Population structure of the South American Estuarine crab, Chasmagnathus granulatus (Brachyura: Varunidae) near the southern limit of its geographical distribution: comparison with northern populations

Abstract

Crabs are among the most conspicuous and ecologically important invertebrates of the large intertidal zones that characterize estuarine and protected coastal areas in temperate regions. The habitat, population structure and breeding cycle of Chasmagnathus granulatus (Brachyura: Varunidae), a semiterrestrial burrowing crab endemic to the warm temperate coasts of the Southwestern Atlantic, were studied in San Antonio Bay (Argentina), near the southern limit of its range. San Antonio Bay has no freshwater input, winter is relatively colder, and summer warmer, than northern habitats of this species. Crabs lived both in vegetated and unvegetated zones, but density and sex ratio varied among dates and zones. The maximum observed density was 136 crabs/m 2 , the maximum carapace width (CW) was 32 mm (males) and 29.8 mm (females), ovigerous females were found only in November and January, and the smallest ovigerous female measured 17 mm CW. The population structure, spatial distribution, and recruitment pattern of C. granulatus did not differ between San Antonio Bay and northern habitats. The higher density, smaller maximum size and shorter reproductive cycle observed in San Antonio cannot be atributed to changes associated with a latitudinal cline and other factors, such as thermal amplitude and food availability, need to be studied. Hydrobiologia (2005) 537: 217-228 Ó Springer 2005

Great unexpected differences between two populations of the intertidal crab Neohelice granulata inhabiting close but contrasting habitats (Crustacea: Decapoda: Brachyura)

“…700 km in straight line from the studied sites. These data were reported by Bas et al (2005Bas et al ( , 2007Bas et al ( , 2008Bas et al ( , 2014 (1994,1996,2012).…”

“…Crab density was higher in saltmarsh than in mudflat in both sites and higher in mudflat in SAO than in RSJ; it did not differ between salt marshes in spite of the higher proportion of gravel found in SAO, which may cause difficulties for digging, and the lower content of organic matter (SAO saltmarsh: 21 (Bas et al 2005).…”

“…This, however, conflicts with morphometric analysis, which did not show a clear geographical pattern of morphological differentiation (although there were some differences among sites) (ituarte et al 2012). Life history traits, activity and feeding differed among several well-studied Argentinean habitats included in the genetic analysis (ituarte et al 2006, Bas et al 2005, 2007, siLva et al 2009, Luppi et al 2013.…”

“…San Antonio Oeste (SAO) is a large intertidal area (143 km 2 ) placed in the western bank of San Antonio Bay and is characterized by extensive sand-cobble intertidal flats; Riacho San José (RSJ) is a smaller intertidal area (2 km 2 ) located in the southwestern extreme of San José Gulf; this is the southernmost population of this species registered so far. The life history, reproductive cycles and behavior of N. granulata in SAO are well known (ituarte et al 2006, Bas et al 2005, 2007, saL moyano et al 2012, Luppi et al 2013) but the population biology of this crab in RSJ has not been previously studied. These two sites have similar climatic and hydrographic characteristics: tidal amplitude and predictability, mean water temperature from November to April, a period that includes the whole reproductive season (Fig.…”

“…After each collection, density and size frequency distributions (SFD) were calculated separately in saltmarsh and mudflat habitats from both sites. Modal components of each distribution were estimated by fitting the observed SFD to the expected values of a mixture of normal distributions by the least squares method; see Bas et al (2005) for details of procedure, parameters and restrictions of the method.…”