A Comparative Study on the Diversity of Seagrass Species in a Selected Area of Puttalam Lagoon

Abstract

Seagrasses are aquatic angiosperms which are widely spread in shallow marine environment (Kuo and Hartog, 2000). Providing habitat grounds for large numbers of fish and shellfish species, act as a largest carbon sink, support a large number of epiphytic organisms, bind the sediment together and stabilizing sea bottom (Johnson and Johnstone, 1995) are the importance of seagrasses. Puttalam lagoon which is located in Puttalam district of Northwestern Province of Sri Lanka that covers 32700 ha (Johnson and Johnstone, 1995). There are fifteen species of seagrasses have been recorded in Sri Lanka including two families, 12 genera (Amarasinghe and De Silva, 2007). Main objective of the research is to compare changes of seagrass distribution from 1991 to 2013 where as to evaluate relationship between distribution of seagrasses with the states of water quality of selected locations of Puttalam lagoon and to compare the distribution of seagrass species according to salinity levels of each location are specific objectives.

Methodology

The present study was carried out in selected areas of Puttalam lagoon during the period of May to September in 2013. Kalpitiya, Kuringipitiya, Palliwasalthurai, Kandakuda, Palavi and Puttalam were the selected sites for the data collection (Figure 1). Geographic Position System (GPS) data of the site were recorded and point transect method was used for the sampling. Three line transects of each location were used. Typically transects were perpendicular to the shore and parallel to each other. Cover of seagrasses within a quadrant with 0.5 m * 0.5 m was measured at every 3 m mark of the 30 m by walking and snorkeling until transect was completed. Transects were selected and procedure was carried out in such a way that as same as Jayasuriya, 1991 conducted. Water quality parameters including water temperature (°C), pH, salinity (ppt), conductivity (mS/cm) and dissolved oxygen (mg/L) were measured at the middle

of transect two at 10 cm below to the sea surface using Multiparameter meter (Orion Water quality testing was repeated at the same time in the same place once a month and average values were calculated. Same procedure was repeated in other selected locations. Average abundance of seagrass distribution of three transects were calculated. Diversity of seagrass species of each sites were calculated using Shannon - Weiner diversity index. Comparision was conducted using analysis of variance (ANOVA). Percentage abundance of each species were calculated by dividing six sites into two regions as Northwestern and Southeastern according to Jayasuriya, 1991 and compared with the values recorded by Jayasuriya, 1991. Linear regression was conducted to find out relationship between seagrass distribution and water quality parameters.