Decay of an invasive ctenophore bloom

Currently, there is a vivid scientific discussion whether jellyfish blooms increased in the global ocean over the past two decades due to global warming. Whether or not the observed increase in jellyfish blooms particularly in coastal waters is triggered by global change, the fate of decaying jellyfish blooms and their impact on coastal marine systems remains largely enigmatic. In this project Slovenian and Austrian scientists interact to study the release of organic matter from decaying jellyfish populations and its utilization by the natural microbial community. Thus, the impact of decaying jellyfish blooms on marine ecosystem functioning and biogeochemical cycles in the ocean is studied. We focus on the invasive bloom-forming ctenophore Mnemiopsis leidyi as a natural and/or anthropogenic perturbation and as the potentially new, sporadically available source of dissolved organic matter for the natural microbial community in the invaded coastal marine ecosystem. We will investigate the process of ctenophore-organic matter degradation by marine microbial communities using state-of-the-art techniques to analyze the ctenophore-organic matter composition at a molecular level and applying cutting edge -omics techniques to characterize the metabolic network of the ctenophore-organic matter degrading bacterial consortia. This study is the first attempt ever to investigate the process of degradation of an invasive bloom-forming ctenophore by marine bacterial communities using an integrated interdisciplinary approach from molecular to ecosystem level.

Jellyfish are widely distributed in the marine environment and can reach high abundances in coastal marine systems. These jellyfish have a boom and bust lifestyle, meaning that they are rapidly developing and subsequently decaying en masse. This leads to a major shifts in the marine food webs. In this project we found that decaying jellyfish blooms release large amounts of organic matter which is then rapidly remineralized by the bacterioplankton community. Some heterotrophic bacteria are reacting with high activity to this released organic matter leading to high microbial biomass and leading to a subsequent release of inorganic mutrients which are utilized by algae. The consequence is that large algal blooms are developing within weeks of mass decay of jellyfish blooms. As the marine systems are becoming increasingly warmer, and jellyfish blooms are well adapted to these conditions, it is predicted that these blooms will alter the food web structure of coastal marine systems.