FECUNDITY OF 2 GRAPSID CRAB SPECIES IN THE LAGUNA-MAR-CHIQUITA, ARGENTINA

In adult females of two euryhaline grapsid crabs, Cyrtograpsus angulat us and Chasmagnathus granulata, which coexist in a brackish coastal la goon in Argentina, we studied the quantitative relationships between b ody size (carapace width, CW), wet weight (WW), dry weight (DW), ash-f ree dry weight (AFDW), and egg production (fecundity). The females of these two species have a similar average body size, gross chemical com position (percentage contents of water, ash, and organic matter), and a similar size and chemical composition of eggs. In both species, all size-weight relationships as well as those between egg number and eith er female size or weight could be described with allometric regression equations (power functions). Significantly different slopes in the si ze-weight regressions of these two species, however, indicate that the re are specific morphometric differences. These are indicated also by a significantly higher average egg production in C. granulata, reflect ing a proportionally larger volume of the body cavity in relation to C W Comparison of the fecundity of females with early or late-stage eggs shows, in both species, that there is a significant loss of eggs duri ng the time of embryonic development (up to 32 % in C. granulata and 6 7 % in C. angulatus). The loss of developing eggs tended to increase w ith increasing female size in C. granulata and with decreasing female size in C. angulatus. In the latter species, a high incidence of mutip le limb loss (autotomy) has been observed as a common specific feature . Females which have lost at least half of their pereiopods show a sig nificantly lower average fecundity and a higher varability in egg numb er as compared with intact individuals. The energetic investment of fe male crabs into egg production is compared with the relation between t he amounts of organic matter deposited in the egg mass and that of the female body. On an AFDW basis, we measured a significantly higher rat io (21 %) in C. granulata than in C. angulatus (16 %). This reflects n ot only a greater fecundity in the former species; in addition, ia egg s have a slightly (but significantly) larger average size, DW, and AFD W. During the course of embryonic development, the egg volume increase s in both species, due to an uptake of water, to about double the init ial value. While organic matter (AFDW) decreases as a consequence of e mbryonic metabolism, there is a significant increase in the mineral fr action and the water content of the eggs.