Session Title

Session S-03A: Changes in Salish Sea Water Quality

Conference Track

Marine Water Quality

Conference Name

Salish Sea Ecosystem Conference (2014 : Seattle, Wash.)

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Start Date

30-4-2014 3:30 PM

End Date

30-4-2014 5:00 PM

Abstract

Hypoxia [dissolved oxygen (DO) < 2 mg L-1] has been identified as a key threat to the Puget Sound ecosystem, particularly in Hood Canal. Hood Canal is subject to seasonal hypoxia in its southern reaches, and prior work has demonstrated avoidance patterns of demersal species from the deep, offshore hypoxia-impacted waters. However, the non-lethal impact of low DO conditions on the nearshore community is not well understood, despite its importance to the estuary (e.g., nursery habitat). We evaluated the nature and extent of the sub-lethal influence of hypoxia on the nearshore community using underwater video monitoring techniques. Within two regions of Hood Canal, a southern highly impacted region and a northern reference region, we recorded weekly underwater video of the benthos via transects at three depths (10, 20, 30m) to measure species density and composition. Weekly monitoring of water quality revealed strong differences in DO over time and space, with the vertical extent of low DO waters increasing markedly at the end of summer in the south. While we were unable to detect acute shifts in nearshore densities, the community composition was significantly different between the two study regions; the south was primarily composed of hypoxia tolerant invertebrates and fewer fish species compared to the north. Moreover, the tolerant invertebrates displayed a three-fold increase in presence below a specific DO threshold (mean threshold ± SE = 3.95 mg L-1 ± 0.22), while the more sensitive species (e.g., fish) declined. Post-hoc comparisons of our findings to long-term DO trends in Hood Canal revealed the potential for a more persistent low DO state in the southern reaches. As a result, this study provides further insight into the complex regional differences in community structure and potential sensitivity of the nearshore community to other perturbations in Hood Canal.

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Language

English

Format

application/pdf

Type

Text

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Apr 30th, 3:30 PM Apr 30th, 5:00 PM

Is hypoxia’s influence restricted to the deep? Evaluation of nearshore community composition in Hood Canal, Washington, a seasonally hypoxic estuary

Room 615-616-617

Hypoxia [dissolved oxygen (DO) < 2 mg L-1] has been identified as a key threat to the Puget Sound ecosystem, particularly in Hood Canal. Hood Canal is subject to seasonal hypoxia in its southern reaches, and prior work has demonstrated avoidance patterns of demersal species from the deep, offshore hypoxia-impacted waters. However, the non-lethal impact of low DO conditions on the nearshore community is not well understood, despite its importance to the estuary (e.g., nursery habitat). We evaluated the nature and extent of the sub-lethal influence of hypoxia on the nearshore community using underwater video monitoring techniques. Within two regions of Hood Canal, a southern highly impacted region and a northern reference region, we recorded weekly underwater video of the benthos via transects at three depths (10, 20, 30m) to measure species density and composition. Weekly monitoring of water quality revealed strong differences in DO over time and space, with the vertical extent of low DO waters increasing markedly at the end of summer in the south. While we were unable to detect acute shifts in nearshore densities, the community composition was significantly different between the two study regions; the south was primarily composed of hypoxia tolerant invertebrates and fewer fish species compared to the north. Moreover, the tolerant invertebrates displayed a three-fold increase in presence below a specific DO threshold (mean threshold ± SE = 3.95 mg L-1 ± 0.22), while the more sensitive species (e.g., fish) declined. Post-hoc comparisons of our findings to long-term DO trends in Hood Canal revealed the potential for a more persistent low DO state in the southern reaches. As a result, this study provides further insight into the complex regional differences in community structure and potential sensitivity of the nearshore community to other perturbations in Hood Canal.