Posts Tagged 'Platyhelminthes'

Impacts of ocean acidification on multiplication and caste organisation of parasitic trematodes in their gastropod host

Ocean acidification is predicted to impact the structure and function of all marine ecosystems in this century. As focus turns towards possible impacts on interactions among marine organisms, its effects on the biology and transmission potential of marine parasites must be evaluated. In the present study, we investigate two marine trematode species (Philophthalmus sp. and Parorchis sp., both in the family Philophthalmidae) infecting two marine gastropods. These trematodes are unusual in that their asexually multiplying stages within snails display a division of labour, with two distinct castes, a large-bodied morph producing infective stages and a smaller morph playing a defensive role against other competing parasites. Using a potentiometric ocean acidification simulation system, we test the impacts of acidified seawater (7.8 and 7.6 pH) on the production of free-living infective stages (cercariae), the size and survival of encysted resting stages (metacercariae), and the within-host division of labour measured as the ratio between numbers of the two morphs. In general, low pH conditions caused an increase in cercarial production and a reduction in metacercarial survival. The ratio of the two castes within snail hosts tended to shift towards more of the smaller defensive morphs under low pH. However, the observed effects of reduced pH were species specific and not always unimodal. These results suggest that ocean acidification can affect the biology of marine parasites and may also impact transmission success and parasite abundance of some trematodes, with possible consequences for marine communities and ecosystems.

Continue reading ‘Impacts of ocean acidification on multiplication and caste organisation of parasitic trematodes in their gastropod host’

Lack of genetic variation in the response of a trematode parasite to ocean acidification

Ocean acidification is already having measurable impacts on marine ecosystems. Intraspecific variation in the responses of marine organisms to ocean acidification can reveal genetic differences in tolerance to low pH conditions and determine the potential for a species to adapt to a changing environment. This study tests for the existence of genetic variation in both the transmission success of the trematode Maritrema novaezealandense to its second intermediate amphipod host, Paracalliope novizealandiae, and the extent of parasite-induced mortality in that host, in response to decreasing pH. Eight parasite genotypes were tested in a custom-built ocean acidification simulation system, at 8.1 pH (current ocean conditions) and under conditions of 7.4 pH (worst-case scenario future prediction). The parasites had significantly higher infection success in the more acidic treatment, but there was no significant difference among genotypes in how infection success was affected by pH. In contrast, some parasite genotypes induced higher mortality in amphipods than other genotypes, but this genetic effect was also independent of pH. Overall, our results reveal no significant intergenotype variation in how the parasite responds to ocean acidification with respect to two key traits, infection success and parasite-induced host mortality, suggesting limited potential for adaptation in the face of acidifying conditions.

Continue reading ‘Lack of genetic variation in the response of a trematode parasite to ocean acidification’

Non-linear effects of ocean acidification on the transmission of a marine intertidal parasite

High levels of atmospheric carbon dioxide are driving the acidification of the world’s oceans, with considerable and generally negative impacts on the physiology, performance and survival of marine organisms. The differential and often idiosyncratic responses shown by different taxa suggest that interspecific interactions may be drastically affected by ocean acidification. Here, we quantified the transmission success of the trematode Maritrema novaezealandense to its intertidal amphipod intermediate host Paracalliope novizealandiae, as well as the host’s survival, under acidified conditions. We used a custom-built system to simulate ocean acidification with 3 different seawater treatments: 8.1 pH, corresponding to current average ocean surface waters, as well as 7.6 and 7.4 pH, the levels predicted for the years 2100 and 2300, respectively. In 2 separate experiments, parasite transmission success tended to peak in the most acidified conditions (7.4 pH), although this was only statistically significant when a wide range of infection doses was used. Because the survival of the parasite’s transmission stages decreases with decreasing pH, this pattern suggests that host susceptibility remains unaffected at 7.6 pH and is only compromised with further acidification. Amphipod mortality was not affected by pH levels, though it tended to be lowest at 7.6 pH, where the longevity of parasite transmission stages was reduced but host susceptibility was unaffected. These results suggest that ocean acidification could change the dynamics of parasite transmission with possible consequences for intertidal community structure, and emphasise the need to consider the transmission and severity of marine parasites and diseases in ocean acidification research.

Continue reading ‘Non-linear effects of ocean acidification on the transmission of a marine intertidal parasite’

Effects of seawater acidification on a coral reef meiofauna community

Despite the increasing risk that ocean acidification will modify benthic communities, great uncertainty remains about how this impact will affect the lower trophic levels, such as members of the meiofauna. A mesocosm experiment was conducted to investigate the effects of water acidification on a phytal meiofauna community from a coral reef. Community samples collected from the coral reef subtidal zone (Recife de Fora Municipal Marine Park, Porto Seguro, Bahia, Brazil), using artificial substrate units, were exposed to a control pH (ambient seawater) and to three levels of seawater acidification (pH reductions of 0.3, 0.6, and 0.9 units below ambient) and collected after 15 and 30 d. After 30 d of exposure, major changes in the structure of the meiofauna community were observed in response to reduced pH. The major meiofauna groups showed divergent responses to acidification. Harpacticoida and Polychaeta densities did not show significant differences due to pH. Nematoda, Ostracoda, Turbellaria, and Tardigrada exhibited their highest densities in low-pH treatments (especially at the pH reduction of 0.6 units, pH 7.5), while harpacticoid nauplii were strongly negatively affected by low pH. This community-based mesocosm study supports previous suggestions that ocean acidification induces important changes in the structure of marine benthic communities. Considering the importance of meiofauna in the food web of coral reef ecosystems, the results presented here demonstrate that the trophic functioning of coral reefs is seriously threatened by ocean acidification.

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Differential tolerances to ocean acidification by parasites that share the same host

Ocean acidification (OA) is predicted to cause major changes in marine ecosystem structure and function over the next century, as species-specific tolerances to acidified seawater may alter previously stable relationships between coexisting organisms. Such differential tolerances could affect marine host-parasite associations, as either host or parasite may prove more susceptible to the stressors associated with OA. Despite their important role in many ecological processes, parasites have not been studied in the context of OA. We tested the effects of low pH seawater on the cercariae and, where possible, the metacercariae of four species of marine trematode parasite. Acidified seawater (pH 7.6 and 7.4, 12.5°C) caused a 40 – 60% reduction in cercarial longevity and a 0 – 78% reduction in metacercarial survival. However, the reduction in longevity and survival varied distinctly between parasite taxa, indicating that the effects of reduced pH may be species-specific. These results suggest that OA has the potential to reduce the transmission success of many trematode species, decrease parasite abundance and alter the fundamental regulatory role of multi-host parasites in marine ecosystems.

Continue reading ‘Differential tolerances to ocean acidification by parasites that share the same host’

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Ocean acidification in the IPCC AR5 WG II

OUP book