Locomotion, orientation, & other behaviours

  As in other sections dealing with jellyfishes, the Atlantic species Aurelia aurita is included, but only if the study offers insight into behaviours of our own west-coast A. labiata.
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Research study 1
 

drawing of stalked jellyfish Haliclystus "sanjuanensis"In San Juan Island, Washington the stalked jellyfish Haliclystus "sanjuanensis" is sometimes common on seaweeds at low tide levels.  Individuals are fastened by their pedal discs and hang in pendent attitudes with their anchors erected.  The anchors are so-named because they appear to be adhesive, but during observation of them at Friday Harbor laboratories they are never seen to be employed by the animal for this purpose. Hyman 1940 Biol Bull 79: 282.

NOTE the stalked haliclystid jellyfishes on this coast have uncertain taxonomic status, including the one featured here informally named sanjuanensis

 
Research study 2
 

photograph of jellyfish Aurelia labiataBuoyancy in many free-swimming gelatinous invertebrates, including jellyfishes Aurelia aurita,  is aided by active exclusion of heavy sulphate ions.  The body fluids become correspondingly lighter than the surrounding seawater and, thus, buoyancy is increased.  Studies show that about 44% of all SO4-2 ions are excluded in Aurelia, thus providing a theoretical lift of 1mg . ml-1.  At the time that the work was done the mechanism involved in the exclusion was not known.  Bidigare & Biggs 1980 Comp Biochem Physiol 66A: 467.

 



 

Jellyfish Aurelia sp. (possibly labiata) 0.5X

 
Research study 3
 

graphs showing vertical position and velocity of juvenile Aurelia aurita while swimmingphotograph of several juvenile jellyfishes Aurelia auritaVideo analysis of juvenile Aurelia aurita of 1.6-cm diameter by researchers in Providence, Rhode Island provide details of power and recovery strokes during swimming. During the power stroke, contraction of circular tissues around the bell circumference reduces the bell diameter and forces water out of the subumbrella cavity as a jet. Relaxation of these contractile tissues and subsequent rebound of the gel-like mesoglea causes the subumbrella cavity to fill with seawater.  The medusa actually moves backwards a short distance during the recovery stroke.  Five pulses over a 3-sec period will raise the medusa about 10cm in the water column (temperature not indicated in the report).  Costello & Colin 1994 Mar Biol 121: 327.

NOTE  other laboratory studies on the east coast in Massachusetts suggest that Aurelia aurita swims more at night than in the day.  Mackie et al. 1981 Mar Behav Physiol 7: 321.


Juvenile Aurelia aurita 0.5X

 
 

CLICK HERE to see a video of juvenile jellyfishes Aurelia labiata swimming.

NOTE the video replays automatically

 
Research study 4
 

map of Saanich Inlet, Vancouver Island, B.C. showing southeasterly swimming direction of jellyfishes Aurelia auritaIn Saanich Inlet, a 22km-long, north-south oriented fjord on southern Vancouver Island, British Columbia, jellyfishes Aurelia aurita tend to aggregate in enormous swarms along the southeastern shore (see map on Left). Investigation of the phenomenon by researchers using boats and SCUBA-diving  reveals a sun-compass migration during the day in a southeasterly direction.  An example of this is shown in the schematic on the Right, which shows swimming directions of medusae in Finlayson Arm that are swimming horizontally during the times indicated, with percentages indicated for each “swimming wedge”.  Close observation of a few individuals suggests that swimming depth is mostly at or below the thermocline (approx. 5m depth), but not usually deeper than about 10-15m.  During cloudy days Aurelia’s orientation is random and individuals are dispersed passively by tidal currents.  At night they tend to float motionless at the surface. On each sunny day their directional swimming causes them to re-aggregate and swim in a southeasterly direction.  Interestingly, although the observation times shown in the schematic are in the early part of the day with the sun in the east/southeast), the medusae continue to navigate towards the southeast throughout the day as long as they are in sunshine.  In early July when the study commences, almost all medusae are found in the nothern two-thirds of the inlet and most or all are reproductively mature.  Reproduction is clearly facilitated by being in swarms and the authors suggest that this may have been a strong selective factor in evolution of the orientation mechanism.  As to whether Aurelia aurita in other west-coast inlets, or throughout the world, for that matter, all swim in a southeasterly direction, is a question not addressed by the authors.  Hamner et al. 1994 Mar Biol 119: 347.

NOTE  densities measured in 3 swarms range from 16-150 individuals . m-2, with most individuals being within the top 2m of the water column

NOTE  sexes can be differentiated by eye, with female gonads being dark brown in colour and males, bluish in colour.  Bell diameters are about 20cm and sizes change little over the 3mo study. The species described here as A. aurita is most likely to have been A. labiata

 
Research study 5
 

photograph of jellyfishes Aurelia labiataInsight into the mechanisms and benefits of aggregating behaviour in jellyfishes comes from observation of large aggregations of Aurelia labiata in Prince William Sound, Alaska.  Acoustic surveys of near-surface aggregations containing several thousand individuals over several summers reveals the following features: 1) most (81%) of the 995 aggregations observed are categorized as “small” in size (around 40m2 in surface area), 2) individuals in an aggregation tend to swim vertically rather than horizontally, 3) swimming is reduced possibly owing to more frequent collisions between members of the crowded aggregations  This last, in particular, may result in the medusae becoming more concentrated and thus may, in part, explain the mechanism of formation of aggregations.  The authors discuss various advantages of aggregating behaviour, with increased fertilisation success, more effective feeding in high densities of prey, and reduced predation being most convincing.  The paper provides information on co-occurrence of A. labiata with various fish species, most notably walleye pollock, and also provides us an unique perspective on in situ behaviour of jellyfishes in aggregations. Purcell et al. 2000 Mar Ecol Progr Ser 195: 145. Photograph courtesy Eric Broberg, British Columbia.

NOTE the authors comment specifically on the lack of directional horizontal swimming in these populations, in contrast with results shown in Research Study 4 above

NOTE  other possibilities tested and rejected as causes by the researchers include swimming in circles, increased klinokinesis (increase in rate of turning), and retention in Langmuir circulation cells through directional swimming.  The authors comment on the possible involvement of chemoreception in aggregation, and this would seem to be a good topic for future research

 

Jellyfishes Aurelia labiata in aggregation 0.33X

 
Research study 6
 

graph showing avoidance by moon jellies of rock wallsObservations on Aurelia labiata in Roscoe Bay, British Columbia reveal several previously unreported behaviours that might generate further research interest.  First, touching the manubrium, but not the bell, with a soft silicone or foam rubber ball at depths  of 1m cause the medusae to swim to the surface.  Second, dense aggregations of medusae are common, but not within 5m of rock walls.  Water currents appear not to be involved, as drogues released among the aggregations will commonly drift onto the shore. Third, medusae avoid water of less than 20ppt.  Finally, a common response to mid- and late-afternoon (1540-1725h) sun in late summer/autumn is a significant directional swimming to the west, in other words, towards the sun.  The function of the behaviour is not known, but has been described earlier for the same species (see Research Study 4 above). Albert 2008 J Sea Res 59: 198.

NOTE other behaviours of Aurelia labiata in Roscoe Bay, British Columbia described by the same author include responses to low salinity, water movements, and depth.  In general, experimentally created freshwater plumes and horizontally oriented turbulent-seawater streams are avoided, as is contact with the sea bottom.  Albert 2012 Hydrobiologia 680: 179

NOTE the author has recently reviewed the various behaviours of Aurelia spp. in the context of sensory components and neural capabilities. The review is useful, but references to "social behaviour", "central nervous system", "brain", and "mind" in reference to moon jellies may be stretching the reader's credulity more than just a bit. Albert 2011 Neuroscience & Biobehavioral Rev 35: 474

 
Research study 7
 

photographs of a real ephyra of the jellyfish Aurelia sp. and a bioengineered synthetic "Medusoid"Along the lines of things “new under the sun”, researchers at the California Institute of Technology and Harvard University have created an artificial ephyra-like jellyfish that they have called “Medusoid”. The synthetic is bioengineered de novo by first printing a pattern of protein onto an ephyra-shaped silicone base (of 20µ thickness).  Cells from the heart muscle of a rat are now grown onto the protein pattern with the cells aligned along the main axes of deformation of the lobes.  Medusoid is just a few mm in diameter (see lower photograph). When placed in seawater and stimulated with a small electric charge, it swims freely for up to 60min with power and recovery strokes remarkably similar to those of a real ephyra.  The muscle cells provide the contraction force, while the silicone base provides the  elastic recoil.  The authors conclude by noting that their design algorithm would be applicable to the assembly of any synthetic muscular pump, presumably referring to a synthetic human heart.  Nawroth et al. 2012 Nature Biotechnology 30: 792.

NOTE  as a model the researchers use the ephyra stage of the jellyfish Aurelia sp.

NOTE  electrical stimulus is applied at 5-8V, 10msec duration, and 1Hz (i.e., at 1 cycle per sec). A wonderful video of Medusoid swimming can be found at http://www.nature.com/nbt/journal/v30/n8/extref/nbt.2269-S4.mov

 
 

CLICK HERE to see a video of a jellyfish Chrysaora colorata swimming. This large oceanic species (up to 70cm bell diameter) is most commonly seen in southern California but occasionally may be found as far north as Bodega Bay, California.

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CLICK HERE to see a video of jellyfishes Chrysaora fuscescens swimming. This common west-coast species reaches a size of 30cm bell diameter and is distributed from Alaska to southern California.

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CLICK HERE to see a video of an unidentified species of Chrysaora (poss. C. fuscescens) swimming.

NOTE the video replays automatically

 
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