Pelseneeria spp.
Pelseneeria are small parasitic snails belonging to the Eulimidae family. They feed on sea urchins by the use of a proboscis which extends into the body cavity of their host.
In their study, Sonnenholzner et al. (2011 Ecology 92: 2276-2284) highlight how over-fishing can deeply affect food webs and thereby parasites.
Pelseneeria snails are preys of the crab Mithrax nodosus in the Galapagos. Increased fishing pressure on the predators of the crab has thus benefited the crab populations, leading to a decrease in the prevalence of the parasitic snail. Under these circumstances, sea urchins are benefiting from over-fishing.
Accordingly, the authors reveal in another study (Sonnenholzner et al. 2009 Mar. Ecol. Prog. Ser.) the impact of sea urchins on algae and anemones. Hence, environmental disturbances can have drastic cascading effects on the whole ecosystems in which parasite can play a crucial role.
(source for picture: http://www.conchology.be)
