|Endolithic parasitism of the intertidal mussel Mytilus galloprovincialis in its native and invaded ranges|
Marquet, N. (2011). Endolithic parasitism of the intertidal mussel Mytilus galloprovincialis in its native and invaded ranges. MSc Thesis. University of Algarve, Centre of Marine Science: Faro. 61 pp.
Parasitism; Mytilus galloprovincialis Lamarck, 1819 [WoRMS]; Marien
Biological invasions are affecting the earth’s ecosystems profoundly, and a major challenge in invasion biology lies in identifying the processes regulating invasion success. The enemy release hypothesis (ERH) proposes that invasive species becomes successfully established in their new range because released from the pressure that maintained them under control in their native ranges such as predation, disease, and parasitism. Microbial endoliths participate in many geologically and ecologically significant processes. Through their activity, they are able to inflict damage on their hosts. Particularly, photoautotrophic endolithic are known to heavily affect mussel populations. The European mussel M. galloprovincialis is a successful invader worldwide, and it is the most successful marine invasive species in South Africa. The main aim of the thesis was to test the ERH in M. galloprovincialis by comparing endolithic parasitism pressure in its native (Portugal) and invasive (South Africa) ranges. In the native range, the incidence of endolith-infested shells and endolith-induced mortality varied over large latitudinal scales. This could be explained by mussels being densely packed (i.e. increased shell abrasion by contact), mussel distribution extending higher on the shore (i.e. increased boring activity of phototrophic endoliths) and the elevated grazer biomass. In general, the incidence of infested shells was higher at the upper tidal levels of mussel distribution where exposure to light is more prolonged. Infestation was highly size dependent, and the proportion of infested mussels increased with size. Moreover, my results showed striking sublethal effects of endolithic parasitism suggesting an energy trade-off effect between the need to repair the shell and the others physiological factors. In the invasive range, incidence of endoliths and endolith-induced mortality varied between locations and again this could be explained by the higher abundance of mussels at the most infested location. Contrary to the native range, mussels were highly and homogenously infested throughout the shore and also small size classes were heavily infested. Finally, I identified five endolithic genera in M. galloprovincialis shells: Hyella, Mastigocoleus, Plectonema, Solentia, Hormathonema and Kyrthutrix. Hormathonema was found only in Portugal, and Kyrthutrix only in South Africa. My study clearly rejects the ERH. Infestation and endolith-induced mortality were higher in the invasive than in the native range. Despite the potential importance of natural enemies in controlling non native species, dynamics of invasions are probably the result of complex interactions between characteristics of the invaded community and properties of the invader.