The impacts of jellyfish bloom and post-bloom scenarios on mesozooplankton - A mesocosm experiment.

Hilbich, Mathias (2013) The impacts of jellyfish bloom and post-bloom scenarios on mesozooplankton - A mesocosm experiment. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 49 pp.

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Abstract

Due to their role as top-predators in many marine ecosystems, jellyfish are an important part of pelagic marine food webs. Since they are hardly preyed themselves, they are capable of altering carbon pathways within the food web and shunting nutrients away from higher levels. Their role as voracious predators has been studied, nevertheless the consequences for the food web as coherent system as such is widely unknown. Especially during outbreaks -which seem to increase globally- their impact as predators and carbon shunt can be massive. For the purpose of studying the impact of mass occurrences during and after jellybloom situations on mesozooplankton, a mesocosm experiment has been designed to distinguish impacts on two different phyla of mesozooplankton. Copepods and tunicates are largely distinguished by their feeding behavior (food spectrum) and life cycle duration and therefore might be impacted differently (due to their dependence on different food sources) during and after jellyfish blooms. Aurelia aurita as common and globally appearing scyphomedusa has been the representative gelatinous toppredator in this study. Different treatments served to simulate three different scenarios:
1. Jellyfish bloom scenario with high densities of A. aurita.
2. Post-bloom scenario with high densities of dead A. aurita.
3. A system where A. aurita as top-predator is missing.
Furthermore a control treatment has been established to track changes in phyto- and microzooplankton. Species/genus-abundance analyses (mesozooplankton, phytoplankton) have been obtained and nutrient analyses from water samples were conducted. The results of this study substantiate previous findings of an exclusion effect of copepods and the appendicuarian Oikopleura sp. During this study this effect was on the one hand triggered by top-down control by A. aurita. On the other hand the decay of A. aurita (nutrient input) and possible presence of toxic phytoplankton species negatively impacted copepod abundances and therefore allowed a bloom of the filterfeeding tunicate Oikop/eura sp. To which extent A. aurita decay may be directly linked to changes in phytoplankton resulting in lower copepod abundances and on the other hand facilitation effects for filter-feeders due to increased microbial activity can only be speculated and is a question needing further research.

Document Type: Thesis (Master thesis)
Thesis Advisor: Ismar, Stefanie M. H. and Javidpour, Jamileh
Keywords: jellyfish; mesozooplankton; mesocosm
Subjects: Course of study: MSc Biological Oceanography
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-N Experimental Ecology - Food Webs
Open Access Journal?: No
Date Deposited: 11 Apr 2013 10:39
Last Modified: 10 Jan 2022 08:37
URI: https://oceanrep.geomar.de/id/eprint/21064

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