Mariculture
Aquaculture in the sea, ie the controlled or sensibly planned and accordingly carried out rearing of aquatic organisms in the sea, is also referred to as mariculture .
It is mostly based on net cages in the sea, in which z. B. Salmon are raised. The enclosure can also be omitted. In its place, there are structures that offer protection or a basis for reproduction, which are not intended to facilitate the catch, but rather make it more difficult at certain points, especially since there is a clear relationship between the fertilization rate, fishing success and cost pressure to which the fishermen have to submit. The lower the fertilization rate of the occurring fish, the closer the network of disturbance points is woven and the more often fishermen have to haul in their nets again. The tightness of these "disturbing" points is chosen so that the nets can only be held in tow from point A to point B, so that you do not want to lose the catch and the net at these points. The combination of wind, tidal and current power plants with protective devices anchored on the sea floor is a useful addition. In this way, fish can be conditioned very well to sound . In the open sea only those “points” are targeted by fish that offer some kind of protection or reproduction basis.
Economically important are the rearing of different shells such as from oysters and mussels as well as the Platzhalte- and maintained action on appropriate walking routes to the spawning grounds.
Other areas of mariculture are micro and macro algae production for feeding seedling cultivation or for obtaining z. B. Agar-agar .
Ecological problems
Through the mariculture of allochthonous species , ie the keeping of living beings outside of their natural distribution such. B. of the Pacific mussels Tapes philippinarum ( Japanese carpet mussel ) or Crassostrea gigas ( Pacific oyster ) in Europe, native species are displaced and the species composition changes. Ultimately, there is usually a decline in biodiversity and, ultimately, a decline in biomass production .
The construction of new facilities and the use of heavy equipment to sow and harvest the mussels also have a significant environmental impact. The type of fishing - e.g. B. Bottom trawl fishing , suction devices - leads to a general disturbance of the equilibrium and to a change in the seabed with possible negative effects on the benthic fauna, which is important as food for fish and water birds . Further effects are a general change in the equilibrium of the sedimentation rhythm and the chemical composition of the sediments. Feeding often leads to pollution and eutrophication of the waters.
The establishment of alien species also increases the risk of parasites being spread. Due to the intensive management - z. For example, there are often 2000 copies of Japanese clam tapes per square meter of seabed - the parasites can multiply explosively. The complex life cycles of most parasites also affect the food chain and the entire ecosystem .
Since mariculture has not been practiced for a long time in many areas, there are few or no studies on the long-term effects on the ecology and economy of the fishing areas.