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Aquaculture

Sargassum: An Overlooked Solution

Saldarriaga-Hernandez, Sara, et al. “Bioremediation potential of Sargassum sp. biomass to tackle pollution in coastal ecosystems: Circular economy approach.” Science of The Total Environment (2020): 136978. https://doi.org/10.1016/j.scitotenv.2020.136978

What is Sargassum?

Sargassum, or Sargassum sp., is a type of seaweed that typically floats on the surface of the ocean. If you have visited a beach, chances are that you have seen this brown scrubby algae washed up along the shore. This seaweed has several important ecosystem functions in marine food webs. First, it provides protection for fish fry and other marine species as a type of “island” patch while buoyant at the surface. These patches can stretch for miles, and in some cases, across the ocean. When Sargassum dies and sinks, it transports nutrients to deep sea environments. It can also nourish beaches, but may become a nuisance when algal blooms cause large amounts to arrive on shore. While Sargassum is extremely important to marine ecosystems, its potential as a bioremediator has been understudied. The authors of this new study reveal that Sargassum’s value can be economical as well as environmental. 

Bioremediation and Circular Economies:

Due to human impacts and industry, many ecosystems around the world face unprecedented threats. One of the largest threats to marine ecosystems is pollution, as many forms of terrestrial pollution also end up in the ocean (Fig 1). Marine pollution is a complex problem and will require collaboration from many different groups, agencies and communities. 

Fig 1. There are many sources or marine pollution. While it is possible to pinpoint the sources of some, others come from a wide variety of companies and industries. This makes it difficult to implement regulations or stop pollution from occurring. From Saldarriaga-Hernandez et al 2020.

Recently, researchers have been exploring the idea of bioremediation or biosorption to remove pollutants from marine ecosystems. Biosorption is the process by which plants absorb pollutants from their surrounding environments. Bioremediation occurs when plants (or other organisms) are specifically used to remediate an environment that has been degraded due to pollution. While this practice has been common in terrestrial environments (check out this project from the 90s), relatively little research has been done to gage its potential in marine environments. Bioremediation provides an interesting opportunity to achieve what is known as a circular economy, or an economic structure focused on minimizing waste. A recent article in Forbes highlights some business start-ups who are committed to implementing circular economics in their respective sectors in order to improve recycling and re-purposing efforts.

Pros and cons of Sargassum:  

One of the main culprits for Sargassum blooms is excess nutrients in the environment. Like other algal blooms, Sargassum blooms can cause environmental, economic, and social issues. Phenolic compounds such as drugs, pesticides and antibiotics are among the primary concerns for pollution and excess nutrients in the marine environment. The authors of this study found that Sargassum has several characteristics that make it particularly well-suited for bioremediation. First, Sargassum can take up toxins along with the macronutrients it uses to grow. If managed correctly, this would remove toxins such as heavy metals from the environment and sequester them until they could be disposed of properly. While most other seaweed can only bioremediate excess nutrients, Sargassum can biosorp a wider range of pollutants due to a compound called phycocolloid found in its cell wall (Fig 2).

Fig 2. Shows the biosorption process with both passive and active uptake.  The cell actively attracts toxins while alive (#1), and continues passively collect toxins when dead (#2).The pycocolloid compound is typically found in the cell wall while the other parts of the cell are responsible for storing the toxins. From Saldarriaga-Hernandez et al 2020.

However, the biosorption potential of Sargassum does have its limits. The process is highly dependent on pH, and as the ocean becomes more acidic, Sargassum and other algae may absorb lower amounts of contaminants. The alkalinity, concentration of ions in solution, temperature and contact time all influence the efficiency of biosorption and removal of toxins by Sargassum. Any changes in these factors could change how many toxins are removed, and the authors indicate that these factors should be studied carefully to maximize the potential of Sargassum.

Toward a New Economy:

The current economic model of capitalism and consumerism has led to extraordinary amounts of waste that threaten humans, animals and our planet. A circular economy approach would allow scientists and businesses to a) design products and solutions with minimal waste, b) recycle materials as long as possible and c) allow natural systems to recover from exploitation. While the authors aren’t advocating for a complete economic overhaul, they do pose the idea that some practices need to change in order to avoid complete marine degradation. They envision a new process (Fig 3) with Sargassum playing an important role.

Fig 3. This figure shows an idealized circular economy with Sargassum acting as the collection point. It would play a vital role in recycling materials and remediating degraded environments. From Saldarriaga-Hernandez et al 2020.

In order to bring this process to fruition, much more research needs to be done on remediating aquatic ecosystems. Due to the complexity of many marine ecosystems, researchers often create idealized conditions for biosorption. Implementing bioaccumulation solutions will likely require a much more intense process that takes into account all the factors mentioned above. While the challenge of creating a sustainable solution for marine pollution may not be easy, the reward of a cleaner ocean is definitely worth trying.

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