Marine ecosystem health and biological pollution: Reconsidering the paradigm.

Our study re-evaluates a fundamental paradigm in marine invasion ecology - whether introduced species are considered as contaminants, i.e. just present in the system, or whether they are pollutants per se, i.e. they cause biological harm. This re-evaluation includes the concepts of marine ecosystem health and biological pollution using the European Marine Strategy Framework Directive (MSFD) as an example. Hence, we clarify the distinction between "biological contamination" (pertaining to Non-Indigenous Species (NIS) introductions) and "biological pollution" (associated with Invasive Alien Species - IAS). We emphasize the need for comprehensive indicators that consider their ecological, economic, and societal impacts. The MSFD Descriptor D2 NIS is analysed using the "biocontamination-biopollution" gradient to better reflect the complexities of ecosystem health. We discuss limitations in current monitoring and evaluation criteria, such as the absence of unified NIS/IAS monitoring, challenges in interpreting ecological impacts, and context-dependent assessment results. We emphasize the importance of context-specific management measures, considering the origin of pressures, whether endogenic (caused within a management area such a regional sea) or exogenic (with causes from outside a management area). Ultimately, we underscore the importance of a holistic and adaptable approach to address the diverse challenges posed by biocontamination and biopollution, protecting both marine ecosystems and human well-being in an ever-changing environment.