Ecological stoichiometry of some macroalgae distributed on the coast of Sinop: C:N:P ratio

This study was conducted to ecologically evaluate the changes in tissue nutrient (C, N, P) concentrations of some macroalgae distributed in the upper infralittoral zone of Sinop coastal waters. Sampling was carried out seasonally at 5 different stations, namely Inceburun (Ist. I), Hamsilos (Ist. II), Akliman (Ist. III), Dış liman (Ist. IV) and İç liman (Ist. V) between October 2019 and July 2020. Common 9 species representing Chlorophyta (green algae), Rhodophyta (red algae) and Ochrophyta (brown algae) groups were collected manually from 0-1 m depth. In addition, the seawater was analyzed for nutrient salts and some physicochemical parameters were measured in the field. Time-, space- and species-specific differences between data were analyzed using Tukey HSD test (after one-way ANOVA) or Dunn-Bonferroni (after Kruskal-Wallis H) tests. Spearman's rank correlation coefficient method and Principal Component Analysis (PCA) were used to understand the relationships of tissue nutrients (C, N, P) with ecological variables. Seasonal, regional and species-specific variations of C, N and P concentrations of macroalgae were found to be significant and the relationships of these elements with ecological variables were also significant (p<0.05). Tissue C concentration was 14.73% (C. officinalis; Spring; Ist. V) - 43.04% (P. capillacea; Summer; Ist. IV), N concentration was 0.50% (C. officinalis; Summer; Ist. II) - 5.14% (Ceramium spp.; Winter; Ist. I), P concentration was 0.02% (Ceramium spp.; Winter; Ist. I and II) - 0.32% (U. rigida; Autumn; Ist. IV), C:P ratio 157 (C. officinalis; Winter; Ist. IV) - 4255 (L. obtusa; Winter; Ist. I), N:P ratio 9 (C. officinalis; Winter; Ist. IV) - 304 (L. obtusa; Winter; Ist. II) and C:N ratio 9 (Ceramium spp.; Winter; Ist. I)) - 51 (U. intestinalis; Summer; Ist. I). The average annual N concentrations of green, brown and red algae groups were 1.98%, 1.76% and 2.20%, respectively, and the average annual P concentrations were 0.12%, 0.11% and 0.09%, respectively. At the end of the study, the average C:N:P atomic ratio of macroalgae was 1187:57:1 and the median ratio was 859:41:1. These rates show that the algae in the current study (except C. officinalis) are subject to P limitation along the coast of Sinop.