Q&A: Kelp, climate and ocean acidification

Kelp forests are a rich and important habitat in coastal oceans across the planet. Kelp farms mimic these underwater forests and thus can help the environment. Animals associated with kelp forests may also use kelp farms as habitat and a source of food. Much of the focus on the environmental benefits of kelp farming is due to the ability of kelp to remove carbon dioxide from surrounding environment through photosynthesis. Indeed, kelp forests worldwide are estimated to sequester up 4.91 megatons of carbon from the atmosphere each year. Expansion of kelp mariculture could increase the amount of carbon dioxide absorbed from the environment. This could potentially helping to mitigate climate change if the carbon is also deposited and sequestered in marine sediments or deep in the ocean, or the kelp crop is used to replace nutrients otherwise provided by more carbon-intensive crops (see more on the scale needed in questions below). Additionally, kelp forests provide important habitat for larval fish and other marine animals, and kelp farms may provide the same ecosystem services, though this is an active area of research in Alaska. In a rapidly changing ocean, kelp farms may provide vital safe refuge for these species important to both subsistence and commercial harvesters.

Kelp farming is not a “silver bullet” to solving climate change. Some of the limitations to kelp farming as a tool for helping the planet will be discussed below. However, farmers should not be discouraged – kelp farming will provide many benefits to Alaska’s communities, ecology, and economy as we transition to a sustainable future.

Kelp can easily uptake carbon for assimilation in its tissues. As seawater carbon concentrations increase, kelp can remove dissolved carbon from the water and thus buffer changes in seawater acidity to a greater extent than other seaweeds and seagrasses. Uptake of carbon by kelp can reduce the concentration of dissolved carbon dioxide and thus have the potential to lower ocean acidification in local areas. These impacts can be most pronounced  in sheltered areas with lower seawater exchange. However, seawater temperature, the species of kelp farmed, and other factors can alter the ability of kelp to lower local ocean acidification. This is an area of ongoing research at kelp farms in Alaska.

Ocean acidification can harm shellfish, as acidified seawater can dissolve the calcium carbonate required for shell formation, leading to energetically stressful conditions for these animals. Some researchers and farmers have considered using kelp to mitigate the impacts of ocean acidification on shellfish used for commercial farming and subsistence harvest.

As with much research on the environmental impact of kelp farming, results are mixed. Some studies show that kelp farming can significantly lower the acidity of a region of coastline, creating refugia for important shellfish species. These findings are often used to support polyculture operations, or the growth of kelp with shellfish in a mixed-species mariculture grove. While this method of mariculture may require more complex farming practices, it may protect shellfish harvests if performed in ideal locations. Polyculture can also protect shellfish species of subsistence concern.

The oceanography of Alaska’s waters is complex, and the coastal waters in which kelp farming occurs can differ widely. Thus, kelp farming should be thought of as a tool to help create possible local refugia from ocean acidification for shellfish or other species in sensitive life stages, and not as a way to decrease acidity across the entire Gulf of Alaska.

One of the most important factors for creating refugia from ocean acidification is seawater flux. Areas with high tidal forcing are constantly exchanging seawater and thus kelp farming will likely not make a noticeable difference in local ocean acidification. However a shallow, sheltered cove with lower tidal flux will have higher potential for refugia creation.

Other variables, such as latitude, temperature, and hours of light will impact the ability of kelp farming to create refugia. Selecting sites which are ideal for kelp growth may increase the chance of creating refugia for shellfish.

The chemistry of ocean waters can be measured both with instrument sensors and by analyzing discrete samples.  Instruments can be deployed on a mooring or at a kelp farm to provide continuous data on ocean chemistry. They are expensive and usually used by university and federal researchers. Discrete samples are hand collected and fixed with mercuric chloride before being analyzed in a laboratory. While they do not provide continuous data, discrete samples do not require deployment or maintenance of complex instruments. They can be collected by community samplers to provide important data on ocean acidification in waters of local concern.

The pH of seawater in Alaska’s oceans ranges from 7.5 to 8.4 depending on the season, temperature, and location, with a lower pH being more acidic. Despite the term “ocean acidification”, seawater is always basic, with the lowest pH levels remaining greater than 7. However, this relatively slight change in acidity can still pose a threat to marine organisms.

Researchers project that we will need to remove 4 gigatons of CO2 each year to limit global warming to 1.5 degrees C, a commonly used international target. While kelp farming does serve as an important carbon sink, one million square kilometers of kelp would need to be farmed worldwide to remove 1 gigaton of CO2 each year. It is unlikely that this level of mariculture expansion (a tripling of global kelp production) will be achieved.

However, kelp farming does offer benefits as one part of a societal shift to a sustainable, low-carbon economy. In Alaska, kelp farming offers a chance for local production of a nutrient rich crop, potentially replacing produce from the lower 48 and other nations. Kelp farming also offers to build community and economic resilience to climate change, especially as Alaska’s marine ecosystems are impacted by increasing temperatures. As stated previously here, kelp farms can provide important refuge for shellfish and other species that may be impacted by ocean acidification. We will learn more about the benefits and impacts of kelp farming as mariculture continues to be established as a key part of Alaska’s blue economy.

The chemistry of ocean waters can be measured both with instrument sensors and by analyzing discrete samples.  Instruments can be deployed on a mooring or at a kelp farm to provide continuous data on ocean chemistry. They are expensive and usually used by university and federal researchers. Discrete samples are hand collected and fixed with mercuric chloride before being analyzed in a laboratory. While they do not provide continuous data, discrete samples do not require deployment or maintenance of complex instruments. They can be collected by community samplers to provide important data on ocean acidification in waters of local concern.

The pH of seawater in Alaska’s oceans ranges from 7.5 to 8.4 depending on the season, temperature, and location, with a lower pH being more acidic. Despite the term “ocean acidification”, seawater is always basic, with the lowest pH levels remaining greater than 7. However, this relatively slight change in acidity can still pose a threat to marine organisms.

• Schery Umanzor (University of Alaska Fairbanks) is working on a tissue analysis project to assess the percent carbon (and nitrogen) assimilated into farmed kelp tissues (Saccharina Alaria). This work was conducted across space and time. Results of this study will show how kelp species grown will influence carbon uptake by kelp farms. Visit Schery’s webpage.
• Nichole Price (Bigelow Laboratory for Ocean Sciences), together with a large team of researchers, is working on analyzing time-series of the carbon chemistry (pCO2, pH, aragonite, and more) of seawater within large-scaled kelp farms and outside of the farm to assess the influence of kelp farms on surrounding waters. The team is also collecting seawater and sediment samples to discover the rate of flux of carbon to the seafloor. This research is being conducted across three farms: Seagrove Kelp Co. on Prince of Wales Island (Alaska, US), Bangs Island Mussels/Wild Ocean Aquaculture/Atlantic Sea Farms (Maine, US), and Seaweed Solutions (Froja, Norway). Preliminary data from Maine demonstrate that sugar and skinny kelp farming does influence the carbon chemistry of surrounding waters and raise pH and aragonite saturation state. Visit Nichole’s page. 
• Lauren Bell (University of California Santa Cruz & Sitka Sound Science Center) and Kristy Kroeker (University of California Santa Cruz) have been monitoring the year-round carbonate chemistry of benthic seawater within wild Giant Kelp Forests in Southeast Alaska since 2015. They have paired their field studies of kelp production rates in Alaska’s seasonally dynamic waters with laboratory studies considering how kelps’ growth, carbon acquisition, and nutritional content may respond to ocean acidification and warming in the future. More on Lauren’s work. 
• Amanda Kelley (University of Alaska Fairbanks) has been deploying sensors to monitor carbonate chemistry at multiple sites in Alaskan nearshore waters. This continuous effort provides important data on coastal carbonate chemistry and how it differs between regions. Recently, the Kelley lab has begun placing sensors both within and outside of kelp farms to analyze the impact that mariculture operations have on seawater pCO2 concentrations. This project is ongoing and will provide important information on how kelp farms sequester carbon and influence ocean acidification in local waters. Visit the Kelley Lab.

Along with these studies, researchers at the University of Alaska Fairbanks are in the beginning stages of working with kelp farms across the state to monitor their effects on local environments. More information will be shared as projects get started and begin to deliver results.