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Doctoral defence in Biology - Teresa Sofia Giesta da Silva

Fri, 14/12/2018 - 10:00 to 12:00


Room 132

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Ph.D. student: Teresa Sofia Giesta da Silva

Dissertation title: Ecology of krill in Icelandic waters

Dr. Bettina Meyer, Professor at the Alfred Wegener Institute, Bremerhaven, Germany and Carl-von-Ossietzky University, Oldenburg, Germany

Dr. Russell Ross Hopcroft, Professor at the University of Alaska, Fairbanks, USA. 

Advisor: Dr. Ástþór Gíslason, Scientist at the Marine and Freshwater Research Institute

Doctoral committee:
Dr. Guðrún Marteinsdóttir, Professor at the Faculty of Life and Environmental Sciences at the University of Iceland.
Dr. Ólafur S. Ástþórsson, Scientist at the Marine and Freshwater Research Institute.

Chair of Ceremony: Dr. Anna Dóra Sæþórsdóttir, Professor at the Faculty of Life and Environmental Sciences, University of Iceland.


Krill are important component of the Icelandic marine ecosystem. Given their important ecological niche, as conveyors of biological production between phytoplankton and higher trophic levels, fluctuations in krill abundance can have large impacts on the dynamics of species at higher trophic levels. For this reason, understanding their population dynamics is of great importance. This thesis aims to contribute new insights into the biology of krill and their ecological role in the Icelandic marine ecosystem. The thesis is based on four scientific publications, three of which are published. One manuscript examines seasonal and long-term changes of krill in the North Atlantic. The results show a significant decreasing trend in annual mean abundance of krill from 1958 to 2007 in the oceanic waters south and southwest of Iceland. It is hypothesized that a weakened temporal synchrony between the development of young euphausiids and the phytoplankton bloom influenced by recent climate warming may have led to the observed decrease in euphausiid abundance. Two manuscripts assess krill abundance, distribution and development, in relation to environmental variables and phytoplankton spring bloom dynamics around Iceland. Krill abundance was closely associated with abiotic factors (mainly temperature, salinity and bottom depth) and biotic factors (phytoplankton concentration and the onset of the phytoplankton bloom). Krill eggs and larvae were much more abundant in the warmer waters south of Iceland than in the colder waters off the north coast. Adults were also most abundant in the warm water. Meganyctiphanes norvegica dominated in the Atlantic water in south and west of Iceland, whereas Thysanoessa inermis was found more evenly distributed around the island, while the highest values were also observed in the southwest for this species. The fourth paper evaluates the effect of temperature on physiological rates of M. norvegica. It is shown that temperature influences the physiological rates of M. norvegica; with increasing temperature, both egestion and mortality rates increased. Moulting frequency increased with temperature.

About the doctoral candidate:

Teresa Silva was born in 1982 in Porto, Portugal. She graduated from the Polytechnic Institute of Leiria, Portugal, in marine biology and biotechnology with a BSc in 2005 and BSc (Hons) in 2006. She worked at the Marine Research Institute as a zooplankton research assistant from 2008 to 2011.

In 2012, she started the doctoral programme at the University of Iceland. Teresa was an assistant teacher at the University of Iceland during the school year 2015/2016. During 2018, she has been working at the Marine and Freshwater Research Institute as a research assistant.

Teresa lives in Hafnarfjörður and has one daughter, Diana, born in 2014.

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Teresa Sofia Giesta da Silva

Doctoral defence in Biology - Teresa Sofia Giesta da Silva