Abstract
Brachyuran crabs constitute the most abundant faunal component of mangrove ecosystems and support a wide range of ecosystem services. In the present study, seasonal variation of population density and biomass along with demographic categories and sex ratios of four species of fiddler crabs (Uca rosea, Uca triangularis, Uca dussumieri and Uca vocans) from Jhorkhali Island in the Sundarban mangrove were studied in relation to some major environmental parameters (salinity, nutrient content, soil organic carbon, dissolved oxygen, total dissolved solute, etc.) during bimonthly sampling for three consecutive years (2010-2012). Maximum population density and biomass of the ocypodid crabs were recorded during the pre-monsoonal month and minimum values during the monsoon. Different peaks in reproductive activity were observed among seasonal breeders (U. triangularis, U. dussumieri). For U. vocans, the sex ratio peaks declined during the ovigerous period. All four populations were characterized by significantly more males than females. Multiple regression analysis suggested a cumulative effect of several ecological parameters on seasonal fluctuations of the crab population. Breeding periodicity might be controlled by a combination of factors, including temperature, quality of the substratum, food availability for the adult and larval stages, and intertidal zonations.
Highlights
Age determination is fundamental for understanding and properly estimating various parameters that determine the biology of cephalopod species, such as growth rate, population structure, longevity, mortality, productivity and the recruitment process (Boyle and Rodhouse 2005)
Summary: Age and growth of the horned octopus Eledone cirrhosa are estimated for the first time by stylet increment analysis
Specimens were collected between March 2009 and March 2010 from the commercial trawl fishery operating off northwestern Iberian coasts
Summary
Age determination is fundamental for understanding and properly estimating various parameters that determine the biology of cephalopod species, such as growth rate, population structure, longevity, mortality, productivity and the recruitment process (Boyle and Rodhouse 2005). Direct ageing methods, based on reading growth increments in hard structures, have been developed to determine age in cephalopods. In octopods, beaks have provided some positive results in reading growth increments of Octopus vulgaris paralarvae (HernandezLopez et al 2001) and adults (Canali et al 2011, PeralesRaya et al 2010). Stylet Increment Analysis has been applied and daily growth increment deposition has been validated in Octopus vulgaris (Hermosilla et al 2010), Octopus pallidus (Doubleday et al 2006), Octopus maya (Rodríguez-Domínguez et al 2013) and Octopus (cf) tetricus (Leporati and Hart 2014)
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