Experiences with beach nourishments in Portugal== |+|
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red_cliffs.jpg|thumb|250px|right| Figure 1: Red sand cliffs [http: //www. dragapor. com (source: DRAGAPOR - Dragagens de Portugal, S. A. ]). ]] |+|
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|−|Vale do Lobo beach is located on the south Portuguese Coast at Quarteira, between Albufeira and Faro in the district of Loulé, about 5km east of Vilamoura. | |
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|−|The cliffs of Vale do Lobo beach are almost vertical formations of red ''Pleistocene'' sands (see also Figure 1). This [[ shoreline]] stretch is characterised by a set of high cliffs, composed of highly fractured formations with weak cohesion, and a narrow subjacent beach. The base of the cliffs is often hit by breaking waves, especially in winter. The width of the subjacent beach is the main factor on which the evolution of the cliffs depends, as it is the main protection against waves breaking directly on the cliffs. |+|
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Revision as of 12:12, 2 January 2008
Effects of fisheries on European marine biodiversity
Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. Journal of Northwestern Atlantic Fishery Science
Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the primary production is required to sustain fisheries in many intensively fished coastal ecosystems.
Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and by-catch
species; an important physical impact on the habitat of benthic organisms is caused by bottom trawling
. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that piscivorous
fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.
- ↑ Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. Nature 374: 255-257.
- ↑ Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. Adv. Mar. Biol. 34: 201-352.