Do Structural Changes in the Macrobenthic Community Drive Differences in the Reproductive Performance of the Pea Crab

AbstractFecundity and egg size vary among females, depending on environmental conditions experienced by mothers, known as maternal effects. Temperature, salinity, food availability, competition, and predation can influence maternal allocation. We evaluated temporal changes in the reproductive biology of the pea crab Austinixa patagoniensis in the context of local spatial competition with the yellow clam Amarilladesma mactroides mediated by the ghost shrimp Audacallichirus mirim. We assessed physical environmental variables and compared size-dependent reproductive parameters-fecundity and egg volume-between two contrasting periods at Monte Hermoso Beach (38°59' S, 61°19' W): clam-period, characterized by the dominance of A. mactroides in the macrobenthic community, and crab-period, marked by the dominance of A. patagoniensis. Additionally, we calculated reproductive output for crab-period and examined the relationship between brood and female size. Fecundity did not differ between periods, whereas egg volume was greater during clam-period across all female sizes. Since no differences were found in physical environmental variables, larger egg volume was interpreted as increased allocation per offspring, suggesting adaptive allocation to counteract the negative effects of density-dependent exclusion of pea crabs, leading to offspring with greater dispersal potential and/or better ability to survive and perform under adverse conditions. Larger eggs without fecundity cost indicate greater reproductive allocation during clam-period, possibly reducing investment in other life history traits. While no correlation was found between brood and female weight, an isometric relationship was observed between brood weight and female size. Future studies should focus on how maternal effects influence the population dynamics of the species.