Exploring marine invasions connectivity in a NE Atlantic Island through the lens of historical maritime traffic patterns

In recent decades, maritime traffic has been increasing globally. Introduction vectors involving ships, hull fouling and ballast water are often cited as having high risk for introducing marine non-indigenous species (NIS) worldwide. Due to its geographical location, Madeira Island (Portugal) had a significant role in past maritime connections, with the ability to serve as a “port of call” facility. However, little is known about past temporal maritime traffic patterns in Madeira, and particularly its relationship with NIS introductions. In this context, the present study was designed to create a first and comprehensive baseline for historical maritime traffic data for Funchal port, Madeira’s main port, between 1936 and 2004. Official marine traffic data with stops in Funchal were documented, including information concerning last port, ship type, ship size, and residence time in port. In addition, a comprehensive literature search of NIS detected in Madeira Island until 2004 was conducted. Based on the frequency of ship arrivals from different origins five statistically different periods of maritime traffic were determined. The most common maritime traffic origin arriving at Funchal was from Portugal (mainland), Great-Britain, Canary Islands and Spain mainland (Mediterranean). The most relevant IUCN bioregions of Madeira’s maritime traffic origins were in accordance with the frequency of the native distribution of the island’s marine NIS inventories until 2004. The present study reports for the first time a significant and positive relationship with native regions of NIS present in Madeira until 2004 with the most relevant maritime traffic routes, confirming maritime traffic as one of the main vectors for the introduction of these species in Madeira Island. Finally, a continuous monitoring, update, and analysis of maritime traffic, identifying invading corridors, needs to be maintained as a fundamental tool for management NIS introductions in Madeira Island.