Beneath the surface: exploring kelp forests for solutions

An area of research currently gaining momentum in the fight against climate change lies beneath the surface of our oceans.

Institute of Marine Science Research Fellow, Caitlin Blain, has dedicated seven years of her career to researching seaweed and kelp forests. After spending two and a half years in freezing Atlantic waters studying the impact of a seaweed called Desmarestia on biodiversity, she came to Aotearoa New Zealand, to complete her PhD.

Her work at the Leigh Marine Lab initially focused on the impact of anthropogenic stressors on kelp forest function and productivity, mainly coastal turbidity. A side component of this work led her to carbon sequestration.

“As kelp photosynthesise, they draw down carbon into their tissues to grow, and they’re kind of like these conveyor belts that keep growing and continually sloughing off tissue as they grow,” she says.

It’s a topic that is also gaining attention outside of academia, with interest from government, community groups, and private industry, all looking to kelp for answers. However, it is a complex process with many unanswered questions.

For this reason, Caitlin explains, that despite being highly effective at processing CO2, kelp forests have typically been excluded from any estimates of blue carbon or climate mitigation schemes. While researchers are doing their best to keep up with industrial and government interest, a lot more work is needed to inform those initiatives.

Compared with terrestrial forests, where fallen leaves provide physical proof to account for carbon, it is much harder to identify what happens to carbon captured by kelp forests. This is because kelp grows on rock, so for the carbon to be sequestered, it has to be exported somewhere conducive.

Carbon comprises a whole suite of different chemical compounds, so Caitlin is looking at the different components of carbon as it is released from a kelp forest, where it might end up, and how long it might stay there. The hope is that scientists can provide measurable data to inform blue carbon budgets by unpacking this process.

She explains a lot of the existing literature is focused on tracing particulate organic carbon (POC). This is much more accessible because the particles are visible. In contrast, research on dissolved organic carbon (DOC) is not as well represented. The release of DOC is much harder to account for, but it’s quite a significant makeup of what’s released from the kelp and potentially longer lived. Closing this knowledge gap has become one of Caitlin’s main focus areas at the moment.

Her research has returned some promising results, indicating that DOC could be important to consider in the future. Some experiments have shown that as much as 40 percent of the carbon released from the kelp forests in the dissolved form is long-lived. She compares this to other research on particulate matter, including her work, which measured around 10 percent of the tissue staying as an organic carbon that can be sequestered.

Caitlin uses a combination of laboratory and in-the-field (in situ) experiments to directly measure variation in POC and DOC production. These include sampling seawater from areas or tanks with and without kelp.

“To collect the DOC associated with kelp in the field, I use photorespirometry chambers to monitor changes in photosynthesis and other biochemical processes in relation to different light levels and environments. Seawater samples are assessed for DOC using a total organic carbon (TOC) analyser,” she says.

The assessment of DOC composition is still under development, but she will be using a range of techniques, including an untargeted assessment of metabolic profiles using gas/liquid chromatography.

To assess the longevity of POC and DOC, Caitlin uses laboratory and in situ degradation experiments across gradients of productivity and environmental factors. It is known from her previous work that there is a larger gradient in the morphology, productivity and chemical composition of kelp associated with the turbidity gradient in the Hauraki Gulf.

“I’ve set up a degradation experiment across this gradient to examine how turbidity and kelp physiology impact carbon degradation. We will link these degradation experiments with microbial activity to see how this varies across environments,” she explains.

While they show great potential in aiding carbon and pollution reduction, kelp forests also confront threats from factors like climate change and other influences.

Caitlin’s earlier work focused on anthropogenic stressors threatening kelp forest function and productivity. This is still heavily integrated into her work today because in order to protect and benefit from kelp forests, it is vital to understand how the services they provide will change in the face of growing anthropogenic and climate-related stressors.

The challenge ahead is complex, and there is no one-size-fits-all solution. One of the most significant threats to kelp forest ecosystems in northeastern New Zealand is the destructive grazing by sea urchins. The Hauraki Gulf now has an abundance of sea urchins that have decimated kelp growth. The result is an imbalanced ecosystem. With fewer predators eating the sea urchins, they become more established.

“Barrens can be extensive in northeastern New Zealand (Northland and the gulf), in some cases covering over 50 percent of the shallow reef. This means there’s greatly reduced productivity and reduced potential for carbon sequestration,” Caitlin explains.

Another concern is increasing turbidity caused by land runoff, particularly near cities and heavily developed coastlines, made worse by the recent storms and precipitation. The shallower water is more susceptible to sediment disruption, clouding the water and reducing the amount of light that can reach the bottom. Because kelp requires sunlight to photosynthesise, the reduction of light reaching the bottom limits the plants' productivity.

Actions should be targeted to address their region’s individual stressors. Caitlin suggests fisheries management to help reestablish sea urchin predator populations responsible for kelp forest degradation.

By establishing a healthy ecosystem, the sea urchin population will return to a more manageable and natural level, allowing kelp forests to regenerate. She says tree planting and better coastal infrastructure management in problem areas will also help reduce sediment runoff.

Caitlin’s postdoctoral research was funded by the George Mason Centre for the Natural Environment (GMCNE), a multi-disciplinary research center in the Faculty of Science.
Her current projects are funded by theLive Ocean Foundation (LOF), established by New Zealand sailing legends Peter Burling and Blair Tuke, to support marine scientists, innovators and communicators working to conserve and protect our oceans.

“A healthy ocean is truly our greatest ally in the fight against climate change, so we see Dr Caitlin Blain’s research as vitally important. Her research will help fill critical knowledge gaps into the value of kelp in the blue carbon context and will help inform better marine management and conservation decisions, both here and globally.

“Live Ocean Foundation partners with exceptional marine scientists to inform action for a healthy ocean. We are incredibly proud to support Caitlin’s work and pleased that we’re able to help retain one of the world’s best and brightest minds in this field here in New Zealand where we are guardians to one of the largest ocean spaces on the planet,” said Sally Paterson, Live Ocean Foundation chief executive.

Caitlin also continues to collaborate with her PhD supervisor and current mentor, Associate Professor Nick Shears, on aspects of kelp forest restoration, with ongoing work in the Hauraki Gulf/Te Moananui-ā-Toi and Queen CharlotteSound/Tōtaranui with the support of local iwi.

Caitlin is optimistic. “Our marine ecosystems can be incredibly resilient when not subjected to the constant pressures we place on them. With more knowledge and outreach, I am hopeful that more people will understand the value and vulnerability of our hidden forests.”