Reproduction & development
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Free-swimming jellyfishes: other species

This section on free-swimming jellyfishes: other species deals with west-coast species other than Aurelia spp. Reports on the latter can be found in their own section at FREE-SWIMMING JELLYFISHES: AURELIA spp.

 
Research study 1
 

Most of the larger commercial aquariums on the west coast use in-house culture facilities to rear jellyfishes, thus ensuring a continuous supply photograph of jellyfish Phacellophora camtschaticaof specimens for display.  This is true at the Monterey Bay Aquarium, California, and one of the researchers there provides this description of the life stages of a large jellyfish  Phacellophora camtschatica.  The species is common in west-coast waters and is medusivorous, that is, it subsists on other jellyfishes, such as moon jellies Aurelia labiata.  Methodology, including water temperature and foods provided are the same as that shown for the rearing of Chrysaora fuscescens in Research Study 9 below.  Planula larvae swim for about 4d before settling and metamorphosing into scyphistoma polyps (see photos below). A major difference from the life cycle of C. fuscescens is that asexual replication in the scyphistoma polyps of P. camtschatica occurs by side-budding, rather than by podocysts, and only one bud seems to be produced.   Stolons, or basal extensions, see to be produced, but their role in asexual reproduction of the scyphistoma is not made clear. When fully developed, the ephyrae pulse rhythmically, and this may aid in their release from the polyp.  About 8-15 ephyrae, of 5mm diameter, are produced from each strobilating scyphistoma.  In laboratory culture a developing ephyra takes about 9mo to reach sexual maturity.  The author makes an interesting comment that habitats for the scyphistoma stages of most west-coast species of Scyphozoa are unknown.  In the author’s view, such knowledge will be essential to a better understanding of the “bloom ecology” of jellyfishes. Widmer 2006 Invert Biol 125 (2): 83.

NOTE  this could be an artifact of laboratory culture

 

scyphistoma polyp of jellyfish Phacellophora camtschatica courtesy Widmer 2006 Invert Biol 125 (2): 83
Scyphistoma polyp with a single side-bud

scyphistoma polyp of jellyfish Phacellophora camtschatica courtesy Widmer 2006 Invert Biol 125 (2): 83
Strobilating scyphistoma with nearly mature ephyra
scyphistoma polyp of jellyfish Phacellophora camtschatica courtesy Widmer 2006 Invert Biol 125 (2): 83
Free-living ephyra
 
Research study 2
 

photograph of jellyfish Chrysaora fuscescens courtesy Widmer 2008 Pac Sci 62 (1): 71Other research at Monterey Bay Aquarium, California provides information on the life cycle of Chrysaora fuscescens.  The author collects specimens from the field and uses in vitro techniques to fertilise eggs.  In culture at 14oC planulae develop after 2d, settle after 3d, and metamorphose at about 5-7d of age into scyphistoma polyps (see photo series below).  The scyphistoma are raised on rotifers Brachionus plicatilis until they are large enough to eat brine-shrimp nauplii Artemia franciscana.  Scyphistomae reproduce asexually both to create new scyphistomae and, by about 33wk of age, to produce strobilae.  Production of scyphistoma clones is done in an unusual manner, by the “mother” scyphistoma producing a single basal stolon from its pedal disc as it crawls over the substratum. The stolon in turn develops several golden brown disc-shaped buds or podocysts, each podocyst taking about 4wk to be produced.   Each podocyst develops into a polyp and, after 33wk, begins to strobilate in the usual way.  The first ephyra is released at about 40wk of age.  Strobillation occurs over a period of about 10wk and leads to about 60 ephyrae being produced per polyp.  After the last ephyra has left the scyphistoma re-develops a mouth, and thus may live for more than a single season.  After 10d of feeding on brine-shrimp nauplii the ephyra are 5mm in diameter and, after about 10mo and at a size of 15-20cm bell diameter, are sexually mature.  The author provides a key to distinguish 7 species of west-coast scyphomedusae.  Widmer 2008 Pac Sci 62 (1): 71. All photographs courtesy the author. For a short video of C. fuscescens swimming go to LOCOMOTION & ORIENTATION.

NOTE  planulae are about 180 x 90um in size

 
photograph of scyphistoma of jellyfish Chrysaora fuscescens courtesy Widmer 2008 Pac Sci 62 (1): 71
photograph of scyphistoma of jellyfish Chrysaora fuscescens courtesy Widmer 2008 Pac Sci 62 (1): 71
photograph of scyphistoma of jellyfish Chrysaora fuscescens courtesy Widmer 2008 Pac Sci 62 (1): 71
photograph of scyphistoma of jellyfish Chrysaora fuscescens courtesy Widmer 2008 Pac Sci 62 (1): 71
Mature 16-tentacle scyphistoma about 8wk of age Scyphistoma with string of podocysts originating from a single stolon Strobilating scyphistoma with ephyra developing at its free end Ephyra with 8 lappets and showing primary and secondary tentacle buds
 
Research study 3
 

photograph of jellyfish Aequorea sp.Recent concern about jellyfish blooms around the world has generated considerable interest in their causes.  Researchers from Alaska and Oregon analyse data on densities of Chrysaora fuscescens and Aequorea sp. off the coasts of Washington and Oregon in the Northern California histograms showing trawl catches of jellyfishes off the Pacific west coast over an 8yr periodCurrent over an 8yr period.  Abundance of the former species peaks in late summer, while that of the latter peaks in early summer.  Correlation of bloom intensities with such features as latitude, temperature, salinity, distance from shore, and cool spring/summer conditions suggest to the authors that upwelling events and other climate conditions are important factors in their formation. The challenge now will be to determine the exact mechanisms involved in bloom formation.  Suchman et al. 2012 Hydrobiologia 690: 113. Photograph of Aequorea sp. courtesy Claudia Mills, Friday Harbor Laboratories, Washington.

NOTE  the authors note that there is taxonomic confusion over species of this genus in Pacific west-coast waters and suggest that, rather than the 3 species A. aequorea, A. forskalea, and A. victoria now used in the scientific literature, there may only be one.  Data on densities of other medusae, including Aurelia labiata, are also provided, but their numbers are comparatively few and are not included here

NOTE  an open-ocean bloom of C. fuscescens is nothing compared with a good bloom of Aurelia labiata in enclosed bays and fjords along the coast.  Numbers provided by the authors for C. fuscescens of about 10,000 individuals per km2  equates to a single individual per 10x10m area.  A comparable bloom of A. labiata in a British Columbia fjord may be 10 or more individuals per m2 or 1000 individuals per 10x10m area (Chrysoraea is a much more voluminous species than Aurelia, but bell diameters of large individuals are comparable at 10-15cm)

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