Human interactions within the ecosystem may have a positive impact on biodiversity such as conservation or a negative affect such as eutrophication. Negative effects include reduced populations, reduced biodiversity or extinction.
As the human population increases, we need more food and increased use of fertilisers has impacted on the biodiversity of aquatic environments through eutrophication. Nitrates in the fertilisers run off from fields into rivers and lakes causing the overgrowth of algae. The light is blocked so plants cannot photosynthesise so they die. This causes bacteria to decompose the plants and use up most of the oxygen in the water. Without oxygen, animals such as fish will die. This is a negative impact as the biodiversity of the river or lake will decrease.
Fish are farmed in large nets or tanks within lakes or in the sea.
Farm waste, chemicals, pathogens and parasites are released into the surrounding water, harming other marine life.
Carnivorous species of farmed fish, such as salmon, need high amounts of protein in their diet. They are often fed on wild fish, reducing their populations.
Sometimes fish can escape and compete with indigenous wild species and compete for resources, resulting in reduced biodiversity. Predators of the fish such as sea lions can become trapped in the nets and die.
A non-indigenous species does not live in an area and may be introduced by humans for a particular purpose such as removal of pest species or for hunting. However, the new species may out-compete or kill indigenous or naturally occurring species. These may be reduced in number, resulting in reduced biodiversity or maybe extinction.
One example is the introduction of cane toads to Australia.
Cane toads are native to South and Middle America but were introduced into Australia in the 1930s to control pests that ate sugar cane, an important crop.
Since their release, the toad population has grown to over 200 million and spread across the country. They have several impacts on biodiversity: