Diversity and distribution of mangrove flora in the Attaragoda wetland, Galle with some notes on avifauna

Abstract

Attaragoda is a mangrove wetland situated in the Southern Coast (Latitude: 6° 1′ 60N, Longitude: 80° 15′ 0E), 3km outside Galle. This luxuriant patch of mangrove forest faces immense pressure due to human activities. Diversity and distribution of mangrove species in relation to salinity levels and species richness of avifauna were studied from January to June 2009The area was subdivided into three zones based on salinity levels. Zone 1 with recurrent tidal effect had a salinity range of 33-40ppt. Salinity of Zone 2 with moderate influence of tides ranged between 26- 32ppt. Salinity of Zone 3 with least influence of tides ranged between 20-28ppt. Diversity and distribution of mangrove flora was carried out using quadrat (20×20m) sampling technique. Species richness of birds were determined by carrying out line transects and opportunistic observations. Shannon-Weiner Diversity Index (DI) was calculated to describe floral diversity. Twelve species of true mangroves and six mangrove associates were recorded. Out of eighteen species six were known to be introduced to the wetland. Species richness of Zone 1, 2 and 3 were seven (No. of plots sampled; n=7), six (n=3) and five (n=4) respectively. Increased species richness of Zone 1 is due to introduced species of true mangroves: Rhizophora mucronata, Ceriops tagal and Aegiceras corniculatum Highest diversity and evenness were recorded from Zone 3 (DI=0.42, J=0.78) and lowest diversity was recorded in Zone 1 (DI=0.23, J=0.46). Dominant species in Zone 1 were Rhizophora apiculata, Excoecarica agallocha and Clerodendrone inerme. Zone 2 (DI=0.33, J=0.46) was dominated by Rhizophora apiculata and Acanthus illicifolius. True mangrove species Sonneratia caseolaris, Avicennia officinalis, Heritiera littoralis, Luminitzera racemosa and mangrove associate Cerbera manghas were recorded opportunistically in Zone 2. Acanthus illicifolius was exclusive to Zone 2. Avifauna consisted of 35 species, of which, 20 were wetland species. There were nine species of migratory birds including one scarce winter visitor- Malayan Night Heron, indicating that Attaragoda wetland is an important destination for migratory birds. Immediate steps should be taken to assure degradation of this wetland habitat by human interventions.