Effect of Physico-Chemical Parameters on Crabs Biodiversity

Varadharajan D^*, Soundarapandian P and Pushparajan N

Faculty of Marine Sciences, Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai-608502, Tamil Nadu, India

*Corresponding Author:

Varadharajan D
Faculty of Marine Sciences
Centre of Advanced Study in Marine Biology
Annamalai University, Parangipettai-608502
Tamil Nadu, India
E-mail: heartvaradhan@gmail.com

Received date: October 01, 2012; Accepted date: November 12, 2012; Published date: November 16, 2012

Citation: Varadharajan D, Soundarapandian P, Pushparajan N (2013) Effect of Physico-Chemical Parameters on Crabs Biodiversity. J Marine Sci Res Dev 3:116. doi: 10.4172/2155-9910.1000116

Copyright: © 2013 Varadharajan D, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

If physico-chemical parameters are not suitable, it will affect the distribution of crabs. So, it is designed to know the effect of physico-chemical parameters on the biodiversity of crabs from Arukkattuthurai to Pasipattinam. Minimum atmospheric temperature was recorded in the months of November and December 26.4°C (stations 2 and 8) and maximum 32.3°C was recorded in the months of April and May (stations 2 and 5). Minimum water temperature was recorded in the month of November 26.3°C (stations 2 and 8) and maximum 31.5°C was recorded in the months of April and May (stations 2 and 5). The salinity was minimum in month of December 25.5% (stations 2, 5 and 9) and maximum was recorded in the month of May 35.5 (stations 2, 5 and 9). The minimum pH 7.6 was recorded in the month November (stations 2, 5 and 8) and maximum was 8.3 in the month of May (stations 2, 5 and 8). Minimum dissolved oxygen 2.58 mg/L was recorded in the month of May (stations 2, 5 and 7) and maximum was 5.83 mg/L recorded in the month of November (stations 2, 5 and 8). Light extension co-efficient was recorded minimum, 1.43 Mcm-1 during the summer season in April (stations 5, 6 and 8), and maximum 7.95 Mcm-1, during monsoon season in November (stations 5, 6 and 8). The minimum turbidity 24.0 NTU was recorded during the monsoon in April (stations 2, 3 and 5) and maximum 35. 0 NTU was recorded during summer in December (stations 2, 3 and 5).

Keywords

Physico-chemical; Crab; Biodiversity; Distribution; Affect

Introduction

The coastal ecosystems provide food and other resources, waste disposal, recreation and inspiration [1]. The crustaceans are highly sensitive to pollution [2-4], and their distributions are strongly influenced by the physico-chemical parameters [5]. Nutrients in coastal waters have caused a number of environmental problems, such as death of benthic fauna, decapod crabs occurrence of nuisance algal blooms [6,7], and the disappearance of seagrass and mangroves [7]. Physico-chemical variations induce changes in immune status of crustaceans. These physico-chemical variations are often stressing crustacea, resulting in a reduction of immune vigour. Water quality monitoring has one of the highest priorities in environmental protection policy. The main objective is to control and minimise the incidence of pollutant oriented problems, and to provide water of appropriate quality to serve various environmental purposes [8,9]. The environmental parameters of coastal areas are very important, because the variations in the physico-chemical properties, such as temperature, salinity, pH, dissolved oxygen and nutrients influence on the crustaceans abundance and life cycles. So, in the present study, effect of physico-chemical parameters on the biodiversity of crabs was studied all along Arukkattuthurai to Pasipattinam coast.

Materials and Methods

The physico-chemical parameters were selected for ten different stations viz., Arukkattuthurai (Station-1), Pointcalimere (or) Kodikkarai (Station-2), Muthupettai (Station-3), Adirampattinam (Station-4), Mallipattinam (Station-5), Sethubavachatram (Station-6), Kattumavadi (Station-7), Manamelkudi (Station-8), Jegathapattinam (Station-9) and Pasipattinam (Station-10). The rainfall data were collected from the meteorological unit (Govt. of India). The surface water samples were collected monthly from all stations (stations 1 to 10) during the study period, from January 2010 to December 2010. The temperature (Atmospheric and Water) and pH were recorded immediately after collection, using a standard centigrade thermometer of 0.01°C accuracy and a field pH ELICO Grip pH meter (Model LC-12 0), respectively. Light penetration in the water column was measured with the help of a Secchi disc, and the Light Extinction Co-efficient (LEC) was calculated using Poole and Atkins [10] formula. Salinity was determined by a Refrectometer (Model-2, ERMA, Japan), while Winkler’ method [11] was adopted for oxygen determination, and turbidity was determined by using the standard Turbidity meter (LP- 2000).

For the analysis of nutrients, surface water samples were collected in clean polythene bottles and kept immediately in an icebox, and transported to the laboratory. The water samples were than filtered using a Millipore filtering system and analyzed for dissolved inorganic phosphate, nitrate, nitrite, reactive silicate and ammonia, by adopting standard procedure of Strickland and Parsons [11]. All the statistical analysis was performed by using SPSS 16 software, particularly Box Plot Method.

Results

Rainfall

Total rainfall recorded from the study area was on average of 788 mm. Minimum rainfall was recorded during the month of March (27.5 mm), and maximum rainfall was recorded during the month of November (289.1 mm) in all stations. There was no rainfall during January, February, April and May.

Atmospheric temperature

In the present study, minimum atmospheric temperature was recorded in the months of November and December 26.4°C (stations 2 and 8), and maximum 32.3°C was recorded in the months of April and May (stations 2 and 5) (Figure 1).

Figure 1: Atmospheric temperature (ºC) in different stations from January-2010 toDecember-2010.

Water temperature

In the present study, minimum water temperature was recorded in the month of November 26.3°C (stations 2 and 8), and maximum 31.5°C was recorded in the months of April and May (stations 2 and 5) (Figure 2).

Figure 2: Water temperature (ºC) in different stations from January-2010 to December-2010.

Salinity (%)

The salinity was minimum in the month of December 25.5% (stations 2, 5 and 9) and maximum was recorded in the month of May 35.5% (stations 2, 5 and 9) (Figure 3).

Figure 3: Salinity (%) in different stations from January-2010 to December-2010.

pH (Hydrogen ion concentration)

The minimum pH 7.6 was recorded in the month November (stations 2, 5 and 8), and maximum was 8.3, recorded in the month of May (stations 2, 5 and 8) (Figure 4).

Figure 4: pH in different stations from January-2010 to December-2010.

Dissolved Oxygen (mg/L)

The minimum dissolved oxygen 2.58 mg/L was recorded in the month of May (stations 2, 5 and 7), and maximum was 5.83 mg/L, recorded in the month of November (stations 2, 5 and 8) (Figure 5).

Figure 5: Dissolved Oxygen (mg/L) in different stations from January-2010 to December-2010.

Light extinction co-efficient (Mcm^-1)

Light extinction co-efficient was recorded minimum 1.43 Mcm^-1 during the summer season in April (stations 5, 6 and 8), and maximum 7.95 Mcm^-1 during monsoon season in November (stations 5, 6 and 8) (Figure 6).

Figure 6: Light Extinction Co-Efficient (Mcm-1) in different stations from January- 2010 to December-2010.

Turbidity (NTU)

The minimum turbidity 24.0 NTU was recorded during the monsoon in April (stations 2, 3 and 5), and maximum 35.0 NTU was recorded during summer in December (stations 2, 3 and 5) (Figure 7). Outliers show to the extreme levels of the values.

Figure 7: Turbidity (NTU) in different stations from January-2010 to December-2010.

Total suspended solids (mg/L)

The total suspended solids were varied from 31.75 to 68.4 mg/L. Minimum was recorded during the post monsoon season in January (stations 2, 3 and 5), and maximum during the monsoon season in December (stations 2, 3 and 5) (Figure 8). Outliers show to the extreme levels of the values.

Figure 8: Total Suspended Solids (mgl/1^-l) in different stations from January-2010 to December-2010.

Biological oxygen demand (mg/L)

The BOD values were varied from 1.137 to 3.214 mg/L. Minimum was recorded during monsoon season in November (stations 2, 3 and 5), and maximum during April (stations 2, 3 and 5) (Figure 9). Outliers show to the extreme levels of the values.

Figure 9: Biological Oxygen Demand (mgl/1^-l) in different stations from January-2010 to December-2010.

Chemical oxygen demand (mg/L)

The COD values were varied from 0.248 to 0.572 mg/L. Minimum was recorded during monsoon in December (stations 2, 3 and 5), and maximum during the summer season in June (stations 2, 3 & 5) (Figure 10). Outliers show to the extreme levels of the values.

Figure 10: Chemical Oxygen Demand (mgl/1^-l) in different stations from January-2010 to December-2010.

Nutrients

Nitrate (μM/1^-l): Nitrate concentration was varied from 0.317 to 5.214 μM/1^-l. Minimum was recorded during summer season in April (stations 2, 3 and 5), and maximum during monsoon season in November (stations 2, 3 and 5) (Figure 11). Outliers show to the extreme levels of the values.

Figure 11: Nitrate (μM/1^-l) in different stations from January-2010 to December-2010.

Nitrite (μM/1^-l)

Nitrite concentration was varied from 0.281 to 3.572 μM/1^-l. Minimum was recorded during May (stations 2, 3 and 5) and maximum during November (stations 2, 3 and 5) (Figure 12). Outliers show to the extreme levels of the values.

Figure 12: Nitrite (μM/1^-l) in different stations from January-2010 to December-2010.

Ammonia (μM/1^-l)

The ammonia concentration was varied from 0.845 to 3.423 μM/1^-l. Minimum was recorded during postmonsoon in March (stations 2, 3 and 5), and maximum during November (stations 2, 3 and 5) (Figure 13). Outliers show to the extreme levels of the values.

Figure 13: Ammonia (μM/1^-l) in different stations from January-2010 to December-2010.

Total Nitrogen (μM/1^-l)

The total nitrogen level was ranged from 5.217 to 25.32 μM/1^-l. Minimum was recorded in August (stations 2, 3 and 5), and maximum in November (stations 2, 3 and 5) (Figure 14). Outliers show to the extreme levels of the values.

Figure 14: Total Nitrogen (μM/1^-l) in different stations from January-2010 to December-2010.

Inorganic phosphate (μM/1^-l)

The phosphate concentration was recorded minimum 0.259 μM/1^-l during the post monsoon season in January (stations 4, 7 and 10), and maximum 4.96 μM/1^-l during monsoon season in November (stations 2, 3 and 6) (Figure 15). Outliers show to the extreme levels of the values.

Figure 15: Inorganic Phosphate (μM/1^-l) in different stations from January-2010 to December-2010.

Total Phosphate (μM/1^-l)

The total phosphate level was ranged from 0.312 to 2.69 μM/1^-l. Minimum was recorded in May (stations 2, 3, 5 and 9), and maximum in November (stations 2, 3, 5 and 9) (Figure 16). Outliers show to the extreme levels of the values.

Figure 16: Total Phosphate (μM/1^-l) in different stations from January-2010 to December-2010.

Reactive silicate (μM/1^-l)

Reactive silicate concentration was varied from 1.173 to 3. 021 μM/1^-l. Minimum was recorded during post monsoon in March (stations 1, 3 and 6), and maximum during monsoon season in December (stations 1, 3 and 6) (Figure 17). Outliers show to the extreme levels of the values.

Figure 17: Reactive Silicate (μM/1^-l) in different stations from January-2010 to December-2010.

Discussion

Climate change is an important factor in determining the past and future distributions of crab biodiversity [12-15]. Crustaceans life patterns are strongly related to environmental factors [16,17]. The eutrophication is also spoiling the biodiversity [18]. Physical and chemical factors are highly affected by crustacean’s inhabitants. This study is agreement with earlier studies [19,20]. In general, the organic waste dump caused environmental stress in coastal waters, which resulted to low landing of important crustacean fisheries, and affect the diversity of decapod crabs [21-23]. The physico-chemical parameters are vital ecological factors, as it directly affects oxygen consumption, metabolism, growth, moulting, hormones and survival of crustaceans [24,25].

Rainfall is one of the important factors, which affect the distribution of aquatic animals. The substances present in the air are affected, and also toxic gases and chemicals dissolved so far, entrapped in rain activities. The mangroves, seagrass, salt marshes and coral reef also contaminated due to raining activities [26,27]. Especially where the large freshwater rivers enter the sea, turbid waters are thick with sediment during the annual monsoon season. Huge volumes of water carry huge volumes of phosphate loaded mud, especially off agricultural land, by increasing the concentrations of such substance as nutrients. This could be a major problem for the seagrass and coral reef associated decapods. It makes a great difference of temperature, salinity and turbidity as important factors associated with crustacean’s abundance [28].

In the present study, summer peaks and monsoonal troughs in air and surface water temperatures were observed by several workers from southeast coast of India [29,30]. Tides controlled changes in temperature are distinct during monsoon months, but during other months, heating of the surface water by solar radiation greatly over shadowed the small changes in temperature, such as those induced by tides. The temperature spread of the spring may be the result of the influx of heat from the sun and atmosphere. It is a limiting factor in the aquatic environment. It will affect the metabolic activities, growth, oxygen consumption, reproduction, moulting, survival, distribution and migratory behaviours of crustaceans [31]. The temperature increased blood cell numbers [32], affects blood clotting times [33] and also the phagocytosis [34], affects the antibacterial activity by haemocytes [35], reduction of metabolic rate [36], and change in osmotic pressure of the haemolymph [37]. It has been direct effect on other environmental parameters, such as salinity and oxygenation of the water. The effects of rain on the physiology of aquatic organisms are discussed [38,39] in Penaeus notalis [40], P. indicus [41], Macrobrachium olfersii [42], and in gammarid, Echinogammarus berrilloni [43].

The salinity is an ecological master factor in the distribution of living organisms, likely to influence decapod crabs distribution and production of the coastal ecosystems [44]. The salinity was found to be high during summer season and low during the monsoon season at the stations [45]. The spectral distribution clearly shows that the premonsoon and summer as the season of abundance and minimum catch, and also no catch during monsoon and spring. As a direct relationship between the trawl catches and salinity, temperature as well as plankters, and an inverse relationship between the rainfall and trawl catches. This is agreement with earlier studies by Sudarsan [46], John Samuel et al. [47] and Varadharajan et al. [48]. The monsoon is the period of spawning of decapod crabs, and the spawning activity is related to the intensity of rainfall. The lower temperature and salinity conditions prevailing throughout the period may be the causative factors of spawning [49-51]. Even in the same position, the size at maturity of individual species of the decapod crabs may vary because the moult occurs over a wide range of size. The fast moulting may possible be fast for a considerable amount of time, when the breeding activity is high [52,53].

The pH is another important parameter affecting crab diversity and distribution in an ecosystem. The uptake of CO₂ by the photosynthesizing organisms, especially phytoplankton from the sea, could have increased the pH levels. It can be due to the influence of seawater penetration and high biological activity [54], and photosynthetic activity [55]. It was also quite low during floods in the peak monsoon season, reduction of salinity and temperature, and decomposition of organic matter [56]. The alkaline pH was found to be associated with more number of crab species. However, with increasing pH, the number of species has been reported to decrease [54]. In decapods, pH influences the metabolism, physiology and maturation process [57].

One of the most important abiotic factors influencing young stages, such as zoea and megalopa in aquatic ecosystem, is the dissolved oxygen [58]. This parameter is more critical because it shows whether there is sufficient oxygen in the water for marine life to survive. Pollution is manifested in the low dissolved oxygen levels and in high nutrient levels in these waters, which can lead to an imbalance of crustacean’s communities through the food web. Do concentrations clearly influence the behaviour of decapods [59,60], and life strategies on the basis of oxygen consumption and energy content [61]. Many previous studies reported that oxygen deficiency and stress condition of crustaceans [2,62]. In summer season, dissolved oxygen decreased due to increased temperature and salinity of water [63], this is attributed to the lesser input of freshwater into the study areas [64]. The current and its associated transport of oxygen and food materials strongly influence the growth of decapod species. Oxygen consumption has been reported in several authors in many species of crustaceans [65,66]. The respiration rates influence the metabolism in crustaceans [67-69], and anaerobic metabolism [67,70], will reduce growth and moulting frequency [71], and cause mortality [72], reduction of metabolic rate [36], and change in osmotic pressure of the haemolymph [37].

Light extinction co-efficient at sampling area was high during the monsoon season due to the monsoonal rains, coupled with low intensity of solar radiation and higher concentration of dissolved organic matter and suspended sediments, which resulted in increased turbulence in the water. The post monsoon season at the sampling area due to the removal of suspended materials from the water column and cessation of freshwater flow, reduces the abiogenic turbidity [73]. The marine invertebrates, light from a significant external signal [74] to control various reproductive activities [75]. The initiation and synchronization of spawning, gonad maturation and sex determination are lightdependent reproductive activities and appear to be mediated through photo-neuroendocrine pathways [76]. The extension of photoperiod lengthens the period of reproduction and delays the moult [77]. In decapod crustaceans such as Pachygrapsus marmoratus [78] and Palaemonetes pugio [79], the administration of longer photoperiod accelerates reproduction. The above mentioned examples clearly suggest the role of day length on the initiation of reproductive processes in lower, as well as higher crustaceans.

Surface water temperatures increased and decreased generally day by day in the study periods. The temperatures in the low tide were generally higher than those in high tide. The variation of the turbidity in the sea may be fairly complicated in the near shore region. Since, the high turbidity reduces the growth of phytoplankton, seaweeds and zooplankton; so naturally, numerical density and biomass of decapods species also reduced [80]. The meteorological conditions, especially the strong wind, affect changes of the turbidity. High values were associated with heavy freshwater flow and turbidity during the northeast season. Besides, this visibility as well was poor due to the cloudy weather, towards the end of December. Soil conditions, organic matter, plankters and other minute organisms cause turbidity in water, recognized as a valuable limiting factor in the crustacean’s productivity of water bodies [81]. So, the provisional changes are mostly observed and sensitive sites almost immediately, leaving the polluted area [3]. The relation between the fishing conditions and oceanographical conditions, especially the turbidity was little understood, because of the unfavorable meteorological conditions.

The total suspended solids degrade optical water quality by reducing water clarity and decreasing light available to support photosynthesis [81]. TSS levels and fluctuations influence aquatic life, from phytoplankton to crustaceans. It is especially when the individual particles are small; carry many substances that are harmful or toxic. As a result, suspended particles are often the primary carrier of these pollutants to coastal zones of oceans where they settle. In coastal zones, these fine particles are food source for filter feeders, which are part of the food chain, leading to biomagnification of chemical pollutants in crustaceans and ultimately, in man. In intertidal area, however, deposition of fine particles effectively removes pollutants from the overlying water by burying them in the bottom sediments of the coastal zones. In coastal areas where erosion is a serious problem, suspended solids can blanket the coastal bed, thereby, destroying crustacean’s habitat [82].

The low BOD values recorded during the monsoon season in the sampling areas indicated effective assimilation of organic load. Biochemical oxygen demand is the amount of oxygen utilized by microorganisms to stabilize the organic matter [64]. This process can severely reduce the available oxygen, so that crustaceans and other aquatic life are suffocated. In crustaceans, the oxygen uptake of Pachygrapus crassipes and Gecarcinus lateralis was found to rise slowly from the intermoult, until few days after moult. The oxygen consumption of C. sapidus from proecdysis to postecdysis was studied by Elizabeth et al. [83]. Taylor [84] reported the respiratory responses of C. meanus to changes in environmental salinity. Effect of temperature, salinity on oxygen consumption in a freshwater population of Paleamonetes antennarius was revealed by Giuseppe [85]. Davenport and Wong [86] have studied the behaviroural responses of S. serrata to salinity and low oxygen tension.

The COD is a measure of the oxygen equivalent of the organic matter content of water that is susceptible to oxidation by a strong chemical oxidant. Maximum COD values were observed during summer seasons because of decrease in land wastes inflow, so far increases in temperature, salinity and plankters productivity and oxygen utilization of microbes involved in decomposition activities, and also due to the cumulative effect of higher wind velocity [54,87]. Minimum values of COD was observed during the monsoon season because of the presence of heavy river run off, increased mixing of land wastes into the coast and decreased biological activity because of decreased temperature and salinity. Thus, COD is a reliable parameter for judging the extent of pollution in water [82]. The COD of water increases with increasing concentration of organic matter [54].

High concentration of nitrate observed during the monsoon season might be due to the heavy rainfall and wastes [88]. The minimum concentration of nitrate observed during the summer season could be due to its utilization by phytoplankton, as evidenced by their high population density and also decreased freshwater flow during this period [30]. The marine systems are generally nitrogen limited, excessive nitrogen inputs can result in water quality degradation due to toxic algal blooms, oxygen deficiency, habitat loss, decreases in biodiversity and fishery losses.

The higher nitrite values recorded during monsoon season in the month of November could be due to the increased planktonic excretion, oxidation of ammonia and reduction of nitrate, by recycling of nitrogen, and also due to bacterial decomposition of plankton detritus present in the environment [89]. Further, the denitrification and air sea interaction exchange of chemicals are also responsible for this increased value [90]. The low nitrite value recorded during summer season may be due to less freshwater inflow and high salinity [91]. Maximum nitrite values recorded in monsoon season could be mainly due to the organic materials received from the catchments areas during the receding or outgoing tide [54,91]. Further, excretion of phytoplankton, reduction of nitrate and oxidation of ammonia could all contribute together or individually to increase the concentration of nitrite in the environment [92]. The nitrites are probably the most important environmental variable, because it directly affects the behavior, influencing growth, reproduction, metabolic activities, and abnormal conditions of crustaceans inhabitants.

Algae blooms cloud the water, blocking the light from reaching important underwater grasses that provide food and habitat for zoea to adult crustaceans. Changing the type of nitrogen entering the water from nitrate to ammonia may also cause a fundamental change in the algae community, the building block for the aquatic food web. Species that best accumulate ammonia may be different from those that have thrived on nitrate [30]. Algae fueled by too many nutrients are the largest water quality problem in the environment. The blooms provide food and shade, prevent the growth of undesirable benthic algae, reduce toxic ammonia concentrations and increase oxygen levels. Ammonia is toxic to aquatic life, which affects crustaceans in various ways, such as food into the energy, nutrients and proteins they use for survival and growth, and also cause impairment in numerous organs [93]. Lethal and sub-lethal effects of ammonia on crustaceans, with respect to metabolism and osmoregulation were studied by Chen and Lei [94]. Higher concentration of ammonia was observed during the monsoon season in all sampling stations, but reported in higher values in few sites (2, 3 and 5), particularly in the month of November. Lower concentration of ammonia was observed during the postmonsoon season in all sampling stations, at the same time reported in lower values in few sites (2, 3 and 5), mainly in the month of March. The higher concentration could be partially due to the death and subsequent decomposition of phytoplankton, and also due to the excretion of ammonia by plankton as opined by Segar and Hariharan [95].

The main cause of eutrophication involves the enrichment of water by excess nutrients. It can cause serious problems in the coastal zone through disturbance of ecological balances and fisheries, ultimately interfering with recreational activities, and also quality of marine life [96]. Due to combination of processes affecting the nitrogen cycle in water, the reduction of nitrogen from agricultural lands to coastal ecosystem is observed. It has important indirect effects, such as sea grasses provide food and shelter for crustaceans cause many diseases. In the present study, total nitrogen in water was high during the monsoon season, especially in the month of November. Lower concentration was observed in the month of August. The higher concentration of nitrogen is due to release from the decay of a large number of phytoplankton [97].

High concentration of phosphate was recorded in the present study during monsoon season, might have resulted from the regeneration of phosphate from the bottom muds, and subsequent release of the same in water column by turbulence and mixing caused by heavy winds prevailing during rainy season. Low concentration of phosphate was observed during the post monsoonal season due to the decreased land drainage, sewage and fertilizer disposal from the agricultural lands. As the water masses are without stratification throughout the year, and are in constant contact with the bottom, the regeneration of phosphate taking place at the bottom is constantly utilised by the phytoplankton. The seasonal variations in the phosphate content of the coastal waters have been conducted by Marichamy and Siraimeetan [98] at Madras, Jayaraman [99], in Gulf of Mannar and Palk Bay, George [100] and Subrahmanyan [101] at Calicut by Reddy et al. [102] for the shelf waters of the Arabian Sea, Seshappa and Jayaraman [103] have studied the phosphates in the mud banks at Calicut and Qasim [104] in the cochin backwaters.

The reactive silicate was maximum in the monsoon season, mainly in the month of December, may be due to heavy inflow of monsoonal freshwater derived from land drainage carrying reactive silicate, leached out from rocks. Further, due to the turbulent nature of water, the reactive silicate from the bottom sediment might have been exchanged with overlying water [105]. In addition to phytoplankton uptake, some other processes like absorption and co-precipitation of soluble silicon might also govern the distribution of dissolved reactive silicate in the environment [90]. The low postmonsoon values could also be attributed to uptake of reactive silicates by phytoplankton for their biological activity [106].

The pollution is due to many pathogens, as well as toxic chemicals can exert harmful effect on crustaceans, and also the health of consumers [107]. The contaminated food, sediment, suspended particles as well as water [108,109], contribute to the bioaccumulation of these compounds in crustaceans. Crustaceans have been unlocking vascular systems, in which many haemocytes generously flow in haemolymph [110,111]. Circulating haemocytes of the immune, functions against parasites and microbes [112]. Since, the moult cycle influences the status of a number of physiological processes, and since, an animal’s physiology influences its behavior and its interaction with its environment also the affected haemocyte antibacterial activity of decreased immune mechanism of decapods [113,114].

Crabs are opportunistic omnivores, eating on a variety of foods, with a preference for plants and animal food, in general. Many crabs are not bottom dwellers. These are the active swimmers, living near the surface, feeding on plankton. The abundance of invertebrate that are known as major copepod grazers, such as chaetognaths, ctenophores and medusae, as suggested by Roff et al. [115] and Mills [116]. Availability plants materials are one of the important factors determining the special composition and diversity of crustaceans [117,118]. The mangrove, seagrass beds and salt marshes are acting as a nursery ground, which provide feed for zoea, megalopa, adult and all stages of the decapod crabs. Zooplankton communities in coastal area such as periphyton, along with protozoans, bacteria and detritus, can serve as an indirect food source for crustacean’s young stages to adult. Utilising the high level of nutrients available in the surface waters, the chlorophyll concentration in diatoms proliferate and occur in high abundance [119,120]. This study is agreement with earlier studies [13,121].

In a coastal ecosystem, zooplankton forms an important link in the food chain, from primary to tertiary level leading to the production of crustacean’s fishery. It has been well established that potentials of pelagic crustaceans, either directly or indirectly, depend on zooplankton [122]. By asset of sheer profusion and intermediatary role between phytoplankton and crustaceans, they are considered as the chief index of utilization of aquatic biotope at the secondary trophic level. The herbivorous zooplanktons are efficient grazers of the phytoplankton, and have been referred to as living machines transforming plant material into animal tissue. Hence, they play an important role as the intermediaries for nutrients and energy transfer between primary and tertiary trophic large density, shorter life span, drifting nature, high group and species diversity levels [123]. Due to their and different tolerance to the stress, they are being used as the indicator organisms for the physical, chemical and biological processes in the aquatic ecosystem [124]. Although most of the species of plankters are helpful in fisheries, a few are detrimental to the fishery potential. The copepods have been considered as being primarily major grazers on phytoplankton in most marine ecosystems [125]. It has been grazers of phytoplankton, but also as being an important copepod prey [126]. Certain zooplankton predators, such as decapod larvae, arrow worms and the copepods may voraciously feed on megalopa, decimating the adult crab’s population. The dominant grazers of phytoplankton, copepods, in turn, function as prey for crustaceans also provided in energy and support developmental stages [117], and are natural feed on crustaceans [127]. This study is in agreement with earlier studies [128,129]. In the present study, physico-chemical parameters showed exceptional values in some locations, and also these could be compared to the effect of decapod crab diversity for different manner in this coastal environment. Marine crustaceans are under the influence of numerous environmental factors. The awareness needed in belongings of over exploitation and pollution is increasingly obvious and serious, as for loss of food species, microbial diseases of marine decapods, contamination of edible crustaceans. However, in marine crustaceans, there is a scarcity of data to support the assumption that environmental changes induce a modification of the pollution, leading to an enhanced susceptibility to infectious disease agents.

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