Littoral benthos of a Victorian lake and its outlet stream: Spatial and temporal variation

Abstract There have been few comparative studies of the fauna in the two major types of freshwater systems, lakes and streams, in the one locality. This study compared the faunal assemblages at two times of the year (summer and winter) on stones in three locations: the littoral zone of two shores in Lake Purrumbete (one wave-exposed and one sheltered) and riffles in the Curdies River, which flows out of the lake. The lake fauna was dominated by crustaceans, gastropods and planarians, whereas the stream fauna was dominated by insects. The most abundant lake taxa were also present, but much less abundant, in the stream. The total number of species and individuals and densities of some common species varied between the three locations and between seasons. However, no consistent pattern reflecting a difference between the two lake shores was evident. Interpretation of MDS ordinations of the lake fauna was dependent on the data standardizations applied, with increased separation of the season-location combinations when species were standardized to equal total abundances; the seasonal difference was always greatest for the exposed (cliff) shore. In contrast, MDS on the stream fauna showed seasonal differences under all standardizations. This was consistent with the high seasonal turnover of species in the stream compared with the lake. These results demonstrate that, even within a local area with similar geology and connected water bodies, lake and stream fauna from the same substratum (stones) can be markedly different. Taxa that occurred in both were more abundant in the lake, whereas seasonal differences in abundance were much greater in the stream.     

Oligochaetes and water pollution in two deep Norwegian lakes

Analyses of the oligochaete fauna of two of the deepest lakes in Scandinavia — the Norwegian lakes Mjösa (450 m) and Tyrifjorden (295 m), revealed a totally different species composition in the deep profundal compared with the upper profundal - in contact with the nutrient-enriched epilimnion. In both lakes a pronounced thermal stratification develops in the summer, thus the epilimnion receiving gross organic pollution behaves differently from the profundal. The lakes are each effectively divided into two bodies of water with limited water exchange between them, i.e. one major oligotrophic body and one minor more nutrient-rich. Since the 1950s both lakes have been exposed to heavy pollution of various kinds. In Lake Mjösa in 1975 and 1976 unpleasant algal blooms of the blue-green alga Oscillatoria bornetii fa. tenuis occurred. Bottom samples obtained at the same time revealed that the deep central bottoms of the lake were totally dominated by oligotrophic oligochaete indicators, i.e. by Stylodrilus heringianus and Spirosperma ferox, while the fauna of the upper profundal in the vicinity of domestic and agricultural sewage outfalls, wood processing industries, etc. was dominated by Limnodrilus hoffmeisteri and Tubifex tubifex in great abundance, indicating enriched conditions. Several other species indicative of eutrophy, were absent, most of them belonging to the genus Potamothrix. A fairly similar situation exists in Lake Tyrifjorden, where, for instance, in the shallow bay of Steinsfjorden — heavily eutrophied by agricultural wastes — blooms of blue-green algae have caused problems from time to time. The same oligochaete communities as in Lake Mjösa distinguish the central oligotrophic bottoms from the regionally more enriched upper profundal. The likely reasons for an intact profundal oligochaete fauna are great volumes of oxygen-rich hypolimnic water of low temperature and a high bottom/lake surface area ratio.     

Trematode fauna of prosobranch snails of the genus Semisulcospira in Lake Biwa and the connected drainage system

The parasite fauna of prosobranch snails of the genus Semisulcospira was surveyed in Lake Biwa and the adjacent water system. One aspidogastrean and 28 digenetic trematode taxa were detected in 19209 snails consisting of 10 morphological species. There was no trematode species peculiar to members of the subgenus Biwamelania that is endemic to the Lake Biwa water system. However, one species, Notocotylus magniovatus, was found only in the non-endemic subgenus Semisulcospira. Of 23 digenean taxa detected in more than one host, 13 were distributed in both the lake and the tributaries. Seven of these had host taxa, more than 1% of which were infected with the parasite in both the lake and the tributaries, four had such hosts only in the tributaries, and two had no such hosts. Three species detected only in Lake Biwa were previously reported from other rivers in Japan. In the seven species detected only in the tributaries, two species had life cycles that could be maintained only in rivers. These results indicate that the core areas for the distribution of parasites of Semisulcospira are tributaries, and the lake is a sink for these species. These results contradict the expectation that the parasite fauna should be richer in the lake than in tributaries because the lake is a stable habitat over a geological time scale and has more divergent freshwater animals than the adjacent water system.     

Aquatic invertebrates of Lake Gregory,northwestern Australia,in relation to salinity and ionic composition

Lake Gregory is a large semi-permanent lake system in arid north-western Australia. Its catchment extends into humid areas and as a result the lake has dried only twice in the last 25 years. Although the system is mostly fresh, parts of it become saline as they dry. We identified aquatic invertebrates and undertook chemical analysis of water samples from several sites at Lake Gregory in 1989, when the main water-body was saline, and in 1991 and 1993, after the system had flooded and was fresh. During the period 1989–1993, salinities varied from 0.1‰ to 82‰, and ionic composition ranged from strong sodium chloride dominance, in saline water and fresh water of the eastern part of the system, to bicarbonate dominance in fresh water of the western area. At least 174 invertebrate species were recorded, including two mollusc species that were never collected live. This species richness is much higher than that recorded from other Australian arid zone lakes, probably owing to long periods of inundation with fresh water. The fauna was dominated by insects (42 per cent of total species richness), crustaceans (27 per cent) and rotifers (22 per cent). Most species (160) were restricted to fresh water; only 12 species were found in saline water. Only one ostracod occurred in saline conditions, although ostracods are a dominant group in Australian saline lakes. Among species restricted to fresh water, the proportion of rotifer and protozoan fauna that occurred in bicarbonate-dominated water was greater than the proportion of insect, crustacean and hydracarine fauna that did so. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Trichoptera of Øvre Heimdalsvatn

Trichopteran larvae were sampled on soft substrata at all depths, on stony substrata in the exposed zone, and the adults in emergence traps, placed along the lake shore. Fourteen species were taken as larvae in the lake. On stony substrata and in the exposed zone Polycentropus flavomaculatus (Pictet) was dominant, followed by Limnephilus nigriceps (Zetterstedt) in terms of numbers. In terms of biomass L. nigriceps dominated followed by Potamophylax cingulatus (Stephens).
Species which usually inhabit running water made up for a larger part of the trichopteran fauna of the exposed zone.
The two most numerous species showed different habit preferences. P. flavomaculatus was most common on stable stony bottom, while L. nigriceps was most common on unstable stony bottom. The other species showed no significant preference. On unstable soft bottom at 3 m and below, Mystacides azureus (L.) dominated, accounting for about 90% of the total trichopteran fauna both in terms of weight and numbers.
The major trichopteran species in the lake were either detritus feeders, such as M. azureus, L. nigriceps and Potamophylax spp. or omnivores such as P. flavomaculatus and Molanna albicans (Zetterstedt).     

Recent brachiopods from the southern Brazilian shelf: palaeontological and biogeographical implications

Until recently, the rhynchonelliform (articulated) brachiopod fauna from the Brazilian continental shelf (western South Atlantic) was represented only by the endemic species Bouchardia rosea (Mawe), reported from coastal waters of the states of São Paulo and Rio de Janeiro. The present study, based on samples from coastal (<30 m), shelf, and continental slope waters (99–485 m), documents the South Atlantic brachiopod fauna and shows that this fauna is more widespread, diverse, and cosmopolitan than previously thought. Based on a total of 16,177 specimens, the following brachiopods have been identified: Bouchardia rosea (Family Bouchardiidae), Platidia anomioides (Family Platidiidae), Argyrotheca cf. cuneata (Family Megathyrididae), and Terebratulina sp. (Family Cancellothyrididae). In coastal settings, the fauna is overwhelmingly dominated by Bouchardia rosea . Rare juvenile (<2 mm) specimens of Argyrotheca cf. cuneata were also found at two shallow-water sites. In shelf settings (100–200 m), the fauna is more diverse and includes Bouchardia rosea , Terebratulina sp., Argyrotheca cf. cuneata , and Platidia anomioides . Notably, Bouchardia rosea was found in waters as deep as 485 m, extending the known bathymetric range of this genus. Also, the record of this brachiopod in waters of the state of Paraná is the southernmost known occurrence of this species. The genera Platidia and Terebratulina are documented here for the first time for the western South Atlantic. The Brazilian brachiopod fauna shares similarities with those from the Atlantic and Indian shelves of southern Africa, and from the Antarctic, Caribbean and Mediterranean waters. The present-day brachiopods of the western South Atlantic are much more cosmopolitan than previously thought and their Cenozoic palaeobiogeographic history has to be reconsidered from that perspective.     

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.     

Dynamics of lake herring (Coregonus artedi) reactive volume for different crustacean zooplankton

Lake Torrens, a large ( 6000 km²), episodic, saline playa lake in arid central Australia, filled for the first recorded time in March 1989. This unique event followed unprecedently heavy rain over its catchment. Water remained in the lake until early 1990. Salinities remained low (<40 g l^-1) until November 1989, then increased rapidly to >200 g l^-1 before the water evaporated completely. Na and Cl probably dominated the ions. Twenty-nine taxa of aquatic animals were recorded. Crustaceans dominated and of these Parartemia minuta (anostracan), Daphniopsis queenslandensis and Moina baylyi (cladocerans), and several species of ostracods were the most important. Other significant taxa included Tanytarsus barbitarsis (chironomid), Brachionus plicatilis (rotifer) and Craterocephalus eyresii (fish). The fauna was dominated by widespread forms that are either part of a distinct assemblage found widely in central Australian salt lakes (especially P. minuta, D. queenslandensis, M. baylyi and Trigonocypris subglobusus [ostracod]), or cosmopolitan forms (B. plicatilis), or forms found widely in Australian salt lakes (e.g. Diacypris compacta, Tanytarsus barbitarsis). However, possibly three new species also occurred: a new species of a new genus of mytilocypridinid, Branchinella nov.sp. and Heterocypris nov. sp. Their occurrence is anomolous. It is suggested that further work will show that they too are widely distributed. Both genera of the latter two taxa are typical of temporary waters and specimens may have been washed in from nearby water-bodies. Sixty-four species of bird were recorded when the lake contained water, many breeding. The breeding of the banded stilt (Cladorhynchus leucocephalus) was notable; breeding of this species had been unknown in South Australia since 1930. A large population built up until breeding was stopped by predation from the silver gull (Larus novaehollandiae). When dry, the lake has a depauperate but well-defined and regionally restricted terrestrial fauna (scorpions, spiders, beetles, ants).     

Rotifers of the Kalahari Gemsbok National Park,South Africa

The Kalahari Gemsbok National Park in the Northern Cape Province, South Africa, is bounded by two dry river beds in which 39 artificial water sources have been provided for the use of the wild animals. The water in these sources varies from fresh to highly saline and an opportunity is thus provided to determine, not only which rotifer species are able to colonise such sources, but what their salinity tolerances are. The rotifer fauna, studied in summer and winter, is dominated by mixed populations of Brachionus calyciflorus, B. plicatilis and Hexarthra jenkinae, with only a few other monogononts and bdelloids. The most striking feature of the rotifer fauna in these troughs is the very low species diversity encountered.     

INTRODUCTION

.In view of the growing importance of fish for native consumption, the resources of the African lakes are sure to be exploited in the near future, but it is essential to have a sound understanding of the fish and other fauna and flora in each lake before exploitation is started. This paper places on record the available data for Lake Rudolf and Lake Baringo, on which no previous ecological work had been attempted.
Lake Rudolf is characterized by a high temperature and very alkaline water, and contains a variety of environments inhabited by different fish-associations. The fauna has pronounced nilotic affinities, except that there is only one member of the family Mormyridae. Several species, however, have come to differ from their nilotic ancestors, and the comparison of the fauna with that of other waters can be used as evidence for past changes in the drainage systems of East Africa.
The fish fauna of Lake Rudolf is roughly divisible into three main associations of species–one in the inshore waters, one in the open water, and one near the bottom. Prom data supplied by large numbers of stomach examinations, the food-chains for each of these habitats can be reconstructed.
Lake Baringo is less warm, the water has a relatively low alkalinity, and is uniformly shallow and muddy. The fish fauna consists of few species, and shows affinities with that of the East African rivers which flow to the Indian Ocean.
Owing to the shallowness of Lake Baringo, there is no differentiation into species-associations, and the food-chains are complicated by the presence of food from the bottom in all the species of fish.
The bulk of this paper contains analyses of field-observations on the size, feeding and breeding habits of each of the species found in the lakes,     

Ecological studies on crater lakes in West Cameroon Lakes Kotto and Mboandong

Lake Kotto is a shallow crater lake, sometimes weakly stratified, and with a dense phytoplankton dominated by blue-green algae. The ecology of Lake Kotto and the similar, smaller lake Mboandong is described in relation to the feeding biology of their fishes. Of the five species of cichlids in Lake Kotto only one is endemic. Two are phytoplankton-feeders, one takes invertebrates as well as phytoplankton, one feeds mainly on chironomid larvae, and one preys on vertebrates as well as on invertebrates. The three phytoplanktivores are the main species eaten by man. One species of Clarias and one of Barbus also occur in Lake Kotto; and in the associated streams are four species of cyprinodont fishes. The fish fauna of Mboandong consists of three species of cichlids and two cyprinodonts, all known from the Kotto system. We contrast Lake Kotto with the oligotrophic lake Barombi Mbo, and conclude that Lake Kotto would probably be less sensitive to human interference than would Barombi Mbo.     

The Radiation of Hydrobioid Gastropods (Caenogastropoda, Rissooidea) in Ancient Lake Poso, Sulawesi

A survey of the fauna of hydrobioid gastropods living in ancient Lake Poso in Sulawesi revealed a total of 16 species, 14 of them new, belonging to two genera, Sulawesidrobia and Keindahan gen. nov. Most species occurred on hard substrates, water plants or rootlets of trees. Since only the upper 0.5 m of the lake have been sampled, many more species probably remain to be discovered. Already, Lake Posoȁ9s fauna ranks among the four most diverse hydrobioid lake faunas worldwide. The Sulawesi lakes including Lake Poso and the Malili Lakes are the only lakes where sizeable radiations of hydrobioid and cerithioid gastropods coexist. Outside Lake Poso, hydrobioid gastropods have not been investigated so far apart from a single species reported from Lake Lindoe similar to or identical with S. bonnei [Abbott, 1945. Occasional Papers on Mollusks 1: 1–4], which has its type locality in Lake Poso and may in fact be a complex of species. Therefore endemicity in Lake Poso cannot be estimated nor is it possible to say, whether the radiation is of lacustrine origin. The introduction of alien fish has had a severe impact on the native fish fauna. The impact on the invertebrate fauna is not known but chances are that this survey based on collections from 1991 no longer reflects the original assemblage in the lake.     

Limnological studies of Lake Wisdom, a large New Guinea caldera lake with a simple fauna

SUMMARY. Lake Wisdom is of interest because it is large and deep, has oxygen throughout, and yet, apparently as a result of its recent formation, its biota has some surprising lacunae. It is nearly circular and fills the central caldera of Long Island, Papua New Guinea (5° 20′ S, 147° 6′ E). Its maximum length is 13.4 km, and area approximately 95 km². A bathymetric map of the lake to depths of 300 m has been constructed from fathometer transects. Repeated soundings in the deeper parts gave depths of about 360 m. The surface of the lake is approximately 190 m above sea-level and water samples from the deepest part of the lake are fresh, so the basin is apparently sealed. The lake level shows annual fluctuations of c. 1.0 m. Limnological information has been collected during seven visits to Lake Wisdom over the period 1969–76. The surface temperature of the lake was constant at 28°C throughout this period and the temperature falls very gradually to 26–27°C at 60 m, except for a relatively rapid drop of approximately 1°C from 10 to 20 m. One of the most unusual features is the relatively high oxygen concentration in the deepest parts of the lake. Living chironomid larvae and molluscs were collected from the bottom in depths of 360 m. Light penetration in the lake varies greatly depending on the amount of rainfall and the volcanic activity of Motmot, a secondary cone within the lake. The biota of Lake Wisdom is rather simple. There is a low standing crop of phytoplankton. Benthic algae are abundant and diverse although they cover only a limited area because of the depth of the lake. There are no vascular aquatic plants. The pelagic fauna consists of two species of Cladocera and one species of notonectid. There is one species of sponge, four species of molluscs, and a small number of species of aquatic insects including Hemiptera. Odonata, and the larvae of chironomids, mayflies, a caddisfly, and a pyralid moth. Water birds, including ducks, grebes and waders, are fairly numerous. The lake also contains one or more crocodiles.     

Benthic fauna in a series of lakes displaying a gradient of pH

The benthic fauna was examined in a series of four isolated headwater lakes, displaying a pH gradient of 5.4–7.0. A slight reduction in number of taxa present occurred below pH 6, with the fauna below 3 m dominated by the Diptera. Although epibenthic gastropods were rare, in contrast with European studies, Amphipoda, Ephemeroptera and Pisidium were common in the least buffered lake, which experiences spring pH values as low as 4.7. There were little relation between the pH or alkalinity, and the abundance, and biomass of the fauna at depths greater than 3 m. However, biomass of the littoral fauna increased significantly in the lakes with lower pH, as a result of an increase in large littoral species normally susceptible to fish predation.     

Contribution by possums to seed rain and subsequent seed germination in successional vegetation, Canterbury, New Zealand

Spider assemblages were sampled by quantitative sampling in pasture and arable habitats under different management regimes in the lower North Island of New Zealand. Density and species diversity increased with decreasing frequency and/or intensity of disturbance from two species and 1.8 individuals per m in wheat to 16 species and 130 indiv. per m in an abandoned, ungrazed pasture. The spider fauna was dominated by introduced species of money spiders (Linyphiidae). The most abundant species, Lepthyphantes tenuis, is also the most abundant one in British cultivated habitats. Additional pitfall trap samples from the same location and the Waikato, central North Island, indicated a similar species range containing mainly European species. A sample from a native tussock habitat had a completely different fauna, with only one species shared with the most undisturbed cultivated area. Comparative samples showed that similarly structured, but about twice as species- rich assemblages live in similar cultivated habitats in England.     

Hydrobiology of the Cochin backwater system – a review

On the south west coast of India, there is an extensiveestuarine system of backwaters, of which Vembanad Lake is the largest. The backwaters of Kerala support as much biological productivity and diversity as tropical rain forests. They are responsible for the rich fisheries potential of Kerala. Cochin backwaters situated at the tip of the northern Vembanad lake is a tropical positive estuarine system extending between 9° 40 and 10° 12N and 76° 10' and 76° 30 E with its northern boundary at Azheekode and southern boundary at Thannirmukham bund. The lake has a length of 80 km and the width varies between 500 and 4000 m. A channel, about 450 m wide at Cochin gut and another at Azheekode, make permanent connections with the Arabian Sea. The depth of the estuary varies considerably. While the shipping channels are maintained at a depth of 10–13 m, the major portion of the estuary has a depth range of 2–7 m. Water from two major rivers viz., Periyar and Muvattupuzha drain into this estuary. During south west monsoon, the estuary is virtually converted into a freshwater basin even in areas around barmouth where salt water penetration occurs below 5 m depth only. The major hydrological variable in the Cochin backwaters is salinity, similar to the situations encountered in estuaries with a gradual declension of salinity from 30 at the entrance of the estuary to 0.2 at the point of entry of the rivers. Salinity gradient in the Cochin backwaters supports diverse species of flora and fauna depending on their capacity to tolerate oligohaline, mesohaline or marine conditions. Low lying swamps and tidal creeks, dominated by sparse patches of mangroves with their nutrient rich physical environment, support larvae and juveniles of many economically important species. Backwaters also act as nursery grounds of commercially important prawns and fishes. The fields around the backwater are suitable for aquaculture. These areas support traditional, seasonal and perennial prawn fishery. The changes in the hydrology controlled by the seasons play an important role in regulating the migrant fauna of the estuary. The Cochin backwater supports a well established endemic fauna. The nutrients and pollutants introduced into the estuary control to a great extent the distribution and abundance of less tolerant species in ecologically sensitive areas in the backwaters. Cochin backwaters, widely regarded as one of the polluted estuaries in India, receive contaminated freshwater inputs and discharges of effluents and partially treated sewage from many points throughout its tidally mixed zone. Recently, changes brought about in the estuary like reclamation and consequent shrinkage of the backwaters and the discharge of pollutants have made an adverse impact on the potential of aquatic ecosystems that used to support high levels of bioproductivity and biodiversity. The construction of Thannirmukham bund and Thottapally spillway to prevent salt water penetration into the paddy fields during pre-monsoon has led to serious ecological problems by interrupting the natural ebb and flow of tides. The hydrography, floral and faunal composition – its spatial and temporal variation plus assessments of the impact of the anthropogenic activities are presented in this review. An attempt to critically evaluate the status of the estuary from the biological and pollutional stand point is also done.     

Modifications in habitat use patterns and trophic interrelationships in the fish fauna of an oligotrophic artificial lake: Sainte Croix (Provence,France)

Lake Sainte-Croix is a hydro-electric reservoir on the river Verdon that came into operation about 16 years ago. The area of the lake is about 22 km² and the volume about 767 Mm³. The water level drops by as much as 16 m in winter. Sainte-Croix is a warm monomictic oligotrophic lake. The indigenous fish fauna of the Verdon originally included 8 species. Successive stocking has raised this number to 17. In catches made in 1976–1977 with 27 mm mesh nets, 80 to 90% of the fish with a body size of between 15 and 25 cm were of the four main species indigenous to the river before the dam was built: Leuciscus cephalus, Barbus fluviatilis, Chondrostoma toxostoma, Salmo trutta. Catches made at same period with 14 mm mesh nets gave only Chondrostoma toxostoma and Leuciscus cephalus.Changes in the fish fauna were apparent from catches made in 1984 and 1987 with nets of the same mesh size. There was a marked demographic increase of roach, and more recently of bleak and gudgeon, all three species introduced after the construction of the dam. At the same time, there was a decrease in catch frequency of Ch. toxostoma, L. cephalus and B. fluviatilis in the downstream area of the lake. Stomach content analysis carried out in different seasons on the six most abundant species of the lake (roach, toxostome, chub, bleak, perch and gudgeon) provided evidence on the trophic organisation of the fish fauna. We have measured niche breadth for each species by the Simpson diversity index and niche overlap by the Pianka index. Bleak is the only species to feed on zooplankton in open water. Roach is a particularly opportunistic feeder, sometimes taking plankton, but at Sainte-Croix it is exclusively herbivorous and benthophagous. Niche overlap between these two species is slight or null, depending on the season. On the other hand, there is a high degree of overlap between roach and chub and between roach and toxostome. The decrease in toxostome and chub frequency in the downstream area of the lake, where roach is most abundant, would appear to be a competitive exclusion phenomenon. There is high niche overlap between bleak and young perch, which partly explains the low abundance of the latter species; other contributory factors are the scarcity of zooplankton inshore, and the scarcity of zoobenthos resulting from the drop in the water level in winter.     

The benthic macrofauna community of Kenyan waters of Lake Victoria

The benthic macroinvertebrates in the Kenya waters of Lake Victoria (ca. 1400 km²) were surveyed during four 10 day sampling periods in February, April, August and November 1984. Fourty three taxonomic groups were recorded. Oligochaetes, molluscs and dipteran larvae were the most abundant and widely distributed groups. The dominant oligochaetes were Branchiura sowerbyii Beddard and the swamp worm Alma emini Michaelsen, which were abundant in all silty and soft mud areas in both littoral and open water zones. Melanoides tuberculata Müller, Bellamya unicolor Olivier and Caelatura spp. were the most abundant molluscs. Different patterns were observed between near-littoral stations (<8 m deep) and deep water stations (8–40 m deep). After 10 years (1994), the macroinvertebrates of Lake Victoria were examined again. No evidence was found of seasonal changes in the composition or benthos density, although local changes occurred in some species which were attributed to swarming behaviour or larval settlement patterns. The spatial distribution of the fauna may be influenced primarily by oxygen availability and industrial effluent discharged from paper mill and agro-based industries in the catchment of the lake. There has been a shift in abundance, from an Oligochaeta and Insecta dominated community in 1984, to the present community dominated by Mollusca and Oligochaeta. The ecological role of the benthic community and its recent changes to fisheries production in the lake is discussed.     

Vegetation analysis of Burullus Wetland: a RAMSAR site in Egypt

We analyzed the vegetation of Lake Burullus at the deltaic Mediterranean coast of Egypt, the sand bar between its northern shore and Mediterranean Sea, the water courses that drain into the lake and the wetland around it. Our ultimate aim was to identify threatened species and communities and the environmental factors that affect their distribution in order to formulate a plan for their conservation. The total number of the recorded species was 197 (100 annuals and 97 perennials), including 12 floating and submerged hydrophytes. Three species are endemic to Egypt: two annuals (Sinapis arvensis subsp. allionii and Sonchus macrocarpus) and one perennial (Zygophyllum album var. album). Thirty-four species are rare allover Egypt (15 annuals and 19 perennials). The lake area included 10 types of habitat (sand formations, salt marshes, lake cuts, terraces, slopes, water edges and open water of the drains, islets, shores and lake). The vegetation was classified into 13 groups (i.e., plant communities). Six groups were dominated or co-dominated by the common reed (Phragmites australis); these groups occupied a wide environmental gradient from xeric to hydric habitats. Five other groups were dominated by halophytic species (Arthrocnemum macrostachyum, Suaeda vera, Sarcocornia fruticosa, Halocnemum strobilaceum and Salsola Kali). The remaining two groups were dominated by the emergent Typha domingensis and the submerged Potamogeton pectinatus. Moisture, salinity and sedimentation were the main factors that governed the plant succession in this wetland.     

Responses of benthic macroinvertebrate communities to altitude and geology in tributaries of the Sepik River (Papua New Guinea): the influence of taxonomic resolution on the detection of environmental gradients

1. Benthic macroinvertebrate communities were sampled in 30 tributary streams at altitudes from sea level to about 3000 m draining three geologically distinct regions within the catchment of the Sepik River, Papua New Guinea. The fauna of this near‐pristine river has been little studied, and the impacts of ongoing and anticipated human impacts on the Sepik are uncertain. 2. Data on community composition were analysed at different levels of taxonomic resolution (species or morphospecies versus family) to compare their responses to environmental variables such as altitude and geology (reflected in water chemistry), and to indicate their potential utility for the detection of environmental change. 3. A total of 183 000 macroinvertebrates representing 250 species were collected, predominantly insects (232 species and >99% of individuals). The fauna was co‐dominated by Diptera (42% of individuals; 32 morphospecies, mainly Orthocladiinae, Simuliidae and Chironominae) and Ephemeroptera (36%; 48 species), although the Trichoptera showed the highest species (67) and family (13) richness, with Coleoptera ranked third (43 species). Naucoridae (Heteroptera) and Crambidae: Acentropinae (Lepidoptera), each represented by 13 species, were distinctive faunal elements. Mayflies were represented by only four families, one consisting of a single species. 4. Multivariate analysis of the species‐level data set revealed that community composition was influenced by geological region, but the effect was largely due to altitude as most streams in one region (the Central Highlands) were at higher elevations (>800 m) than streams in the other two regions (<500 m). However, altitude had no direct effect on species richness. A secondary influence of current speed and a subsidiary effect of water chemistry (pH and N‐NO₃) on community composition were also detected. Naucorid bugs showed evidence of altitudinal zonation and some species replacement, plus a tendency for certain genera to be associated with highland or lowland streams. 5. Analysis of the family‐level data set failed to uncover strong effects of any environmental variable, either individually or in combination, although some sensitivity to altitude plus slope was detected. 6. These findings suggest that attempts to use macroinvertebrates to detect environmental change in New Guinea streams will require species‐level monitoring of community composition.