First record of Laminaria ochroleuca Bachelot de la Pylaie in Ireland in Béal an Mhuirthead, county Mayo

Abstract Background During a biodiversity survey of Béal an Mhuirthead, Co. Mayo, a small population of Laminaria ochroleuca Bachelot de Pylaie was discovered in a semi-protected cove on the northwest part of the headland among a mixed macroalgal assemblage including the kelps Laminaria digitata and Saccharina latissima. This is the first record of this southern European species in Irish waters. Methods Individuals were morphologically identified by their smooth stipes, conical, claw-like holdfasts, broad golden blades and all regions of the thallus were devoid of epibiota. Individual L. ochroleuca were genetically identified using the mitochondrial atp8 gene, and all belonged to the same haplotype previously found in France and Portugal. Results Using 12 microsatellite loci, we found 34 alleles from 15 genotyped sporophytes. Multilocus estimates of allelic diversity and expected heterozygosity were comparable to sites sampled in the Iberian Peninsula (0.427 and 0.562 on average respectively) despite strong genetic differentiation between Scots Port and other sites throughout the known European range. There was a general trend of heterozygote excess which may indicate recent admixture following a founder event(s). Conclusions The appearance of this southern European kelp species raises many questions including i) how widely distributed it is in Ireland, ii) how it arrived at this northwestern point of the country if it is not widely distributed in Ireland, and iii) whether it can withstand low winter temperatures L. ochroleuca was previously thought not to endure. More detailed surveys in Irish kelp forests should take place to determine the distribution of this kelp and its impact on the Irish kelp forest ecosystem.