By Sarah-Anne Rohlfing
Growing seaweed could become one of the most effective bioremediation tools in our oceans.
Photo by Matt Koller
Seaweed is one of the fastest-growing plants in the world, thriving on nutrients suspended in the water surrounding them . It is particularly good at absorbing nitrogen and phosphorus, as well as toxins. A new study from the University of California, Santa Barbara shows evidence that growing seaweed could quickly reduce the harmful levels of nitrogen and phosphorus in the Gulf of Mexico, where excess levels currently feed harmful algal blooms .
In 2019, the Gulf of Mexico experienced a record-breaking algal bloom in the western hemisphere that was roughly the size of New Jersey . Algal blooms result from high levels of nitrogen and phosphorus from farmland and urban runoff. Decomposers then break down the short-lived algae and use up the surrounding dissolved oxygen, suffocating remaining sea creatures and creating dead zones . Reducing these events seems like an impossible task with no notable decrease in runoff levels in the past 20 years. These events are not predicted to slow down, either, as the global population increases and the need to farm and develop more land continues to grow.
The study, “A case for seaweed aquaculture inclusion in U.S. nutrient pollution management,” looks at the effectiveness of farming native seaweeds throughout the Gulf of Mexico for nutrient pollution assimilation.
Phoebe Racine, the lead researcher and a Bren Ph.D. student, stated that “what we found when we were investigating the different co-benefits of seaweed aquaculture is that a very potentially promising avenue is its ability to take up lots of nitrogen and phosphorus and it could be used on a bigger scale.”
Racine and her research team mapped out how much area within the Gulf could be used for this potential large-scale seaweed aquaculture. Over 63,000 km² (8.9 % of the Gulf) was identified as ideal area for algal growth. Of this area, it is possible that less than 3% would be needed to effectively reduce nitrogen and phosphorus levels by 20% in the next 5 years .
“We chose a few different species that are being looked at now and are native to the Gulf of Mexico. They have different rates of nitrogen and phosphorus uptake, but some species — depending on water temperature, salinity, the environment — will have different uptake rates, so there is a lot of variability in how they will perform,” said Racine.
The researchers have illuminated seaweed’s ability as a tool for bioremediation, but they also highlight the monetary possibilities.
“There’s a lot of products that seaweed aquaculture can become, but if you’re going to grow at the scale we are talking about, you need some big market development around this,” said Racine.
The seaweed would be inedible for humans or animals, but it could still be used for biofuels, bioplastics, textiles, fertilizers, and building materials . These industries need to develop further in order to use the large amount of seaweed that would be produced.
The EPA is also renewing its interest in the Water Quality Trading (WQT) program, where incentives will be paid for the capture of phosphorus, nitrogen, sediment load, and other pollutants by the ton [2, 4]. The WQT was highlighted in the analysis to show the environmental benefits of growing seaweed in a tangible way rather than to predict future market potential.
“I would actually say the incentives are there for people to grow seaweed right now without using the Water Quality Trading program,” said Racine.
By incentivizing people to grow more seaweed for business, we could see a fast decline in nutrient overloads while seeing a rise in the amount of dissolved oxygen and fish populations in dead zone areas. Cultivating seaweed would also promote possibilities to use the seaweed for sustainable solutions and encourage the growth of kelp industries. Seaweed is making its mark as a solution for many environmental challenges, but nutrient remediation could be the most promising application to maximize kelp’s potential.
 Yong, Y.S., Yong, W.T.L. & Anton, A. Analysis of formulae for determination of seaweed growth rate. J Appl Phycol 25, 1831–1834 (2013). https://doi-org.proxy.library.ucsb.edu:9443/10.1007/s10811-013-0022-7
 Racine, P., Marley, A., Froehlich, H., Gaines, S., Ladner, I., MacAdam-Somer, I., Bradley, D. A case for seaweed aquaculture inclusion in U.S. nutrient pollution management. Marine policy, Vol.129, 2021, p.104506.
 N.H. Ye, X.W. Zhang, Y.Z. Mao, C.W. Liang, D. Xu, J. Zou, Q.Y. Wang, Green tides’ are overwhelming the coastline of our blue planet: taking the world’s largest example, Ecol. Res. 26 (3) (2011) 477–485.
 “Hypoxia 101 What Is Hypoxia and What Causes It?” EPA, Environmental Protection Agency, 13 Dec. 2020,https://www.epa.gov/ms-htf/hypoxia-101