Potential effects of different salinities on the survival of the mangrove crab, Uca urvillei and its associated chemoautotrophic bacterial symbionts

The ability of natural populations to maintain fitness is important to their long-term persistence and has further relevance in the light of climate change scenarios. Fitness is however also influenced strongly by interactions with other species of the community. It is, therefore, important to focus on how environmental change can alter key biological interactions. The present study aimed to investigate the effects of different salinity levels on one species of mangrove crab, Uca urvillei and the associated chemoautotrophic bacterial symbionts, from the Mngazana estuary, South Africa. To examine the influence of different salinities over time on the symbiotic bacterial community, salinity experiments were set up, choosing three salinity exposures (5, 20 and 35percent) and four time exposures (3, 7, 14 and 21 days). The results showed that microbial community associated with U. urvillei was generally stable throughout the three salinity treatments, while the survival of the host (crab), was influenced by high salinities, particularly after day 14. Overall, the results of this study suggest that over time, environmental salinity (35percent) has the potential to affect significantly the physiology of U. urvillei, but this might not necessarily be the case for the associated microbial communities. The modes at which the significant symbionts are transferred from mother to offspring were also investigated by analysing the bacterial profiles from eggs, ovigerous and non-ovigerous females, along with mud. The results were fairly complex, but with significant differences in the bacterial communities of eggs from mud and females. These differences were driven mostly by two dominant phyla: Actinobacteria and Proteobacteria. The presence of both these phyla throughout the categories (even though in different percentages) suggest that U. urvillei might employ a mixed mode strategy of acquiring and maintaining the bacterial symbionts. Overall, this study contributes to further understand the dynamic and complex effects of environmental Abstract ii change on symbiotic communities, with overall potential cascading repercussions to the persistence of mangrove systems.Thesis (MSc) (Zoology) -- Faculty of Science and Agriculture, 201