Masters Thesis

The impact of coastal dredging on avian and intertidal macroinvertebrate biodiversity of Morro Bay, California

Sandy beaches support dynamic and diverse, but physically narrow intertidal ecosystems that are vulnerable to the effects of anthropogenic disturbance, such as coastal dredging and beach nourishment. Our study site in Morro Bay, California has been a site of coastal dredging by the U.S. Army Corp of Engineers (USACE) since the 1960’s. In February of 2017, 240,000 cubic yards of sediment were dredged from the harbor and deposited onto the beach as beach nourishment. We assessed the impacts of this beach nourishment over two years on three aspects of beach ecosystems: 1) beach width, 2) avian biodiversity, and 3) intertidal macroinvertebrate biodiversity. We designated seven sampling sites and at each collected monthly measurements of beach width, monthly avian point counts, and quarterly macroinvertebrate samples. We found spatiotemporal variation present across months and sites, and beach width at the deposition site was significantly higher than the six control sites pooled together. Avian and macroinvertebrate biodiversity was not significantly different at the deposition site compared to the pooled control sites. Our results suggest that the dredge deposition had low or very short-term impacts to both avian and intertidal macroinvertebrate biodiversity at the deposition site over our two years of sampling. Positive impacts include a wider beach at the deposition site.