Reproductive cycle of two Modiolus capax (Bivalvia: Mytilidae) beds at different depths at Ensenada de La Paz, Gulf of California, Mexico

Abstract

Background: The fat horsemussel Modiolus capax is a commercially important resource in northwest Mexico; however, few studies evaluate its reproduction. Goals: Compare the reproductive cycle of M. capax in two beds at different depths in Ensenada de La Paz, B.C.S., Mexico, and its relationships with the environmental variables. Methods: Approximately 25 (±4.5) specimens were collected between October 2008 and December 2010, in a shallow bed in the intertidal zone (Bed A), and 23 (±4) at a five meters deep bed (Bed B), in Ensenada de La Paz, B.C.S., Mexico. Monthly assessments of individual biological information were complemented by histological analyses of the gonads at different moments of the reproductive cycle, taking in environmental changes. The size at the first sexual maturity (L50) was estimated using a logistic model to obtain the size at 50% maturity. The relationship between gonad development stages and the gonadosomatic index was estimated, as well as the relationship between these stages with temperature and chlorophyll. Results: A peak spawning occurred in March in Bed A and in January in Bed B. In both beds, mature and post-spawning females showed follicular atresia, up to 82% in Bed B. The estimated L50 was 74.12 mm for Bed A and 71.74 mm for Bed B. The gonadosomatic index differed between beds, and was positively correlated with the increase in chlorophyll-a (Bed A). A significant negative correlation was observed between temperature and the frequency of the maturing stage (Bed A). Conclusions: The reproduction of M. capax revealed that the beds have a different reproductive periodicity and that environmental changes affect the activity and favor the development of follicular atresia.