Invasive algae cut young Posidonia biomass in Mallorca study

Invasive algae can reduce the biomass of young Posidonia plants by up to 50 per cent, according to experimental research reported in Palma, Mallorca, on 18 August 2026. The study by the Institute for Mediterranean Studies (Imedea), a joint centre of the Spanish National Research Council and the University of the Balearic Islands, examined the effects of two invasive macroalgae in the Mediterranean.

Researchers found that Caulerpa cylindracea and Lophocladia trichoclados hindered the development of Posidonia seedlings. Plants exposed to the algae produced fewer leaves, had a smaller leaf area and recorded biomass losses of between 40 and 50 per cent.

The experiment followed the plants’ earliest life stages for more than five months, considering rising carbon dioxide levels, the resulting acidification of seawater and the spread of invasive algae. Higher carbon dioxide levels had a limited effect on the seedlings and did not bring significant gains in photosynthesis, growth or biomass production.

The invasive macroalgae also reduced the diversity of bacteria associated with the plants’ roots and changed the composition of their microbiome. Imedea said these microbial communities are linked to plant nutrition and responses to stress.

Lead researcher Iris Hendriks said controlling the spread of invasive algae could help the natural recovery of Posidonia meadows in the Balearic Islands, where their conservation is an environmental priority.

Source: Europa Press / Mallorca.com