Non-Native Marine Macroalgae of the Azores: An Updated Inventory

Abstract

Non-native species (NNS) represent a threat to biodiversity, and their occurrence and distribution should be periodically updated and made easily available to researchers and policymakers. An updated inventory of macroalgal NNS currently present in the Azores was produced based on published reports. Data concerning the first report and the distribution in the archipelago are provided for each species, as well as their respective native ranges and possible vectors of introduction. The resulting list comprises 42 taxa, i.e., 8.05% of the marine flora presently reported in the Azores, with 16 new NNS recorded over the last decade. The most isolated islands of the Western Group presented lower numbers of NNS (4.25% and 6.25%). In contrast, the two islands with the most used marina for transatlantic recreational sailing presented higher numbers (12.90% and 16.87%). Shipping is the main introduction vector (68%), whereas most macroalgal NNS are originally from the Pacific Ocean (31%) and the Indo-Pacific (31%). The presence of 13 species is restricted to single islands, and no species is reported exclusively in the Western group. Asparagopsis armata is the only algal NNS reported from all islands of the Azores. Future work is proposed to support policymaking.

Quantification of the invasiveness risk of non‐native macroalgae in the Azores to support conservation measures

“…The 42 non-native marine macroalgal species currently reported to the Azores (Gabriel et al, 2023) were screened for their invasiveness risk. The list encompasses 37 species belonging to Plantae (33 Rhodophyta and four Chlorophyta) and five to Chromista (Ochrophyta).…”

“…Hence, prevention and monitoring measures are recommended for all islands, whereas control measures are recommended for species with a high risk of invasion according to the islands where they occur (Table 3). The success of the proposed measures will be evaluated based on the results of annual prospections, with the rate of new NNS introductions expected to decrease (currently 1.6 species per year; Gabriel et al, 2023) and the spread of high-risk NNS to other islands expected to be contained (currently only one species is present in all islands; Data S3). Further changes to the proposed measures are likely to be made based on meetings with stakeholders (Calado et al, 2021).…”

“…Only one species, namely R. okamurae, of the five NNS belonging to Ochrophyta was ranked as high risk. This species is known to be one of the most aggressive invasive algae recently reported for European waters (Gabriel et al, 2023;García-G omez et al, 2020). R. okamurae was first recorded to the Azores in 2019, where it has rapidly spread and caused severe impacts on the native communities, such as losses of natural variability and species richness, as well as reductions in the populations of articulated coralline and corticated algae (Faria et al, 2022, b).…”

“…Although the levels of diversity and endemism in the Azorean marine ecosystems are relatively low (Freitas et al, 2019), its macroalgal flora is at a crossroad of native distributional ranges (Tittley & Neto, 2006), with a combination of species from Macaronesia, North Africa, the Mediterranean Sea, and the Atlantic coasts of Europe and America (Neto et al, 2021). The diverse intertidal and subtidal habitats of the Azorean rocky shores (Tittley & Neto, 2006) have also provided a variety of substrata for the establishment of numerous non-native macroalgal species, namely 8% of its marine flora, which represents almost three times the 3% global average (Gabriel et al, 2023;Guiry, 2012;Williams & Smith, 2007). Due to its location on transatlantic maritime routes, the Azores seem vulnerable to NNS arrivals via maritime traffic, either by commercial shipping or cruise yachting (Cardigos et al, 2015).…”

“…The first non-native macroalgal inventory for the Azores was published by Cardigos et al (2006), with later updates (e.g. Castro et al, 2022;Gabriel et al, 2023;Micael et al, 2014). However, besides the NNS inventories, reports on new NNS introductions (e.g.…”