Ragworm (Nereidae: Tylorrhynchus SP.) in soil macro-fauna community structure in Hai Duong province - A Northern coastal area of Vietnam

Abstract. The study is focused on ragworm (Polychaeta: Nereidae: Tylorrhynchus) in soil macrofauna community structure in a Northern Coastal Area of Vietnam. Field study was conducted during April and May 2016, at An Thanh, Tu Ky district of Hai Duong province. From Thai Binh river into inhabited areas, five habitat types were investigated including: (a) Thai Binh river bank, (b) Ragworm rearing rice field, (c) Dike, (d) Grassland, and (e) Cultivated field. Determined were 17 soil macrofauna families and 14 orders, belonging to 10 classes: Nematoda, Arachnida, Diplopoda, Chilopoda, Insecta, Oligochaeta, Polychaeta, Hirudinea, Mollusca, and an unidentified. Soil macrofauna family biodiversity recorded decreases in the following order of habitat types: (a), (d) > (e) > (b), (c), respectively identified 10 > 9 > 7 animal families. Among the five habitat types studied, the average macro-fauna density recorded in the habitat (b) - ragworm rearing rice field - was the smallest one of which,, the soil macro-fauna density is counted according to the order of decreasing as follows: Oligochaeta > Coleoptera > Polychaeta > Hirudinea > Mollusca, and Insect larvae, respectively 8.8 > 7.2 > 3.2 > 2.4 > 0.8 individuals per 1 m² of soil area. Ragworm (Nereidae: Tylorrhynchus sp.) was recorded in only one habitat type - the (b) Ragworm rearing rice field in which five other macro-faunal groups including insect larvae, coleopterans, earthworms, leaches and mollusks lived. In this habitat type, the distribution frequency of ragworms found was lower than that of earthworms.

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JOURNAL OF SCIENCE OF HNUE DOI: 10.18173/2354-1059.2016-0064 Natural Sci. 2016, Vol. 61, No. 9, pp. 123-131 This paper is available online at 123 RAGWORM (NEREIDAE: Tylorrhynchus SP.) IN SOIL MACRO-FAUNA COMMUNITY STRUCTURE IN HAI DUONG PROVINCE - A NORTHERN COASTAL AREA OF VIETNAM Vu Quang Manh¹, Nguyen Thi Ha¹, Tran Le Truc Anh², Vu Duc Manh³, Nguyen Thanh Hai³ and Ha Tra My¹ ¹Faculty of Biology, Hanoi National University of Education ²Hanoi University of Science and Technology, ³Hanoi University of Education No. 2 Abstract. The study is focused on ragworm (Polychaeta: Nereidae: Tylorrhynchus) in soil macrofauna community structure in a Northern Coastal Area of Vietnam. Field study was conducted during April and May 2016, at An Thanh, Tu Ky district of Hai Duong province. From Thai Binh river into inhabited areas, five habitat types were investigated including: (a) Thai Binh river bank, (b) Ragworm rearing rice field, (c) Dike, (d) Grassland, and (e) Cultivated field. Determined were 17 soil macrofauna families and 14 orders, belonging to 10 classes: Nematoda, Arachnida, Diplopoda, Chilopoda, Insecta, Oligochaeta, Polychaeta, Hirudinea, Mollusca, and an unidentified. Soil macrofauna family biodiversity recorded decreases in the following order of habitat types: (a), (d) > (e) > (b), (c), respectively identified 10 > 9 > 7 animal families. Among the five habitat types studied, the average macro-fauna density recorded in the habitat (b) - ragworm rearing rice field - was the smallest one of which,, the soil macro-fauna density is counted according to the order of decreasing as follows: Oligochaeta > Coleoptera > Polychaeta > Hirudinea > Mollusca, and Insect larvae, respectively 8.8 > 7.2 > 3.2 > 2.4 > 0.8 individuals per 1 m² of soil area. Ragworm (Nereidae: Tylorrhynchus sp.) was recorded in only one habitat type - the (b) Ragworm rearing rice field in which five other macro-faunal groups including insect larvae, coleopterans, earthworms, leaches and mollusks lived. In this habitat type, the d istribution frequency of ragworms found was lower than that of earthworms. Keyword: Ragworm (Tylorrhynchus), soil macro-fauna, Northern coastal area of Viet Nam. 1. Introduction Soils are natural resources that are important to ecosystem and biosphere processes such as plant production, cycling of organic matter and nutrients, storage of carbon and water, and release of nitrous oxygen, carbon dioxide and methane. Soil biota are thought to harbor a large part of the world’s biodiversity and to govern processes that are regarded as globally important components in the recycling of organic matter, energy and nutrients [1-3]. Received September 16, 2016. Accepted November 30, 2016. Contact Vu Quang Manh, e-mail address: vqmanh@hnue.edu.vn Vu Quang Manh, Nguyen Thi Ha, Tran Le Truc Anh, Vu Duc Manh, Nguyen Thanh Hai and Ha Tra My 124 The importance of the functions performed in soils by macro-fauna together with the physico-chemical and biological changes induced in a soil environment. Soil macrofauna including ragworm (Polychaeta: Nereidae: Tylorrhynchus), is involved in degrading organic matter and mineralizing nutrients, controlling pathogen populations, improving and maintaining soil structure, mixing organic matter in the soil [4-6]. Playing an important role, soil macro-fauna is also considered as a bioindicator. They are very sensitive with the environmental changes, reflecting through quantity of individuals, activity cycles or reproductive cycle [7-9]. This study is focused on ragworm (Nereidae: Tylorrhynchus) in soil macro-fauna community structure, their distribution characteristics according to habitat types at An Thanh, Tu Ky district, Hai Duong province - a coastal area of Northern Vietnam. 2. Content 2.1. Materials and methods Hai Duong is located in the coastal area of Northern Vietnam, covering an area of 1,648.4 km². The province is endowed with a fairly-dense waterways network consisting of Thai Binh and Luoc rivers which deposit, fields with alluvia, supply water for economic production. Thai Binh River starts from the area of Bac Giang Province, where Thuong and Cau Rivers join together, tnext, flows to Hai Duong province becoming a natural boundary between Bac Giang and Hai Duong province, then enters Thai Binh province, finally flows to the East Sea (South China Sea) through Ba Lat river mouth. From that comes the name of the river - Thai Binh river [10]. The study methods are described in details by Ghilarov, Krivolutsky (1975), Mohamed (1999), Nereidae (2005), Pierre Fauvel (1953), Schinner et al. (1995), Thanh, Bai, Pham (1979) [11-16]. The study is carried out in An Thanh, Tu Ky district of Hai Duong province, which is 29.6 kms far from the estuary. The field study for obtaining material samples was in April - May 2016. Figure 1. Map of the study area (red square) in An Thanh, Tu Ky district of Hai Duong province (source: Google map) Ragworm (Nereidae: Tylorrhynchus sp.) in Soil Macro-fauna Community structure 125 Along a straight line of about 2 kilometers from Thai Binh river into inhabited areas, five habitat types were studied, namely: (a) Thai Binh river bank, 20°48’894”N. X 106°27’200”E; (b) Ragworm rearing rice field, 20°48’865”N X 106°27’233”E; (c) Dike between (b) and (d), 20°48’767” X 106°96’930”E; (d) Grassland, 20°48’732”N X 106°26’979”E; and (e) Cultivated field, 20°48’816”N X 106°27’255”E (Figure 1) [10]. Soil macro-fauna were collected from five soil vertical layers, including: (-1) 0 - 10 cm, (-2) > 10 - 20 cm, (-3) > 20 - 30 cm, (-4) > 30 - 40 cm, and (-5) > 40 - 50 cm). Soil macro-fauna samples were taken with 5 replications [5, 15, 17]. 2.2. Results and discussion 2.2.1. Ragworm (Polychaeta: Tylorrhynchus) in soil macro-fauna systematic structure in the coastal area of Northern Vietnam Table 1 and figure 2 present a systematic structure of the soil macro-fauna recorded in An Thanh, Tu Ky District, Hai Duong Province. Recorded are 17 soil macro-fauna families (including five un-identified) and 14 orders (including four un-identified), belonging to 10 classes, namely Nematoda, Arachnida, Diplopoda, Chilopoda, Insecta, Oligochaeta, Polychaeta, Hirudinea, Mollusca, and one unidentified (Table 1, Figure 2). The bio-diversity of macro-faunal families recorded varies according to the five habitat types studied. It decreases according to the following order: (a), (d) > (e) > (b), (c), respectively identified 10 > 9 > 7 animal families (Table 1, Figure 2). Figure 2. Soil macro-fauna community structure (%) according to study habitat types and to animal groups Legend. Habitat types: (a) Thai Binh river bank, (b) Ragworm rearing rice field, (c) Dike between (b) and (d), (d) Grassland, and (e) Cultivated field Vu Quang Manh, Nguyen Thi Ha, Tran Le Truc Anh, Vu Duc Manh, Nguyen Thanh Hai and Ha Tra My 126 Table 1. Ragworm in soil macro-fauna systematic structure according to five study habitat types No. Habitat types Macrofaunas (a) Thai Binh river bank (b) Ragworm rearing rice field (c) Dike (d) Grassland (e) Cultivated field I 1 Nematoda Order ?: (1) Family ? + II Arachnida 2 Arachneida: (2) Family ? + + + + III Diplopoda 3 Glomerida: (3) Glomeridae + + + IV Chilopoda 4 Geophilomorpha: (4) Geophilidae + + V Insecta 5 Blattoptera (5) Blattidae + + 6 Orthoptera (6) Locustidae + (7) Gryllidae + + 7 Hemiptera (8) Belostomatidae + + 8 Hymenoptera (9) Braconide + (10) Formicidae ++ ++ + + 9 Homoptera (11) Cicadidae + 10 Coleoptera (12) Dytiscidae + + + + + (13) Insecta larvae + + + + + VI Oligochaeta Ragworm (Nereidae: Tylorrhynchus sp.) in Soil Macro-fauna Community structure 127 11 Order ? (14) Family ? ++ ++ ++ ++ VII 12 Polychaeta Nereidimorpha ? (15) Nereidai: Tylorrhynchus + VIII 13 Hirudinea: Order ? (16) Family ? + IX 14 Mollusca: Order ? (17) Family ? + + X Unidentified + + Total 9 classes, 14 orders and 17 families 10 7 7 10 9 Note. Habitat types: (a) Thai Binh river bank, (b) Ragworm rearing rice field, (c) Dike between (b) and (d), (d) Grassland, and (e) Cultivated field. Distribution frequency: +Less common: 0-30%,++Common: 31-70%, +++Very common: 71 - 100% Insect larvae and coleopterans were all found in the five studied habitat types, including (a) Thai Binh river bank, (b) ragworm rearing rice field, (c) dike between (b) and (d), (d) grassland, and (e) cultivated field. Three soil macrofaunal groups namely spiders, ants and earthworms (Arachnida: Arachneida, Hymenoptera: Formicidae and Oligochaeta) were recorded in four study habitat types, 80% of all habitat types were studied. Five soil macrofaunal groups, namely Locustidae, Braconidae, Cicadidae, Polychaeta and Nematoda, were recorded in only one habitat type. The ragworm (Polychaeta: Tylorrhynchus sp.) were recorded in only one habitat type, particularly in (b) Ragworm rearing rice field. In this habitat type, other six soil macro-faunal groups were found, namely insect larvae, coleopterans, earthworms, leaches, mollusks, and an identified. An interesting finding is that in the (b) Ragworm rearing rice field, the distribution frequency of ragworms was recorded lower than that of earthworms, respectively identified less common (+0 - 30%) and common (++ 31 - 70%). 2.2.2. Ragworm (Polychaeta: Tylorrhynchus) in soil macrofauna density in the coastal area of Northern Vietnam Table 2 and Figure 3 present the density of soil macrofauna groups counted per 1m² of soil surface in five habitat types studied in An Thanh, Tu Ky District, Hai Duong Province. Vu Quang Manh, Nguyen Thi Ha, Tran Le Truc Anh, Vu Duc Manh, Nguyen Thanh Hai and Ha Tra My 128 The results presented show that the average macrofauna density recorded was different among between study habitats. It decreases according to the following order: (c) dike between (b) and (d) > (d) grassland > (e) cultivated field > (a) Thai Binh river bank > (b) ragworm rearing rice field, respectively obtained 92.0 > 58.4 > 45.6 > 28.8 > 24.0 individuals per 1m² of soil surface (Table 2 and Figure 3). Figure 3. Soil macro-fauna density (individuals per 1m²) according to study habitat Legend: Habitat types studied: (a) Thai Binh river bank, (b) Ragworm rearing rice field, (c) Dike between (b) and (d), (d) Grassland, and (e) Cultivated field Table 2. Ragworm in soil macro-fauna density according to five study habitat types No. Habitat types Macro-faunas (a) Thai Binh river bank (b) Ragworm rearing rice field (c) Dike (d) Grassland (e) Cultivated field I 1 Nematoda Order ?: (1) Family ? 0 0 0 0 0,8 0.8 0 0 0 0 II Arachnida 2 Arachneida: (2) Family ? 4.8 0 2.4 0.8 0.8 III Diplopoda 3 Glomerida: (3) Glomeridae 0.8 0 0 1.6 5.6 IV Chilopoda 0 0.8 0 0 1.6 4 Geophilomorpha: (4) Geophilidae 0.8 0 0 3.2 0.8 Ragworm (Nereidae: Tylorrhynchus sp.) in Soil Macro-fauna Community structure 129 V Insecta 20.8 7.2 51.2 23.2 7.2 5 Blattoptera (5) Blattidae 0.8 0 0 0 0.8 6 Orthoptera (6) Locustidae 0 0 0 3.2 0 (7) Gryllidae 0.8 0 0 0.8 0 7 Hemiptera (8) Belostomatidae 3.2 0 0.8 0 0 8 Hymenoptera (9) Braconide 0 0 0 1.6 0 (10) Formicidae 15.2 0 45.6 16.8 1.6 9 Homoptera (11) Cicadidae 0 0 0 0 2.4 10 Coleoptera (12) Dytiscidae 0.8 7.2 4.8 0.8 2.4 (13) Insecta larvae 0.8 0.8 2.4 2.4 6.4 VI Oligochaeta 0 8.8 35.20 27.2 23.2 11 Order ? (14) Family ? 0 8.8 35.2 27.2 23.2 VII 12 Polychaeta Nereidimorpha ? 0 3.2 0 0 0 (15) Nereidai: Tylorrhynchus 0 3.2 0 0 0 VIII 13 Hirudinea: Order ? (16) Family ? 0 2.4 0 0 0 IX 14 Mollusca: Order ? (17) Family ? 0 0.8 0 0 1.6 X Unidentified 0.8 0.8 0 0 0 Total 28.8 24.0 92.0 58.4 45.6 Note. Habitat types: (a) Thai Binh river bank, (b) Ragworm rearing rice field, (c) Dike between (b) and (d), (d) Grassland, and (e) Cultivated field Vu Quang Manh, Nguyen Thi Ha, Tran Le Truc Anh, Vu Duc Manh, Nguyen Thanh Hai and Ha Tra My 130 The highest macro-faunal density was recorded in habitat (c), 92 individuals were obtained per 1m² of soil surface. An interesting fact found is that, in habitat (b) ragworm rearing rice field, the smallest macrofaunal density was recorded, with 24 individuals per 1m² of soil surface. In this habitat type, densities of soil macro-fauna, according to animal group decrease in the following order: Oligochaeta > Coleoptera > Polychaeta (Tylorrhynchus) > Hirudinea > Mollusca and Insect larvae, respectively recorded 8.8 > 7.2 > 3.2 > 2.4 > 0.8. 3. Conclusion In the coastal area of Hai Duong province, Northern Vietnam determined were 17 families and 14 orders of soil macro-fauna, belonging to 10 classes: Nematoda, Arachnida, Diplopoda, Chilopoda, Insecta, Oligochaeta, Polychaeta, Hirudinea, Mollusca, and one un-identified. Soil macro-fauna family bio-diversity decreases in the following order of habitat types: (a) Thai Binh river bank and (d) Grassland > (e) Cultivated field > (b) Ragworm rearing rice field and (c) Dike, respectively identified 10 > 9 > 7 animal families. It is found out that among five study habitat types studied, the average macro-fauna density recorded in the habitat (b), ragworm rearing rice field is the smallest. 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