Relevance of Meiobenthic Research: Indian Perspectives

Coastal and marine biodiversity play a crucial role in economy by virtue of their resources, productive habitats and rich biodiversity. Within sixty kilometres of the shoreline more than half the world’s population lives, and this could rise to three quarters by the year 2020 [1,2]. The population surge along the narrow coastal strip is the ultimate driver for escalating pressures on the world’s coastal area, which are dominated by sandy beaches [1]. Thus, much of today’s and near future anthropogenic pressure on global ecosystem is directed at coastal wetlands. India has a coastline of about more than 7500km of which the mainland accounts for 5422km, Lakshadweep coast extends up to 132km and Andaman and Nicobar Islands have coastline of 1962km. More than two hundred fifty million people live within a distance of fifty kilometres from the coast. The dissimilarities between the west and east coasts are remarkable. The west coast is generally exposed with heavy surf and rocky shores and headlands whereas the east coast is generally shelving with beaches, lagoons, deltas and marshes [3].


Introduction
Coastal and marine biodiversity play a crucial role in economy by virtue of their resources, productive habitats and rich biodiversity. Within sixty kilometres of the shoreline more than half the world's population lives, and this could rise to three quarters by the year 2020 [1,2]. The population surge along the narrow coastal strip is the ultimate driver for escalating pressures on the world's coastal area, which are dominated by sandy beaches [1]. Thus, much of today's and near future anthropogenic pressure on global ecosystem is directed at coastal wetlands. India has a coastline of about more than 7500km of which the mainland accounts for 5422km, Lakshadweep coast extends up to 132km and Andaman and Nicobar Islands have coastline of 1962km. More than two hundred fifty million people live within a distance of fifty kilometres from the coast. The dissimilarities between the west and east coasts are remarkable. The west coast is generally exposed with heavy surf and rocky shores and headlands whereas the east coast is generally shelving with beaches, lagoons, deltas and marshes [3].
The benthic system comprehends a highly diverse community, composed of bacteria, micro-meio-and macrobenthos, with the classification of benthic organisms generally relying on the organism size. The term "meiofauna" is actually derived from the Greek word meio meaning "smaller". Research on meiobenthic fauna have been known since the 18th century. The study of meiofauna was probably initiated during the eighteenth century and was carried out by Loven [4] who described the worm under new genus. The term "meiobenthos" was introduced and defined by Mare in her account of the benthos of muddy substrates off Plymouth, England [5]. The term 'interstitial fauna' introduced by Nicholls (1935) was used to denote that the animals living in the interstitial spaces between all types of sediment particles. During the year 1940, Remane [6] proposed the equivalent term "Mesopsammon". The other eminent pioneer meiofaunal researchers are Moore & Neil [7] and Moore [8].
The term "meiobenthos" was introduced and defined in 1942 by Mare [5] in her account of the benthos of muddy substrates off Plymouth, England [5,9] to indicate those benthic metazoans smaller than the 'macrobenthos', but larger than 'microbenthos'. In practice, meiobenthic organisms consist of animals with size ranging from 63µ to 500µ [10] and are also named as maiofauna. The meiofauna are by no means a homogenous ecological group of meiobenthos. Meiofauna inhabits in an array of diversified habitats and niche of freshwater and marine water bodies. Sediments of all kinds from the softest of muds to the coarsest shell gravels and all those in between harbour meiofauna. Meiofauna plays an important role in maintaining ecological balance by predating within their community.
The response of ecosystem to environmental impacts are typically complex and diverse. It has been recognized that chemical and physical measurements are unable to properly assess impacts. The use of faunal diversity as indicator of environmental health, is the most effective, advantageous and cost-effective approach. Benthic infaunal monitoring is widely accepted as the fundamental step to most recent interdisciplinary studies of contaminant effects on ecosystems. Responses of the infauna are representative of overall ecosystem status, because the infauna generally depends upon and interact with biological process in the water column. The Phylum, Nematoda was used as an indicator for assessing the ecological quality of marine ecosystems by the European Water Framework Directive (WFD), Directive 2000/60/EC [13,14].
Not only in pollution monitoring, meiofauna also plays important roles in benthic community processes such as bioturbation (organic decomposition, nutrient cycling, redistribution of organic material, oxygenation of the sediment) and an effective link in food web [15]. These organisms are also being used as indicator for global climate change. Meiofauna stimulate bacterial growth by mechanically breaking down the detrital particles, excrete nutrients or by producing slime trails through the secretion of mucus. The significant top-down control of meiofauna in microbial mineralization of polycyclic aromatic hydrocarbon such as naphthalene has already been proved using molecular tools like RFLP etc. High concentration of Sodium Channel Blockers (SCB), a group of neurotoxin such as tetradotoxin (TTX) and saxitoxin (STX), in free-living marine nematodes were already confirmed using a tissue culture bioassay and their role in accumulation and transfer in marine environment has been proved significant. The analysis of mitochondrial Cytochrome oxidase subunit 1 (COI) gene, nuclear rDNA, rRNA etc. are used generally to reveal the cryptic diversity, intra-genomic variation as well as identification of the meiofaunal groups and new procedures are still waiting to add the accuracy in phylogenetic anlysis. Different laboratory cultural procedures were developed for meiofauna, depending on their feeding and behavioural ecology [16][17][18]. Therefore, smaller marine meiofaunal organisms like free-living nematoda, gastrotricha, ostracoda, foraminifera, oligochaeta, nemaertea etc. can be effectively utilized in translational and regenerative biological research. Free-living marine nematodes represent the major faunal group in respect of their density and divsity in any meiobenthic fanal assemblage. In a recent report, Ghosh and Mandal (2016) published a huge compilation list of free-living nematodes (288 species) recorded from India but need a through revision. Some interesting works on meiobenthos including nematodes were provided by Sinha & Choudhury [76], Sinha et al. [77]. The occurrence of stylet bearing nematodes from Gangetic delta reported by Sinha & Choudhury [78] from Sagar island, West Bengal were not actually free-living forms. Sinha et al. [77] discovered free-living marine nematode Anoplostoma macrospiculum from Indian coast after independence. Some research studies undertaken by Datta et al. [79], Datta et al. [80][81][82], Jacob et al. [83][84][85] have been able to describe some free-living marine nematodes in recent time from North-East coast, West coast and around Andaman sea of India respectively.
Most of the meiobenthic researches from several coastal sites of Indian coastal tract have been concentrated basically on ecological work. Free-living nematofaunal taxonomy relative to ecological work was largely neglected for long time. Some new records and checklists of free-living nematode were published in different journals, but clear taxonomic identity was neither given nor clear taxonomic description provided [86]. Therefore the true taxonomic information of marine nematodes at the northern part of east coast of India as well as from whole Indian coast is still very scant. only on ecology. But in reality, most of the times, it is difficult to get same organisms from those study sites because of the improper taxonomic validation [87]. When a good portion of the recorded data falls into uncertain and incorrect confirmation then the subsequent checklist and the distributional record becomes irrelevant. Museum collection and subsequent registration of the specimens cannot be achieved for the living organisms. For the higher faunal groups, this process cannot be supported sometimes because of conservational purpose. But, for the very delicate meiobenthic fauna, the morphological study without preservation is difficult.
Therefore, the organisms must be euthanized prior to taxonomic work. From this point of view, the demand of the time is to stop the improper way of biodiversity recording and at the same time, it is imperative to develop and adopt better parallel scientific procedures to record the taxonomic diversity by which the scientific community of the world can be benefitted. For such, the proper way of biodiversity recording by comparative morphology can be achieved by detail morphological description as best as possible, clear and unimaginable illustration with photographic support, ecological data and proper registration for museum collection [87]. 16