Turnover of dead jellyfish: stimulation and retardation of microbial activity

Little is known about the fate of jellyfish biomass after their populations crash. We mea- sured 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 inter- actions between bacteria and dead jellyfish were examined in a shipboard experiment in Lurefjor- den, 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. periphylla as a substrate, we suggest that the role of dead jellyfish as trophic links in specific pelagic foodwebs depends partly on bacterial community composition.