Impacts of Egregia menziesii, a foundational alga, on intertidal communities in the San Juan Islands
Streaming Media
Presentation Abstract
Canopy-forming seaweeds provide shade for smaller algae and invertebrates in intertidal communities, ameliorating low tide abiotic stressors such as ultraviolet radiation, desiccation, and high temperatures. Conversely, canopies can negatively affect understory organisms by limiting settlement, causing physical disruption, and trapping sand. We examined the effect of Egregia menziesii, a canopy-forming foundation species, on intertidal communities, using manipulative experiments at Cattle Point, San Juan Island, WA. We hypothesized that plots with Egregia would have a higher abundance and richness of other invertebrates and algae than plots without Egregia. In the field, we set up 20 low intertidal plots, each 0.25m2 in size, where we randomly assigned the following four treatments (five replicates of each): Natural Egregia (no manipulation), –Egregia (Egregia removed), No-Natural Egregia (no manipulation), or +mimic Egregia (plastic Egregia mimic). We conducted community surveys of sessile and mobile organism cover/abundance for four seasons (Summer 2019, Winter 2020, Summer 2020, and Winter 2021). We also measured sand depth, temperature, and light intensity across treatments. Our data show significant temperature and light differences between plots with Egregia and without Egregia, confirming that Egregia can ameliorate heat stress when present. We predicted Egregia plots would trap more sand during the winter but have seen no strong evidence of sediment trapping in any treatment. Treatment and Season were both significant factors in determining community structure across the four seasons of data collection, but there were no significant differences in species richness indicating a similar number of species regardless of canopy cover.
Session Title
Poster Session 2: The Salish Sea Food Web and Cycles of Life
Conference Track
SSE14: Posters
Conference Name
Salish Sea Ecosystem Conference (2022 : Online)
Document Type
Event
SSEC Identifier
SSE-posters-237
Start Date
26-4-2022 4:30 PM
End Date
26-4-2022 5:00 PM
Type of Presentation
Poster
Genre/Form
conference proceedings; presentations (communicative events)
Contributing Repository
Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.
Subjects – Topical (LCSH)
Algae--Washington (State)--San Juan Islands; Intertidal ecology--Washington (State)--San Juan Islands
Geographic Coverage
Salish Sea (B.C. and Wash.); San Juan Islands (Wash.)
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
Format
application/pdf
Included in
Marine Biology Commons, Natural Resources and Conservation Commons, Terrestrial and Aquatic Ecology Commons
Impacts of Egregia menziesii, a foundational alga, on intertidal communities in the San Juan Islands
Canopy-forming seaweeds provide shade for smaller algae and invertebrates in intertidal communities, ameliorating low tide abiotic stressors such as ultraviolet radiation, desiccation, and high temperatures. Conversely, canopies can negatively affect understory organisms by limiting settlement, causing physical disruption, and trapping sand. We examined the effect of Egregia menziesii, a canopy-forming foundation species, on intertidal communities, using manipulative experiments at Cattle Point, San Juan Island, WA. We hypothesized that plots with Egregia would have a higher abundance and richness of other invertebrates and algae than plots without Egregia. In the field, we set up 20 low intertidal plots, each 0.25m2 in size, where we randomly assigned the following four treatments (five replicates of each): Natural Egregia (no manipulation), –Egregia (Egregia removed), No-Natural Egregia (no manipulation), or +mimic Egregia (plastic Egregia mimic). We conducted community surveys of sessile and mobile organism cover/abundance for four seasons (Summer 2019, Winter 2020, Summer 2020, and Winter 2021). We also measured sand depth, temperature, and light intensity across treatments. Our data show significant temperature and light differences between plots with Egregia and without Egregia, confirming that Egregia can ameliorate heat stress when present. We predicted Egregia plots would trap more sand during the winter but have seen no strong evidence of sediment trapping in any treatment. Treatment and Season were both significant factors in determining community structure across the four seasons of data collection, but there were no significant differences in species richness indicating a similar number of species regardless of canopy cover.
