TABLE 1: CRAB SPECIES RECORDED IN CHITHRAPU

TABLE 2: THE CRAB SPECIES RECORDEDIN NITK-BEACH

TABLE: 3

FIGURE 3:  THE GIVEN FIGURE SHOWS MANGROVE CRABS FAMILY DISTRIBUTION

RESULT AND DISCUSION:
A total of 226 individuals belonging to 8 species and 250 individuals belonging 6 species were recorded in mangrove and NITK beach respectively. Uca annulipes belonging to the family Ocypodidae was most dominant species in mangrove vegetation (95ind.) and play a vital role in recycling and decay of plant materials (Kwok et al.1995). Dotilla myctiroides belonging to the family Dotillidae was dominant in NITK beach (85ind.). A Total 12 species of decapods belonging to the families Portunidae (6 species), Grapsidae (3 species), Sesarmidae (2 species), Ocypodidae (1 species), Xanthidae (1 species) and Dotillidae (1 species) were recorded. Most common species at Chitrapu were Scylla serrata, Metopograpsus messo, Uca annulipes, Sesarma bidens, Metopograpsus latiforons, Sesarma qudratum and Diogenes pugilator (table 1) and at NITK beach were Dotilla myctiroides, Grapsus albolineatus, Ozius tuberculosis, Portunus pelagicus and Portunus sanguinolentus (table 2). The diversity study of crabs in Karwar byPrandnya et al. (2011) recorded 13 species in mangrove environment. They reported that crabs belonging to families Grapsidae and Ocypodidae were most dominant. Uca annulipes, Metopograpsus messor, Sesarma quadratum, Metopograpsus latiforons, Grapsus albolineatus and Scylla serrata were common species found in Karwar and Chitrapu mangrove sites.  Factors like substrate suitability, effect of tidal inundation and distribution of mangrove plants influenced the zonation and abundance of crabs (Prandnya et al., 2011). The same environmental conditions like rainfall, humidity and temperature in Karwar and Chitrapu may be the reason for the similar results in these two mangrove sites. NITK beach is represented by two families, 62% of Portunidae and 38% of Dotillidae (fig4). A total of 19 species belonging to 8 families and 15 genera were recorded by Trivedy et al., 2012 in Gulf of Cutch, Gujarath. Out of this 10 species belonging to 8 families and 10 genera were reported from mangrove mud flat habitat and 11 species belonging to 6 families and 10 genera were reported from open mud flat. They also reported that the maximum species were recorded in open mud flat compared to mangrove mud flat. Our study on habitat preference showed the opposite result.

Monthly variation in the species diversity (Shannon-Wiener diversity index, H1 loge) and Evenness, J1 are given in table 3. During the study period maximum species diversity was observed in September 2016 (1.668), when 106 individuals belonging to 8 species were recorded in mangrove vegetation. This is followed by July 2016 (1.496), when 59 individuals belonging to 6 species were recorded. In NITK beach maximum species diversity was observed during September 2016 (1.627), with 80 individuals belonging to 6 species were recorded followed by July 2016 (1.617) with 85 individual belonging to 6 species. The maximum evenness (0.7574) was recorded in September 2016 at Chithrapu and minimum was in August 2016 (0.6033). In NITK beach maximum evenness was in the month of August 2016 (0.9386). Species diversity and even distribution of organisms was noticed during post monsoon season in both the sites which may be due to breading activity in monsoon seasons i.e. July, August. A good number of crabs were seen during this monsoon and post monsoon seasons this may be due to environmental effects or low salinity (Prandnya et al., 2011). The decline in crab population may affect the food chain and also the soil and water enrichment. The discharges from the different kinds of industries growing in the proposed smart city of Mangaluru may be a threat to the diversity of crabs in the area and therefore the conservation of crabs is very important.

ACKNOWLEDGEMENT:
We wish to thank Dept. of Zoology, St. Aloysius College (Autonomous), Mangaluru for providing necessary facilities to carry out this work.We would like to give a special thanks to Dr. Hemachandra for helping in the identification of the species.We also express our gratitude to the organizers of Lake Conference for providing us this opportunity. We would like to express our gratitude to all fishermen who helped during the data collection and all associated groups met in the study those have given a lot of valuable information for completing the project.

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