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Aquaculture

The Life of an Aquatic NOMAD: A Study of Macroalgae in the Pacific

References: Whiting, Johnathan M.; Wang, Taiping; Yang, Zhaoqing; Huesemann, Michael H.; Wolfram, Phillip J.; Mumford, Thomas F.; Righi, Dylan. (2020). Simulating the Trajectory and Biomass Growth of Free-Floating Macroalgal Cultivation Platforms along the U.S. West Coast. J. Mar. Sci. Eng. 8, 938-956.

DOI: https://doi.org/10.3390/jmse8110938

Reading Time: 5 minutes

You open your eyes. You are on a raft adrift at sea. Where are you going? Where did you come from? Where will you end up? These are all the kinds of questions scientists ask about the ocean. There are a multitude of different currents with different speeds, directions, and depths, and they all push massive amounts of water around the ocean. As a helpless raft, you are caught up in their flow, travelling wherever they do.

Scientists have begun to understand that these currents can do much, much more than they have thought for our coastlines. Currents drive the temperature of the water at the coast, circulate nutrients, and create the conditions for certain plants and animals to live in the areas they do. One of these organisms is macroalgae. Macroalgae, otherwise known as seaweed, is a large family of algae that grow in the ocean. There are thousands of macroalgae species and they all need unique currents and environments to grow. Seaweeds have traditionally been farmed for animal consumption and human usage. They are usually grow in large, stationary farms or harvested from natural sources in the ocean. Unfortunately, growing macroalgae is a taxing process both financially and environmentally: seaweeds need a lot of space to grow and it is expensive to provide all of their essential nutrients. Even with these problems macroalgae farming is a rapidly growing industry, so scientists and seaweed growers alike are interested in the question: can we increase the scale of seaweed farming and make it more efficient?

A cartoon depiction of NOMAD along with the forces that pushed it around. Image Credit: Whiting et. al.

A team of scientists from Seattle, Washington decided to investigate this problem using currents. They asked, what if we grow seaweed in a way that harnesses the power of currents? The group set to work and invented the NOMAD, which stands for Nautical Off-shore Macroalgal Autonomous Device. The NOMAD is a 5km long line made of carbon fiber that has macroalgae seeds implanted in it. These lines are let loose out into the Pacific Ocean near Washington and allowed to float south for three months before being retrieved off the coast of California. Today, we are going to find out how they work.

How does NOMAD work?

Macroalgae growing along a simple line. Image Credit: Benjamin Jones

The group released 30 lines off the coast of Washington and, once they retrieved the rope, they found that each line could house up to 30kg of seaweed per meter. That totals a gargantuan 330,693 pounds per line! Before the lines were released, the team performed a multitude of calculations. They planned both the trajectory of the lines (or where they would go as they floated) as well as the macroalgal growth along their journey. For the trajectory, the group used a set of data collected by the National Oceanographic and Atmospheric Administration (NOAA) which told them about the behavior of the currents and the wind. Furthermore, the group estimated the amount of seaweed growth on their lines by calculating the amount of light, available nutrients, and temperature of the water along their journey. The team decided where they would release the lines and how long they should let them float, based on their predictions about where the lines would travel and how much the macroalgae would grow.

Where did the lines go? What happened?

All of the lines went on their own unique journey, travelling different trajectories as they headed south. Fortunately, none of them washed up on the beach and none passed through any protected marine sanctuaries. The lines were pushed by the currents, winds, and waves off the coast south until they were retrieved off the coast of southern California. The group noted that the growth of the macroalgal sped up significantly as the water got warmer and when the nutrient nitrate (which is very important to macroalgae) became more available. Interestingly, some of the lines actually lost some seaweed near the end of their journey as they moved into waters that were too warm for the seaweeds.

Each line is a unique NOMAD line, and the color of the line represents how much macroalgae grew on it (with red representing the most and dark blue being the least). Image Credit: Whiting et. al.

Why does it matter?

This preliminary study for the growth of seaweed with free

-floating lines in the Pacific ocean exhibit a more efficient way to grow an important product for humans. As this technology develops, it may allow us to grow seaweed without putting more money and energy into problems like the availability of nutrients and the space needed for large farms. Furthermore, scientists and farmers can accurately predict the amount of seaweed they have grown to harvest by the time of their retrieval. All in all, this system of free-floating lines is a design for a more sustainable future.

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