Abundance and spatio-temporal distributional pattern of Dotilla myctiroides (Milne-Edwards) on exposed sandy beach of Aksa, Mumbai.

Abstract

The abundance and distributional pattern of Ocypodid crab, Dotilla myctiroides (Milne-Edwards) was studied on a sandy beach of Mumbai from January 2005 to December 2006. The area experiences semidiurnal tides. The beach is intermediate dissipative type and consists of medium to fine grade sand. The data were collected after fixing a transect line from high to low shore zone based on tidal heights. A mean abundance of 40 ± 4.55 ind.m-2 was found during 2005, while it was 37.82±7.31 ind.m -2 during 2006. Although no significant difference (p>0.05) in abundance was observed on seasonal scale, there was a marked variation (p<0.05) in the vertical distribution with an obvious increasing trend in abundance from high to low shore zone. The zonal variation in the abundance was distinct in different seasons and it increased from pre- to post-monsoon with decreasing tidal heights during both the years. A significant difference (p<0.05) in the abundance was recorded between high and mid shore zone during all the seasons while mid shore zone showed significantly higher (p<0.05) abundance during post-monsoon season. Data on distributional pattern of different maturity stages (juvenile, immature, young adult and adult) based on carapace width were also collected. The juveniles were mostly observed in mid and low shore zone, while adults dominated mostly the high shore areas. The factors like morphodynamic state of beach and behavioural ecology of this species seemed to play important role in its high abundance and vertical distribution on the sandy beach of Aksa, Mumbai.