The competitive dynamics of toxic and non-toxic ribotypes of the harmful dinoflagellate Alexandrium tamarense in Scottish waters

Abstract

Scottish harmful phytoplankton monitoring programmes, and previous research studies, have shown that the saxitoxin producing (Group I) and, recently, the non-saxitoxin producing (Group III) ribotypes of Alexandrium tamarense are present in Scottish waters, co-occurring in some locations. Shellfish toxicity events may have been in decline in recent years, possibly
due to increasing presence of the benign Group III ribotypes. This thesis investigated the interactions between these two A. tamarense ribotypes. To study these morphologically identical organisms a fluorescence in situ hybridization-flow cytometry (FISH-FC) based method of cell identification and enumeration was developed, allowing, for the first time, Group I and Group III A. tamarense strains to be studied in co-culture. In isolation, toxin
production of the Group I strain was elevated under P limitation as well as at low temperature and short light (spring) conditions. In co-culture a competitive interaction between Group I and Group III ribotypes was clear, with growth rates, maximum cell densities and total toxicity per cell showing marked changes compared to monocultures. Both strains showed a preference for the intermediate temperatures of 15 and 18 °C. Yet despite this, strain differences did occur. The Group III strain out-competed the Group I strain, having a higher biomass and maximum specific growth rate across most of the temperatures studied. The Group III strain also appeared to be able take up and utilise P more effectively that the Group I strain. Mathematical modelling revealed that the observed growth patterns (i.e. dominance of the Group III strain) in mixed culture was not solely due to more efficient nutrient uptake
but, additional interaction(s) such as allelopathy were also involved. Laboratory studies assessing a number of Scottish sediment samples identified the presence of Group I, Group III and hybrid cysts, highlighting the possibility that the more dominant ribotype may outbreed the other over time, if as the literature suggests, hybrid crosses fail to produce viable progeny.

Date of Award	10 Sept 2013
Original language	English
Awarding Institution	University of Edinburgh
Sponsors	NERC
Supervisor	Keith Davidson (Supervisor), Eileen Bresnan (Supervisor) & Elizabeth Turrell (Supervisor)