Het Friese Front: hydrografie, geologie en biologie, met nadruk op de zeevogels

On the Dutch continental shelf in the North Sea a sudden transition exists between the shallow (ca. 25 m) waters of the Broad Forteens in the southern half, and the deeper Oyster Grounds (ca. 50 m) in the north. Between these two areas of sea a sudden increase in water depth is accompanied by dropping tidal current velocities, resulting in deposition of mud and detritus on the bottom. Between the 30 and 40 m depth contours, a narrow zone is found with a high mud and organic carbon content, and abundant benthic life. This rich zone is known as the Frisian Front. As a result of the high local remineralisation of detritus, and possibly further enhanced by mixing water masses of different origin and nutrient load, phytoplankton may be relatively abundant during periods of good weather in summer. The benthic and pelagic production is consumed by a large numbers of animal species, at all trophic levels. Several species of demersal and pelagic fish are locally abundant, attracting both seabirds and human fishermen. The offal and discards produced by the fishing operations attract scavenging seabirds to the area, while schools of small pelagic fish (clupeids and scad) attract large numbers of Guillemots, particularly shortly after the breeding season and in winter. The hydrography of the southern North Sea prevents particles with neutral or slightly negative buoyancy from being deposited south or west of the front. Therefore, such particles tend to accumulate at the front, enriching marine life. On the other hand, the influence of pollutants, from discharges at the front itself or from areas to the south or west of the area, may also have a large impact on the life at the front.