Marine invasion science has been steadily growing in the past three decades, achieving notable advances in both baseline research and technical tools, and eventually resulting in innovative policies.
Inventories of marine non-indigenous species (NIS) have been produced for several countries and regions, hotspots of introduction identified, techniques for identification of NIS improved, impacts of NIS on environment and economy quantified, major vectors of introductions recognized. Integration of disciplines (biogeography, taxonomy, molecular biology, experimental ecology and biology, environmental economy) has been activated and increasing. The progress of science has prompted national and international regulations and agreements, that have addressed the threat posed by NIS in the marine realm and promoted monitoring surveys.
Yet, the problem is far from being comprehensively understood and correctly managed, and trends of new introductions are still increasing. First, the advancement of knowledge on marine bioinvasions is geographically non-homogeneous, thus a global phenomenon is only known from patches of coastal regions. Second, most small-sized taxa (meiofauna, unicellular taxa, microbes and viruses) are very poorly known and studied, and the pattern of their global dispersion is largely ignored. Even many larger-sized taxa are affected by unresolved taxonomic and uncertain origin, and muddle the picture of marine bioinvasions. Impacts of marine invaders on ecosystems and economy are known only from a very tiny subset of all marine NIS, often confounding the understanding and quantification of impacts. As a result, the issue of marine bioinvasions is poorly acknowledged by the civil society and faces negationism, thus suffering delays or impediments in developing effective policies and control strategies.
While we have a still fragmented and incomplete knowledge of what has happened in the past, future scenarios promise new challenges. Global environmental change, novel or strengthened transportation networks, and political instability, are expected to alter rates of invasion. National or regional regulations should aim towards international agreements and homogeneous policies, while implementation of policies has to be supported by the most recent scientific and technological advancements. This process, accompanied by an increased citizen awareness, will be achieved through adequate communication actions as summarized in the following table.
| 3 decades of invasion science | Knowledge gaps | Policy indications |
| Monitoring, taxonomic evidence, Hotspot evidence, Biogeographical interpretation | Uneven geographical coverage, taxonomic revisions, molecular tools, especially for small sized taxa | Funding of monitoring surveys, strengthening of scientific collaboration |
| Vector and routes analysisPathways of introductions | Spatial analysis | Border surveillance through harbor and navigation rules |
| Impacts of introduced species Cause–effect relationships, magnitude and quantification | Rigorous case histories, generalization | Economy, Health and Ecosystem regulation |
| IAwarenessCitizen science, media communication | Stakeholder collaboration, outreach and contrast to negationism | Public opinion consciousness leading to consensus on rules |
| Concurrent trendsClimatic change, navigation routes | Interpretation of time scale trends of introductions, ecophysiology and environmental matching | Global change international agreements |
The aim of this research topic is to synthesize the main achievements obtained so far by marine invasion science, address current gaps and future challenges, and propose trends for policy action.
