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In the present paper, Dictyota hauckiana is reported for the first time from Vietnam. It was found growing with other marine macroalgae nearshore, at 1–2 m depth in Ninh Hai waters, Ninh Thuan province. Morphological observations and phylogenetic analysis based on the concatenated rbcL and psbA are presented. There are now 13 species of Dictyota known from Vietnamese waters. [ABSTRACT FROM AUTHOR]

Despite a rich seaweed flora, information about Vietnamese seaweeds is scattered throughout a large number of often regional publications and, hence, difficult to access. This paper presents an up-to-date checklist of the marine macroalgae of Vietnam, compiled by means of an exhaustive bibliographical search and revision of taxon names. A total of 827 species are reported, of which the Rhodophyta show the highest species number (412 species), followed by the Chlorophyta (180 species), Phaeophyceae (147 species) and Cyanobacteria (88 species). This species richness is comparable to that of the Philippines and considerably higher than Taiwan, Thailand or Malaysia, which indicates that Vietnam possibly represents a diversity hotspot for macroalgae. A comparison of the species composition with neighbouring countries yielded surprisingly low similarities. Rather than an indication of a biogeographical pattern, we are of the opinion that the low similarity with neighbouring countries is primarily an artifact resulting from taxonomic inconsistencies. The checklist presented here could serve as a valuable tool to reveal the seaweed diversity in Vietnam and to stimulate intraregional comparative research. [ABSTRACT FROM AUTHOR]

Levels of δ15N and molar C/N ratios were determined for the first time in 73 species of green, brown and red macroalgae at nine sites from differently polluted coastal areas of southern Vietnam in order to identify sources of dissolved inorganic nitrogen (DIN) used by seaweeds for their growth and development. The study sites were provisionally divided into two groups: open coast localities with presumably clear seawater and relatively isolated localities (bays and lagoons) polluted by waste from mariculture and sewage from cities and large villages. The algae collected at 'pristine' and polluted sites had on average δ15N signatures of 3.3±0.9‰ and 8.6±1.1‰, respectively. Macroalgae from the west shore of Phu Quoc Island, O Lan Lagoon and Nha Trang Bay assimilated DIN from wastewater enriched with the heavy nitrogen isotope. Among the macroalgae investigated, bioindicators of DIN source were identified. These indicator algae belong mainly to the genera Ulva, Padina, Turbinaria, Gracilaria and Hydropuntia. Analysis of molar C/N ratios in algal tissue showed that thalli collected at 'pristine' sites suffered limitation in nitrogen (on average, the C/N ratios=21.6±13.3). In most of the polluted areas, macroalgae were also N limited (on average, the C/N ratios=15.3±8.2). [ABSTRACT FROM AUTHOR]