No abstract

Data on characteristics of phytoplankton communities is important scientific information in marine ecosystem, especially in assessment of environmental impacts on biodiversity in a specific waters. In the present study, two-year phytoplankton data was analyzed for species diversity, community structure changes and variation in 4 adjacent waters:  Lower Thu Bon river  (TB), transition waters (CT), Cu Lao Cham island (CLC) and offshore site (BM) to provide basic scientific data of phytoplankton communities, compare and assess seasonal changes and possible linkage of these adjacent waters. A total of 364 phytoplankton taxa of 12 classes were identified, showing high diversity and with seasonal variation of the investigated waters. There was strong difference of phytoplankton communities among the adjacent waters with low similarity index and the change of dominant species seasonally in each area. The species richness and diversity in the lower Thu Bon river were lower than in other areas. Variation of phytoplankton abundance and diversity along the river transect showed changes in species composition between the dry and rainy seasons but with similar trend in abundance. The low community similarity between the adjacent waters and the transition waters may indicate low impacts of river flow on phytoplankton communities in the coastal waters.

Từ khóa: Cá Mú giống, hiện trạng khái thác, thành phần loài, vịnh Quy Nhơn. MỞ ĐẦUHọ cá Mú (Serranidae) trên thế giới có 475 loài thuộc 64 giống [11]. Trong đó phân họ Epinephelinae gồm các loài cá có giá trị kinh tế cao, sản lượng khai thác chiếm 90% tổng sản lượng của tất cả các loài thuộc họ này. Các loài thuộc phân họ Epinephelinae thường sống trong các vùng biển có nhiều đảo, rạn đá và san hô [4]. Thị trường cá Mú sống trên thế giới rất có tiềm năng, nhiều nước trong khu vực Đông Nam Á và lân cận có giá trị xuất khẩu cá Mú cao như Indonesia, Philippin, Đài Loan, Singapore, Úc [19] [10,[12][13][14]. Hiện nay ở nước ta nhu cầu tiêu thụ trong nước và xuất khẩu cá Mú tương đối cao, vì vậy cá Mú trong tự nhiên đang bị khai thác quá mức. Nghề nuôi cá Mú ở nước ta đã hình thành và đang phát triển mạnh, có hai vùng nuôi tập trung:

Impacts of El Niño Southern Oscillation (ENSO) on the phytoplankton community have been studied in many different waters in the world. However, these effects on phytoplankton communities in coastal upwelling waters are still in need in various aspects such as specific responses of phytoplankton and its dynamics. Phytoplankton data of 15 stations in Ninh Thuan  - Binh Thuan coastal area collected in July 2016 (post El Niño year) and July 2017 (ENSO neutral year) was analyzed and comparing using diversity indices, composition and density of the phytoplankton to measure influences of ENSO on the phytoplankton community structure in coastal upwelling of South Centre Viet Nam. The results revealed significant differences of average species number, the Margalef, Shannon, and Simpson diversity indices and the density of phytoplankton between the two years. These values and indices were significant higher in ENSO neutral year (2017) than the post El Niño year (2016), except the Pielou evenness index. Phytoplankton community structures of two periods were different by 82.26% based on SIMPER analyzing.

The study was carried out during the period from June, 2003 to October, 2004 in the coastal waters of southern central Vietnam (from Da Nang city to Vung Tau city). There were 39 species of poisonous marine  products that can causes a number human deaths. They belonging to three Phyla: Mollusca: 3 species:  (Cephalopoda: I species: Greater blue-ringed octopus (Hapalochaena lunulata Q. & G., 1832); Gastropoda: 2 species: Geographus conus snail (Conus geograpus L., 1758) and Textile conus snail (onus textile L., 1758), Arthropoda: 4 species: (Crustacea: 3 species: Devil crabs (Zosimus aeneus L., 1958); Floridus crabs  (Atergastis floridus L., 1758); (Platrpodia granulosa Ruppell, 1830); Merostomata: 1 horseshoe crabs (Carcinoscorpius rotundicauda Latreille, 1826) and Vertebrata 32 species: Snapper: 1 species: Two-spot red  snapper (Lutjanus bohar Forskal, 1775); Goby: 1 species: Shadow goby (Yongeichthys ne bulosus Forskal, 1775), mainly 21 species puffer of family Tetraodontidae. The Reptilia are 9 species sea snake of subfamily Hydrophinae.