Temporal genetic diversity in phytoplankton in the Gulf of Naples

McDonald, Sarah Margaret (2006). Temporal genetic diversity in phytoplankton in the Gulf of Naples. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000fe69

Abstract

This thesis dealt with genetic diversity in groups of phytoplankton on a temporal scale. The aim of the study was to investigate diversity and the seasonal distribution of that diversity during the year.

Chapter Two examined the diversity and seasonal distribution of ultraplankton <5 μm in surface waters between 2003 and 2004 using 16S class level probes and clone libraries. Chapter Three examined the distribution of ultraplankton using the 16S probes over four depth profiles during 2005. The results showed the presence of Prymnesiophyceae and Cryptophyceae during the whole year and at most depths. The Chrysophyceae showed a marked preference for summer. All three classes showed highest signal just below the surface between 2 and 10 m. The Pelagophyceae were present in February in surface waters, but at 50 to 70 m in May and August. Diversity within these classes was high and other taxonomic classes were detected in the clone libraries. The seasonality within genotypes in the Cryptophyceae was visible and comparisons to known cultures could be made.

The diatom genus Pseudo-nitzschia was investigated in Chapter Four using newly developed genus specific primers. Thirteen genotypes were detected during the year, some of which showed seasonal preferences, for example P. multistriata in October, and others that were present most of the year, for example P. galaxiae LSU-clade 2 present from May until October. The three annual blooms of P. galaxiae were investigated in Chapter Five using LSU and ITS. The blooms were shown to be dominated by different ITS genotypes that recur in the same period of the year, every year. The results from P. galaxiae indicated a possible mechanism for speciation whereby populations may become separated in time rather than space.

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