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  • 1
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    Grazing by mesozooplankton from Kiel Bight, Baltic Sea, on different sized algae and natural seston size fractions (2000)
    Inter Research
    In:  Marine Ecology Progress Series, 199 . pp. 43-53.
    Details
    Publication Date: 2018-05-09
    Description: Grazing experiments were conducted with natural mesozooplankton from Kiel Bight, Germany, using radioactive labelled phytoplankton cultures and seston size fractions. The results of experiments using phytoplankton cultures indicated that bivalve veligers performed highest clearance of particles within a size range of 4.7 to 6.3 µm, whereas optimum particle size for copepods was 15 µm. The results of experiments using labelled natural seston size fractions identified bivalve veligers and appendicularians as those responsible for the removal of particles within the smallest size class (〈2 µm). Seston size fractions larger than 5 µm were mainly cleared by copepods and nauplii. As particle size increased, the contribution of copepod clearance to total zooplankton clearance within size classes increased from 57% (〈5 µm size class) to more than 81% (30 to 100 µm size class). When the nauplii clearance rates were included, the total copepod clearance accounted for 90 to 97.6% of the total volume cleared of particles bigger than 10 µm. Despite low abundances of bivalve veligers and appendicularians in Kiel Bight at the time of the experiment, we calculated that approximately 10 and 8.5%, respectively, of the carbon ingested by total mesozooplankton was due to veliger and appendicularian grazing. The importance of bivalve veligers might be seen in their grazing on seston particles that escape predation by copepods and on the amount of energy that is therefore directed from the water column to the benthos when larvae settle.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps199043
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  • 2
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    'Co-consumption' and 'protective coating': two new proposed effects of epiphytes on their macro algal hosts in mesograzer-epiphyte-host interactions (2000)
    Inter Research
    In:  Marine Ecology Progress Series, 205 . pp. 85-93.
    Details
    Publication Date: 2018-05-08
    Description: Multiple-choice feeding experiments were performed with the isopod Idotea granulosa and the amphipod Gammarus locusta as consumers. In a first experiment, 2 different types of tissues of the brown seaweed Fucus vesiculosus and its main macroepiphytes, Ulva lactuca and Elachista fucicola, were offered. I. granulosa rejected apices of F. vesiculosus and preferred E. fucicola, while G. locusta clearly preferred F. vesiculosus tissue, especially the meristematic apices. In a second experiment, F. vesiculosus tissue with and without E. fucicola was offered together. For I. granulosa, the consumption of F. vesiculosus was enhanced by the presence of the epiphyte, while for G. locusta there was no difference in consumed F. vesiculosus mass. G. locusta, however, showed behavioural rejection of E. fucicola, and thus, the epiphyte acted as Œprotective coating¹. We conclude that host (F. vesiculosus) tissue could be Œco-consumed¹ by mesograzers (I. granulosa) that were attracted by the presence of epiphytes and that these epiphytes therefore may have a 2-fold negative effect on the host (i.e. competion for light, nutrients etc. and attraction of consumers). ŒCo-consumption¹ and Œprotective coating¹ add 2 more facets to the very variable and case-dependent interrelationships of mesograzer-epiphyte-host systems; their relevance in nature, however, remains to be demonstrated.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps205085
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  • 3
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    Rapid direct and indirect effects of a single nutrient pulse in a seaweed-epiphyte-grazer system (2000)
    Inter Research
    In:  Marine Ecology Progress Series, 202 . pp. 283-288.
    Details
    Publication Date: 2019-09-23
    Description: In the Baltic Sea, rye tested how short nutrient pulses of different lengths and frequencies affect macroalgae, epiphytes, grazers and their interactions. We hypothesized that even small-scale variations in nutrient supply may have significant impacts by favoring fast-growing epiphytes which can cause large-scale declines of canopy-forming macroalgae. In a factorial field experiment single plants of the canopy-forming macroalga Fucus vesiculosus with and without epiphytes were exposed to pulses of elevated nutrients (N and P) over 25 d. Five 1 h pulses given every 5 d had no significant effects. A single 5 h pulse increased the epiphyte load but not F. vesiculosus growth rate. In contrast, increasing epiphyte load caused F. vesiculosus growth rate to decline and attracted higher densities of gastropod grazers. These results indicate that a single nutrient pulse can have rapid direct and indirect effects on macroalgae and their associated epiphytes and grazers. Temporal variability of nutrient supply (five 1 h vs one 5 h pulse) plays a significant role in determining the response of primary producers and consumers to elevated nutrients.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps202283
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  • 4
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    Grazing during the spring bloom in the Gulf of Aquaba and the Northern Red Sea (2002)
    Inter Research
    In:  Marine Ecology Progress Series, 239 . pp. 251-261.
    Details
    Publication Date: 2018-05-28
    Description: Zooplankton grazing on bacterio- and phytoplankton was studied in the Gulf of Aqaba and the Northern Red Sea during Meteor Cruise Me 44-2 in February-March 1999. Protozoan grazing on bacterioplankton and autotrophic ultraplankton was studied by the Landry dilution method. Microzooplankton grazing on phytoplankton 〉6 µm was studied by incubation experiments in the presence and absence of microzooplankton. Mesozooplankton grazing was studied by measuring per capita clearance rates of individual zooplankton with radioactively labelled food organisms and estimating in situ rates from abundance values. Protozoan grazing rates on heterotrophic bacteria and on algae 〈6 µm were high (bacteria: 0.7 to 1.1 d-1, ultraphytoplankton: 0.7 to 1.3 d-1), while grazing rates on Synechococcus spp. were surprisingly low and undetectable in some experiments. Mesozooplankton grazing was weak, cumulative grazing rates being ca. 2 orders of magnitude smaller than the grazing rates by protozoans. Among mesozooplankton, appendicularians specialised on smaller food items and calanoid copepods on larger ones.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps239251
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  • 5
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    Persistence of phytoplankton responses to different Si:N ratios under mesozooplankton grazing pressure: a mesocosm study with Northeast Atlantic plankton (2004)
    Inter Research
    In:  Marine Ecology Progress Series, 278 . pp. 67-75.
    Details
    Publication Date: 2018-05-30
    Description: We fertilised 12 mesocosms with NE Atlantic phytoplankton with different Si:N ratios (0:1 to 1:1). After 1 wk, we added mesozooplankton, mainly calanoid copepods at natural densities to 10 of the mesocosms; the remaining 2 mesocosms served as controls. A trend of increasing diatom dominance with increasing Si:N ratios and species-specific correlations of diatoms to Si:N ratios were not changed by the addition of mesozooplankton. Large unicellular and chain-forming diatoms, thin-walled dinoflagellates (Gymnodiniales) and ciliates were reduced by copepod grazing while armoured dinoflagellates remained unaffected. Nanoplanktonic flagellates and diatoms profited from the addition of copepods, probably through release from ciliate grazing.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps278067
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  • 6
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    The scarcity of medium sized phytoplankton in the northern Red Sea explained by strong bottom -up and weak top-down control (2000)
    Inter Research
    In:  Marine Ecology Progress Series, 197 . pp. 19-25.
    Details
    Publication Date: 2018-05-09
    Description: This study tested whether the extreme scarcity of larger nanophytoplankton and microphytoplankton in the Gulf of Aqaba and in the open northern Red Sea is caused by nutrient limitation or by selective removal by grazers. Samples of near surface phytoplankton were incubated on board under a fully factorial combination of release from grazing pressure and release from nutrient stress. Release from grazing pressure by different size classes was obtained by sieving through 100, 20, and 10 µm size mesh screens. Release from nutrient stress was obtained by enrichment of Si alone and a full enrichment by N, P, Si and trace elements. Growth rates of most phytoplankton taxa showed a strong, positive response to the full nutrient enrichment and a weaker, but significant response to grazer exclusion. Several diatom taxa showed a weak positive response to Si enrichment. Thus, bottom-up control of medium-sized algae appears to be more important than top-down control.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps197019
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  • 7
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    Spatial and temporal distribution of Trichodesmium spp. in the stratified Gulf of Aquaba, Red Sea (2002)
    Inter Research
    In:  Marine Ecology Progress Series, 239 . pp. 241-250.
    Details
    Publication Date: 2018-05-28
    Description: Phytoplankton (〉100 µm) abundance was studied in the open waters of the Gulf of Aqaba during the summer stratification period of 1996. A succession took place among the major phytoplankton groups, with diatom numbers decreasing throughout the summer. The diazotrophic cyanobacteria Trichodesmium spp. became more prominent as the stratification period progressed; 5 Trichodesmium species were identified: T. thiebautii, T. erythraeum with tuft-shaped colonies and Trichodesmium sp. with puff-shaped colonies were common at ~102 colonies m-3 throughout the stratification period, whereas T. tenue and T. hildebrandtii were more rare. A bloom of T. thiebautii and T. erythraeum with 〉106 tuft colonies m-3 was observed in coastal waters of the Gulf during fall 1997. Tuft-shaped colonies were dominant near the surface, while puff-shaped colonies of Trichodesmium sp. were mainly found in the bottom half of the photic zone. These depth distributions were maintained for more than 2 mo, suggesting that the 2 colony types occupied distinct niches. Puff-shaped colonies were found to have higher chlorophyll a contents than tufts, but their photosynthetic activities were not significantly different. Fatty acid analysis of dominant plankton species yielded new trophic relationships for Trichodesmium spp. The Trichodesmium spp.-specific fatty acid C22:2 ω6 was found in Macrosetella gracilis (the sole copepod to graze on Trichodesmium spp.) and in chaetognaths, suggesting that these carnivorous zooplankton fed on M. gracilis. Furthermore, this fatty acid was observed in the filter-feeding Salpa maxima, which was abundantly present in the Gulf of Aqaba during June 1997.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps239241
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  • 8
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    Changes in the plankton community and the microbial food web of Blanes bay (Catalan Sea. NW Mediterranean) under prolonged grazing pressure by doliolids (Tunicata), cladocerans and copepods (Crustacea) (2002)
    Inter Research
    In:  Marine Ecology Progress Series, 234 . pp. 55-69.
    Details
    Publication Date: 2018-05-28
    Description: We report how different zooplankton groups (doliolids, cladocerans and copepods) are able to influence the coastal pelagic food web, including the microbial food web, in waters of the NW Mediterranean. We studied the effect of grazing and of grazing-induced nutrient recycling mediated by different types of zooplankton grazing on a natural phytoplankton community. Experiments were conducted in semicontinuous 2-stage chemostats. The 1st stage vessels contained seawater from Blanes Bay, Spain (NW Mediterranean) including its natural phytoplankton community; the 2nd stage vessels contained the same seawater and copepods, cladocerans or doliolids. At daily intervals we transferred part of the medium from the 2nd to the 1st stage flasks, which contained ungrazed algae and excreted nutrients. In this way, the zooplankton could influence phytoplankton dynamics both by selective grazing and by differential excretion of limiting nutrients. In the 2nd stage flasks grazing changed the algal community composition. Doliolids and cladocerans promoted the growth of large algae and copepods shifted the size spectrum towards small sizes. This effect was transferred to the 1st stage flasks. Doliolids, cladocerans and copepods also affected the microbial food web in different ways. Size-selective grazing led to differences in the nanoplankton concentrations. These in turn affected bacterial concentrations in a trophic cascade. The potential to modify a given algal population increased with increasing selectivity of the grazer.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3354/meps234055
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