Invertebrates are common throughout the water columns (plankton and nekton), on plants, litter, and rocks (periphyton) and in the soil (benthos). Most invertebrates have complex life cycles with multiple life stages that may be found in different parts of a wetland, or even entirely outside the wetland. The distribution of aquatic invertebrates within and among wetlands are affected by its hydrological charac-teristics, including depth, frequency and duration of flooding, and physical-chemical characteristics, in-cluding pH, salinity, temperature and oxygen levels. As with other animals in wetlands, wetland inverte-brates need to adapt to low level or even periodic absence of oxygen in the water column and especially in the soil (Chapman et al., 2004). 

Freshwater bodies contain diverse habitats which sup-port myriads species of both plants and animals and support important ecosystem services for human well-being (Adeogun, 2011). Aquatic environments are important habitats for a multitude of species, complex food web and the predominant source of the essential requisite for all life in the biosphere. The aquatic habitats are the most important ecosystem in the whole of the biosphere, which are greatly influenced by water pollution (Gunnarsson et al., 2004). Because of water pollution, many important species especially predators which control many pest are swiped off. Insects con-tribute to several levels of the food web in aquatic systems and a multitude of terrestrial organisms that in turn, depend on them. Kay Thi Moe, (2019) recorded that species composition, occurrence, and relative abundance of some aquatic macro invertebrates in Kan Thone Sint Lake of Pathein Township, Ayeyarwady Region in Myanmar (Ahmad et al., 2018). She recor-ded eight species of order Hemiptera, three species of order Decapoda and Caenogastropoda, two species of order Odonata, Diptera and Coleoptera, and one spe-cies each of Araneae, Amphipoda and Hygrophila under phylum Arthropoda. Among them, nine species were observed in the open water, six species were re-corded in the surface water and attached to the aquatic plants and only three species were recorded from the bottom dweller. 

The highest number of species Gerris remigis was recorded. The highest value of species richness index was (741.596) in site IV and Shannon index (2.522) in site III were observed in Kanthonesint Lake. The objectives of the present research were to -

1) Identify and record the occurrences of macro in-vertebrate species in freshwater wetland,

2) Evaluate the diversity and other related features of the macro invertebrates community in the wet-land and

3) Document habitat characteristics and comment on the opportunities for their conservation.

Study area

The selected study area was the Lan-Kuu freshwater wetland in Mingin Township, Sagaing Region in Myanmar. Mingin is a town on the Southern side of the Chindwin River in Kale District in Sagaing Divi-sion of Burma (Myanmar). Mingin Township is situ-ated between Latitude 22˚ 55́ 30̋ N & 94˚ 37́ 0̋ E. Lan-Kuu wetland is about 2 miles from the Mingin Town-ship, near Auk Satha village (Fig 1). The wetland came into existence in 2008-2009 after the flooding of paddy fields and is called Lan-Kuu Htoo. Presently, it covers about 0.8 ha (i.e. 2 acres), surrounded by three villages – Auk Satha, Atet Satha & Pwetnyet. Water is available in this wetland all year round, with a depth of about 3.05-3.66 meters during the rainy season and about 1.22-1.52 meters during the summer and winter seasons. The farmers, unable to cultivate paddy any-more, now use the water from this wetland for their plantations and cattle. Local villagers are often involved in catching fish & birds from this wetland.

Wetland Plants

There are many macrophytes such as water hyacinths, cattails, hydrilla, duckweed, willow trees and grasses in LanKuu freshwater wetland. The depth of water is a primary determinant of their distribution. As water levels in many wetlands change seasonally and from year to year, most wetland plants grow in varying water depths, including no standing water at all (Cook et al., 1974; Cook 1990, 1999). There are also paddy fields, and farms cultivating sesame, groundnut, and beans are near the LanKuu freshwater wetland.

Sampling of macro invertebrates

Macro invertebrate samples were collected once a month from the study site during the study period from June (2020) to January (2021). A net made of bamboo and wood, and insect nets, were used to collect sam-ples from four different habitat types – surface water, water column, macrophytes, and the bottom. The external morphological characters and coloration of each specimen were noted immediately, morph metric measurements were conducted, and photographs were taken. The collected specimens were then counted and preserved in plastic boxes for identification and detailed studies. The collected species were identified using keys of Subramanian and (Sivaranakrishnan, 2007; IOWATER 2005; Epler, 2006; Easton et al., 2012).

Physico chemical parameters

Monthly data on ambient temperature and rainfall were obtained from Department of Meteorology and Hy-drology, Mingin Township, Sagaing Region in Myan-mar. The water temperature and pH were measured in Lan-Kuu freshwater wetland by the thermometer and PH Test Kit and dissolved oxygen (DO) Test Kit once per month (Rubel et al., 2019).

Data Analysis

Relative abundance

Relative abundance was analyzed following Bisht et al. (2004).

 Number of individual species

Relative abundance = Total number of all species in a particular site

uC = Uncommon (having relative abundance less than 0.0100)

C   = Common (having relative abundance of 0.0100 and above but less than 0.0500)

vC = Very common (having relative abundance of 0.0500 and above).

Estimation of species diversities

Three indices – species richness, Shannon index, and evenness – were used to assess the species diversity of macro invertebrates (Krebs, 2001; Stiling, 1999). Species richness (S) is indicated by the number of species in a sample. The formula of Shannon index of species diversity is as: Hˊ =

-Σ Pi Ln Pi ………………… (1)

Where, Pi is the proportion of individuals found in the ith species Ln is the natural logarithm. A high number of species a more even distribution both increase diversity as measured by the Shannon index (Stilling, 1999). The Shannon index has a minus sign in the calculation so the index actually becomes positive. The higher number of species and a more even distribution both increase diversity as measured by the Shannon index. The actual diversity and the maximum possible can be compared by a measurement called the even-ness value. The formula is –

Evenness = Hˊ/LnS ……………….. (2)

Where, S is total number of species. Evenness is us-ually range between 0 and 1.0.

Species Composition

A total number of 30 species of 27 genera belonging to nineteen families and eleven orders under five classes of three phyla of freshwater invertebrates were re-corded in Lan-Kuu wetland. The highest number of species was found in phylum Arthropoda (77%) fol-lowed by phylum Mollusca (20%) and phylum Anne-lida (3%) in study site during study period. The highest numbers of orders were found in Hemiptera (23%) and lowest numbers of Hymenoptera, Araneae, Decapoda and Opisthopora (3%, each) in Lan-Kuu wetland 

Abundance of macro invertebrates

The total number of macro-invertebrates collected from the studied wetland was 1779 individuals. Hemi-ptera (with 467 individuals) were predominant, follo-wed by Odonata (with 330 individuals), Coleoptera (214 individuals), Decapoda (170 individuals), Lepi-doptera (151 individuals), Architaenioglossa (142 individuals), Orthoptera (133 individuals), Araneae (91 individuals), Sorbeoconcha (83 individuals), Hymeno-ptera (five individuals) and Opisthopora (three indi-viduals) (Table 2).

Occurrence of macro invertebrates

The highest population of macro invertebrates (265 individuals) was recorded in January, closely followed by December (262 individuals), while the lowest (178 individuals) was recorded in June. Dytiscus verticalis was the predominant species (with total 185 indi-viduals), 50 of which were recorded during December-January, while Arocatus rusticus was the rarest (with only two individuals) (Table 2).

Distribution of macro invertebrates

In the present study, a total of 30 species were re-corded in different habitat types of the wetland. Among them, three species each were observed in the surface waters and in the water column, while 17 species were attached to the macrophytes and seven species were recorded from the bottom zone. (Plate 2 and Table 3)

Relative abundance of macro invertebrates

The relative abundance of specimens revealed that nine species were uncommon, 14 were common, and seven were very common in the studied wetland (Table 2).

Species diversity of macro invertebrates

Minimum 20 species were observed in July, while the maximum numbers of species (27 species) were ob-served in December. The Shannon diversity index was minimum (2.746) in January and maximum (3.016) in December (Table 4 and Fig 3 to 5). It is interesting to note that while both the species richness and the di-versity peaked in December, the evenness peaked in July (0.956) when the diversity was low, and the species richness was the lowest. Both the diversity and the evenness are lowest in January. 

Climatic variations at the study site

The monthly temperature (°C) and rainfall (mm) were obtained from the Department of Meteorology, Min-gin, for all the months between June 2020 and January 2021. The ambient temperature (maximum) ranged between 30.5°C-39.0°C and ambient temperature (minimum) between 8.7°C-22.0°C. The maximum and minimum temperatures, otherwise reasonably stable over the summer months, declined between November 2020 and January 2021, the winter season. Rainfall was recorded every month, except December 2020, with a maximum of 167 mm in July (Table 5 & Fig 6).

Physicochemical parameters of water

The water temperature ranged from 30°C to 40°C, the pH values were between 7.4 and 9.0, while dissolved oxygen content ranged from 7.0 to 12.0 mg/l (Table 6 and Fig 7 to 9). The lowest pH value was recorded in August, whereas the highest value was recorded in September.

Species richness, evenness, and the Shannon diversity remained relatively high throughout the study period in the Lan-Kuu freshwater wetland, with a slight increase in the richness and diversity exhibited during the winter months, particularly in December.

The total macro invertebrate population was also reasonably consistent throughout the study period but peaked in December-January. While the ambient tem-perature was lower during the winter months, perhaps the lack of rainfall in December 2020 accounts for the increase in total population, species richness, and diversity of macro invertebrates. Water regimes, parti-cularly permanence and hydro periods, are the prime determinants for wetland macro invertebrate diversity (Gleason and Rooney, 2018). The distribution of aqua-tic macro invertebrates within and among wetlands is also affected by water chemistry, especially pH and salinity, temperature, and oxygen levels. Dissolved oxygen is one of the critical factors affecting inver-tebrate abundance and diversity (Thorp et al., 1991). Temperature and pH also affect the abundance and diversity of invertebrates (Covich et al., 1999). Of the 30 species encountered, 17 were associated with macrophytes. However, none of these has the potential to become pests. While snails from the genus Pomacea are common in the Lan-Kuu wetland, the potential pests such as the golden apple snail (Pomacea can-aliculata) or the island apple snail (Pomacea insul-arum) are notable by their absence. These pest species, initially introduced in Asia-Pacific from their native habitat in South America around the 1980s, can sig-nificantly reduce macrophytes and paddy biomass, shifting the wetlands towards an algal dominated sys-tem. It is not just the absence of pests but the presence of diverse species that draw special attention to this wetland. Even at the order level, the dominant group (Hemiptera) constitutes barely more than a quarter of the total macro invertebrate assemblage. The species diversity index combines species richness and even-ness indices into a single quantity (Yazdian et al., 2014). The consistently high values of the macro invertebrate diversity are perhaps best explained by the permanence of the water body, supported by regular rainfall in the Lan-Kuu freshwater wetland. The lack of rainfall in December supports this idea since there is a marked change in the diversity of macro inverte-brates in January.

The Lan-Kuu freshwater wetland has emerged as a mature habitat for diverse macro invertebrates, in-dicating robust ecosystem functions that merit con-servation initiatives. As the base of the ecological food chain is diverse and productive, the possibility of Lan-Kuu freshwater wetland to attract waterfowl is high, opening up possibilities for ecotourism in the region. The introduction of tourism will benefit farmers in the region who may have lost their paddy fields to the wetlands and have shifted to fisheries and waterfowl capture. The key hydrologic driver of the Lan-Kuu freshwater wetland appears to be rainfall, which means that conservation efforts may be limited to protecting it from either over-extraction of biological material or introducing pest species into the system. However, there is a strong need to continue monitoring its bio-logical diversity, particularly those of the macro-physics and the macro invertebrates.

Firstly, I wish to greatly express my gratitude to my supervisor Dr. Somnath Bandyopadhyay, Associate professor, School of Ecology and Environmental Studies (EES), Nalanda University, India for his gui-dance, cooperation and advice throughout the study period. Secondly, I am grateful thank to my younger sisters and brothers for helping in collection of speci-mens. Last, I wish to express my deepest gratitude to my parents for their kindness and helping in collection of specimens throughout the period of this work.

The author declares there is no conflict of interest to publish it.