Biomass and abiotic variable data in the study of the ecosystem engeneering effect of oysters on Suaeda linearis distribution in Georgia salt marshes (2008-2009)

Oysters are ecosystem engineers in marine ecosystems, but the functions of oyster shell deposits in intertidal salt marshes are not well understood. The annual plant Suaeda linearis is associated with oyster shell deposits in Georgia salt marshes. We hypothesized that oyster shell deposits promoted the distribution of Suaeda linearis by engineering soil conditions unfavorable to dominant salt marsh plants of the region (the shrub Borrichia frutescens, the rush Juncus roemerianus and the grass Spartina alterniflora). We tested this hypothesis using common garden pot experiments and field transplant experiments. Suaeda linearis thrived in Borrichia frutescens stands in the absence of neighbors, but was suppressed by Borrichia frutescens in the with-neighbor treatment, suggesting that Suaeda linearis was excluded from Borrichia frutescens stands by interspecific competition. Suaeda linearis plants all died in Juncus roemerianus and Spartina alterniflora stands, indicating that Suaeda linearis is excluded from these habitats by physical stress (likely water-logging). In contrast, Borrichia frutescens, Juncus roemerianus and Spartina alterniflora all performed poorly in Suaeda linearis stands regardless of neighbor treatments, probably due to physical stresses such as low soil water content and low organic matter content. Thus, oyster shell deposits play an important ecosystem engineering role in influencing salt marsh plant communities by providing a unique niche for Suaeda linearis, which otherwise would be rare or absent in salt marshes in the southeastern US. Since the success of Suaeda linearis is linked to the success of oysters, efforts to protect and restore oyster reefs may also benefit salt marsh plant communities.

牡蛎是海洋生态系统中的生态系统工程师（ecosystem engineers），但潮间带盐沼内牡蛎壳沉积物的生态功能尚未被充分阐释。一年生植物碱蓬（Suaeda linearis）与美国佐治亚州盐沼中的牡蛎壳沉积物存在显著关联。我们提出假说：牡蛎壳沉积物通过调控土壤条件，使该区域的优势盐沼植物——灌木博里基娅滨藜（Borrichia frutescens）、灯芯草属柔花灯芯草（Juncus roemerianus）以及禾本科互花米草（Spartina alterniflora）——的生存环境变得不适宜，进而促进碱蓬的分布。我们通过同质园（common garden）盆栽实验与野外移植实验验证了这一假说。在无邻株的情况下，碱蓬在博里基娅滨藜群落中生长良好，但在有邻株处理组中则会被博里基娅滨藜抑制，这表明种间竞争（interspecific competition）将碱蓬排除在了博里基娅滨藜群落之外。在柔花灯芯草与互花米草群落中，所有碱蓬植株均死亡，这说明物理胁迫（大概率为积水water-logging）导致碱蓬无法在这些生境中存活。与之相反，无论邻株处理如何，博里基娅滨藜、柔花灯芯草与互花米草在碱蓬群落中的生长表现均较差，这可能是由土壤含水量低、有机质含量不足等物理胁迫所致。综上，牡蛎壳沉积物通过为碱蓬提供独特生态位（niche），在调控盐沼植物群落结构中发挥了重要的生态系统工程作用；若缺乏这一独特生境，碱蓬在美国东南部盐沼中或将极为罕见甚至无法存续。由于碱蓬的生存状况与牡蛎种群的存续紧密相关，因此保护与修复牡蛎礁的相关举措，也将有益于盐沼植物群落的健康发展。