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Mapping the distribution and evaluating the impacts of marine non-indigenous species (NIS) are two fundamental tasks for management purposes, yet they are often time consuming and expensive. This case study focuses on the NIS gilthead seabream Sparus aurata escaped from offshore farms in Madeira Island in order to test an innovative, cost-efficient combined approach to risk assessment and georeferenced dispersal data collection. Species invasiveness was screened using the Aquatic Species Invasiveness Screening Kit (AS-ISK), and revealed a high invasion risk. Occurrences of S. aurata were assessed involving citizens in GIS participatory mapping and data from recreational fishing contests. A probability map showed that S. aurata is well dispersed around Madeira Island. This assessment proved to be a cost-efficient early warning method for detecting NIS dispersal, highlighting the urgent need for additional surveys that should search for sexually mature individuals and assess the direct and indirect impacts in the native ecosystem.

The synergistic effects of biological invasions have long been considered significant causes of biodiversity loss worldwide. Therefore, early detection monitoring is crucial in mitigating nonindigenous species (NIS) threats. In the marine environment, settlement plates were used as monitoring devices in ports, but this method was mainly applied to assess the sessile benthic community and is less efficient in collecting the mobile biota and accessing its diversity. Moreover, as the potential expansion of NIS to the surrounding coastal environment is still poorly understood, a pilot study was conducted focusing on two aspects: (i) improving the feasibility of the settling method under different environmental contexts and (ii) enhancing the capacity of the developed prototypes to collect more representative samples (i.e., sessile and mobile biota). Three different prototypes were designed: a box prototype consisting of PVC plates encapsulated by a plastic bottle, a CD prototype with CDs surrounded by a net, and a PVC prototype with uncovered PVC plates. The prototypes were deployed inside a marina and in an outside area on Madeira Island, Portugal. Results indicate that the PVC prototype was the most efficient regarding monitoring the sessile community, whereas the box prototype showed the highest abundance of the mobile fauna. The location influenced both the sessile community composition and the number of mobile taxa. Our findings suggest combining features from prototypes to encompass the whole benthic community better.

Marinas are a gateway for the introduction and establishment of non-indigenous species (NIS). In these habitats, competition and predation are crucial determinants for NIS establishment and invasiveness. However, fish trophic preferences and biotic effects inside marinas are poorly known. This study proposes a novel method that combines the deployment of settlement plates to recruit different assemblages, followed by their use as bait in remote underwater video systems. This combined approach, addressed as a remote video foraging system (RVFS), can record fish foraging behaviour, including feeding choices and their impacts on fouling assemblage composition. An experimental RVFS trial carried out in a marina of Madeira Island, Portugal (NE Atlantic), identified the Mediterranean parrotfish, Sparisoma cretense, as the most important fouling grazer in the area. S. cretense behaved as a generalist and increased the heterogeneity of fouling assemblages, which can hamper NIS dominance of the fouling and reduce the pressure of propagules from the marina to the natural environment. The RVFS tool was useful to understand the trophic links between foragers and fouling and has the potential to provide relevant information for the management of NIS introductions, establishment and spread.