Differences in δ13C and δ15N stable isotopes in the pearly razorfish Xyrichtys novacula related to the sex, location and spawning period

In the present study, Xyrichtys novacula (Labridae) were sampled at five locations around the islands of Ibiza and Formentera (western Mediterranean Sea). Isotopic signatures of delta 13C, delta 15N and the C:N ratio were analysed in relation to locality, sex and size differences. delta 13C and delta 15N partitioning was also studied in the reproductive spawning period. There were significant differences in the delta 13C signature between localities for both sexes, but not for delta 15N. Sex differences were also found with a mean +/- s.e. value of -17.38 +/- 0.06 parts per thousand delta 13C and 8.36 +/- 0.05 parts per thousand delta 15N for females and -17.17 +/- 0.07 parts per thousand delta 13C and 8.80 +/- 0.06 parts per thousand delta 15N for males. Increasing total length in both sexes was positively correlated with delta 15N enrichment and a significant positive linear regression was established for both variables. During the reproductive spawning period, there were changes in delta 13C fractioning with enrichment in postspawning females and males (with respect to prespawning and spawning periods) and delta 15N impoverishment in postspawning females (with respect to prespawning and spawning periods). Xyrichtys novacula uses local food sources, as confirmed by delta 13C and delta 15N, and females and males use different food sources, thus avoiding intraspecific competition. This was confirmed by delta 15N enrichment as size increased. Spawning leads to special requirements for gonad maturation, which is reflected in the isotopic signatures for both sexes.