Research projects

Katja Pulkkinen


Sources and sinks of columnaris disease in natural waters and in aquaculture

Maj & Tor Nessling foundation 2013

PI Katja Pulkkinen, PhD-student Sari Aaltonen, collaborators  Dr. Heidi Kunttu, Prof. Jouni Taskinen, Dr. Lotta-Riina Sundberg, Prof. E. T. Valtonen, Dr. Päivi Rintamäki, Prof. Mathias Wegner IfM Geomar

The aim of the project is to study the sources and sinks of the pathogenic Flavobacterium columnare –bacterium in natural waters, and factors affecting the persistence and growth of biofilms at fish farms.


Evolution of virulence in a fish pathogen under variable resource stoichiometry

Academy of Finland -project 2012-2016

PI Prof. Jouni Taskinen, collaborators Dr. Lotta-Riina Sundberg, Dr. Heidi Kunttu, Prof. Andrew Read, Prof. E. T. Valtonen, Dr. Päivi Rintamäki, Prof. Jouni Laakso, Dr. Tarmo Ketola


The ability to use nutrients available in the environment to achieve growth is a fundamental trait affecting the fitness of organisms. Resource nutrient ratios might therefore select for organisms capable of optimal utilization of nutrients in that environment. We propose to study whether high nutrient concentrations prevailing at fish farms have contributed to an increase in the virulence of a bacterial pathogen of fish, Flavobacterium columnare. Previous studies indicate that 1) high growth rates correlate with virulence in F. columnare,  2) the strains isolated outside fish farms have low virulence and 3) the strains currently encountered from fish farms are more virulent than those present in 1980´s, at the start of epidemics in Finland. We suggest, that the nutrient rich fish farming environment is selecting for fast growing F. columnare strains and has promoted the expression of virulence in this bacterium. The study will contribute significantly to understanding agents of selection in the evolution of virulence, as well as in managing the biggest threat to salmonid farming in Finland, cured currently by large amounts of antibiotics.  


The neglected role of parasites in planktonic trophic cascades

Academy of Finland -project 2007-2011

Prof. Kalevi Salonen, PhD-student Sanni Aalto and MSc-student Outi Kaski, collaborators Prof. Dieter Ebert, Dr. Paula Kankaala, Prof. Dag Hessen, Dr. Marcin Wojewodzic


Parasites reduce host growth, reproduction and survival and alter for example their feeding behaviour. Changes at the individual level lead to changes in host populations and further at the community level. The effect of parasites on food web structure may thus be as strong as that of predators, which traditionally are considered as the major biotic determinant of food web structure. In spite of the ubiquitous presence of parasites and variety of ways they impact on their hosts, the role of parasites in trophic cascades has been largely neglected.

In this project we will study the role of parasites of the water flea Daphnia in planktonic trophic cascades. Daphnia waterfleas are an important part of food webs in lakes: they feed on algae and bacteria and are themselves eaten by many fish and fish fry. The stoichiometry (C:N:P-ratios) of Daphnia has been studied extensively, as well as the effect of different parasites on Daphnia hosts. By combining these two subjects, our goal is to achieve fresh insights into a previously neglected aspect of the control of energy and nutrient flow in aquatic food webs.


Collaborator in:

Evolution of virulence in Flavobacterium columnare

Prof. E. T. Valtonen, Dr. Lotta-Riina Sundberg, Dr. Päivi Rintamäki, Prof. Dieter Ebert, Prof. Andrew Read


Pulkkinen, K., Suomalainen, L.-R., Read, A. F., Ebert, D., Rintamäki, P. & Valtonen, E.T. 2010: Intensive fish farming and the evolution of pathogen virulence: the case of columnaris disease in Finland. Proceedings of the Royal Society of London, Series B, 277:593-600.  


The effect of introduced signal crayfish on the littoral fauna of large Boreal lakes

Dr. Heikki Hämäläinen, Prof. Juha Karjalainen, MSc Timo Ruokonen, MSc-students Marjut Mykrä, Gordon Tambe and Sari Aaltonen


The North-American signal crayfish (Pacifastacus leniusculus) was introduced into Finnish lakes and rivers to replace plague devastated native crayfish stocks. Almost two million signal crayfish have been released during the last 20 years to our waters. Populations are now developing rapidly, but the ecological impacts of this invasive species on lake ecosystems have not been studied properly. As a part of this larger project we are studying how crayfish predation can modulate the parasite communities of fishes. See our publication in Ecosphere.