The Trematode fauna of a brackish coastal lagoon in Tasmania

Calvert's Lagoon, a land-locked, brackish lagoon on the south-east coast of Tasmania, Australia, serves as a focus for the life-cycles of a wide variety of digenetic trematodes. A gastropod, Coxiella badgerensis (Johnston), is the only molluscai inhabitant, and it is heavily infected by trematodes throughout the year. The incidence of primary trematode infections was found to vary seasonally, with a peak in autumn. Developmental stages of 17 species from 7 trematode families were recorded in snails collected at the lagoon from April 1976 to September 1978. In order of abundance'of primary infections, the families were: Microphallidae (3spp.), Schistosomatidae (lsp.), Notocotylidae (4spp. 1, Renicolidae (2spp.) Psilostomidae (3spp.) , Heterophyidae (3spp.) and Strigeidae (lsp.). Gravid adults of 9 of these species were found infecting a wide range of birds at the lagoon, including swans, ducks, grebes, dotterels and coots. Two of the flukes, Apatemon gracilis (Rudolphi) and Psilochasmus oxyurus (Creplin) are cosmopolitan; however the geographical distributions of the others are unknown. About 80% of primary trematode infections at the lagoon were caused by the 3 microphallid species: Maritrema calvertensis Smith, Levinseniella tasmaniae (Smith) and Atriophallophorus coxiellae Smith. M. calvertensis and L. tasmaniae have typical 3 host life-cycles, however, A. coxiellae is one of 10 known microphallids that exhibit a reduced life-cycle, with metacercarial cysts being formed in the molluscan host. The daughter sporocysts and xiphidiocercariae of M. calvertensis and L. tasmaniae are distinguished by several morphological characteristics. The behaviour and ecology of the cercariae were also found to differ in ' many respects. There is a distinct periodicity in the patterns of emergence of both cercariae from their snail host, however the cercaria of L. tasmaniae emerges during the day, wiiereas that of M. calvertensis emerges at night. Although both species encyst in the amphipod Austrochiltonia australis gayce)only M. calvertensis is infective to the ostracod, Mytilocypris tasmanica McKenzie. Metacercarial cysts of L. tasmaniae induce a colour change, from green to bright orange, in the amphipod host. The hoary-headed grebe, the most abundant bird at Calvert's Lagoon, harbours the minute adults of each of the microphallids: L. tasmaniae inhabits the intestinal caeca and Maritrema calvertensis and Atriophallophorus coxiellae have overlapping, but different distributions in the lower small intestine. The life-cycles of the three microphallids, the psilostomes Psilochasmus oxyurus and Psilostomum spp.A and B, and the notocotylids Paramonostomum bursae n.sp. and P. caecai n.sp., were demonstrated experimentally. Growth and development in laboratory ducklings were studied. At Calvert's Lagoon, gravid adults of dpatemon gracilis were found in a black duck, and intramolluscan stages were found in C. badqerensis, however no second intermediate host was found. Metacercarial cysts of A. qracilis were found infecting the freshwater Q native fish, Galaxias auratus Johnston, at Lake Crescent, about 100 km NW of Calvert's Lagoon, (life-history notes on A. qracilis and another strigeoid, Diplostomum qalaxiae n.sp., infecting G. auratus at Lake Crescent, are presented in Appendix 2). A comparison was made of the in vitro development of metacercariae of the 3 microphallids developing in C. badgerensis atcalvert's Lagoon, and 4 microphallids, Gynaecotyla hickmani n.sp., G. macrocotylata n.sp., Maritrema eroliae Yamaguti and Microphallus paraqrapsi n.sp., that encyst in an estuarine crab, Paragrapsus gaimardii (M. Edw.), at Bruny Island, about 20 km SW of Calvert's Lagoon (descriptions of the microphallids infecting P. qaimardii are presented in Appendix 3). All of the microphallids produced eggs in vitro; however, the rates of egg production in different culture media varied between species. A direct relationship is suggested between the longevity of each species in its definitive host and its nutritional requirements in vitro, such that very short-lived flukes, like L. tasmaniae, relying on endogenous food reserves, can produce eggs at normal rates in balanced salt solution, whereas relatively long-lived flukes require more complex culture media for normal development. Preliminary investigations of the ecology of other water bodies in Tasmania revealed that the trematodes found at Calvert's Lagoon are widely distributed on the E and NE coasts of Tasmania in enclosed, brackish lagoons inhabited by C. badgerensis. The distributions of these trematodes probably extend to similar water bodies that occur on the Bass Strait Islands and in the SE of the Australian mainland.