Human activities are accelerating the rate of global climate change. The atmospheric concentration of carbon dioxide (CO₂) has essentially doubled since pre-historic times due to the combustion of fossil fuels. In the marine environment, a dominant manifestation of such climate change is ocean acidification (OA), the reduction of seawater pH and the saturation state of calcium carbonate. As atmospheric and seawater CO₂ concentrations come into equilibrium, CO₂ dissolves into seawater producing carbonic acid and ultimately, OA. Low pH levels and increased calcium carbonate solubility inhibit the formation and maintenance of shells and exoskeletons in a large number of marine organisms, such as barnacles and mussels. Additionally, the efficiency of basic metabolic processes conducted by all marine organisms may be compromised by a decrease in the pH of their environment.

 

Additional factors such as coastal upwelling, freshwater inputs, and nutrient enrichment create geographic and temporal variation in the strength of OA. Upwelling brings deep, naturally low pH seawater to the surface near the coast, exacerbating OA impacts on biota. Similarly, freshwater inputs have lower pH relative to seawater, so areas that receive high runoff also have a higher OA vulnerability. Nutrient enrichment associated with human development increases CO₂ production in seawater via respiration, further lowering local seawater pH.

 

The intertidal zone is particularly sensitive to climate change impacts. The organisms that inhabit this zone experience two low tides and two high tides each day and during this fluctuation in seawater height, marine invertebrates, seaweeds, and fish are forced to react to periods of extreme heat, desiccation, and low pH water. This familiarity with the extreme makes this suite of organisms well adapted to change; however, the rate at which the current climate is changing may outstrip their ability to adapt.

 

OA is already impacting marine organisms in the California Current Large Marine Ecosystem (CCLME). The deleterious effects of OA on planktonic pteropods, a prime food source for Pacific salmonids, along with devastating impacts on oyster aquaculture in the Pacific Northwest are well documented. The NPS is well positioned to characterize the geographic and temporal variation in OA intensity impacting the rich marine communities conserved by the NPS. The marine parks in the inventory and monitoring networks that span the CCLME represent a gradient of oceanographic and human development regimes. A pilot intertidal OA monitoring program has been established in 4 parks within the Mediterranean (MEDN) and North Coast and Cascades (NCCN) networks (Figure 1) that follows a common NPS protocol. In the MEDN, Cabrillo National Monument (CABR) is situated on the open mainland coast at the mouth of San Diego harbor, while Channel Islands National Park (CHIS) is a set of five islands located offshore of the greater Los Angeles metropolitan area. In the NCCN, the remote Olympic National Park (OLYM) outer coastline is the longest stretch of congressionally designated Wilderness shoreline in the lower 48 states. San Juan Island National Historical Park (SAJH) is located in the San Juan archipelago in the inland Salish Sea, adjacent to the metropolitan areas of Seattle, WA and Vancouver, British Columbia.

Steven Fradkin
Jonathan Jones

Last revised 09-Nov-16