A Histological Assessment of the Reproductive Cycle of the Sea Urchin, Lytechinus variegatus

The regular echinoid Lytechinus variegatus is a valuable model for the study of early embryological development. Lytechinus variegatus inhabits nearshore seagrass beds in the Gulf of Mexico and Caribbean, and the species ranges from the Carolinas along the US Atlantic coast to Brazil. Evaluating the natural reproductive cycle of L. variegatus will aid in understanding its role in community structure and in the management of this resource when housed in the laboratory. From April 2001 to September 2003, at intervals of 4—6 weeks, L. variegatus (41−50 mm diameter; n = 32 individuals/collection) were collected at Eagle Harbor in St. Joseph’s Bay, FL. A histological staging system for gamete development and maturation of the gonad was devised for female and male L. variegatus. The annual minimum gonad index was observed in September or October and increased to a maximum in March or April. A period of nutrient storage and limited gametogenic activity along the germinal epithelium in the fall and winter preceded spring gamete production and maturation. Observations of the mature reproductive stage in L. variegatus were associated with the new and full moon, suggesting that lunar cycle or tides influenced the timing of spawning. Peak periods of spawning occurred in spring and, occasionally, in the summer. Spawning probably did not occur from October to January. These data indicate field collections can be timed for early spring to ensure gravid adults for developmental studies.