δ13C and δ15N isoscapes from the Coastal Gulf of California based on Pyropia (Bangiales: Rhodophyta)

Abstract

This study describes the isotopic values of the Gulf of California (GC), establishing predictive coastal isoscape maps based on macroalgae. The GC has a different oceanographic characteristic and anthropogenic factor that have effects in both peninsular and continental coasts. The aim of this study was evaluated δ¹³C and δ¹⁵N values in Pyropia species, to established if any spatial gradient exists and the effect of environmental variables (sea surface temperature (SST) and Chlorophyll a (Chl a)) on the isotopic values. Significant differences were established in the δ¹³C and δ¹⁵N values between locations along the GC, and only in δ¹⁵N values between peninsular and continental coast. Generalized additive models (GAMs) suggest no effect of the environmental variables in δ¹³C values, however for δ¹⁵N values models suggest an important influence of Chl a. We observed that environment and spatial based models (GAMs) better capture spatial variability of the isotopic values. Isoscape maps indicated high δ¹³C values in the middle and at the mouth region of the GC, while higher δ¹⁵N values were mainly determined in the peninsular coast, however in less proportion also in continental coast. There was no isotopic latitudinal gradient in Pyropia from the GC. Different oceanographic process like mixing tidal and upwelling process generate variation in isotopic values through the GC, and additionally, the anthropogenic activities influence the isotopic dynamics. This result emphasizes the importance of consider environmental variables in the isoscape maps, and the fact that δ¹⁵N and δ¹³C coastal maps are important to improve the knowledge of baseline values in the GC.