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

Density banding provides a record of per- formance of coral colonies over time and across envi- ronments, 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, cal- cification rate is hypothesized to be different for each gender. To evaluate differences in skeletal growth be- tween 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 meas- ured using photo-densitometry of X-radiographs. Ex- tension 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 calcifica- tion differently in male and female colonies.