Data from: Washington, Oregon, and California eelgrass restoration database

Seagrass habitats, which provide essential ecosystem functions such as
water quality improvement, biodiversity support, ocean acidification
amelioration, and sediment carbon storage, are declining worldwide.
Eelgrass (Zostera marina) habitats along the contiguous U.S. west coast
are threatened by conflicting human uses and global change, resulting in
significant protections and efforts to restore areas where habitat is
extant or degraded. Despite a history of eelgrass restoration in this
region spanning nearly 60 years, very little work has been published on
the subject. Here, we conduct a review of all available literature on
eelgrass restoration projects conducted in California, Oregon, and
Washington. Of the 82 restoration projects included in this analysis,
which occurred from 1989 to 2020, only 6 were published in peer-reviewed
journals. Thus, despite the precedent for conducting restoration, a lack
of data availability makes assessing regional success, drivers of failure,
and best practices extremely difficult. From this synthesis, we find that
the majority of restoration projects (73%) have occurred for mitigation
(compliance) purposes, contributing to the lack of peer-reviewed
literature on the subject. We find that while eelgrass mitigation policies
serve to maintain eelgrass structure and regional acreages, they do not
facilitate assessments of habitat function or incentivize advancements in
regional best practices. We also find that when we could evaluate project
outcomes, 32.3 to 59.6% of restoration plots were unsuccessful by the end
of the project, but this percentage is highly dependent on how success is
defined. According to restoration practitioners, failure was likely to
result from environmental factors such as light, nutrients, or macroalgal
blooms, but was occasionally due to logistical factors such as restoration
method or approach. From this work, we recommend a standardized,
evidence-based approach to restoration, improved data sharing practices,
and careful consideration of existing eelgrass mitigation practices. As
marine habitat restoration enters a new global stage, backed by public and
private investment, burgeoning carbon markets, and global biodiversity
initiatives, it is essential to learn from past work to understand and
improve seagrass conservation and restoration success.