Marine protected areas (MPAs) are an essential tool for marine biodiversity conservation. Yet, their effectiveness in protecting marine ecosystems from global stressors is debated. Biological invasions are a major driver of global change, causing biodiversity loss and altering ecosystem functioning.

This study explored the relationships between MPAs and alien/native range-expanding fishes in the Mediterranean Sea, the world’s most invaded sea. For this purpose, the authors surveyed fish and benthic communities in nine MPAs and adjacent unprotected areas across six countries.

The obtained results show how in the South and Eastern Mediterranean MPAs, the biomass of alien and native range-expanding fishes often exceeded 50% of the total fish biomass, while in the North and Western Mediterranean alien fishes were absent.

Sea surface temperature (SST) was found to be positively correlated with the total biomass of alien species and no alien fishes were recorded below 20,5 ºC average SST. The study also found a negative relationship between alien fishes’ biomass and the distance from the Suez Canal (the main species introduction pathway).

Interestingly, the biomass of alien and native range-expanding fishes was found to be higher in the South and Eastern MPAs than in adjacent unprotected sites. The authors attribute this to the contrasting levels of fishing pressure exerted on these species in unprotected sites vs. MPAs. Regarding this, the authors suggest that complementary management actions, such as species-targeted removals, should be taken in MPAs to effectively control invasive fish populations.

Giakoumi et al. (2019) Exploring the relationships between marine protected areas and invasive fish in the world’s most invaded sea. Ecological Applications 29:e01809.