Replacement of a native freshwater macroinvertebrate species by an invader: implications for biological water quality monitoring

The rate of freshwater invasions may be increasing, and macroinvertebrate invaders can have significant impacts on native macroinvertebrate assemblage structure through biotic interactions. More pollution-tolerant invaders can often replace native species. We examined implications of a species replacement for accurate biological monitoring of river systems using biotic indices. Our study uses Northern Ireland and the Isle of Man as examples of countries that possess river networks with many riverine macroinvertebrate assemblages subject to invasion. The introduced amphipod crustacean Gammarus pulex has replaced the native species G. duebeni celticus in many rivers in N. Ireland and the Isle of Man. Extensive seasonal data sets (119 sites) from three river networks, Lough Neagh and the Lagan in N. Ireland, and island-wide in the Isle of Man, were used to investigate the assumed equivalence of the native and invader in biotic indices concerned with the water quality monitoring system. Based on the derivation of the Biological Monitoring Working Party (BMWP) score, the Average Score Per Taxon (ASPT), as an example of a commonly used biotic index of water quality, we found index scores were lower in G. pulex sites compared to G. d. celticus-only sites. This indicated that assemblages were dominated by taxa more tolerant of organic pollution in the invader sites and more sensitive in the native sites. Inclusion of the invader in generation of the ASPT index, overinflated the ASPT values obtained compared to those with the native’s inclusion. This questions the accuracy of the ASPT and similar indices in rivers where the invader had replaced the native. We argue that with invasion pressures increasing, the validity of water quality indices such as the BMWP/ASPT needs to be re-examined in catchments where invaders have replaced natives. Indices such as the BMWP/ASPT are based on family level taxa and are inevitably coarse in their resolution given the wide range of water qualities tolerated by different genera within families. We argue that this resolution is even more compromised by the presence of very pollution-tolerant invaders, who may have replaced natives in disturbed or degraded river systems. The whole structure of water quality indices such as the BMWP/ASPT may need revising to take into account the presence of invasive species within monitored assemblages.     

Ephemerum hibernicum sp. nov. (Bryopsida: Ephemeraceae) from Ireland

Abstract

Ephemerum hibernicum sp. nov. is described from inundation zones of two lakes and a river in north-central Ireland and a river in western Ireland. It is most similar to E. crassinervium and E. sessile, but differs from both of these in several characters of the leaves. In particular, papillae on the upper lamina are much lower than in most E. crassinervium, while the leaves are longer and wider than in E. sessile, with a wider lamina towards the leaf apex, less well-defined costa and sometimes with large spinose marginal teeth. Ephemerum hibernicum is a rare species and its specialized habitat merits conservation.     

Phylogeography of the European brook lamprey (Lampetra planeri) and the European river lamprey (Lampetra fluviatilis) species pair based on mitochondrial data

The European river lamprey Lampetra fluviatilis and the European brook lamprey Lampetra planeri (Block 1784) are classified as a paired species, characterized by notably different life histories but morphological similarities. Previous work has further shown limited genetic differentiation between these two species at the mitochondrial DNA level. Here, we expand on this previous work, which focused on lamprey species from the Iberian Peninsula in the south and mainland Europe in the north, by sequencing three mitochondrial marker regions of Lampetra individuals from five river systems in Ireland and five in southern Italy. Our results corroborate the previously identified pattern of genetic diversity for the species pair. We also show significant genetic differentiation between Irish and mainland European lamprey populations, suggesting another ichthyogeographic district distinct from those previously defined. Finally, our results stress the importance of southern Italian L. planeri populations, which maintain several private alleles and notable genetic diversity.     

Distribution,prevalence and intensity of Anguillicola crassus (Nematoda) infection in Anguilla anguilla in the Republic of Ireland

This study is the first comprehensive documentation of the geographical range of Anguillicola crassus in its host, the European eel Anguilla anguilla, in the Republic of Ireland. The prevalence and intensity of infections across 234 sites and 93 river basins in Ireland comprising rivers, lakes and transitional waters (estuaries) were analysed. While only 32% of the river basins were affected by this nematode, they correspond to 74% of the total wetted area. Significant differences in infection levels among water body types were found with lakes and transitional waters yielding the highest values, which can be attributed to the proportions of juvenile (total length, L_T < 300 mm) A. anguilla caught. There were no significant differences in infection levels between water body types for adult A. anguilla or between sexes for any water body type. Prevalence was significantly lower in juvenile compared with adult A. anguilla captured in rivers and a positive correlation between infection levels and host size‐classes was found. Future efforts should focus on monitoring the spread of A. crassus infections and assessing the swimbladder health of A. anguilla in Ireland.     

Trophic flexibility and opportunism in pike Esox lucius

The first comprehensive investigation of pike Esox lucius trophic ecology in a region (Ireland) where they have long been thought to be a non‐native species is presented. Diet was investigated across habitat types (lake, river and canal) through the combined methods of stable‐isotope and stomach content analyses. Variations in niche size, specialization and the timing of the ontogenetic dietary switch were examined, revealing pronounced opportunism and feeding plasticity in E. lucius, along with a high occurrence of invertivory (up to 60 cm fork length, L_F) and a concomitant delayed switch to piscivory. Furthermore, E. lucius were found to primarily prey upon the highly available non‐native roach Rutilus rutilus, which may alleviate predation pressure on brown trout Salmo trutta, highlighting the complexity of dynamic systems and the essential role of research in informing effective management.     

Distribution patterns of blackfly (Diptera: Simuliidae) associations in two Irish river systems

Nine blackfly species were found in two river systems in south western Ireland. Their distribution patterns reflected the three main types of running waters: head waters and mountain brooks; meadow streams and river sections at lower altitudes; lake outlets. Cluster analyses showed correlations between the five most dominant blackfly species and stream sites, as well as with some environmental factors. Larval gut analyses demonstrated that in general the supply of suspended algae determined larval gut content, but there were distinct differences in food utilization between associated larvae.     

Differential physico-chemical tolerances of amphipod species revealed by field transplantations

Physico-chemical regimes of river systems are major determinants of the distributions and relative abundances of macroinvertebrate taxa. Other factors, however, such as biotic interactions, may co-vary with changes in physico-chemistry and concomitant changes in community composition. Thus, direct cause and effect relationships may not always be established from field surveys. Equally, however, laboratory studies may suffer from lack of realism in extrapolation to the field. Here, we use balanced field transplantation experiments to elucidate the role of physico-chemical regime in determining the generally mutually exclusive distributions of two amphipod taxa, Gammarus (two species) and Crangonyx pseudogracilis. Within two river systems in Ireland, the former species dominate stretches of well oxygenated, high-quality water, whereas the latter dominates stretches of poorly oxygenated, low-quality water. G. pulex and G. duebeni celticus did not survive in bioassay tubes in areas dominated by C. pseudogracilis, which itself survived in tubes in such areas. However, both C. pseudogracilis and Gammarus spp. survived equally well in tubes in areas dominated by Gammarus spp. Physico-chemical regime thus limits the movement of Gammarus spp. into C. pseudogracilis areas, but some other factor excludes C. pseudogracilis from Gammarus spp. areas. Since previous laboratory experiments showed high predation rates of Gammarus spp. on C. pseudogracilis, we propose that predation by the former causes exclusion of the latter. Hence, presumed effects of physico-chemical regime on macroinvertebrate presence/abundance may often require experimental field testing and appreciation of alternative explanations. Received: 14 June 1999 / Accepted: 20 January 2000     

An intensive study of allozyme variation in freshwater resident and anadromous trout,Salmo trutta L., in western Ireland*

Ten polymorphic enzyme coding loci were assayed using starch gel electrophoresis in anadromous (sea trout) and freshwater-resident trout, Salmo trutta, from two neighbouring river systems draining into Clew Bay in western Ireland. Samples were collected from the Burrishoole and from the neighbouring Newport river system. In the Burrishoole system, two samples were from above waterfalls impassable to migratory trout, two consisted of anadromous smolts or post-smolts and the remainder were freshwater-resident trout from freely accessible areas. There were large differences in gene frequency between trout from above impassable barriers and all others sampled, and these two groups also differed substantially from each other. More minor differences were evident between some other samples, particularly between trout from the upper lake and streams entering it and a stream associated with the lower lake. Two anadromous populations therefore occur in the Burrishoole system. In contrast, no differences were evident in two sampling years between anadromous trout and cohabiting freshwater-resident trout from the upper part of the Burrishoole system. Thus, in the upper part of this system, anadromous trout do not appear to comprise a separate population from non-migratory trout and interbreeding may occur.     

Phylogeographic structure of brown trout Salmo trutta in Britain and Ireland: glacial refugia,postglacial colonization and origins of sympatric populations

The phylogeographical structure of brown trout Salmo trutta in Britain and Ireland was studied using polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) analysis of four mitochondrial DNA segments (16S/ND1, ND5/6, COXIII/ND5 and ND5/12S). Analysis of 3636 individuals from 83 sites–morphotypes revealed a total of 25 haplotypes. These haplotypes were nested in seven two‐step clades. Although there was a clear geographical patterning to the occurrence of derived clades, admixture among ancestral clades was extensive throughout the studied area. A relevant feature of the data was that some populations contained mixtures of highly divergent clades. This type II phylogeographic pattern is uncommon in nature. Clade intermixing is likely to have taken place during earlier interglacials as well as since the Last Glacial Maximum. The anadromous life history of many S. trutta populations has probably also contributed to clade mixing. Based on the data presented here and published data, postglacial colonization of Britain and Ireland most likely involved S. trutta from at least five potential glacial refuges. Probable locations for such refugia were: south of England–western France, east of the Baltic Sea, western Ireland, Celtic Sea and North Sea. Ferox S. trutta, as defined by their longevity, late maturation and piscivory, exhibited a strong association with a particular clade indicating that they share a common ancestor. Current evidence indicates that the Lough Melvin gillaroo S. trutta and sonaghen S. trutta sympatric types diverged prior to colonization of Lough Melvin and, although limited gene flow has occurred since secondary contact, they have remained largely reproductively isolated due to inlet and outlet river spawning segregation. Gillaroo S. trutta may reflect descendents of a previously more widespread lineage that has declined due to habitat alterations particularly affecting outlet rivers. The mosaic‐like distribution of mtDNA lineages means that conservation prioritization in Britain and Ireland should be based on the biological characteristics of local populations rather than solely on evolutionary lineages.     

Long‐term declines in winter body mass of tits throughout Britain and Ireland correlate with climate change

The optimum body mass of passerine birds typically represents a trade‐off between starvation risk, which promotes fat gain, and predation pressure, which promotes fat loss to maintain maneuvrability. Changes in ecological factors that affect either of these variables will therefore change the optimum body masses of populations of passerine birds. This study sought to identify and quantify the effects of changing temperatures and predation pressures on the body masses and wing lengths of populations of passerine birds throughout Britain and Ireland over the last 50 years. We analyzed over 900,000 individual measurements of body mass and wing length of blue tits Cyanistes caeruleus, coal tits Periparus ater, and great tits Parus major collected by licenced bird ringers throughout Britain and Ireland from 1965 to 2017 and correlated these with publicly available temperature data and published, UK‐wide data on the abundance of a key predator, the sparrowhawk Accipiter nisus. We found highly significant, long‐term, UK‐wide decreases in winter body masses of adults and juveniles of all three species. We also found highly significant negative correlations between winter body mass and winter temperature, and between winter body mass and sparrowhawk abundance. Independent of these effects, body mass further correlated negatively with calendar year, suggesting that less well understood dynamic factors, such as supplementary feeding levels, may play a major role in determining population optimum body masses. Wing lengths of these birds also decreased, suggesting a hitherto unobserved large‐scale evolutionary adjustment of wing loading to the lower body mass. These findings provide crucial evidence of the ways in which species are adapting to climate change and other anthropogenic factors throughout Britain and Ireland. Such processes are likely to have widespread implications as the equilibria controlling evolutionary optima in species worldwide are upset by rapid, anthropogenic ecological changes.     

Adult lake sturgeon (Acipenser fulvescens Rafinesque, 1817) occurrence in the Muskegon River system,a Lake Michigan drowned river mouth,USA

Recent advancements in telemetry have allowed managers and researchers to conduct comprehensive studies on the movement ecology of lake sturgeon (Acipenser fulvescens), a species of conservation concern in most of the Laurentian Great Lakes basin. In Michigan waters of Lake Michigan, drowned river mouth systems (a protected lake-like habitat that connects a river to lake) support 4 of 11 remaining lake sturgeon populations. One of those remnant populations is supported by the Muskegon River, a drowned river mouth system consisting of both Muskegon Lake and the Muskegon River. The objectives of this 6-year telemetry study were to determine whether adult lake sturgeon occupied the Muskegon River system outside of the spawning season (defined as March to July), to quantify their use of the system annually, and to identify and characterize patterns in occurrence. A total of 21 adult lake sturgeon implanted with acoustic transmitters were passively monitored throughout the year during 2012–2017. Eighty-two percent of tagged fish at large were detected ≥1 day in the Muskegon River system annually, and tagged lake sturgeon were frequently detected during both spawning and non-spawning time periods. Residency index (i.e., no. detection days/365 days) values indicated that adult lake sturgeon were not only detected throughout the year but that they occupied the Muskegon River system for an average of 130 days each year (residency index = 0.36 ± 0.05 SE) during our most spatially intensive acoustic monitoring in 2016–2017. Additionally, 24% of tagged lake sturgeon were primary residents (i.e., residency index >0.5) of the Muskegon River system in both years. Adult lake sturgeon followed 1 of 3 patterns of occurrence based on individual detection histories, and those patterns varied temporally and by the relative amount of use (i.e., high, medium, and low). Our findings build on previous research that found drowned river mouth systems in Lake Michigan can be important nursery habitats for juvenile lake sturgeon by showing that these habitats also can be used extensively by adult lake sturgeon throughout the year.     

Phylogeography of a freshwater sculpin, Cottus nozawae, from the northeastern part of Honshu Island, Japan

 The fluvial sculpin, Cottus nozawae, is a coldwater-adapted fish distributed in Hokkaido Island and the northeastern part of Honshu Island (Tohoku District), Japan. Mitochondrial DNA (mtDNA) control region sequencing was used to investigate the geographic distribution of genetic variation and phylogeography of C. nozawae. Most populations possessed unique haplotypes, few being shared across river systems. Phylogenetic analysis of the sequences of the mtDNA control region and adjacent regions of C. nozawae revealed three distinct phylogenetic groups that differed by 3.05% to 3.11%, corresponding to distinct geographic regions, Hokkaido Island, northern Tohoku District, and Yamagata Prefecture (southwestern Tohoku District), respectively. The divergence times of three groups were estimated to be about 1.5 million years ago by applying a general rate for mtDNA, suggesting that the divergence among them might have occurred in the early Pleistocene. Divergence among the haplotypes within the group from the northern Tohoku District was also high (1.84%), no haplotypes being shared by local populations in different river systems in this region. Local populations from a single river system in this region comprise a distinct lineage that differed from other river systems. Such genetically divergent population structures among the different regions and river systems are considered to have resulted mainly from long-term isolation and restricted gene flow among river systems, probably promoted by the fluvial benthic life history and low dispersal ability of this species. Received: April 12, 2001 / Revised: December 1, 2001 / Accepted: December 19, 2001     

Sea-level changes, river capture and the evolution of populations of the Eastern Cape and fiery redfins (Pseudobarbus afer and Pseudobarbus phlegethon, Cyprinidae) across multiple river systems in South Africa

Aim The phylogeography of the two closely related species Pseudobarbus afer and Pseudobarbus phlegethon was investigated to assess the association of evolutionary processes, inferred from mitochondrial DNA (mtDNA) sequence variation, with hypothetical palaeoriver systems and other climatic and landscape changes. Location One western and several southern river systems in South Africa. Methods We sampled known populations and confirmed known distribution gaps. This was followed by an assessment of mtDNA control region sequence variation for 31 localities across 17 river systems across the range of the species complex. A map of possible offshore drainage patterns during the last major regression event was constructed based on bathymetry and geological studies. Results The genetic distinction of four major lineages of P. afer strongly correspond with proposed palaeoriver systems. However, a western ‘Forest’ lineage, is widespread across two such proposed systems and is closely related to P. phlegethon on the west coast of South Africa. Both the ‘Krom’ and ‘St Francis’ lineages were identified in the single palaeoriver system proposed for St Francis Bay. A fourth ‘Mandela’ lineage is restricted to the one or two palaeoriver systems proposed for Nelson Mandela Bay. Four minor lineages were identified within the Forest lineage and two within the Mandela lineage. Main conclusions The close relationship between P. phlegethon and the Forest lineage of P. afer can only be explained by a series of river captures. We suggest the Gourits River system as a historical link that could account for this relationship. On the south coast, lower sea levels than at present allowed confluence between currently isolated river systems, offering opportunities for dispersal among these populations. At present, isolation between different river systems rather than dispersal appears to have a dominant influence on mtDNA diversity.     

Freshwater and coastal migration patterns in the silver‐stage eel Anguilla anguilla

The unimpeded downstream movement patterns and migration success of small female and male Anguilla anguilla through a catchment in north‐west Europe were studied using an acoustic hydrophone array along the River Finn and into the Foyle Estuary in Ireland. Twenty silver‐stage A. anguilla (total length, L_T, range: 332–520 mm) were trapped 152 km upstream from a coastal marine sea‐lough outlet and internally tagged with acoustic transmitters of which 19 initiated downstream migration. Migration speed was highly influenced by river flow within the freshwater (FW) compartment. Anguilla anguilla activity patterns were correlated with environmental influences; light, tidal direction and lunar phase all influenced the initiation of migration of tagged individuals. Migration speed varied significantly between upstream and lower river compartments. Individuals migrated at a slower speed in transitional water and sea‐lough compartments compared with the FW compartment. While 88·5% survival was recorded during migration through the upper 121 km of the river and estuary, only 26% of A. anguilla which initiated downstream migration were detected at the outermost end of the acoustic array. Telemetry equipment functioned efficiently, including in the sea‐lough, so this suggests high levels of mortality during sea‐lough migration, or less likely, long‐term sea‐lough residence by silver A. anguilla emigrants. This has important implications for eel management plans.     

The occurrence of Homalothecium nitens (Hedw.) Robins. in Ireland

Abstract

Eight new localities for Homalothecium nitens (Hedw.) Robins are recorded from north Co. Mayo, Ireland. The first observations of H. nitens in fruit in Ireland are reported.     

Genetic diversity and hierarchical population structure of a rare autotetraploid plant,Aster kantoensis (Asteraceae)

We sampled 17 populations of a rare autotetraploid Aster kantoensis (Asteraceae) from three river systems located in central Japan, and studied them for allelic variation at 22 enzyme loci. There was no significant correlation between the actual population size and three genetic diversity parameters, suggesting that the effective population size was very small even for the large populations, i.e., even large populations may still have a high probability of being of recent origin and remain influenced by the founder effect. Compared to other autotetraploid species, the total genetic variation of A. kantoensis is small. The number of alleles and gene diversity of a population were not significantly different among the river systems, although the percentage of polymorphic loci was different. Genetic differentiation among river systems was larger than between populations within the river systems, thereby indicating that gene flow between river systems is small, especially between the Kinu River system and Tama or Sagami River systems.     

Living Rivers: Trends and Challenges in Science and Management

This paper discusses and summarizes the major conclusions of the special issue entitled ‘Living rivers: trends and challenges in science and management’ of Hydrobiologia/Developments in Hydrobiology. It is structured along three lines: (1) Functioning of river systems; (2) Ecological rehabilitation of river systems; (3) Challenges and obstacles to sustainable management. Sustainable river basin management requires a thorough understanding of natural, physical, chemical and ecological processes as well as socio-economic functioning. Environmental rehabilitation of river systems inevitably requires an ecosystem-based approach involving solutions supported by the public. The challenge is to combine ecological and socio-economic sustainability. Rethinking our efforts in both directions must lead to more innovative solutions than those available at present.     

A freshwater‐feeding Lampetra fluviatilis L. population in Lough Neagh, Northern Ireland

Pollan Coregonus autumnalis , caught in the fresh waters of Lough Neagh, Northern Ireland, were scarred by river lamprey Lampetra fluviatilis and adult river lamprey were found for much of the year with full guts, indicating a freshwater‐feeding population.     

A review of the status and decline in abundance of the Irish Hare (Lepus timidus hibernicus) in Northern Ireland

The Northern Ireland Hare Survey documented the distribution of the Irish Hare (Lepus timidus hibernicus). Historical game bag records and other, more contemporary, records of hare distribution were examined. These data indicate how numbers of L. t. hibernicus may have changed over the last 140 years. The results of the Northern Ireland Hare Survey suggested that L. t. hibernicus was widespread throughout Northern Ireland. Current average densities are no more than 0.65 hares/km². Game bag records indicate that hare densities may have been much higher in the past, with a maximum of 138 hares/km² recorded on Crom Estate, Co. Fermanagh, in 1864. Evidence from hare distribution recorded during the Northern Ireland Rabbit Survey indicates that hare numbers declined between 1984 and 1994. Evidence from all sources suggests that L. t. hibernicus has declined in abundance substantially, with present total population estimates for Northern Ireland ranging from 8250 to 21 000 individuals. Flushing data indicate that rushes and hedgerows are important diurnal resting areas for hares. While the principal reason for the decline in numbers of L. t. hibernicus in Northern Ireland is not clear, more species‐rich pasture and provision of areas of cover, such as rushes, may arrest further declines, or indeed promote numbers of hares, particularly in lowland areas.     

Has a river dam affected the life‐history traits of a freshwater prawn?

In recent years, species richness and diversity in aquatic ecosystems has declined as environments are increasingly impacted by anthropic actions. Freshwater prawns are well adapted to survive in a disturbed and heterogeneous environment. For instance, Amazon river prawn (Macrobrachium amazonicum) populations vary in migratory behavior between rivers and estuaries, depending on factors such as dams. However, there is limited information on the influence of environmental conditions on life‐history traits of this species, which we investigate here using two distinct and unconnected aquatic systems, a dammed river and an estuary, in the eastern Brazilian Amazon. The biological characteristics of M. amazonicum populations in the two environments were compared and related to environmental parameters, which differed significant differences between the two environments and between seasons. Dissolved oxygen, precipitation, and temperature varied most significantly with the seasons in both the estuary and river. M. amazonicum prawns in the estuary were larger and heavier than those in the river during rainy periods. The mass–length ratios and condition factor varied significantly between the M. amazonicum populations in the estuary and river, with negative allometric growth (grows faster in length than in weight) predominating in both populations, and condition factor was better in the estuary for males and in the river for females. The relative frequencies of occurrence of the different female maturation stages and the male morphotypes were related to precipitation and turbidity in both environments and also to salinity in the estuary. In these two distinct aquatic systems, the abiotic parameters determined by the seasonal precipitation cycle profoundly influenced the development of this crustacean, despite its ecological plasticity. Overall, the study showed that river damming triggered environmental changes in the freshwater river ecosystem and played a key role in determining the life‐history characteristics of M. amazonicum in these contrasting aquatic systems.