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

number of stations out of 17 at which the species/group was recorded, and mean frequency of occurrence (%) in 12 quadrats per station across all stations in 1969, 1994 and 2016. For addi- tional notes on occurrence and natural history of these species and associated photographic records, see iNaturalist Project https://www.inaturalist.org/projects/seagrass-bed-flora-fauna- of-carriacou-grenada-2016. (PDF) S3 Table. Multivariate analysis of seagrass bed community composition. Results of a one factor permutational multivariate analysis of variance (PERMANOVA) based on a Bray–Cur- tis similarity matrix generated from arcsine sqrt transformed frequency of abundance of spe- cies/groups in stations (n = 17) in 1969, 1994 and 2016. Year is a fixed factor and all tests used 9999 permutations and unrestricted permutation of raw data and Type III partial sums of squares. Pairwise tests and average similarity are shown for communities between years. (PDF) S1 Fig. Wave exposure for transects. Relative Exposure Index (REI) for transects at Low Wave Energy (LWE, n = 4) and High Wave Energy (HWE, n = 6) sites. (TIFF) S2 Fig. Depth profiles for transects at 6 HWE sites and 4 LWE sites in 1969 and 2016, and 3 HWE sites and 1 LWE site in 1994. Extent of seagrass-free inshore zone shown as dashed line at start of transects. Scarps (depth measured at base and peak) shown as circles. (TIFF) S3 Fig. Photographs illustrating blowout and scarps in seagrass beds at Carriacou. A. Typi- cal blowout. B. Actively eroding scarp. C. Old scarp, non-eroding; new growth of seagrass on

blowout floor and over scarp face. (Photographs by David Patriquin). (PDF) S4 Fig. Photographs of Acropora palmata-dominated fringing reef on seaward side of Sandy Island (12.4855, -61.4829), Carriacou, illustrating the process of reef flattening between 1969 and 2016. 1969: Intact, living A. palmata reef. 1996: A. palmata entirely dead but mostly still in-place following die-off from White Band Disease in late 1970s/early 1980s; a few small colonies of a new generation of A. palmata were present. 2016: Original A. palmata framework reduced to rubble, no substantive replacement by newer colonies. (Photographs by David Patriquin.) For details of changes from 1969 to 1996, see Patriquin DG, Hunte W. Pre- liminary observations of the status of shallow water reefs at Sandy Island, Carriacou, Grenada. Report to the Grenada Board of Tourism and the Kido Project Environment Station, Carria- cou. 1997. Available at: https://dalspace.library.dal.ca/handle/10222/82532. (PDF) Acknowledgments Graham Patriquin and Lotus Vermeer assisted with field sampling in 1994. Coy Coy McLaren in 1969 and 1994, and Ivan McLaren in 2016, provided able boat assistance to reach offshore sites. Nina Patriquin provided essential support throughout. Author Contributions Conceptualization: David Patriquin, Robert E. Scheibling. Data curation: David Patriquin, Karen Filbee-Dexter. PLOS ONE Seagrass bed biodiversity and structure and across 5 decades PLOS ONE | https://doi.org/10.1371/journal.pone.0306897 August 1, 2024 20 / 25