Document Type

Thesis

Date of Degree Completion

Fall 2018

Degree Name

Master of Science (MS)

Department

Cultural and Environmental Resource Management

Committee Chair

Anthony Gabriel

Second Committee Member

Cinde Donoghue

Third Committee Member

Mary Poulson

Abstract

There are more than 9,000 overwater structures in the Puget Sound casting an estimated 9 km2 of anthropogenic created shade to the seafloor. Subtidal kelp, over 20 species in total, are abundant in the Sound but little data exists on how they are impacted by these overwater structures. The purpose of this research is to quantify various overwater structures’ impacts on the productivity and distribution of subtidal kelp beds and to create a subtidal kelp monitoring protocol. Three sets of floating docks and paired controls were sampled twice during the summer of 2017 for subtidal kelp distribution, biomass, photosynthetically active radiation (PAR), substrate, and fish presence. Georeferenced benthic video surveys were conducted along parallel transects to create 1 m grid cell maps encoded for subtidal kelp presence/absence at each site. Wet biomass and morphometric measurements were taken from kelp collected from 30 samples at each site. Light extinction coefficients were calculated using an array of 11 PAR sensors deployed at various depths and distances from each dock and within each paired control site. Substrate samples were analyzed for organic content and particle size distributions. Proportional coverages and densities of subtidal kelp were statistically compared for significant differences between the docks and their paired control sites and were correlated with related environmental conditions using nonparametric tests. Overall, subtidal kelp distribution and productivity were negatively related to dock presence. Significantly less kelp presence by transect was found at every dock site (medians = 0 – 20.4%) than paired controls (medians = 96.2 – 100%), as well as significantly less kelp biomass (dock medians = 0 – 199.6 g; control medians = 282.1 – 565.9 g), while available PAR was found to be less on the north of the docks (means = 26.2 – 193.4 µmol m-2 s-1) than paired controls (means = 58.2 – 219.0 µmol m-2 s-1) in all but one case. PAR appears to be the limiting environmental factor to kelp distribution and productivity while sediment size and percent organics do not appear to play a significant role.

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