Abstract
Freshwater systems on remote oceanic islands are particularly vulnerable to biological invasions. The case of freshwater ecosystems in the Azores Archipelago is especially relevant considering the islands’ youth and remoteness, and low natural connectivity. This study presents a review of the introduction and presence of non-indigenous freshwater species in the Azores, retrieved from various historical records, paleoenvironmental reconstructions, published records, and field data from two decades of the Water Framework Directive (WFD) monitoring programs. At least 132 non-indigenous freshwater species have successfully established in the Azores, belonging to several taxonomic groups: cyanobacteria (10), synurophytes (1), desmids (1), diatoms (20), plants (41), invertebrates (45), amphibia (2), and fishes (12). Intentional and accidental introductions have been occurring since the establishment of the first human settlers on the archipelago, impacting freshwater ecosystems. The first reported introductions in the Azores were intentional fish stocking in some lakes. Non-deliberate introductions have recently increased through transport-contaminants (51%) associated with the aquarium trade or agricultural products. In the Azores, the highest number of non-indigenous species occur on the largest and most populated island, São Miguel Island (116), followed by Flores (68). Plants constitute the most representative group of introduced species on all islands, but invertebrates, diatoms, and fishes are also well established on most islands. Among invertebrates, non-indigenous arthropods are the most well-established group on all islands except on the smallest Corvo Island. Many non-indigenous species will likely benefit from climate change and magnified by globalization that increases the probability of the movement of tropical and subtropical species to the Azores. Present trends in international trade, importations, and enhanced connectivity of the archipelago by increasing flights and shipping will probably promote the arrival of new species. Augmented connectivity among islands is likely to improve non-indigenous species dispersal within the archipelago as accidental transportation seems to be an essential pathway for non-indigenous freshwater species already present in the Azores.
Highlights
Human activities have for centuries promoted the transport of multiple species across huge biogeographical barriers (Gippoliti and Amori, 2006; Clavero and Villero, 2014), and this has accelerated exponentially since the beginning of the twentieth century (Vander Zanden and Olden, 2008; Clavero and Villero, 2014)
Freshwater ecosystems are among the systems most heavily affected by non-indigenous species introduction (Amat-Trigo et al, 2019)
Systems already impaired by non-indigenous species are susceptible to additional disturbance, as non-indigenous species often facilitate each other’s establishment and/or their continued existence, increasing the likelihood and the magnitude of the global environmental impact inflicted by biological invasions (Gherardi, 2007)
Summary
Human activities have for centuries promoted the transport of multiple species across huge biogeographical barriers (Gippoliti and Amori, 2006; Clavero and Villero, 2014), and this has accelerated exponentially since the beginning of the twentieth century (Vander Zanden and Olden, 2008; Clavero and Villero, 2014). The effects of intensive human usage and hydromorphological changes to aquatic systems, such as the impoundment of rivers (e.g., dams and weirs, water removal), water quality deterioration (e.g., pollution, eutrophication, acidification), habitat degradation and fragmentation (e.g., channelization and land-use change), resources overexploitation (Ricciardi, 2001), as well as climate change (Rahel and Olden, 2008) have been enhancing the dispersal of aquatic organisms (Gherardi et al, 2008a; Oscoz et al, 2010) Both anthropogenic habitat disturbance and the introduction of non-indigenous species are today the main drivers of biodiversity change in these ecosystems (Didham et al, 2005). More than 400 non-indigenous aquatic and semi-aquatic species of plants are currently traded in Europe, and many are considered potentially invasive in European freshwater habitats (Hussner, 2012) Most of those introductions arrived in Portugal via Spain (García-Berthou et al, 2005). The intensification of agricultural activity, the excessive application of agrochemicals, building roads, effluent discharge of livestock farms, and the release or non-deliberate introduction of non-indigenous species are some of the main factors currently affecting the water quality and ecosystems services provided by these islands’ freshwater habitats (Pereira et al, 2014; Raposeiro et al, 2014)
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