Publication Date

Summer 2019

Degree Type


Degree Name

Master of Science (MS)


Moss Landing Marine Laboratories


Michael H. Graham


Ecotono, Elkhorn Slough, Phycology, Ulva spp., Wetland science, Zostera marina

Subject Areas

Ecology; Systems science; Aquatic sciences


Ecotones are transitional areas between adjacent ecological communities that have unique ecological qualities defined by space and time scales, and by the interactions between adjacent systems. Ecotones play an essential role in supporting biologically diverse communities, and are sensitive indicators of global change. An Ulva-Zostera ecotone extends along the northern shore of Seal Bend in Elkhorn Slough, an estuary located in central California. Although previous studies have mentioned the presence of the Ulva-Zostera ecotone, this was the first study to focus on understanding its driving factors, spatiotemporal dynamics, and overall ecological implications. A combination of habitat monitoring, water quality assessments, sediment analyses, and recruitment and transplants experiments across the ecotone was used to describe the ecological characteristics of the system. Ecotone dynamics were driven by seasonality of Ulva spp. Distribution of Ulva spp. across the ecotone was limited by processes affecting its early developmental stages. The presence of Zostera marina initiated these mechanisms via modification of the environment and recruitment of grazers. Grazing was found to regulate macroalgal abundance, and specific grazer groups played an essential role in this. These results can be widely applied to guide future research efforts focusing on understanding and predicting habitat shifts and consequent ecosystem transformations.