MEPS 628:55-71 (2019)  -  DOI: https://doi.org/10.3354/meps13096

ABSTRACT: Kelp forests are some of the most productive habitats in the oceans, supporting diverse, ecologically, and often commercially, important ecosystems. This study of 8 geographically separate sites in 2 seasons highlights the natural variability of stable isotope values (δ¹³C and δ¹⁵N), at different spatial and temporal scales, within the 2 dominant kelp species along the west coast of South Africa. Additionally, stable isotope variability was investigated within and among different tissues within both kelp species. Within a kelp plant, δ¹³C values had a variance of 1.7‰ for Ecklonia maxima and 1.5‰ for Laminaria pallida. The δ¹⁵N values had a variance of 3.8‰ for E. maxima and 4.2‰ for L. pallida. There were also consistent variability patterns along the length of a single frond in both species, for both isotopes. Among the localities, E. maxima and L. pallida were highly variable with variances in δ¹³C (9.4‰ and 11.2‰) and δ¹⁵N (3.4‰ and 4.5‰) for the 2 species respectively. The δ¹³C values of L. pallida and E. maxima displayed a clear pattern coinciding with depth, particularly for L. pallida. Within-site variability was a major contributor to the overall spatial variability for both species. This study provides further evidence for the importance of understanding basal variability of stable isotope values when determining the carbon sources of bottom-up controlled ecosystems.

KEY WORDS: δ¹³C · δ¹⁵N · Laminariales · South Africa