Sargassum

Sargassum

Introduction

Sargassum is a type of brown algae which often serves as a Macroalgal Bed in oceans. Sargassum algae serves several benefits to marine life, providing food, refuge, and breeding grounds to much fishlife. Due to impacts of climate change, in recent years sargassum has grown at an uncontrollable rate and beginning to threaten reefs.

Habitats and Location of Sargassum

Sargassum are generally found in “tidal splash zones, rocky marine pools, the intertidal zone, coral reefs and moderately deep coastal zone waters”. Sargassum is found in throughout the Gulf of Mexico and North Atlantic. Sargassum typically circulates in those regions and towards the Sargasso Sea in the North Atlantic Ocean, which is 1000 km wide and 3200 km long. Scientists estimate that the Sargasso sea contains up to 10 million metric tons of Sargassum. In the spring and summer, the seaweed typically arrives on shores in the Gulf of Mexico, the southern U.S. Atlantic coast and the northern Caribbean, crowding beaches. As the seaweed has become more dense and widespread it washes up on these beaches more frequently, and has even been found on the Western Coast of Europe where it is invasive and non-native to these coastal areas.

Biology

Appearance and Composition

Sargassum is a type of brown algae, genetically similar to yellow-green algae which can appear anywhere from green to red in color. There are over 2800 estimated species, a number which has grown in recent years . Brown algae are slender, and often branch with multiple thin tubes and large leaves. Additionally, it often branches oxygen filled “berries”. Sargassum may be macroscopic or microscopic. Sargassum typically grows to about 2-3 meters, but there have been documented cases of Sargassum growing up to 16 meters. A sargassum plant lives for approximately 3-4 years.

Reproduction

Sargassum has the ability to reproduce both sexually and asexually via floating fragments. Sargassum’s flagellate spores alternate between releasing haploid and diploid gametes during external fertilization. Sargassum’s ability to reproduce sexually has caused its spike in species variety. It is this variety which has allowed sargassum to survive in diverse environments throughout the Atlantic. If sexual reproduction continues at its current rate, it is expected that Sargassum will become more abundant in non-native regions. Sargassum lacks much scientific research due to its inability to sample , however scientists believe that “a decline in pH, increase in summer temperatures, and changes in the abundance” and distribution of Sargassum in an area lead to this instability in reproduction .

Ecology

Floating Sargassum beds serve critical ecosystem functions to a variety of marine species. These habitats contain a diverse assemblage of creatures including fish, sea turtles, and over 145 species of invertebrate, including sponges, fungi, bacteria, and protists.

Ecological Roles

Sargassum beds can form floating rafts that extend for miles across the ocean. The majority of sargassum is found in the Sargasso Sea, known as the "golden floating rainforest" because of its rich biodiversity. These rafts provide habitats, food, and breeding grounds for a variety of marine organisms, and some creatures, like the Sargassum fish, live their entire lives in sargassum.

Nurseries

Sargassum beds provide a nursery area for many commercially important fish species such as mahi mahi, jacks, and amberjacks. Additionally, juvenile sea turtles often hide from predators among the sargassum.

Food

Sargassum rafts serve as feeding grounds for fish, seabirds, and other organisms in the open ocean. When the algae dies, it sinks and provides organic carbon to the water column and seafloor. It may act as a supplementary food source for bottom-dwelling organisms in the deep sea.

Shelter

Floating sargassum rafts provide shelter in the otherwise completely open ocean. Juveniles from many species can mature to adulthood in the safety of the algae, and larger creatures such as dolphins and even whales use it as a shelter. Within the water column the sargassum creates layers in which different species occur. Smaller filefishes and triggerfishes are found within the algae network, while juveniles of larger fish species swim just below the raft and larger predators, like dolphins, are further down.

Environmental Impacts

As sea-surface temperatures have been rising, winds in the subtropics have been growing weaker. These factors affect ocean currents, especially the North Atlantic Gyre that creates the Sargasso Sea. As a result of these changing currents, the Caribbean has experienced an influx of Sargassum in recent years. The algae has also begun to spread because of an increase in nutrients in the oceans due to human pollution. This overabundance of algae on beaches and among coral reefs has implications for the health of local and global environments. Sargassum is generally harmless to humans and other organisms when it occurs naturally, and when it washes ashore many animals use it for food and shelter. However, in large amounts, the washed-up algae can prevent hatchling sea turtles from reaching the ocean. Additionally, concerns have arisen in many Caribbean communities about the affect Sargassum could have on the tourism industry, as many beach-goers are deterred by the unpleasant smell it creates.

Effects on Coral Reefs

While many macroalgae have proven to be detrimental to the health of coral reefs, studies conducted on Sargassum reveal that the relationship between the organisms can be complex. Research done on Sargassum in the Great Barrier Reef determined that while conditions favorable to macroalgae are unfavorable for corals, the presence of the algae did not directly impact the reefs. In some instances, the algae may in fact prevent coral bleaching by blocking sunlight and reducing water temperatures. However, this same phenomenon also prevents that sunlight from being photosynthesized. While many algae compete with corals and cause reef degradation, non-allelopathic algae such as Sargassum may actually protect the corals from excessive stress, producing benefits that exceed the cost of competition.

Managing Sargassum

There are two courses of action to prevent Sargassum from initiating the negative ecological effects stated above on turtle hatchlings and the tourism industry: responsive and preventative. The responsive approach is to organize cleaning efforts along the beach to remove the sargassum once it has washed ashore. The low-cost approach is through the use of manually raking and collecting the Sargassum. The more cost-effective approach involves running a beach-sweeping vehicle. Beach sweeping vehicles have a rake attached to the back of them and collect sargassum as they drive down the beach. There are two associated drawbacks with this manual approach. When the clean-up initiative is financially restricted, manually removing the sargassum is the best option, the drawback of this approach is that this takes a larger amount of time and must be done as frequently as the sargassum washes ashore. When a clean-up project is not financially restricted, there will require a hefty initial investment in machinery. The second major drawback is that both of the aforementioned approaches regardless of financial restriction will require operators. Due to the fact that Sargassum continuously washes ashore, there will always be some Sargassum that reaches the shore between cleanups.

The preventative approach involves intercepting the sargassum before reaching the beach through the employment of floating aquatic barriers. These barriers are employed outwards from the beach and float atop the water catching buoyant objects approaching the shore. Once significant amounts are accrued behind the barrier, a vessel can skim the water and collect the Sargassum for disposal or recycling. When the floating aquatic barriers prevent the Sargassum from washing ashore, sea turtle hatchlings are able to reach the water and swim underneath the floating sargassum. Additionally, barriers reduce the foul smell produced by Sargassum due to decomposition which produces hydrogen sulfide gas that smells like rotten eggs. While preventative measures seem like the obvious choice, there are cost-associated drawbacks associated with these structures. The main drawback is the fouling of the barriers, which implies heavy disassembling, cleaning, and reassembly costs. (2) Additionally, these structures are subject to damage by natural disasters which may dislodge or rupture the barriers.

Uses of Sargassum

Food

Sargassum is being used in drinks in the Caribbean with other uses being explored such as biofuel, fertilizer, livestock feed or fish food. An example of a drink is the Pineapple Cocktail in the Caribbean which uses Sargassum in its ingredients.

Using sargassum as food comes with risks of heavy metals and often trash mixed into it so many stay away. However, it is incorporated into a select few Asian dishes and medicines.

Thomas Tennent, a daring chef and owner of Tomfoodery Kitchen in the Cayman Islands, is using Sargassum in his Fiyah hot sauces. He makes sure to use fresh Sargassum that does not smell, since this implies it has not started to decompose, and then washes and soaks the Sargassum to clean away impurities. He is exploring other food options for the brown seaweed such as stuffed snapper.

Medical Benefits

Sargassum has been studied for health benefits recently with a few focusing on possible thyroid treatments due to sargassum tea and other sargassum medicines having traditional roots in Chinese medicine. In 2012, Southern Cross University tested its bioactive compounds and found that sargassum has potential for treating thyroid diseases such as Hashimoto’s thyroiditis but wants further research on the matter . A similar study was done by Beijing University of Chinese Medicine in 2017 of seaweed's effects on thyroid problems . They tested different seaweed teas, some sargassum, on rats with enlarged thyroid glands and found it had an effect but it was still unclear why and if any side effects were attached. More research is still needed on Sargassum's health benefits and the different effects different varieties of seaweed might have, but it does seem promising since this traditional Chinese medicine has been used for around two millennia to treat thyroid and other diseases .

Two species of Sargassum, Sargassum pallidum and Sargassum fusiforme, have been listed in Chinese Pharmacopeia, 2010 edition, while other species are being considered . These other possible candidate species include Sargassum fulvellum, Sargassum henslowianum, Sargassum thunbergii, and Sargassum horneri .

Beach Nourishment

Although there are current ecological problems due to excess Sargassum in the ocean and subsequent large amounts washing up on beaches, washed up Sargassum is a natural source of vital nutrients for beach dunes. To keep the shoreline and dune plants healthy the Virgin Islands’ often let the Sargassum decompose into their beaches even with the foul smell it produces . However, when Sargassum piles up excessively on beaches it needs to be disposed of due to reasons provided above.

Some places dispose of excess Sargassum by integrating the Sargassum into other shoreline dunes with a lack of Sargassum. The downside to this method is that it requires more shoreline with a lack of sargassum, something that the Virgin Islands lack with its smaller circumferences. Another problem with this solution is that shorelines are getting smaller due to rising sea levels and erosion .

Composting

Composting excess Sargassum has been studied and found to be a viable option for disposal once it is removed from marine environments. A study conducted off the coast of Texas assessed the breakdown of Sargassum in combination with discarded food and wood chips to determine if it was worth composting the material instead of putting it in landfills. The experiment proved to be successful with all of the test piles producing compost that met industry quality standards. The composted Sargassum boasted adequate levels of pH, salt content, total nitrogen, total carbon, carbon: nitrogen ratio, particle size, bioassay, and respirometry measurements, as compared to universally accepted benchmarks within the composting industry .

This study presents a promising prospect for the future of sargassum disposal especially in areas that have strong rural industry like the Gulf Coast of Texas where this study was conducted. Additionally, using compost in places like the U.S. or British Virgin Islands cuts down on the need for synthetic fertilizers which would benefit the reef ecosystems there in the form of reduced nutrient loading from runoff. It also provides an opportunity for domestic industry to both solve an environmental problem and bolster local economies within the Caribbean Islands .

More research needs to be conducted before these methods can be conducted on a large scale. There are many factors that play into the viability of this strategy, and its cost is a major influence on its implementation in areas overrun with Sargassum. The cost of removing sargassum varies by method and there are a wide variety of different ways it can be removed from the ocean each having different monetary costs, timeframes and environmental impacts. These costs need to be assessed in detail in order to determine if the value of compost produced from Sargassum outweighs the price to harvest it from the ocean and produce the compost. The price for sargassum compost also has to be competitive with the price of synthetic fertilizers, which could prove difficult if the production process is costly. This effort will likely benefit greatly as technology for safely removing sargassum from coastal environments improves, making it cheaper and more efficient. Additionally, in places like the Caribbean where domestic resources are often scarce and islands are heavily reliant on imports for many things, having a way to produce quality fertilizer on islands could result in a price far cheaper than that of imported synthetic fertilizers .

Biofuel

Another potentially lucrative use of sargassum seaweed is converting it into biofuel which would benefit the environment greatly not only through the removal of the seaweed but also by providing a sustainable alternative to fossil fuels. Studies have shown that treating sargassum through acid hydrolysis causes it to release large amounts of ethanol which can be used as a source of energy. After the initial treatment, sargassum can be refined into biogas through anaerobic digestion and can even be converted into biodiesel through further sugar metabolization and lipid extraction. The challenges that arise from this process are the energy yield as well as the cost effectiveness. While it is entirely possible to derive gas and diesel fuel from sargassum, the processes required cost far more than other industry alternatives such as fossil fuels as mentioned earlier. The total energy yield per unit is also considerably smaller than alternatives but research is currently underway that involves using waste oil as a substrate to increase the energetic value of the harvested sargassum . In short, the viability of using sargassum as biofuel is dependent on several factors such as how big of a problem it is on the beaches and in the oceans, how badly and how soon we will need a fuel alternative, and how much the process can be optimized in terms of cost and yield. Biofuel is a very important field due to the limited supply of fossil fuels as well as how destructive they have been for the environment already so funding and research in topics like this is paramount. Sargassum is already causing problems for the environment and for beach-goers so finding a way to make it benefit our world while also mitigating its negative effects would be a huge step in the right direction.