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Ecosystem Engineering Impacts of Water Primrose in the Sacramento-San Joaquin Delta

December 17, 2020

Many non-native fish, invertebrates, and plants have colonized the Delta over the past century. Included among these species is the water primrose (Ludwigia grandiflora ssp. hexapetala and Ludwigia peploides), an aggressive floating aquatic plant native to South and Central America and parts of the US, but invasive in California.

Water primrose infestation in the Sacramento-San Joaquin Delta.
Water primrose infestation in Middle River in the Sacramento-San Joaquin Delta.

Recently, in addition to expanding its range from the marsh edge to the marsh interior in the Delta, water primrose is also causing mortality of key wetland plants including bulrushes and cattails. The mechanism by which this marsh mortality is occurring is currently unknown. This knowledge gap prevents effective management actions that could preserve marsh habitat. To address this, California Water Science Center scientists, Dr. Judith Drexler, Dr. Michael Gross, and Dr. Michelle Hladik have begun a project to determine the cause of marsh mortality following water primrose invasion in the Sacramento-San Joaquin Delta of California.

The aim of this research will be to gain an improved understanding of water primrose invasion processes. In particular, USGS scientists will seek to identify allelopathic chemicals (substances toxic to plants and animals) exuded by water primrose that may be killing marsh plants. Another component will be to determine whether particular plant traits of water primrose lead to marsh mortality. The status of marsh loss over the past 15 years and the vulnerability of current marshes to plant mortality will also be investigated as part of the study. The information gleaned from the project will enable management actions to be focused on protecting marshes most vulnerable to invasion.

Learn more about this project.