Non-indigenous seaweeds in the Northeast Atlantic Ocean, the Mediterranean Sea and Macaronesia: a critical synthesis of diversity, spatial and temporal patterns

ABSTRACT

Effective monitoring of non-indigenous seaweeds and combatting their effects relies on a solid confirmation of the non-indigenous status of the respective species. We critically analysed the status of presumed non-indigenous seaweed species reported from the Mediterranean Sea, the Northeast Atlantic Ocean and Macaronesia, resulting in a list of 140 species whose non-indigenous nature is undisputed. For an additional 87 species it is unclear if they are native or non-indigenous (cryptogenic species) or their identity requires confirmation (data deficient species). We discuss the factors underlying both taxonomic and biogeographic uncertainties and outline recommendations to reduce uncertainty about the non-indigenous status of seaweeds. Our dataset consisted of over 19,000 distribution records, half of which can be attributed to only five species (Sargassum muticum, Bonnemaisonia hamifera, Asparagopsis armata, Caulerpa cylindracea and Colpomenia peregrina), while 56 species (40%) are recorded no more than once or twice. In addition, our analyses revealed considerable variation in the diversity of non-indigenous species between the geographic regions. The Eastern Mediterranean Sea is home to the largest fraction of non-indigenous seaweed species, the majority of which have a Red Sea or Indo-Pacific origin and have entered the Mediterranean Sea mostly via the Suez Canal. Non-indigenous seaweeds with native ranges situated in the Northwest Pacific make up a large fraction of the total in the Western Mediterranean Sea, Lusitania and Northern Europe, followed by non-indigenous species with a presumed Australasian origin. Uncertainty remains, however, regarding the native range of a substantial fraction of non-indigenous seaweeds in the study area. In so far as analyses of first detections can serve as a proxy for the introduction rate of non-indigenous seaweeds, these do not reveal a decrease in the introduction rate, indicating that the current measures and policies are insufficient to battle the introduction and spread of non-indigenous species in the study area.

HIGHLIGHTS

• Non-indigenous seaweed species in the Northeast Atlantic Ocean, the Mediterranean Sea and Macaronesia are critically reanalysed.

• > 19,000 distribution records revealed considerable variation in diversity of non-indigenous seaweed species in the study area.

• Taxonomic and biogeographic uncertainties hamper a critical evaluation of the non-indigenous status of many seaweed species.

KEYWORDS:

• Biodiversity
• Chlorophyta
• Europe
• invasive alien species
• non-indigenous species
• Phaeophyceae
• Rhodophyta

Acknowledgements

The research was carried out as part of the ERANET INVASIVES project (EU FP7 SEAS-ERA/INVASIVES SD/ER/010), with infrastructure provided by EMBRC Belgium – FWO project GOH3817N and I001621N. This paper benefited from surveys and studies that FV carried out in the IDEALG (ANR-10-BTBR-04) and Interreg IVa Marinexus projects. This is publication ISEM 2023-173 of the Institut des Sciences de l’Évolution – Montpellier. ES acknowledges EU-BiodivERsA BiodivRestore-253 (RESTORESEAS, funded by FWO and FCT). AP and EC acknowledge the support of activities from: (1) the Apulian Region through the POR PUGLIA FESR-FSE 2014/2020, Asse VI, Action 6.5; and (2) the Italian National Recovery and Resilience Plan (PNRR) funded by the Italian Ministry of University and Research, Mission 4, Component 2, ‘From research to business’: 1. NBFC, Investment 1.4, Project CN00000033.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2023.2256828

Author contributions

LM. van der Loos, Q. Bafort, S. Bosch: concept, data acquisition, analyses, writing; F. Leliaert, O. De Clerck: concept, data acquisition, analyses, writing. All other authors: data acquisition, writing.

Additional information

Funding

This work was supported by the European Marine Biological Resource Centre Belgium [GOH3817N]; European Marine Biological Resource Centre Belgium [I001621N]; Fonds Wetenschappelijk Onderzoek [3F020119]; POR PUGLIA FESR-FSE 2014/2020 [Asse VI, Action 6.5]; RESTORESEAS [EU-BiodivERsA BiodivRestore-253]; Institut des Sciences de l’Évolution – Montpellier [ISEM 2023-173]; Italian National Recovery and Resilience Plan [Mission 4, Component 2, ‘From research to business’: 1. NBFC, Investment 1.4, Project CN00000033]; IDEALG [ANR-10-BTBR-04; Institut des Sciences de l’Évolution – Montpellier Institut des Sciences de l’Évolution – Montpellier [ISEM 2023-173].