Nictimeral variations of freshwater crabs activity at “Río Pilcomayo National Park, Argentina

RENZULLI, P.; COLLINS P.

Puerto Vallarta Mexico

Congreso; The Crustacean Society 2000 Summer Meeting; 2000

Instituto de Ciencias del Mar y Limnología & Instituto de Biología Univ. Nac. Aut. de Mexico

Circadian rhythmus is one of the natural cycles which affect animal population on aquatic environment but it has only been described for a few species of crustacean and these are mainly marine and/or brackiswater species. The daily variations of activity on two freshwater crabs (Trichodactylus borellianus and Dilocarcinus pagei) were analyzed during three days. The same activity patterns for both crabs can be explained under two interespecific aspects, besides the internal clock, the predatory or injury risk and food availability. During nighttime, the mayor activities may have been related to the fish and birds predation decrease, if the efficiency of vidual predators is reduced at night. The diminished risk of injury could provide an opportunity to movement and feeding. Furthermore, there is more potential preys occurrence (microcrustacean, oligochaets and insect larvae) at night.