Macroalgal Blooms Caused by Native and Non-Native Species: Causes and Possible Scenarios

This review examined 275 papers containing 344 relevant mentions of blooms of native and non-native species of macroalgae along with the causes attributed to these phenomena. The aim of the study was to test the hypothesis that blooms of non-native macroalgal species are caused by a similar complex of factors that cause harmful blooms of native species rather than by aggressive traits of the non-native species themselves. From the reviewed literature, we extracted the main factors that triggered the blooms. Our analysis showed that in 96% of the cases examined, the ecosystem was already disturbed prior to the arrival of non-native species and the onset of macroalgal blooms. The causes were commonly attributed to eutrophication in 59.9% of cases and global warming in 15.7%, and only 3.5% of cases attributed the ecosystem damage to the aggressive characteristics of non-native species. Based on the literature, we developed a conceptual model of possible scenarios for both healthy and damaged ecosystems following the introduction of non-native opportunistic species of macroalgae. We argue that the current approach to combating non-native species cannot achieve results until the ecosystem is restored to health or finds a new balance.