Analysis of mangrove vegetation cover and the present status of aquaculture

Abstract

Mangrove forests are complex ecosystems that occur along intertidal accretive shores in the tropics. Mangroves play a significant role in both ecology and economy. In Sri Lanka many estuaries and lagoons are fringed with vastly diverse mangrove forests. The northwestern coastline represent all three major climatic zones in Sri Lanka. It also has the largest mangrove forest patch which is located in Puttlam – Kalpitiya lagoon. From the recent past the mangrove forest cover in Puttalam District is experiencing severe pressures from the adjoining settlements, the fishery industry, aquaculture and other activities in the catchment. An abrupt decline in the forest cover is evident due to being converted into industrial shrimp farms.

An attempt was made in the present study to analyse the spatial pattern of mangrove destruction related to shrimp farm development and to analyse the distribution of mangrove species. For this purpose, shrimp farms of 2008 were mapped using IRS – LISS III image (2008) to identify the operational and abandoned shrimp farms. The results were verified by using Google Earth. In order to study the mangrove species distribution, a total of 40 sampling sites were selected to cover the whole study area. Data collection was done at each sampling point by a 10 m traverse established from the water level to the edge of the mangrove vegetation at the landside. Species and the number of individuals in each traverse were recorded during this survey.

According to the findings of the study in 2008 there is a total of 5355 ha of land is used for shrimp farms but only 3872 ha is in operation and others are abandoned. These barren lands could be cultivated with mangroves if suitable restoration programme is implemented while natural regeneration is also evident in some areas.

It was evident that Chilaw lagoon area is the richest when it comes to mangrove diversity. Rhizophore mucronata, Avicennia marina and Lumnitzera racemosa were the most dominant species in the study area. The most significant finding was the recording of Scyphiphora hydrophyllacea Gaertn. f. from Udappwa (854883.4 N 366900.8 E) which has now become very rare species in Sri Lanka. Only a few trees were previously recorded to be restricted to one locality on the Kalpitiya Peninsula in Puttalam lagoon.