH 7 and 1.09 mg Pb l^-1 at pH 4.5.
3. The mayflies lost their escape behavior, when exposed to the metals, the effects being more pronounced at low than at circumneutral pH for both metals (p < 0.05). The 96 h-EC₅₀ values for Fe were 70.0 mg Fe l^-1 at pH 7 and 63.9 mg Fe l^-1 at pH 4.5.

     

Seasonal dynamics of a mayfly (Insecta: Ephemeroptera) community in a Laurentian stream

The purpose of our study was to compare on a seasonal basis the emergence, the drift and the benthos on a short and uniform section (18.5 m)of a stream in the Laurentian Hills of Québec. Nineteen species occurred on this stretch, but only six were abundant: Leptophlebia cupida (Say), Habrophlebia vibrans Needham, Baetis pygmaeus (Hagen), Eurylophella verisimilis (McDunnough), Stenonema modestum (Banks), and Stenonema vicarium (Walker). Emergence was monitored for 5 years; densities differed from one trap to the next, as did species dominance, but total densities were similar. These data conform to Illies' rules of constancy and harmony. Nymphal densities were high (mean of 16000 m⁻²). The dominant species were univoltine, except H. vibrans (semivoltine), and B. pygmaeus (polyvoltine). Larger species contributed relatively more to the production of the reach despite their low densities than did the more abundant smaller species, especially those with long life cycles. Drift was low during most of the year, except during spring and species composition varied considerably. A comparison of the three data sets (emergence, drift and benthos) shows a general agreement for the less abundant species, but for three of the dominants, H. vibrans, L. cupida and E. verisimilis , movements of individuals to and from the reach at various times in the life cycle (adult flight, nymphal drift and migration) must be taken into account in order to correlate the data. None of the methods alone gives a satisfactory picture of the community structure, each is to some extent misleading and needs to be used in conjunction with the others; the conflicting results obtained from the data sets often reveal interesting life history traits which otherwise would not have been detected.     

Ecology of Potamanthus myops (Walsh) (Ephemeroptera: Potamanthidae) in a Michigan stream (USA)

The ecology of Potamanthus myops (Potamanthidae) was examined for a one year period in a central Michigan fourth order stream. Lowest nymphal densities (4.7 m^-2) occurred in mid-summer after adult emergence, while highest densities were found during late summer and fall (68.0 m^-2 and 66.2 m^-2) after the new cohort had hatched. Biomass was the inverse of density with highest values, 67.7 mg m^-2, just prior to peak adult emergence in June and lowest in late summer (16 mg m^-2). Nymphs maintained a contagious spatial distribution with k values ranging between 0.19 and 1.40. P. myops nymphs fed mostly on detritus (96.8%), placing them in the collector-gatherer functional group. Nymphs were always found in erosional zones associated with rock substrate. Nymphs used their mandibular tusks for positioning themselves beneath rocks, while also appearing to use them for defensive purposes.     

Responses of Chironomidae (Diptera; Insecta) to the exclusion of shrimps and Ephemeroptera in a coastal forest stream, Rio de Janeiro, Brazil.

In a benthic community on a continuous flat granite substrate in a third-order coastal forest stream, the dominant chironomid (Cricotopus) increased in number when shrimps (Macrobrachium olfersi and Potimirim glabra) and baetid ephemeropterans were excluded by electricity. The response appeared to be mediated by an increase in periphyton and sediments, rather than a reduction of direct predation or interference. Chironomids, periphyton and sediments decreased significantly compared to the control when shrimps only were excluded. Baetid ephemeropteran appeared to be the most important determinants of periphyton and sediment mass; the density of chironomids appeared to follow the quantity of periphyton and sediments.     

Species composition and distribution patterns of baetid nymphs (Baetidae: Ephemeroptera) in a Japanese stream

Species composition and distributional patterns among nymphs of five baetid genera (Ephemeroptera), Baetis, Tenuibaetis, Labiobaetis, Nigrobaetis and Alainites were investigated in Yura Stream, Kyoto Prefecture. I collected 13 species: B. sahoensis, B. thermicus, B. sp. F, B. sp. J, B. sp. M1, B. sp. S1, T. sp. E, T. sp. H, L. sp. G, N. chocoratus, N. sp. D, N. sp. I and A. yoshinensis, among which B. thermicus, B. sp. S1 and T. sp. E were dominant, whereas B. sahoensis, B. sp. F, B. sp. M1 and N.sp. I were scarce. Based on their longitudinal distribution patterns, the 13 species were classified into upper species, upper-middle species, middle species, middle-lower species and lower species. Baetis thermicusand A. yoshinensis showed long downstream tails. Baetis sp. J and N. sp. D extended their longitudinal distribution upstream in summer. With regard to habitat preference, Alainites and Labiobaetis were restricted to riffle and vegetated zones, respectively. Tenuibaetis consisted of riffle-vegetated zone species, whereas Baetis and Nigrobaetiscontained both riffle species and ubiquitous species. Habitat partitioning (`sumiwake') along the watercourse (macro-sumiwake) was evident in Tenuibaetis, and that between habitat types (micro-sumiwake) in Labiobaetis vs. Baetis (rhodanigroup species) and Labiobaetis vs. Alainites.     

Life history and secondary production of Electrogena ujhelyii (Ephemeroptera: Heptageniidae) in a small forest stream in West Carpathians

In this study we focused on life history parameters of Electrogena ujhelyii. We studied life cycle, nymphal growth pattern, biomass and secondary production in a small, calcareous stream in Malé Karpaty Mts (West Carpathians). The life cycle was univoltine with a large range in the size of nymphs during most samples dates. Mean annual density was 40 ind. m^?2 and the annual secondary production reached 183 mg DW m^?2 y^?1. There are no published data available on the secondary production values of this species, therefore these are the first published data.     

The ingestion and digestion of algae by Chloeon dipterum L. (Ephemeroptera)

Summary The ability of larvae of Chloeon dipterum L. to ingest various species of algae was investigated in the laboratory. There was a direct relationship between the size of an alga and the frequency with which it was ingested by different sizes of larva. The frequency of ingestion of Anabaena, Cladophora, and Hydrodictyon appeared to be governed by factors in addition to their size.Several species of algae were thoroughly and rapidly digested by C. dipterum in the laboratory.Cultures of the hind-gut contents of larvae collected in the field, and of those fed upon algae in the laboratory, showed that cells of several species of algae remained viable in the gut for periods of at least 20 hours. These were narrow filamentous forms or small cells with or without a gelatinous sheath. It is suggested that such species pass between the mouthparts without being damaged so that in the absence of a cellulase the digestive enzymes of the gut are unable to penetrate the cell walls.     

Production of Gammarus pulex L. (Amphipoda) in a small Danish stream

Quantitative samples of Gammarus pulex L. taken from a small Danish stream during 1975 showed mean annual population densities varying from 500 m^–2 in early May to 5 500 m^–2 in late September. The mean annual biomass was 1.5 g dry weight m^–2. No discrete cohorts could be distinguished from the size frequency distributions. Annual production, estimated by the size-frequency method, was 3.9 g dry weight M^-2 and P/B ratio was 2.6. The contribution to trout energetics may have been as much as 17%.     

Mussel culture in a changing environment: the effects of a coastal engineering project on mussel culture (Mytilus edulis L.) in the Oosterschelde estuary (SW Netherlands)

To evaluate the effects of a large scale coastal engineering project on the mussel (Mytilus edulis) bottom culture in the Oosterschelde estuary (S.W. Netherlands), mussel growth and production in the period 1980–1990 are studied in relation to food supply and the hydrodynamic conditions. Due to the construction of a storm-surge barrier and two additional dams, the risk that mussels are swept away by high current velocities decreased, resulting in an increase of the area in the Oosterschelde potentially suitable for mussel culture and in food availability now being more important as a limiting factor. For the Oosterschelde, a clear relation between mussel growth, stock sizes, and phytoplankton dynamics has been demonstrated. The meat yield of mussels landed in autumn — which is an index for growth rate — seems to be determined by the phytoplankton production in the preceding summer. In years with dense bivalve stocks, phytoplankton production and meat yields are relatively low. It is concluded that an increase of the mussel biomass cultured can result in a reduction of the primary production and, consequently, in a deterioration of the growing conditions for suspension-feeders in the estuary. This conclusion is supported by model calculations. An expansion of mussel culture in the new Oosterschelde is therefore dissuaded. Apart from primary production and stock sizes, food supply for mussels on culture lots appeared to be controlled by the horizontal advection of phytoplankton between and within the tidal channels. An observed decline in mussel landings from certain areas is attributed to the reduced mixing energy of the estuary in relation to the present distribution of the lots over the estuary. Production figures from the experimental lots, established in 1988 in the newly available areas, demonstrate that the yield of mussels can be enhanced by relaying culture lots towards the areas where the phytoplankton is produced. It is expected that by redistributing the culture lots, without expanding the biomass cultured, the carrying capacity of the Oosterschelde for mussel culture can be maintained.     

Life history and production of Caenis luctuosa (Burmeister) (Ephemeroptera, Caenidae) in two nearby reaches along a small stream

Population dynamics and production of C. luctuosa were compared in two reaches of the Agüera stream (northern Spain). This species showed univoltine winter life history in both sites. However, the start of the recruitment period, and the cohort production interval differed in 1 month between reaches. Secondary production of C. luctuosa ranged from 76 mg m^–2 year^–1 (upper site) to 93 mg m^–2 year^–1 (lower site). Although annual production seemed to be mainly influenced by the biomass found at each site, changes in life history may have also been important. The need to have accurate information about life history of the analysed species at the study sites when assessing secondary production is highlighted.     

Life history of a lowland burrowing mayfly, Ephemera orientalis (Ephemeroptera: Ephemeridae), in a Korean stream

Life history aspects of Ephemera orientalis, a common lowland burrowing mayfly that resides in temperate East Asia, were studied in terms of voltinism, secondary production, and accumulated degree days for larval development. From March 1998 to June 1999, larvae were sampled monthly (weekly or biweekly during the emergence period) from a lower reach of the Gapyeong stream in Korea, a stream typical of temperate East Asia, using a Surber sampler (0.25 m², mesh 0.25 mm). As a result, the mean density of E. orientalis was 47.21 ± 13.58 indiv. m⁻² during the study period. Very small larvae less than 2 mm in body length were sampled on three separate occasions, and emergence was observed between late April and early October, except during late May. Based on the larval body length distribution and emergence time, two different developmental groups could be distinguished: the slow developmental group (S-group) and the fast developmental group (F-group). The F-group completed its life cycle within 4 months, whereas the S-group had a one-year life cycle. The S-group could be divided into two subgroups, dubbed the S1 and S2-groups, based on larval development. The developmental groups alternate their life cycles in the order: S1→F→S2→S1. Estimated annual production of the larvae was 68.81 mg DW m⁻² y⁻¹; mean biomass was 8.43 mg DW m⁻²; the annual production to mean biomass ratio was 8.16. The annual mean water temperature of the study year was 14.76 ± 6.63°C. The total accumulated degree days for larval development was 1396°C for the F-group, 2,055°C for the S1-group, and 1,975°C for the S2-group. Two different adult body size groups were distinguished (P < 0.001 by t-test): larger adults, which belonged to the S-group, were present throughout the emergence period, whereas smaller adults, which belonged to the F-group, were mainly present later in the emergence period (August–October). The difference in the accumulated degree days between the developmental groups may explain the size differences of adults.     

Life cycle, growth, mortality and production of Ephemerella major Klapalek (Ephemeroptera) in a trout stream in Belgium

SUMMARY. 1. The life cycle of Ephemerella major Klapalek in a chalk trout stream in Belgium took 1 year. Emergence was highly synchronized with a flight period from mid-May to mid-June. Tiny nymphs occurred from June to late August.
2. The mean instantaneous growth rate was high in autumn (3.6% wet wt day⁻¹), very low from November to February (0.8% wet wt day⁻¹) and high until emergence (2.3% wet wt day⁻¹); short day length seemed to be the major factor reducing growth rate during winter.
3. Mortality was close to zero during winter and 1.4—1.7% day⁻¹during other seasons. Total mortality from egg to adult was 99.6%.
4. The annual production was about 9g wet wt m⁻² year⁻¹ and the annual P/ ratio was 7.5. There was good agreement between the production values estimated by four methods. Production rate was highest in May (13 mg wet wt m⁻² day⁻¹) and zero in February.