ONTOGENY OF OSMOREGULATION IN THE GRAPSID CRAB ARMASES MIERSII (CRUSTACEA, DECAPODA)

Osmoregulation was studied in the zoeal stages I to III, the megalopa, juvenile crab stages I and II, and in adults of the grapsid crab Arma ses miersii. The larvae hatch and develop in tropical supratidal rock pools, where ample variations of salinity occur. To cope with this har sh environment, the capacity for osmoregulation is well developed at h atching, and becomes further accentuated in the larvae and juveniles. All zoeal stages hyper-regulated at low salinity (5 to 26 PSU), but at higher salinity (33 to 44 PSU), they were hyper-osmoconformers. The t ype of osmoregulation changed in the megalopa stage to a hyper-hypo-re gulation pattern. While the hyper-osmoregulatory capacity increased gr adually throughout postembryonic development from hatching to adult, t he hypo-osmoregulatory capacity increased from the megalopa to the adu lt. The ontogenic acquisition of osmoregulation was faster for hyper-t han for hypo-regulation: 85 and 41% of the adult capacity, respectivel y, was acquired in the crab I stage. These findings confirm that impor tant physiological changes occur at metamorphosis. A correlation is es tablished between the osmoregulatory ability of each developmental sta ge and its salinity tolerance. The ecological implications and the ada ptive and evolutionary significance of osmoregulation in early Life-hi story stages of A. miersii and other aquatic crustaceans are discussed .