Discovery of Flabellia petiolata (Halimedaceae, Chlorophyta) in the southern British Isles: A relict population or a new introduction?

Abstract

The known distribution of seaweed species often requires updating after findings of new records outside the known range. The green algal family Halimedaceae is predominantly distributed in tropical and subtropical regions. Flabellia petiolata was considered endemic to the Mediterranean, but has also been recorded in the Canary Islands and Cape Verde. Recent marine biodiversity surveys by the citizen science group Seasearch in England led to the surprising discovery of plants that morphologically resemble F. petiolata. In this work we aimed to clarify the taxonomic identity of these specimens using morphological and molecular data. We obtained two rbcL and four tufA sequences for the English specimens that were identical to the two and nine sequences, respectively, available in GenBank for Mediterranean specimens of F. petiolata. This result is in agreement with morphological observations. Therefore, molecular and morphological data confirm that F. petiolata is established in southern England. Whether it is a new introduced species or a relict population is uncertain and we conclude that it is a cryptogenic species in England. This study provides an example of the contribution of citizen science to the better understanding of marine biodiversity.