Extreme Storms Could Limit the Expansion of the Invasive Species Caulerpa Cylindracea in the Rocky Shore

Abstract

Invasive species constitute a major environmental concern worldwide and extreme events, favoured by climate change, are expected to enhance their invasibility. However, more scientific evidence is needed to better understand under which circumstances this assumption holds. Here, it was manipulatively tested how storm intensity and frequency affected re-colonization of rocky boulders by the non-indigenous species Caulerpa cylindracea following mechanical disturbance. It was found that low intensity storms with a high frequency enhanced the invasibility of Caulerpa cylindracea, while extreme storms, limited the invasibility of this alga. These effects did not only occur on the short-term, but up to 9 months after the disturbance could be observed. Caulerpa cylindracea, has a low attachment capacity to the substrate, and its colonization capacity may be favoured by the existence of other canopy-forming algae that create structures to where Caulerpa cylindracea can establish. While in situations after high intensity disturbances that lead to bare rock, Caulerpa cylindracea may be too exposed to uproot and dislodgement by shear stress driven by waves on rocky shores, hindering colonization of upper subtidal zone. This study suggests that extreme events do not necessarily enhance the invasibility of exotic species and can have contrasting effects depending on the habitat. Thus, the effects of extreme events on the invasibility of exotic species needs to be studied in different habitats, to optimize management strategies that can be adapted to each habitat in pursuit to mitigate as much as possible the effects of alien species under the current context of climate change.

Keywords: invasion ecology, climate change, extreme events, coastal ecology, alien species, storm