Marine Research Findings of the VECTORS Project

This website provides access to the research results of the VECTORS project, which can be used to support marine management decisions, policies and governance as well as future research and investment. VECTORS was a large scale project that brought together more than 200 expert researchers from 16 different countries. It examined the significant changes taking place in European seas, their causes, and the impacts they will have on society.

High fecundity and predation pressure of the non-indigenous Gammarus tigrinus cause decline of indigenous gammarids

The North American amphipod Gammarus tigrinus was first detected in the north-eastern Baltic Sea in 2003 and has rapidly expanded ever since. This non-indigenous amphipod has been notably successful in shallow, soft and mixed bottom habitats becoming one of the most abundant gammarid colonising such environments. Concurrent with the invasion of G. tigrinus the diversity and density of native amphipods has been decreasing indicating competitive dominance of G. tigrinus over native gammarids. During this study we experimentally studied if interspecific competition among the invasive G. tigrinus and the native gammarids explain the retreat of native gammarids.


Experiments showed that G. tigrinus had no direct effect on native gammarids. Instead, the combined effect of predation on juvenile amphipods and large brood production of G. tigrinus could be plausible explanations behind increased abundance of G. tigrinus and decrease of local gammarid populations in the north-eastern Baltic Sea.

Invasion biology needs to have the capacity to compare, evaluate and predict the impact of various alien species such as G. tigrinus in the Baltic Sea in order to determine and prioritise management actions. The current study demonstrated that the mechanism how G. tigrinus replaces the native amphipods is related to high reproductivity of invasive species and strong predation pressure of adult gammarids on their juveniles. Our initial expectation that a decline of the native gammarid amphipods was due to predation among adults was not supported. G. tigrinus had no specific effects on benthic communities other than predation pressure on native juvenile gammarids. This suggests that different regulating mechanisms may lead to similar ecological consequences and the detection of cause-effect relationships is only made possible via experimental research.

Relevance for Policy:
  • Alien Invasive Species Directive
  • Convention on Biological Diversity
  • Directive on Maritime Spatial Planning and Integrated Coastal Management (forthcoming)
  • Marine Strategy Framework Directive

Lead Author:

Jonne Kotta
Estonian Marine Institute (EMI-UT)
Date of research: July 2014

Related articles:

Ecological impact of a non-indigenous cladoceran 

Vital rates of fish larvae 

Early life stage survival of Baltic cod

Growth model for jellyfish Pelagia noctiluca 

Non-indigenous and invasive alien species

Population dynamics of sprat in the Baltic Sea 

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This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 266445
© Vectors 2015. Coordinated by Plymouth Marine Laboratory.