Scientists discovered that some invasive seaweed can travel from rocky shorelines out into seagrass beds by hitching rides on the backs of foraging limpets, helping the seaweed spread into new habitats and competing with native plants.

Marine ecosystems around the world are experiencing an influx of non-native species as global trade and traffic increases. Scientists have long studied how factors like shipping contribute to the spread of invasive organisms, but new research by Louise Firth and colleagues, published in Annals of Botany reveals an overlooked player: the humble limpet. 

The research team found that the Atlantic brown alga Sargassum muticum, an invasive seaweed widespread in the UK and Europe, has been hitching rides on the backs of common intertidal limpets. By surveying rocky shores and seagrass beds at two sites, they discovered over 15% of S. muticum individuals attached to live limpets on rocks, and 5% hitched to dead limpets among Zostera marina seagrass beds. 

Images of Sargassum muticum (A) colonizing a Zostera marina bed (photo credit Georgie Bull); (B) attached to the limpet Patella ulyssiponensis on a rocky shore (photo credit Louise Firth); (C) attached to a detached limpet shell washed up on the beach (photo credit Tony Legg).

“S. muticum was found living attached to limpets both on rocky shores and in seagrass (Zostera marina) beds suggesting that limpets may represent a vector of spread for S. muticum across landscapes from rocky shores into seagrass beds.” 

Firth et al. 2023

Researchers conducted a four-year field study comparing eelgrass Z. marina beds with and without the invasive seaweed. Results showed lower densities and decreased phenolic compounds in eelgrass growing alongside S. muticum. Phenolics help Z. marina defend against threats, so reduced levels may weaken its resistance. 

To further probe the relationship, the team tested how S. muticum impacted eelgrass health under controlled conditions. While photosynthetic responses varied between years, the seaweed had no effect on Z. marina nutrient uptake – suggesting resilience in at least one aspect of its physiology. 

This work unveils a previously overlooked dispersal mechanism that may help introduce invaders beyond coastal habitats. By hitching rides on the daily commute of constant-grazing limpets, S. muticum gains transport into sensitive environments like eelgrass beds that would otherwise be inaccessible. Though Z. marina shows some tolerance, proliferation of the invasive seaweed remains a threat where it gains a foothold. 

The findings carry implications for managing marine invasions, emphasizing the importance of reducing vectors like ship biofouling while highlighting nature’s own accidental carriers. Limpets, it seems, are inadvertently facilitating the disruption of ecosystems through their inadvertent, bivalve feature. 


Firth L. B., Foggo A., Watts T., Knights A.M., deAmicis S. (2023) “Invasive macroalgae in native seagrass beds: vectors of spread and impactsAnnals of Botany.  Available at:

Cover: Sargassum muticum. Image: Gabe Schp / iNaturalist

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