Relationship of Free - Lingving Nematode Communities to Some Environmental Characteristics in the Organic Shrimp Farms, Ca Mau Province

Abstract

Nematode communities (NC) in Tam Giang’s organic shrimp farms ponds (TGOSFP), Nam Can district, Ca Mau province were investigated in three seasons (March - dry, July - transfer and November - wet season) of 2015. Our findings underlined that the NC were expressed by high density and diversity. In addition, the environmental characteristics in TGOSFP may also be not quite optimal for shrimp farming because of high percentage of TN, TOC, low pH and anaerobic condition in sediment. The results of CCA analysis showed that main environmental parameters, such as TN, TOC, depth, DO, salinity and pH almost completely governed the abundances of several dominant gennera, things like Desmodora, Sabatieria, Terschellingia, Dichromadora, Pomponema, Halalaimus, Ptycholaimellus and Sphaerotheristus. Subsequently, the results of Pearson correlation confirmed that the abundances of genus Sabatieria, Terschellingia were significantly positive correlated with TOC, TN and depth. In contrast, genera like the Desmodora, Halalaimus and Ptycholaimellus had negative correlations with organic enrichment (TOC and TN). Additionally, almost genera were positively correlated with salinity. Analysis of the dominant nematode genera in combination with maturity index (MI) value are able to determine the ecological quality status of sediment (EcoQ) in TGOSFP. Results showed that moderate and poor EcoQ in most of TGOSFP throughtout the dry - trans - wet season. The attribute of NC and their correspondence with environmental characteristics can be considered as a good tool for environmental monitoring.

The Seasonal Variability in The Genus-Family Structure of Free-Living Nematode Communities in Organic Shrimp Farming Ponds, Ca Mau Province

“…Similar results have been reported by Hourston et al (2009) in Swan river estuary (West coast of Australia), nematode densities were also generally highest in spring, due to increases in the abundance of natural food (microphytobenthos) [10]. The unplanned expansion in shrimp farming in the Mekong Delta region has also had negative effects on the environment and caused devastating damage to mangrove forests [11]. A model of organic shrimp farms is developed to combat this problem.…”

“…Overall, the nematode communities in eight organic shrimp ponds, Tam Giang commune, Nam Can district, Ca Mau province consisted of 75 genera belonging to 24 families, 7 orders, in dry season. However, in rainy season the number of collected genera was relatively low, with 57 genera, 26 families, and 9 orders [11].…”

“…Tran et al (2018) underlined that the environmental sediment in dry season of an organic shrimp ponds was separated from that ịn rainy season. Salinity was a main environmental variable in the dry season, whereas in rainy season was governed by total nitrogen (TN), total organic carbon (TOC), and dissolved oxygen (DO) [11]. It is well known that the nematode community characteristics (density, diversity, distribution, and functional properties) can be affected by several abiotic/biotic variables such as salinity, temperature, organic matter and nitrogen, sediment grain size, oxygenation level, and food availability [17][18][19][20].…”

“…Thus, several studies have been performed for the ecology of nematodes in organic shrimp farm pond's sediments. Free-living nematode communities in the Tam Giang's organic shrimp farms ponds, Nam Can district, Ca Mau province were expressed by high density and diversity [11]. This characteristic of free-living nematode communities in organic shrimp farming ponds might provide a suitable natural food source for shrimps and enrich the benthic food web [15].…”

“…Additionally, salinity was a main environmental variable in the dry season, whereas in the trans and wet seasons were governed by Fe 2+ , Fe 3+ , TN, TOC, DO, pH, and depth. These environmental characteristics almost completely governed the dominant genera such as Desmodora, Sabatieria, Terschellingia, Dichromadora, Pomponema, Halalaimus, Ptycholaimellus, and Sphaerotheristus [11].…”