Human activities along the coast and in open ocean areas can result in the addition of chemicals, particles, and other waste materials into the marine environment.
- The addition of nutrients into the ocean can change levels of primary production. Primary producers are often nutrient limited, so growth increases rapidly when nutrients are added. Fast-growing primary producers can deplete nutrients in the surrounding water. When necessary nutrients run out, primary producers will die and begin to decompose. Oxygen in the surrounding water is rapidly used up by decomposers, creating large areas of the ocean with very lot oxygen levels, called dead zones.
- Sometimes nutrient addition favors the growth of some species of primary producers over others, which can cause shifts in they types of species that make up an ecosystem. This can then effect the way the ecosystem functions.
- Toxic materials can be absorbed or consumed by primary producers or consumers, which may affect their physiological processes or even cause them to die. Species that consume these primary producers or consumers can incorporate these toxic chemicals into their bodies. Toxins accumulate in consumers over time as they continually consume affected organisms. Humans that consume species with toxic chemicals in their tissues are also at risk of negative impacts.