Improving the predictability of harmful algal blooms around the Shetland Islands

  • Paul Dees

Student thesis: Doctoral ThesisDoctor of Philosophy (awarded by UHI)


Toxin producing harmful algal blooms (HABs) are one of the principal challenges facing the shellfish aquaculture industry. This is important because biotoxins are a serious threat to human health. Symptoms of algal toxin poisoning can range from the embarrassing and debilitating to neurological damage and death. It is imperative that shellfish are sold to consumers only if they are safe in order to maintain the confidence that clients have in them. This is especially important for the Shetland Islands, where approximately 80% of the UK’s farmed mussels are grown.
Results of cell abundance measurements from routine coastal monitoring were analysed and have shown that Dinophysis spp. can accumulate very rapidly near Shetland mussel farms. Abundance measurements were compared to environmental conditions to show there is an undeniable link between exceptional Dinophysis spp. blooms and strong westerly winds. A particle tracking model was developed using current velocities modelled by AMM15. This particle tracking model also showed that Dinophysis spp. blooms can be advected to Shetland from as far away as the European shelf edge. These findings have demonstrated increased care should be taken when harvesting of mussels after prolonged periods of westerly winds.
CTD transects completed during 2017 and 2018 were graphically represented in a way which demonstrated the density and distribution of chlorophyll in the water column. Analysis of these data demonstrated the presence of a front near the most offshore manifestation of the 100 m isobath west of Shetland during late spring and early summer, and an additional front at the mouth of a restricted region of exchange. Previous studies hypothesising the presence of a front near the 100 m isobath were thus corroborated, although the influence of this front on advected HABs has not been confirmed during this study.
Contrary to a recent study, no evidence of increasing Dinophysis spp. abundance measured by continuous plankton recorder with increasing sea surface temperature was detected in the North Sea or around Shetland between 1982 and 2016. A significant positive relationship was found with the potentially toxic Pseudo-nitzschia seriata complex and increasing temperatures in the North Sea, exemplifying the differences between HAB genera around Scotland.
Date of Award3 Nov 2021
Original languageEnglish
Awarding Institution
  • University of the Highlands and Islands
SponsorsESF studentship
SupervisorKeith Davidson (Supervisor), Beth Mouat (Supervisor) & Andrew Dale (Supervisor)

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