Control and Mitigation of Aquatic Invasive Species in Pacific Island Streams

Dr. Michael Blum | Tulane University



Ensuring the continuity and long-term sustainability of Department of Defense (DoD) activities on Pacific islands requires stewardship of ecosystems altered by non-native species. Because eradication is not always feasible, consideration must be given to alternative management approaches, including restoration of key ecological processes that enable threatened, endangered, or at-risk native species (TER-S) to persist in the presence of non-native species. Management of aquatic invasive species (AIS), which are consistently identified as a primary threat to biodiversity in Pacific island streams, is particularly challenging because approaches have not been developed that account for insular stream conditions. As a result, AIS control is poorly understood, and even less is known about mitigative approaches, such as stream flow restoration, that can suppress AIS and sustain TER-S. The objective of this project is to characterize genes-to-ecosystem outcomes of experimental AIS removals across a stream flow gradient and two flow restoration scenarios as well as to build model-based decision tools to determine the extent to which AIS control, mitigation, or some combination thereof fosters recovery of key ecological processes and TER-S in Pacific island streams.

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Technical Approach

This project will be conducted in watersheds across the Koolau Range on the Hawaiian island of Oahu where many DoD installations and TER-S are located. Following a before-after-control-impact study design, genes-to-ecosystem outcomes of removing non-native fish will be assessed in 12 watersheds selected to represent stream flow variation on Oahu. After 6 months of pre-manipulation assessment, non-native fish will be removed from one 100-m stream reach in each watershed, with efforts targeting drift-feeding poeciliids (i.e., guppies) and algae-eating loricariids (i.e., catfish). Responses to removals will be tracked for a period of two years, with adjacent upstream and downstream reaches serving as references.

Assessment of whether removals elicit an increase in genetic diversity will be accomplished by genotyping the native goby Awaous stamineus in each study reach. Whether removals alleviate predation will be determined through surveys of larval productivity and transport. The influence of removals on stream food webs and the trophic level of A. stamineus will be assessed through stable isotope assays. In addition, whether removals yield conditions favorable to native fish will be determined by snorkel surveys of population densities and community composition, as well as mark-recapture assessments of A. stamineus demography. Finally, A. stamineus otolith microchemistry will be examined to determine whether removals influence life-long outcomes of life-history variation. Following a paired catchment study design, genetic variation, life history, and demography of A. stamineus, as well as community and ecosystem responses to AIS removal also will be characterized under conditions of diverted continuous low flow, undiverted continuous high flow, and pulsed high flow matching diurnal biotic rhythms. Comparisons will be made within and among watersheds to assess outcomes of flow modification with and without AIS removal.

Data from the two removal studies will be used to parameterize a coupled biophysical individual-based model (IBM) to evaluate the sensitivity of native species to AIS removal and flow restoration. The data also will be used to build systematic conservation planning (SCP) models to evaluate cost and benefit functions for selecting sites and watersheds to maximize return on investments in AIS management.

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Development of actionable information and innovative approaches for managing AIS can substantively improve stewardship of stream ecosystems that cross DoD lands, especially on islands where installations harbor native species under federal or state protection. Native fishes and invertebrates are becoming increasingly imperiled in Pacific island streams, including streams that cross DoD installations on Oahu and elsewhere in Hawaii. Yet DoD resource managers currently have a limited tool kit to improve conditions for the benefit of TER-S in Pacific island streams. This project will demonstrate a novel approach to AIS management, advance understanding of the response of native species and ecological processes to AIS control, and determine whether outcomes of AIS control differ according to hydrological conditions. This project also will demonstrate whether flow restoration can be an effective tool for AIS management, and whether mitigation augments at-risk native species responses to AIS control in Pacific island streams. Finally, the project will deliver model-based prioritization tools that will provide defensible and transparent analytical frameworks for adaptive watershed management and aquatic species conservation on Pacific islands. (Anticipated Project Completion – 2019)

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Points of Contact

Principal Investigator

Dr. Michael Blum

Tulane University

Phone: 504-214-9964

Program Manager

Resource Conservation and Resiliency