A comparative study of colonization by benthos in a lake and its outflowing stream

1. The patterns of colonization of littoral benthos onto hard substrata on an exposed and a sheltered shore of Lake Purrumbete in Victoria, Australia, and the riffles of its outflow stream (Curdies River) were examined experimentally in winter and summer. The common taxa in the lake (gastropods, amphipods, isopods, planarians, ostracods) also occurred in the stream, although they were not abundant. The stream fauna was dominated by insects. 2. Defaunated half-bricks were sampled at each of three sites at the three different locations (exposed shore, sheltered shore, stream) in winter and summer at weekly or biweekly intervals, with natural stones also being sampled during the colonization period. Colonization patterns of individual taxa which occurred in both the lake and stream, and stream-only taxa, were compared using ANOVA, and the changes in the assemblage through time and between locations were analysed with non-metric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM). 3. Colonization in the lake was very rapid, with species richness and assemblage composition on bricks after just one day matching that of natural stones. Colonization in the stream was slower, the assemblage composition not matching natural stones after 42 days in winter but being comparable after 28 days in summer. There was considerable species turnover during colonization in the stream, but little turnover in the lake, with most common taxa back after one day. There was little difference between the two lake shores in colonization patterns. 4. Taxa that occurred in both lake and stream showed broadly similar patterns of colonization, with early occupancy at high densities. In contrast, stream insects showed a variety of colonization strategies. 5. These results indicate that rates and patterns of colonization on to hard substrata are quite different in Lake Purrumbete compared with its outflowing stream. The rapid colonization in this lake indicates great mobility for much of the fauna on hard substrata, possibly by swimming, benthic crawling or passive drift (even attached to floating vegetation). This may be an appropriate strategy in lake littoral zones where the amount of inhabitable hard substrata and accompanying food resources may be limited.     

The benthos of a natural West African lake, with emphasis on the diel migrations and lunar and seasonal periodicities of the Chaoborus populations (Diptera, Chaoboridae)

SUMMARY. 1. Three Chaoborus species dominated in abundance and biomass the mid-lake benthic fauna of a small, natural Nigerian lake. Each population showed distinct seasonal varialitions. C. anomalus being most abundant during the early rainy season, while ( ceratopogones and C edults were most abundant during the dry season. A fourth species. C. fuscinervis (not reported previously from West Africa), was collected only in the adult stage. Also abundant at mid-lake were the Chironomidae. Chironomus seydeli, Prodadius brevipetiolatus and Tanypus brevipalpis. all of which showed a seasonal pattern most resembling that of C. anomalus .
2. Second. third and fourth instar larvae and pupae of the Clutoborus species underwent a diel vertical migration between the lake sediments (diurnal) and the water column (nocturnal) which was strongly related to prevailing light conditions.
3. Lunar periodicities of Chaoborus emergence determined from emergence trap collections are described for the first time. Corresponding lunar periodicities of larval abundance were observed in two of the species. The statistical techniques employed in describing the lunar periodicities permit the estimahon of generation times.
4. C. anomalus is believed to be parthenogenetie in the study lake (no males collected). while the other Chaoborus species are bisexual (1:1 sex ratios). The biology of this species is discussed in relation to the parthenogenetie condition.     

The invertebrate fauna of the streams in Øvre Heimdalen

The lotic communities in Øvre Heimdalen were completely dominated by insects. The species distribution of stoneflies (Plecoptera), mayflies (Ephemeroptera) and caddisflies (Trichoptera) is given together with autecological notes on the Plecoptera and certain other major species. The species distribution of these groups, especially the Plecoptera, was clearly related to the deciduous vegetation along the streams. There was a reduction in species parallel to a reduction in Salix vegetation.
The main inlet stream to the lake, Øvre Heimdalsvatn, the outlet and the outlet stream had different faunal compositions. The inlet fauna consisted to a large extent of winter growing species, mainly detritus feeders, while the outlet and outlet stream had a fauna dominated by summer growing species, several of which were filter feeders.     

A comparative study on planktonic ciliates in two shallow mesotrophic lakes (China): species composition, distribution and quantitative importance

The species richness and seasonal development of planktonic ciliates were studied and compared in two shallow mesotrophic lakes, one covered with dense submerged macrophytes, the other macrophyte poor. Considerable differences in ciliate species composition, dominant taxa, abundance and biomass were observed. Ciliates were much more species rich in the macrophyte-rich lake, while they were more abundant numerically in the macrophyte-poor lake. Altogether, 96 species, included in 53 genera, 14 orders were identified. Among them, 80 species (included in 45 genera, 14 orders) observed from the macrophyte-rich lake, against 49 species (36 genera, 12 orders) were from the macrophyte-poor lake. In the macrophyte-rich lake, the mean abundance and biomass were 13.5 cells ml^-1 and 547.10 g l^-1 f.w.; abundance and biomass were higher in spring and winter; naked oligotrichs dominated total ciliate abundance and Peritrichida dominated the biomass. In the macrophyte-poor lake, ciliate mean abundance and biomass were 35.5 cells ml^-1 and 953.39 g l^-1 f.w.; abundances peaked in autumn; Scuticociliates dominated the abundance and Tintinnids dominated the biomass. Possible causes for the observed differences are discussed.     

Spatial and temporal patterns in the fish assemblages of individual pools in a midwestern stream (U.S.A.)

Synopsis The composition and consistency of fish assemblages in 14 adjacent pools (6–120 m long) of a clear-water, limestone and gravel creek in midwestern U.S.A. were quantified in eight snorkeling surveys over 19 months, to establish a baseline of natural variation in the system at this scale. The fauna of the stream was dominated numerically by minnows (Cyprinidae), sunfish and black bass (Centrarchidae), and topminnows (Fundulidae). The pool fish fauna of the total 1 km reach (including all 14 pools) was highly consistent throughout the study, despite two major floods. Assemblages in individual pools generally were consistent, but there was more variation within pools than at the scale of the entire reach. Throughout the study, most individual pools remained within discrete subsets of the total occupied multivariate space in a principal components analysis based on fish species abundances. Sunfishes (Lepomis spp.) and bass (Micropterus spp.) were more consistent in their distribution among pools than were minnows (Cyprinidae) or a topminnow (Fundulus). There were 25 significant correlations in occurrence of species pairs among stream pools, out of 91 possible comparisons of the 14 most abundant taxa in the reach. Many pools contained assemblages either dominated by large centrarchids or by abundant cyprinids and juvenile centrarchids, but intermediate assemblages also were observed. The dynamics of distribution of fish species and fish assemblages among individual stream pools are likely influenced by a combination of species-specific behaviors and habitat selection, predator constraints on use of individual pools by small fishes, riffles as size-selective barriers to fish movements between pools, dispersal of young-of-the-year fishes, and abiotic phenomena like floods. Individual stream pools appear to be discrete habitat units for fishes, and do represent an appropriate scale for biologically meaningful studies of fish assemblages or their effects on streams.Department of Zoology, University of Oklahoma     

Studies on the tributaries of Char Lake,Cornwallis Island,Canada

As part of studies on the production of arctic Char Lake in Cornwallis Island, the inflow of organic matter carried annually by tributaries into the lake, was investigated. In late June tremendous avalanches of snow, stones and slush make accurate measurements impossible, but afterwards drift could be estimated with nets, and benthic samples were gathered with scoops. Published data on erosion of similar streams were used to estimate the quantity of organic matter carried into the lake during the spring spate. About 600 kg of organic matter passes down stream from the watershed. The passage of organic matter during the brief season of free water provides the chief source of food for the limited benthic fauna, dominated by Chironomidae-Diamesa and Orthocladinae- and Enchytraeidae. The flora is dominated by diatoms. The biomass of the fauna of those parts of the stream investigated, amounted to 2.54 g/m². Some ecological features of animals living in running water in this extreme habitat were studied.Contribution No. 253 from the CCIBP (Char Lake Project No. 22)Contribution No. 253 from the CCIBP (Char Lake Project No. 22)     

Filters and templates: stonefly (Plecoptera) richness in Ouachita Mountains streams, U.S.A.

1.  We collected adult stoneflies periodically over a 1-year period at 38 sites in two headwater catchments in the Ouachita Mountains, Arkansas, U.S.A. The 43 species collected were a subset of the Ozark-Ouachita fauna and the much larger fauna of the eastern U.S.A. We estimated 78–91% species coverage in the two catchments using jackknife extrapolation of species richness from our survey.
2.  Many streams, especially small ones, lacked surface water for months, but others, both small and large, flowed permanently.
3.  Using published regional presence–absence and coarse ecological data in a discriminant function analysis (DFA), we identified stream size (negative) and regional frequency of occurrence (positive) as predictors of presence in these headwater catchments. For the combined catchments, the extrapolated richness (51 spp.) was similar to an estimate (48 spp.) based on predicted absences from DFA and the Ouachita provincial total of known stonefly species (57 spp.).
4.  Local species richness (1–27 spp. per site) was correlated strongly with stream size (catchment area) but was independent of stream drying. Generic richness was correlated negatively with stream drying and positively, but less strongly, with stream size.
5.  Regionally endemic stoneflies dominated in drying streams, and widely distributed species dominated in more permanent streams. The composition of stonefly assemblages was associated with regional factors (species pools, regional abundance, evolution of tolerant endemic species, regional climate) and local factors (drying, stream size).     

Colonization of artificial substrata by macro-invertebrates in a stream and variations according to stone size

SUMMARY. Plastic cages containing artificial substrata were placed on the stony bottom of a stream in a section where the environmental conditions appeared to be homogeneous. The section was divided into eight equal sub-sections (A-H) and four cages were placed in each sub-section. The stone-size of the artificial substrata was similar within each cage but differed between the four cages with average diameters of 14, 24, 48 and 96 mm, respectively. The baskets were removed one month later and the catches of macro-invertebrates were recorded.
Analysis of the catches (density and number of taxa in each cage) revealed no significant differences in connection with the position of the cages in the section of stream. Cages with 48-mm stones contained the least abundant fauna. The taxa which colonized cages with 14- or 24-mrn stones were more numerous than those collected from cages with 48- or 96-mm stones.
Statistical analysis by laxon confirmed the preceding results. Variability in connection with the position of the cages along the section of stream was never significant. A little more than half the taxa were distributed independently of stone size but always showed a contagious type distribution. The density of the other taxa was higher, either in cages with 14- or 24-mm stones (particularly Gammarus ) or only in cages with 96-mm stones (especially Hydropsyche ). Only one taxon was more abundant in cages with 48-mm stones, the type of substratum in which the overall density was lowest.
Catches in the cages were not the same as those taken with a Surber sampler because the two samplers did not take samples from the same habitats and also because the baskets offered a more specialized habitat than the surrounding bottom. The basket with 24-mm stones gave the least distorted picture of the natural population.     

The effect of diapause emergence on the seasonal dynamics of a zooplankton assemblage

1. The role of seasonal phenology in the emergence of zooplankton from diapause in patterns of seasonal abundance in the water column was investigated in Oneida Lake, New York. Replicate emergence traps, placed in contact with the lake sediments at two locations (one at a shallow site and one at a deep site), were monitored between May and August.
2. Although six rotifer taxa showed a clear seasonal succession in the water column throughout the study period, all but one taxon emerged exclusively in spring. Three cladoceran and three calanoid copepod species, also present in the water column throughout the study period, again showed predominantly spring emergence. In contrast, three cyclopoid copepod species had distinct seasonal periods of emergence that corresponded, at least in part, to the timing of abundance peaks in the plankton.
3. These results for a single lake are largely consistent with patterns observed or inferred by other investigators for other lakes: variable dependence of abundance in the plankton on diapause emergence for species with long-lived diapausing eggs (i.e. rotifers, cladocerans and calanoid copepods), and much closer dependence for species with short-lived diapausing immature stages (i.e. cyclopoid copepods).     

The macroinvertebrate fauna of a New Zealand forest stream

Abstract

The distribution, abundance, and life histories of benthic invertebrates were investigated in a small, Nothofagus forest stream in North Canterbury, South Island, New Zealand. The fauna was dominated by Trichoptera and Plecoptera; Mollusca and fish were absent. Large particle detritivores and scrapers were the predominant functional groups found. Larval Philopotamidae (Trichoptera) were the only abundant filter feeders. Nymphs of the stonefly Spaniocerca zelandica and of mayflies, Deleatidium spp., were the most abundant animals on plant detritus; Deleatidium spp. were abundant on stones also. The distribution of invertebrates in riffles, loose stones, pools, and plunge pools was examined using mesh colonisation trays lifted in September, November, February, and May after respectively 88, 69, 98, and 94 days in situ. Most species were widely distributed, and sample densities of the more abundant insect species showed weak positive correlations with the biomass of detritus present in trays in most months. The turbellarian Neppia montana was overrepresented in trays compared with stream samples, but the relative abundance of most other species appeared to be similar to that on the stream bed. A large amount of silt accumulated in trays during a heavy flood, and was colonised mainly by the oligochaete Eiseniella tetraedra. Information on the life histories of 15 species of Plecoptera, Trichoptera, Ephemeroptera, and Coleoptera was obtained from a 1-year monthly sampling programme, in which 36 taxa were distinguished, and from collections of adult insects made over a 3–4-year period. Most species had poorly synchronised life histories, in that a wide size range was apparent among individuals in most months. Eight species emerged in at least 4 months; S. zelandica and the philopotamid Hydrobiosella stenocerca were taken in 8 and 9 months respectively.     

Diversity and seasonality of adult Trichoptera captured in a light-trap at Yuccabine Creek,a tropical Australian rainforest stream

Seventeen light-trap samples were taken over a 20 month period at Yuccabine Creek, an upland rainforest stream in north-eastern Queensland. Seventy-eight species of Trichoptera were recorded from a total catch of 6431 individuals. The fauna was dominated by the Hydroptilidae (25 species and 5131 individuals) and, though composed primarily of Torresian genera, some Bassian elements were recorded. A seasonal pattern of change of abundance was observed with the majority of tax a exhibiting maxima between December and January (summer) and minima between July and September (winter).     

Ecological studies on crater lakes in West Cameroon. Debundsha Lake

Cape Debundsha receives 10 m (400 inches) of rain per year, and the water of the small crater lake on the cape has one of the lowest conductivities in Africa (11–13 µmho/cm/20 C). The lake has a maximum depth of 13·5 m. At the time of our visit in April 1972 the lake was stratified with a depletion of oxygen in the hypolimnion. The phytoplankton was dominated by Botryococcus , and the zooplankton was dominated by the ostracod Oncocypris debundshae. Both these organisms are closely associated with the surface film. Other zooplankters included Thermocyclops hyalitws , and in deeper water during the daytime the larvae of Chaoborus ceratopogones.
The fauna of the lake includes 12 species of testacean rhizopods, six species of rotifers, two oligochaetes, one snail, seven crustaceans, 15 insects and three acarines. Of the last group two species were new to science and one had been found only once previously. The ectoproct polyzoan, Lophopodella carteri , is recorded for the first time from West Africa, and the second time from Africa. The general impression of the fauna is one of sparseness, with an unusually high proportion of larval Odonata.     

Food borne parasites as indicators of trophic segregation between Arctic charr and brown trout

The habitat and diet choice and the infection (prevalence and abundance) of trophically transmitted parasites were compared in Arctic charr and brown trout living sympatrically in two lakes in northern Norway. Arctic charr were found in all main lake habitats, whereas the brown trout were almost exclusively found in the littoral zone. In both lakes the parasite fauna reflected the niche segregation between trout and charr. Surface insects were most common in the diet of trout, but transmit few parasites, and accordingly the brown trout had a relatively low diversity and abundance of parasites. Parasites transmitted by benthic prey such as Gammarus and insect larva, were common in both salmonid host species. Copepod transmitted parasites were much more common in Arctic charr, as brown trout did not include zooplankton in their diets. Parasite species that may use small fish as transport hosts, were far more abundant in piscivorous fish, especially brown trout. The seasonal dynamics in parasite infection were also consistent with the developments in the diet throughout the year. The study demonstrates that the structure of parasite communities of charr and the trout is highly dependent on shifts in habitat and diet of their hosts both on an annual base and through the ontogeny, in addition to the observed niche segregation between the two salmonid species.     

Patches of barnacles and ascidians in soft bottoms: Associated motile fauna in relation to the surrounding assemblage

Epibenthic patches dominated by barnacles Balanus crenatus Bruguiere and solitary ascidians Styela spp., Bolthenia echinata (L.) and Molgula spp. in the White Sea shallow subtidal develop on bivalve shells and small stones surrounded with muddy sand. The space between barnacles and ascidians is filled with muddy sediment inhabited by motile taxa. We hypothesized that (i) epibenthic patches and unstructured sediment would attract different motile fauna and (ii) motile fauna of the patches would be affected by local abundances of epibenthic foundation species. Most dominant motile species demonstrated a significant difference in abundance between the two microhabitats. In contrast to the fauna of the sediment, species composition observed in aggregations of barnacles and ascidians was stable across different locations. In the field experiment initially clear bivalve shells after 5 years of exposure developed barnacle clusters with motile fauna similar to that observed in natural aggregations. Amphipods, isopods and bivalves, capitellid polychaets, Cirratulus cirratus (Müller) and Pholoe minuta Fabricius (Polychaeta) dominated in the sediment inside epibenthic patches. The proportion of capitellids, known to be sensitive to organic enrichment, was much higher within the patches than outside. The abundances of motile taxa found in aggregations were mostly determined by the number of barnacles of different size and of their empty shells, the biomass of ascidians, and the effect of location. Different dominant species demonstrated sensitivity to different parameters.Physical structure of the habitat, provided by barnacles and ascidians, as well as their biodeposition activity are regarded as the main factors structuring the motile fauna in the community studied. The spatial pattern observed seems to imply a range of pattern-generating biogenic processes, similar to those previously revealed in patches of filter-feeding bivalves, tube-building worms and seagrass.     

Arthropod fauna of jarrah (Eucalyptus marginata) foliage in Mediterranean forest of Western Australia: Spatial and temporal variation in abundance,biomass, guild structure and species composition

Abstract A 2 year study (using a branch-clipping technique) of the arthropod fauna of jarrah crowns (14 m above ground level) in a 7500km² area centred on Manjimup, Western Australia, yielded 7461 individuals belonging to 396 species. Lepidoptera, Hemiptera and Araneae dominated the fauna in abundance and biomass but Lepidoptera less so in number of species. Consequently, leaf chewers, sapsuckers and predators were the dominant guilds. Most species showed great spatial and temporal variation in their occurrence, with some 73% being recorded on only one or two of the nine sampling occasions. In addition 77% of species were recorded on four or fewer of the 45 trees sampled. Crowns of these trees tended to have highly dissimilar assemblages of arthropods. Dissimilarity between trees was not predictable from the distance between them. Total species richness was greatest in samples collected in summer. Predators and sapsuckers tended to be the most speciose guilds. Within-stand differences were much less pronounced than between-stand differences: ants were more abundant on jarrah foliage within 2 m of ground level and the pest defoliator Uraba lugens (Lepidoptera, Noc-tuidae) was more abundant on foliage of jarrah pole crowns 14 m above ground. The most abundant arthropod, U. lugens, did not reduce appreciably the biomass or abundance of other arthropod groups present in jarrah pole crowns. This is consistent with the paradigm that competition between species of herbivorous insects is infrequent. After comparison with other studies in jarrah forest, we tentatively conclude that there is no single fixed pattern of organization or predictable assemblage of invertebrates on jarrah foliage.     

Patterns in benthic food webs: a role for omnivorous crayfish?

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty-one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond. 2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance. 3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment-dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)). 4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte-associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish. 5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density. 6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.     

Effect of Seasonality on Distribution of Macroalgae in a Stream System （Xin＇an Spring）in Shanxi Province, North China

A survey of the seasonal distribution of macroalgae in a stream system in Shanxi Province, north China, was undertaken from July 2004 to April 2005. The relative abundance and percentage cover of macroalgae, and several environmental factors were monitored along a 20-m stretch at each of four sites, at intervals of approximately three months （one sampling per season）. Several stream conditions were relatively constant over the sampling period （pH, maximum width and maximum depth）, whereas others exhibited a distinct seasonal pattern （water temperature and specific conductance）, and some fluctuated with no discernable seasonal pattern （current velocity and dissolved oxygen）. Forty-two species of macroalgae were found, with a predominance of Chlorophyta （26 species, 61.9%）. Rhodophyts and Charophyta represented the smallest proportion （1 species each, 2.38%）. Six macroalgae species were the most widespread, occurring in all four sampling sites. Twelve species were found at only one site each. In terms of seasonality, eight species occurred throughout the year, whereas 16 species were found in only one season each. The macroalgal community at Xin＇an Spring was species rich relative to other streams. Species richness per sampling site was negatively correlated with pH. Principal component analysis revealed that no single variable had much influence on the macroalgal seasonal dynamics. We calculated Sorensen similarity indices to compare our study with other continent-wide surveys of stream macroalgae, but the similarity indices were all very low. This study also shows that macroalgae in different locations have significant reproductive isolation.     

Habitat structure and invertebrate assemblages on stream stones: A multivariate view from the riffle

Abstract Highly structured habitats, those with complex or heterogeneous physical structure, commonly contain more species than simply structured ones. However, tests of this relationship have been hampered by habitat-specific definitions and measurements of habitat structure and, in stream studies, by insufficient information on spatial variation in faunal abundances. We sampled the fauna of 90 stones collected from an order 4 section of the Taggerty and Steavenson Rivers, southeastern Australia. The spatially nested sampling design encompassed three spatial scales (sites within the same stream order, riffles at the same site and groups of stones within the same riffle) but no temporal replication, as we were only able to sample once. Habitat structure of stones was quantified by measuring the amount and type of epilithon on stones, together with stone shapes, sizes, textures and surface complexities. For the latter two attributes, we used a new method, involving image analysis, which can be used to quantify habitat structure in comparable ways in other systems. Species richness (S) was related to some measures of habitat structure, being higher on stones with a rough texture and weakly related to the amount of epilithon present. Total numbers of individuals (N) were also higher on rough stones, and faunal composition (as quantified by hybrid multidimensional scaling) was related to abundance of epilithon. However, flow environments, as quantified by water velocities and depths, were also related to faunal composition. Riffles varied in both faunal densities and near-bed flow environment, but not in any consistent way. Such variability means that individual riffles cannot be reasonably used to ‘represent’ stream sections or orders, an assumption commonly made in stream studies. Neglect of such issues has also resulted in poor conceptual integration between large- and small-scale studies in stream ecology.