The distribution of Heterotrissocladius oliveri Saether (Diptera: Chironomidae) in Lake Michigan

Fifty one chironomid species were identified from 504 samples collected at depths ranging 8 to 267 m in Lake Michigan, U.S.A. Heterotrissocladius oliveri Saether occurred in 32% of these samples and had an average abundance of 22 m^–2 which was similar to other estimates from the Great Lakes. Maximum average lake-wide density was at 30 to 60 m (41 m^–2). At depths 60 m, H. oliveri was the dominant chironomid species comprising 75% of total Chironomidae. The substrate preference of H. oliveri differed within each depth regime considered: at 30–60 m, 2–3 ; at 60–120 m, 3–5 , 7–9 ; and at 120–180 m, 6–8 . Abundance was notably reduced at all depths in substrates characterized as medium silt (5–6 ). On a lake-wide basis, the distribution pattern suggested H. oliveri was most numerous from 30 to 60 m along the southwestern, eastern, and northern shorelines and at 60–120 m depths along the southern and eastern shorelines. Increased abundance in the South Basin was concurrent with evidence of increased sedimentation at 60 to 100 m. However, in several other areas of the lake, high densities were associated with medium to very fine sands relatively free of silts and clays. This observation suggested occurrence of H. oliveri was minimally affected by sediment type.Widely variable, but generally elevated water temperatures likely prevent H. oliveri from establishing a substantial population density at depths < 30 m. With increased depth, temperature fluctuation is negligible and food is more stable, though the source is variable. Factors limiting abundance of H. oliveri at depths 30 m were related to decreased food supply due to distance from shore, food sources of lower value (clays), and, most importantly, to reproductive replenishment.Although still oligotrophic in nature, high density occurrences in both high and low sedimentation areas of the lake suggest the trophic indicator status of H. oliveri might be broader than previously thought.     

Emergence patterns of three species of Caenis Stephens (Ephemeroptera: Caenidae)

Distribution of the watermould Achlya americana in Jabalpur, India, was investigated. The influence of temperature, pH, BOD, CO₂ and pollution is discussed.     

Ecology of a cyanobacterial mat community in a Korean thermal wastewater stream

Cyanobacterial mats along a small stream receiving thermal wastewater from an artificial hot spring in the mid-upper part of the Mankyeong River system, Korea, were studied during the winter of 1995-1996. In the cyanobacterium, Oscillatoria terebriformiscomprised >95% of total biomass. Ash-free dry-weight (AFDW) and chlorophyll a in the cyanobacterial mats decreased significantly (r²= 0.78 and 0.83, respectively) with distance downstream from the thermal water outlet, while primary productivity increased slightly. The concentrations of the majority of ions sharply decreased with distance downstream, although they were not markedly related with spatial changes in AFDW, Chl a and primary productivity. O. terebriformis appeared to have a tremendous potential in wastewater treatment because of its marked ability to glean ions.     

Observations on the biology of nymphs of Povilla Adusta Navas (Ephemeroptera: Polymitarchidae) in Lake Kainji,Nigeria

Observations onPovilla adusta Navas nymphs in Lake Kainji revealed that seasonal fluctuations in abundance were due to a shortage of food during the period of rising lake level rather than a depletion of oxygen in the water column; this shortage was caused by the increased turbidity of the flood waters restricting the growth of both planktonic and periphytic algae. Planktonic algae apparently formed the diet of nymphs <4–6 mm and also of larger nymphs if their preferred diet of periphytic algae was in short supply. Both depth distribution and individual size of the nymphs were closely related to the distribution of periphytic algae. Depth distribution patterns of the nymphs revealed a peak between 2–4 m below the surface.The dimensions of the nymphs and the duration of the aquatic stages (3–4 months) in Lake Kainji correspond closely with results obtained elsewhere as does the mean percentage of males in the population (28%±10%). Seasonal fluctuations in the sex ratio were apparently caused by variations in the intensity of predation.Department of Zoology, University of Reading     

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.     

Mayfly fauna (Ephemeroptera) and the biology of the species Potamanthus luteus (L.) in a warmed stretch of the Oslava River

Cooling waters of the Oslavany power station show a depressive effect on the species diversity of mayfly nymphs. Only seven of 35 taxons found in the study area occurred in all localities. In the warmed stretch of the river, the abundance and biomass of mayfly nymphs as well as the production of the most important speciesPotamanthus luteus decreased; a gradual regeneration of the disturbed mayfly population could be observed downstream. In Locality 5, situated 3.5 km downstream from the mouth of cooling waters, the species diversity, abundance, and biomass of mayflies were 69, 30, and 66 per cent, resp., of values found in Locality 1 with natural temperatures; the production ofPotamanthus luteus was 70 per cent of that found in Locality 1.     

Ecology of aquatic Lepidoptera (Crambidae: Nymphulinae) in South Carolina, USA

An ecological study was conducted in May and June of 1995 and 1996 in South Carolina to determine the factors associated with distributions of aquatic Lepidoptera (Crambidae: Nymphulinae). Larvae were found at 65 lotic and lentic sites in three ecoregions (Piedmont, Sandhills, Coastal Plain). Nine species of aquatic Lepidoptera were collected from 12 species of aquatic vascular macrophytes. One to six plant species were used as hosts, depending on the species of lepidopteran; however, the number of host plants used by a lepidopteran was significantly correlated with the lepidopteran's frequency of occurrence. Significant habitat associations were found for five species. Langessa nomophilalis (Dyar) was found under the widest range of temperature and width and occurred in both lotic and lentic habitats. Munroessa icciusalis (Walker) was found in lotic and lentic habitats and had the widest range of recorded depths. Parapoynx maculalis (Clemens) occurred at stream sites with lentic-like conditions. Parapoynx obscuralis (Grote) occupied the widest range of pH and was restricted to lotic habitats, and P. seminealis (Walker) was found in both lotic and lentic habitats. Additional species, collected at fewer than 8% of sites, included M. gyralis, P. allionealis, Synclita obliteralis, and S. tinealis. Overall, the distributions of aquatic Lepidoptera in South Carolina were nonrandom and predictable on the basis of habitat characteristics. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

The microdistribution of mayflies (Ephemeroptera) in myriophyllum beds in Pennington Creek,Johnston County,Oklahoma

I studied the population densities and the microdistributions of the four most abundant mayfly (Ephemeroptera) nymphs in Myriophyllum heterophyllum beds in Pennington Creek, Johnston County, Oklahoma, from May to December, 1977. The section of the stream studied has relatively constant flow rates and temperatures throughout the year due to continuous inflow from groundwater. This uniform physical environment allows the plant beds to grow throughout the year and provide a permanent habitat. The four mayflies are Tricorythodes fictus (Tricorythidae), Caenis delicata (Caenidae), Baetis favistriga and B. quilleri (Baetidae). All four species are of similar size and feed by scraping periphyton from the surface of the Myriophyllum. T. fictus and the two species of Baetis have overlapping microdistributions in the leafy, upper one-half of the plant bed. T. fictus and C. delicata have overlapping microdistributions in the lower portion of the plant bed and roots. Each species has similar population densities where their distributions overlap. There is no significant selection for position with respect to current flow in the Myriophyllum for any of the species. Food and space are always abundant, especially in the top one-half of the Myriophyllum. There are no major changes in these trends over the year.     

Ecology of rhesus macaques (Macaca mulatta) in northwest Pakistan

The feeding ecology of rhesus monkeys,Macaca mulatta, was studied between 1978 and 1981. The study site, located in the Murree Hills of northwestern Pakistan, supported a mixed coniferous-deciduous forest community and was characterized by a high degree of human disturbance. We used a linear transect method to sample the species composition and structure of the vegetation. Comparison of these data with historical records showed that the forest has undergone major changes in the last hundred years. Data on feeding behavior were collected through on-the-minute focal animal sampling. The monkeys spent about 45% of the day feeding. Their preferred foods were grass, clover, and other ground herbs that occur in the disturbed sites. Fruit accounted for less than 9% of feeding records. The rhesus monkey may be pre-adapted to living in disturbed-site, forest-edge communities. The evolutionary history of Macaca mulatta may be tied closely to the disappearance of forest and the spread of meadows and savannahs over the last million years.     

A New Ichnospecies of Arthrophycus from the Late Carboniferous (Pennsylvanian) of Michigan,USA

A unique ichnofossil assemblage from Pennsylvanian-age sandstones near Eaton Rapids, Michigan, USA, comprises straight-to-curved traces preserved in convex hyporelief, with the transverse ridges and median grove associated with the ichnogenus Arthrophycus. The Michigan traces show some branching or pseudo-branching (also known from other Arthrophycus specimens) and are among the smallest structures (millimeters in diameter) attributed to this ichnogenus. The orientation of the Michigan Arthrophycus burrows is distinct from other ichnospecies of this taxon in the pronounced co-planar alignment of the burrows, as opposed to the multiplanar, interweaving, “bundled” nature typical of the ichnogenus. On this basis we assign the Michigan specimens to a new ichnospecies of Arthrophycus. The “paralleling behavior” of the new taxon may reflect a strategy of the tracemaker to avoid previous burrows and reflect differences in resource availability or current energy. This new taxon supports previous records of the occurrence of this ichnogenus in Upper Carboniferous strata.     

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.     

In situ predatory behavior ofMysis relicta in Lake Michigan

Selectivity coefficients (W) and predation rates on Lake Michigan zooplankton were determined forMysis relicta during spring through fall using anin situ method. W values indicated the following ranked order of prey preference: Cladocera > copepod copepodites and copepod nauplii > adult diaptomids and cyclopoids. With few exceptions, W values for different prey categories remained fairly constant despite greatly changing relative abundances of prey. Predation rates and prey selectivity were similar in most cases to those determined in laboratory studies. Ingestion rates (percent dry body weight · day^–1) were correlated to total prey biomass (r = 0.38) and to effective prey biomass (r = 0.85), where the weighting factors were overall mean selectivity coefficients for the different prey categories. This result suggested that seasonally varying composition of prey caused much of the variation in ingestion rates among experiments. Feeding trials performed at the same depth with daytime and nighttime assemblages of zooplankton indicated that Cladocera may escape heavyMysis predation at night by migrating from the metalimnetic-hypolimnetic interface into the epilimnion.Contribution 333 from the Great Lakes Research Division, The University of Michigan and contribution 287 from the Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration.Contribution 333 from the Great Lakes Research Division, The University of Michigan and contribution 287 from the Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration.     

Habitat characterization of the morphologically similar mayfly larvae,Caenis and Tricorythodes (Ephemeroptera)

The larvae of Caenis (Caenidae) and Tricorythodes (Tricorythidae), once considered to be confamilial, have notable morphological and behavioural similarities. Univariate and multivariate (discriminant analysis) techniques were used to determine which environmental variables best characterized the larval habitats of Caenis and Tricorythodes at 40 sample sites on 29 rivers within the Interior Plains of Alberta, Canada. River width, depth and substrate type distinguished riverine habitats of the two genera. Larvae of Tricorythodes occurred in wide rivers of varying depths that possessed coarse substrates. Although larvae of Caenis occurred in a variety of habitats, they were found more frequently on stable substrates in narrow, deep rivers.     

Reproductive ecology and growth of a population of brown trout (Salmo trutta L.) in an aquifer-fed stream of Old Castile (Spain)

In the River Lobos-Ucero and its tributary the River Avión-Milanos (Duero basin, Old Castile, Central Spain), two limestone streams fed by aquifers, the population of brown trout, as compared with the populations of other European streams, shows a high growth rate, high condition coefficients, short life-span and early age at first maturity. Gonad cycle was also studied. Size distributions of unshed eggs exhibit a dynamic activity with a bi-modal distribution from June onwards, spawning occurred in the last days of November. Fecundity (F) can be predicted from trout length (L, mm) according to the equation: F= –646.47+5.6167 · L. Numbers and standing crop of trout range from 18 to 3903 ind. ha^–1 and 3.6 to 452.9 Kg ha^–1, reaching higher values in the sites close to the aquifers. Egg production had values of 22.4 and 18.0 eggs m^–2 in the Rivers Ucero and Avión-Milanos respectively. Some factors suggested as regulators of these demographical characteristics are discussed in the light of recent literature.     

Borrelia, Coxiella, and Rickettsia in Carios capensis (Acari: Argasidae) from a brown pelican (Pelecanus occidentalis) rookery in South Carolina, USA

Argasid ticks are vectors of viral and bacterial agents of humans and animals. Carios capensis, a tick of seabirds, infests the nests of brown pelicans, Pelecanus occidentalis, and other ground nesting birds along the coast of South Carolina. This tick is associated with pelican nest abandonment and could pose a threat to humans visiting pelican rookeries if visitors are exposed to ticks harboring infectious agents. We collected ticks from a pelican rookery on Deveaux Bank, South Carolina and screened 64 individual ticks, six pools of larvae, and an egg mass for DNA from Bartonella, Borrelia, Coxiella, and Rickettsia by polymerase chain reaction amplification and sequencing. Ticks harbored DNA from “Borrelia lonestari”, a novel Coxiella sp., and three species of Rickettsia, including Rickettsia felis and two undescribed Rickettsia spp. DNA from the Coxiella and two undescribed Rickettsia were detected in unfed larvae that emerged in the laboratory, which implies these agents are transmitted vertically by female ticks. We partially characterize the novel Coxiella by molecular means.     

The influence of diet on the growth of Stenonema vicarium (Walker) (Ephemeroptera: Heptageniidae)

Laboratory studies compared the growth rate of Stenonema vicarium (Walker) nymphs on diets of detritus and natural stream periphyton. In three consecutive runs of the experiment, growth rates were consistently higher on periphyton (mean growth rate = 2.1% wet wt. d⁻¹) than detritus (mean = 1.8% wet wt. d⁻¹). The starting date of each run also significantly influenced growth rates. In each treatment growth rates generally decreased over the course of the 3 runs, and ca. one-half of the nymphs in the last run did not molt or grow. It appeared that growth of S. vicarium may be partially controlled by seasonal factors.     

Keratella cochlearis (Gosse) in Africa

Keratella cochlearis occurs over the complete latitudinal range of Africa, and over a considerable altitudinal range, but not in the highest mountain tarns. Physical, chemical, and biological factors may affect the distribution of this species. Lack of suitable food, and competition or predation by larger zooplankters are probably important limiting factors. Morphometric variation in samples from Zimbabwe is much less than in samples from the Auvergne. In particular, posterior spine length shows a much lower relative growth in relation to lorica size.     

Ocellar fine structure inCaenis robusta (Ephemeroptera), Trichostegia minor,Agrypnia varia,andLimnephilus flavicornis (Trichoptera)

Summary Three dorsal ocelli are present inCaenis robusta (Ephemeroptera), Trichostegia minor, Agrypnia varia, andLimnephilus flavicornis (Trichoptera). The dioptric apparatus of the ocelli differs between the four species. InTrichostegia andAgrypnia a biconvex corneal lens is present, inLimnephilus the corneal lens is convexo-concave complemented by an underlying haemocoelic space, whereas a cellular vitreous body is found between the cuticle and the retinal layer in the ephemerid. In the three trichopteroid species the ocelli are surrounded by an array of longitudinally arranged tracheoles; inCaenis a layer of screening pigments is found in this position. In this species the rhabdoms formed by microvilli of neighbouring retinula cells have a randomly arranged meshwork pattern; in the three trichopteroid species the rhabdoms are isolated, built up of four retinula cells. Cells with basally situated nuclei and lamellar extensions between the retinular cells are found in the ocelli ofTrichostegia, Agrypnia, andLimnephilus.     

Decline in zoobenthos densities in the profundal sediments of Lake Mendota (Wisconsin,USA)

High densities of zoobenthos inhabited Lake Mendota's profundal zone in the early 1900s through the mid-1940s. Chaoborus punctipennis was the most abundant organism during the winter, along with moderate densities of Chironomus spp., Pisidium sp., oligochaetes, and Procladius sp. By the early 1950s, Chaoborus punctipennis densities had declined to 10% of former levels, while Chironomus increased significantly. However, by the mid-1960s, Chaoborus, Chironomus, and Pisidium densities had decreased to very low population levels. By 1987–89, Pisidium was no longer found. Zoobenthos that had not decreased from earlier surveys were oligochaetes and Procladius, although further sampling of oligochaetes is needed to confirm current densities. These organisms are the most tolerant of severe anoxia.Four possible reasons for this decline were evaluated: (a) decline in food availability, (b) increase in fish predation, (c) use of toxic insecticides in the drainage basin, and (d) changes in the profundal sediment environment. Based on literature information and long-term data for Lake Mendota, a change in the profundal sediment environment is the most likely explanation for the decline in the less-tolerant zoobenthos species. Although the duration and extent of anoxia in the hypolimnion have not changed since the early 1900s, hypolimnetic ammonia and hydrogen sulfide concentrations apparently have increased as Mendota became more eutrophic after the mid-1940s. However, further study is needed to determine if these higher concentrations or other factors were responsible for the dramatic decline in lake Mendota's profundal zoobenthos.