Seasonal Variation of Phytoplankton Community in Navigable Channel of Gopalpur Port, East Coast of India: A Taxonomic Study

The aim of this paper is to determine the current biological state of phytoplankton in the pelagic zone of Gopalpur Port navigable channel. The plankton samples were collected from a fixed sampling location in two different tides i.e. high tide and low tide during three different seasons i.e. pre-monsoon, monsoon, and post-monsoon of the year 2010. Ninety four species of phytoplankton were observed, of which diatom constituted 71 species, dinoflagellate 11 species, green algae 8 species and blue green algae (cyanobacteria) 4 species. Comparing the population of all the groups, the contribution of each group of phytoplankton was in the order of diatoms > dinoflagellates > blue green alga > green alga in all the seasons. The population density of phytoplankton ranged from 2360 Nos./L to 53240 Nos./L (avg. 29683 Nos./L). In premonsoon and post monsoon, Asterionellopsis glacialis, an important bloom forming member of diatom group dominated the phytoplankton population. Among these ninety four species, Asterionellopsis glacialis, Thalassiothrix longissima, Chaetoceros curvisetus, Coscinodiscus gigas, Ditylum brightwellii were recorded in all the seasons and the other species have shown seasonal variation. The toxic phytoplankton such as Pseudonitzschia pungens, Dinophysis caudata were also recorded during our observation. Our study is a first attempt made in this environmentally sensitive region, being sensitive due to coastal erosion, port activities and adjacent mass nesting beach for Olive Ridley sea turtles.


Introduction
Phytoplankton are the main primary producers of marine and freshwater ecosystems. They play specific roles in biogeochemical cycling in marine ecosystems. Their roles in calcification, silicification, dimethyl sulphide (DMS) production and nitrogen fixing have been well established. These tiny organisms initiate the marine food chain by the process of photosynthesis and serve as primary food in marine pelagic zone [1]. Phytoplankton, as the basis of the trophic chain, forms the biological community which regulates the food chain for which scientific attention is focused when a management plan is needed or an evaluation of the ecosystem health is required [2][3][4]. Knowledge on taxonomy of phytoplankton is essential to study the community dynamics in spatio-temporal scale and to characterize it into functional groups [5]. The species composition and population density of phytoplankton are sensitive to environmental changes. Their documentation in relation to d yna mic e nviro nme nt is a valuab le characteristic of water quality. Coastal and near-shore waters are more productive regions in the marine environment due to nutrient add by means of regeneration, upwelling and land run-off. Phytoplankton blooms in these waters follow a seasonal pattern that shapes the coastal marine ecosystem. Environmental forcing, nutrient availability, predator communities and land-driven inputs are the major factors that control coastal and near-shore phytoplankton community and blooms [6]. Several anthropogenic factors in these environments can result in alteration of coastal water quality (eutrophication), introduction of non-native species (ballast action), alteration of predator community (overfishing), etc. As a result, non-periodic and exceptional blooms of both non-toxic or toxic phytoplankton species lasting for few weeks to months are frequently reported, influencing the seasonal patterns of dominant phytoplankton community structure, thereby affecting coastal and estuarine biogeochemical processes [7].
In harbour/port areas, the water quality is changing rapidly due to multiple human activities. The phytoplankton due to its importance in food web requires frequent study under such changing of environment. Regular cargo handling, fishing trawler movements and shipping intensification, anthropogenic pollutant influx are the key sources of water quality alteration that led the scientific community for regular monitoring. We focus this study as a first attempt in this region to explore the phytoplankton composition in simultaneous seasonal and tidal basis. The outcome of this study will certainly useful for the coastal planners for environmental monitoring and impact assessment work.

Materials and Methods
The present research work was carried out on a fixed sampling point (19⁰18' 4.08"N, 84⁰ 58' 0.64"E) in the navigable channel of Gopalpur Port, a seasonal port of Odisha, East Coast of India. This area ( Figure.1) is sensitive due to port activities, and adjacent mass nesting beach for olive Ridley sea turtles. Rainfall of this region is primarily concentrated in Monsoon (South-West), which is the major climatic factor of this region. Though Gopalpur Port is a seasonal port, regular fishing trawler and boat movements are common. The navigational channel selected for this study was due to apprehending future pollution as a result of Petroleum Hydro-Carbon (PHC), oil spills and anthropogen ic load of organic and inorganic nutrients.
Sampling was carried out during three seasons i.e. pre-monsoon (PRM), monsoon (MON) and post-monsoon (POM) of year 2010 from a fixed location during high tide and low tide to determine the temporal and tidal variation in phytoplankton composition. Phytoplankton samples were collected from surface and stored in polythene bottles after preservation with Lugol's iodine solution. After concentrati ng the sample by sedimentation method, 1 ml of sample was taken and examined with a Sedgwick rafter counting chamb er under a compound microscope (Nikon Eclipse-E600) with different magnifications. For taxonomical analysis, standard literatures [8][9][10] were referred.

Results and Discussion
A total of 94 phytoplankton species under four different groups were observed during the study, of which diatoms constituted 71 species, dinoflagellates 11 species, green alga 8 species and blue green alga (cyanobacteria) 4 species. Population wise Diatoms evolved as the major phytoplankton group followed by dinoflagellate, green algae and cyanobacteria. The dominance of diatoms followed by dinoflagellates is well reported in coastal waters [11].
As far as seasonal abundance of phytoplankton isconcern ed, the trend pre-monsoon (45080 Nos./L) > post-monsoon (36970 Nos./L) > monsoon (7000 Nos./L) was observed ( Table-1). Highest abundance of phytoplankton during pre-monsoon season might be due to the dominance of diatoms and the lowest during monsoon might be due to the stratification of water column to a large extent because of heavy rainfall, high turbidity caused by river run-off/land run-off, reduced salinity, decreased temperature and pH, overcast sky and cool conditions [16]. Species composition varied considerably in the three seasons. This might be attributed to change in environmental variables specially nutrients and temperature in different seasons [17] [18].
As far as temporal species number is concerned more number of species (tidal mean) were identified during pre-monsoon (26) followed by monsoon (23) and post-monsoon (20) ( Table-2). Tidal examination of phytoplankton samples for qualitative purpose revealed that more number of species were abundant during high tide than low tide with an exception in post monsoon. As phytoplankton species composition determines the health of the food chain, our result depicts a healthy condition of the surrounding environment. Diatom dominance without any bloom can be treated as a major stable result for justifying the healthy condition. Presence of few toxic species is normal in occurrence in a port environment. The outcome of the present study will serve as baseline data to carry out future environmental impact assessment (EIA) studies for both existing port and another adjacent major all weather port under construction.
Kumar and Dr. A. A Lotliker of INCOIS for their valuable suggestions during the course of study.