Egg production by colonies of a gorgonian coral

Reproductive success, the production and fertilization of gametes, is a key component of fitness. Among many colonial marine invertebrates, the production of gametes by a colony is a function of both gamete production per module (e.g., polyp, zooid) and the number of modules in the colony (i.e., colony size). We examined variance in gamete production per polyp and egg production per colony over a range of colony sizes, and the relationship between egg production and growth in the common Caribbean gorgonian Plexaura flexuosa. The number of polyps per colony and the average number of mature eggs per polyp both were greater among larger female colonies (>70 cm in height) than among smaller colonies (< 70 cm), resulting in a 1 to 2 order of magnitude increase in whole colony egg release for the larger colonies. In a group of 24 colonies, 98% of the 9.2 x 10⁶ eggs produced in one spawning event came from the 12 colonies taller than 70 cm. Branch extension rates showed no relationship to colony size, but whole colony relative growth appears to decrease as colony size increases. This suggests that proportionately less energy is used for growth as a colony gets larger, and thus may be available for reproduction.