BioConsult SH

Husum, Germany

BioConsult SH

Husum, Germany
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Reise K.,Alfred Wegener Institute for Polar and Marine Research | Buschbaum C.,Alfred Wegener Institute for Polar and Marine Research | Buttger H.,BioConsult SH | Rick J.,Alfred Wegener Institute for Polar and Marine Research | Wegner K.M.,Alfred Wegener Institute for Polar and Marine Research
Marine Biology | Year: 2017

Invasion trajectories of introduced alien species usually begin with a long establishment phase of low abundance, often followed by exponential expansion and subsequent adjustment phases. We review the first 26 years of feral Pacific oysters Crassostrea gigas around the island of Sylt in the Wadden Sea (North Sea, NE Atlantic), and reveal causal conditions for the invasion phases. Sea-based oyster farming with repeated introductions made establishment of feral oysters almost inevitable. Beds of mussels Mytilus edulis on mud flats offered firm substrate for attachment and ideal growth conditions around low tide level. C. gigas mapped on to the spatial pattern of mussel beds. During the 1990s, cold summers often hampered recruitment and abundances remained low but oyster longevity secured persistence. Since the 2000s, summers were often warmer and recruitment more regular. Young oysters attached to adult oysters and abundances of >1000 m−2 were achieved. However, peak abundance was followed by recruitment failure. The population declined and then was also struck by ice winters causing high mortality. Recovery was fast (>2000 m−2) but then recruitment failed again. We expect adjustment phase will proceed with mean abundance of about 1000 m−2 but density-dependent (e.g., diseases) and density-independent (e.g., weather anomalies) events causing strong fluctuations. With continued global warming, feral C. gigas at the current invasion fronts in British estuaries and Scandinavian fjords may show similar adjustment trajectories as observed in the northern Wadden Sea, and also other marine introductions may follow the invasion trajectory of Pacific oysters. © 2017, The Author(s).

PubMed | University of Groningen, Bielefeld University and BioConsult SH
Type: Journal Article | Journal: PloS one | Year: 2015

Parents may adapt their offspring sex ratio in response to their own phenotype and environmental conditions. The most significant causes for adaptive sex-ratio variation might express themselves as different distributions of fitness components between sexes along a given variable. Several causes for differential sex allocation in raptors with reversed sexual size dimorphism have been suggested. We search for correlates of fledgling sex in an extensive dataset on common buzzards Buteo buteo, a long-lived bird of prey. Larger female offspring could be more resource-demanding and starvation-prone and thus the costly sex. Prominent factors such as brood size and laying date did not predict nestling sex. Nonetheless, lifetime sex ratio (LSR, potentially indicative of individual sex allocation constraints) and overall nestling sex were explained by territory quality with more females being produced in better territories. Additionally, parental plumage morphs and the interaction of morph and prey abundance tended to explain LSR and nestling sex, indicating local adaptation of sex allocation However, in a limited census of nestling mortality, not females but males tended to die more frequently in prey-rich years. Also, although females could have potentially longer reproductive careers, a subset of our data encompassing full individual life histories showed that longevity and lifetime reproductive success were similarly distributed between the sexes. Thus, a basis for adaptive sex allocation in this population remains elusive. Overall, in common buzzards most major determinants of reproductive success appeared to have no effect on sex ratio but sex allocation may be adapted to local conditions in morph-specific patterns.

Brandt M.J.,BioConsult SH | Hoschle C.,BioConsult SH | Diederichs A.,BioConsult SH | Betke K.,Institute for Technical and Applied Physics itap | And 3 more authors.
Aquatic Conservation: Marine and Freshwater Ecosystems | Year: 2013

Although seal scarers are widely used both to reduce economic losses at fish farms caused by seal predation and to reduce risks posed to marine mammals by offshore pile driving activities, the spatial extent of their deterrent effect on harbour porpoises is still largely unclear. However, this information is crucial to understanding the effects these devices have on the marine environment and to judge their potential as a mitigation measure. A study was conducted in the German North Sea, using passive acoustic monitoring and to some extent simultaneous aerial surveying to specifically study the spatial extent of the deterrence effects of a seal scarer on harbour porpoises. In order to link porpoise detections at various distances to actual sound levels, sound measurements of the seal scarer signal were carried out at several distances from the source. C-POD recordings revealed a significant deterrence effect on harbour porpoises up to 7.5 km away (at about 113 dB re 1 μParms), much further than previously reported. During seal scarer operation the number of porpoise detections within 750 m of the C-PODs decreased by between 52 and 95% of the value before the seal scarer was activated. An aerial survey revealed a significant decrease in porpoise density from 2.4 porpoises km-2 before to 0.3 porpoises km-2 during seal scarer operation within the 990 km2 study area, showing that the decrease in porpoise detections by passive acoustic monitoring was probably indeed the result of a decrease in porpoise abundance. These results may raise serious concerns about unwanted disturbance effects on harbour porpoises in the context of seal scarer use at fish farms and also highlight the need for caution when applied as a mitigation measure during offshore construction. © 2012 John Wiley & Sons, Ltd.

Grunkorn T.,BioConsult SH | Potiek A.,Bielefeld University | Looft V.,University of Kiel | Jonker R.M.,Bielefeld University | And 2 more authors.
Journal of Avian Biology | Year: 2014

Density-dependent reproduction is commonly explained by either the habitat heterogeneity (HHH) or individual adjustment (IAH) hypothesis. Under the HHH, high quality territories are assumed to be occupied first. At higher density, occupation of low-quality territories increases due to lower availability of high-quality territories, which reduces mean reproductive success. Alternatively, the IAH assumes that increased competition at higher densities reduces reproductive success in all territories. For birds of prey, HHH plays an important role in territorial species, and IAH in socially breeding species. To test the generality of this hypothesis, we studied the mechanism behind density dependence in raven Corvus corax, a long-lived passerine bird, using long-term population data from a large number of territories. Population density decreased reproduction, which was explained by increased usage of low quality territories at higher density, supporting the HHH. Density reduced reproduction in low quality territories, but not in high and intermediate quality territories. We additionally compared the explanatory power of different models describing brood size, representing IAH, HHH, or a combination of both. The best model represented a combination of both hypotheses, in which the effect of density depended on territory quality. Our conclusion that both IAH and HHH are supported can be explained by the biology of ravens, where territorial adults not only experience interference competition with other territorial adults, but also with social groups of juveniles and floaters. We conclude that the relative importance of IAH and HHH may depend on variation in territory quality and social structure. © 2013 The Authors.

Brandt M.J.,BioConsult SH | Hoschle C.,BioConsult SH | Diederichs A.,BioConsult SH | Betke K.,Institute for Technical and Applied Physics ITAP GmbH | And 2 more authors.
Marine Ecology Progress Series | Year: 2013

Offshore pile driving, e.g. during wind farm construction, produces substantial noise emissions into the water column, which may harm marine mammals. Therefore, it is common practice to attempt to deter the mammals out of potential danger zones beforehand. Seal scarers are commonly used as a deterrent for harbour porpoises in spite of a lack of clear evidence in support of their effectiveness. We investigated the responses of harbour porpoises to a Lofitech seal scarer by conducting visual observations in conjunction with sound measurements. Porpoise sighting rates within 1 km of the seal scarer significantly decreased to only 1% during seal scarer activity. During 22 trials, when the seal scarer was deployed between 300 m and 3.3 km distance, all observed porpoises always avoided the seal scarer within 1.9 km (translating to sound levels of ≥122 dB re 1 μParms), avoided the seal scarer half the time within 2.1 to 2.4 km (119 to 121 dB re 1 μParms) and never avoided the seal scarer at distances beyond 2.6 km (≤118 dB re 1 μParms). The closest observed approach distance of a porpoise to the activated seal scarer was 798 m (132 dB re 1 μParms). Thus, the deployment of a Lofitech seal scarer during offshore pile driving activities can greatly reduce the risk of acoustic traumata to harbour porpoises. However, danger zones and thus the necessary deterrence zones have to be calculated specifically for each project based on measurements of sound transmission in the area. © Inter-Research 2013.

Welcker J.,BioConsult SH | Nehls G.,BioConsult SH
Marine Ecology Progress Series | Year: 2016

The number of offshore wind farms in Europe and elsewhere has substantially increased in recent years. This rapid development has raised concerns about potential impacts on marine wildlife, particularly on seabirds, as these can be negatively affected through collision and displacement. While collision risk has been the focus of a number of studies, information about displacement of seabirds is scarce. Here we present data from an extensive survey program that aimed at determining the effects on seabirds of the first German offshore wind farm, 'alpha ventus'. Data were collected by line transect surveys during the first 3 yr of operation. We found significant displacement of 5 species with 75-92% lower abundance inside compared to outside the wind farm. For 3 species, the response distance to the outermost turbines was estimated to exceed 1 km. Two gull species were attracted to the wind farm site. Our results and a review of the available literature revealed good agreement with respect to the sign of the response (avoidance vs. attraction) but considerable differences in the strength of the response and the spatial extent of the disturbance outside the footprint of wind farms. While it seems unlikely that small-scale displacement by single wind farms would have an impact at the population level, the extent of the proposed development of offshore wind energy warrants further research into cumulative effects and their biological significance for seabird populations. © Inter-Research 2016.

Folmer E.O.,Netherlands Institute for Sea Research | Drent J.,Netherlands Institute for Sea Research | Troost K.,Institute for Marine Resources and Ecosystem Studies | Buttger H.,BioConsult SH | And 6 more authors.
Ecosystems | Year: 2014

Intertidal blue mussel beds are important for the functioning and community composition of coastal ecosystems. Modeling spatial dynamics of intertidal mussel beds is complicated because suitable habitat is spatially heterogeneously distributed and recruitment and loss are hard to predict. To get insight into the main determinants of dispersion, growth and loss of intertidal mussel beds, we analyzed spatial distributions and growth patterns in the German and Dutch Wadden Sea. We considered yearly distributions of adult intertidal mussel beds from 36 connected tidal basins between 1999 and 2010 and for the period 1968-1976. We found that in both periods the highest coverage of tidal flats by mussel beds occurs in the sheltered basins in the southern Wadden Sea. We used a stochastic growth model to investigate the effects of density dependence, winter temperature and storminess on changes in mussel bed coverage between 1999 and 2010. In contrast to expectation, we found no evidence that cold winters consistently induced events of synchronous population growth, nor did we find strong evidence for increased removal of adult mussel beds after stormy winter seasons. However, we did find synchronic growth within groups of proximate tidal basins and that synchrony between distant groups is mainly low or negative. Because the boundaries between synchronic groups are located near river mouths and in areas lacking suitable mussel bed habitat, we suggest that the metapopulation is under the control of larval dispersal conditions. Our study demonstrates the importance of moving from simple habitat suitability models to models that incorporate metapopulation processes to understand spatial dynamics of mussel beds. The spatio-dynamic structure revealed in this paper will be instrumental for that purpose. © 2014 The Author(s).

Witte S.,BioConsult SH | Buschbaum C.,Alfred Wegener Institute for Polar and Marine Research | van Beusekom J.E.E.,Alfred Wegener Institute for Polar and Marine Research | Reise K.,Alfred Wegener Institute for Polar and Marine Research
Biological Invasions | Year: 2010

Invading alien species may have to await appropriate conditions before developing from a rare addition to the recipient community to a dominance over native species. Such a retarded invasion seems to have happened with the antipodean cirripede crustacean Austrominiusmodestus Darwin, formerly known as Elminius modestus, at its northern range in Europe due to climatic change. This barnacle was introduced to southern Britain almost seven decades ago, and from there spread north and south. At the island of Sylt in the North Sea, the first A. modestus were observed already in 1955 but this alien remained rare until recently, when in summer of 2007 it had overtaken the native barnacles Semibalanus balanoides and Balanus crenatus in abundance. At the sedimentary shores of Sylt, mollusc shells provide the main substrate for barnacles and highest abundances were attained on mixed oyster and mussel beds just above low tide level. A. modestus ranged from the upper intertidal down to the subtidal fringe. Its realized spatial niche was wider than that of the two natives. We suggest that at its current northern range in Europe a long series of mild winters and several warm summers in a row has led to an exponential population growth in A. modestus. © 2010 Springer Science+Business Media B.V.

Conservation decisions often rely on defining a reference status for habitats and species to enable targets to be set and progress measured. Long-lasting and continual anthropogenic impacts on habitats and species make the setting of undisturbed reference values such as diversity, distribution, population size or other ecological characteristics, difficult. In turn this hampers assessment of ecological status.Within the Wadden Sea, intertidal blue mussel beds are important biogenic structures which can be clearly defined from the surrounding flats. As mussel beds are highly productive habitats, they are considered as biological quality indicators for coastal waters. Nonetheless the reference status provokes controversy in discussions between policymakers, stakeholders and researchers. In order to build on existing knowledge of intertidal blue mussel beds in the North Frisian Wadden Sea, we analysed aerial photographs from the 1930s, 1958, 1989, 1998 and 2010. We supplemented this remote sensing data with annual monitoring data from 1999 to 2009 obtained from analysis of aerial photographs and field surveys.Results show a generally high persistency of blue mussel beds likely over eight decades, although sites were probably not permanent throughout the time period and their areal extent had changed. Mussel beds occur mainly on the east side of the islands which provide shelter against storms from the west. Studies of aerial photographs for the 1930s and 1958 demonstrate the importance of historical data to an assessment of the current status of the beds. In particular they help assess the distribution and extent of mussel beds over time. © 2013 Elsevier B.V.

Buttger H.,BioConsult SH | Nehls G.,BioConsult SH | Witte S.,BioConsult SH
Helgoland Marine Research | Year: 2011

Mortality of introduced Pacific oysters (Crassostrea gigas) was studied in the northern Wadden Sea in response to an ice winter. After a decade of mild winters, in January and February 2010, the first severe winter occurred since the Pacific oysters became dominant on former intertidal blue mussel (Mytilus edulis) beds in the North-Frisian Wadden Sea. After the ice winter, mortality of Pacific oysters on densely populated beds in the List tidal basin reached about 90%, indicating much higher losses in comparison to former mild winters. At lower densities between the islands of Amrum and Föhr, oysters were less or even not affected. Although Pacific oysters are assumed to be very tolerant to frost, the duration of cold water- and air temperatures accompanied by mechanical stress of the ice burden might have caused the high mortality in the winter 2009/2010 in formerly dense beds. © 2011 Springer-Verlag and AWI.

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