Reise, Karsten

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    Item-typ:Veröffentlichung,
    Annual Dynamics of Pelagic Carbon Fluxes in a Tidal Lagoon
    (2006-01-19)
    Loebl, Martina
    ;
    Reise, Karsten
    ;
    Smetacek, Victor
    ;
    Beusekom, Justus van
    In aquatic ecosystems, phytoplankton primary production, zooplankton grazing, and pelagic respiration are important processes of carbon dynamics. The aim of this study is to quantify the annual dynamics of pelagic primary production, zooplankton grazing, and respiration in a shallow coastal system and to investigate possible benthic impacts. Pelagic primary production, zooplankton grazing, and respiration were investigated as weekly/monthly time series over a one year period in the northern Wadden Sea. Studies were related to the Sylt long term time series, providing data on temperature, salinity, inorganic and organic nutrients, chlorophyll a and suspended matter concentrations (e.g. MARTENS&ELBRÄCHTER 1998). This study was conducted in the framework of the European Research Project COSA (Coastal Sands as Biocatalytical Filters) to relate the temporal dynamics of pelagic carbon dynamics with benthic processes.
    Dissertation
      267  154
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    Item-typ:Veröffentlichung,
    Ecosystem engineering in intertidal sand by the lugworm Arenicola marina
    (2006-12-21)
    Volkenborn, Nils
    ;
    Reise, Karsten
    ;
    Arntz, Wolf E.
    Large-scale permanent experimental exclusion of bioturbating lugworms (Arenicola marina) from intertidal sand revealed manifold implications of this polychaete for ecosystem functioning. Sediment properties, biogeochemical processes and the benthic community were analysed over a three year period on six lugworm exclusion areas, each 400 m2, and corresponding lugworm populated plots. Lugworms reduced microphytobenthic biomass and prevented a clogging of the sediment with fine particles maintaining sediment permeability and facilitating sediment-water exchange. Changes in sediment properties caused a functional shift in the benthic community from tube-building worms to discretely motile worms. Sediment mediated effects of an ecosystem engineer on associated species appear to be subtle and contingent in a variable environment.
    Dissertation
      422  310
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    Item-typ:Veröffentlichung,
    IMPACTS OF NON-NATIVE FISHES ON THE FISH COMMUNITY AND THE FISHERY OF THE CIENAGA GRANDE DE SANTA MARTA ESTUARY, NORTHERN COLOMBIA
    (2008-02-08)
    Leal-Florez, Jenny
    ;
    Reise, Karsten
    ;
    Saint-Paul, Ulrich
    ;
    Wolff, Matthias
    In tropical coastal ecosystems very little is known about the impacts of non-native fish species on the native ichthyofauna and to the author's knowledge, there are no published studies focusing on Caribbean estuaries. This study aims to determine the impacts of the non-native fish Oreochromis niloticus on the abundance, species composition, feeding habits and fishery of native fishes, as well as the impacts of the non-native fish Trichogaster pectoralis on the abundance of native ichthyofauna, in the Cienaga Grande de Santa Marta estuary, Northern Colombia. No clear evidence has been found that indicates a negative impact of O. niloticus and T. pectoralis on the abundance and species composition of the native ichthyofauna. Additionally competition for food between O. niloticus and the native fishes does not seem probable due to the high abundance of their shared preys and the generalist and mixed feeding strategies of most native fishes. In fact, the fishery of O. niloticus represented an alternative income during a period when the most valued native fishes were scarce. However, there are indications of a high probability of negative impacts to occur: the proliferation of the Nile tilapia modified the species composition of the native fish communities dominating during a period of low salinity, and a potential impact on native benthic fish and fish biodiversity of the estuary can not be ruled out. Oreochromis niloticus and T. pectoralis have biological features that facilitate their proliferation in new environments and food resources seem not to be a limitation. However, until now their long term establishment seems to have been restricted by drastic environmental fluctuations (e.g. salinity) in the estuary. The findings indicate that the establishment of alien fishes with opportunistic feeding habits in tropical estuaries with a high environmental variability is more influenced by abiotic factors than biotic interactions like competition. However, further research should be conducted to establish the role of other biotic interactions (e.g. predation, competition for space, facilitation) and human factors like overfishing on hindering naturalization of non-native fishes in this type of ecosystems.
    Dissertation
      286  84
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    Item-typ:Veröffentlichung,
    Benthic and Pelagic Coupling of Diatoms Bacillariaceae) in Response to Hydrodynamic Forces in the Wadden Sea
    (2006-08-04)
    Klein, Georgia
    ;
    Reise, Karsten
    ;
    Smetacek, Viktor
    ;
    Crawford, Richard
    Within the microbenthic community, diatoms play an important role in terms of food source for grazers and suspension feeders. Furthermore, they contribute significantly to the primary production on intertidal flats and in coastal waters world wide. Numerous studies have now documented microalgal biomass, primary production and other aspects of their ecology in many habitats. However, knowledge on the resuspension of diatoms or the effect of hydrodynamic forces at the species level is sparse but a better understanding of processes at the sediment/water interface and of potential consequences for the ecosystem regarding climate change is urgently required. In addition, knowledge of the effect of hydrodynamics in the intertidal is important because this force links and alters various processes from small scale areas at the sediment/water interface to ecosystem as a whole.The microscopic algae inhabit the sediment and water column and a terminology exists for referring to the habitats occupied by the diatoms, including pennate and centric forms, concerning their life mode: epipsammic (attached to a substratum), epipelic (cells are associated with the sediment, mainly motile) and pelagic diatoms that will occur mainly in the water column. A variety of diatoms are frequently found in both habitats, and often described as tychopelagic: a life mode with pelagic forms that are likely to have settled from the plankton and conversely, benthic diatoms that are readily resuspended. One aim of this thesis was to investigate the diatom community in the water and on the sediment surface and to establish the life mode of selected species in order to gather background information for further studies concerning bentho-pelagic coupling. The increased resolution of the identification and cell counts revealed a discrimination at the species level. Several species, notably of the genera Diploneis and Achnanthes, were found to react to altered flow conditions by presenting enhanced cell numbers on the sediment under increased flow or reduced flow, respectively. Furthermore, Diploneis, previously assumed to be a benthic species, is now shown to adopt a tychopelagic life style. Settling processes during slack water phases and resuspension caused by wind-induced waves and tidal currents lead to a blurring of the boundaries between the two communities. The present study investigated for the first time the influence of altered flow conditions and turbulence on diatoms in situ. This enabled us to take into consideration the effects of wind direction, wind force and tidal currents on the coupling. For this purpose a three-current-flume construction was deployed modifying the flow velocity. The study was carried out on a Wadden Sea intertidal flat at Sylt island in the North Sea, Germany, on 6 dates between July and September 2003. Analyses of chlorophyll a (chl a), suspended matter (SPM), cell counts, particulate organic carbon (POC), particulate organic nitrogen (PON) and species analysis on the sediment surface and in the water column served to characterise the relationship between the two communities. Flow characteristics were measured using the Acoustic Doppler Velocimeter (ADV) technique to calculate the physical parameters describing bottom shear stress and turbulence in order to assess the impact of hydrodynamics on diatom species and cell-size groups.Results showed that wind direction, à ?à ¯Ã ?à ¿Ã ?à ½velocity and fetch had the greatest influence on the variability of the samples, superimposed as they were on tidal forces. An increase in flow velocity reduces turbulence, whereas under reduced flow conditions turbulence exerts stochastic resuspension events by lowering the critical bed shear stress. This affects small diatoms (< 20 à ?�à ?à µm) of the benthic community that are entrained into the water column.
    Dissertation
      254  226
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    Item-typ:Veröffentlichung,
    ANALYSING BRACKISH BENTHIC COMMUNITIES OF THE WESER ESTUARY:SPATIAL DISTRIBUTION, VARIABILITY AND SENSITIVITY OF ESTUARINE INVERTEBRATES.
    (2004-11-03)
    Witt, Jan
    ;
    Reise, Karsten
    ;
    Arntz, Wolf
    ;
    Arntz, Wolf
    This study analyses the benthic invertebrate fauna of the brackish-water zone of the Weser estuary from km 45 to km 115, based on personal sampling and observation in the years 1994 to 2002 and additional data from the region since 1980. In order to provide the biological information for an evaluation and the conservation management of the Weser estuary, the spatial distribution of benthic invertebrates and their sensitivity to human interference was investigated in three case studies. Additional external data of benthic invertebrates were added to provide a comprehensive database that allows a transfer of recognized principles from the case studies to a benthic characterisation of the entire estuary.By including the supratidal areas in the analysis, 10 brackish subzones were identified and compared by area and benthic assemblages. In contrast to earlier characterisation by dominant or frequent species, a biotope characterisation by brackish-water species is suggested, which allows the identification of small-structured biotopes. The strong gradients from land to water and river to ocean result in a variety of special biotopes demanding extreme adaptive skills from benthic inhabitants. A low point diversity, which reflects the strong species selection of such an environment, combined with an increase of species richness on larger scales is found to be characteristic for a transitory environment as represented by an estuary.Sensitivity to impacts depended on certain biological criteria both at the species and the community level. An efficient conservation and management strategy for estuarine features as recently claimed by the EU directives needs to take into account the observed different spatial scales of individually structured biotopes and the specific sensitivity of estuarine benthic communities to impacts to ensure the continuance of the estuarine environment as an entity.
    Dissertation
      281  114