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，但潮间带盐沼内的牡蛎壳沉积物的生态功能尚未得到充分阐释。在佐治亚州的盐沼中，一年生植物线叶碱蓬（Suaeda linearis）与牡蛎壳沉积物存在显著关联。本研究提出假说：牡蛎壳沉积物可通过改造土壤微环境，使其不利于该区域优势盐沼植物——灌木博瑞奇滨藜（Borrichia frutescens）、灯心草属柔花灯心草（Juncus roemerianus）以及禾本科互花米草（Spartina alterniflora）——的生长，从而促进线叶碱蓬的分布。随后，本研究通过同质园盆栽实验与野外移栽实验对该假说进行了验证。实验结果显示：在无邻株的条件下，线叶碱蓬可在博瑞奇滨藜群落中良好生长，但在有邻株的处理组中，其生长会受到博瑞奇滨藜的抑制，这表明线叶碱蓬会通过种间竞争被排除出博瑞奇滨藜群落；而在柔花灯心草与互花米草群落中，所有线叶碱蓬植株均死亡，说明物理胁迫（大概率为渍水）会将线叶碱蓬排除出这类生境。与之相反，无论是否存在邻株，博瑞奇滨藜、柔花灯心草与互花米草在线叶碱蓬群落中的生长状况均不佳，这可能是由土壤含水量低、有机质含量低等物理胁迫导致的。综上，牡蛎壳沉积物通过为线叶碱蓬提供独特的生态位，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；若缺乏这类沉积物，线叶碱蓬在美国东南部盐沼中或将极为稀少甚至完全消失。鉴于线叶碱蓬的生存与牡蛎种群的存续密切相关，保护与修复牡蛎礁的举措也可惠及盐沼植物群落。