Effects of salinity on multiplication and transmission of an intertidal trematode parasite
Salinity levels vary spatially in coastal areas, depending on proximity to freshwater sources, and may also be slowly decreasing as a result of anthropogenic climatic changes. The impact of salinity on host–parasite interactions is potentially a key regulator of transmission processes in intertidal areas, where trematodes are extremely common parasites of invertebrates and vertebrates. We investigated experimentally the effects of long-term exposure to decreased salinity levels on output of infective stages (cercariae) and their transmission success in the trematode Philophthalmus sp. This parasite uses the snail Zeacumantus subcarinatus as intermediate host, in which it asexually produces cercariae. After leaving the snail, cercariae encyst externally on hard substrates to await accidental ingestion by shorebirds, which serve as definitive hosts. We found that at reduced salinities (25 or 30 psu), the cercarial output of the parasite was lower, the time taken by cercariae to encyst was longer, fewer cercariae successfully encysted and encysted parasites had lower long-term survival than at normal seawater salinity (35 psu). The strong effect of salinity on the replication and transmission of this parasite suggests that there may be sources and sinks of transmission to birds along coastal areas, depending on local salinity conditions. Also, unless it evolves to adapt to changing conditions, the predicted reduction in salinity as a consequence of climate change may have negative impact on the parasite’s abundance.
KeywordsSalinity Level Salinity Treatment Snail Host Infected Snail Trematode Parasite
We thank Anja Studer, Tommy Leung and Christoph Matthaei for assistance with logistical and statistical aspects of this study and Melanie Lloyd, Devon Latoa and Nathan Brown-Haysom for assistance during snail collection.
- Adam P (1993) Saltmarsh ecology. Cambridge University Press, CambridgeGoogle Scholar
- Graczyk T, Shiff C (1994) Viability of Notocotylus attenuatus (Trematoda: Notocotylidae) metacercariae under adverse conditions. J Wildl Dis 30:46–50Google Scholar
- Ingole B, Parulekar A (1998) Role of salinity in structuring the intertidal meiofauna of a tropical estuarine beach: Field evidence. Indian J Mar Sci 27:356–361Google Scholar
- Intergovernmental Panel on Climate Change (IPCC) (2007) Climate Change 2007: the physical science basis. Contribution of working group I to the fourth assessment report of the intergovernmental panel on climate change. Cambridge University Press, CambridgeGoogle Scholar
- Kalantan A, Arfin M, Al-Arefi H, Bobshait H, Hamadah S, Al-Thawab F, Al-Shamrani A (1997) Occurrence of larval Philophthalmus gralli (Mathis and Leger, 1910) in freshwater snail Melanoides tuberculatus (Muller) from Al-Hafuf, Saudi Arabia and its development into adult in various experimental hosts. Parasitol Int 46:127–136CrossRefGoogle Scholar
- Kanev I, Radev V, Fried B (2005) Family Philophthalmidae Looss, 1899. In: Jones A, Bray RA, Gibson DI (eds) Keys to the Trematoda, vol 2. CABI Publishing, Wallingford, pp 87–97Google Scholar
- Knauss J (1978) Introduction to physical oceanography. Prentice Hall, New JerseyGoogle Scholar
- Martorelli SR, Fredensborg BL, Leung TLF, Poulin R (2008) Four trematode cercariae from the New Zealand intertidal snail Zeacumantus subcarinatus (Batillariidae). N Z J Zool 35:73–84Google Scholar
- Moore J (2002) Parasites and the behavior of animals. Oxford University Press, OxfordGoogle Scholar
- Mouritsen KN, Poulin R (2002) Parasitism, community structure and biodiversity in intertidal ecosystems. Parasitology 124:S101–S117Google Scholar
- Sousa W (1991) Can models of soft-sediment community structure be complete without parasites? Am Zool 31:821–830Google Scholar
- Southgate V (1971) Observations on the fine structure of the cercaria of Notocotylus attenuatus and formation of the cyst wall of the metacercaria. Cell Tissue Res 120:420–449Google Scholar