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.

Effects of macroalgal blooms on marine biodiversity and ecosystem functioning: a global meta-analysis

The combined effects of human pressures such as eutrophication, habitat destruction, and over-harvesting of marine herbivores have led to an increase in the incidence and severity of outbreaks by bloom-forming seaweeds. In addition to having direct social and economic consequences (e.g. interference with recreation, tourism, fishing), these macroalgal blooms can alter the structure and functioning of the ecosystems. This study reviewed and synthesised the evidence examining the effect of macroalgal blooms on the abundance and biodiversity of marine life, as well as the productivity and respiration of marine ecosystems.


Macroalgal blooms alter marine and estuarine communities, reducing the abundance of organisms and the number of species.

Overall, the abundance and species richness of marine and estuarine communities affected by macroalgal blooms are significantly smaller than those that are not. This suggests that ecosystem services relying on plentiful, diverse biological communities are likely to suffer following macroalgal blooms.


Macroalgal blooms are themselves highly productive but they may reduce the productivity of other primary producers.

We found that macroalgal blooms had a positive effect on total gross primary productivity, net productivity and community respiration. This was not surprising because seaweeds contribute directly to these ecosystem functions, and because macroalgal blooms often occur in response to increases in the nutrients that typically limit primary productivity. However, our results also suggest that this enhanced productivity overall comes at a cost to the productivity and respiration of other organisms both of which appeared to decrease in the presence of blooms.


The effects of macroalgal blooms vary, depending on factors such as the the habitat where they occur and the species of seaweed involved.

Despite having significant trends towards particular kinds of effects overall, the effects of blooms varied considerably from study to study. Our results suggest that some of this variation can be explained by differences in the effects of blooms by different algal species, by different effects in different habitats, as well as by differences in how scientists conduct their studies. For example, some macroalgal species tended to have positive or neutral effects on the abundance and species richness of marine organisms while others had negative effects. Sandy and muddy habitats below the low tide mark tended to experience stronger, negative effects on abundance and biodiversity measures than many other habitats, as did invertebrate communities (compared to those composed of other kinds of organisms). Much of the variation in the effects observed in different studies remains unexplained.

Lead Author:

Devin A. Lyons
University College Dublin (UCD)
Date of research: October 2013

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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
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