Patriquin David, Scheibling Robert E, Filbee-Dexter Karen
Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
University of Western Australia, Perth, Australia.
PLoS One. 2024 Aug 1;19(8):e0306897. doi: 10.1371/journal.pone.0306897. eCollection 2024.
Caribbean seagrass beds are facing increasing anthropogenic stress, yet comprehensive ground-level monitoring programs that capture the structure of seagrass communities before the 1980s are rare. We measured the distribution of seagrass beds and species composition and abundance of seagrass and associated macroalgae and macroinvertebrates in 3 years over a 47-year period (1969, 1994, 2016) at Carriacou, Granada, an area not heavily impacted by local human activity. Seagrass cover and physical parameters of fringing beds were measured in transects at high (HWE) and low wave energy (LWE) sites; frequency of occurrence of all species, and biomass and morphology of seagrasses, were measured at 100 m2 stations around the island. Losses in nearshore seagrass cover occurred at HWE but not LWE sites between 1969 and 2016 and were associated with increases in the seagrass-free inshore zone (SFI) and erosional scarps within beds. Total biomass did not vary across years although there were progressive changes in seagrass composition: a decline in the dominant Thalassia testudinum and concomitant increase in Syringodium filiforme, and establishment of invasive Halophila stipulacea in 2016 at LWE sites. Species richness and diversity of the seagrass community were highest in 1994, when 94% of macroalgae (excluding Caulerpa) were most abundant, and sea urchins were least abundant, compared to 1969 and 2016. Multivariate statistical analyses showed differences in community composition across the 3 years that were consistent with trends in urchin abundance. Increases in SFI and scarp number in seagrass beds at HWE sites occurred mainly after 1994 and likely were related to increased wave forcing following degradation of offshore coral reefs between 1994 and 2016. Our observations suggest that landward migration of seagrass beds with rapidly rising sea level in future will not be realized in reef-protected seagrass beds at Carriacou barring reversal in the processes that have caused reef flattening.
加勒比海的海草床正面临着日益增加的人为压力，然而，能够记录20世纪80年代之前海草群落结构的全面地面监测项目却很少见。我们在格林纳达卡里亚库一个受当地人类活动影响较小的地区，于47年期间（1969年、1994年、2016年）的3年里，测量了海草床的分布、海草以及相关大型藻类和大型无脊椎动物的物种组成与丰度。在高波能（HWE）和低波能（LWE）站点的样带中测量了边缘海草床的海草覆盖度和物理参数；在岛屿周围100平方米的站点测量了所有物种的出现频率以及海草的生物量和形态。1969年至2016年期间，近岸海草覆盖度在高波能站点有所损失，而在低波能站点没有，并且这与无海草近岸区域（SFI）的增加以及海草床内侵蚀陡坎的出现有关。尽管海草组成有渐进变化：优势种泰莱草减少，丝状针蔺随之增加，并且2016年在低波能站点出现了入侵的有托叶盐藻，但总生物量多年间没有变化。与1969年和2016年相比，1994年海草群落的物种丰富度和多样性最高，当时大型藻类（不包括羽藻）最为丰富，海胆数量最少。多变量统计分析显示，这3年的群落组成存在差异，与海胆丰度趋势一致。高波能站点海草床中无海草近岸区域和陡坎数量的增加主要发生在1994年之后，可能与1994年至2016年期间近海珊瑚礁退化后波浪作用力增强有关。我们的观察结果表明，除非导致珊瑚礁变平的过程发生逆转，否则在卡里亚库受珊瑚礁保护的海草床中，未来随着海平面迅速上升，海草床向陆地迁移的情况将不会实现。
