Structure and regeneration status of mangrove patches along the estuarine and coastal stretches of Kerala, India

This study presents the structural characteristics and regeneration potential of mangrove patches in the estuarine and coastal areas of Kerala, a tropical maritime state in India. Field surveys were carried out at 46 selected sites during August 2015 to May 2016. In each site, the vegetative structure and regeneration status were assessed using the quadrat method. Altogether 219 quadrates were laid out and a total of 13 true mangrove species, belonging to 5 families and 8 genera, were recorded. The total tree density and stand basal area of the study region was1678.08/ha and 20.33 m^2/ha respectively. The low basal areas indicate the reduced structural development in mangroves. Of the 13 tree species, Avicennia constitutes 56%of the total Important Value Index(IVI) and Avicennia officinalis represents 41% of the IVI in Kerala, followed by Avicennia marina(15%), Rhizophora mucronata(15%),Sonneratia alba(8%) Rhizophora apiculata(7%) and Excoecaria agallocha(7%). The diameter at breast height(DBH) in the study area revealed that 47% of the tree species came under the 1–10 cm DBH class. Total sapling and seedling density in Kerala was 2238.35 and 3232.42 individuals/ha respectively. Density of young plants(seedlings ? saplings) was only 31% greater of tree density and varied from 3–63%, which indicates poor regeneration potential. The Maturity index value(MIV) and complexity index(Ic) value of mangroves were 18.30 and 109.81 respectively. However, the low Ic value(\ 10) observed in seven out of ten coastal districts indicated poor structural development of mangroves in Kerala. Therefore, locationspecific conservation and management measures, guided by the knowledge on spatial distribution and habitat requirements of mangrove varieties should be taken to preserve the mangrove diversity of Kerala.

Ecosystem Responses in the Distribution of Black Clam (<i>Villorita cyprinoides</i>) Beds in Vembanad Estuary during Environmental Changes Using GIS and RS

The biomass and distribution of black clam (Villorita cyprinoides) in Vembanad, a tropical estuary located along the southwest coast of India varied significantly. Sampling was done in freshwater-dominated zone in the south (distal) and brackish water zone in the north (proximal), during pre and post monsoon seasons. Clam biomass was estimated from samples, collected from different stations during the study period. Water transparency and temperature were measured at the sample sites. Water samples were collected and analysed for salinity, dissolved oxygen (DO), pH and hardness. There was a significant difference in the clam biomass during the two seasons in the distal zone, and those collected from the distal and proximal zones during pre-monsoon season. The data were further analysed to determine the factors affecting the clam biomass distribution in the two zones and seasons. Factor analyses, comparing the distal zone during two seasons and zonal variations were similar to earlier observations. Step wise regression analyses found that dissolved oxygen (adjusted R2 = 0.3) is the only variable affecting clam survival during pre-monsoon period in the distal and proximal zones. A geographic map of the region obtained from the Indian satellite sensor LISS (Linear Image Self Scanner) was used along with in situ data to map the results using inverse distance weightage model.