Zeacumantus Subcarinatus Research Articles

Significant northern range extension of the non-native batillariid Zeacumantus subcarinatus in Australia, with observations of new habitat usage

The New Zealand batillariid gastropod Zeacumantus subcarinatus has been recorded as an invasive species in Australia since at least 1924, with populations established in rocky shore habitats at multiple locations in Greater Sydney. We observed a large population (10,000+ individuals) of Z. subcarinatus at an estuarine tidal mudflat on the New South Wales mid-north coast, representing a ~ 250 km northern range extension, and the first known record of this species in a sheltered, muddy habitat in Australia. We discuss the possible establishment means of this new population.

Stable isotopes unravel the feeding mode-trophic position relationship in trematode parasites.

Stable isotopes have been sporadically used over the last two decades to characterise host-parasite trophic relationships. The main reason for this scarcity is the lack of an obvious pattern in the ratio of nitrogen stable isotope values (δ15 N) of parasites in comparison to their host tissues, which would be key to understand any host-parasite system dynamics. To circumvent this, we focused on a single snail host, Zeacumantus subcarinatus, and three of its trematode parasites. We used stable isotopes to investigate each host-trematode trophic relationship and shed light on the mechanisms utilised by the parasite to reroute its hosts' biomass. All our trematodes were found to be 15 N-enriched compared to their host, with their δ15 N values strongly related to their feeding behaviours: passive versus active. It was possible to 'rank' these parasite species and assess their 'relative' trophic position using δ15 N values. We also demonstrated that including a broader range of samples (e.g. host food and faeces, multiple parasite life stages) helped understand the metabolic mechanisms used by the various participants, and that using carbon stable isotope values and C:N ratios allowed to identify an important lipid requirement of these trematode parasites. Finally, we show how critical it is to not ignore parasitic infections as they can have a great influence on their host's trophic position. We have shown that by focussing on a single host species and a single taxonomic group of parasites, we can remove a certain amount of variation recorded by broader isotope studies. We hope that these data will ultimately improve our ability to place parasites in food webs, and thus improve our understanding of the connections and interactions that dictate food web dynamics.

Galactosomum otepotiense n. sp. (Trematoda: Heterophyidae) infecting four different species of fish-eating birds in New Zealand: genetically identical but morphologically variable.

Trematodes of the genus Galactosomum are cosmopolitan parasites that infect the intestines of fish-eating birds and mammals. Adults of named Galactosomum species have not been recorded from bird hosts in New Zealand, despite their cercarial stage being known from various studies of the first intermediate host, Zeacumantus subcarinatus. Here we describe a new species of Galactosomum infecting four different piscivorous birds in New Zealand: Caspian terns, red-billed and black-backed gulls and little blue penguins. Specimens from each of these hosts are genetically identical in the genes sequenced, but show considerable morphological variability. Galactosomum otepotiense n. sp. is distinguished from most other members of the 'bearupi-group' in having a single circle of spines on the ventral sucker, and spines, as opposed to scales, over most of the body. It is most similar to G. bearupi and G. angelae, both from Caspian terns in Australia, but differs in the relative sizes of the reproductive organs and in the possession of a very long forebody. Molecular data confirm that G. otepotiense is not conspecific with G. bearupi, but 28S and ITS2 phylogenies show its close relationship to G. bearupi and other Australian species. We use the cox1 sequence to confirm identity with the larval stage infecting Z. subcarinatus, as previously described in the literature. We discuss briefly the relationships between Australian and New Zealand Galactosomum spp. and their hosts, variability between genetically identical specimens found in different hosts and their potential for harm to mariculture economy.

Morphology and molecules resolve the identity and life cycle of an eye trematode, Philophthalmus attenuatus n. sp. (Trematoda: Philophthalmidae) infecting gulls in New Zealand.

Trematodes of the genus Philophthalmus are cosmopolitan parasites that infect the eyes of birds and mammals. They have the potential to affect the survival of their hosts and a few cases of human philophthalmiasis have occurred worldwide. Adults of known Philophthalmus species have never been recorded from bird hosts in New Zealand, despite their cercarial stage being a focus of various studies. Here, we describe a new species of Philophthalmus infecting New Zealand red-billed and black-backed gulls, Philophthalmus attenuatus n. sp. It is distinguished from other marine species of Philophthalmus by its long, thin body shape, consistently longer vitelline field on the left, and its body reflexed at the ventral sucker. We use molecular methods to complete the life cycle of this species, matching it with the larval stage infecting the mud whelk, Zeacumantus subcarinatus, and present a preliminary cox1 phylogeny. In addition, we comment on the validity of some taxonomic characters used to differentiate species of this genus, discuss potential colonisation routes to New Zealand and comment on the potential for zoonotic infection.

Save your host, save yourself? Caste-ratio adjustment in a parasite with division of labor and snail host survival following shell damage.

Shell damage and parasitic infections are frequent in gastropods, influencing key snail host life‐history traits such as survival, growth, and reproduction. However, their interactions and potential effects on hosts and parasites have never been tested. Host–parasite interactions are particularly interesting in the context of the recently discovered division of labor in trematodes infecting marine snails. Some species have colonies consisting of two different castes present at varying ratios; reproductive members and nonreproductive soldiers specialized in defending the colony. We assessed snail host survival, growth, and shell regeneration in interaction with infections by two trematode species, Philophthalmus sp. and Maritrema novaezealandense, following damage to the shell in the New Zealand mud snail Zeacumantus subcarinatus. We concomitantly assessed caste‐ratio adjustment between nonreproductive soldiers and reproductive members in colonies of the trematode Philophthalmus sp. in response to interspecific competition and shell damage to its snail host. Shell damage, but not parasitic infection, significantly increased snail mortality, likely due to secondary infections by pathogens. However, trematode infection and shell damage did not negatively affect shell regeneration or growth in Z. subcarinatus; infected snails actually produced more new shell than their uninfected counterparts. Both interspecific competition and shell damage to the snail host induced caste‐ratio adjustment in Philophthalmus sp. colonies. The proportion of nonreproductive soldiers increased in response to interspecific competition and host shell damage, likely to defend the parasite colony and potentially the snail host against increasing threats. These results indicate that secondary infections by pathogens following shell damage to snails both significantly increased snail mortality and induced caste‐ratio adjustments in parasites. This is the first evidence that parasites with a division of labor may be able to produce nonreproductive soldiers according to environmental factors other than interspecific competition with other parasites.

Molluscan death assemblages from uplifted Holocene terraces, Mahia Peninsula, New Zealand, interpreted from present-day intertidal ecology

Beu, A.G., August 2016. Molluscan death assemblages from uplifted Holocene terraces, Mahia Peninsula, New Zealand, interpreted from present-day intertidal ecology. Alcheringa 41, xxx–xxx. ISSN 0311-5518.Macrofossils from cover beds of marine terraces at Table Cape, Mahia Peninsula, uplifted coseismically ca 250, 1400, 1850 and 3500 years ago are compared with the fauna living on the nearby 200-m-wide intertidal rock platform. The inner platform is dry at low tide, apart from shallow pools containing Diloma aethiops and abundant but unexpected specimens of Zeacumantus subcarinatus and Cominella glandiformis exposed to the sun; all are common fossils in the terrace cover beds. The outer platform is carpeted densely with the alga Hormosira and shelters a diverse fauna, again all common fossils in the terrace cover beds. Sand and gravel containing shell fragments and supporting Zostera sea-grass turf unexpectedly covers ca 5% of the platform in low areas along the east coast. The fossil fauna is listed from 47 samples from two trenches excavated east–west and north–south through the terrace cover beds. Death assemblages of 158 molluscs, including 24 new records as fossils, and 11 taxa in other phyla delimit sediment derived from four shell accumulation sites identified around the present cape: storm beach, high-tidal strand line, hollows in the rock platform and Zostera flats. Up to 32 of the 47 samples (68%) possibly were deposited in Zostera flats; the rest were sand beach accumulations deposited at and near the high-tidal strand line. All fossils common in the cover beds lived on the rock platform. Differences between the deposits in the two trenches result from two factors. Protection along the east coast by protruding tephra beds and an outer rampart armoured with the macroalga Durvillaea prevented erosion of Zostera-supporting sediment which, therefore, was retained after each uplift event. The exposed eastern position of Table Cape also caused sediment to be transported predominantly westwards, onshore on the east coast but away from Table Cape along the north coast.A.G. Beu [a.beu@gns.cri.nz], Paleontology Department, GNS Science, PO Box 30368, Lower Hutt 5040, New Zealand.

Parasitic infection alters the physiological response of a marine gastropod to ocean acidification.

Increased hydrogen ion concentration and decreased carbonate ion concentration in seawater are the most physiologically relevant consequences of ocean acidification (OA). Changes to either chemical species may increase the metabolic cost of physiological processes in marine organisms, and reduce the energy available for growth, reproduction and survival. Parasitic infection also increases the energetic demands experienced by marine organisms, and may reduce host tolerance to stressors associated with OA. This study assessed the combined metabolic effects of parasitic infection and OA on an intertidal gastropod, Zeacumantus subcarinatus. Oxygen consumption rates and tissue glucose content were recorded in snails infected with one of three trematode parasites, and an uninfected control group, maintained in acidified (7·6 and 7·4 pH) or unmodified (8·1 pH) seawater. Exposure to acidified seawater significantly altered the oxygen consumption rates and tissue glucose content of infected and uninfected snails, and there were clear differences in the magnitude of these changes between snails infected with different species of trematode. These results indicate that the combined effects of OA and parasitic infection significantly alter the energy requirements of Z. subcarinatus, and that the species of the infecting parasite may play an important role in determining the tolerance of marine gastropods to OA.

Impacts of a non-native gastropod with a limited distribution; less conspicuous invaders matter too

Most studies focus on fast-spreading invasive species with high impacts, whilst invasive species with restricted distributions tend to be neglected in the ecological literature. The New Zealand gastropod, Zeacumantus subcarinatus, introduced into the Sydney region during the 1920�1930s, typically occurs in rock pools in the mid- to high intertidal. Surveys conducted in 2004 indicated Z. subcarinatus had a restricted distribution, but little is known about whether it is spreading, the environmental conditions that may promote or inhibit its spread, or its interactions with native species. Surveys conducted in 2012 and 2015 showed Z. subcarinatus maintained a similar distribution to that described in 2004. However, rock pools at sites where Z. subcarinatus was present or absent differed in key characteristics. Rock pools at sites lacking Z. subcarinatus had higher cover of macroalgae, reduced cover of bare substratum and higher densities of native gastropods. At invaded sites, there was a significant negative relationship between Z. subcarina- tus and native gastropod densities. Experimental manipulation of Z. subcarinatus confirmed negative effects on the colonization of rock pools by the native gastropod Bembicium nanum, possibly via competition for resources. Impacts on B. nanum were discernable at low and high densities of Z. subcarinatus. By contrast, Z. subcarinatus responded positively to density manipu- lations of B. nanum — possibly higher densities of B. nanum indicate higher resource availability. We have shown that invasive species that have restricted distributions can have significant effects on native fauna and that they potentially deserve more research and management consideration than they currently receive.

Interactive effects of parasitic infection and ocean acidification on the calcification of a marine gastropod

The interactive effects of ocean acidification (OA) and parasitic infection have the potential to alter the performance of many marine organisms. Parasitic infection can affect host organisms' response to abiotic stressors, and vice versa, while the response of marine organisms to stressors associated with OA can vary within and between taxonomic groups (host or parasite). Accordingly, it seems likely that the combination of infection stress and the novel stressors associ- ated with OA could alter previously stable host-parasite interactions. This study is a detailed investigation into the changes to shell growth, dissolution, and tensile strength in the New Zealand mud snail Zeacumantus subcarinatus caused by trematode infection in combination with exposure to simulated OA conditions. This study also tests the effects of reduced pH on snails infected by 3 different trematode species to investigate potential species-specific effects of infec- tion. After a 90 d exposure to 3 pH treatments (pH 8.1, 7.6, and 7.4), acidified seawater caused sig- nificant reductions in shell growth, length, and tensile strength in all snails. Trematode infected snails displayed increased shell growth and dissolution and reduced shell strength relative to uninfected conspecifics. In all measured variables, there were also significant differences between snails maintained at the same pH but infected by different species of parasite. These results indicate that parasitic infection has the potential to alter host organisms' response to OA and that the magnitude of this effect varies among parasite species.

Technical Note: Maximising accuracy and minimising cost of a potentiometrically regulated ocean acidification simulation system

Abstract. This article describes a potentiometric ocean acidification simulation system which automatically regulates pH through the injection of 100% CO2 gas into temperature-controlled seawater. The system is ideally suited to long-term experimental studies of the effect of acidification on biological processes involving small-bodied (10–20 mm) calcifying or non-calcifying organisms. Using hobbyist-grade equipment, the system was constructed for approximately USD 1200 per treatment unit (tank, pH regulation apparatus, chiller, pump/filter unit). An overall tolerance of ±0.05 pHT units (SD) was achieved over 90 days in two acidified treatments (7.60 and 7.40) at 12 °C using glass electrodes calibrated with synthetic seawater buffers, thereby preventing liquid junction error. The performance of the system was validated through the independent calculation of pHT (12 °C) using dissolved inorganic carbon and total alkalinity data taken from discrete acidified seawater samples. The system was used to compare the shell growth of the marine gastropod Zeacumantus subcarinatus infected with the trematode parasite Maritrema novaezealandensis with that of uninfected snails at pH levels of 7.4, 7.6, and 8.1.

Broad geographic analyses reveal varying patterns of genetic diversity and host specificity among echinostome trematodes in New Zealand snails.

Host specificity is a fundamental component of a parasite's life history. However, accurate assessments of host specificity, and the factors influencing it, can be obscured by parasite cryptic species complexes. We surveyed two congeneric species of intertidal snail intermediate hosts, Zeacumantus subcarinatus and Zeacumantus lutulentus, throughout New Zealand to identify the number of genetically distinct echinostome trematodes infecting them and determine the levels of snail host specificity among echinostomes. Two major echinostome clades were identified: a clade consisting of an unidentified species of the subfamily Himasthlinae and a clade consisting of five species of the genus Acanthoparyphium. All five Acanthoparyphium species were only found in a single snail species, four in Z. subcarinatus and one in Z. lutulentus. In contrast, the Himasthlinae gen. sp. was found in both hosts, but was more prevalent in Z. lutulentus (97 infections) than Z. subcarinatus (10 infections). At least two of the Acanthoparyphium spp. and the Himasthlinae gen. sp. are widespread throughout New Zealand, and can therefore encounter both snail species. Our results suggest that host specificity is determined by host-parasite incompatibilities, not geographic separation, and that it can evolve in different ways in closely related parasite lineages.

Differential effects of temperature variability on the transmission of a marine parasite

Temperature variability is particularly pronounced in intertidal systems. The importance of considering this variability has been increasingly recognised, especially in the context of climate change and disease dynamics. Here, we investigated the effects of temperature variability on the transmission of the intertidal trematode Maritrema novaezealandensis. The experimental treatments were 15 °C (control), 15 + 5 °C daily, 15 + 10 °C every second day, 15 + 15 °C every third day (overall equal thermal loading), and a heat wave treatment (15 + 10 °C daily). Daily 6 h incubations were carried out corresponding to daytime low tides over a 12-day period. Effects on output of transmission stages (cercariae) from infected Zeacumantus subcarinatus snail hosts and transmission success of cercariae to Paracalliope novizealandiae amphipod hosts were quantified, as well as the survival of amphipods. Results showed differential effects on output and transmission success. The number of cercariae emerging was similar for treatments with equal thermal loading, but was substantially increased in the heat wave treatment. Transmission success was highest and comparable for the treatments with regular daily temperature increases (i.e. 15 + 5 °C and heat wave), compared to other treatments. Amphipod survival was not affected by temperature treatment directly, but by the number of parasites infecting an amphipod, as well as amphipod sex. These results demonstrate that cercarial output depends mostly on total thermal loading, whereas successful infection of amphipods is determined by total time above 15 °C. Repeated exposure to ~25 °C, as expected under a heat wave scenario, therefore increases both transmission pressure and success, and hence, the risk of parasite-induced mortality in amphipods.

Complex genetic patterns and a phylogeographic disjunction among New Zealand mud snails Zeacumantus subcarinatus and Z. lutulentus

The comparative analysis of genetic structure and phylogeography of marine species can reveal the relative importance of common biogeographic barriers and species-specific evolutionary histories. In the present study, mitochondrial COI sequences from a total of 724 individuals collected from 38 localities throughout New Zealand during 2006 and 2007 were used to examine the genetic structure and demographic histories of the intertidal gastropods Zeacumantus subcarinatus and Zeacumantus lutulentus. For both species, results revealed isolation of populations located along the northern South Island and southern and western North Island, and extensive genetic structure throughout the remainder of their ranges. Despite this, long-distance dispersal and secondary admixture of divergent haplotypes was evident, especially for the widespread Z. subcarinatus. These findings reveal the importance of common barriers to gene flow and highlight how the interaction of inherent dispersal limitations of direct-developing marine organisms and periodic long-distance movements can produce complex genetic patterns.

Parasite-induced behavioural changes to the trade-off between foraging and predator evasion in a marine snail

Trophic interactions in ecological communities not only affect consumer-resource densities, but also induce phenotypic responses that can ripple through a food web to influence prey resources, competitors and other predators (i.e. trait-mediated interactions). Predators affect short-term trade-off decisions in prey species through behavioural alterations, yet the role of parasites in the context of trait-mediated interactions is rarely discussed, despite our extensive knowledge of parasite-induced behavioural alterations. Adding parasites to the picture, the foraging–predation trade-off presents an interesting case where the effects of predator- and parasite-induced behavioural responses occur in conjunction. Empirical studies on the effect of parasites on trait-mediated anti-predator responses are still scarce, especially in marine systems. Our experiments used marine mud snails, Zeacumantus subcarinatus (Batillariidae), infected with the trematode parasites Maritrema novaezealandensis and Philophthalmus sp. to investigate the effects of trematode-induced behavioural alterations on the trade-off between food acquisition and predator avoidance in the presence of a range of predation cues. We found that the time taken to initiate anti-predator responses was overall significantly shorter in M. novaezealandensis-infected snails than in uninfected snails, while it was significantly longer for Philophthalmus-infected snails. In the simultaneous presence of odours from an injured conspecific and a crab predator, however, the reaction time between uninfected and M. novaezealandensis-infected snails did not differ while Philophthalmus-infected snails were still markedly slower than the former groups. Our results demonstrate species-specific parasite-induced behavioural changes in the presence of imminent predation risk. However, effects of the trematodes on overall feeding and fleeing times were not detected in our experiments; thus, the net effect of parasitism on the foraging–predation trade-off remains unknown.

Seasonal dynamics in an intertidal mudflat: the case of a complex trematode life cycle

Seasonal fluctuations of host densities and environmental factors are common in many ecosystems and have consequences for biotic interactions, such as the transmission of par- asites and pathogens. Here, we investigated seasonal patterns in all host stages associated with the complex life cycle of the intertidal trematode Maritrema novaezealandensis on a mudflat where this parasite's prevalence is known to be high (Lower Portobello Bay, Otago Harbour, New Zealand). The first intermediate snail host Zeacumantus subcarinatus, a key second inter- mediate crustacean host, the amphipod Paracalliope novizealandiae, and definitive bird hosts were included in the study. The density (snails, amphipods), abundance (birds), prevalence, i.e. percentage of infected individuals, and infection intensity (snails, amphipods) of the studied organisms were assessed. Furthermore, temperature was recorded in tide pools, where transmis- sion mainly occurs, over a 1 yr period. Overall, the trematode prevalence in snail hosts was 64.5%, with 88.4% of infected snails harbouring M. novaezealandensis. There was a strong sea- sonal signal in prevalence and infection intensity in second intermediate amphipod hosts, with peaks for both parameters in summer (over 90% infected; infection intensity: 1 to 202 parasites per amphipod). This peak coincided with the highest abundance of definitive bird hosts and of small and still uninfected snails present on the mudflat. Our observations indicate that all of the transmission events necessary to complete the complex life cycle of this parasite primarily occur during warmer months.

Effects of ultraviolet radiation on the transmission process of an intertidal trematode parasite

The transmission of parasites takes place under exposure to a range of fluctuating environmental factors, one being the changing levels of solar ultraviolet radiation (UVR). Here, we investigated the effects of ecologically relevant levels of UVR on the transmission of the intertidal trematode Maritrema novaezealandensis from its first intermediate snail host (Zeacumantus subcarinatus) to its second intermediate amphipod host (Paracalliope novizealandiae). We assessed the output of parasite transmission stages (cercariae) from infected snail hosts, the survival and infectivity of cercariae, the susceptibility of amphipod hosts to infection (laboratory experiments) and the survival of infected and uninfected amphipod hosts (outdoor experiment) when exposed to photo-synthetically active radiation only (PAR, 400-700 nm; no UV), PAR+UVA (320-700 nm) or PAR+UVA+UVB (280-700 nm). Survival of cercariae and susceptibility of amphipods to infection were the only two steps significantly affected by UVR. Survival of cercariae decreased strongly in a dose-dependent manner, while susceptibility of amphipods increased after exposure to UVR for a prolonged period. Exposure to UVR thus negatively affects both the parasite and its amphipod host, and should therefore be considered an influential component in parasite transmission and host-parasite interactions in intertidal ecosystems.

Effects of salinity on an intertidal host–parasite system: Is the parasite more sensitive than its host?

Intertidal habitats are characterised by highly fluctuating environmental conditions including varying salinity regimes. Changes in salinity may be gradual or abrupt; for example, heavy rainfall or evaporation during warm periods can either decrease or increase salinity. Trematodes are the most common parasites in intertidal ecosystems and their transmission is known to be highly influenced by environmental conditions. However, effects of salinity on the transmission of intertidal trematodes are not well studied. Here, we investigated the effects of long-term (i.e. several weeks) exposure to different salinities (25, 30, 35 and 40 psu) on the transmission of Maritrema novaezealandensis from its first intermediate snail host ( Zeacumantus subcarinatus) to a second intermediate amphipod host ( Paracalliope novizealandiae), in order to evaluate overall net effects. The following steps were assessed: output of parasite transmission stages (cercariae) from infected snail hosts, survival and infectivity of cercariae, susceptibility of amphipod hosts to infection and survival of amphipod hosts including parasite development within amphipod hosts. Output and survival of cercariae increased with increasing salinity whilst infectivity of cercariae and susceptibility of amphipods to infection were not clearly affected. Survival of amphipods was significantly longer at lower salinities and parasite development in infected amphipods was concomitantly more advanced. Overall, the results suggest that the parasite and the amphipods are differentially affected, and that under normal to increased salinities conditions are more favourable for the parasite than for the amphipod host.

In vitro culture of marine trematodes from their snail first intermediate host

The ability to culture parasites outside their host (i.e. in vitro) is essential for several aspects of parasitological research. Here, a culture medium for marine trematode parthenitae was optimized using Philophthalmus sp. rediae from the intermediate snail host, Zeacumantus subcarinatus. The medium was optimized by sequentially testing the suitability of different levels of osmolality, different commercially available media, and different concentrations of supplemented chicken serum, while controlling for genetic variation among cultures. Philophthalmus sp. rediae survived up to 56days in cultures of the best tested medium, remaining active and continuously shedding cercariae. The broader suitability of the culture medium was tested using five other trematode species from different families (using either the same or other marine snails as first intermediate hosts): Galactosomum sp., Acanthoparyphium sp., Maritrema novaezealandensis, Curtuteria australis, and an undescribed species of the family Opecoelidae. Survivorship of rediae and sporocysts from these species ranged from eight days to 42days. The culture procedures developed here can therefore be used in the future as a system under which to culture marine trematode parthenitae for experimental studies.

Parasitized snails take the heat: a case of host manipulation?

Infection-induced changes in a host's thermal physiology can represent (1) a generalized host response to infection, (2) a pathological side-effect of infection, or (3), provided the parasite's development is temperature-dependent, a subtle case of host manipulation. This study investigates parasite-induced changes in the thermal biology of a first intermediate host infected by two castrating trematodes (genera Maritrema and Philophthalmus) using laboratory experiments and field surveys. The heat tolerance and temperatures selected by the snail, Zeacumantus subcarinatus, displayed alterations upon infection that differed between the two trematodes. Upon heating, snails infected by Maritrema sustained activity for longer durations than uninfected snails, followed by a more rapid recovery, and selected higher temperatures in a thermal gradient. These snails were also relatively abundant in high shore localities in the summer only, corresponding with seasonal elevated microhabitat temperatures. By contrast, Philophthalmus-infected snails fell rapidly into a coma upon heating and did not display altered thermal preferences. The respective heat tolerance of each trematode corresponded with the thermal responses induced in the snail: Maritrema survived exposure to 40°C, while Philophthalmus was less heat tolerant. Although both trematodes infect the same tissues, Philophthalmus leads to a reduction in the host's thermal tolerance, a response consistent with a pathological side effect. By contrast, Maritrema induces heat tolerance in the snail and withstood exposure to high heat. As the developmental rate and infectivity of Maritrema increase with temperature up to 25°C, one adaptive explanation for our findings is that Maritrema manipulates the snail's thermal responses to exploit warm microhabitats.

Distribution and abundance of the introduced gastropod Zeacumantus subcarinatus in the Sydney Region

Zeacumantus subcarinatus is an endemic New Zealand gastropod which was first collected in the Sydney region in 1924. Although records have been maintained on the Australian Museum Database, there has been no formal assessment of its distribution and abundance since then. We undertook timed searches for this invader in 32 locations in the Sydney Region in Autumn 2004. It was present in nine locations, including one not previously recorded—Umina in Broken Bay. Further, Z. subcarinatus had disappeared from eight locations from which it had previously been reported. Population sizes were generally small, with the exception of Kurnell (Botany Bay), with an estimated 10,000 individuals. Comparisons of mobile and sessile fauna in pools confirmed that pools with the introduced gastropod were different from those lacking it, although there was considerable overlap in the ordination (nMDS) plots. Densities of littorinids (predominantly Austrolittorina unifasciata but also Afrolittorina acutispira) were three-fold lower when Z. subcarinatus was present in the pool. Zeacumantus subcarinatus is now present in the four major estuarine systems in the Sydney region and this may allow it to spread to additional locations within these systems. Management, such as manual removal, does not appear to be necessary at this stage, but we recommend a periodic re-examination of its distribution and abundance.