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

Hydrographical parameters and phytoplankton assemblages along the Pondicherry-Nagapattinam coastal waters,southeast coast of India

Pitchai SAMPATHKUMAR*,Srinivasan BALAKRISHNAN, Krishnamoorthy KAMALAKANNAN,Rethinavelu SANKAR,Lakshmanan RAMKUMAR, Subramani RAMESH,Neelamegam KABILAN,Thambusamy SURESHKUMAR, Chellam THENMOZHI,Mookapillai GOPINATH,Sekar JAYASUDHA, Amalanathan AROKIYASUNDRAM,Thiruvarasan LENIN,Thangavelu BALASUBRAMANIAN

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

Hydrographical parameters and phytoplankton assemblages were determined along the Pondicherry,Parangipettai and Nagapattinam coastal waters,southeast coast of India.All the hydrographical parameters such as sea surface temperature,salinity,pH,total alkalinity,dissolved oxygen and nutrients like nitrate,nitrite,inorganic phosphate and reactive silicate,chlorophyll a and phytoplankton assemblages were studied for a period of fve months(May,August,September 2010,March and November 2011).Over 121 species of phytoplankton represented by 93 species of diatoms,16 species of dinofagellates,9 species of blue-green algae,2 species of greens and 1 species of silicofagellate were recorded.High phytoplankton species diversity was found in March 2011 when salinity and nitrate concentrations were low and reactive silicate and inorganic phosphates were moderate.Species diversity was low during May 2010 when increased sea surface temperature,salinity and low nutrients availability were observed.Coscinodiscus centralis,Diatoma vulgaris and Proboscia alata were dominant,especially Coscinodiscus sp.distributed in all stations whereas Skeletonema costatum,Odontella sinensis and Ditylum brightwellii were abundant in August and September 2010.From principal component analysis and multiple regression analysis,it is evident that variables like sea surface temperature and dissolved oxygen are the most important factors infuencing the seasonal pattern of phytoplankton population.

Hydrographical parameters;Phytoplankton;Southeast coast;Bay of Bengal;Seasonal variations

1.Introduction

A multitude of physical,chemical and biological process affects marine organisms in coastal areas.Physico-chemical parameters,species composition and seasonal variation in phytoplankton abundance in Indian coastal waters have been well studied(Perumal et al.,1999;Govindasamy et al.,2000; Rajkumar et al.,2012).Marine phytoplankton communities usually comprise several taxonomic groups,and contribute to primary production and interaction between tropic levels(Roy et al.,2006).Phytoplankton initiates the marine food chain, being served as food to primary consumers like zooplankton,shellfsh and fnfsh(Sridhar et al.,2006;Tas and Gonulol, 2007;Saravanakumar et al.,2008).Biomass and productivity of phytoplankton in different size ranges are important factors regulating the productivity of higher tropic-level organisms. Phytoplankton contributes about half of the global primary production,the other half being due to terrestrial plants.According to NASA,phytoplankton produces 50%-90%of all the oxygen in the air,depending on the seasons(Thangaradjou et al.,2012).Besides serving as a primary producer,the freeliving phytoplankton serves as feed and caters for the energy needs of planktivorous organisms and is the key factor capable of determining the fshery potential of the region(Falkowski et al.,1998).The distribution of phytoplankton is not always uniform and varies spatially and temporally.Phytoplankton dynamics or the time dependent changes in phytoplankton biomass are the result of a complex interplay of physical, chemical and biological processes.Among all nutrients, availability plays a key role in determining the phytoplankton population density(Grenz et al.,2000;Elliott et al.,2002).

The qualitative and quantitative studies of phytoplankton have been utilized to assess the quality of water(Adoni et al., 1985;Chaturvedi et al.,1999;Ponmanickam et al.,2007; Shekhar et al.,2008).Phytoplankton are the primary producers forming the frst trophic level in the food chain.Diversity of planktonic organisms is quite high in fertile standing water bodies.Phytoplankton diversity responds rapidly to changes in the aquatic environment particularly in relation to silica and other nutrients(Eggs and Aksnes,1992;Chellappa et al.,2008).Several phytoplankton species have served as a bioindicators(Vareethiah and Haniffa,1998;Bianchi et al., 2003;Tiwari and Chauhan,2006;Hoch et al.,2008)and it is a well suited tool for understanding water pollution studies, information on relationship between physico-chemical parameters and plankton indicators of water pollution is limited (Ahmad and Siddiqui,1995;Rana,1996;Rajagopal et al., 2006).Earlier works in Bay of Bengal were mainly concentrated on the taxonomic identifcation of different phytoplankton genera and very confned to the specifc regions of Bay of Bengal,while the studies on regional and seasonal distribution of phytoplankton were meager.Phytoplankton ecology at different parts of Bay of Bengal coast was well documented over a period of time(Edward and Ayyakkannu, 1991;Gouda and Panigrahy,1996;Saravanane et al.,2000, 2004;Panigrahi et al.,2004).Despite these facts of phytoplankton assemblages of near shore waters of the Bay of Bengal is in isolation and not holistic.The present study was made to obtain the present status of hydrographical parameters and phytoplankton assemblages along the Pondicherry,Parangipettai and Nagapattinam coastal waters,southeast of India. This information would be helpful in the ecological monitoring of this ecosystem.

2.Materials and methods

In-situ hydrographical parameters were recorded at ten sites in three sampling stations along southeast coast by the organized cruises using CRV Sagar Paschmi of NIOT(National Institute ofOcean Technology)during May,August, September 2010,March and November 2011.Three sampling stations were fxed at 0.5 km,1.0 km,1.5 km,2.0 km,2.5 km, 3.0 km,3.5 km,4.0 km,4.5 km and 5.0 km distance points off Pondicherry(12.442°N;80.551°E)coastal region is having harbor with lot of fshing activities and a number of industries are situated along the coast which are discharging lot of effuents.Further it is an important tourism centre with related activities.Numbers of rivers are joining into the sea.Parangipettai(11.852°N;80.525°E)coast is an interesting region having Bengal Sea,Vellar and Coleroon estuaries,Kille back water besides Pichavaram mangroves.The Vellar estuarine complex has luxuriant mangroves and is of important nursery ground for many fnfsh and shell fshes.Further,there is lot of fshing activities,agriculture activities and number of shrimp farms operations are going on in this region.Various branches of the river Cauvery such as Vellaiaru,Kaduviaru River, Odampokkiaru and Vettaru pass through in the surrounding areas of Nagapattinam(11.301°N;80.168°E)coast.In the Nagapattinam harbor,there are about many hundreds of mechanized boats and catamarans,employed for fshing. These stations were selected as they represent the north and central part of the southwest Bay of Bengal.Gulf of Mannar National Park area covered with coral distribution where the environmental variables behave differently.

Several environmental variables were monitored and water samples were examined from over a period of fve months.Sea surface temperature(SST)was measured using a digital multistem thermometer of 0.1°C accuracy.Salinity was estimated using a hand-held refractometer(Atago hand refractometer, Japan)and the pH(hydrogen ion concentration)was measured using a pH pen(pH tester,Malaysia)with the accuracy of ±0.1.Dissolved oxygen(DO)was estimated by the modifed Winkler's Method(Strickland and Parsons,1972).Surface water samples were collected(11 samples)by using the Niskin water sampler and were stored in the deep freezer after adding 1 ml of saturated mercury chloride to avoid any further degradation of nutrients by phytoplankton and transported to the laboratory.Samples were fltered using a Millipore fltering system through a 0.45 μm GF/C flter paper and dissolved micronutrients such as the NO2was measured by a colorimetric method using sulfanilamide,NO3by the cadmium reduction method,inorganic phosphorus(IP)and total phosphorus(TP)by the ascorbic acid method and reactive silicate by the molybdate method using a PC based double beam spectrophotometer(Systronics-2202).Chlorophyll a concentration was estimated by the method of Strickland and Parsons(1972).

Phytoplankton samples were collected by towing a phytoplankton net made of net gauze of bolting silk or nylon cloth (mesh size 48 μm)for half an hour on the surface of the water at all the sampling stations at different months.These samples were preserved in 5%neutralized formalin and used for further analysis.The volume of water fltered was calculated by using the formula V=r2dπ,where V is the volume of water fltered,r is the radius at the mouth of the net,d is the distance through which net was towed.This was used for quantitative analysisof phytoplankton.Phytoplankton dominance index(Y)in each collection was calculated using the formula:

where niis the number of the individuals of species i,fiis the frequency of species i that occurred in any particular sample and N is the total number of species.

Phytoplankton was identifed using the standard literatures (Desikachary,1959,1987;Taylor,1976;Anand et al.,1986). The phytoplankton samples were sorted and assigned to fve major groups viz.diatoms,dinofagellates,silicofagellate, blue-green algae and greens.Different statistical tools were used to know the diversity indices,richness and evenness using the bio-diversity software,PRIMER (Ver.6.1.11). Biodiversity indices were calculated following the standard formulas;species diversity(H')was calculated using the following formula (Shannon and Wiener, 1949)log2pi,where piis the proportion of individuals of each species belonging to the ith species of the total number of individuals.Species richness(D')was calculated using the followingformulagiven by Simpson(1949)D'=1-C;pi=ni/N;evenness or equitability(J')was calculated using Pielou(1996)formula:J'=H'/Jns or J'=log2S. The entire exercise was repeated for three stations for wider spatial representation with respect to different seasons such as post-monsoon(March),summer(May and June)and pre-monsoon(August and September)which are classifed based on northeast monsoon prevails in the region during November.

Multivariate techniques like principal component analysis (PCA)and multiple regression are used for relating environmental variables with the phytoplankton population density. PCA was used to analyze the environmental parameters and multiple regression was to calculate the values of a dependent variable,given a set of predicted variables which was used to determine the extent to how the variables contributed to the phytoplankton population density.These tests were performed by SPSS Ver.16.0 statistical software.

3.Results

Hydrographical parameters are considered as one of the most important features that are capable of infuencing the growth,abundance and diversity of phytoplankton in the marine environment and have showed wide temporal and spatial differences.Variations in hydrographical parameters of the surface seawater are given in Fig.1.All the hydrographical parameters showed clear seasonal patterns,which are very typical to the tropical marine environment.SST recorded at three different coastal stations ranged from 25.0°C to 36.2°C. The minimum SST was observed during August 2010 at station I and the maximum was registered during May 2010 at station III.The observed salinity values ranged between 26.0 g L-1and 35.1 g L-1(November 2011 and May 2010) and it did not vary dramatically among all three stations. Hydrogen ion concentration also did not show much variation among all the stations and seasons and it ranged from 7.9 (station III during September 2010)to 8.5(station I and III during May 2010 and November 2011).The DO concentration varied between 2.40 mg L-1and 5.25 mg L-1,registering maximum at station II during November 2011 and minimum at station I during August 2010.Total alkalinity was ranged from 58 mg L-1to 149 mg L-1with the maximum at station I during May 2010 and minimum at station II during November 2011.Total suspended solids(TSS)were ranged from 28 mg L-1to 112 mg L-1with the maximum during May 2010 and November 2011 and minimum during September 2010 at station I and III.

Both the maximum(3.677 μmol L-1)and minimum (0.047 μmol L-1)nitrate concentration was registered during March 2011 at station III and November 2011 at station I and II respectively. The nitrite concentration varied from 0.02 μmol L-1(November 2011 at station I)to 1.353 μmol L-1(September 2010 at station I).The minimum inorganic phosphateconcentration(0.048μmolL-1)wasrecordedduringMay 2010 and November 2011 at station II&III and the maximum concentration (1.094 μmolL-1)was registered during September 2010 at station I.The total phosphorus was maximum(2.392 μmol L-1)during September 2010 at station III and minimum concentration 0.048 μmol L-1was noticed at station I during November 2011.The reactive silicate concentration ranged from 4.012 μmol L-1to 25.320 μmol L-1with the highest value during September 2010 at station I and the lowest during May 2010 at station I.The NH4concentration ranged 0.005 μmol L-1to 0.431 μmol L-1with the maximum during May 2010 and minimum during November 2011 at station I.Chlorophyll a concentration ranged from 0.001 μg L-1(November 2011 at station III)to 8.758 μg L-1(March 2011 at station I).

3.1.Species composition

Totally 121 species of phytoplankton were identifed from three stations.Of which,93 belonging to diatoms(Bacillariophyceae)16 belonging to dinofagellates(Dinophyceae),9 belonging to blue-green algae(Cyanophyceae),2 species of greens(Chlorophyceae)and 1 species of silicofagellate (Chrysophyceae)(Fig.2).Highphytoplanktonspeciesdiversity was found in March 2011 when salinity and nitrite concentrations were low and reactive silicate and inorganic phosphates were moderate.Species diversity was low during May 2010 whenincreasedSST,salinityandlownutrientsavailabilitywere observed.During May 2010 Coscinodiscus centralis,Diatoma vulgaris and Proboscia alata were dominant,especially Coscinodiscus sp.distributed in all stations whereas Skeletonema costatum,Odentella sinensis and Ditylum brightwellii were abundant in August and September 2010.

3.2.Population density

The phytoplankton population density varied differently at stations,10-6883 Cells L-1(station I),10-6350 Cells L-1(station II)and 8-8310 Cells L-1(station III).The maximum density was recorded during pre-monsoon and minimum during post-monsoon and monsoon.The maximum and minimum phytoplankton population density was observed in station III.The number of individual species in different phytoplankton groups started to increase from the postmonsoon season and reached its maximum in the premonsoon season.The observed high population density and species diversity during the pre-monsoon season might be due to the predominance of diatoms such as Asterionellopsis japonica,Chaetoceros affnis,D.brightwellii,S.costatum, Chaetoceros laciniosus,Navicula clavata and Triceratium reticulatum.During summer season,C.centralis,D.vulgaris and P.alata are found to be abundant.The dinofagellate, Prorocentrum micans was observed once during the premonsoon season and there was no much change in Cyanophyceae species composition between seasons.

3.3.Phytoplankton species diversity indices

In the present study,species diversity index was varied from 3.810 to 3.950.The minimum was in station II during May 2010 and the maximum was in station I during August 2010,but low species diversity was observed in the present study(Fig.3).The species richness index fuctuated between 0.972 and 0.976.The minimum species richness was observedin station II during May 2010 and the maximum was in station I during May,August 2010,March and November 2011 (Fig.4).The species evenness index was varied from 0.645 to 0.666.The minimum species evenness was in station II during May 2010 and the maximum was in station I during August 2010(Fig.5).

3.4.Principal component analysis

Principal component analysis was performed on the normalized data set.Only the components with eigen concentrations greater than 1 were considered for interpolation. Different physico-chemical variables and phytoplankton population density was subjected to PCA using varimax rotation. PCA of the whole data set yielded four components explaining 87%of the total variance and the component's loadings greater than 0.5 has been taken into consideration for the interpretation.Further,the initial communalities were more than 0.5 for all variables which provide an index to the effciency of the reduced set of components and degree of contribution of each variable in the selected four components.Phytoplankton population density was considered as the dependent variable and the physico-chemical variables are considered as independent variables.The approximately 80%of the variability of phytoplankton population is accounted for by the variables in the model are viewed for all stations among the variables where pH,DO,nitrite,reactive silicate and IP are positively infuencing the phytoplankton population density whereas SST,salinity,nitrate and TP are negatively infuencing the phytoplankton population density.

4.Discussion

This short time series data may allow us to understand the effects of short time variations in the biological and physicochemical conditions on the eutrophication in the coastal waters,southeast coast of India.Bay of Bengal is considered to be relatively less productive compared to its western counterpart Arabian Sea(Qasim,1977;Radhakrishna et al.,1978; Prasannakumar et al.,2002).The seasonal upwelling and cold core eddy and some sporadic events(cyclones)to enhance moderate phytoplankton production of the Bay of Bengal were observed at isolated patches(Gomes et al.,2000;Madhu et al., 2002;Prasannakumar et al.,2004).Besides this spring intermonsoon,eddies and recirculation zones form in the coastal region of the bay due to the western Bay of Bengal current found to enhance phytoplankton growth to some extent (Gomes et al.,2000;Prasannakumar et al.,2004).Whereas in monsoon seasons(southwest and northeast monsoon),the nutrient inputs from river runoff trigger primary production of the coastal waters of the Bay of Bengal(Gomes et al.,2000; Madhu et al.,2002;Madhupratap et al.,2003).All these make the Bay of Bengal phytoplankton distribution as more seasonally infuenced by varied physical and chemical parameters.Hence,the present study investigated the seasonal change in phytoplankton assemblages and primary production in the southeast coast of India with respect to the prevailing hydrographical environment through planned systematic new data collections.

Generally,SST has been infuenced by the intensity of solar radiation,evaporation,freshwater infux and cooling and mixup with ebb and fow from adjoining neritic waters.Infuence of temperature in phytoplankton community dynamics has been investigated for different species and certain phytoplankton species have been observed to have a unique temperature range for growth(Eppley,1972).Change in SST tend to alter biological,physical and chemical reactions within an organism,thus affecting community structure by selecting those best suited to survive(Dupuis and Hann,2009)and exert controls on seasonal succession of plankton community structure.The phytoplankton characteristic of the Bay of Bengal was largely dominated by diatoms in all seasons, contributing up to 80%of total abundance with low phytoplankton abundance during summer when there was high water temperature confrming the abundance of diatoms was inversely related to temperature(da Silva et al.,2005;Turner et al.,2009).

The SST varied from 25.0°C to 36.2°C mainly with changes in monthly variations.Higher SST recorded during the May 2010 might be due to the increased solar radiation (Satpathy and Nair,1990;Richardson et al.,2000).Though the SST is capable of altering the reproduction,growth,metabolism,microbial processes and especially photosynthesis rates,the observed ranges are not alarming and are within theoptimal range(18.3-37.8°C)for production of plankton in tropical waters(Hossain et al.,2007;Shah et al.,2008).

Salinity was not fuctuated much between the seasons registering the maximum(35.1 g L-1)during May 2010. Coinciding to the low amount of rainfall and higher rate of evaporation(Govindasamy et al.,2000)prevail in the region during this season.The salinity is the main physical parameter that can be attributed to the plankton diversity which act as a limiting factor and infuence the distribution of planktonic community(Kouwenberg,1994;Ramaiah and Nair,1997; Chandramohan and Sreenivas,1998;Balasubramanian and Kannan,2005;Sridhar et al.,2006).The composition of phytoplankton during each season was dominated by different species,which most likely adapts to change in the physical and chemical environment.During May 2010,phytoplankton assemblages are mainly composed by neritic species such as Coscinodiscus sp.,O.sinensis,D.brightwellii and S.costatum,indicating the decrease in river discharge due to reduction in rainfall resulting in high salinity,especially distribution of Coscinodiscus sp.in all stations confrms the fact. On contrary,S.costatum,O.sinensis and D.brightwellii were mainly found in the August and September 2010.This is explained by neritic species S.costatum,which is distributed in the coastal water with low salinity(Varona-Cordero et al., 2010)due to fresh water infux during southwest monsoon because of its euryhaline nature being able to tolerate wide range of salinities.Species diversity usually becomes very low at high salinities.pH was maximum in March 2011 at station I due to the infuence of daily photosynthetic activity by phytoplankton(Das et al.,1997)which removes dissolved CO2in the water column thereby increasing the pH level. Generally,fuctuations in pH values during different seasons of the year can be attributed to factors like removal of CO2by photosynthesis through bicarbonate degradation,dilution of seawater by freshwater infux,reduction of salinity and temperature and decomposition of organic matter as stated by (Upadhyay,1988;Rajasegar,2003;Paramasivam and Kannan, 2005).The observed high pH values might be due to the infuence of seawater inundation and the high density ofphytoplankton (Dasetal.,1997;Subramanian and Mahadevan,1999).

The DO level varied between 2.40 mg L-1(August 2010) and 5.25 mg L-1(November 2011).Salinity and SST are showing negative relationship with phytoplankton biomass, whereas DO represent the balance between photosynthesis and respiration and showed a positive relationship.The increased DO(5.25 mg L-1)level during November 2011 can be attributed to comparatively low SST and salinity recorded during this season and above all the turbulent nature of the sea during this season triggers vertical mixing of water column.Present fndings are contradictory to the earlier reports(Satpathy et al.,2009)that recorded increased DO level from April 2009 to March 2010 in this part of Bay of Bengal.

The silicate content was higher than that of all other nutrients except the total nitrogen registering maximum during pre-monsoon(September 2010)(25.32 μmol L-1).This could be largely due to the heavy infow of monsoon inputs.In coastal waters,apart from the physical mixing of seawater with freshwater,factors like adsorption of reactive silicate from suspended sedimentary particles,chemical interaction with clay minerals,co-precipitation with humic substances and biological removal by phytoplankton(diatoms and silicofagellates)can signifcantly infuence the spatio-temporal variation of silicate(Satpathy et al.,2010).In the present study,the low silicate concentrations and high abundance of Coscinodiscus sp.,were found in all stations during summer (May 2010)favoring the presence of Coscinodiscus sp.,the big-celled diatom,which prefers silicate for their growth (Rousseau et al.,2002).Phosphate concentration in coastal waters was infuenced by the mixing of the freshwater with the seawater in the land-sea interaction zone,addition through localized upwelling and uptake of phytoplankton (Satpathy et al.,2010).Maximum inorganic phosphate (1.094 μmol L-1)concentration was recorded in premonsoon (September 2010) while low concentration (0.048 μmol L-1)was observed during monsoon season (November 2011).This might be possibly due to the utilization of phosphate by the increased phytoplankton population during the season.The maximum level(2.392 μmol L-1) of total phosphorous(TP)was recorded during pre-monsoon (September 2010)and the minimum(0.048 μmol L-1)was recorded during monsoon(November 2011)also supports the above fact.The limiting nutrient concentrations vary with season,location and phytoplankton community structure (Fisher et al.,1992),and phosphate is one of the important organic nutrients that can limit the phytoplankton population in tropical waters.

Seasonal variations of phytoplankton population density could be attributed to a wide range of physico-chemical parameters such as temperature,salinity,nitrate-nitrogen and phosphate-phosphorous.From this study,it is obvious that the southwest Bay of Bengal was productive with high phytoplankton densities during pre-monsoon(August and September 2010).Naik et al.(2006)noted that surface phytoplankton population in the Bay of Bengal showed seasonal variations and the abundance peaked during the beginning of northeast monsoon.The present study showed the abundance of nutrients at the southern Bay that might have resulted due to the discharge of nutrient-rich water from the rivers at the southeast coast of India.Phytoplankton species composition was more in pre-monsoon season(August and September 2010)compared to other two seasons.Diatoms dominated in all the stations,as they thrive well in widely changing hydrographical conditions(Mani,1992;Gowda et al.,2001).Such abundance and diversity of diatoms in the neritic zone of the Bay of Bengal are common(Panigrahi et al.,2004;Sridhar et al.,2010).Percentage composition indicated the preponderance of diatom during summer(May 2010)when compared to pre-monsoon season(August and September 2010)a characteristics feature of Bay of Bengal, whereas species diversity and richness indices were minimum during summer(May 2010)and it increased during the premonsoon season (Augustand September2010).Theobserved less species diversity during summer(May 2010) might be due to the dominance of few species of diatoms.The percentage composition,diversity,richness and evenness indices of phytoplankton species are registered narrow range of temporal variation without any spatial variation.This indicates that the plankton assemblage in this part of the Bay of Bengal is not much varying spatially.Principal component analysis has been widely used to group the physico-chemical parameters which are infuencing the phytoplankton growth by common spatial or temporal changes under given conditions(Gupta et al.,2009).Current results suggest that the phytoplankton population density was infuenced by the seasonal fuctuation of the environmental variables.Component loadings larger than can be taken into consideration in the interpretation(Mazlum et al.,1999;Mishra,2010)and the same is applied for the present study also.

Phytoplankton abundance and taxonomic groups depended upon the supply of nutrients in natural waters.The higher cell density and species diversity of phytoplankton were found in pre-monsoon,when salinity and nitrate concentration was low and reactive silicate,and inorganic phosphates are moderate. This is probably due to the rapid uptake of phosphate by phytoplankton during the pre-monsoon season when there is only a limited external supply.Silicate,nitrate and phosphate ratios are therefore useful for predicting the phytoplankton abundance and assemblages in the tropical coastal waters.The ability to identify limiting nutrients thus becomes of considerable importance for our understanding of the plankton ecology(Havens,2000).However,such limiting nutrient factors vary for closed water bodies and water bodies infuenced by the external discharges.

5.Conclusions

The present study attempted to record the seasonal variations of phytoplankton population density in relation with hydrographical parameters along the southeast coast of India. Analyses of our data sets revealed that southwest of Bay of Bengal is not exhibited large-scale spatial variability rather than seasonality in phytoplankton diversity and population density.All the hydrographical parameters showed clear seasonal patterns,and are typical to the tropical marine environment without any marked variation between the stations. Increased thermal stratifcation especially on surface waters and utilization of essential nutrients by phytoplankton makes the Bay of Bengal oligotrophic during summer when there is no external input.Parangipettai coastal water is subjected to seasonal fuctuations in physico-chemical parameters depending upon the seasonal tidal amplitude and freshwater infux resulting in a continuous exchange of organic,inorganic,plant and animal matters.This coastal water is rich in resources allowing phytoplankton to attain high abundance and diversity.As evident from the results of multivariate analysis,variables like SST and DO are the most important factors and negatively infuencing the seasonal pattern of phytoplankton population,although other chemical factors (nitrate,inorganic phosphate and silicate)have also the important contributors for the temporal distributions of the phytoplankton population density along the coastal waters of southeast coast of India.

Acknowledgements

All authors are thankful to the Indian National Centre for Ocean Information Services(INCOIS),Satellite Coastal and Oceanographic Research(SATCORE)(G4/515/2008),Ministry of Earth Sciences(MoEs),Government of India,Hyderabad for fnancial assistance.We are grateful to the Annamalai University for support and encouragement.We thank the Vessel Management Cell,masters and the crew of the Coastal Research Vessel Sagar Paschmi of National Institute of Ocean Technology(NIOT)for their timely help.The second author S. Balakrishnan thank the University Grants Commission,Govt. of India,New Delhi for fnancial support through UGCResearch Award(No.F.30-1/2014(SA-II)/RA-2014-16-SCTAM-4364 dated 05/02/2015).We also thank the anonymous referees for the valuable comments,which greatly improved our manuscript.

Adoni,A.,Joshi,D.G.,Gosh,K.,et al.,1985.Work Book on Limnology. Pratibha Publisher,Sagar.

Ahmad,M.S.,Siddiqui,E.N.,1995.Freshwater diatoms of Darbhanga.J. Freshw.Biol.7,41-48.

Anand,N.,Mohan,E.,Hopper,R.S.S.,et al.,1986.Taxonomic studies on blue green algae from certain marine environments.Seaweed Res.Util.9, 49-56.

Balasubramanian,R.,Kannan,L.,2005.Physico-chemical characteristics of the coral reef environs of the Gulf of Mannar biosphere reserve,India.Int. J.Ecol.Environ.Sci.31,265-271.

Bianchi,F.,Acri,F.,Aubry,F.B.,et al.,2003.Can plankton communities be considered as bioindicators of water quality in the laggon of Venice?Mar. Pollut.Bull.46,964-971.

Chandramohan,P.,Sreenivas,N.,1998.Diel variations in zooplankton population in mangrove ecosystem at Gaderu canal,south-east coast of India. Indian J.Mar.Sci.27,486-488.

Chaturvedi,R.K.,Sharma,K.P.,Kamayani,S.,et al.,1999.Plankton community of polluted water around Sanganer,Jaipur.J.Environ.Pollut.61, 77-84.

Chellappa,N.T.,Borba,J.M.,Rocha,O.,2008.Phytoplankton community and physical-chemical characteristics of water in the public reservoir of Cruzeta,RN,Brazil.Braz.J.Biol.68,477-494.

da Silva,C.A.,Train,S.,Rodrigues,L.C.,2005.Phytoplankton assemblages in a Brazilian subtropical cascading reservoir system.Hydrobiology 537, 99-109.

Das,J.,Das,S.N.,Sahoo,R.K.,1997.Semidiurnal variation of some physicochemical parameters in the Mahanadi estuary,east coast of India.Indian J.Mar.Sci.26,323-326.

Desikachary,T.V.,1959.Cyanophyta.IndianCouncilofAgricultural Research,New Delhi.

Desikachary,T.V.,1987.Atlas of Diatoms.In:Monographs Fasicle II,III and IV.Madras Science Foundation,Madras,p.80.

Dupuis,A.,Hann,B.J.,2009.Warm spring and summer water temperatures in small eutrophic lakes of the Canadian prairies:potential implications for phytoplankton and zooplankton.J.Plankton Res.31, 489-502.

Edward,J.K.P.,Ayyakkannu,K.,1991.Studies on the ecology of plankton Community of Kollidam estuary,South-east coast of India,I.Phytoplankton.Mahasagar-Bull.Natl.Inst.Oceanogr.24,89-97.

Eggs,J.K.,Aksnes,D.L.,1992.Silicate as regulating nutrient in phytoplankton competition.Mar.Ecol.Prog.Ser.83,281-289.

Elliott,J.A.,Irish,A.E.,Reynolds,C.S.,2002.Predicting the spatial dominance of phytoplankton in a light limited and incompletely mixed eutrophic water column using the PROTECH model.Freshw.Biol.47(3), 433-440.

Eppley,R.W.,1972.Temperature and phytoplankton growth in the sea.Fish. Bull.70,1063-1085.

Falkowski,P.G.,Barber,R.T.,Smetacek,V.,1998.Biogeochemical controls and feedbacks on ocean primary production.Science 281 (5374), 200-206.

Fisher,T.R.,Peele,E.R.,Ammerman,J.W.,et al.,1992.Nutrient limitation of phytoplankton in Chesapeake Bay.Mar.Ecol.Prog.Ser.82,51-63.

Gomes,H.R.,Goes,J.I.,Saino,T.,2000.Infuence of physical processes and freshwater discharge on the seasonality of phytoplankton regime in the Bay of Bengal.Cont.Shelf Res.2,313-330.

Gouda,R.,Panigrahy,R.C.,1996.Ecology of phytoplankton in coastal waters off Gopalpur,east coast of India.Indian J.Mar.Sci.2,13-18.

Govindasamy,C.,Kannan,L.,Jayapaul,A.,2000.Seasonal variation in physico-chemical properties and primary production in the coastal water biotopes of Coromandel coast,India.J.Environ.Biol.21,1-7.

Gowda,G.,Gupta,T.R.C.,Rajesh,K.M.,et al.,2001.Seasonal distribution of phytoplankton in Nethravathi estuary,Mangalore.J.Mar.Biol.Assoc. India 43,31-40.

Grenz,C.,Cloern,J.E.,Hager,S.W.,et al.,2000.Dynamics of nutrient cycling and related benthic nutrient and oxygenfuxes during a spring phytoplankton bloom in South San Francisco Bay(USA).Mar.Ecol.Prog.Ser. 197,67-80.

Gupta,I.,Dhage,S.,Kumar,R.,2009.Study of variations in water quality of Mumbai coast through multivariate analysis techniques.Indian J.Mar.Sci. 38(2),170-177.

Havens,K.E.,2000.Using trophic state index values to draw inferences regarding phytoplankton limiting factors and seston composition from routine water quality monitoring data.Korean J.Limnol.33,187-196.

Hoch,M.P.,Dillon,K.S.,Coffn,R.B.,et al.,2008.Sensitivity of bacterioplankton nitrogen metabolism to eutrophication in sub-tropicalcoastal water of Key West,Florida.Mar.Pollut.Bull.56,913-926.

Hossain,M.Y.,Jasmine,S.,Ibrahim,A.H.M.,et al.,2007.A preliminary observation on water quality and plankton of an earthen fsh pond in Bangladesh:recommendations for future studies.Pak.J.Biol.Sci.10, 868-873.

Kouwenberg,J.H.M.,1994.Copepod distribution in relation to seasonal hydrographic and spatial structure in the north-western Mediterranean(Gulf du Lion).Estuar.Coast.Shelf Sci.38,69-90.

Madhu,N.V.,Maheswaran,P.A.,Jyothibabu,R.,et al.,2002.Enhanced biological production off Chennai triggered by October 1999 super cyclone (Orissa).Curr.Sci.82(12),1472-1479.

Madhupratap,M.,Gauns,M.,Ramaiah,N.,et al.,2003.Biogeochemistry of the Bay of Bengal:physical,chemical and primary productivity during summer monsoon.Deep Sea Res.II 50,881-896.

Mani,P.,1992.Natural phytoplankton communities in Pichavaram mangroves. Indian J.Mar.Sci.12,278-280.

Mazlum,N.,Ozer,A.,Mazlum,S.,1999.Interpretation of water quality data by principal components analysis.Turk.J.Eng.Environ.Sci.23, 19-26.

Mishra,A.,2010.Assessment of water quality using principal component analysis:a case study of the river Ganges.J.Water Chem.Technol.32(4), 227-234.

Naik,R.,Hegde,S.,Anil,A.C.,et al.,2006.Phytoplankton community structure in the Bay of Bengal:spatial and temporal variation,poster abstract.In:International Workshop on Sustained Indian Ocean Biogeochemical and Ecological Research.National Institute of Oceanography, Dona-Paula,Goa,India.

Panigrahi,S.N.,Acharya,B.C.,Das,S.N.,2004.Distribution of diatoms and dinofagellatesin tropical waters of Orissa and West Bengal with emphasis on neritic assemblages.In:Proceedings of National Seminar,New Frontiers in Marine Bioscience Research,pp.535-543.

Paramasivam,S.,Kannan,L.,2005.Physico-chemical characteristics of Muthupettai mangrove environment,southeast coast of India.Int.J.Ecol. Environ.Sci.31,273-278.

Perumal,P.,Sampathkumar,P.,Karuppasamy,P.K.,1999.Studies on the bloom forming species of phytoplankton in the Vellar estuary,southeast coast of India.Indian J.Mar.Sci.28,400-403.

Pielou,E.C.,1996.The measurement of diversity in different types of biological collections.J.Theor.Biol.13,131-144.

Ponmanickam,P.,Rajagopal,T.,Rajan,M.K.,et al.,2007.Assessment of drinking water quality of Vembakottai reservoir,Virudhunagar district, Tamil Nadu.J.Exp.Zool.India 10,485-488.

Prasannakumar,S.,Muraleedharan,P.M.,Prasad,T.G.,et al.,2002.Why is the Bay of Bengal less productive during SM as compared to the Arabian Sea? Geophys.Res.Lett.29(24),2238-2435.

Prasannakumar,S.,Nuncio,M.,Narvekar,J.,et al.,2004.Are eddies nature's trigger to enhance biological productivity in the Bay of Bengal?Geophys. Res.Lett.31(7),L07309.

Qasim,S.Z.,1977.Biological productivity of the Indian Ocean.Indian J.Mar. Sci.6,122-137.

Radhakrishna,K.,Devassy,V.P.,Bhargava,R.M.S.,et al.,1978.Primary production in the Northern Arabian Sea.Indian J.Mar.Sci.7, 271-275.

Rajagopal,T.,Thangamani,A.,Archunan,G.,et al.,2006.Studies ondiurnal variation certain physico-chemical parameters and zooplankton components of Chinnapperkovil pond in Sattur.J.Nat.Conserv.18,97-105.

Rajasegar,M.,2003.Physico-chemical characteristics of the Vellar estuary inrelation to shrimp farming.J.Environ.Biol.24,95-101.

Rajkumar,M.,Thillairajasekar,K.,Sun,J.,et al.,2012.Phytoplankton diversity in the Parangipettai coastal waters,southeast coast of India.J. Environ.Biol.33,1115-1125.

Ramaiah,N.,Nair,V.,1997.Distribution and abundance of copepods in the pollution gradient zones of Bombay harbour-Thane creek-Basin creek, west coast of India.Indian J.Mar.Sci.26,20-25.

Rana,K.S.,1996.Assessment of pollution in the river Jamuna part II phytoplankton.J.Nat.Environ.13,41-48.

Richardson,T.L.,Gibson,C.E.,Heaney,S.I.,2000.Temperature,growth and seasonal succession of Phytoplankton in Lake Baikal,Siberi.Freshw.Biol. 44,431-440.

Rousseau,V.,Leynaert,A.,Daoud,N.,et al.,2002.Diatom succession, silicifcation and silicic acid availability in Belgian coastal waters (Southern North Sea).Mar.Ecol.Prog.Ser.236,61-73.

Roy,R.,Pratihary,A.,Mangesh,G.,et al.,2006.Spatial variation of phytoplankton pigments along the southwest coast of India.Estuar.Coast.Shelf Sci.69,189-195.

Saravanakumar,A.,Rajkumar,M.,Thivakaran,G.A.,et al.,2008.Abundance and seasonal variations of zooplankton in the arid and zone mangrove of Gulf of Kachchh Gujarat.J.Environ.Biol.29,71-274.

Saravanane,N.,Nandakumar,K.,Durairaj,G.,et al.,2000.Plankton as indicators of coastal water bodies during south-west to north-east monsoon transition at Kalpakkam.Curr.Sci.78(2),173-176.

Saravanane,N.,Dharani,G.,Venkatesan,R.,et al.,2004.Hydrography and plankton distribution in Gulf of Mannar,off Tuticorin.In:Proceedings of MBR 2004 National Seminar on New Frontiers in Marine Bioscience Research,pp.421-429.

Satpathy,K.K.,Nair,K.V.K.,1990.Impact of power plant discharge on the physico-chemical characteristics of Kalpakkam coastal waters.Mahasagar 23,117-125.

Satpathy,K.K.,Sahu,G.,Mohanty,A.K.,et al.,2009.Phytoplankton community structure and its variability during southwest to northeast monsoon transition in the coastal waters of Kalpakkam,east coast of India.Int.J. Oceans Oceanogr.3(1),43-74.

Satpathy,K.K.,Mohanty,A.K.,Natesan,U.,et al.,2010.Seasonal variation in physicochemical properties of coastal waters of Kalpakkam,east coast of India with special emphasis on nutrients.Environ.Monit.Assess.164, 153-171.

Shah,M.M.R.,Hossain,M.Y.,Begum,M.,et al.,2008.Seasonal variations of phytoplanktonic community structure and production in relation toenvironmental factors of the Southwest Coastal waters of Bangladesh.J. Fish.Aquatic Sci.3,102-113.

Shannon,C.E.,Wiener,W.,1949.The Mathematical Theory of Communication.University of Illinois Press,Urbana,p.117.

Shekhar,R.T.,Kiran,B.R.,Puttaiah,E.T.,et al.,2008.Phytoplankton as index of water quality with reference to industrial pollution.J.Environ.Biol.29, 233-236.

Simpson,E.H.,1949.Measurement of diversity.Nature 163,638-688.

Sridhar,R.,Thangaradjou,T.,Kannan,L.,2010.Spatial and temporal variations in phytoplankton in coral reef and seagrass ecosystems of the Palk Bay southeast coast of India.J.Environ.Biol.31(5),765-771.

Sridhar,R.,Thangaradjou,T.,Senthil Kumar,S.,et al.,2006.Water quality and phytoplankton characteristics in the Palk Bay,southeast coast of India. J.Environ.Biol.27,561-566.

Strickland,J.D.H.,Parsons,T.R.,1972.A practical handbook of seawater analysis.Bull.Fish.Res.Board Can.167,311.

Subramanian,B.,Mahadevan,A.,1999.Seasonal and diurnal variations of hydro biological characters of coastal waters of Chennai(Madras)Bay of Bengal.Indian J.Mar.Sci.28,429-433.

Tas,B.,Gonulol,A.,2007.An ecologic and taxonomic study onphytoplankton of a shallow lake,Turkey.J.Environ.Biol.28,439-445.

Taylor,F.J.R.,1976.Dinofagellates from the International Indian Ocean Expedition.Bibl.Bot.132,1-226.

Thangaradjou,T.,Vijayabaskarasethubathi,G.,Raja,S.,et al.,2012.Infuence of environmental variables on phytoplankton foristic pattern along the shallow coasts of southwest Bay of Bengal.Algal Res.1,143-154.

Tiwari,A.,Chauhan,S.V.,2006.Seasonal phytoplanktonic diversity of Kithamlak,Agra.J.Environ.Biol.27,35-38.

Turner,J.W.,Good,B.,Cole,D.,et al.,2009.Plankton composition and environmental factors contribute to Vibrio seasonality.ISME J.3, 1082-1092.

Upadhyay,S.,1988.Physico-chemical characteristics of the Mahanadhi estuarine ecosystem,east coast of India.Indian J.Mar.Sci.17, 19-23.

Vareethiah,K.,Haniffa,M.A.,1998.Phytoplankton pollution indicators of coirretting.J.Environ.Pollut.3,117-122.

Varona-Cordero,F.,Guti'errez-Mendieta,F.,Castillo,M.E.M.,2010.Phytoplankton assemblages in two compartmentalized coastal tropical lagoons (Carretas-Pereyra and Chantuto-Panzacola,Mexico).J.Plankt.Res.32, 1283-1299.

Received 3 February 2015;revised 12 August 2015;accepted 9 September 2015

Available online 25 September 2015

*Corresponding author.

E-mail address:marugalbalu82@gmail.com(SAMPATHKUMAR P.).

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