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Dissertation zugänglich unter
URN: urn:nbn:de:gbv:18-77323
URL: http://ediss.sub.uni-hamburg.de/volltexte/2016/7732/


Ecophysiology and Life Cycle Dynamics of North Sea Gelatinous Zooplankton

Ökophysiologie und Lebenszyklus von gelatinösem Zooplankton in der Nordsee

Gambill, Maria

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Freie Schlagwörter (Englisch): scyphozoa , temperature , respiration , growth rate , Mnemiopsis
Basisklassifikation: 42.94 , 42.65 , 42.63 , 42.72 , 42.92
Institut: Biologie
DDC-Sachgruppe: Biowissenschaften, Biologie
Dokumentart: Dissertation
Hauptberichter: Peck, Myron A. (Prof. Dr.)
Sprache: Englisch
Tag der mündlichen Prüfung: 05.02.2016
Erstellungsjahr: 2015
Publikationsdatum: 12.02.2016
Kurzfassung auf Englisch: Reports of gelatinous zooplankton blooms around the world are increasing. Gaining a cause‐and‐effect understanding of mechanisms behind jellyfish blooms is important to predict possible impacts on the structure and functioning of marine ecosystems. Life cycle dynamics of bloom forming gelatinous zooplankton such as cnidaria and ctenophora are complex, including benthic and pelagic stages. This impedes conclusions for taxa based on information obtained from only one life stage. Each life stage needs to be investigated in order to gain a full picture of the dynamics behind jellyfish blooms. This thesis focuses on the impact of temperature on different life stages of scyphozoan jellyfish, as well as larvae of the ctenophore Mnemiopsis leidyi. In addition, possible habitats of the benthic life stages are simulated using data based on abundances of scyphomedusae collected in 2012 in the southern North Sea. The ecophysiology of polyps was studied, measuring routine respiration rate (RR) of four scyphozoan species acclimated to six temperatures. With increasing test temperatures (e.g. 12 to 15°C) RR strongly increased (Q10~7 to 13). In some of the tested species the data suggested that sub-optimally warm temperatures were approached when RR at 20°C was lower than at 15 or 18°C. In Aurelia aurita RR was measured under hypoxic conditions. Below 11, 22 and 24% oxygen saturation at 8.0, 15.5 and 19.0°C respectively, polyps of A. aurita were not able to perpetuate RR. A literature review exhibited respiration rates of polyps, ephyrae and medusa of A. aurita at 15°C to be akin when considering differences in body size, irrespectively from differences in activity and habitat. The results on RR together with previously published data suggest thermal windows to be narrower in individuals collected from higher latitudes. Temperature dependent feeding and growth of larval ctenophore M. leidyi from the North Sea was investigated. Tentaculate larvae (1.5 mm) were tested at temperatures between 6 and 30°C. Linear increase of carbon specific clearance and ingestion rates between 6 and 25°C and rapid declines between 25 and 30°C were observed. With rising temperatures, both absolute- and carbon specific growth increased linearly (0.87d‐1 at 25°C). At low and high temperatures (6 and 30°C) extremely low or negative growth rates were observed, thus defining limits to population growth of M. leidyi. Settlement dynamics of two species of scyphozoan planula larvae from the North Sea were researched, examining broad temperature ranges in different experiments. Between 9 and 27°C more than 50% of the larvae of Cyanea capillata settled within the first five days. Warmer waters (>18°C) were associated with faster settlement as well as increased settlement success of larvae. In a second experiment settlement was prevented, maintaining larvae in the water column at different temperatures (11.3, 13.4 and 19.4°C). After being removed from the water column, they remained competent to settle for 21, 21 and 14 days, respectively. A simulation of a hydrodynamic model in the North Sea suggested that larvae released in May could be transported up to 100 km, retaining the ability to settle. In a substrate choice experiment with planulae of Chrysaora hysoscella covering three temperatures (10, 15, 20°C) and two different light regimes (12/12 light/dark and total darkness), larvae settled in similar numbers onto wood, concrete and PET. Highest settlement was found at regimes with light at 20°C and lower settlement at 10 and 15°C in total darkness. The results propose that warming of the North Sea will not hinder settlement of planulae in the two resident species observed. Differences in species and/or populations may exist, which need to be investigated in order to understand underlying mechanisms promoting the establishment of benthic populations. Scyphozoan medusa were collected in the German Bight in 2012 and 2013. Species composition, distribution and biomass were analyzed and compared to the existing literature. The abundances found in the German Bight were much lower than previously reported abundances from the North Sea. The water body sampled due to the large trawl may have provided a more realistic assessment of jellyfish abundances in the North Sea. For large-scale evaluations, comparable measures are needed when collecting jellyfish. A hydrodynamic drift model using the data from 2012 and previously published data approximated potential habitats for polyps and thus release areas of ephyrae. The work of this thesis demonstrates how different life stages of gelatinous zooplankton react differently to changing temperature regimes and consequently display different, presumably population-specific borders of thermal boundaries. As changing environmental conditions do not seem to impede the proliferation of these organisms, jellyfish are expected to benefit from warming waters and become even more dominant in the future.

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