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

Discussion Temporal and spatial context of this study Longitudinal (multidecadal) studies of seagrass beds at individual sites in the Tropical Atlantic Bioregion have mapped changes in relative cover or extent of these beds, typically by aerial photography [22, 23, 52]. Our island-wide study, spanning 5 decades, to our knowledge, is the longest of those that record taxonomically detailed, replicated measures of abundance of sea- grass and associated macroalgae and sessile invertebrates (percent cover, frequency of occur- rence, biomass, density) as well as concurrent measures of seabed erosion (recession of inner bed margins, blowout frequency within beds) related to hydrodynamic forces. Although the temporal resolution is minimal, our study encompasses a period that spans a relatively undis- turbed state in 1969 to an increasingly perturbed state in 2016, with a midpoint in 1994 that appears to capture a period during which biodiversity is highest but erosional features— including those indirectly related to biogenic changes such structural degradation of barrier reefs due to coral mortality—are in transition from relative stasis to an increase in magnitude. 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. https://doi.org/10.1371/journal.pone.0306897.g008 PLOS ONE

Seagrass bed biodiversity and structure and across 5 decades PLOS ONE | https://doi.org/10.1371/journal.pone.0306897 August 1, 2024 14 / 25