Aquacultures’ Effect on the Environment

Authors: Katie Clark, Mackenzie Radock & Matt Wah

In 2014, hundreds of dolphins, manatees, octopuses, fish and crabs were killed, beaches closed and tourism declined. That was all because of a massive red tide that occurred off of the coast of Florida.

Red tide, a common term used for a harmful algal bloom, according to the National Oceanic and Atmospheric Administration, appears around the tail end of the summer. The red tide off the coast of Florida in 2014 led to a devastated economy. Red tide, Karenia brevis, are microscopic algae that take over coastal waters, they deplete the oxygen supply and release toxins that are harmful to both animals and humans. Fishermen that work along Florida’s coast were seen with surgical masks for protection. These fishermen had to make a living despite the dangerous conditions. Aquaculture is a causative agent to red tide and pollutes the environment in other ways (Wagstaff, 2014). Aquaculture can also have a negative effect on the environment through nutrient and sediment pollution, but its impact can be reduced using federal incentives to regulate feeding practices and food composition.

“Aquaculture is the cultivation of aquatic plants and animals especially fish, shellfish and seaweed, in natural, controlled, or freshwater environments” (, 2010). Just over the past forty years the industry has intensified (Fisheries and Aquaculture Department, 1988). Aquaculture was introduced to expand certain species as a result of high export demand. For example, there is a high demand for salmon in the aquaculture industry. Aquaculture has helped solve the global environmental problem of overfishing (Fisheries and Aquaculture Department, 1996). Illegal fishing and other problems, such as lack of international regulations that are not enforced or implemented, lead to constant overfishing (World Wildlife Fund, 2016).

The demand for farmed fish has increased because it is cheaper overall and desired fish can be purchased year-round (Weber, 2003). The cost for farmed fish depends on the scale, intensity and duration of the operation, while cost for wild fish is solely dependent on the fisherman. The fishermen have to worry about the costs of a boat, permits and the time it took to fish. The consumer wants to save their money and will likely choose fish at a cheaper price, regardless of whether it’s farmed or wild (Weber, 2003).

One of the adverse effects of aquaculture is on the nutrient concentration of the surrounding environment. Edwards (2015) notes that due to the intensity of modern aquaculture practices, the use of pelleted feed is increasing, which drops down to the ocean floor and leads to eutrophication (excessive richness of nutrients) of the water. The problem has a larger impact when fish are fed in excess, because the feed that the fish do not eat begins to dissolve as it descends and releases nutrients into the water. The nutrients that are released change the chemical composition of the water, and aid in the formation of algal blooms. Two nutrients in particular that have an effect are nitrogen and phosphorus. According to Stead and Laird (2002), the crude protein requirement (which is measured as percent nitrogen) at which Atlantic salmon best developed at was forty-nine percent. That means that about half of each fish pellet is pure nitrogen. Fishmeal is frequently used as a main component in pelleted feeds to supplement protein. As an animal byproduct, fishmeal has a very high phosphorus content that can be released into the water as the feed dissolves. In a study performed by Tovar, Garcia-Vargas, Manuel-Vez and Moreno (2000), nitrogen and phosphorus concentrations was measured in areas of a river near aquaculture farms, and areas that were further away. The nitrogen concentration was at least three times greater near the fish farms, and the phosphorus concentration was seven times greater.

Another problem is that if the fish food is not carefully balanced, additional nutrients are put into the feed that are then excreted by the fish into the surrounding environment. According to the Coastal Alliance for Aquaculture Reform (2013), “Hundreds of thousands of salmon excreting in the confined area of a farm can cause a localized level of nutrient loading that may not be completely absorbed by the surrounding environment; hence, nutrient loading from salmon farms may be linked to algal blooms” (para. 2). This statement can be applied to other marine fish species as well. Algae blooms are a widespread problem in marine environments. According to the National Oceanic and Atmospheric Administration (2015), algae blooms can grow out of control and some secrete toxins that can kill marine animals and cause human illness. Even those that are nontoxic can take up the water’s oxygen, block fish’s gills, and contaminate drinking water.

Beyond nutrient pollution, the feed used in marine aquaculture systems leads to sedimentation as well. As the leftover food descends, not all of it dissolves. This is similar to how leftover food settles to the bottom of a pet fish’s tank, but on a larger scale and without the ability to rinse it down the drain after. Ocean sediment contains nitrogen and phosphorus, two key components in fish feed. As more layers of sediment are piled on top of each other, plants and other small organisms can be buried underneath it, or killed by an excess nutrient load. Results of a study performed by Piniak (2004) found that sediment reduced the amount of light that could reach coral reefs, and as it settled it, bury corals or force them to spend a vast amount of energy to keep their surfaces clean. In a site with high sediment loads, Piniak found that corals had a high mortality rate and those that survived did not grow. Das, Kahn, and Das (2004) performed a study on how sedimentation affects shrimp in particular, and found that an increased load of nutrients at the mouth of a river lead to acidic sulfate formation in sedimentation which negatively impacts shrimp. After sediment has settled to the ocean floor, it can also affect the environment by releasing its nutrients into the surrounding water when agitated by the tides or practices such as bottom trawling. Researchers Cheng, Zeng, Guo and Zhu (2014), performed a study in Daya Bay, a popular site for cage-based aquaculture farms in China. The researchers measured the release rates of nitrogen as ammonia and phosphorus as dissolved reactive phosphorus (DRP) from bottom sediment. Ammonia and DRP were released from sediments in this area at a rate twice as fast as those in Fubao Bay, which is not populated by aquaculture. The researchers concluded “the nitrogen and phosphorus pollution in the aquaculture area of Daya Bay is pretty serious… the release rates of nitrogen and phosphorus are so large that they will have an effect on water body for several years, even if the nutrients from outer sources are controlled effectively” (p. 1567).

Young and Matthews (2010) wrote a book on the controversy of the aquaculture industry in Canada. In Canada, it has become more than just an issue for the natural sciences, but an issue in politics and for the public. There are some people who argue that aquaculture is purely beneficial, and others who believe the practice hurts more than it helps. The authors took a survey of comments from people on both sides of the issue, and thirty three percent of respondents said aquaculture poses no threat to humans. However, that is not the case. Aquaculture not only impacts the environment, but also the economy and poses a threat to human health. Red tide, a massive form of algal bloom, can cause the closing of beaches. This can hit local economies hard by reducing revenue from tourism and the fishing industry. According to the National Oceanographic and Atmospheric Administration (NOAA) algal blooms cost the United States $82 million each year. Red tide can also cause illnesses in humans, especially for those with asthma or other upper respiratory illnesses, who breathe in the air coming off the coast. For those who like to eat seafood, there is an additional risk present. Watkins, Reich, Fleming and Hammond (2008) state, “Neurotoxic shellfish poisoning is caused by consumption of molluscan shellfish contaminated with brevetoxins primarily produced by the dinoflagellate, Karenia brevis” (p. 1). Blooms of Karenia brevis are what constituted the Florida red tide. When ingested, eating these contaminated shellfish can lead to nausea, vomiting, dizziness, and possible hospitalization. According to Wagstaff (2014), hundreds of Florida’s 5,000 endangered manatees have been killed, and 100 dead dolphins have been washed up on the coast. Upon necropsy, scientists found fish contaminated from the algae in their stomachs. Cyanobacteria are another type of prokaryote that form blooms and require both nitrogen and phosphorus for growth. According to the National Ocean Service (2016), Cyanobacteria secrete toxins that cause paralytic shellfish poisoning, are harmful to the liver, and can promote tumors.

To address this issue, stricter federal regulations are necessary in order to reduce the amount of nutrient and sediment pollution that is released into the environment as a result of intensive aquaculture operations. This is accomplished by regulating the contents, as well as the feeding practices, of current aquaculture operations. Current operations tend to use trash fish as the primary source of food. This leads to high levels of nutrient and sediment pollution as described previously. To combat that, highly researched feeds aimed to promote nutrient retention must be formulated and produced to fit each species being farmed. For example, by selecting grains low in phytate for the formulation of trout feeds, less phosphorus will be released by the fish (Bureau 2010). Also, the selection of high-energy feeds is another management tool that can be used to reduce waste. The use of nutritionally adequate dry feeds reduces waste outputs in marine net pens by fifty percent while having the same growth rates (Bureau 2010). Recently the high-energy extruded pellet has been shown to increase feed conversions in trout without a reduction in growth, thereby reducing waste (Bureau 2010). In regards to feeding practices, administering floating feed reduces sedimentation and helps train farmers on the proper amount of feed to administer during each feeding, as the uneaten food remains visible at the surface (Miller & Semmens, 2002). Federal implementation regulating aquaculture feeds and feeding practices will result in less nutrient and sediment pollution that can be emitted into the environment.

According to Bailly and Willmann (2001), in order to reach high levels of participation, economic and other incentives must be given to farmers to reduce the amount of pollution that results from aquaculture operations. For example, a pollution tax, taxing a farmer for the amount of pollution outputted from his/her operation, can incentivize the reduction of pollution transferred to the environment. That would work, because the more the farm pollutes, the higher the tax the farm is going to have to pay. In order to save money it is in the farm’s best interest to lower pollution levels. Other incentives such as subsidies should also be implemented to further a reduction in pollution. By offering subsidies to farms that choose to be more environmentally friendly, the government can encourage farms to produce less pollution. For example a farm that purchases high-energy extruded pelleted feed is more likely to purchase this more expensive feed if given a subsidy. The use of economic and other incentives from the federal government will help promote a more sustainable aquaculture industry (Bailly & Willmann 2001).

A change in feed does not come cost-free, however. Changing to a nutrient-rich feed is more expensive than the latter on a pound-per-pound basis due to the fact that with nutrient-rich feed, more is paid upfront (Bureau 2010). However, what is not factored into the price, is the amount of feed that would be necessary for each feeding. Using a nutrient-rich feed would in theory require less feed if you were to compare the two types of feed side by side, which in turn would reduce the cost of a single feeding, despite the increased cost of a nutrient-rich feed over normal trash fish feed. While cheap trash fish feeds are less expensive than nutrient-rich feeds, cheap trash fish feeds come with the hidden cost of excess pollution and its cost to clean up, as described earlier with regards to red tide and eutrophication events (Bureau 2010).

In conclusion, aquaculture has a negative effect on the environment through both sediment and nutrient pollution. This pollution is produced largely due to inefficient feed composition and feeding practices. It causes eutrophication, which can lead to significant damage to the natural environment. Implementing new feed regulations such as nutrient-rich floating feed will reduce waste without lowering growth rate and production and overfeeding will be caught and in turn nutrient pollution will decrease. With federal help, it is possible to efficiently and sustainably operate intensive aquaculture systems that lessen the effects of sediment and nutrient pollution on the environment.


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