Effects of salinity on larval and early juvenile growth of an extremely euryhaline crab species, Armases miersii (Decapoda: Grapsidae)

Abstract

The neotropical crab Armases miersii (Rathbun, 1897) breeds in supratidal rock pools, where great salinity variations occur. In laboratory experiments, all larval stages and the first juveniles were reared at six different salinities (5-55 PSU, intervals of 10 PSU). In five series of experiments, exposure to these conditions began either from hatching (Zoea I) or from the onset of successively later stages (Zoea II, III, Megalopa, Crab I). Growth was measured in terms of dry weight, carbon, nitrogen and hydrogen content. At osmotically extreme conditions (5 and 55 PSU, resp.), all stages showed minimum biomass accumulation; this was consistent with maximum mortality and longest duration of development (data presented in a separate paper). Successively later exposure to these salinities tended to reduce these effects. Lowest mortality and shortest time of development occurred generally at 15-25 PSU, indicating an optimum at moderately reduced salinities. This response pattern, however, was not congruent with that observed in growth. Biomass accumulation was initially maximum within a wide range of salinities (15-45 PSU), but in the Zoea II and III stages, this range tended to narrow and to shift towards higher salinities (35-45 PSU). These trends reversed in the Megalopa and Crab I, where maximum growth occurred again in a wider range and at lower salinities (15-35 PSU). The reduction of zoeal growth in moderately dilute media (15-25 PSU), which were optimal for survival and development, is interpreted as an energetic cost of hyperosmoregulation, which begins already at hatching. Five PSU caused hypo-osmotic stress, exceeding in the long term the larval capacity for hyper-regulation. Poor zoeal survival and growth at 55 PSU are interpreted as effects of hyper-osmotic stress. In the Megalopa and Crab I, reduced growth at salinities ≥35 PSU may reflect the energetic costs of hypo-osmoreguation beginning in these stages. Our data suggest that the physiological adaptations of larval and early juvenile A. miersii allowing for survival and development in a physically harsh and unpredictable habitat imply a trade-off with reduced growth, due to energetic costs of osmoregulation.

Effects of reduced salinity on the biochemical composition (lipid, protein) of zoea 1 decapod crustacean larvae

“…The energy necessary for this process must have originated primarily from the catabolism of lipids, making protein degradation unnecessary. The same explanation should apply to the strongly osmoregulating zoea of A. miersii, whose carbon content was shown to vary only slightly in a very wide range of salinities (15 -45x ; Anger et al, 2000), and in those of C. maenas, where salinity affected DW and the lipid content but not the protein fraction of biomass. The fact that the zoea 1 of this species is able to survive for several days at 15xbut not to moult to the zoea 2 indicates a limited euryhalinity, and some osmoregulatory capacity.…”

“…They typically show a high percentage of protein (>30%), followed by lipids (<20%), chitin (<15%) and free carbohydrates (<5%). Variation is due to differential phylogenetic position and variation in environmental factors such as temperature (Dawirs and Dietrich, 1986;Anger, 1987), food availability (Anger and Dawirs, 1982;Dawirs, 1986Dawirs, , 1987Harms et al, 1991Harms et al, , 1994, and salinity (Pfaff, 1997;Anger et al, 1998Anger et al, , 2000. Temperature, for instance, may affect the reserves accumulated during growth through simultaneous but not always equal changes in instantaneous growth rate and development time (Anger, 1998).…”

Effects of osmotic stress on crustacean larval growth and protein and lipid levels are related to life-histories: The genus Armases as a model

“…Protein Lipids term cultivation, see Anger et al, 2000;Torres et al, 2006). Ovigerous females were isolated in individual aquaria and kept under otherwise identical conditions until larvae hatched.…”

“…In coastal and estuarine waters, changes in salinity play therefore a central role for the survival and growth of planktonic larvae and other invertebrates, as well as fish (Kinne, 1971). In particular, biomass and chemical composition are affected by reduced salinities (Anger, 2001(Anger, , 2003Anger et al, 2000;Torres et al, 2002).…”

Larval growth in the estuarine crab Chasmagnathus granulata: the importance of salinity experienced during embryonic development, and the initial larval biomass

“…brachyuran crabs) growth is species and stage dependent (Anger 1990(Anger , 1998. Food availability and quality (Anger and Dawirs 1982;Dawirs 1986Dawirs , 1987Harms et al 1991Harms et al , 1994, temperature (Dawirs and Dietrich 1986;Anger 1987), and salinity (Anger et al 1998(Anger et al , 2000 stress can have detrimental effects on growth, decreasing the rate of accumulation of biomass.…”