| Main results | - Theoretical results;
(i) A total of 112 nematode species from 23 families belongs to 8 orders was found in the estuary and mangrove ecosystems, in which there were one new genus – Isocanthonchus Gagarin et Nguyen Vu Thanh, 9 new free-living species and one new plant parasitic species.
(ii) In mangrove habitat, where was mostly consisted of Kandelia obovata, 65 marine nematode species were found, whereas there were 65 species occurring in the intertidal mudflat with 22 species were solely inhabit in the tidal flat. Among them, 9 genera were first recorded in Vietnam.
(iii) Family Xyalidae was widely distributed and numerically dominant in both dry and rainy seasons (21 species, 7 genera), followed by Leptolaimidae (13 species, 6 genera), Desmodoridae (10 species, 6 genera), Comesomatidae (9 species, 5 genera), Oxystomidae and Chromadoridae.Genus Daptonema (Xyalidae) was particularly not only abundant but also the most species-diverse (12 species).
(iv) The genera that were first recorded in Vietnam included Curvolaimus, Polygastrophora, Lanzavecchia Chromadora, Prochromadorella, Paracyatholaimus, Croconema, Chromaspirina, Parasphaerolaimus, Eleutherolaimus, Paralinhomoeus, Metalinhomoeus, Southerniella, Desmoscolex, Desmotimmia and Dolichodorus.
(v) Microcosm experiment results showed the significant differences among species structure along both temperature(23oC, 28oC, 33oC) and salinity gradient (25‰, 30‰, 35‰). The elevated temperature caused speedy water evaporation that leaded to salt-accumulated process. Therefore the salinity in the modified temperature treatments increased proportionally with the temperature.Diversity index (H’) for communities in coarse-habitat was highest in 28oC and reduced in 33oC with the salinity 32‰ and 39‰, respectively. Communities in fine mud habitat showed rapidly numerically change with the elevation of temperature (28oC, 33oC).The results once again demonstrated salinity was the key factor that determined the development and distribution of meiofauna. But the affect of acute changing salinity was more severe in comparison with its gradually salt accumulation. Algae and bacteria seemingly showed important roles on species structure by top-down control.
(vi) Study of Amphipoda had found 17 species in 11 genera belongs to 7 families. Genus Ampelisca – Family Ampeliscidae, was abundant the most. Number of species was higher in the beginning and the end of dry season and lower in the rainy season. The individual densities in the studied area were rather similar except for the station at Ba Lat estuary (BL7). The number of individual here was 2-10 times higher than the amphipod density in the other stations. The most dominant group in BL7 was Sinocorophium which belongs to family Corophiidae.
(vii) 22 copepoda specieshad been identified. They belong to 20 genera in 10 following families: Ameiridae, Canuellidae, Cletodidae, Darcythompsoniidae, Ectinosomatidae, Laophontidae, Miraciidae, Tachidiidae, Cyclopidae and Oncaeidae.
(viii) Based on the collected specimens, there were 10 polychaete species that belong to 9 genera in 9 families of two subclasses Polychaeta Errantia và Polychaeta Sedentaria. The number of collected species comprised 15,4% of the total species in the North and 40% of the total species number in Xuan Thuy. All species had been found in the previous researches.
(ix) Among studied stations, BL1 had the highest number of polychaete species (7 species), comprised 70% of total number of species. Simultaneously, the density in BL1 was also rather high (26,6 – 46,7 ind/m2). Hence, it is scientifically recommended to use BL1 as a climate change monitoring station with higher reliable.
- Applied results
(x) The nematode species showed high potential to be used as environmental bioindicators. They were abundant in both dry season and rainy season. The propounded climate change indicator species in Red River wetland can beDaptonema paraoxyuroides n. sp; Sphaerotheristus validum; Sphaerolaimus maeoticus; Parodontophora obscurus; Sabatieria foetida và Terschelligia lissa Timm, 1962.
(xi) Some polychaete species also can be promising indicator for climate change in Red River wetland because of their wide distribution and high density. They are: Nephthys polybranchisa (73,1 ind/m2), Prionospio sp. và Capitellethus sp. (46,7 ind/m2) |
