Kelp blade carbon and nitrogen in 2021
For a random subsample of adult kelps (≥ 2 years) that were investigated for dry weight, additionally the blade %carbon, %nitrogen and C:N ratio was compared across the three kelps and at the depth levels 2.5m and 5m (Table 5, Figure 9). Detailed data for A. esculenta ,S. latissima and ‘Digitate Kelps’ are provided in Appendix 7. Additionally, blade carbon and blade nitrogen DW per m² is presented in Figure 10.
Overall, the three parameters %carbon, %nitrogen and C:N ratio in the blades of adult kelp individuals ≥2 years (2.5 – 5m) varied significantly between kelp species (Table 5). However, the factor depth did not exhibit a significant effect on any of the investigated parameters.
Relative carbon content was highest in A. esculenta (34 ± 5 %carbon), followed by S. latissima (32 ± 5 %carbon) which was itself significantly 1.2 fold higher compared to ‘Digitate Kelps’ (28 ± 5 %carbon) (A. esculenta > S. latissima> ‘Digitate Kelps’, p < 0.03, Wilcoxon test).
In contrast, relative blade nitrogen in A. esculenta (2 ± 0.9 %nitrogen) and ‘Digitate Kelps’ (1.8 ± 0.5 %nitrogen) was similar and significantly 1.4-1.3 fold higher than in S. latissima (1.4 ± 0.8 %nitrogen) ((A. esculenta = ‘Digitate Kelps’) >S. latissima , p < 0.02, Wilcoxon test).
Interestingly, depth integrated C:N ratio in S. latissima was 26.5 and thereby significantly 1.3 fold higher compared to A. esculenta (19.8) and 1.5 fold higher than in ‘Digitate Kelps’ (17.3) (S. latissima > (A. esculenta = ‘Digitate Kelps’), p < 0.03, Wilcoxon test) (all: mean ± SD).
In contrast to the carbon and nitrogen parameters measured per kelp individual, blade carbon and nitrogen per m2 (2.5 – 5m) were not different between species or depth levels and there was no interactive effect of species x depth (Figure 10). Even though statistical tests did not reveal significant differences, depth integrated blade carbon was highest in blades of A. esculenta(82.6 ± 78.1 g C m-2) followed by ‘Digitate Kelps’ (69.3 ± 144.3 g C m-2) and was lowest in S. latissima (28.1 ± 28.2 g C m-2). Interestingly, depth integrated blade nitrogen was highest in ‘Digitate Kelps’ (5.1 ± 10.8 g N m-2) and A. esculenta (5 ± 5.1g N m-2) which was 4 fold higher compared to S. latissima (1.2 ± 1.1 g N m-2). Overall the blades of adult kelps (≥ 2 years) of the local kelp forest stored 277 ± 123 g C m-2 and 18 ± 9 g N m-2 at 2.5m in contrast to only 83 ± 34 g C m-2 and 4 ± 2 g N m-2 at 5m (all: mean ± SD).