Aquaculture is also in direct competition with natural marine and freshwater habitats for space.
For example, marine fish farms often need the shelter of bays and estuaries to avoid damage from storms and currents. In addition, farmed fish need good water quality, frequent water exchange, and other optimal environmental conditions.
But these locations are also very often ideal for wild fish and other marine life.
Some European fish farms have been placed in the migratory routes of wild salmon, while in Asia and Latin America, mangrove forests have been cleared to make space for shrimp farms.
Landfills, harbours, shipping channels, fisheries and aquaculture (fish farms) occupy or destroy areas that cetaceans need for feeding, resting and breeding.
The deposition/ accumulation of
organic matter farming shellfish can have signicant feefects on bottom-dwelling invertebrates. Potential loss or reduced diversity through
smothering of sea bed
habitats and through oxygen depletion and hydrogen sulphide
production during bacterial decomposition of organic matter;
leads to community domination by a small
number of pollution indicator
species, such as capetellid worms and other scavengers and
deposit feeding species.
Industrial scale and congested aquaculture facilities often create pollution leading to severe habitat destruction, The pollution comes from faeces and food wastes flushed into the surrounding environment, The siting of culture facilities often does not take into consideration their interaction with the surrounding environment. They are often placed in inappropriate locations where environmental damage and/or aesthetic problems are maximized.
Nowhere are the negative impacts on the natural environment more apparent than with shrimp farming and the associated destruction of mangrove forests. In Asia, over 400,000 hectares of mangroves have been converted into brackishwater aquaculture for the rearing of shrimp. Farmed shrimp boost a developing country's foreign exchange earnings, but the loss of sensitive habitat is difficult to reconcile. For example, shrimp ponds are often constructed by cutting down mangrove habitats along tropical coastlines. This activity has been responsible for the loss of two-thirds of mangrove forests in the Philippines, more than half in Thailand, and more than a fourth in Ecuador.
Tropical mangroves are analogous to temperate salt marshes, a habitat critical to erosion prevention, coastal water quality, and the reproductive success of many marine organisms. Mangrove forests have also provided a sustainable and renewable resource of firewood, timber, pulp, and charcoal for local communities. To construct dyked ponds for shrimp farming, these habitats are razed and restoration is extremely difficult.
Unfortunately, shrimp ponds are often profitable only temporarily as they are subject to disease and to downward shifts in the shrimp market. Growing political pressure in western countries may restrict the shrimp market in response to consumers' avoidance of environmentally-unfriendly products. More significantly, Japan's economy is experiencing difficulty at present, and Japan is the world's largest market for shrimp; when the market falls, ponds are abandoned. A return to traditional fishing is not always possible because the lost mangroves no longer serve as nursery areas which are critical for the recruitment of many wild fish stocks. Unemployment prospects cannot always balance short-term gains. It is clear that socio-economic effects are as important as pollution and ecological damage when evaluating the sustainability of aquaculture.
Aquaculture, if not managed and designed correctly can destroy vast quantities of natural biota and release large quantities of nutrients into the surrounding region. As shown in the photo of a fish farm to the right, large quantities of land can be converted into fish ponds, destroying much of the original biota. The shrimp farming industries destruction of mangrove swamps is a popular target for this criticism. However, the practice of locating shrimp farms in mangrove forests has diminished as it has proven to be a poor site for shrimp culture.