Morphotaxonomic, phylogenetic and phytochemical study of the invasive, green-tide-forming macroalga Ulva tepida (Chlorophyta) firstly recorded from the African-Mediterranean coastal waters

Abstract

As a part of our extensive survey on macroalgal distribution along the Egyptian-Mediterranean coasts, a green-tide-forming filamentous Ulva was collected from Alexandria city, and identified as Ulva tepida by a combined integrative approach, including a multilocus sequence dataset of the chloroplast–encoded rbcL gene, the nuclear–encoded SSU rRNA gene and internal transcribed spacer (ITS), and state-of-the-art morphotaxonomy. The species features are consistent with the original description, i.e. tube-like thalli with radial branching in the basal region, chloroplasts covering the outer cell wall, and 1–5 pyrenoids. Biochemical assessment (primary metabolites) showed that the species is rich of carbohydrates, proteins, lipids, phenolics, and flavonoids. Additionally, it has high antioxidant activity and DPPH˙ (2,2-diphenyl-1-picrylhydrazyl) scavenging % value. The fatty acid profile, characterized by gas chromatography–mass spectrometry (GC-MS), revealed high concentrations of palmitic (C16:0) and oleic (C18:1, ω–9) fatty acids (30 % and 24 %, respectively), pointing to the biodiesel-production potential of this species. This is the first record of U. tepida, likely originated from the Indo-Pacific, from the African-Mediterranean coastal waters. Stricter regulations and regular water-quality monitoring, particularly in areas exposed to strong nutrient inputs, are required for this green-tide-forming species. Rapid biological invasions and climate change will significantly alter the native Mediterranean-Sea algal flora, and we believe that U. tepida will be reported as an alien invasive species in other Mediterranean countries.