Taxonomic identification and chlorophyll content variation of dominant green macroalgae belonging to genus Ulva in Huong Phong area, Tam Giang Lagoon, Hue City

Abstract

Species of the genus Ulva are widely distributed worldwide, play an important role in aquatic ecosystems, and have high potential for applications in various fields; however, they can also cause “green tide” events under nutrient-enriched conditions. This study aimed to identify the dominant Ulva species in aquaculture ponds in Huong Phong, Tam Giang Lagoon, and to investigate temporal variation in chlorophyll a and b contents. The samples were collected from March to September 2025 and identified by using a combination of morphological characteristics and two molecular markers, tufA and rbcL. The DNA sequence analysis revealed that the samples exhibited 99–100% similarity to Ulva limnetica and clustered within the same clade in the phylogenetic trees based on both markers. Morphological characteristics were also consistent with the descriptions of this species. The chlorophyll a and b contents showed significant seasonal variation (p < 0.05). The chlorophyll a and b content ranged from 0.23 to 1.20 and 0.20 to 0.61 mg·gww⁻¹, respectively, from March to September, except for a sharp decline in June to 0.01 mg·gww⁻¹ for both pigments (p < 0.05). These findings provide a scientific basis for the occurrence of Ulva limnetica in Tam Giang Lagoon, contributing to the prediction and control of green tide events and supporting the sustainable utilisation and potential applications of this species in the future.