Benjamin C. Grime’s research while affiliated with The Nature Conservancy and other places

The high ecological and economic value of seagrass has been long recognized, with these foundational habitats providing myriad ecosystem services. Yet through cumulative anthropogenic impacts, seagrasses are exhibiting extensive declines globally. A litany of studies and active restoration trials have demonstrated practical methodologies to restore seagrass habitats and effectively return critical habitat functions to degraded coastal zone systems worldwide. Seagrass loss along the U.S. West Coast has precipitated decades of seagrass protection, conservation, and restoration efforts. Yet, mitigation transplanting efforts have prioritized Zostera marina (narrow-leaved eelgrass) in shallow, protected environments, while a dearth of information is available on species inhabiting offshore islands and exposed mainland coasts. In this study, we conducted a novel transplant of Zostera pacifica, a wide-leaved species found in depths of 7 – 20 m along the offshore islands and mainland coast of California. Transplants were conducted at three geographically distinct sites in Santa Monica Bay, coupled with continuous monitoring of biophysical parameters providing insight into physical drivers at transplant and donor sites. Utilizing in situ data, and environmental thresholds adapted from the literature for Z. marina, we performed exposure analyses to evaluate factors influencing Z. pacifica transplant performance. Exceedances of threshold values for environmental parameters, specifically, wave exposure and near-bed flow speeds (Hrms > 0.59 m and Urms > 0.1 m s⁻¹), photosynthetically active radiation (< 3 and > 5 mol m⁻² day⁻¹) and dissolved oxygen (< 3 mg O2 L⁻¹) exposure impacted transplant survivorship. These results suggest Z. pacifica persist in biophysically dynamic conditions and are sensitive to exceedances of thresholds, underlining the importance of pre-transplant site-selection processes to this species. These data represent the first holistic study of Z. pacifica transplanting on an exposed mainland coast, which provides a view into the baseline environmental envelopes within existing Z. pacifica habitat, and further, may serve as a model for investigating scalable open coast seagrass restoration for temperate regions.

Along the Palos Verdes Peninsula in southern California, high densities of Strongylocentrotus purpuratus (purple sea urchin) have consumed almost all macroalgae on large expanses (61 ha) of rocky reef habitat, creating urchin barrens. Mesocentrotus franciscanus (red sea urchin) harvesting comprises an important fishery in the region, as their gonads are sold as a high-value sushi product called uni. However, with a lack of macroalgal food resources, urchins in barrens are smaller and exist in a starved state, meaning little, if any, gonad product is available to the fishery. To restore local kelp forests and increase gonad biomass available to the M. franciscanus fishery, beginning in October 2013, S. purpuratus were culled in barrens to a target density of 2 per m2 across 5.2 ha of rocky reef on the Palos Verdes Peninsula. Mesocentrotus franciscanus were collected from urchin barren, restoration, and kelp reference sites from April to November 2014 to compare differences in gonad production among the three site types. Culling S. purpuratus resulted in the recovery of normal seasonal M. franciscanus gonad production throughout the 8-month study. Mesocentrotus franciscanus gonad weights at a given test diameter length in restoration sites were equivalent to, and sometimes exceeded, the gonad production of those from the kelp reference sites. The urchin test length distributions of collected M. franciscanus were consistently smaller at urchin barren sites than at kelp reference sites, while those in restoration sites generally fell in between.