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Restoring an endemic species to native tidelands: Olympia oysters in Swinomish pocket estuaries

This project is a continuation of a 2015-2016 CREOi award, supporting restoration of the Olympia oyster (Ostrea lurida), which has played an important ecological and cultural role as Washington’s only native oyster. Since 2012, Swinomish Indian Tribal Community (SITC) has been collaborating with regional partners on a long-term restoration project to reestablish, expand, and research Olympia oyster, Ostrea lurida, populations on Reservation tidelands. By reintroducing a historically-important species and the ecosystem services it once provided, SITC hopes to promote fishing resources and traditions even as local habitat conditions become increasingly impacted by climate change and ocean acidification. 

To assess environmental conditions before and after the O. lurida restoration efforts, we measured temperature and salinity, two parameters affected by climate change that influence reproduction, growth, and survival of bivalves. In addition to climate change, another growing concern is ocean acidification. For most bivalves, as seawater pH decreases it becomes more difficult to build and maintain shell. Understanding the impacts of both climate change and ocean acidificationon biological communities is especially difficult because interactions between temperature, salinity, and pH are particularly complex, making abiotic and biotic responses difficult to predict. Unfortunately, pH measurements at a spatial and temporal scale relevant to our restoration project do not exist. Therefore, we used the 2017 CREOi award to increase the capacity of SITC to monitor pH for the Olympia oyster restoration project and incorporate the environmental parameter in our habitat assessment. 

Because pH monitoring equipment is expensive and multiple monitoring setups are necessary to assess pH at both restoration sites, we initially used award funds to build a prototype low-cost pH sensor unit (Fig. 1). The design was based on pH units custom-built by Washington Department of Natural Resources, but modified so the waterproof housing unit could be created from supplies purchased from the local hardware store. We also purchased temperature and salinity loggers so a suite of measurements could be collected simultaneously at a scale that appropriately characterizes the local environment in which the Olympia oysters reside. 

In August 2018, the sensor unit prototype was successfully deployed and retrieved at Lone Tree Lagoon (one of our two primary O. lurida restoration sites). Measurements were collected every 15 minutes over the enhanced Olympia oyster reef. Results indicate that from 22 August to 29 August the average temperature, salinity, and pH was 14.7 °C (±0.084 SE), 28 (±0.041 SE), and 7.6 (±0.0057 SE), respectively, and pH ranged from 7.3 to 8.2. Although conditions in the lagoon were not acidic during the sampling period, measurements did drop below 7.5. This is most notable because a pH of 7.5 is considered to be the threshold at which the buffering ability of seawater declines and seawater chemistry becomes more sensitive to environmental changes. Climate change predictions suggest this 

may result in more extreme fluctuations in pH and other carbonate chemistry parameters. Therefore, it is especially important to continuously monitor these parameters over long periods of time to better understand the conditions oysters and other marine organisms are exposed to. 

Following the successful deployment of the prototype, we purchased equipment to build another four pH units. Not only will this allow us to monitor conditions within the two lagoons, but we will have the capacity to conduct research on and off the oyster beds and investigate strategies to reduce the impact of ocean acidification on tribally-important marine organisms. ($10,500)