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.

Variation in the impact of non-native seaweeds along gradients of anthropogenic disturbance

Biological invasions represent a major threat to marine and terrestrial biodiversity. Non-native species can severely impair the structure and functioning of natural ecosystems, with dramatic ecological, social and economic consequences1. Non-native species can be expected to strongly affect resident assemblages in pristine habitats which, due to favourable environmental conditions, are mainly structured by negative species interactions (e.g. competition)2. In contrast, weaker impacts are expected in degraded habitats, where physical conditions would limit the performance of both resident and non-native species. Alternatively, if non-native species impacts are proportional to their invasive success, we can expect that degraded habitats would show stronger impacts of the non-native species, when compared to pristine, more diverse assemblages3.


Efforts for controlling the impacts of alien seaweeds should be mostly directed to prevent their spread into relatively pristine areas. An effective way of achieving this goal could be that of preserving patterns of diversity and abundance of resident communities.

By mean of meta-analyse we summarized the relationship between non-native seaweed effects on primary producers or consumers and a cumulative human impact score4, at global scale. Non-native seaweed effects on most of the response variables did not vary among areas subjected to different human impact degrees. However, the effects on the abundance of consumer species were negative in relatively pristine areas while neutral or slightly positive in areas heavily impacted by human activities. A similar trend emerged for community diversity. We experimentally compared the effects of the non-native Caulerpa racemosa on resident assemblages among locations exposed to different human pressures in the Western Mediterranean (urban vs. extra-urban vs. pristine areas). C. racemosa altered the structure of resident assemblages at sites exposed to intermediate to low anthropogenic disturbance levels. In particular, the structure of the a ssemblages at pristine sites were more similar to those at urban sites in presence than in absence of C. racemosa (Fig. 1).

These results suggest that impacts can be more negative in less degraded or pristine sites, where biotic interactions are presumably the driving force structuring resident communities. Following a precautionary approach, our results suggests to direct our efforts into controlling the arrival and spread of non-native seaweeds in more pristine environments, where impacts on resident assemblages could have major ecological and economic consequences. Understanding how the impacts of non-native seaweeds vary according to other anthropogenic drivers of change is crucial to forecast their social and economic consequences, as proposed in VECTORS.

Relevance for Policy:
  • Alien Invasive Species Directive
  • Directive on Maritime Spatial Planning and Integrated Coastal Management (forthcoming)
  • EU Biodiversity Strategy
  • Guidelines for the Control and Management of Ships’ Biofouling to Minimize the Transfer of Invasive Aquatic Species
  • International Convention on the Control of Harmful Anti-Fouling Systems on Ships
  • International Convention for the Control and Management of Ship's Ballast Water and Sediments
  • Marine Strategy Framework Directive
Data availability:

Data used: Existing and new data on invading seaweed effects at sites with a different anthropogenic impact

Where it is held: Dipartimento di Biologia, University of Pisa

Contact: Dr. Fabio Bulleri

Availability: Password protected


Lead Author:

Fabio Bulleri
University of Pisa (UPISA)
Date of research: May 2014

Related articles:

Invading seaweeds and resident assemblages

Ecosystem impacts of non-indigenous species

Impact of invasive mussels on carbon flow 

Invasive ecosystem engineers and biodiversity

Invasive species and ballast waters mitigation 

Vital rates of fish larvae 

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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.