Sex-associated variations in coral skeletal oxygen and carbon isotopic composition of Porites panamensis in the southern Gulf of California
RAFAEL ANDRES CABRAL TENA
ALBERTO SANCHEZ GONZALEZ
HECTOR REYES BONILLA
EDUARDO FRANCISCO BALART PAEZ
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Coral δ 18O variations are used as a proxy for changes in sea surface temperature (SST) and seawater isotope composition. Skeletal δ 13C 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 δ 18O and δ 13C 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 δ 18O and δ 13C are hypothesized to be different in each sex. To test this, this study describes changes in the skeletal δ 18O and δ 13C 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 δ 18O, and of δ 13C, respectively, in the isotope record between colonies. Both isotope records were different between sexes. δ 18O was higher in female colonies than in male colonies, with a 0.31 ‰ difference; δ 13C was lower in female colonies, with a 0.28 ‰ difference. A difference in the skeletal δ 18O could introduce an error in SST estimates of ≈ 1.0 to ≈ 2.6 ◦C. The δ 18O 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 δ 18O–SST relation. Seasonal variation in coral δ 18O represents only 52.37 and 35.66 % of the SST cycle; 29.72 and 38.53 % can be attributed to δ 18O variability in seawater. δ 13C data did not correlate with any of the environmental variables; therefore, variations in skeletal δ 13C appear to be driven mainly by metabolic effects. Our results support the hypothesis of a sex-associated difference in skeletal δ 18O and δ 13C signal, and suggest that environmental conditions and coral growth parameters affect skeletal isotopic signals differently in each sex..."
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