Streaming Media
Presentation Abstract
Understory kelp provide most of the kelp diversity and abundance in the Salish Sea, create three-dimensional habitat, and are major primary producers. Yet much less is known about their dynamics and current status than for canopy kelp. We surveyed benthic macroalgae (including 11 kelp species), invertebrates and fish annually, 2011-2021, at 15 sites in the central Strait of Juan de Fuca. Our original goal was to evaluate responses to Elwha River dam removal, which occurred during 2012-2014, but our time series also coincided with a marine heat wave in 2014, and sea star wasting disease (SSWD) which starting in 2014 impacted several species and nearly extirpated sunflower stars, a major predator of invertebrates including sea urchins. Dam removal resulted in a large influx of sediment with two main consequences. Persistent burial with sand and mud mostly eliminated kelp where it occurred (5 sites). Elevated turbidity and reduced light from suspended sediment caused declines in kelp, but all species recovered (except at buried sites) after dam removal when waters cleared. A key finding was strong differences in kelp species composition among sites before dam removal and a return to near-original densities and species compositions with recovery. In addition to responding to dam removal, Elwha understory kelp covaried inter-annually with western Strait of Juan de Fuca canopy kelp, suggesting that both were responding to large-scale regional drivers. One driver may have been varying ocean conditions including the marine heat wave. Another may have been increases in urchins or other herbivores due to losses of predatory sea stars from SSWD. We will explore these possibilities more fully in our presentation. Our surveys demonstrate how long-term subtidal monitoring allows detection of species status and trends in the face of forecasted and unforeseen environmental variation, and promotes understanding of interrelationships among ecosystem components.
Session Title
Kelp Monitoring - Collaboration & Technology
Conference Track
SSE9: Nearshore
Conference Name
Salish Sea Ecosystem Conference (2022 : Online)
Document Type
Event
SSEC Identifier
SSE-traditionals-104
Start Date
26-4-2022 11:30 AM
End Date
26-4-2022 1:00 PM
Rights
Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Type
Text
Language
English
Lessons learned about understory kelp from 11 years of sub-tidal monitoring during Elwha dam removal, a marine heat wave, and sea star wasting
Understory kelp provide most of the kelp diversity and abundance in the Salish Sea, create three-dimensional habitat, and are major primary producers. Yet much less is known about their dynamics and current status than for canopy kelp. We surveyed benthic macroalgae (including 11 kelp species), invertebrates and fish annually, 2011-2021, at 15 sites in the central Strait of Juan de Fuca. Our original goal was to evaluate responses to Elwha River dam removal, which occurred during 2012-2014, but our time series also coincided with a marine heat wave in 2014, and sea star wasting disease (SSWD) which starting in 2014 impacted several species and nearly extirpated sunflower stars, a major predator of invertebrates including sea urchins. Dam removal resulted in a large influx of sediment with two main consequences. Persistent burial with sand and mud mostly eliminated kelp where it occurred (5 sites). Elevated turbidity and reduced light from suspended sediment caused declines in kelp, but all species recovered (except at buried sites) after dam removal when waters cleared. A key finding was strong differences in kelp species composition among sites before dam removal and a return to near-original densities and species compositions with recovery. In addition to responding to dam removal, Elwha understory kelp covaried inter-annually with western Strait of Juan de Fuca canopy kelp, suggesting that both were responding to large-scale regional drivers. One driver may have been varying ocean conditions including the marine heat wave. Another may have been increases in urchins or other herbivores due to losses of predatory sea stars from SSWD. We will explore these possibilities more fully in our presentation. Our surveys demonstrate how long-term subtidal monitoring allows detection of species status and trends in the face of forecasted and unforeseen environmental variation, and promotes understanding of interrelationships among ecosystem components.
