II. FACTORS CAUSING THE DECREASING OF OYSTER REEFS.
Nowadays in many literature are represented the most important threats for oyster beds, as overharvest, development and pollution, changes in freshwater inflows, erosion from boats, diseases, invasive species, global change… (Coen et al. 2000; Seavey et al. 2011; Gregalis et al. 2008; Piazza et al. 2005).
1. Overharvest. Overharvest is one of the major threats to oysters worldwide (Beck et al 2011; Seavey et al. 2011). At the beginning of oyster harvest history, oysters were collected hand picking. Although, as the public demand increase, farmers develop new techniques, that allow the collections of bigger volumes of oysters, in less time. These techniques would end up with a destruction
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But some of these shrimps just moved into the oyster reef when the predators are present, but they don´t go in absence of predator. (Coen et al. 2000)
In the oyster reefs three different categories of species could be defined: Reef residents are those species which use the reef as their primary habitat; facultative residents are those species generally associated with structure habitats, and finally transient species are those species which forage or may forage on or near the oyster reef, consider as a wide-ranging. (Coen et al. 2000)
Resident reef fish species, use these special microhabitats created in the reef, for theis reproduction, laying eggs on the side of some shells, underside of the shells … Oyster reefs, create an special environment for fish larvae, due to the crurents created by the reef. (Coen et al. 2000)
Not only fish species colonize the oyster reef, also micro-organisms and small macro-organisms species, colonize oyster shells surfaces. The oyster reef includes many food web levels. Reef species attract many other grazers, browsers and predators. Attached and infaunal sessile plants and animals complete the ecosystem (Hargis et al.