The spawning location of vulnerable ferox trout (Salmo trutta L.) in the Lough Corrib and Lough Mask catchments,Western Ireland

Ferox trout are large, long-lived, piscivorous trout normally found in deep lakes; they are highly prized by trophy anglers. Lough Corrib and Lough Mask, Western Ireland, have recorded the majority of Irish specimen ferox trout since angling records began. Little was known regarding the spawning location of ferox trout relative to sympatric brown trout, and a radio telemetry study was initiated in both catchments in 2005. Over the period 2005–2009, 79 ferox were captured by angling and radio tagged in Lough Corrib, while 55 ferox were tagged in Lough Mask. Manual and helicopter tracking were carried out on all spawning streams entering both lakes over the autumn/winter period to detect tagged fish. Overall, 37 radio-tagged trout (46.8%) were detected in Lough Corrib streams and 21 tagged trout (38.2%) were recorded from Lough Mask streams. Results from radio tracking indicate that the majority (92%) of ferox trout tagged in Lough Corrib spawned in a single spawning stream, the Cong river, while the majority (76%) of ferox trout tagged in Lough Mask spawned in the Cong canal and Cong river. These results suggest that these streams are most likely the principle spawning locations of ferox trout in both lakes. The occurrence of ferox trout predominantly in single spawning rivers in both catchments highlights the vulnerability of the study ferox populations. As a result of these findings, conservation measures were introduced for ferox trout in both catchments.     

The relationship between water velocity,energetic costs,and microhabitat use in four North American stream fishes

Freshwater crayfish are key members of aquatic communities due to their large size and abundance. Although most commonly regarded as herbivores and detritivores, they are also selective predators. The crayfish plague fungus Aphanomyces astaci (Schikora) led to the elimination of a stock of white-clawed crayfish, Austropotamobius pallipes (Lereboullet) from Lough Lene, Co. Westmeath, in 1987. Samples taken of the flora and benthic communities of two Irish lakes, one (Lough Bane) formerly containing crayfish and the other (Lough Lene) immediately following a plague outbreak, were compared to similar samples taken a year later and ecological shifts were noted and compared to laboratory feeding results. Over time, Chara strands increased in mean length, and molluscs became more abundant.     

Persistence, extinction and different species pools within the flora of lake islands in western Ireland

The vascular flora on twenty-nine lake islands in Lough Corrib, western Ireland was surveyed in 1992–93. Thirteen of these islands had been surveyed by the author in 1974 (Roden, 1979). Data on species–area curves and species turnover between 1974 and 1992 are presented. Species numbers on each island did not change greatly in the 18-year interval and extinctions were most common on smaller islands. It is known that six of the islands surveyed are less than 150 years old and their flora must have immigrated over open water during that period. It is shown that this group of species has a different log species/log area regression than the remaining flora, with a much shallower slope (low Z value). The proportion of less widespread species was greatest on islands nearest to the mainland. The implication of different slopes in different species groups and the restriction of turnover to rare species is discussed with reference to the island Theory of Biogeography.     

A study of Lough Corrib,western Ireland and its phytoplankton

During 1980/1981, a twelve month study was carried out on the phytoplankton of Lough Corrib, a large freshwater lake in western Ireland. Cell counts indicated low phytoplankton productivity and this was reflected in low chlorophyll a values and high Secchi readings. Diatoms predominated in spring and were succeeded by blue-green algae in late summer. The spring diatom crop was apparently limited by either silicate or nitrogen. Mineral uptake by rooting macrophytes and benthic algae and phosphate recycling as a result of bottom sediment disturbance may be important elements in the nutrient cycling regime of the lake. Differences in morphology between the upper and lower basins of the lake are reflected, to some extent, in species composition and areal productivity.     

Observations on the natural diet of Cymatia bonsdorfi (C. Sahlb.) (Heteroptera: Corixidae): an immunological analysis

Immunological analyses of the gut contents of 1769 adult and 486 nymphal instars of the lesser waterboatman, Cymatia bonsdorfi, from Lough Corrib, western Ireland, were performed using a double immunodiffusion technique. Antisera against six potential prey categories (Oligochaeta, Cladocera, Copepoda, Gammarus, Diptera and Ephemeroptera), identified on the basis of field and laboratory observations, were utilized. Diptera larvae formed over 90% of the diet of adult bugs and were also the principal prey group of all nymphal instars.     

The ecology of the Corixidae (Hemiptera: Heteroptera) in the Corrib catchment,Ireland

Two surveys were carried out in the Corrib catchment (Ireland) to determine the physical and chemical factors that govern the distribution of Corixidae. Of the twenty one species recorded, five species, Sigara scotti (Fieber), S. distincta (Fieber), S. fossarum (Leach), S. fallenoidea (Hungerford) and Cymatia bonsdorffii (Sahlberg) comprised 82% of the numerical total. Although individual species occurred in chemically diverse sites species assemblages and changes in the relative abundance of the majority of species and in species richness and diversity were evident in the progression from hard to soft water. High altitude soft water sites had a much lower number of species compared with chemically similar low altitude sites. In Lough Corrib, the main body of water in the catchment, most species were abundant only in sheltered areas with mud substrates and high percentage vegetation cover. Species diversity was high in these areas and either C. bonsdorffii, S. fossarum, S. fallenoidea or Callicorixa praeusta (Fieber) dominated numerically. However, S. scotti, S. dorsalis (Leach) and Arctocorisa germari (Fieber) were more abundant in exposed areas with sand, gravel or mearl substrates. In temporary ponds and in lotic water species diversity was also high but species composition (mainly C. praeusta, Sigara nigrolineata (Fieber), Corixa punctata (Illiger), C. panzeri (Fieber), C. bonsdorffii) was different to that of temporally stable lentic habitats.     

Vegetation, landscape and human activity in Midland Ireland: mire and lake records from the Lough Kinale-Derragh Lough area, Central Ireland

A high-resolution pollen record for the Holocene has been obtained from Derragh Bog, a small raised mire located on a peninsula in Lough Kinale-Derragh Lough, in Central Ireland as part of the Discovery Programme (Ireland) Lake Settlements Project. The data are compared with two lower resolution diagrams, one obtained from Derragh Lough and one from adjacent to a crannog in Lough Kinale. The general trends of vegetation change are similar and indicate that landscape-scale clearance did not occur until the Medieval period (ca. a.d. 800–900). There are, however, significant differences between the diagrams due primarily to core location and taphonomy, including pollen source area. Only the pollen profile from Derragh Bog reveals an unusually well represented multi-phase primary decline in Ulmus ca. 3500–3100 b.c. (4800–4750¹⁴C b.p.) which is associated with the first arable farming in the area. The pollen diagram indicates a rapid, and almost complete, clearance of a stand of Ulmus with some Quercus on the Derragh peninsula, arable cultivation in the clearing and then abandonment by mobile/shifting late Neolithic farmers. Subsequently there are a number of clearance phases which allow the colonisation of the area by Fraxinus and are probably associated with pastoral activity. The pollen sequence from adjacent to a crannog in Lough Kinale shows clear evidence of the construction and use of the crannog for the storage of crops (Hordeum and Avena) whereas the Derragh Bog diagram and the diagram from Derragh Lough reflect the growth of the mire. This study reveals that in this landscape the record from a small mire shows changes in prehistoric vegetation caused by human agriculture that are not detectable in the lake sequences. Although in part this is due to the higher temporal resolution and more consistent and complete chronology for the mire, the most important factor is the closer proximity of the raised mire sequence to the dry land. However, the pollen sequence from adjacent to a crannog does provide detailed evidence of the construction and function of the site. It is concluded that in order to ascertain a complete picture of vegetation changes in a lowland shallow lake-dominated landscape, cores from both the lake and surrounding small mires should be analysed.     

The impact of drainage maintenance strategies on the flora of a low gradient, drained Irish salmonid river

In 1990, the Central Fisheries Board initiated research on how drainage maintenance practices and strategies might be modified to enhance the salmonid carrying capacity of the affected water while maintaining an acceptable degree of conveyance. Much of the maintenance requirement was caused by dense in-channel weed beds impeding discharge and facilitating siltation. The impact of various maintenance regimes on the aquatic flora was examined in the course of pilot studies on channels of base width 3–9 m. The findings from one of these, the R. Tullamore Silver which chokes annually with Sparganium erectum L., are presented. Overdigging the centre of the channel and placement of spoil at the margins confined S. erectum to a narrow marginal zone and facilitated development of a submerged, open-water flora.     

Resting cysts of someChaetoceros species,identified and figured by A. Van der Werff

This note is dedicated to Albert van der Werff (1903–1991), the Dutch diatom expert, distributing his extended knowledge to numerous students interested in aquatic ecology. His drawings of the resting cysts ofChaetoceros affine Lauder andCh. constrictum Gran, not figured in his diatom flora (van der werff andhuls, 1957–1974), are published and discussed. The figures represent a valuable contribution to taxonomical literature. Publication no. 661 Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, Yerseke, The Netherlands.     

武汉东湖水生植物区系四十年间的变化与分析

本文根据作者近年的研究结果,并结合前人的有关研究资料,对东湖四十年间（１９５４－１９９４）水生植物区系组成变化进行了讨论。文中分析了东湖水生植物区系组成、东湖水生植物在中国与世界水生植物区系中的位置、东湖水生植物种属的分布区类型、单种属和寡种属的地理分布格局、东湖水生植物区系的性质、东湖与１０个湖泊水生植物种属相似性的分析。最后对东湖水生植物分类群及种类变化进行了探讨。     

云南武定中泥盆世晚期植物与腹足动物共生标本的发现及其古生态意义

中泥盆世晚期陆生植物的演化已经达到相当高的水平,我国以云南中泥盆世晚期植物群为代表,称为Lepidodendropsis arborecense-Minarodendron cathaysiense-Eocladoxylou minutum (LME)组合。当前在云南武定中泥盆世晚期地层(西冲组上部)中发现的植物主要有Lepidodendropsis arborescense,Eocladoxylon minutu,Rhipidophyton acanthum等,其中,在R.acanthum的茎干基部密集共生有腹足动物Valvata sp.。根据植物表面无动物咬食痕迹,以及腹足动物生态特性和演化分析,当前陆生植物与水生动物共生的原因是植物茎干飘落水体后,为水生的腹足动物提供了新的栖息场所,并随水流、风浪载运至异地埋藏。这种水生腹足动物寄栖于水中物体的生活方式很普遍,是腹足动物迁徙、扩散的一种重要途径。     

The association between the phytoplankton, Rhopalosolen species (Chlorophyta; Chlorophyceae), and Anopheles gambiae sensu lato (Diptera: Culicidae) larval abundance in western Kenya

Algae are important food resources of the larvae of the African malaria vectors, Anopheles gambiae Giles and Anopheles arabiensis Patton (Anopheles gambiae sensu lato), and other zooplankton, but empirical evidence remains meager about the agal flora in ephemeral water bodies. The animals present in natural aquatic habitats in western Kenya were sampled from July to November 2002 to study abiotic and biotic environmental factors determining A. gambiae sl larval abundance. The five highest concentrations of third and fourth instars and pupae (hereafter referred to as old-stage larvae) were sampled in conjunction with the unicellular epizoic green algae, Rhopalosolen species (Chlorophyta; Chlorophyceae). Canonical correspondence analysis revealed that the presence of Rhopalosolen species was the most important determinant of the animal assemblage. The density of old-stage A. gambiae sl larvae was positively correlated with the presence of Rhopalosolen species, but the density of first and second instars of A. gambiae sl was not. The water bodies with Rhopalosolen sp. yielded larger mosquitoes in spite of the higher density of larvae. We demonstrated that the productivity of water bodies in terms of the larvae of malaria vectors can differ in magnitude depending on the agal flora. We discuss phytoplankton as a regulator of mosquito larval populations.     

Observations on the diatom flora of Braunton Burrows,N. Devon

Summary The diatom flora has been analysed in 31 samples from the dune area at Braunton Burrows. Samples have been examined from (a) aquatic habitats, (b) soil, plants and mosses subject to seasonal flooding and (c) sand and mosses from dry dunes. The diatom flora of all these has been discussed and compared with data from elsewhere.Department of Botany, University of Bristol     

Environmental change over two decades since dredging and excavation of the lower Boro River, Okavango Delta, Botswana

The Okavango Delta, southern Africa's largest wetland, is situated on the fringe of the semi-arid Kalahari Desert. It is a large alluvial fan, occupying a graben structure which is an extension of the East African Rift system. Of the 16 km³ of water which enters the Delta each year, 96% is lost to the atmosphere by evapotranspiration, 2% to groundwater and only 2% leaves as surface flow. In order to increase surface outflow to meet human needs, the distal Boro channel–floodplain system was dredged, excavated and bunded between 1971 and 1974. The immediate impact of these measures was the destruction of in-channel flora. After 20 years, the aquatic flora has recovered in the excavated channel. However, little recovery has occurred along the channel reach which was dredged. Moreover, there has been significant encroachment of terrestrial species onto the floodplain in the region of the dredged channel. In addition, dredging created a nick point which has been migrating upstream by headward erosion since dredging ceased. The average rate of advance of the nick point has been about 500 m per year. Incision associated with nick point migration has produced a channel which is indistinguishable in form from the dredged channel and, like the dredged channel, is almost completely devoid of in-channel aquatic flora. The adverse environmental impact of dredging has therefore continued to propagate in an upstream direction, although the height of the nick point has decreased, suggesting a natural attenuation process. This is likely to result in eventual elimination of the nick point.     

The composition and zonation of a Fucus serratus community in strangford lough,co. down

The flora and fauna associated with the serrated wrack, Fucus serratus L., in Strangford Lough have been studied. Fucus plants were larger where they were most abundant and their distribution was determined largely by the availability of suitable substratum; however, plant size was reduced under turbulent conditions. The fauna contained 79 taxa, of which eleven were common: these comprised four polyzoans, two tunicates, two sponges, two hydroids and a serpulid. All except three were more abundant on plants with low silt loads in turbulent, weedy areas. All species except Electra pilosa (L.) tended to occur on the concave surfaces of the plant. Evidence of zonation in each species' distribution along the plants was obtained. Analysis of association coefficients for the commonest species suggested that there are two distinct species groupings within the community.     

Parasite community similarity between four Irish lakes

A total of 140 trout were examined from four lakes in north west Ireland, Loughs Craghy, Waskel, Meela and Owennamarve. Eleven species of metazoan parasite were recorded, ten of which were of freshwater origin and Anisakissp. was the only marine species. No acanthocephalan species were found. Diphyllobothrium ditremum, D. dendriticum and Anisakissp. were the only allogenic species. Lough Owennamarve had the largest component community with nine species recorded. Lough Meela, the only brackish water lake had the smallest component community with six species recorded. Lough Waskel and Craghy had intermediate component community values. Lough Meela showed the lowest levels of similarity to any of the other lakes. Values for the Shannon-Wiener diversity index were highest for Lough Owennamarve and lowest for Lough Meela and intermediate for the other two lakes. Lough Meela had the highest values for the Simpson's dominance index and the Berger-Parker index. Lough Owennamarve had the highest Brillouin's index and Lough Meela had the lowest. The use of multiple regression techniques to control for the potentially confounding effect of geographical distance as a predictor of community similarity was discussed. No parasite species found could be considered as regionally and locally abundant and therefore described as a core species. The helminth community appears to have some degree of predictability, but chance colonization events are also important.     

Possible competitive interactions between overwintering tufted duck (Aythya fuligula (L.)) and fish populations of Lough Neagh,Northern Ireland: evidence from diet studies

The overwintering population of tufted duck (Aythya fuligula) on Lough Neagh, Northern Ireland, has varied over the last three decades, with numbers declining in the early 1980s but then increasing to former levels in the late 1980s. Population fluctuations of recently introduced roach (Rutilus rutilus) mirrored these trends. The present study explores the possibility that competition for benthic food resources is responsible for these changes by examining the diets of tufted duck, roach and other major fish species of the lake. Diet overlaps were generally high due to the common consumption of chironomid larvae. The diet of tufted duck overlapped most with that of roach because these two species were the only significant consumers of molluscs. This evidence provides further support for a tufted duck — roach competition hypothesis.     

Genetic differences in physiology, growth hormone levels and migratory behaviour of Atlantic salmon smolts

Out of five strains of Atlantic salmon Salmo salar of 1+ years released upstream of a fyke net in the River Gudenaa in 1996, three, Lagan, Ätran and Corrib, migrated immediately, 50% of the recaptured fish reaching the net in 3–6 days. Burrishoole and Conon fish migrated with a 15–19 day delay. Smolt development in 1997 at the hatchery showed a spring surge in gill Na⁺, K⁺-ATPase activity in all strains which was correlated with increased seawater tolerance. Differences in the timing of gill enzyme development matched the observed migration pattern well. Lagan, Ätran and Corrib strains reached high enzyme activity earlier than the Burrishoole and Conon strains, and strains with delayed enzyme development and migration showed a delayed regression of seawater tolerance compared with the early strains. Inter-strain differences in plasma growth hormone profiles could not be related to the observed patterns of Na⁺, K⁺-ATPase and seawater tolerance development. The study gives evidence of genetic influence on the timing and intensity of smolting and subsequent migration in Atlantic salmon.     

Implications of temporal and spatial variability in Paracentrotus lividus populations to the associated commercial coastal fishery

Analysis of population structure and behaviour of a semi-enclosed and theoretically non-fished population of the echinoid Paracentrotus lividus at Lough Hyne marine nature reserve, Co. Cork, Ireland, showed distinct variability. Aspects of the behavioural variability in this species have significant consequences for the natural fishery harvest potential of this species. Whether or not, when and where individuals migrate to the upper surfaces of rocks varies on a local and regional scale as well as seasonally. The effect of this is apparent changes in (a) the population structure, (b) the population size and (c) the population centres of abundance. The population structure and size of the Lough Hyne population has changed substantially, as have those on a larger spatial scale, although the causative agents are debatable. Such changes are the result of large-scale mortality of adults and failure of cohort recruitment. Despite the undeniable pressures of overfishing at many localities, it seems likely there is a strong `natural' and possibly predictable element to the variability in P. lividus population size and structure. For the restoration and sustainable harvest of Irish P. lividus aspects of its behavioural ecology need to be taken more closely into consideration.     

Aulacoseira subarctica: taxonomy,physiology, ecology and palaeoecology

Knowledge of the morphology, taxonomy, physiology, ecology and palaeoecology of the filamentous freshwater diatom Aulacoseira subarctica (O. Müller) Haworth is reviewed from the literature. The species is widely distributed across Northern Europe, Scandinavia and North America, Japan, China, Australia and New Zealand, in the last usually as fo. subborealis. The species is rare in the Tropics and positive identifications are lacking for Africa. The importance of correct identification is stressed because literature reports of its occurrence often need revision. A comparison is made between two sites with detailed records of its seasonal cycle. Blelham Tarn, England, is a clear-water seasonally stratified lake; Lough Neagh, Northern Ireland, is a very large turbid and unstratified lake. In spite of their contrasting characters, Aulacoseira subarctica succeeds in both lakes. In Blelham Tarn, there is a strong seasonal cycle of growth, dormancy on the sediment and further growth on re-suspension. In Lough Neagh, there is a large deposition of cells at the end of the spring bloom but few of these cells survive grazing by benthic animals. Fossil occurrences are summarized from the species’ initial appearance in the Pliocene and its later occurrence during the last inter-glacial (Eemian) deposits in NW Europe, where it is an important ecological indicator. Palaeolimnological studies are reviewed to describe the contemporary distribution and ecological preference of this widespread diatom. Aulacoseira subarctica usually appears in response to moderate increases in nutrients but is disadvantaged by further enrichment. In Blelham Tarn the species only became abundant during the twentieth century, reaching a peak between 1930 and 1960. With nutrient enrichment, abundance has declined. In Lough Neagh, it has been present for much of the post-glacial period and still thrives today in spite of the highly enriched state of the lake. The species has disappeared from many eutrophic lakes and its sustained existence in Lough Neagh is anomalous. Lough Neagh may continue to offer a favourable habitat in spite of the poor light climate because the water depth, lack of stratification and long water retention time reduce losses to a sustainable level.