Abstract
Episodic blooms of voracious gelatinous zooplankton, such as the ctenophore Mnemiopsis leidyi, affect pools of inorganic nutrients and dissolved organic carbon by intensive grazing activities and mucus release. This will potentially influence bacterioplankton activity and community composition, at least at local scales; however, available studies on this are scarce. In the present study we examined effects of M. leidyi on bacterioplankton growth and composition in incubation experiments. Moreover, we examined community composition of bacteria associated with the surface and gut of M. leidyi. High release of ammonium and high bacterial growth was observed in the treatments with M. leidyi relative to controls. Deep 454 pyrosequencing of 16 S rRNA genes showed specific bacterial communities in treatments with M. leidyi as well as specific communities associated with M. leidyi tissue and gut. In particular, members of Flavobacteriaceae were associated with M. leidyi. Our study shows that M. leidyi influences bacterioplankton activity and community composition in the vicinity of the jellyfish. In particular during temporary aggregations of jellyfish, these local zones of high bacterial growth may contribute significantly to the spatial heterogeneity of bacterioplankton activity and community composition in the sea.
Highlights
In the past decade, the lobate ctenophore Mnemiopsis leidyi, which is native to the American east coast (Kremer, 1994), has spread to the Black and Caspian Seas (Finenko et al, 2006), the Mediterranean Sea (Shiganova et al, 2001), and more recently to the North Sea and the southern part of the Baltic Sea (e.g., Tendal et al, 2007)
Salinity 32, obtained from the fjord was 0.2 μm filtered (Supor filter, Pall), amended with 10% v/v 0.65 μm filtered (Millipore) fjord water, and 100 ml volumes were distributed in ten 100 mL acid-washed flasks, and manipulated in the following manner: three “control” treatments contained (1) water and inoculum as described above, (2) water and inoculum but with M. leidyi dipped into the water for 1 min to examine the potential immediate release of loosely associated bacteria from the M. leidyi tissue, and (3) water and inoculum with added copepods to examine potential release of bacteria from the copepods used as food items
The ammonium release was more variable in fed M. leidyi, which may be due to variations in digestion time and start of starvation between specimens
Summary
The lobate ctenophore Mnemiopsis leidyi, which is native to the American east coast (Kremer, 1994), has spread to the Black and Caspian Seas (Finenko et al, 2006), the Mediterranean Sea (Shiganova et al, 2001), and more recently to the North Sea and the southern part of the Baltic Sea (e.g., Tendal et al, 2007). High bacterial growth has been observed in the vicinity of decaying jellyfish (Titelman et al, 2006; Tinta et al, 2010); even more importantly, growth of bacterioplankton surrounding live jellyfish may be stimulated by the release of nutrients and bioavailable carbon (Condon et al, 2011). Release of bioavailable carbon would presumably select for specific bacterial groups, as recently observed using fluorescence in situ hybridization (Condon et al, 2011), but in addition release of specific bacterial taxa from colonized jellyfish tissue or from the jellyfish gut could affect composition of bacterioplankton in close proximity to the jellyfish, assuming that tissue or gut harbor specific communities. As reported for e.g., non-gelatinous zooplankton (Grossart et al, 2010), fecal pellets (Jacobsen and Azam, 1984), or model aggregates (Kiørboe et al, 2003), a continuous exchange of bacteria between jellyfish surfaces and the surrounding water is conceivable
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