In the larval stages of three euryhaline species of the genus Armases, we tested if changes in biomass (dry mass, W; protein; lipid) under hyposmotic stress were related to their salinity tolerance, capabilities of osmoregulation, and migration patterns. As model species, we compared Armases miersii, which breeds in supratidal rock pools, the riverine crab Armases roberti (showing a larval export strategy), and Armases ricordi, whose larvae probably develop in coastal marine waters. At each stage, larvae were exposed to different salinities (selected according to previous information on larval survival; range: 5‰-32‰ for A. miersii, 10‰-32‰ for A. roberti, and 15‰-32‰ for A. ricordi). Biomass was measured in early postmoult and intermoult. The larvae of the strongly osmoregulating species A. miersii, which develop in habitats with highly variable salinity conditions, showed the smallest variations in biomass. The effect on A. roberti varied during its ontogeny: the Zoea I and the Megalopa, which carry out downstream and upstream migrations, respectively, showed lower biomass variations than the intermediate zoeal instars, which develop in coastal waters. The larvae of A. ricordi showed generally the highest variations in biomass, reflecting poor adaptation to salinity variations. In addition, a common pattern was found for these estuarine species: the maximum of biomass shifted during ontogeny from 32‰ to 25‰, reflecting changes of the iso-osmotic point. The ontogeny of osmoregulation reflected ontogenetic migration patterns, which allow for avoiding detrimental effects of salinity variations. © 2007 Elsevier Inc. All rights reserved.
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