摘要:

SUMMARY.Fungal infection of calanoid copepod (Diaptomus novamexicanus) eggs was observed in each of three years in an alpine lake (Castle Lake, California, U.S.A.). Stages in the infection process were examined by light and scanning electron microscopy and evidence was obtained that theLagenidium‐like fungus concerned was a virulent parasite. Fungal destruction of eggs varied in timing and severity from year to year. The maximum impact of the disease was an estimated 48.4% decrease in potential copepod recruitment in 1976 due to the onset of a severe epidemic early in the summer growing season. The minimum impact, a 5.6% decrease in potential recruitment, was recorded in 1975. In this year the proportion of infected eggs was reduced and large numbers of juveniles had been released before the fungal disease began. The 1974 epidemic was intermediate in severity. The effect of these epidemics on Castle Lake calanoid populations is discussed in relation to temperature, food availability and predatio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01534.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.The discovery of a third species of alderfly (Sialis nigripes) in Britain and Ireland necessitates a new larval key for the group in these islands. Characters are now provided to distinguish the larvae of the three species, and their habitat and distribution in the British Isles are outlined.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01535.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.The development times of the egg, nauplius and copepodite stages of seven species of freshwater benthic copepods (Paracyclops fimbriatus, Canthocamptus staphylinus, Attheyella crassa, Moraria brevipes, M. mrazeki, Bryocamptus echinatusandParacamptus schmeili) were determined at constant temperatures ranging from 1.5 to 24°C using detritus as food. Several regression models used earlier to describe the temperature dependence of development were tested on this material.Species differed both in the rapidity of development and in the magnitude of the effect of temperature. Development times usually decreased with increasing temperature, but inM. brevipestemperatures exceeding 16°C retarded postembryonic development.P. fimbriatusdeveloped at a rate comparable to that reported earlier for littoral cyclopoids. All the harpacticoid species developed more slowly than planktonic, littoral or benthic copepods previously studied, but faster than subterranean species. The effect of temperature was most marked in species reproducing in warm water.The relationship between rate of development and temperature was not linear. None of the curvilinear temperature functions tested was statistically adequate in all cases. However, three of the models gave a reasonable fit to all egg development data, and one of these, the semilogarithmic quadratic equation, lnD= Ina+TInb+T2Inc, also satisfactorily described postembryonic development. This model accommodates the retardation of development at higher temperatures, and can therefore be recommended for further testin

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01536.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.The annual cycle of intraovarian egg size in 124 mature barbel caught during a 3‐year period was investigated. Storage methods, subsampling and measuring procedures were assessed and found to be reliable. Estimates of fecundity were made on thirty‐two barbel containing developing ripening eggs. A new egg separation and counting technique was used modified from the volumetric ratio method described by Bagenal&Braum (1968). Fecundity estimates were found to be accurate by comparison with manual counts. Barbel ovaries contained two egg groups throughout the year. A third large, ripening egg group developed prior to spawning. The diameter of the ripening eggs, measured in arbitrary optical units, was significantly correlated with fork length. Large fish spawned bigger eggs than small fish. Fecundity was logarithmically related to fork length and ovary weight and linearly related to somatic weight. The mean diameter of the ripening intraovarian egg group was also logarithmically related to ovary weight. Heavier ovaries contained proportionally fewer, but larger, ripening eggs than small ovar

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01537.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.The life‐cycles of green and white morphs of the freshwater spongeSpongilla lacustriswere examined in the light of past evidence that zoochlorellae may augment their sponge host's nutrition. Field collections from a lotic population ofS. lacustriswere supplemented by laboratory experiments on gemmule hatching and gemmule size. Both white and greenS. lacustrisproduced sperm for a 6‐week period in 1976 starting in the middle of May. Out of thirty white and thirty green sponges examined during this period, twenty white and ten green sponges contained sperm. Sperm production in both morphs was limited primarily to the basal 3.18mm of sponge tissue, and the density of sperm packets in the two morphs was the same. Out of 180 white and green sponges examined in 1976, only four eggs, no embryos, and no larvae were observed. White sponges gemmulated a week or two earlier, and produced smaller gemmules which were more uniform in size than those of green sponges. White and green gemmules hatched synchronously in the spring. In 1977 one female and numerous male specimens ofS. lacustris, and numerous females but no males of another sponge,Eunapius fragilis, were found. The life‐cycles are discussed in the light of other recent studies on freshwater sp

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01538.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.Seasonal changes in photosynthetic rates of phytoplankton and underwater light in four Kenyan fresh waters (Lake Naivasha, Crescent Island Crater, Oloidien Lake and Winam Gulf) were measured in 1973 and 1974. Daily variations in water temperature were only slightly less than seasonal changes, and complete vertical mixing usually occurred each day. Well oxygenated water from top to bottom provided evidence for daily mixing.The vertical profiles of photosynthetic rates in the four lakes had the familiar feature of subsurface maxima. Of the photosynthetically available radiation (PAR), 1% coincided with the limit of detection of photosynthesis in Naivasha and Crescent Island Crater. The PAR at the depth of the maximal photosynthetic rate was higher for Naivasha (mean= 1.71 einsteins (E) m−2) than for the Oloidien and Crescent Island Crater (means = 1.23 and 1.20 E m−2h−1, respectively).The maximal rates of photosynthesis (mg O2 m−3h−1) were usually higher in Oloidien (260–750) and Winam Gulf (230–640) than in Naivasha (150–240) and were least in Crescent Island Crater (50–180). Chlorophyll‐a concentrations were directly related to photosynthetic rates. Because of the inverse relation between euphotic zone depth and maximal photosynthetic rates, the areal rates varied less among the lakes than the volumetric rates (i.e. 3.0–12.1 g O2 m−2day−1).The efficiency of utilization of PAR expressed on a molar basis ranged from 6.1 to 1.9 mmol O2E−1, but was usually 2–4 mmol O2E−1.The seasonal changes over a 12‐month period in the areal photosynthetic rates ranged from a 3‐fold variation in Oloidien and Crescent Island Crater to a 1.5‐fold variation in Naivasha. In Winam Gulf over a 5‐mon

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01539.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.A study of the vertical distribution of benthic macro‐invertebrates in the upper Wye, Wales, using basket samplers, indicated no difference between the number of organisms collected, at one sampling time, after 28, 61 and 93 days. However, densities in samples collected after periods greater than 370 days were generally lower than might have been expected. Overall, 59.4%, 22.6% and 18.0% of the benthic invertebrates were recorded in the top (0–11 cm), middle (12–22 cm) and bottom (23–33 cm) levels of the basket samplers. Some organisms were generally confined to the top level (e.g. Ephemeroptera, Simuliidae, Mollusca), others were more evenly distributed (e.g. Oligochaeta, Chironomidae) and some increased with depth at certain times (Sericostoma personatum). Except for organisms confined to the upper layer it was not possible to predict with any certainty the vertical distribution of most organisms within the substratum. The community structure and abundance of invertebrates in the basket samplers differed from collections obtained with a conventional surface

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01540.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SUMMARY.A pigment ratio representing the ratio of carotenoid pigments to chlorophyll‐awas calculated by dividing the optical density at 480 nm by that at 664 nm for a 90% acetone extract of phytoplankton. Its seasonal variation in three Norfolk broads was examined and, except for nitrogen‐fixing species, it was found to vary independently of the algal species composition.A good inverse correlation with the particulate nitrogen to carbon ratio was found. The seasonal variation in the pigment ratio was considerably affected by measurable lake concentrations of inorganic nitrogen supplied from ttie catchment. Other sources of nitrogen such as nitrogen fixation and release from the sediment were also indicated by changes in the ratio.By comparison with the distinctions of extreme, moderate and no nitrogen deficiency drawn by Healey (1975) for the nitrogen/carbon ratio, values for the pigment ratio of2.4 were found to indicate no, moderate and extreme nitrogen deficiency respectively in the phytoplankton. The relation ship is attributed to the measurement of secondary carotenoids in response to nitrogen defic

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1979.tb01541.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY