Search

The upper thermal tolerances of 12 New Zealand freshwater invertebrate taxa were compared using a laboratory lethality testing protocol. Temperatures that were lethal to 50% of the test organisms (LT50S), following acclimation to 15°C, generally declined over the 4 day period of the tests. LT50 values after 48 and 96 h exposure ranged from 24.5 to > 34°C and 22.6 to 32.6°C, respectively, indicating that temperatures that occur in summer in many NZ streams and rivers may limit the distribution and abundance of some of these invertebrate species. Larval insects included both the most sensitive species (a plecopteran and two Ephemeroptera) and the most tolerant (the larvae of the elmid beetle Hydora sp.) in this study. The two molluscs studied (Potamopyrgus anti- podarum (Prosobranchia: Hydrobiidae) and Sphaerium novaezelandiae (Bivalvia: Sphaeriidae)) showed high thermal tolerance, whilst two crustaceans {Paratya curvirostris (Atyidae) and Paracalliope fluviatilis (Eusiridae)) were moder- ately tolerant. The effect of a higher acclimation temperature (20°C) on thermal tolerance was also investigated for the three most sensitive species. This appeared to increase the thermal tolerance of the two Ephemeroptera {Deleatidium spp. and

The composition of the hydrobiid fauna in a coastal water of the southern Baltic was studied in 1990/91 at three stations with different sediment characteristics (grain size, organic content). Four species were found (Hydrobia ventrosa, H. ulvae, H. neglecta and Potamopyrgus jenkinsi). H. ventrosa was dominant at all stations. The mean hydrobiid abundances were 4,000 (stn. C), 18,000 (stn. B) and 40,000 (stn. A) ind./m2 respectively. Abundance was found to correlate with the organic content of the sediment. The reproduction and growth of H. ventrosa was studied. Two reproduction phases were observed, one in summer and the other in late autumn. The autumn reproduction peaks were staggered owing to the different growth rates at the various stations. Possible correlations between the differences in shell size of H. ventrosa at the various stations and both sediment characteristics and abundance are discussed.

Farm slurry is an important contaminant of rural catchments in the U.K., causing both major pollution incidents and more subtle chronic effects. An ecological and ecotoxicological assessment of contaminated (Clarbeston Stream) and uncontaminated (Deepford Brook) river stations revealed significant differences in the abundance of invertebrate taxa and sublethal effects on the amphipod Gammarus pulex. Fewer Leuctridae, Rhyacophilidae, Limnephilidae, Limnius volckmari, Elmis aenaea, Potamopyrgus jenkinsi and G. pulex were found in the contaminated stream and the feeding rate of caged G. pulex was also reduced. There was no significant reduction in either macroinvertebrate abundance or G. pulex feeding rate below the confluence of the contaminated and uncontaminated streams.

International audience; The monitoring of contaminated environments via multilevel biomarker studies is a classical approach in ecotoxicology. Nevertheless, mechanistic links are rarely set up between the different levels of biological organization (sub-organism, organism, population). Population models are now recognized as useful tools to solve this extrapolation issue in predictive approaches, but environmental realism of these models could be improved in order to yield more pertinent risk assessment at the population level. This work proposes a new way to take advantage from the complementary nature of population modelling and in situ caging methodologies. On the basis of case studies with two environmental relevant species, the main purpose is to improve the extrapolation procedure by linking in situ biomarkers classically used in ecotoxicology at the organism level (laboratory bioassays or in situ biotests) and their consequences at a level of ecological interest: the population. Our approach proceeds in two steps. (i) Population models are developed to mechanistically link life history traits (survival, growth, reproductive activity, fecundity) and the dynamics of reference native populations all along a year. For this, we use a dual approach combining laboratory and field experiments. The latter consisting in a demographic follow-up based on monthly population census (evolution of densities and age-size structures) and an individual approach with field organisms caged in situ (reproduction, growth, survival). (ii) Effects of contamination, observed at the organism level through the exposure of transplanted individuals caged in contaminated stations, will be projected into the dynamics of these reference populations in order to propose a diagnostic assessment of water quality at the population level.

The relationships among four species of the molluscan genus Potamopyrgus have been investigated using cellogel electrophoresis. Electrophoretic variability at nine presumptive loci was calculated. Cladograms were constructed using both electromorph and locus as characters. Results indicate two major groupings within the genus. P. estuarinus and P. pupoides appear to represent sister taxa and, as a grouping, are closely related to P. antipodarum. The relationship of P. troglodytes to other species of the genus remains problematical. The cladograms obtained are congruent with that based on morphology with respecttoP. antipodarum, P. estuarinus, and P. pupoides.

The trematode Microphallus sp. alters the behavior of its snail intermediate host, Potamopyrgus antipodarum, in ways that seem to increase transmission to its final host, e.g., waterfowl, and decrease the probability of being eaten by other predators, e.g., fish. The parasite seems to cause the snail to move from the top to the bottom of rocks at about 0900 hr. Waterfowl feed predominantly before 0900 hr, and fish feed predominantly after 0900 hr. In the present study, we tested the hypothesis that Microphallus sp.-infected snails exhibit a change in behavior at around 0900 hr by examining their response to light and vertical orientation before and after 0900 hr. Results demonstrated that uninfected snails generally move toward light, oriented downward, and move a greater distance in the light compared with the dark at all times of day. Microphallus sp.-infected snails behaved differently from uninfected snails in the early morning but similarly to uninfected snails in the late morning with regard to downward orientation and distance moved in response to light. Snails infected with parasites other than Microphallus sp. behaved similarly to uninfected snails during both time periods. These results suggest that Microphallus sp. manipulates the behavior of Potamopyrgus sp. by altering rates of movement in response to light and vertical orientation in a manner consistent with the hypothesized 0900-hr shift.

Granular activated carbon (GAC) adsorbers are often the penultimate stage of surface water treatment and provide ideal habitats for invertebrates. Proliferation of chlorine-resistant invertebrates in GAC adsorbers may lead to their efflux into distribution systems, possibly resulting in contamination of customers' tap water. GAC adsorber sampling and laboratory experiments were undertaken to determine the effects of routine backwashing on GAC adsorber populations of the chlorine-resistant snail Potamopyrgus jenkinsi at a water treatment works. GAC adsorber sampling results suggested that routine backwashing altered the spatial distribution of snails, but not their overall abundance. In small-scale glass columns 40-50% of the smallest (0.3-0.6 mm shell height) juvenile snails were removed by a GAC backwash bed expansion of 30-40%; however, bed expansions of greater than 20% were not possible in the GAC adsorbers.

We studied the role of host ploidy and parasite exposure on immune defence allocation in a snail–trematode system (Potamopyrgus antipodarum-Microphallus sp.). In the field, haemocyte (the defence cell) concentration was lowest in deep-water habitats where infection is relatively low and highest in shallow-water habitats where infection is common. Because the frequency of asexual triploid snails is positively correlated with depth, we also experimentally studied the role of ploidy by exposing both diploid sexual and triploid asexual snails to Microphallus eggs. We found that triploid snails had lower haemocyte concentrations than did diploids in both parasite-addition and parasite-free treatments. We also found that both triploids and diploids increased their numbers of large granular haemocytes at similar rates after parasite exposure. Because triploid P. antipodarum have been shown to be more resistant to allopatric parasites than diploids, the current results suggest that the increased resistance of triploids is because of intrinsic genetic properties rather than to greater allocation to defence cells. This finding is consistent with recent theory on the advantages of increased ploidy for hosts combating coevolving parasites.

We studied herbivory and grazer performance (i.e., fitness correlates) for the hydrobiid snail Potamopyrgus antipodarum, the leptophlebiid mayfly Deleatidium spp., and the conoesucid caddisfly Pycnocentrodes aeris, common, co-occurring algivores in many New Zealand streams. Grazing effects and costs of coexisting differed among these taxa reared at ambient densities in different combinations in microcosms with algal food conditions (on clay tiles) characteristic of heavily grazed streams. The prostrate diatoms Staurosirella leptostauron, Cymbella novazealandia, and Achnanthidium minutissimum were the dominant algal species on pre- and post-grazed tiles. The relative abundance of erect physiognomic forms, dominated by Synedra ulna and Fragilaria vaucheriae, were 2–3× higher in ungrazed controls and in snail alone treatments than in other grazer treatments. The green filamentous algae Mougeotia sp. and Stigeoclonium lubricum, and the cyanophyte Merismopedia glauca were present only in ungrazed controls. Grazers significantly reduced algal community biomass in treatments by 26–52% relative to controls, except snails alone. Snails (15–30%) burrowed into surrounding sand substrates, dampening their grazing impact on tiles. Caddisflies were more effective than mayflies or snails at removing algae because of higher foraging rates, a larger body size, and an abrasive sand-grained case. Algal biomass reductions did not affect grazer growth. However, pre-pupation rates of caddisflies and emergence rates of subimago mayflies were significantly higher in caddisfly-alone and mayfly-alone treatments, respectively, than in combined-species treatments. These results imply that a limited periphytic food supply ( < 0.3 mg AFDM cm−2) even over a relatively brief period ( ≤ 16 d) may have population-scale consequences for co-existing P. aeris and Deleatidium spp.

Parasitism often influences the phenotype of individuals. Many of the resulting changes are due to changes in resource allocation that come with infection. Here we examine the effect of a trematode parasite on the shape and defence morphology of a New Zealand freshwater snail, Potamopyrgus antipodarum. The trematode Microphallus sp. asexually produces hundreds of metacercarial cysts in the snail. The length, width and 2-dimensional area of each snail were measured. Snails were also assessed for their degree of spininess. Snails were dissected to determine gender, brooding condition and parasitism. Snails infected with Microphallus sp. were found to be significantly less spiny than uninfected snails. Microphallus-infected snails were also found to have a significantly greater width to length ratio at larger sizes than their uninfected counterparts. These trends could be explained in at least 3 ways. (1) Infection causes the snails to not produce spines and to become wider. (2) Spiny and narrower snails are more likely to die when they become infected. (3) Spiny and narrower snails are more resistant to infection. The changes in phenotype observed are unlikely to be adaptive for either the host or parasite and probably represent physiological by-products of the host-parasite relationship.

The small aquatic snail Potamopyrgus antipodarum is an important invading species in Europe, Australia and North America. European populations are generally believed to derive from accidental introductions from New Zealand, probably dating back to the mid-19th century. We have employed mitochondrial DNA sequences to test the proposed New Zealand origin of European Potamopyrgus, and to learn more about its genealogical history. Using a 481-bp region of the 16S ribosomal RNA gene, we identified 17 distinct haplotypes among 65 snails from New Zealand. In marked contrast, only two haplotypes were found across all European samples, which cover a large geographical area. Importantly, these two haplotypes are shared with snails from the North Island of New Zealand. Due to sampling limitations we cannot rule out a South Island origin for one of the haplotypes, but our results clearly demonstrate the New Zealand origin of European populations. The marked divergence among the two European haplotypes implies the successful colonization by two distinct mitochondrial lineages, which is consistent with previous data based on nuclear markers.

Background The outcome of parasite exposure depends on the (1) genetic specificity of the interaction, (2) induction of host defenses, and (3) parasite counter defenses. We studied both the genetic specificity for infection and the specificity for the host-defense response in a snail-trematode interaction (Potamopyrgus antipodarum-Microphallus sp.) by conducting a reciprocal cross-infection experiment between two populations of host and parasite. Results We found that infection was greater in sympatric host-parasite combinations. We also found that the host-defense response (hemocyte concentration) was induced by parasite exposure, but the response did not increase with increased parasite dose nor did it depend on parasite source, host source, or host-parasite combination. Conclusion The results are consistent with a genetically specific host-parasite interaction, but inconsistent with a general arms-race type interaction where allocation to defense is the main determinant of host resistance.

Measurements of shell growth rate showed that a difference in the population structure of Potamopyrgus jenkinsi between the northern and the southern shore of a small Dutch lake could be a result of food quality of the sediment. In further studies, a series of diets differing in organic C and N content was offered to the snails. There was no functional relationship between growth rate and C or N content of the diets. Growth rate plotted against the C/N ratios of the diets followed an optimum curve with a maximum at a C/N value of 15.9. Highest growth rate was followed by successful reproduction. In the lower C/N range, growth rate rapidly increased with small increases in C/N values. This kind of relationship supports previously disregarded findings for Artemia.

The role of invasions has been repeatedly discussed and elucidated in Russian and foreign literature [1‐4]. Problems related to invading species are especially acute in water bodies of arid zones, manly closed water bodies, such as the Caspian Sea, the Sea of Azov, and formerly the Aral Sea. The Sea of Azov and its catchment area are among the most vulnerable ecosystems. This is mainly because the sea is relatively (incompletely) isolated (a continental body of water) and has an unstable hydrological and hydrochemical regimen, which allows invaders with a potentially wide capacity for osmoregulation to adapt. This is entirely true for the catchment areas of the above seas (including the Don, Kuban’, Volga, Ural, Kuma, Syr-Darya, and smaller rivers). These rivers serve as a reserve of the Pontocaspian relict fauna, which is very sensitive to all environmental changes, including invasions. The expansion of invading species may be strikingly rapid. One example is the finding of Potamopyrgus jenkinsi in the Don basin in June and July of 2007. Potamopyrgus Stimson, 1865 was first found in Europe in the late 19th century (the species Potamopyrgus jenkinsi (Smith, 1889) described from the Themes mouth). During the 20th century, Potamopyrgus was found in many regions of Europe. The species composition of the genus Potamopyrgus in the area of invasion is still a matter of discussion. It has been hypothesized that all European Potamopyrgus belong to the same New Zealand species P. antipodarum (Gray, 1843), that there are several species in Europe [5], and that two discrete lineages (clones) have invaded Europe in different periods from different local populations of New Zealand [6, 7]. The existence of a number of European species (probably, pure parthenogenetic strains) of Potamopyrgus differing in ecology and salinity preferences that have no analogues in the New Zealand fauna, as well as some paleontological data, allowed Anistratenko [5] to hypothesize that they are autochthonous in Europe. Anistratenko regards ecologically different strains of Potamopyrgus as separate species P. jenkinsi ; P. alexenkoae Anistratenko in Anistratenko et Stadnichenko, 1995; and P. polistchuki Anistratenko, 1991. Molecular genetic studies on Potamopyrgus from some Western European habitats demonstrated the existence of two strains both genetically and morphologically differing from each other [6, 7]. They are assumed to have invaded from isolated habitats on the North Island of New Zealand in different periods of time. Potamopyrgus may also form new pure strains or species in the area of invasion (saltatory speciation, which is possible for clonal invading species) [8].

Dugesia polychroa, D. lugubris and Planaria torva preyed upon snails of differing morphologies and while the Dugesia spp. fed approximately in proportion to snail abundance, PL torva was more selective on Potamopyrgus jenkinsi. The incidence of feeding on four snail taxa by the Dugesia spp. was significantly correlated and differed strikingly from that of PI. torva where feeding was related to its annual life cycle. Large peaks of feeding coincided in the Dugesia spp. for the four snail types; this was attributed to snail vulnerability being increased by environmental disturbance. Comparison of feeding by Dugesia spp. in the presence and absence of PI. torva indicated that severe competition was occurring for food with PI. torva having a food refuge in P. jenkinsi. The distribution of PI. torva in Britain is largely confined to productive habitats in the Glasgow-Edinburgh and East Anglia regions. It is concluded that historical rather than ecological events have played the major part in its distribution to date. The strong association of PL torva with port areas and the canal system suggests that it is a recent introduction via the timber trade with Fennoscania.

Populations of coexisting and of allopatrically occurring species of hydrobiid snails (Hydrobia ulvae, H. neglecta, H. ventrosa and Potamopyrgus jenkinsi) have been studied in 90 localities within three different areas. When H. ventrosa coexists with H. ulvae they show character displacement, i.e., the average body size of the former is smaller and that of the latter is larger. When these species live alone they are of approximately the same size. It is shown here that the size ratio between the coexisting species usually found (1.3-1.5) allows stable coexistence based on food praticles size selectivity alone. Variation in the degree of character displacement from locality to locality is explained by different degrees of genetical isolation of the populations. Coexisting H. ventrosa and H. ulvae have shorter, more well-defined periods of reproduction than they do when they occur alone. H. neglecta is larger than coexisting H. ventrosa and smaller than coexisting H. ulvae. Due to the patchy distribution and the fluctuating populations of this species, and due to the fact that pure H. neglecta populations are rare, data on this species are difficult to interpret. Potamopyrgus jenkinsi shows a different food particle size selection than the Hydrobia spp. of identical sizes. Competitive interactions between P. jenkinsi and coexisting Hydrobia spp. are therefore probably weak. In accordance with this, P. jenkinsi does not show character displacement when coexisting with, e.g., H. ventrosa.The fact that the major study area, the Limfjord, is only 150 years old as a marine habitat as well as various more recent man-made changes of the coast line allow estimates of the time scale of the microevolutionary changes which lead to character displacement.

Macroinvertebrates from six macro‐phyte communities and from an intermittently vegetated sublittoral community were collected from Lake Alexandrina during a period of 2.5 years. Each of the six communities was dominated by one native species (Myriophyllum triphyllum, Isoetes alpinus, Chara fibrosa var. acanthopitys or Chara globularis) or by the adventive Elodea canadensis. Thirteen of the 21 macroinvertebrate taxa associated with these communities were herbivores and/or detritivores and these contributed at least 90% to total abundance; the remaining eight were predators. The gastropod Potamopyrgus antipoda‐rum was dominant in all communities; overall, gastropods (four species) contributed between 66 and 90% to total abundance. A few species showed a marked preference for certain communities. Seasonal changes in macroinvertebrate abundance and biomass are discussed and the results compared with those from other New Zealand lakes. Biomass data for all communities and the extent of the oscillation...

Both Hydrobia ulvae (Pennant) and Potamopyrgus jenkinsi Smith climb vertically in the laboratory but stop or crawl horizontally if presented with a sharp salinity drop. 50% of Hydrobia ulvae respond to a difference of 18–26% from the original solution. 50% of Potamopyrgus jenkinsi respond to a difference of 53–55%. In both species, the response is impaired at high temperatures, and in Hydrobia ulvae it is also impaired at low temperatures. From 9–22 °C no temperature influence is evident. From acclimation experiments it is suggested that the snails respond not to the gradient across the interface, but to the gradient between body fluids and the upper solution presented. Snails respond to non-ionic gradients when these are presented either as density gradients or as solutions separated by a semi-permeable membrane, and it is argued that they detect osmotic pressure directly. The sense organs are probably located in the tentacles.

The defence reaction of operculum closing in response to the presence of the molluscivorous leech Glossiphonia complanata (L.) and the non-molluscivorous Erpobdella octoculata (L.) was studied in four species of freshwater prosobranch gastropod. Bithynia tentaculata (L.) and Valvata piscinalis (Muller) can distinguish between the leeches, reacting only to G. complanata. V. piscinalis is capable of a greater degree of distance chemoreception of the leech ‘scent’. Valvata cristata Muller and Potamopyrgus jenkinsi (Smith) did not react to either leech. V. cristata may not be a potential prey item for G. complanata, while P. jenkinsi is fed on by the leech, but is a relative newcomer to the freshwater fauna.

Une prospection malacologique effectuee en octobre 1980 confirme l’extension en Corse de Potamopyrgus jenkinsi. Toutefois deux types de gites semblent pouvoir etre distingues : les uns ou Potamopyrgus est particulierement abondant et d’ou Isidora truncata (= Bulinus truncatus) a disparu ; les seconds ou des Potamopyrgus en nombre plus reduit coexistent avec les Bulins. L’anciennete de la colonisation par Potamopyrgus conduit a penser qu’il ne s’agit pas, dans ces derniers gites, d’une phase preliminaire de contamination, mais de l’etablissement d’un etat d’equilibre.

The four species of Hydrobiid mudsnails found in Danish brackish water habitats are ranked with respect to reproductive effort. The biology of the species indicate that Hydrobia neglecta and Potamopyrgus jenkinsi, showing the highest reproductive effort are also more r-selected than the other species, H. ventrosa and H. ulvae.

Summary Figures are presented for the proportions of the sexes and shell types in collections of the fresh water prosobranch Potamopyrgus from area of Australia. Findings are compared with those from populations in New Zealand. N.B. Representative material from these collections has been deposited in the Australian Museum, Sydney, and from the Victorian localities, also in the National Museum of Victoria, Melbourne.

Potamopyrgus jenkinsi n’est pas un vecteur intermediaire de Fasciola hepatica. Dans les habitats a Limnees tronquees soumis a une dessiccation periodique, ce Mollusque ne survit pas : la presence d’un niveau d’eau permanent est necessaire. Dans ces conditions, Lymnaea truncatula est tres sensible a la competition exercee par Potamopyrgus.

SynopsisThree main types of Hebridean freshwater lochs occur in the Loch Druidibeg National Nature Reserve; eutrophic calcareous machair lochs near the Atlantic coast, mesotrophic lochs on the edge of the moor and oligotrophic lochs on the peatlands. Chloride/calcium concentrations, highest in lochs near the sea, fall away rapidly inland and are lowest in the moor lochs. The fauna of eutrophic and mesotrophic lochs includes a few euryhaline brackish-water species Potamopyrgus jenkinsi, Diaptomus wierzejskii, Neomysis integer and Gammarus duebeni. G. duebeni alone penetrates the oligotrophic lochs. Freshwater sponges are widespread but are absent from the machair lochs and there are no triclad planarians. The fauna of fast and slow stream segments is described. Loch Bee, a man-made lagoon, unlike the open brackish lochs of North Uist, is an unstable habitat and its fauna has changed considerably since it was investigated in 1933. The fauna consists mainly of brackish-water species and a few stenohaline marine species which are confined to its seaward ends. The sequence of faunistic change in the Howmore estuary, Lochs Roag and Fada, a Site of Special Scientific Interest (SSSI), is described; the brackish-water fauna is reduced by the volume of fresh water passing through the system. A brief account is given of the unusual dominance of Hyalinella punctata and Potamopyrgus jenkinsi in Loch Ardvule (SSSI), South Uist.

The diet of brown trout (Salmo trutta) and rainbow trout (S. gairdnerii) was studied in specimens from Lake Benmore, a deep, oligo‐trophic lake in South Island, New Zealand. Between November and July, both species fed mainly on small molluscs (Potamopyrgus antipodarum, Physa sp., and Gyraulus corinna) gleaned from the littoral weed beds. Energy values for the three species of mollusc were determined: P. antipodarum, 6000 J g‐1; G. corinna, 5500 J g‐1; Physa sp., 9800 J g‐1. Potamopyrgus antipodarum yielded little energy to the fish, unless its shell broke during passage through the gut. Physa sp. was the most profitable mollusc, irrespective of shell breakage and Potamopyrgus antipodanim the least profitable. The mean energy value per snail for G. corinna and Physa sp. eaten by rainbow trout was 25–30% less than for snails eaten by brown trout, possibly because rainbow trout ingested empty shells from the sediment surface. Rainbow trout extracted about 20% more energy than brown trout from unbrok...

SUMMARYThe occurrence, in September 1979, of Echinoparyphium recurvatum metacercarial cysts in a community of molluscan hosts at Harting Pond, West Sussex, was investigated. The parasite exhibited broad host specificity with all 7 species comprising the molluscan community being infected. There were marked differences, however, in the extent to which each host species was utilized and using the mean number of parasites/ individual mollusc as a parameter of infection the mollusc species may be ranked in descending order of utilization as follows: Sphaerium corneum, Lymnaea peregra, Valvata piscinalis, planorbids, Pisidium subtruncatum and Potamopyrgus jenkinsi. Combination of basic infection data with population estimates for each mollusc species in the study area showed that the bivalve P. subtruncatum and the prosobranch V. piscinalis were the most important hosts because they contained approximately 90% of the total number of cysts. In both of these hosts the cyst population was over-dispersed and the degree of over-dispersion increased with host size. The pattern of second intermediate host utilization is discussed in relation to the likely flow of E. recurvatum between the first intermediate host (L. peregra) and wildfowl definitive hosts at Harting.

The population of sand smelt, Atherina presbyter, breeding in the Fleet, Dorset, shows a high infection of diplostomiasis. The population was studied in 1983 to clarify aspects for this parasitic condition previously analysed for the sand smelt population at Fawley, Southampton Water. All age classes showed a higher percentage infection and mean number of metacercaria per fish than at Fawley. Analysis of postlarvae and juveniles showed that infection can occur at 1 week old, and verified the hypothesis that the scales of older fish inhibit cercarial settlement. Circumstantial evidence suggests that Potamopyrgus jenkinsi may be the first vector host for this parasite, and the densities of this species and of nesting little tern colonies would account for the differential infection between these two sand smelt populations. The increase in infection of 2 fish at Fawley cannot be attributed to mixing with the Fleet population, and the different infection levels demonstrate population isolation. High levels of infection are limited to this part of the English Channel: sand smelt samples from around the coasts of the British Isles show minimal infection rates elsewhere and suggest a southerly distribution of the parasite, away from Atlantic oceanic waters.

SUMMARY. 1. Predation on the mollusc genera Potamopyrgus, Bithynia, Valvata, Lymnaea, Physa, Planorbis and Pisidium by the leeches Glossiphonia complanata (L.) and Helobdella stagnalis (L.) was examined in five eutrophic lakes at monthly intervals over one year using a serological technique. 2. Feeding intensity varied seasonally, being lowest in winter and highest in summer. Small, medium and large leeches preyed to the same extent on the several mollusc genera; this was true for both leech species. Qualitatively, the diet of both glossiphoniids was similar throughout the year. Snail genera were consumed in proportion to their relative abundance in the field. Quantitatively, Glossiphonia preyed more heavily on snails than did Helobdella. 3. It is concluded that both leech species are opportunistic predators.

The distribution of the mud snails Hydrobia ventrosa (Montagu), H. neglecta Muus, and Potamopyrgus jenkinsi (Smith) was studied in the Kysing Fjord estuary, Denmark, from November 1977 to February 1979. The hydrobiids show habitat selection with regard to salinity but coexist in large areas of the estuary: P. jenkinsi at the innermost parts of the estuary together with H. ventrosa, with the latter species extending its distribution further to the mouth of the estuary, where H. neglecta dominates. H. ventrosa and H. neglecta are the only species that have permanent populations in the estuary. P. jenkinsi dies out in the estuary in the winter, but recolonizes there from a small river in the spring and builds up a population in the innermost parts of the estuary during the summer. H. ventrosa and H. neglecta coexist in the middle part of the estuary due to continued dispersal into this area.

96-h acute toxicity tests were made, using a flow-through system, to determine the toxicity of ammonia and copper to Potamopyrgus jenkinsi . Both lethal and sub-lethal behavioural responses were monitored for three different age groups of snail—juvenile, prime adult and senescent. Juvenile snails were much less tolerant than adults of both toxicants. Senescent adults were also less tolerant of ammonia than prime adults. 96-h LC 50 values of 0·315, 0·49 and 0·85 mg N litre −1 unionised NNH 3 and 0·054, 0·079 and 0·077 mg Cu litre −1 total copper were recorded for juveniles, senescent adults and prime adults, respectively, in separate experiments. EC 50 values were clearly lower in adult snails. Potamopyrgus jenkinsi was relatively intolerant of both ammonia and copper compared with other invertebrate taxa reported in the literature. It is concluded that Potamopyrgus jenkinsi could be a valuable indicator species of these pollutants.

The author's earlier ideas on the distribution and systematics of New Zealand Hydrobiidae are reviewed and revised. There are two main components to the fauna — an ancient subterranean group whose ancestors were widespread before rifting of Gondwanaland and have a distribution taking in New Zealand, Europe and Japan, and a more recently evolved group. The more recent group was probably a Gondwanian development and is typified by Australasian Hemistomia group and Fluviopupa group genera such as Potamopyrgus Stimpson and Opacuincola Ponder. Kuschelita Climo, 1974 and Phreatica Velkovrh, 1970 are synonymised with Saganoa Kuroda and Habe, 1958, the latter elevated from sub generic ranking in Akiyoshia Kuroda and Habe, 1954. Iglica Wagner, 1927 may be an earlier name for this complex. The genus Horatia Bourguignat, 1887 is tentatively introduced to the New Zealand fauna with description of a new species, H. nelsonensis. Opacuincola troglodytes Climo, 1974 is transferred to Potamopyrgus. Potamopyrgus c...

Population density, biomass, growth and reproduction rate of the gastropods Lymnaea peregra (Muller) and Potamopyrgus jenkinsi (Smith) were monitored over a 21 month period in three experimental earth channels, one carrying clean river water and the others 25 and 50% treated sewage effluent mixed with river water. Each channel was divided into riffle and pool stretches; the abundance and biomass of both species were higher in the riffles. The abundance and biomass of L. peregra were significantly greater (P < 0.01) in the riffle in the presence of effluent. Concentration of effluent did not have a significant effect on abundance or biomass. The abundance and biomass of P. jenkinsi were significantly greater (P < 0.001) in riffle and pool in the absence of effluent. In addition, the abundance and biomass of P. jenkinsi were significantly greater (P < 0.05) in the 25% effluent channel than in 50% effluent. No significant differences in the growth of L. peregra between channels were observed. The average number of eggs and of egg masses laid by L. peregra was significantly greater (P < 0.01) in riffle and pool in the presence of effluent. In the riffle, significantly more masses (P < 0.05) and more eggs per adult (P < 0.01) were laid in the 25% effluent channel than in 50% effluent. No differences were observed in the reproduction rate per adult of P. jenkinsi between the 0 and 25% effluent channels. It is concluded that population differences between channels are probably largely the result of differing mortality rates.

The edibility of two endemic Australian macrophytes (Ottelia ovalifolia and Triglochin procera) to three species of herbivorous stream invertebrates (Triplectides ciuskus and Notalina fulva: (Trichoptera: Leptoceridae) and Potamopyrgus niger (Gastropods: Hydrobiidae)) was investigated. Each macrophyte species was offered to the test animals in 5 different conditions: fresh, boiled, and three conditions of decomposition. In 5 out of 6 feeding trials, consumption rates of animals were greatest on decomposed tissues. Boiling increased edibility of both plant species to Triplectides larvae and of Triglochin to Notalina larvae. Boiled tissue was consumed least by Potamopyrgus. Analysis of nitrogen, phosphorus, and calorific content of macrophyte tissue and some terrestrial plant materials known to be eaten by the animals suggested that nutritional enrichment of decomposed and boiled tissues was unlikely to explain their greater edibility. Instead, the loss of anti-gustatory compounds is implicated.

Osmotic balance was studied in Hydrobia ulvae and Potamopyrgus jenkinsi over the range 100% sea water to fresh water, by determining the freezing-point depression of the urine in the different solutions. Hydrobia ulvae was slightly hyperosmotic from 100 to 50 % sea water, and sometimes initially markedly hyperosmotic in 25 % sea water at 5° C. The urine was always markedly hyperosmotic relative to fresh water, and the animals were withdrawn. Experiments with phenol red indicated that the tissues were not shut off from the medium. Potamopyrgus jenkinsi was hyperosmotic from fresh water to 100% sea water. Osmotic balance in fresh water is maintained in part by the excretion of a urine hypo-osmotic relative to the blood. There was some variation in the reaction of different ecological groups of Hydro-bia ulvae and Potamopyrgus jenkinsi to the experimental conditions. In the Hydrobiidae, whether transformed from a lower to a higher salinity or vice versa, survival outside the viable range was longer at 5° C. than at 15° C., although, within the range, activity occurred more rapidly at 15° C. In fresh water, winter animals of both species had a higher osmotic concentration of the urine than summer animals, but no differences in osmotic concentration correlated with temperature were demonstrated.

Summary Potamopyrgus antipodum has been found in thermal waters only at temperatures below 28°c. Experimental work indicates that 28°c represents the temperature at which snail activity is first curtailed when temperatures are progressively raised. Although the reduction in available oxygen found at high temperatures appears to have some effect on snail activity, the increase in temperature itself is the major factor depressing activity and consequently limiting snail distribution. No difference in the temperature at which activity is reduced has been found between snails living at different environmental temperatures. When temperature was raised 1°c/24 hours, heat death occurred at 30–32°c.