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- Riemann, L., et al.
(author)
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Links between jellyfish and microbes in a jellyfish dominated fjord
- 2006
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In: Marine Ecology-Progress Series. - 0171-8630. ; 325, s. 29-42
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Journal article (peer-reviewed)abstract
- Research on the impact of mass aggregations of jellyfish on foodweb structure has mainly focused on trophic control of copepods and fish larvae, while impacts on lower trophic levels have received little attention. Jellyfish release nutrients and dissolved organic matter through their activities. Hence, both direct and cascading impacts of jellyfish on the bacterial community are conceivable. In the Norwegian Lureflorden, the abundance of the deepwater scyphomedusa Periphylla periphylla reaches concentrations much higher than in any other area investigated. We used Lurefjorden as a model system to examine effects of high jellyfish biomass on the microbial planktonic foodweb, and targeted bacterial activity and community composition in relation to the distribution of P. periphylla as monitored using a Remotely Operated Vehicle. P. periphylla performed pronounced diel vertical migrations; however, no significant diel effects on microbial activity were observed in surface waters. Surface waters were characterized by a high biomass of mesozooplankton. Integrating over 24 h, the highest jellyfish biomass was found at 200 to 300 m depth. This concurred with elevated total organic carbon, bacterial production and ectoenzymatic activities. Analysis of bacterioplankton community composition by denaturing gradient gel electrophoresis (DGGE) and 16S rDNA sequencing revealed that specific phylotypes related to Bacteroidetes and to delta-Proteobacteria were found with depth. Overall, phylotypes related to Bacteroidetes dominated the bacterial community. Our results indicate that P. periphylla has a structuring impact on the pelagic deep-water microbial community in Lurefjorden. We suggest that jellyfish proliferations may also be quantitatively important for lower trophic levels of the pelagic foodweb.
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- Titelman, Josefin, 1973, et al.
(author)
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Turnover of dead jellyfish: stimulation and retardation of microbial activity
- 2006
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In: Marine Ecology-Progress Series. - 0171-8630. ; 325, s. 43-58
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Journal article (peer-reviewed)abstract
- Little is known about the fate of jellyfish biomass after their populations crash. We measured turnover rates of dead Periphylla periphylla in a pelagic in situ experiment in Raunefjorden, Norway. Decay was exponential, with decay-coefficients of 0.67 to 1.12 d(-1); smaller jellyfish turned over faster than larger ones. The rapid turnover suggests that large amounts of carbon and nitrogen are transferred to the pelagic and/or benthic foodwebs at the collapse of jellyfish blooms. The interactions between bacteria and dead jellyfish were examined in a shipboard experiment in Lurefjorden, Norway, using natural bacterial assemblages. Growth and morphology of the bacteria in the incubations suggested that only certain morphotypes proliferated in the vicinity of jellyfish tissue. Subsequent experiments with homogenized P, periphylla tissue and bacterial isolates from various phylogenetic groups confirmed that some bacteria could use jellyfish as substrate, while others were inhibited. Tests with sensitive isolates revealed that inhibition of bacterial growth depended on the body part, size and concentration of P. periphylla used. Because only some bacteria were able to use P. pehphylla as a substrate, we suggest that the role of dead jellyfish as trophic links in specific pelagic foodwebs depends partly on bacterial community composition.
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