Gerner, Nadine (2009) Does stress tolerance differ between indigenous and non-indigenous marine species and between populations from pristine and anthropogenically impacted habitats?. (Diploma thesis), Johann Wolfgang Goethe-Universität , Frankfurt am Main, Germany, 75 pp.

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Abstract

Marine bioinvasions are becoming more and more frequent due to shipping traffic and the increasing importance of aquaculture. The interaction of introduced species with resident communities can be neutral, negative or positive. In parallel, changing climatic conditions are altering environmental regimes, amplifying the frequency and intensity of extreme events. Such enhanced abiotic stresses are acting on marine organisms, especially in intertidal systems where fluctuations in various environmental factors are high. Both processes, climate change and the increasing number of bioinvasions, are amplified by human activities and mostly affect coastal areas. The question arises, if enhanced stress might be tolerated better by invasive species, and thus, be of advantage when competing with native species. As an approach to these questions, salinity stress tolerance of the native intertidal bivalves Saccostrea glomerata and Perna canaliculus was compared with the tolerance of the invasive oyster Crassostrea gigas. Experimental studies were conducted with populations of the south-western Pacific at the north-eastern coast of New Zealand. Oxygen consumption rates were measured as an immediate, and mortality and growth as a longterm response towards hypo- and hyper-salinity stress. Under severe low salinity regimes, oxygen consumption decreased significantly compared to respiration under ambient salinity conditions, indicating a strong response towards stress. The invasive oyster, however, showed a smaller decrease in respiration under stress than the native oyster and lower mortality rates compared to the native mussel, indicating a higher tolerance under these stress regimes. Different models are discussed as possible explanations for the better performance of the invasive species under stress. Besides bioinvasions and climate change, human activities also cause pollution and eutrophication, that have direct impacts on coastal regions, especially in harbour areas. This puts additional strain on the animals in these systems. Thus, a second aspect investigated in this thesis was, whether populations of the same species, but from sites with different anthropogenic impacts, differ in their tolerance towards additional stress. This question was assessed in similar experimental designs, comparing populations of P. canaliculus from a pristine site, Pakiri, and a disturbed yacht harbour, Weiti. This comparison, however, could not answer the study question. Since stressful events are becoming more important, in the long-term, a higher salinity stress tolerance of the invasive oyster, might result in modifications of competitive hierarchies in favour of the invasive species.
Competitive symmetries between local and introduced species can have consequences for the
structure of whole benthic communities in costal ecosystems.

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