Risk analysis of invasive species by ballast water: Case study in the Port of Gijón, Bay of Biscay

Global transportation is increasing significantly, with maritime transport playing a central role in global trade, as approximately 90 % of goods are transported via sea routes. While ballast water is essential for maintaining ship stability and manoeuvrability, it also presents a major environmental risk due to its potential to unintentionally transport invasive species to new environments. If these species survive and establish in the recipient ecosystem, they may disrupt native communities, impact the economy, and pose threats to human health. Ships are therefore recognised as a primary vector for aquatic biological invasions, with the associated risk varying depending on the type and volume of ballast water carried. This study aims to assess the risk of invasive species introduction via ballast water by analysing maritime traffic at the Port of Gijón over a 21-year period. Located in the Bay of Biscay, Gijón is particularly vulnerable to the ecological impacts of intensive maritime activity. Based on traffic data, we developed a semi-quantitative procedure to estimate the biological contamination risk posed by each vessel arriving at the port. The analysis identifies countries of origin associated with risk and, through the use of biological databases and an evaluation of environmental conditions for species survival, generates a risk map that categorizes potential invasive species. The results suggest that vessels arriving from national ports pose the highest risk (40.59 %), followed by those from Portugal (10.48 %), the United Kingdom (8.89 %), and France (7.05 %). Based on traffic patterns, 23 potential invasive species were identified. Of these, 20 were categorized as high risk on the generated map, and 6 have already been confirmed as present in the study area. A simple and easily replicable procedure is proposed, which port authorities can implement using only existing records of port entries and exits. • Most ballast water arriving at Gijón port comes from Spain, followed by the UK and France. • A method for early detection of invasive species has been developed. • Potential threats to the Gijón port have been identified as 19 invasive species in total. • One of the predicted species, Bugula Neritina , has already been detected in the area. • The need to detect and prevent AIS at an early stage is emphasised in this study.