Testing temporal stability of the larval digenean community in Heleobia conexa (Mollusca: Cochliopidae) and its possible use as an indicator of environmental fluctuations

Abstract

Larval digeneans have been proposed as indicators of abundance and diversity of vertebrate and other hosts as well as environmental disturbances. To evaluate its response to environmental changes and its potential use as an indicator of environmental fluctuations, the temporal stability of the community of larval digeneans in Heleobia conexa was comparatively analysed in 4 separate years (1996, 1999, 2004 and 2005) in Mar Chiquita coastal lagoon (Buenos Aires province, Argentina). In total, 4579 specimens of H. conexa were collected and 22 digenean species were observed. Overall prevalence presented inter-annual and seasonal differences. These differences correlate with seasonal changes in composition of the vertebrate definitive host community and with the elimination of the preferred habitat of H. conexa in 1999. In general, the larval digenean community of H. conexa showed a yearly re-establishment following the annual cycle of H. conexa and the presence of definitive hosts. This annual restructuring allowed inferences about the effects of short-term environmental changes in the lagoon. According to these observations, the larval digenean community of H. conexa could be considered as a good bio-indicator with quick response to environmental disturbances.

Larval trematodes infecting the South-American intertidal mud snail Heleobia australis (Rissooidea: Cochliopidae)

“…references in Ostrowski de Núñez 2001, Merlo and Etchegoin 2010). In Heleobia australis from Bahía Blanca estuary, however, we found only one species of heterophyid: A.…”

“…In H. conexa from the Mar Chiquita coastal lagoon, the individual prevalences were also low, except for those of a notocotylid, a heterophyid, and two microphallids (Microphallus szidati and M. simillimus); but none of them present at higher levels than 9% (Merlo and Etchegoin 2010). Microphallus szidati was not found in the Bahía Blanca estuary-where, as mentioned previously, marine conditions prevail (Freije and Marcovecchio 2004)-probably because this species is, rather, a brackish and freshwater trematode, having been described as a parasite of H. conexa in the Mar Chiquita coastal lagoon and of H. parchappii in a freshwater environment from Buenos Aires province.…”

“…Finding such a high species richness of trematodes is not uncommon among Heleobia spp. In the Mar Chiquita coastal lagoon, some 260 km northeast of the Bahía Blanca estuary, Merlo and Etchegoin (2010) found 22 species of larval trematodes parasitizing H. conexa, while Etchegoin (1997) found 13 species of larval trematodes parasitizing H. australis. Cryptogonimidae gen.…”

“…This kind of larval trematode assemblage-i. e. with most trematode species showing low prevalence except for one or two species with a high abundance-is in fact, common in larval trematode assemblages of the rissooids from Europe, Oceania, and America (Deblock 1980, Jokela and Lively 1995, Kube et al 2002, Skirnisoon et al 2004, Thieltges et al 2009, Merlo and Etchegoin 2010.…”

Can the studies at a spatial scale of 100s meters detect the spatiotemporal fluctuations of a parasite assemblage?

“…Positive relationship between bird abundance and the presence of larval digenean parasitizing snail hosts on small to medium spatial scales were found by several studies (e.g. Curtis and Hurd 1983;Hechinger and Lafferty 2005;Koprivnikar et al 2007;Merlo and Etchegoin 2011). In addition, Prinz et al (2010) observed that the temperature increase coincides with a large number of definitive hosts and with a consequent increase in parasite prevalence in the mollusc hosts.…”