摘要:

SUMMARY.The number of flagellar segments on the antennules ofGammarus pulexwas quantitatively related to body size in animals from natural populations and to moulting and instar number of isolated animals grown from birth in the laboratory. The number of segments was 5.0 at birth increasing to means of 19–20 in females and 21–22 in males at sexual maturity orc.5 mg wet wt reached after nine or ten moults. Addition of segments to the paired flagellae of juveniles was not regular and the number of segments cannot be used to identify particular instars of individuals or to determine their age. The mean interval (days) between moults progressively increased in the later juvenile instars and was exponentially related to moult number, age and the number of flagellar segments; the moult interval is also exponentially related to these variables in adu

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01281.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The interval between moults is an extension of egg development time, increasing from birth to sexual maturity which is probably reached at instar 6 or 7. The duration of each instar increased with the animal's age. Incubation time for eggs and the intermoult interval have the same curvilinear inverse relationship with water temperature in the range 3.5–25°C. Results are expressed as degree‐days above predicted threshold temperatures of 3.8°C for eggs and 3.2°C for instar 1 after birth, but inverse power‐law relationships were a better fit to the results, with exponents of ‐ 1.355 for eggs, ‐ 1.263 for instar 1 and ‐ 1.37 to ‐ 1.92 for instars 2–4. Temperature — dependence apparently altered in instars 5 and 6 at 15–25°C. From a multiple regression of geometric mean moult interval (Mi, days) against mean age (A) and temperature (T, °C),Mi= 56.4T−0.7e0.016A, with mean ages of 106 days at 15°C and 85 days at 25°C after six moults.The mean number of primary flagellar segments on the antennules increased from 4.0 in instar 1 to 6.0 in instar 2 and 8.0 in instar 3. Thereafter, segments were added less regularly to give a mean of 13.2 in instar 7. In a natural population, when the sexes became distinctive they had 11–13 flagellar segments.From birth atc. 0.05 mg wet wt, individual growth rates were highly variable; mean growth rates (Gs, % wet wt day−1) were similar in animals fed on dried, leached elm leaves and living, green leaves ofCallitriche; there was a power‐law relationship with temperature in the range 3.5–25°C, (Gs= 0.27T0.59). Faster growth rates were obtained on living leaves ofElodea. Sexual maturity is reached atc. 0.4–0.5 mg wet wt. A brief comparison is made withGammarus pulex;C. pseudogracilismay b

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01282.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.Changes in macrophyte richness, relative abundances, depth distributions and dominant species from 1937 to 1975 were assessed in Chautauqua, a eutrophic lake. Change was greatest in dominant species, with several formerly abundant nativePotamogetonspecies being replaced by the exotics,Potamogeton crispusandMyriophyllum spicatum. Two extensively practiced management techniques, herbicidal poisoning and mechanized cutting, were considered to be primarily responsible for the observed macrophyte changes.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01283.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.Seasonal changes in population structure, standing stock levels and production ofCaridina niloticawere studied at three sites in the littoral margins of subtropical Lake Sibaya between January 1975 and March 1976. Average population density at these sites declined from a maximum ofc. 1400 to a minimum ofc. 350 individuals per m2(3.4–0.4 g m−2dry wt) during the study, possibly as a result of emigration into peripheral vegetation inundated by rising lake levels.Shrimps bred perennially and, although egg stocks and instantaneous birth rates (b) were highest during summer, no corresponding increases in populaton density were observed, suggesting that the seasonally higher birth rates were offset by higher mortality rates. Population size structure and size‐specific sex ratios did not change seasonally to any marked extent. Relative abundance declined with size and females grew larger than males. Clutch size increased linearly as a function of female carapace length.Estimates of overall mean annual somatic production (g m−2year−1dry wt) for the three sites between January 1975 and January 1976 ranged betweenc. 132 (egg‐ratio method), 37.5 (summation of growth increments) and 24 (Hynes‐Hamilton method) at an annual mean standing stock level of 2.7 g m−2dry wt (calorific value, 20.34 kJ g−1dry wt). Production at sites 1, 2 and 3 decreased in line with declining annual mean standing stocks (5.32, 3.67 and 0.23 g m−2, respectively). The growth increment method gave an overall mean annual P/B value of 13.9. Egg production amounted to a further 5.6, 3.6 and 0.1 g m−2year−1dry wt (calorific value, 28.01 kJ g−1) at sites 1, 2 and 3, or

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01284.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The effects of a sewage effluent discharge into the River Cole, Birmingham, were determined by regular collections of water and biological samples from six comparable stations, one above and five below the sewage effluent. The effluent reduced the dissolved oxygen concentration and increased the ammonia, orthophosphate and BOD concentrations in the water. The effects were much more severe during the summer.The Chironomidae were very important constituents of the benthic macroinvertebrate community at the stations downstream of the effluent. Larval densities of over 30,000 m−2were recorded. Eleven species were common and of theseChironomus ripariuswas the most tolerant. There was considerable variation in the seasonal incidence of the different species.Brillia longifurcawas most abundant in the spring whileCricotopus bicinctuswas most abundant in the summer.Brillia longifurca, Paratrichocladius rufiventris, Prodiamesa olivacea, Micropsectra atrofasciataandEukiefferiella claripennishad three peaks in numbers of larvae during the year.The increase in the polluted state of the river in the summer resulted in changes in the chironomid populations. Some were suppressed, e.g.E. claripennis, whileC. ripariusextended its range and achieved maximum abundance further downstream during the summe

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01285.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The concentration of zinc in the scales of unripe, prespawning, estuarine sea trout was compared to that in the scales of sea trout about to spawn in fresh water. Zinc concentrations in scales from estuarine sea trout were in agreement with a published concentration factor but those from fresh water were not — a 43–52% reduction in the zinc concentration of the scales was observed. This withdrawal of trace metals from scales was also likely for iron but these data were less conclusive. This reclamation of trace metals from scales may represent the withdrawal of stored nutrients from body reserves to be used in gonad development and maturat

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01286.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The phytoplankton and zooplankton of Grafham Water reservoir, Cambridgeshire, are described and discussed for the 5 years 1974–78 together with the main physical variables and macro‐nutrients believed to affect them. This follows on from the Water Pollution Research Laboratory study of 1969–74. The rationale for the work was to provide short‐term warning of treatment and management problems caused by algae and to gain insight into the factors controlling them.During the period reviewed the 1976 drought occurred with a massive draw‐down. Afterwards replenishment of the lake from the River Great Ouse resulted in its enrichment with high concentrations of nitrate, orthophosphate and silica. The algal cycles changed to some extent over this period with a few species becoming even more dominant and others diminishing in importance. The effect of the drought and post‐drought pumping is discussed; a return to former nutrient levels seems likely. The effects of weather, particularly radiation and wind, on algae may be of equal importance to nutrient levels in Grafham and will be further i

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01287.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.Calorific determination of twenty‐three species of aquatic invertebrates from various life stages, collected from prairie wetlands, ranged from 3682 cal g−1dry wt for adult amphipods,Hyalella azteca, to 6270 cal g−1dry wt for an adult female beetle,Agabus bifarius. The aggregate mean for the specimens was 5225 cal g−1dry wt. All genera analysed here are eaten b

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01288.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Morris, I(Ed)(1980)The Physiological Ecology of Phytoplankton.Alexander M.(Ed.)(1980)Advances in Microbial Ecology, Volume 4.Edington, J.M.&Hildrew, A.G. (1981)A key to the caseless caddis larvae of the British Isles with notes on their ecology.Lackey R.T.&Nielsen L.A.(Eds)(1980)Fisheries Management.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01289.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01290.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY