Assessment of Changes in the Algal Diversity of Chilika Lagoon after Opening of New Mouth to Bay of Bengal

Eighty one algal taxa comprising of 24 species of Cyanophyta, 2 Rhodophyta, 19 Chlorophyta, 6 Euglenophyta and 30 Bacillariophyceae under Heterokontophyta were recorded in Chilika lagoon in different seasons of 2010-2011 in a survey after opening of new mouth to Bay of Bengal. Of these Cyanobacterium diachlloros, Aphanocapsa marina, Microsystis aeruginosa, Microsystis wesenbergii, Pseudanabena limnetica, Arthospira ambiguum, Oscillatoria perornata, Oscillatoria proteus, Oscillatoria simplicissima under Cyanophyta, Scenedesmus bijugatus, Urenema elongatum under Chlorophyata, Trachelomonas abrupt, Trachelomonas hispida under Euglenopyta and Coscinodiscus subtilis, Navicula amphirhynchus, Navicula major, Gomphonema micropus, Gomphonema olivaceu, Gomphonema sphaerophorum, Cyclotella meneghiniana, Pinnularia subsimilis, Pleurosigma javanicum, Stephanophyxis turris, Synendra tabulata, Stauroneis pusilla and Cymbella affinis under Bacillariophyceae of Heterokontophyta recorded in the survey have not been reported in the lake before opening of the mouth. Maximum number of algal species was observed in winter followed by summer and post monsoon seasons. Northern sector showed maximum algal diversity followed by Central, Southern and Outer channel sectors. The Cyanophytes followed by Chlorophytes were rich in Northern, Central and Southern sectors where as the diatoms were abundant in Outer channel sector and Northern sector. The agarophyte Gracilaria verrucosa recorded in the Outer channel sector of the lagoon for the first time showing extended distribution of the species due to increase in salinity coupled with consistent wave action in the lagoon after opening of the new mouth.


Introduction
Chilika lagoon in the east coast of India is the largest brackish water lake with an average depth of approximately 2 m and an area varies from 1165 to 906 km 2 during rainy and summer seasons respectively [1]. It was declared as Ramsar site, a wetland of international importance in 1981. The fresh water input into the lagoon is from Daya and Bhargabi rivers, several other rivulets and also salt water from Bay of Bengal. Due to confluence of fresh and salt water, a distinct salinity gradient is maintained in different seasons in the lagoon ranging from 1 -33 ppt basing on which it is divided into four sectors i.e. Southern, Central, Northern and Outer channel sector. Prior to 2001 in Southern sector the salinity was moderate (8 -20 ppt), in Central sector showed a seasonal variation in salinity level (5 -30 ppt) and in the Northern sector the salinity was low varying from (0. 1 -13 ppt) due to opening of several rivers. Due to tidal impact, coupled with closure of the mouth connecting to the sea the salinity level in the Outer channel sector was nearly similar to the seawater during most times of the year except the rainy season [1]. To restore the lagoon characteristics with appropriate flux of seawater into the lake a new mouth was dredged in 2000 in the Outer channel sector near Sipakuda area. Again in March 2008, a natural mouth was opened near Gabakunda and was subsequently widened [2]. Both these new openings to the sea facilitated extensive mixing of saltwater with freshwater resulting in a wide variation in the hydrology of the lake. Several authors have reported the changes in the physico-chemical parameters of the lagoon after opening of these new mouths [2][3][4][5][6][7], however, assessment of algal diversity changes after 2001 has not been made so far.
An assemblage of marine, brackish and freshwater ecosystems in Chilika lagoon encourages occurrence of di-verse group of phytoplankton, aquatic flora and fauna, hence is one of the biodiversity of hot spots in India. The phyco-diversity in the lagoon is a subject of interest since 1930s to estimate the trophic status of the lake and its direct relevance to fisheries. The algal flora of the lagoon was studied first by Biswas [8] and subsequently Roy [9], Ahmed [10], Patnaik [11,12], Raman [13] Adhikary & Sahu [14], Rath & Adhikary [1,15] have documented the algal flora including their seasonal variation at different salinity gradient of the lagoon.
In the present work algal forms occurring in different seasons at the four sectors of the lagoon was studied and the changes in their diversity were assessed upon comparing with the results published as a check list [15] before opening of the new mouth in 2001.

Materials and Methods
Algal taxa were sampled during summer (May 2011), post monsoon (September 2011) and winter (December 2011-January 2012) at seven different locations in the Chilika lagoon covering all the four sectors. These were SI (Mangaljodi, Northern sector), SII (Barakul, Central sector), SIII (Kalijai, Central sector), SIV (Pathara, Central sector), SV (Rambha, Southern sector), SVI (Ghantashila, Southern sector) and SVII (Sipakuda, Outer Channel sector) (Figure 1). Samples were stored in Tarson made specimen tubes, fixed on sport with 4% formalin and brought to the laboratory for analysis. For sampling of plankton a 45 µm pore size plankton net was used. Attached algae, e.g. epilithic, epiphytic and epipelic forms were collected using forcep, scalpel and nylon brush. Each sample was given a voucher number and deposited at the Department of Biotechnology, Visva Bharati. Microscopic observation and microphotography was done using Olympus B47 phase contrast research microscope fitted with Nikon 4500 coolpix digital camera. The organisms were identified following Kützing [16], Huberpestalozzi [17], Desikachary [18][19][20][21]

Algal Diversity in Chilika Lagoon in 2011-12
A total of eighty one algal species were documented from seven different collection sites of Chilika lagoon during different seasons of 2011. These belonged to Cyanophyta (24 species), Rhodophyta (2 species), Chlorophyta (19 species), Euglenophyta (6 species) and Heterokontophyta under class Bacillariophyceae (30 species). Seasonal variation in the distribution of these algal species in different collection sites is given in Table 1 and Plates 1-3. Only few cyanobacterial and algal species and Amphora elliptica (SVII) were recorded consistently in specific sectors in all the seasons. During summer 59 algal species were recorded from different sectors of the lagoon. These were mostly of the class Bacillariophyceae under Heterokontophyta (21) followed by Chlorophyta (17), Cyanophyta (16), Euglenophyta (3) and Rhodophyta (2). The algal species exclusively occurred in the lake during summer were 6 Cyanophytes, 13 diatoms, 11 Chlorophytes and 2 Euglenophytes. A significant decrease in occurrence of algal taxa was observed during the post-monsoon period (September 2011) in comparison to preceeding summer (May 2011) due to flooding of riverine silted freshwater into the lake resulting in alteration in the physico-chemical characteristics of water. Totally 8 species of Cyanophyta, 1 Rhodophyta, 6 Chlorophyta, 2 Euglenophyta and 7 Bacillariophycean members occurred during post monsoon season in the lake and Pseudanabaena limnetica under Cyanophyta and Amphora elliptica under Bacillariophyta were exclu- Table 1.   post monsoon period.

Comparison of Algal Diversity in Chilika Lagoon before and after Opening of the New Mouth to Bay of Bengal
Sector wise comparison of the algal diversity recorded in the present work with the documentation of their occurrence in different sectors of the lagoon in the immediate past 2000-2001 [1] is given in  [1]. The number of Bacillariophycean taxa which are principally benthic and epilithic increased in number in the lagoon in response to the change in the hydrological parameters especially increase in the saltwater influx to the lake. Biswas in 1932 [8] reported first occurrence of 22 algal species comprising of Cyanophyta (11), Chlorophyta (5) and Rhodophyta (6) in Chilika lagoon. After almost 20 years Roy [9] reported 33 Bacillariophycean members in the entire lagoon. Subsequently Ahmed [10] reported 13 algal species comprised of 1 Cyanophyta, 5 Chlorophyta, 1 Bacillariophceae and 6 Rhodophyta, and Patnaik [11,12] reported 57 algal species comprising 6 Cyanophyta, 8 Chlorophyta, 40 Bacillariophyceae, 7 Dinophyta, 1 Xanthophyta and 4 Rhodophyta in the lagoon. Raman [13] reported 4 species of Cyanophyta, 3 species of Chlorophyta, 10 species of Bacillariophyceae, and only 1 species of Dinophyta from the lake. Adhikary and Sahu [14] reported 9 Cyanophyta, 8 Chlorophyta, 1 Xantho-  [15]. Analysis of these reports along with those species occurred in the lake after opening of the new mouth showed that of the 81 algal taxa, 20 species were recorded in the lagoon since the first report in 1932 [8] or later in 1954 [9], 1966 [10], 1973 [11], 1978 [12], 1990 [13], 1992 [14], 1999 [28] and 2001 [15], and 61 algal taxa occurred first after opening of the new mouth. Of these, 20 species belonged to Cyanophyta, 17 to Chlorophyta, 6 to Euglenophyta and 18 to Bacillariophyceae. These finding showed that salinity increase in the lagoon due to influx of seawater through the new mouth resulted in change of the algal forms in the lagoon. Further, occurrence of 6 Euglenophyta primarily in the Northern sector and part of the Central sector at SI and SII indicated the increase in eu-trophication in the lagoon at these locations due to anthropogenic discharge by human habitation nearby. Two species of algae, of which one desmid, Closterium venus and one diatom, Chaetoceros diversus which were recorded earlier in 1973 [11] were not reported in subsequent times [15], however, appeared again in the lagoon due to increase of salinity.

Diversity of Seaweeds in Chilika Lagoon at Different Salinity Gradient
Occurrence of seaweeds in estuaries and lagoon is generally dependant on the salinity of the water bodies. Four species of seaweed, comprising three under Chlorophyta, Chaetomorpha linum, Enteromorpha compressa, Enteromorpha intestinalis and one under Rhodophyta, Gracilaria verrucosa were found growing luxuriantly in different sectors of Chilika lagoon. Comparative study of their qualitative and quantitative occurrence with the earlier reports [1,28] showed that Chaetomorpha linum was recorded in all the sectors of the lagoon though it did not occur earlier in the Northern sector prior to opening of the new mouth. Similarly Enteromorpha compressa pre-sently recorded in Northern sector and Central sector at low to moderate salinity which was earlier confined to Central sector only. Enteromorpha intestinalis presently occurring all through the lake in abundance was earlier recorded in lower quantity in the Central and Southern sectors at moderate salinity levels. Growth of Gracillaria verrucosa was earlier occurring in abundance in Southern and Central sector, however, presently also appeared in Outer channel sector due to increase in salinity all through the lagoon. Quantitative increase in the agarophyte Gracillaria verrucosa in the Southern, Central as well as in the Outer channel sector which was earlier confined only to a pocket in the Central and Southern sector of the lagoon is an important finding of the present work. Consequent upon mixing of saltwater and freshwater due to high and low tide in the Outer channel sector, and at the nearby locations in the Central sector, salinity of the lagoon increased in these area varying from 10 -30 ppt with continuous diurnal change, hence is now suitable for maximum occurrence of the agarophyte which can be harvested for use in cottage industry.