Sean Arsenault

"The use of macroalgae cultivation to capture carbon through photosynthesis and sequester it in the deep ocean, sediments, or long-lived products is a promising and priority marine carbon dioxide removal strategy, with relatively low costs and high potential for social and environmental co-benefits." More research needs to be done on the ability of seaweed and macroalgae to capture carbon. Macroalgae also benefits its surrounding ecosystem and can be used as a less impactful food source to replace fishing.
https://www.globalseafood.org/advocate/macroalgae-aquaculture-as-a-potential-carbon-dioxide-removal-strategy/

During its growth period, seaweed can absorb carbon through photosynthesis. It can also sequester carbon in the ocean floor when it dies, which can stay there for a long period of time. Seaweed as a food product has a very low carbon and ecological footprint, which can replace more demanding foods that we consume. Bioplastics and biostimulants, that can be derived from seaweed, could substitute for other products that have a larger carbon footprint. The industry needs to be developed before it can have an impact on carbon emissions.
https://www.nature.org/en-us/what-we-do/our-insights/perspectives/blue-carbon-seaweed-nature-based-climate-solution/

Efforts to protect and restore seaweed and macroalgae can enhance marine biodiversity, support coastal communities, and contribute to global carbon sequestration. It is important to target areas with maximum climate change mitigation potential. Encouraging local involvement and implementing financial incentives are also necessary for this initiative. Implementing policies that promote macroalgae protection and restoration, and increasing investment for technology, are important for future development.
https://www.climatetechhandbook.com/solution-macroalgae-protection-and-restoration/

"Protecting 160–199 million hectares of macroalgae forests globally by 2050 could sequester 1.84–2.28 gigatons of carbon dioxide." As you can see, seaweed and macroalgae are important to the global management of carbon dioxide emissions. Globally, the area covered by macroalgae is decreasing 1.8 percent annually due to a combination of factors related to anthropogenic activity and climate warming. Protecting macroalgae from climate change can be done by protecting predators, minimizing its harvest, and reducing eutrophication due to runoff.
https://drawdown.org/solutions/macroalgae-protection-and-restoration#:~:text=Marine%20Protected%20Areas%20(MPAs)%20and,and%20resilience%20to%20climate%20change.

Seaforester is one organization that aims to restore seaweed and their ecosystems. Stones are seeded with seaweed spores, grown in specialized nurseries and scattered by boat to replant underwater land with seaweed. This is driven by communities and related industries. Local authorities and scientific institutions must also participate in this movement to restore seaweed ecosystems globally. It is also important to spread awareness about this issue in education.
https://www.seaforester.org/our-solution

Seaweed can be protected from the effects of climate change and diseases in the context of seaweed farming. By developing pathogen identification, establishing seed-banks and nurseries, implementing standards for farming, encouraging the use of local species and investing in innovation of the industry, we can protect seaweed from diseases and climate effects. This is due to the lack of genetic diversity currently present in the industry.
https://thefishsite.com/articles/eight-ways-to-ensure-a-sustainable-seaweed-farming-sector

Seaweed can be harmed by the effects of climate change in many ways, such as the effects experienced by seaweed in New Zealand. Firstly, warming oceans contribute to increased frequencies, durations, and intensities of heatwaves in the ocean. These heatwaves caused range shifts towards the poles and shifts in phenology. Extreme weather events also cause accelerated erosion of sediments which are suspended in the ocean. This reduces the growth rates and habitat of seaweed. Ocean acidification, also contributed to by climate change, reduces the growth of coralline algae which disrupts the surrounding ecosystem.
https://www.tandfonline.com/doi/full/10.1080/0028825X.2023.2245786

Macroalgae are threatened by climate change in a few ways. Carbon emissions lead to ocean acidification, increases in the frequency of heatwaves and the warming ocean temperatures. These factors can harm macroalgae, such as reducing the calcification of some species. Also, other human activities leading to changes in the UV radiation that macroalgae are exposed to can be harmful for it.
https://www.sciencedirect.com/science/article/abs/pii/S0065288120300602

Macroalgae are important to the ecosystem as they are part of the food chain. Preserving macroalgae prevents the destabilization of the food chain as other animals would be impacted if it were to be threatened by climate change. Macroalgae also acts as a habitat for marine life. They are also commercially important in terms of food, scientific products and compounds used in the production of many commercial products.

Macroalgae are also often used as indicators of water quality and reef health because they can store water, which can be analyzed by scientists to determine nutrient concentration in the water. Storm damage or coral bleaching, which could be due to climate change, causes macroalgae to take over coral reefs, leading to their degradation.
https://eatlas.org.au/content/macroalgae#:~:text=They%20are%20also%20commercially%20important,water%20quality%20and%20reef%20health.