• Sharavathi estuary: Figure 7 depicts the Sharavathi estuary dynamics during 1989 to 2010.The Sharavathi River has a catchment area of 3600 sq. km. The spatio temporal dynamics as listed in Table 6 indicate the decline open fields from 28.28% to 26.09% due to enhanced agricultural activities. Non-mangroves plantations have increased in this region, evident from the conversion of open fields for coconut or other cash crop cultivations. Increase in vegetation cover from 59.7% to 60.49% is due to the plantation activities. The continuous discharge of freshwater with the construction of dams and reservoirs has changed flora and faunal dynamics in this estuary.

Figure 7. Sharavathi estuary (buffer).

The mangroves species distribution (figure 8) shows that this region is dominated by natural growth of Sonneratia caseolaris followed by other mangrove species like Sonneratia alba, Kandelia candel (Table 7). All species present in the region other than Sonneratia caseolaris are due to the extensive reforestation activities. The presence of moderate salinity favorable species is due to lowered salinity levels in the estuary due to the continuous flow of fresh water from the reservoir. The mangroves associated with higher salinity, such as Rhizophora spp., Avicennia marina, Sonneratia alba etc. have vanished almost totally in the lower part of estuary. Plantations other than mangroves constitute 20.53 % of the estuarine region. The Sonneratia caseolaris also grows well around the river, islands and contributes to some extent the firewood needs of the locals. The region is mainly facing a threat due to the large scale anthropogenic activities involving conversion of land for cash crops and coconut plantations. This necessitates constant vigil through regular monitoring to minimize the impacts of human induced disturbances.

Table 6à

alin=

Figure 8. Sharavathi estuary

Figure 9. Venkatapura estuary (buffer).

Table 8: Spatio temporal dynamics of Venkatapura estuary (buffer).

The species wise distribution map shows Sonneratia alba is the most dominant species among all (figure 10, Table 9)). Parallel to the coast, approximately at 2 m depths and at the confluence of the river mouth of the Venkatapur, concentric submerged bar is developed. The availability of 34.38% open fields shows that there are ample chances for reforestation of mangrove species. This estuary has good oyster deposits.

Table 9: Species wise distribution of Venkatapura estuary.

Figure 10. Venkatapura estuary

Accuracy assessment is done through the computation of overall (OA), user’s (UA) and producer’s (PA) accuracies and Kappa coefficient. Training sites and transects data ensures the independence of the reference data for species mapping. Table 10 (a, b) provides the accuracy details of the study. Accuracy assessment for species wise mapping also shows greater overall accuracy and Kappa statistic. The integration of ground based field monitoring with the remote sensing data provided species level spatial distribution of mangroves. Training sites of exclusive species referred to mangrove tree species that restricted to the mangrove habitat were selected for the most common species encountered in the mangrove regions. Other species which did not form enough mono specific patches for training site selection are considered as other vegetation types. The improvement can be achieved in future by incorporating new high resolution remote sensing data for further analysis. Rate of expansion, indicates the mangrove’s ability to occupy new habitats. However degradation of mangrove habitats due to anthropogenic activities has contributed the decline in some pockets. The available open fields clearly illustrate the opportunity for effective management activities. Planting of Avicennia marina, Avicennia officinalis saplings of high salt tolerates (>25 ppt (parts-per trillion)) are suggested in the seaward end of estuaries where the freshwater discharge is low. Mangrove plant species of Rhizophora apiculata,  Kandelia candel, Acanthus ilicifolius species are appropriate to be planted in  seaward areas of estuaries and lagoons in the wet zone of moderate salinity tolerance (15- 25 ppt). Mangrove plant species of low salinity tolerance (< 15 ppt) Sonneratia caseolaris, Sonneratia alba, Excoecaria agallocha plants are suitable to be planted in the upper reaches of estuaries with high freshwater input (wet zone). The plantation of Avicennia marina & Avicennia officinalis are prompted in Aghnashini, Ganagavali estuaries due to their excellence in source of honey production. Apiculture has to be promoted in mangrove areas, which assists the dual purpose of increasing area under mangroves and to increase honey production.

Table 10(a): Accuracy assessment from 1989 to 2010.

Table 10(b): Species wise accuracy assessment.