Different calcification rates in males and females of the coral Porites panamensis in the Gulf of California

Density banding provides a record of performance of coral colonies over time and across environments, and offers 3 measurable variables: skeletal density, extension rate, and calcification rate. Skeleton formation is energetically expensive for corals and may be associated with other energy-dependent processes, such as reproduction. Egg production requires more energy expenditure than sperm production. Thus, calcification rate is hypothesized to be different for each gender. To evaluate differences in skeletal growth between males and females, we studied a gonochoric massive coral, Porites panamensis, from 3 regions of the Gulf of California. Colony sex was identified using histology methods, and growth parameters were measured using photo-densitometry of X-radiographs. Extension and calcification rates were significantly higher in male colonies than in females (by 18 to 23%) at 2 of our 3 study sites, while skeletal density was similar in both genders. Our results support the hypothesis of a gender bias in growth characteristics and suggest that environmental conditions may impact coral calcification differently in male and female colonies.