Shifts in biodiversity and physical structure of seagrass beds across 5 decades at Carriacou, Grenadines

On average the number of scarps had increased 1.6-fold at HWE sites (from 2.8 to 4.6) between 1969 and 2016 (we excluded T5 from analysis as there was no possibility for scarps to form by 2016). At 3 HWE sites (T1, T6, T7), scarp number increased 3-fold between 1969 and 2016, with most or all of the increase occurring between 1994 and 2016. At the other 2 sites (T8, T9), a small decline in scarp number occurred between 1994 and 2016/2019. 2-way ANOVA showed a significant effect of wave energy (F1,21 = 51.1, P <0.001) and year (F2,21 = 5.3, P = 0.014) on scarp number, but no interaction between wave energy and year (F2,21 = 0.36, P = 0.702). Tukey’s HSD post hoc test showed a significant increase in scarp number between 1969 and 2016 (P = 0.019) and 1994 and 2016 (p = 0.042), but not between 1969 and 1994 (P = 0.927). Fig 7. Non-metric MDS of seagrass bed community at each station and year. Points are arcsine transformed proportional frequency of occurrence measures using Bray Curtis dissimilarity matrix of square-root transformed data. Vectors (black) show correlations between ordinations for benthic communities and average frequencies of occurrence for functional groups (seagrass, brown algae, green algae and sponges) at each station and year. The size of each point indicates the frequency of sea urchins at each station and year. https://doi.org/10.1371/journal.pone.0306897.g007 PLOS ONE Seagrass bed biodiversity and structure and across 5 decades PLOS ONE | https://doi.org/10.1371/journal.pone.0306897 August 1, 2024 13 / 25