Distribución y estructura poblacional del cangrejo Halicarcinus planatus (Brachyura, Hymenosomatidae) en el Canal Beagle, Tierra del Fuego Distribution and population structure of the crab Halicarcinus planatus (Brachyura, Hymenosomatidae) in the Beagle Channel, Tierra del Fuego

The crab Halicarcinus planatus is the only hymenosomatid that inhabits the southern tip of South America and has a sub-Antarctic distribution, including the peri-Antarctic islands and New Zealand. In this paper, we report the abundance and population structure of H. planatus for a year in the intertidal zone of Bahia Brown, Beagle Channel, Tierra del Fuego. Moreover, we show variations in the population structure in other beaches and environments of the channel. In contrast with males, female density showed monthly variations and was higher during austral summer months. High densities of H. planatus could be related with low mortality during the larval stage and oceanographic features of Bahia Brown, probably enhanced by the presence of both culture and mussel beds, substrates where settlement would occur. The populational sex ratio was biased towards females only in summer, while the operational sex ratio was biased towards males during all periods studied, suggesting strong competition among males for mating. In turn, males were present only in the intertidal zone of Bahia Brown and Macrocystis pyrifera but were absent in the other studied intertidal areas.This is perhaps related to the lack of shelter in the subtidal zone of Bahia Brown. Recruitment occurs in two different periods, summer (January- February) and autumn-winter (May-June), which corresponds with the two larval cohorts of H. planatus in the Beagle Channel.