Fig 1.
Sites where seagrass beds were sampled at Carriacou.
Sampling stations (S) were distributed across representative seagrass beds around the island (green circles); transects (T) were sampled at low wave energy (orange triangles) and high wave energy (red triangles) sites. See S1 Table for GPS coordinates and additional site description. Also shown is a diagrammatic representation of coral reefs around Carriacou and surrounding islands, after [37].
Fig 2.
Substratum cover in seagrass beds.
Mean (+ SE) % cover of transects in 6 HWE sites 4 LWE sites in 1969 and 2016, and 3 HWE sites and 1 LWE site in 1994 (top row). Cover on individual transects at HWE and LWE sites in each year (subsequent 3 rows). Height of bars indicates total cover of seagrass bed; remainder is cover of seagrass-free inshore zone (SFI). The large component “Other” in 2016 consists mainly of a mixture of Thalassia testudinum, Syringodium filiforme, and Halodule wrightii on Transect T9.
Fig 3.
Abundance of seagrass species/groups at stations (n = 17) in 1969, 1994 and 2016.
Mean (+ SE) of a) frequency of occurrence (%) and b) biomass (kg m-2) of Thalassia testudinum, Syringodium filiforme and Halophila stipulacea. (Halodule wrightii is not included as it occurred at very low frequencies and biomass at stations).
Fig 4.
Shoot density and leaf dimensions of Thalassia testudinum at stations (n = 17) in 1969, 1994 and 2016.
Mean (+SE) of a) shoot density (shoots m-2), b) maximum leaf length (cm), and c) leaf width (cm).
Fig 5.
Frequency of occurrence of more common species of macroalgae and sessile macroinvertebrates, and of sea urchins, at stations (n = 17) in 1969, 1994, 2016.
Mean (+ SE) frequency (%) in 12 quadrats per station. Green algae: Avrainvillea nigricans (AvNi*), Avrainvillea rawsonii (AvRa*), Dictyosphaeria cavernosa (DiCa*), Halimeda incrassata (HaInc), Halimeda opuntia (HaOpu), Udotea cyathiformis (UdCya), Udotea flabellum (UdFla), Valonia ventricosa (VaVe*); brown algae: Canistrocarpus cervicornis (CaCer), Dictyopteris delicatula (DiDel), Dictyopteris justii (DiJu*), Dictyota ciliolata (DiCil), Dictyota dichotoma (DiDic), Dictyota implexa (DiImp), Dictyota mertensii (DiMer); Caulerpa: Caulerpa cupressoides (CaCup), Caulerpa cupressoides var. lycopodium (CaLyc), Caulerpa mexicana (CaMex), Caulerpa prolifera (CaPro), Caulerpa scalpelliformis (CaSca), Caulerpa sertularioides (CaSer); red algae: Amphiroa fragilissima (AmFra), Amphiroa rigida (AmRig), Amphiroa tribulus (AmTri), Hypnea cervicornis (HyCer), coral: Manicina areolata (MaAre), Porites Furcata (PoFu*); sponges: Amphimedon erina (AmEri), Cliona varians (ClVar), Halichondria melanodocia (HaMe*), Hyrtios violaceus (HyVio), Tedania ignis (TeIgn); sea urchins: Tripneustes ventricosus (TrVe*).
Fig 6.
Taxon richness and diversity of the seagrass bed community.
Mean + SE richness and diversity (Shannon Index) at stations (n = 17) in 1969, 1994, 2016.
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.
Fig 8.
Offshore extent of the seagrass-free inshore zone (SFI, m) on transects in 1969, 1994 and 2016.
Mean (± SE) extent of SFI for 6 HWE sites and 4 LWE sites in 1969 and 2016, and 3 HWE sites and 1 LWE site in 1994. Also shown (right column) is cover on replicate transects at HWE and LWE sites in each year.
Fig 9.
Number of scarps on transects in 1969, 1994 and 2016.
Mean (± SE) scarp number for 6 HWE sites and 4 LWE sites in 1969 and 2016, and 3 HWE sites and 1 LWE site in 1994. Also shown is scarp number on replicate transects at HWE and LWE sites in each year.