The right species: trophic position predicts impact
So as stated in the previous post, aquaculture has the potential to be a sustainable method of food production depending on the combination of species, location, and scale. In this post, let’s explore what factors make a species “right” for aquaculture from an ecological sustainability perspective?
We first need to consider the realities of a food web or the trophic levels of an ecosystem. The basic idea is that the higher an animal is positioned in the food web the more energy it takes to grow that animal. Ecology tells us that 90% of the energy is lost for every level that you go up the food web (or higher trophic levels). To visualize this, think of an African Savannah with abundant grasses and insects, the wildebeest and zebra are abundant but not as abundant as the grasses and insects, and the lions and leopards even less abundant than the wildebeest and zebra. Each level of a food web is limited by how much energy there is available and therefore the number of animals decreases as you go higher.
If we apply this idea to aquaculture we see that it takes a lot of energy to farm an animal that is at the top of the food web (e.g. tuna or salmon) and much less to farm something that is closer to the bottom (e.g. seaweed or shellfish). Consider that as a general rule, impact is correlated with the amount of inputs (e.g. feed, chemicals, etc) that are used in aquaculture production because the more inputs you require the more likely that it is that you will have an impact. With this in mind, it’s easy to see why salmon and tuna can have far greater impacts than shellfish or seaweed farms. They simply require more energy or inputs for production. Therefore, a general conclusion is that the lower an animal is on the food web the less likely its production will have a significant impact on the environment. This is the first important factor that makes a species a good or bad candidate for aquaculture. Exceptions of course can happen when the scale and location of production is not appropriately considered (we will explore that in future posts).
While the position of the animal in the food web is only one factor predicting the environmental impact. In the next few posts we will explore a few more reasons.