Population Structure, Fecundity, and Reproductive Patterns of Erichsonella attenuata (Isopoda: Valvifera: Idoteidae) in Tamiahua Lagoon, Veracruz, Mexico

Erichsonella attenuata is a free-living marine isopod distributed across the Gulf of Mexico; however, quantitative information on its population structure and reproductive biology remains limited. We examined 2315 individuals collected in Tamiahua Lagoon, Veracruz, Mexico, to describe body-size structure, reproductive activity, and reproductive output. Males exhibited a broader body-size distribution and attained larger maximum sizes than females. Gravid females occurred only above a minimum body-size threshold, and the probability of being gravid increased significantly with total length. Reproductive-structure counts were analyzed separately for females containing coelomic reproductive structures and those carrying marsupial embryos. Marsupial embryo counts increased significantly with female body size, whereas no significant relationship was observed for coelomic reproductive structures. Reproductive-structure counts also differed significantly between the two anatomical categories, supporting their treatment as separate reproductive conditions rather than as a single measure of reproductive output. Reproductive activity was observed during six of the seven sampling dates. These findings provide one of the first quantitative descriptions of the population structure and reproductive biology of E. attenuata from the Gulf of Mexico and provide a baseline for future studies of reproductive ecology in valviferan isopods.