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Sargassum is a genus of brown macroalgae in the class Phaeophyta, distributed widely in all oceans, including those of Vietnam. Species of this genus have been proven to possess diverse biological activities, such as antioxidant, anti-fungal, and anti-inflammatory, along with many benefits and applications for human health, including anti-diabetic, obesity, and thrombosis. These benefits arise from a diverse chemical composition, with compounds such as fucoidan, mannitol, and especially phlorotannin—a group of phenolic derivatives found predominantly in brown algae. In this study, we evaluated and optimized the factors that affected the extraction process of phlorotannins from Sargassum swartzii (Turn.) C. Ag., a common species of brown macroalgae in Vietnam. The process utilized ethanol and water as the solvent system, and the extraction process was assisted with the use of microwaves. To carry out optimization studies, Response Surface Methodology (RSM) was adopted according to a Central Composite Desisgn (CCD), taking four processing factors into consideration, ethanol concentration (%, v/v), extraction time (minutes), solvent/material ratio (v/w), and microwave output power (W) as independent variables. Phlorotannin concentration (mgPhE/g) and extract mass (mg) were regarded as optimization outcomes. Experimental conditions that produced the highest phlorotannin yield from 10 g of S. swartzii are as follows: Extraction time of 65 minutes, ethanol concentration of 52%, microwave output power of 613 W, and solvent/material ratio of 33/1 (v/w). These conditions corresponded to a phlorotannin concentration of 5.59 ± 0.11 mg PhE/g, and a total extract content of 27.88 ± 0.13 mg/g.

Submerged caves and marine lakes are two iconic and common ecosystems in Ha Long-Cat Ba area. However, their biological characteristics are poorly known since very limited studies have been conducted. The aim of this study was to investigate biodiversity in these ecosystems. Three submerged caves (Hang Sang, Hang Toi and Qua Bang) and three marine lakes (Dau Be, Ang Du and Qua Bang) were chosen for study. The results showed that organism communities in submerged caves were abundant with over 142 species found. The popular groups comprised sponge and soft coral which were distributed along the length of the caves. Several species with high economic value were widespread in the caves, including stone crab Myomenippe hardwickii, flower crab Portunus pelagicus, cone snails Trochus pyramis, shoemaker spinefoot Siganus sutor, snapper Lutjanus russellii. Species that permanently live in caves were not detected. In the lakes where water is well exchanged to the sea, coral reefs were found and they usually formed a narrow band around the lakes. Sandy beaches were often observed around the lakes at the depths of 0.5-2 m, containing specialty species as clam (Sanguinolaria diphos), snout otter clam (Lutraria rhychaena), sea cucumbers with high density (in Dau Be, Qua Bang). There was no coral reef in the enclosed lake (Ang Du) because of low salinity.

This paper presents results on species composition and distribution of seaweeds at Nai lagoon, Ninh Thua province from 2013 until 2014 at 12 sites was showed that, at Nai lagoon area we was recording 43 species of marine seaweeds, they are belonging to four divisions, as: Cyanophytes, Rhodophytes, Phaeophytes and Chlorophytes. Among them, eight species are classified in Cyanophytes (comprising 18.6% of total species); eleven species in Rhodophytes (25.6%); four species in Phaeophytes (9.3%) and twenty two species in Chlorophytes (46,5%). The species composition of marine seaweeds from Thi Nai lagoon show significant differences in the species composition as follows: 8 species (side number 4, 13 and 18) to 21 (side number 10) and average value is 12.2 species per side. The number species at dry season is 40 and rainy season is 30 (there are 30 species in of boots dry and rainy seasons) Coefficient homogeneous is oscillating from 0.10 (side number 4 and 5) to 0.66 (5 and 7). The current investigations show that 39 species of 43 species were collected in the littoral zone and 35 species in sub-littoral zone (31 species are distributing in both the tide and the sub tide). Marine algal flora in Thi Nai lagoon is represented by tropical elements as defined by Cheney.

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MỞ ĐẦURong biển là một nhóm thực vật bậc thấp sống ở biển, đây là một hợp phần quan trọng của tài nguyên biển. Rong biển là một nguồn tài nguyên biển quan trọng, có giá trị kinh tế mà từ lâu đã được con người sử dụng rất nhiều trong các ngành công nghiệp (ydược, thực phẩm, phân bón ...). Các đảoNam Yết, Sơn Ca, Song Tử Tây và Sinh Tồn là các đảo nhỏ thuộc quần đảo Trường Sa, huyện Trường Sa, tỉnh Khánh Hoà. Cho đến nay, các công trình nghiên cứu về rong biển tại các đảo thuộc quần đảo Trường Sa còn chưa nhiều. Công trình đầu tiên về rong biển tại quần đảo này là của Josephine Th. Koster (1936) với 23 loài tại đảo Nam Yết [1]. Một số công trình khác từ sau 1990, chủ yếu của các tác giả như Đàm Đức Tiến, Phạm Hữu Trí, Lê Như Hậu, … [2-7]. Bài báo giới thiệu về thành phần loài và phân bố của rong biển tại các đảo (Nam Yết, Sơn Ca, Song Tử Tây và Sinh Tồn) thuộc quần đảo Trường Sa. ABSTRACT: Marine algae are one important component of marine resources. Different compounds such as agar, alginat, carrageenan, biological activities can be extracted from marine algae … They have been used in fields as follows: fabric weave, refresher, medicine, ... Nam Yet, Son Ca, Song Tu Tay and Sinh Ton are small islands of Truong Sa archipelago in Truong Sa district, Khanh Hoa province, Central Vietnam. This paper presents results on species composition and distribution of seaweeds at Nam Yet, Son Ca, Song Tu Tay and Sinh Ton islands of Truong Sa archipelago. The study results show that at four islands we recorded 133 species of marine seaweeds that belong to four divisions: Cyanophytes, Rhodophytes, Phaeophytes and Chlorophytes. Among them, 13 species are classified into Cyanophytes (comprising 10.0% of total species); 67 species into Rhodophytes (50.3%); 20 species into Phaeophytes (15.0%) and 33 species into Chlorophytes (24.7%). The distribution of marine seaweeds from Nam Yet, Son Ca, Song Tu Tay and Sinh Ton islands show significant differences as follows: 34 species (Son Ca island) to 77 species (Nam Yet island) and the average value is 57.3 species per island. Homogeneous coefficient oscillates from 0.30 (Nam Yet and Sinh Ton) to 0.49 (Son Ca and Sinh Ton) and the average value is 0.39. The current investigations show that 75 species were collected in the littoral zone (56.4%), 28 species in sub-littoral zone (28.0%) and 30 species in sub-littoral and littoral zone (15.6%)

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