Using a difference-in-differences and synthetic control approach to investigate the socioeconomic impacts of Oregon's marine reserves

Abstract

As Marine Protected Areas (MPAs) expand in size and number, it is critical that we understand how they are impacting local communities. However, social impact evaluations on MPAs are often conducted with limited data points before and after MPA implementation, which can weaken the reliability of their results. To address this gap, we collected longitudinal American Community Survey (ACS) socioeconomic data on coastal communities and counties adjacent to marine reserves in Oregon. Oregon has both limited-take MPAs and stricter no-take marine reserves. This study focused solely on the marine reserves. We compared treatment and control units before and after marine reserve implementation using both difference-in-differences (DID) and synthetic control approaches. Each approach yielded different results, potentially providing a more complete picture of marine reserve impacts and long-term trends while also highlighting the need to consider the variability of ACS data collected from small communities. The percent of the population employed in tourism-related industries was the only significant model in both the DID and synthetic control approaches. Tourism employment increased post marine reserve implementation more in communities adjacent to the marine reserves than in more distant coastal communities. This result could indicate that marine reserves are bringing more visitors to the coast, thereby increasing the need for a more tourism-based economy. However, this may not be the case since most coastal visitors are unaware of Oregon's marine reserves and fewer than 10% of business owners think the reserves have impacted their business. An alternative hypothesis is that the marine reserves were placed near communities with a prominent land-sea connection that were already shifting their economic base to focus more on tourism. This study contributes to the literature by demonstrating how secondary data sources can be used to aid in a more comprehensive MPA impact evaluation, how two different impact evaluation approaches (i.e., synthetic control and DID) can result in differing conclusions, and how the robust synthetic control approach can be easily applied to improve MPA impact evaluations. As one element of a large-scale assessment of marine reserve impacts, this study also broadens our understanding of underlying trends on the Oregon coast and how the recently implemented marine reserves may be impacting nearby communities.