The invasion of Caulerpa cylindracea in the Mediterranean: the known, the unknown and the knowable

The spread of the green macroalga Caulerpa cylindracea is one of the most threatening invasions in the Mediterranean Sea. Many correlative and experimental studies have focused on different aspects of C. cylindracea invasion. This paper aims to evaluate the main factors influencing the spread of this alga through an overview of the results from 47 published papers on this topic; a conceptual model synthesizing the main biotic and abiotic factors that influence C. cylindracea spread was proposed. Mechanical destruction of habitats, enhanced sedimentation rate and nutrients loading directly promote the spread of C. cylindracea. Indirect effects due to factors that foster the spread of turf-forming algae at the expense of canopy-forming species and decrease substrate complexity emerged as an important determinant of the success of C. cylindracea. Ultimately, the spread of C. cylindracea appears to be regulated by a complex net of interactions between abiotic and biotic factors. Our conceptual model represents a general tool for the rapid assessment of the factor underpinning the spread of non-native species, a critical step for the control of non-native species that have successfully established viable populations.