Meiobenthos assemblages in the mekong estuarine system with special focus on free-living marine nematodes

Abstract

Meiobenthos assemblages in eight estuaries of the Mekong river system were investigated in August 2008 (from the Cua Tieu estuary to the Tran De estuary). In each estuary, one sampling station was established for meiobenthos sampling. Twelve major taxa of meiobenthos were recorded in this estuarine system, including Nematoda, and Crustacean Nauplii larvae. The densities of the meiobenthos range from 581 to 3168 inds/10 cm 2 . Nematodes always occupy the highest numbers with a percentage ranging from 64-99%. There are 135 nematode genera recorded in this study with the following as dominant genera Desmodora, Leptolaimus, Halalaimus, Thalassomonhystera, Theristus, Daptonema, Rhynchonema, Parodontophora, and Oncholaimus. Although the biodiversity of the meiobenthos at higher taxa level is not high compared to other marine environments, the estimates of nematode biodiversity at the genus level indicates high values. The increase in number of genera with increasing sampling intensity illustrate that the diversity is underestimated and would have been higher if the authors had considered a larger number of individuals, more replicates per station, and more sampling stations.

The nematode community distribution in two estuaries of the Me Kong delta: Cung Hau and Ham Luong, South Vietnam

“…The dominant families of this study are little similar compared with the study by Adão et al (2008) [1] because of two dominant families Comesomatidae and Desmodoridae were not recorded in Ham Luong and Cung Hau estuaries while at the Mondego and the Mira estuaries the authors found the nematode dominant families were Comesomatidae,Desmodoridae, Chromadoridae and Xyalidae. This result is also quite similar with the recent study byQuang et al (2010) [29] on the marine stations at the mouth of eight estuaries of the Me Kong delta. The authors recorded the family Xyalidae as the most important family in the nematode communities, followed by the Desmodoridae, Monhysteridae and Chromadoridae.…”

“…In Ham Luong, the mean nematode density varied between 90 ± 31 inds/10 cm² (EHL2) and 1524 ± 269 inds/10cm² (EHL4) on the average, while in Cung Hau, the mean nematode density was varying between 105 ± 79 inds/10 cm² (ECH2) station and 1120 ± 534 inds/10 cm² at station ECH1 ( Figure 2). This result is much lower compared with the recent study by Quang et al (2010) [29], where nematode density ranged from 454.0 ± 289.9 to 3137.7 ± 337.1 inds/10 cm². However at the same two stations in the mouth of Ham Luong and Cung Hau, the author recorded nematode densities in the rainy season of 454 ± 290 inds/10 cm² at ECH1 and 683.7 ± 374.4 inds/10 cm² at EHL1.…”

“…In Ham Luong estuary, 71 genera of nematodes were found belonging to 20 families and 10 orders, while, 62 genera belonging to 28 families and 9 orders of nematodes were identified in the Cung Hau estuary. The total number of genera was lower than the 135 genera identified by Quang et al (2010) [28] in the mouth of eight estuaries of Me Kong river, while the number of families is quite similar since 35 families were recorded. In another study on nematode communities in the Thi Vai estuary by Doan Canh and Nguyen Vu Thanh (2000) [9], only 45 nematodes species belonging to 25 genera were found, however in an area which was impacted by industrial sewage water and located approximately 37 km north of the Me Kong river.…”

“…This study found higher records on nematode genera compared with the study by Adão et al, (2008) [1] where 45 and 48 nematode genera were recorded belonging to 19 families in the Mondego and Mira estuaries, Portugal. Sphaerotheristus, Syringolaimus and Theristus; these were also the most common genera in the other intertidal estuarine mudflats systems as observed by Pavlyuk et al (2008) [25] in Cua Luc, north Vietnam and Quang et al (2010) [29] in the Me Kong delta. However, only a few similar dominant genera are observed in the other European systems [3,18,32,23,30] where the dominant common genera were found as Sabatieria, Metachromadora, Daptonema, Anoplostoma, Sphaerolaimus, and Terschellingia.…”

A Checklist of Free-Living Marine Nematodes at Different Ecosystem in Northern Straits of Malacca, Malaysia

“…Food sources such as bacteria or microalgae were abundant in mudflat sediment, and Daptonema which has been characterized as 1B (non-selective feeder) mostly consumed bacteria and microalgae. Heip et al (1985) states that several nematode genera common in many estuarine ecosystems were Adoncholaimus, Anoplostoma, Axonolaimus, Daptonema, Leptolaimus, Microlaimus, Monhystera, Metachromadora, Ptycholaimellus, Sabatieria, Theristus, Tripyloides, and Viscosia. In a different study, Quang et al (2010) found other genera that were also present in high abundance in the Mekong estuarine ecosystem, i.e., Halalaimus, Rhynchonema, Parodontophora, Terschellingia, Desmodora, Onyx, Leptolaimoides, Oncholaimellus, Omicronema, Rhinema, and Haliplectus. However, in our study, Spilophorella, Onyx, Rhynchonema, Viscosia, and Paredesmodora were present in high abundance (Figure 2) in the estuarine ecosystem.…”