摘要:

SUMMARY.Prymnesium parvum, an ichthyotoxic phytoplankter, has been recorded, at times abundantly, in the River Thurne, Norfolk, and its associated Broads. Its occurrence has been apparently more frequent and its population sizes probably larger since the late 1960s than previously and fish mortalities due to it now occur almost annually.The Thurne system is brackish and may have become more so, due to exploitation by drainage pumps, of a saline water table, in recent years. Evidence for this is conflicting, but in any case an increase in salinity is unlikely to have made increasedPrymnesiumgrowth more likely. Eutrophication of some Broads in the system is most likely to have increased the populations ofPrymnesiumsince the late 1960s and data are presented on the present water chemistry of the system for comparison with previous records, and on current phytoplankton andPrymnesiumcrops in different parts of it.P. parvumhas been isolated from the system as a unialgal culture and compared in morphology, salinity tolerance and ichthyotoxicity with a strain ofP. parvumfrom Israel. The Broads strain differs slightly in size and pigmentation, but not in salinity tolerance. In culture it produces more ichthyotoxin than the Israeli strain.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01451.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Morphological variability inDaphniapopulations has often been uncritically ascribed to phenotypic plasticity. For instance, detailed study revealed that the ‘cyclomorphic species’D. carinatas. l. was a complex of nine species. Several of these species often cohabit and seasonal change in their relative frequencies causes phenotypic cycles which mimic true cyclomorphosis. Intraspecific genetic variation in head shape also seems widespread and is likely to be important in explaining phenotypic changes in many single species populations.The hypothesis that helmet formation inDaphniais primarily related to predator avoidance is not supported by work on theD. carinatagroup. Seasonal trends in species composition can be explained without reference to differential predation. Natality differences exist between species with disparate head size suggesting that helmet formation may have direct effects on fitness. Two possibilities are considered. The length of the anterior adductor muscle is directly correlated with helmet size and such variation may affect swimming efficiency. In addition the laminar design of helmets suggests a role in gas excha

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01452.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Gut contents of adult copepods from Lake Kainji were analysed. The calanoid copepodTropodiaptomus banforanuswas exclusively herbivorous withMelosiraandPeridiniumforming a large proportion of the diet. Of the cyclopoid copepods,Mesocyclops leuckartiwas mainly carnivorous while the smallerThermocyclops neglectuswas mainly herbivorous. Experiments withDiplocystis (Microcystis)showed that it was not ingested by these three copepod species even after starvation and possible explanations for the results are discussed.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01453.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.The results of laboratory experiments on ciliate reproductive and respiratory rates have been combined with field data for ciliate numbers, to produce estimates of production and respiratory energy losses by communities of benthic ciliates. Annual production decreased with increasing depth, and it was estimated to be 345, 149 and 40 J cm−2year−1at three sites in Airthrey Loch, Scotland. A similar trend with increasing depth was recorded for annual respiratory energy losses, being 16, 11 and 4 J cm−2year−1at the three sites. The corresponding annual net production efficiencies (%) were 95.2, 93.1 and 91.5. When net production efficiencies were calculated for each period (the time between successive sampling occasions) as 100 (daily production/daily assimilation), the range extended from 63 to 98. The energetic efficiencies of the ciliate populations are discussed with reference to data in the literature for higher or

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01454.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Eggs of bullhead (Cottus gobio) were found with damaged shells and with the contents removed. Experiments in laboratory aquaria indicated that the damage was caused by caddis larvae and that the type of caddis involved in egg predation might be identified by the nature of the shell damage.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01455.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Seasonal changes in dissolved organic carbon (DOC) concentrations were monitored biweekly for 1 year at seven stations in the Shetucket River watershed in eastern Connecticut, U.S.A. Nine monthly diurnal studies revealed 24‐h fluctuations of up to 53% of the seasonal range of 250–2200 μmDOC.Net DOC removal along a 1.9‐km stretch below a secondary sewage treatment plant (activated sludge effluent diluted to a final average volume of 1.4% in the river) ranged from 0 to 1600 and averaged 68 ± 64 mmol m−2day−1. Removal of DOC further downstream could only be observed during a severe 3‐h October storm when net uptake ranged from 16 to 92 mmol m−2h−1, using upstream‐downstream techniques. Oxygen respiration could account for about half of the net DOC removal during the October storm.Even though net uptake was somewhat greater than reported in other lotic studies, about 97% of the DOC potentially available to benthic heterotrophs was exported

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01456.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Naidids live in a wide range of aquatic habitats but are particularly important numerically as part of the benthic fauna of rivers with stony substrates. In general they graze on bacteria and algae although some, particularlyChaetogasterspp., are mainly predaceous, andC. limnaei vaghiniis a parasite of molluscs, chiefly Gastropoda. Food selection seems to be based largely on particle size although the food quality of the particles within the appropriate size‐range influences rates of growth and reproduction.Major factors determining the distribution and abundance of naidid species are the nature of the substratum and the presence and kind of vegetation. Plants with a highly dissected form, a thick growth habit, and which permit the greatest periphyton development generally support the most abundant naidid populations. The oligochaete fauna of coarse substrates (stones and gravels) is often dominated by the Naididae but both species‐richness and abundance of naidid populations are generally reduced where fine substrates (silts and muds) occur. The occurrence of worms within the substratum is also determined by its nature; naidids penetrate to depths of 20–70 cm in coarse substrates but rarely penetrate below 6 cm in mud. The principal factor limiting both depth penetration and the dominance of naidids in fine substrates is probably oxygen availability.Naidids reproduce both asexually and sexually, the former method predominating for most of the year. Asexual reproduction usually involves the budding‐off of zooids but a few species fragment. Sexual reproduction is often infrequent; populations of some species produce few or no sexually mature individuals. In mature worms asexual reproduction virtually ceases. In populations that produce mature individuals there is apparently one sexual generation a year, usually occurring during the summer and autumn. Adults die soon after laying their cocoons.In general, naidids are most abundant during the summer months when rates of growth and asexual reproduction are stimulated by higher temperatures and a plentiful supply of food. A few species, however, e.g.Nais elinguis and Paranais litoralis, are more abundant in the spring.The response of naidid species to different kinds of pollution is varied but generally organic enrichment of rivers which have stony substrates results in a considerable (ten‐ to twenty‐fold) increase in naidid abundance.Nais elinguis, N. barbata, N. communis, N. variabilis, andChaetogaster diaphanusare often abundant in such rivers, the foremost species reaching densities of 200 000 m−2.Nais alpina, N. bretscheri, andN. pardalisappear to be relatively intolerant of organic enrichment. A substantial increase in naidid abundance is also promoted by the deposition of biologically inert particles (coal dust, china clay, sand) on the river bed.The importance of Naididae in relation to pollution surveillance of fresh waters

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01457.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.A method for determining the prey of a damselfly larva under natural conditions is described, with its shortcomings.Within the limits of the method, it would appear thatIschnura elegansconsumes different prey items in roughly the same proportions as their occurrence in the field.Anomalous results are explained in terms of differences in encounter rates between predator and prey and/or ease with which prey can be handled.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01458.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Age and growth rates of the coarse fish of thirty‐nine gravel‐pit lakes in south‐east England are compared. Species composition was very variable, the commonest species being roach (Rutilus rutilus), bream (Abramis brama), tench (Tinca tinca), perch (Perca fluviatilis) and pike (Esox lucius). Two main kinds of fish community were identifiable from the survey: (1) those consisting of a mixture of cyprinids, usually roach and bream; and (2) those in which cyprinids were rare or absent and the fish community was composed of perch and pike. The majority of the lakes fell into the first category. Comparison of growth curves derived by back‐calculation showed that, in all species, variation occurred from lake to lake and from year to year. The majority of gravel‐pit lake fishes had ‘medium’ growth rates when compared with published data by other workers on different waters. Seasonal growth of roach infected with plerocercoids ofLigula intestinaliswas observed at monthly intervals. Annulus formation on the scales of these fish occurred at the onset of growth in May. The heavyLigulaburden in 89% of these fish had not caused the formation of any additional o

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01459.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01460.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY