Zoology
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Item Effect of vegetation structure on primary productivity of mangroves at Kadolkele in Negombo lagoon(Sri Lanka Association for Fisheries and Aquatic Resources, 2006) Jayakodi, J.M.A.L.; Amarasinghe, M.D.; Pahalawattaarachchi, V.Item Mangrove soils are superior carbon sinks: Evidence from Sri Lankan mangrove ecosystems(Sri Lanka Association for Fisheries and Aquatic Resources, 2015) Perera, K.A.R.S.; Amarasinghe, M.D.Mangroves are among the most carbon rich ecosystems in the tropics. Inundation with tides and land-based surface runoff leads to anaerobic soil conditions that are conducive for accumulation of partially decomposed organic carbon. Present study was conducted to assess quantitatively the capacity of mangrove soils in retaining organic carbon. Distribution of total organic carbon (TOC) in soils of mangrove ecosystems in Negombo, Chilaw, Kala Oya, Malwathu Oya, Uppar, Batticaloa and Rekawa lagoons/estuaries, that represent western eastern and southern coasts as well as wet and dry climatic zones of Sri Lanka, was determined by using soil samples taken along the water-land gradient at 0-15 cm, 15-30 cm and 30-45 cm depths. Dichromate oxidation followed by colorimetric measurements were used to determine the percentage TOC and TOC densities were calculated using bulk density and % TOC values. Except for Batticaloa and Uppar lagoons in the dry zone, relatively a high soil TOC contents were observed in the surface soil layers (0-15 cm depth). By and large, the area between 10-30 m from the shoreline retained the highest average TOC in all mangrove areas. The highest percentage TOC in Sri Lankan mangrove soils is found not at the surface layer (4.92 - 15.1 % at the surface – 15 cm depth), but the layer below it down to a depth of 30 m (5.31 – 9.87 % at 16 – 30 cm depth). Soil beneath 30 cm contained the lowest amount (3.05 – 8.34 % at 31 -45 cm depth). Average TOC density of surface soil was 0.066 - 0.145 g cm-3 and in it was higher in mangroves of wet and intermediate climatic zones than those in the dry zone. The carbon retention capacity of Sri Lankan mangrove soils therefore was calculated to range between 313 – 492 t ha-1 and the highest was found to occur in the wet zone while it was 414 t ha-1in the intermediate zone. Soils of mangroves in the dry zone retained approximately 361 t ha-1 .of organic carbon up to a depth of 45 cm. The TOC retained by the soils of mangrove areas in Sri Lanka can be estimated as 5816 x 103 t. Inundation frequencies and durations as well as other bio-physical factors may affect the magnitude of TOC in mangrove soils.Item Investigation of the Negombo estuary (Sri Lanka) brush park fishery, with an emphasis on community-based management(Fisheries Management and Ecology, 2002) Amarasinghe, U.S.; Amarasinghe, M.D.; Nissanka, C.The Negombo estuary brush park fishery in Sri Lanka was investigated from June 1998 to March 1999. The mean fish yield (all species) in the fishery was 12.46 t ha?1 yr?1. Fin fish species formed about 91% of the yield and the rest was formed by penaeid shrimps and crabs. Fish yield and the twig density in the brush park exhibited a second order polynomial relationship indicating a minimum yield at an intermediate value of twig density in the brush parks. The relationship between fish yield and duration of implantation of brush parks showed an optimal period of 30?40 days for high fish yields. Income levels of fishermen, availability of construction material and suitable sites for implantation of brush parks are some of the factors determining size and number of brush parks per fisherman and duration of installation. Indigenous knowledge within the fishing community about the effect of salinity variations, twig density and mangrove species used on the harvests greatly contribute to effective operation of this fishing practice. Cultivation of mangroves to obtain twigs and branches is a unique feature in this estuary. Indigenous knowledge on mangroves has led to the adoption of sound silvicultural practices. Although cultivating mono-specific mangrove stands may not increase diversity of mangrove forests, it reduces denudation of naturally occurring mangrove forests because of brush park construction, and retains habitats for other organisms. Mangrove management plans in the Negombo estuary should therefore be viewed and treated in an integrated manner that takes into account both resource and social components.