The number of offshore wind farms is increasing rapidly, leading to questions about the environmental impact of such farms. In the Netherlands, an extensive monitoring programme is being executed at the first offshore wind farm (Offshore Windfarm Egmond aan Zee, OWEZ). This letter compiles the short-term (two years) results on a large number of faunal groups obtained so far. Impacts were expected from the new hard substratum, the moving rotor blades, possible underwater noise and the exclusion of fisheries. The results indicate no short-term effects on the benthos in the sandy area between the generators, while the new hard substratum of the monopiles and the scouring protection led to the establishment of new species and new fauna communities. Bivalve recruitment was not impacted by the OWEZ wind farm. Species composition of recruits in OWEZ and the surrounding reference areas is correlated with mud content of the sediment and water depth irrespective the presence of OWEZ. Recruit abundances in OWEZ were correlated with mud content, most likely to be attributed not to the presence of the farm but to the absence of fisheries. The fish community was highly dynamic both in time and space. So far, only minor effects upon fish assemblages especially near the monopiles have been observed. Some fish species, such as cod, seem to find shelter inside the farm. More porpoise clicks were recorded inside the farm than in the reference areas outside the farm. Several bird species seem to avoid the park while others are indifferent or are even attracted. The effects of the wind farm on a highly variable ecosystem are described. Overall, the OWEZ wind farm acts as a new type of habitat with a higher biodiversity of benthic organisms, a possibly increased use of the area by the benthos, fish, marine mammals and some bird species and a decreased use by several other bird species.
During a study on population dynamics of copepods in the southern North Sea some semiin-situ experiments were performed on predation by adult copepods on CO-occurring nauplii. In a period with a strong decline in naupliar abundance, experimental naupliar mortality by cannibalism amounted to 35% of the standing stock per day. Simultaneous observations on chlorophyll a and &atom concentrations in situ and on egg production by adult females suggested poor food conditions for adults. There appeared to be a tendency for increased predatory behaviour in the absence of other food, indicating the possible importance of cannibalism as a factor in naupliar mortality. Microscopic observations and a series of experiments on laboratory cultured Temora longicornis revealed adult female predation on stages N I through N V. Rates of capture declined with ascending developmental prey stage. Prey-specific predation rates increased continuously with prey density, but were significantly depressed m the presence of alternative algal food. Estimates of naupliar mortality in situ due only to cannibalism, based on experimentally determined predation rates, explained 5 to over 100 % of the estimated total naupliar mortality. It is suggested that cannibalism may act as a major factor in naupliar mortality and may contribute significantly to a rapid fall in naupliar densities in periods of algal food shortage.
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