Research Study 1

Fig. 1.  Longitudinal section of a strobilating scyphistoma of a jellyfish Aurelia aurita

Fig. 2.  Scyphistomae of an unknown jellyfish.  Densities of scyphistomae may be locally great owing to the propensity of the polyps to bud off new polyps when conditions are good for growth 

An early study done on Aurelia in Northumberland, England provides a detailed account of the process of strobilation. Prior to separation of the ephyra from the “parent” polyp, it is attached by only a fine strand of connecting tissue.  Final separation may be by contraction of tissues at the site of joining, by physical action of currents, or perhaps a combination of the two. Note in Fig. 1 the contiguous form of the gastrovascular cavity, which extends from the polyp into all the budding ephyrae.  Not all ephyrae released become juvenile jellyfishes; some may drop to the sea bottom and develop into new polyps, which eventually bud off their own ephyrae.  Before strobilating and when conditions for growth are good, the polyps bud off new polyps and, since a polyp may live for several years, densities in areas favourable for growth may be quite high (Fig. 2).  After the last ephyra is released in the spring season, the polyp may die or over-winter to commence growing and budding in the following spring. Note that polyps may be either male or female, and all ephyrae produced from a single polyp are genetically identical and, hence, of the same sex.

NOTE  the species is not mentioned by the author, but is presumably A. aurita. The life-cycle features described here can be applied to the endemic west-coast species A. labiata

NOTE  also known as transverse fission

Research Study 2

Fig. 2.  "Adult" scyphistoma producing stolons and new polyp buds

Fig. 3.  Types of medusae/polyps produced from regenerating segments of "adult" scyphistoma.  Note the gradation in non-medusa shapes produced in different areas of the scyphistoma body

Fig. 1.  Scyphistoma of Aurelia aurita

There are actually three modes of reproduction in scyphozoans: 1) sexual by means of gametes produced by free-swimming adult medusae, 2) asexual budding and pedal-stolon production in scyphistomae that develop from fertilised eggs, and 3) asexual transverse fission in scyphistomae (strobilation) that give rise to a series of juvenile medusae (ephyrae).  The second mode, or stolon production, is described for Aurelia aurita scyphistomae collected at Pacific Grove, California.  Buds and stolons develop from the wall of the lower body/stalk (Fig. 1). Stolons themselves later grow buds, which may crawl away from the parent until the stolon connection is stretched thin and breaks (Fig. 2).  Stolons are also used in locomotion of the polyp, extending outwards from the polyp base with the remainder of the polyp following.  Scyphistomae have good powers of regeneration and new polyps will form from fragments, as long as they are not too small and have both body layers (epidermis and gastrodermis) present.  Fig. 3 shows regeneration from transverse segments and a gradation of medusa-forming potential from top to bottom of the original polyp (especially areas a - b). Note the stolon-forming tendency in segments c - f and the base-forming tendency in segment g.  As noted above, budding has the potential to greatly increase the number of scyphistomae in a given area.

NOTE  all budded polyps and stolons are genetically identical to the parent polyp

NOTE  although cited here as A. aurita, this species is likely to have been A. labiata

Research Study 3

Scyphistomae of Aurelia aurita collected from the Gulf of Mexico can be maintained in the laboratory on a diet of live brine shrimp for at least 3yr.  Depending upon season, mature medusae are produced in 4mo.  The author divides the life cycle into 9 somewhat arbitrary stages, four of the main ones of which are shown in Figs. 1 - 4.  Stage 1 ephyra, newly released from scyphistoma; Stage 3 ephyra, 13mm bell diameter; Stage 5 juvenile jellyfish, 20mm; Stage 9 adult jellyfish, 40mm.  The adult stage is reached in as little as 40d depending upon culture conditions.  In truth, the "stages" as described are too generalised to be useful.

Fig. 1.  Newly released Stage 1 ephyra of Aurelia aurita

Fig. 2.  Late Stage 3 ephyra

Fig. 3.  Juvenile Stage 5 jellyfish

Fig. 4.  Young Stage 9 adult jellyfish

Research Study 4

Fig. 1.  Population-density effects on budding of polyps in jellyfish Aurelia aurita.  This graph seems unnecessarily complicated...maybe it could be presented in a more understandable and simpler form

In favourable conditions, jellyfish scyphistomae bud off junior versions of themselves and as we have seen densities of polyps may become quite high.  A study on scyphistomae of Aurelia aurita in Virginia shows that not only do conditions of low temperature and starvation decrease the extent of budding, but so does increased density.  Note in Fig. 1 that populations with high initial densities have lower growth rates than populations with lower initial densities.  For example, a culture that starts off at five polyps multiplies to about 35 polyps (i.e., 7 times 5) after 21d, or a 7-fold increase. In comparison, a culture with 100 polyps at the start multiplies only about two-fold in the same time. The author suggests that a water-soluble substance may be released that inhibits growth of the polyps.  Inter-polyp competition for food does not seem to play a role. 

NOTE  24°C, fed on brine shrimp Artemia salina every 3d at a standardised “per-polyp” ration

Research Study 5

Laboratory observation of settling Aurelia aurita planulae indicate that more than 90% settle on the undersides of objects.  Thus, the resulting scyphistomae hang with their oral surfaces downwards as sometimes seen in the field.  There is no significant preference of the planulae for rough or smooth surfaces, but there is a trend for selection of grooved over smooth surfaces.

NOTE  textural differences in substrata are created by sanding or cutting grooves into 2 x 2cm plastic coverslips

Research Study 6

Research on the life cycle of moon jellies Aurelia labiata in Roscoe Bay, British Columbia reveals that eggs are held in special brood sacs and hatch to planulae in autumn (Oct-Nov).  The planulae are released in March and ephyrae appear in June.  The medusae mainly stay in the Bay throughout their 1 - 2yr lifespan, although some are washed out through tidal flushing over a shallow gravel sill at the Bay’s mouth.

NOTE  these are not described by the author.  Apparently, though, in A. labiata they are located on the manubrium, while in A. aurita they are on the oral arms

NOTE  late summer temperatures are about 18^oC and salinities about 23ppt ('"parts per thousand", equivalent to 2.3g per 100ml seawater, about 2/3rds the concentration of oceanic seawater)

Research Study 7

Fig. 1.  Roscoe Bay, British Columbia, Canada showing gravel-sill connection to the open ocean, shown on the Right

The author of the previous Research Study later writes that despite being entrained in a twice-daily tidal exchange involving about one-quarter of the total water volume in Roscoe Bay, Aurelia labiata appear to reside there year-round and to maintain stable breeding aggregations.  Apparently, on being moved out of the bay on ebb tides, the medusae sink from the ebbing turbulence into still or counter-current water below.  The counter current is created by the hydrodynamics of the ebb flow of water over a shallow gravel sill at the mouth of the bay (Fig. 1).  Later, when the tide begins to flood into the bay, the medusae rise up, join the flood stream, which is less turbulent than the ebbing one, and are carried back into the bay.  Another related observation is that medusae are rarely stranded on beaches in the bay during ebbing tides.  The reason for this appears to be that when they touch the bottom in shallow waters they immediately rise to the surface, and there they are entrained in the ebbing stream at the surface.  In this way they are carried out of the intertidal zone.  The study is apparently the first to show that scyphomedusae are able to utilise vertical migration to remain in a location subject to tidal currents.  The author remarks that the strategy of vertical migration tends to enhance survival by keeping the population in a favourable location, and by keeping males and females in close proximity for handier reproduction.

NOTE  the author is able to monitor numbers and depths of the jellyfish by use of a floating viewing box.  Some vertical tows of a conical drift net are also done

NOTE  there are actually many reports of jellies in other parts of the world being able to hold their positions in inner parts of estuaries by migrating to the moving surface waters during flood tides and to the still waters near the bottom during ebb tides

Research Study 8

Fig. 1.  Larval settlement preferences of Aurelia labiata for various construction-type materials used in marina constructions.  Although the results are statistically significant, the values are so similar that one would think they have no real biological significance.  One wonders if use of natural materials might have been more interesting

A study by researchers at Shannon Point Marine Center, Washington focuses on settlement preferences of Aurelia labiata planulae for 6 different dock-building materials.  The study is really outside the purview of the ODYSSEY but, as the results may be useful for marinas and portside managers concerned with jellyfish blooms, they are presented here briefly.  Medusae are spawned in the laboratory and settlement of planulae onto replicates of the 6 materials are recorded after a 1mo period.  Results, shown in Fig. 1, may be of interest to port and dock authorities interested in ways of minimising general biofouling and possibly jellyfish blooms. 

NOTE  most floating docks in Washington State are apparently constructed from combinations of 6 primary materials:  polystyrene++ matprp (blue), polystyrene foam (white beads), hard plastic (enclosing flotation material), shrink-wrap sheeting (enclosing flotation material), wood (pressure treated with copper and zinc arsenate), and rubber (ordinary tire rubber)

NOTE  a 2mo field study produces similar results to the laboratory study