Abstract Title

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

Keywords

Marine Water Quality

Location

Room 615-616-617

Start Date

30-4-2014 3:30 PM

End Date

30-4-2014 5:00 PM

Description

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.

Share

COinS
 
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.