Sex-associated variations in coral skeletal oxygen and carbon isotopic composition of Porites panamensis in the southern Gulf of California

Abstract. Coral δ¹⁸O variations are used as a proxy for changes in sea surface temperature (SST) and seawater isotope composition. Skeletal δ¹³C of coral is frequently used as a proxy for solar radiation because most of its variability is controlled by an interrelationship between three processes: photosynthesis, respiration, and feeding. Coral growth rate is known to influence the δ¹⁸O and δ¹³C isotope record to a lesser extent than environmental variables. Recent published data show differences in growth parameters between female and male coral in the gonochoric brooding coral Porites panamensis; thus, skeletal δ¹⁸O and δ¹³C are hypothesized to be different in each sex. To test this, this study describes changes in the skeletal δ¹⁸O and δ¹³C record of four female and six male Porites panamensis coral collected in Bahía de La Paz, Mexico, whose growth bands spanned 12 years. The isotopic data were compared to SST, precipitation, photosynthetically active radiation (PAR), chlorophyll a, and skeletal growth parameters. Porites panamensis is a known gonochoric brooder whose growth parameters are different in females and males. Splitting the data by sexes explained 81 and 93 % of the differences of δ¹⁸O, and of δ¹³C, respectively, in the isotope record between colonies. Both isotope records were different between sexes. δ¹⁸O was higher in female colonies than in male colonies, with a 0.31 ‰ difference; δ¹³C was lower in female colonies, with a 0.28 ‰ difference. A difference in the skeletal δ¹⁸O could introduce an error in SST estimates of  ≈  1.0 to  ≈  2.6 °C. The δ¹⁸O records showed a seasonal pattern that corresponded to SST, with low correlation coefficients (−0.45, −0.32), and gentle slopes (0.09, 0.10 ‰ °C⁻¹) of the δ¹⁸O–SST relation. Seasonal variation in coral δ¹⁸O represents only 52.37 and 35.66 % of the SST cycle; 29.72 and 38.53 % can be attributed to δ¹⁸O variability in seawater. δ¹³C data did not correlate with any of the environmental variables; therefore, variations in skeletal δ¹³C appear to be driven mainly by metabolic effects. Our results support the hypothesis of a sex-associated difference in skeletal δ¹⁸O and δ¹³C signal, and suggest that environmental conditions and coral growth parameters affect skeletal isotopic signals differently in each sex. Although these findings relate to one gonochoric brooding species, they may have some implications for the more commonly used gonochoric spawning species such as Porites lutea and Porites lobata.