Physical and Physiological Growth Contraints of Key, North Sea Gelatinous Zooplankton
Final Report Abstract
This project, a close cooperation between the two research groups in Hamburg and on Helgoland, investigated poorly studied life-stages of gelatinous zooplankton. Especially scyphozoans have a complex life-cycle with benthic stages reproducing asexually and free-living medusae which produce sexually. The polyps that typically grow on hard-substrates are very difficult to find in the field and hence we know next to nothing on the autecology of these stages. In this study, we observed that the growth conditions of these stages are highly variable, even in a relatively small region around Helgoland. Depending on the exposure of the site, all organisms died, or grew better or less well. Especially with the large building activity in the North Sea as a result of the implementation of the wind parks we predict that the availability of hard substrates suitable for polyps will increase. Hence, we expect a larger reproductive capacity for gelatinous zooplankton in the North Sea. We observed significant effects of nutritional quality on growth and condition of some gelatinous species, but not on others. Where we observed significant effects (polyps of Cyanea capillata) the direction of the response was similar to what had been found before in other species: food with low phosphorus content is of lower quality than food with higher P-contents. In experiments with realistic end-of-the-century scenarios for CO2 (800-1000 ppm) we observed no significant effects on growth and condition of either polyps or ephyrae in any of the species which we investigated. We, therefore, conclude that if anything the impact of ocean acidification on gelatinous zooplankton will be indirect, through changes in the quality of the food, but direct (pH) effects are not likely to impact gelatinous zooplankton populations. Substantial intra- and interspecific variation was detected in the response of gelatinous zooplankton to temperature differences. Moreover, different response variables showed different sensitivities to temperature. Where respiration rates were highly sensitive to temperature changes growth of polyps was much less so, and growth of ephyrae of the species Chrysaora hysoscella showed no response to a temperature range of 15°C at all. Polyps of the species Aurelia aurita collected from different backgrounds seemed to be adapted to the local environments they were collected from. Hence, we conclude that to properly understand the impact and influence of gelatinous zooplankton on marine communities it does not suffice to include single species in the investigations. Variation exists on all levels of integration and we need more data to be able to understand the role of these species.
Publications
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2011. The invasive ctenophore Mnemiopsis leidyi: a threat to fish recruitment in the North Sea? J. Plankton Res 33: 137-144
Hamer, H.H., Malzahn, A.M. & Boersma, M.
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2012. Auswirkungen auf marine Lebensräume. In: Klimawandel und Biodiversität - Folgen für Deutschland (eds: V. Mosbrugger, G.P. Brasseur, M. Schaller & B. Stribrny) Wissenschaftliche Buchgesellschaft, Darmstadt. Pp. 106-127
Kröncke, I., Boersma, M. Czeck, R., Dippner, J.W., Ehrich,S., Exo, M.K., Hüppop, O, Malzahn, A.M, Marencic, H., Markert, A., Millat, G., Neumann, H., Reiss, H., Sell, A., Sobottka, M., Wehrmann, A., Wiltshire, K.H. & Wirtz, K.
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2014. Respiration rates of the polyps of four jellyfish species: Potential thermal triggers and limits. Journal of Experimental Marine Biology and Ecology 459: 17–22
Gambill, M. & Peck, M.A.
