ชนิดและการกระจายของจักจั่นทะเล (Crustacea : Hippoidea) บริเวณหาดชลาทัศน์ จังหวัดสงขลา

Abstract

The study of species and distribution of sand crabs in Chalathat beach, Songkhla province was investigated. The beach was divided into 8 stations 500 m interval. Sand crabs were collected in the intertidal zone by dredges (20x60 cm) and the physical parameters were measured monthly from August 2015 to July 2016. The result showed that the annual air temperature, sea water temperature, wet sand temperature and salinity were significantly different (P<0.05). The air temperature ranged from 27-39°C while the seawater and wet sand temperature ranged from 27-33°C and the salinity ranged from 23-35 psu. The salinity was lowest in November and highest in June and July. The monthly median grain size showed no significant difference (P>0.05) but the median grain size was significantly different at each station and the median grain size ranged 345.49 - 504.79 pm. The slightly gravelly sand was a major composition in every month and station. The monthly beach slope showed no significant difference (P>0.05) but the slope was significantly different at each station and the slope ranged 4.10-8.75 degree. The monthly organic matter was significantly different and varied from 0.33-0.55%. The organic matter showed no significant difference at each station (P>0.05). The sand crab species found in Chalathat beach were Emerita sp. and Hippa truncatifrons. The highest abundances of Emerita sp. occurred in March (38 + 36 individual/m?) and at station 3 (30 + 32 individual/m*). The highest abundances of H. truncatifrons occurred in May (5 + 3 individual/m*) and at station 1 and 2 (4 ÷ 2 and 4 + 3 individual/m*). The sex ratio of male and female in Emerita sp. and H. truncatifrons were 0.89: 1 and 1: 0.85, respectively. The mean carapace length of Emerito sp. was 6.4 mm for male and 8.5 mm for female. The mean carapace length of H. truncatifrons was 5.0 mm for male and 6.2 mm for female. The carapace length of both species related to weight as allometric pattern. The carapace width and number of eggs related with carapace length. Fecundity for Emerita sp. and H. truncatifrons were 8 - 2,492 and 6 - 845 eggs/individual, respectively. Spatial distribution of these sand crab species were not correlated with grain size, slope and organic matter. Both sand crabs density was higher in no sand bags area than in sand bags area. Temporal distribution showed no significant difference by season (P>0.05) but the highest abundance of Emerita sp. occured in summer. The physical parameter affecting distribution of Emerita sp. was the slightly gravelly sand but the distribution of H. truncatifrons was not clear. The Canonical correspondence analysis (CCA) indicated that slope and sand affecting to density of Emerita sp. and the slightly gravelly sand was not more effective for H. truncatifrons.