Management of invasive water hyacinth as both a nuisance weed and invertebrate habitat

Authors: Donley Marineau, Erin; PERRYMAN, MATTHEW - University Of California; LAWLER, SHARON - University Of California; HARTMAN, ROSEMARY - University Of California; Pratt, Paul

Submitted to: San Francisco Estuary and Watershed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2019
Publication Date: 6/17/2019
Citation: Donley Marineau, E.E., Perryman, M., Lawler, S.P., Hartman, R.K., Pratt, P.D. 2019. Management of invasive water hyacinth as both a nuisance weed and invertebrate habitat. San Francisco Estuary and Watershed Science. 17(2):1-19. https://doi.org/10.15447/sfews.2019v17iss2art5.
DOI: https://doi.org/10.15447/sfews.2019v17iss2art5

Interpretive Summary: Globally, invasive species have a multitude of ecological and socio-economic impacts. However, invasive species can provide novel structure and habitat for native species. The growing rate of biological invasions world-wide presents an urgent dilemma: how can natural resource managers minimize negative impacts of invasive species while valuing the invader’s novel ecological role? Reconciliation ecology, an effort to maximize biodiversity in human-dominated landscapes, can provide a means to address this dilemma when crafting invasive species management plans. We present a case study of an adaptive management process that reconciles invasive water hyacinth management with aquatic food web functioning in the Sacramento-San Joaquin River Delta of California, U.S.A. (the “Delta”). Delta managers address water hyacinth invasions with herbicides which are applied in strips and generate large areas of mixed decaying and living vegetation. We hypothesized that herbicide treatment would reduce invertebrate abundance and diversity by reducing dissolved oxygen and altering habitat. We sampled invertebrates before and four weeks after herbicide applications in treated and untreated locations to assess whether decaying hyacinth sustained invertebrate communities. There were more invertebrates at all sites after treatment but no detectable differences between control and treated sites in species richness or evenness for either sample period. This case study demonstrates that even decaying water hyacinth serves as habitat for invertebrates that are forage for endangered Delta fishes and we concluded that current management practices using glyphosate allowed sustained secondary productivity of invertebrates during a month-long period of weed decay. These results provide valuable feedback for the “evaluate and respond” component of the adaptive management process for water hyacinth and present a framework for reconciling invasive species management efforts with food web functions anywhere water hyacinth occurs with food webs that support threatened and endangered fish species.

Technical Abstract: Globally, invasive species have a multitude of negative ecological and socio-economic impacts. However, invasive species can provide novel structure and habitat for native species. The growing rate of biological invasions world-wide presents an urgent dilemma: how can natural resource managers minimize negative impacts of invasive species while valuing the invader’s novel ecological role? Reconciliation ecology, an effort to maximize biodiversity in human-dominated landscapes, can provide a means to address this dilemma when crafting invasive species management plans. We present a case study of an adaptive management process that reconciles invasive water hyacinth (Eichhornia crassipes management with aquatic food web functioning in the Sacramento-San Joaquin River Delta of California, U.S.A. (the “Delta”). Delta managers address water hyacinth invasions with herbicides which are applied in strips and generate large areas of mixed decaying and living vegetation. We hypothesized that herbicide treatment would reduce invertebrate abundance and diversity by reducing dissolved oxygen (DO) and altering habitat. Using a Before, After, Control, Intervention (BACI) experiment, we sampled invertebrates per gram water hyacinth biomass before and four weeks after glyphosate applications in treated and untreated locations to assess whether decaying hyacinth sustained invertebrate communities. There were more invertebrates per gram water hyacinth at all sites after treatment but no detectable differences between control and treated sites in species richness or evenness for either sample period. DO levels decreased in some treated areas, but not to levels likely to harm invertebrates. This case study demonstrates that even decaying water hyacinth serves as habitat for invertebrates that are forage for endangered Delta fishes and we concluded that current management practices using glyphosate allowed sustained secondary productivity of invertebrates during a month-long period of weed decay. These results provide valuable feedback for the “evaluate and respond” component of the adaptive management process for water hyacinth and present a framework for reconciling invasive species management efforts with food web functions anywhere water hyacinth occurs with food webs that support threatened and endangered fish species.