| Summary: | Philosophiae Doctor - PhD (Biodiversity and Conservation Biology) The primary objective of this study was to investigate patterns in diversity, abundance, distribution and community structure of epi-pelagic copepods across the South West Indian Ocean Ridge (SWIOR). A survey was conducted across the SWIOR at two off-ridge and five seamount stations between 26.94 oS to 41.48 oS in November and December 2009. Copepod species richness and abundance was compared at vertical and horizontal scales day and night, at irregular time intervals across the Agulhas Return Current (ARC), Subtropical Front (STF) and Sub-Antarctic Front (SAF). A total of 49 genera and 135 epi-pelagic copepod species were identified along the SWIOR transect, and the Order Calanoida had the most genera. Species richness was highest in the ARC and lowest at the stations associated with the frontal areas of the STF and the SAF. The total number of copepod species was higher during the night than day. Total copepod abundance along the transect was highest towards the frontal area of the STF, and the genus Oithona spp. comprised almost 50% of the total number in all copepod samples. Three distinctive copepod assemblages were identified by multivariate analysis, and communities were associated with the STF, ARC and SAF. Clausocalanus laticeps, Metridia lucens and Calanus simillimus were only recorded in the southern part of the survey area and their absence in the north may demonstrate the strong stratification of the STF, and more likely to be the physiological properties, adaptation to their environment and life histories.
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