|dc.description.abstract||This study examines how ocean acidification affects parasite transmission. Ocean acidification is a global process which has already started to have negative impacts on the marine environment, and these are predicted to escalate with future acidification. These include impacts on reproduction, development, calcification, osmotic regulation, and survival. Parasites are key components of all marine ecosystems, influencing the survival of their hosts, and also indirectly affecting other species within marine communities. Many parasite species possess vulnerable life history stages, which are sensitive to abiotic changes. Intertidal parasites have therefore been proposed as good bio-indicators for the impacts of ocean acidification.
This research used Maritrema novaezealandense and its first and second intermediate hosts as a model system to look at the impact of ocean acidification on parasite transmission. It was hypothesised that acidified conditions would affect transmission from the Zeacumantus subcarinatus snail host to the Paracalliope novizealandiae amphipod host. Parasite transmission was tested under three pH levels (pH 7.4, pH 7.6 and pH 8.1) and infection success within amphipod hosts was determined. Parasite infections in amphipods were significantly higher at the pH 7.4 level. Infection by this parasite may therefore increase with future ocean acidification. Amphipods were more vulnerable to parasitism under seawater acidification and may be the weak link in this model system.
To see whether parasite genotypes vary in their sensitivity to acidified conditions, the transmission success of eight different parasite genotypes was examined. Genotype was not found to significantly impact infection success, with pH level being the main determinant of infection success, regardless of genotype. The virulence of parasite genotypes did vary, however, with some genotypes inducing greater amphipod mortality following infection. Parasites which are less virulent may therefore have an increased chance of reaching the definitive host and this could be particularly important when this sensitive amphipod species is faced with both the stress of parasitism and ocean acidification.||