Vol. 5(7), pp. 408-417, July 2013 DOI: 10.5897/IJBC12.132 International Journal of Biodiversity ISSN 2141-243X ©2013 Academic Journals http://www.academicjournals.org/IJBC and Conservation Full Length Research Paper Seasonal variations in seagrass biomass and productivity in Palk Bay, Bay of Bengal, India C. Govindasamy*, M. Arulpriya, K. Anantharaj, P. Ruban and R. Srinivasan Department of Oceanography and Coastal Area Studies, School of Marine Sciences, Alagappa University, Thondi Campus - 623 409, Tamilnadu, India. Accepted 15 June, 2013 Seagrass meadows are valuable habitats having economic and ecological importance in coastal ecosystem. The major seagrass meadows in India exist along the southeast coast of India, particularly in Palk Bay region. The dominant seagrass species of this region was Cymodocea serrulata and Syringodium isoetifolium and these two species were taken for the survey. In this study, a survey was carried out for a period of two years from August 2009 to November 2011 on the seasonal and spatial variability of these two seagrass species. There was a distinct seasonal and spatial variation in the total biomass, productivity and above ground biomass, leaf canopy height and shoot density of these two species between the stations. The seasonal variation in the biomass, productivity, leaf canopy height and shoot density could be influenced by the abiotic variables and the nutrient factors. Results conclude that the particulate organic carbon, inorganic phosphate and total organic nitrogen (p>0.001 level) influenced the enhancement of biomass, productivity, leaf canopy height and shoot density. Increase in seagrass growth was observed in the monsoon season, due to optimum temperature, low salinity, pH and addition of nutrients. Key words: Seagrasses, seasonal changes, biomass, productivity, leaf canopy height. INTRODUCTION Seagrasses are flowering plants (angiosperms) living tropical regions where people along the coasts depend their full lifecycle submerged in marine environment. largely on the seagrass ecosystem for their daily They are found in all coastal areas of the world except in subsistence in terms of food and per capita income (de la Antarctic (Green and Short, 2003; Duarte and Gattuso, Torre-Castro and Ronnback, 2004). Cymodocea 2010). They comprise less than 0.02% of the angiosperm serrulata and Syringodium isoetifolium belongs to the species and have relatively fewer species than other family Potamogetonaceae, commonly found along the marine organisms (Short et al., 2007). Despite their low coastal area of the tropical Indo-West Pacific region. Out diversity, seagrass beds are ecologically and economi- of the twelve species of seagrasses identified in the east cally highly important. They are among the world’s most coast of India and among twelve species, two species productive coastal ecosystems (Duarte and Chiscano, were selected for this study. C. serrulata can be distin- 1999). Seagrasses are not only supportive to marine guished from other seagrass species by their shoots with biota, but also to human populations, especially in the distinctive open leaf scars, triangular, flat leaf sheath, *Corresponding author. E- mail: [email protected]. Govindasamy et al. 409 fibrous roots on the shoot and serrated leaf tips (Oliviera charge from Vaigai and Cauvery rivers has created a good et al., 2005). S. isoetifolium can be distinguished by its breeding ground for pelagic and demersal fishes. tubular leaf, scars in rhizome, root and flowers. Manamelkudi (Site I; Lat. 10°2’3”N and Long. 79°15’39”E) is located in the middle part of the Palk Bay (Figure 1). The coastal A number of general parameters are critical to whether region is muddy in nature and the muddy bottom of this area seagrass will grow and persist. These include physical provides a suitable substratum for the rich growth of seagrasses. parameters that regulate the physiological activity of Thondi (Site II) was popular as the historical port in ancient times. seagrasses (temperature, salinity, waves, currents, Here the coastal region was muddy, swamp in nature and depth, day length, substrate, etc.), natural phenomena Manimutharu River drain into the sea. Human population was high in the coastal region due to high fishing activity. Devipattinam (Site that limit the photosynthetic activity of the plants (light, III; Lat. 9°28’11”N and Long. 78°54’4”E) is located at a distance of nutrients, epiphytes and diseases) and anthropogenic 45 km south of Thondi. Here, the littoral zone is muddy and clay in inputs that inhibit the access to available plant resources nature thereby it support the luxuriant growth of seagrasses (nutrient and sediment loading). Seagrasses as any other (Sriramkumar et al., 2011). Devipattinam is characterized by plants require nutrients for their growth, development and channel environment where the southwest monsoon is able to push metabolism, but too much of some nutrients and the waves much into this Bay (Suresh Gandhi and Rajamanickam, 2004). Small patches of mangroves are present in this coastal environmental factors may limit rather than promote region. When compared with other two sites in Devipattinam region, growth. The nutrients most commonly limiting seagrass human population is high and in addition tourist activities are also growth in natural systems are nitrogen and phosphorus high. (Duarte, 1990; Romero et al., 2006). These essential nutrients may be derived from the decomposition of Water column characteristics organic matter in the water column and sediments (Holmer and Olsen, 2002; Kilminster et al., 2006), in Water temperature, salinity, pH were measured at the sampling which seagrass litters are the main source (Holmer and sites itself once in three months using a mercury thermometer, Olsen, 2002; Romero et al., 2006). Various combinations refractometer (Model 2491 Master- S/Milla) and pH meter (Model of these parameters will permit, encourage or eliminate pH-873), respectively. For the analysis of nutrients, surface water seagrass from a specific location. Although many studies samples were collected in clean polyethylene bottles and kept in an ice box and immediately transported to the laboratory. The samples have investigated how light, temperature and salinity were filtered using Whatman glass filter paper (70mmø; GF/C) for affect the seagrass beds, little work has been done particulate organic carbon analysis by adapting standard method of regarding the relationships between seagrass biomass, Strickland and Parson (1972). The nutrients such as total inorganic productivity, leaf canopy height and shoot density in the phosphate, nitrate, nitrite, reactive silicate, total dissolved organic Palk Bay region. Fong and Harwell (1994) have nitrogen were analyzed by adopting the standard methods attempted to model seagrass communities and tempe- described by Strickland and Parson (1972). rature, salinity and light as three of the primary environ- mental factors affecting seagrass growth. Recently, Seagrass biomass and productivity Govindasamy and Arulpriya (2011) reported that the reduction and degradation of the seagrass beds occurs The abundance of seagrasses was quantified by estimating the due to the increase intemperature and salinity in northern total biomass and above ground biomass. All the collections were made by using SCUBA diving equipment in the seagrass meadows part of Palk Bay region. This investigation, therefore, with its average depth of 3 to 5 m. For biomass estimation, a attempts to examine the effects of both environmental quadrat (0.25 m2) was placed ten times at random and seagrass factors and nutrients on the biomass, above ground materials found in the quadrat were collected and washed biomass, productivity, leaf canopy height and shoot thoroughly with the habitat water to remove debris. Moisture from density of C. serrulata and S. isoetifolium in Palk Bay the samples was removed using adsorbent paper and weighed to region, the eastcoast of India. get the total biomass. The mean of ten quadrat samplings was considered for computing the seagrass biomass per square meter and the mean values were expressed in terms of gram fresh weight per square meter (g.fr.wt.m-2). For the estimation of above ground MATERIALS AND METHODS biomass samples, leaves and sheaths were oven dried at 60°C for 48 h and weighed and the values were expressed in terms of dry Study sites weight per square meter (g.drywt.m-2). Changes in dissolved oxygen concentration in the water surrounding a plant community Palk Bay is situated in the southeast coast of India encompassing was used by several workers as measurements of the products of the sea between Point Calimere in the north and the northern photosynthesis. Dissolved oxygen was measured by light and dark shores of Mandapam to Dhanushkodi in the south. It is situated bottle method and productivity of seagrasses was estimated (Qasim between Latitude 9°55’ - 10°45’N and Longitude 78°58’ - 79°55’E. et al., 1972). The Palk Bay itself is about 110 km long and is surrounded on the northern and western sides by the coastline of the State of Tamilnadu in the mainland of India. The present study was Leaf canopy height and shoot density conducted for the period of two years from August 2009 to November 2011 in the Palk Bay region of India. The saline water Prior to drying of samples, the shoot density and leaves canopy and the muddy substratum coupled with seasonal rains and dis- height was recorded. For the sake of convenience and interpret- 410 Int. J. Biodivers. Conserv. Figure 1. Map showing the study areas. tation, a calendar year was divided into four seasons based on the values recorded in the summer season could be northeast monsoon which alone brings bulk rain fall to the attributed to a higher degree of evaporation, reduction of southeast coast of India where the present study area is situated. rainfall with decreased fresh water inflow and drainage The seasons are: Post monsoon season (January-March), summer season (April-June), premonsoon season (July-September) and (Govindasamy et al., 2000).