CONICET | Buscador de Institutos y Recursos Humanos

The crab Halicarcinus planatus is the only decapod that reproduces twice a year in sub-Antarctic South America. The aim of this study was to quantify total dry mass (W) and elemental composition (CHN) during the larval development of this species comparing two reproductive periods, August and December, at the southernmost limit of its geographical distribution. Ovigerous females were caught in the intertidal zone of Bahía Brown, Beagle Channel (ca. 54º 52´S; 67º 32´W), and kept in individual 1.4 L-flasks. After hatching, larvae from 14 females were randomly collected and kept in individual bowls containing 100 ml of seawater at 8±0.5ºC in darkness conditions. Water was changed every second day and freshly hatched Artemia nauplii were supplied as food. Determinations of W and CHN were done in all three zoeal stages and in the first juvenile instar, using in both months of reproduction different larval hatches from 7 females each. The dry mass of freshly hatched zoea I of Halicarcinus planatus differed significantly between the reproductive periods (F = 5.41, p<0.03) and females (F = 17.03, p<0.001), with heavier produced larvae in August. When larval biomass was expressed as CHN (µg/individual), these values were always higher in August than in December. The C/N mass ratio also was significantly higher in August. Throughout larval development from hatching to metamorphosis, W showed a continuous increase. Changes in CHN and energy content (Joules/individual) indicate that the lipid and protein fractions of larval biomass were also increasing throughout the larval development. The C/N ratio varied between the two spawnings: was constant in the August hatching and decreased through the larval development in the December hatching. After metamorphosis, the C/N ratio in the Crab I instar was higher than in the Zoea III stage. The differences found in our study may indicate seasonal variation in the energetic condition of reproducing females.