1. Vortices Bio 325 Lecture 9 Remember that air is a fluid just as water.
When I draw a canoe paddle through still water on a lake, I see small vortices trail off the paddle edges. Coffee stirring uses vortices to mix cream. Smokers blow smoke rings and cetaceans blow bubble rings. There are crickets that communicate with air vortices.
This picture from the web is of a vortex forming on the upstream side of a tidal turbine*. These rings may travel through the fluid or stay fixed (e.g., over a drain). Fluids (both water and air) exhibit flow and a vortex is simply flow that spins.
Toroid: doughnut-shaped object, e.g., O ring.
songofthepaddle
*the ‘hole’ in the centre is ~15 cm in diameter

2. Assigned reading re sphagnum spores:
Fluids are difficult to compress/effectively incompressible, a fact which allows for translocation of forces by hydrostatic skeletons (worms).
This same fluid property of incompressibility allows for changes of body shape hydraulically when fluids are actually displaced (tube feet).
And if fluid incompressibility gets together with an opening its squeezing results in expulsion: jet propulsion (squids).
Jet propulsion in plants: seed dispersal by detonation: sphagnum spores as an example.
Assigned reading re sphagnum spores:
Van Leeuwen J.L Launched at 36,000g. Science 329:

3. Sphagnum or peat moss
Genus of roughly mosses in the Phylum Bryophyta.
Sphagnum grows in a thick carpet that can hold “15-20 times the moss's dry weight in water”. Sphagnum creates wet, acidic, anoxic conditions wherever it grows. …conditions …ideal for the moss and inhospitable to competing species (modified from Wikki). As a bryophyte, Sphagnum moss lacks a vascular system (xylem, phloem), making it incapable of growing very tall above the ground. Shortness makes difficulties for spore dispersal.
“Most mosses … disperse their
spores by turbulent wind.” Spore
capsules on 1-cm stalks can’t reach
boundary layer (10 cm up).
Solved by an ‘air-gun’ mechanism of
explosive discharge.
Van Leeuwen 2010

4. Field Site ‘Junior Woodsy’ Black spruce sphagnum bog
Northwest of Upsala ON, Trans Canada Hwy

5. Hyaline cells of Sphagnum showing pores that absorb water.

6. Spore capsules of Sphagnum, some already discharged are cylindrical smaller, no cap; the more swollen have yet to dry out.
Epidermis of capsule dries in sun and shrinks, so capsule volume decreases increasing internal air pressure ready for spore discharge.
S. Whitehead
Moreover, a spore …capable of being carried by the wind must also be subject to significant drag [keeping it aloft], meaning that the ballistic launch of a [single] Sphagnum spore from the ground would be incapable of propelling [it] to … [the] necessary height.
Spore must reach breezes that begin cm above the ground. Sphagnum shoots only ~1 cm, so spores have to be propelled through a significant region of still air, a ‘boundary layer’.

7. Propelling small spores vertically is difficult because the low terminal velocity that keeps them aloft also means they rapidly decelerate in still air.
Definition of terminal velocity: when the sum of the drag force and buoyancy equals the downward force of gravity: net force on an object is zero and the object has zero acceleration.

8. Initially spherical (A), the capsule containing spores is dried by the sun, becoming (B) cylindrical at reduced volume and with elevated internal pressure; the lid gives way and pressure/force launches the spore mass, creating a toroid vortex ring. ‘The jet of spores and air rolls up into a turbulent ring vortex that carries spores up to 15 to 20 cm.’
‘Without forming a vortex ring, which keeps the spores clumped together the moss's spores would disperse …and fall uselessly to the ground...[from ‘livescience.com’] Quoting Whitaker.
J L van Leeuwen Science 2010;329:
Published by AAAS

9. The vortex ring (toroid) generated in this context is a single vortex, unlike the situation in jellyfish locomotion where vortices follow each other in a series-- starting vortex alternating with stopping vortex.
Can the vortex contribute to the height gained by the spore cluster?
The question I addressed in lecture: does the expanding rising vortex ring, by its clockwise rotation adjacent to the spore mass and the entrainment this implies, somehow contribute to how high the spore mass rises?

10. Dragonfly nymphal/larval stage
Some aquatic insects use jetting to escape and to breathe.
Ventilation and
Locomotion needs satisfied by the same system. Abdomen a tagma telescoping for changes in body volume.
Source: Mill P.J. & Pickard R.S Jet-propulsion in anisopteran dragonfly larvae. J. comp. Physiol. 97(4):

11. Some dragonfly immatures (Order Odonata) jet water out of their rectum (posterior gut chamber) which is also a respiratory chamber. The insect uses a nozzle (see tapered terminal sclerites) to increase momentum (mass X velocity) and to aim the jet flow just as a squid siphon does. Telescoping in and out of abdominal segments changes abdomen volume and so haemocoel pressure which powers water intake and outflow; filaments filled with tracheae* project into rectum lumen for gas exchange.
nozzle
*Gas exchange in insects via tracheal system of air tubes.

12. Jetting used to ‘launch at prey’ or ‘escape when disturbed’ or ‘in water without a foothold’.
Jet propulsion in insects is limited to dragonfly larvae; note this Mill & Pickard paper written with comparison in mind, e.g., to squids (Cephalopoda).
Cycles of nymph jetting repeated at 2.2 per s for sustained progress; see Mill & Pickard’s longitudinal and oblique muscles diagram of 9th and 10th abdominal segments.
“The effectiveness of the jet-propulsion mechanism is largely dependent upon a) velocity and mass of water ejected from the respiratory chamber b) the mass of the whole animal and c) magnitude of induced drag forces.” ‘cuticular restoring forces’.
Mill P.J., Pickard R.S Jet-propulsion in anisopteran dragonfly larvae. J. comp. Physiol. 97(4):

13. Nectophore zooids in a hydrozoan Cnidarian
A colony of zooids: at one end specialized as swimming individuals called nectophores, also called swimming bells. They jet seawater out of their subumbrellar openings, moving the colony that trails behind on a fishing stem (stem transports nourishment by a shared coelenteron).
National Geographic
Kevin Raskoff

14. Tunicate: Urochordata
Barrington, E.J.W The Biology of Hemichordata and Protochordata. Oliver & Boyd, Edinburgh, London.
Scanned from Barrington, p. 84; os inhalant siphon, ats exhalant siphon. In B ic is the direction of the incurrent which moves out of the pharynx lumen through the pharynx slits into an atrial cavity, thence to the ats. The current is created by beating cilia. Sheets of mucus on the pharynx walls trap the diatoms and other tiny organisms that are then concentrated and passed on down the gut. This sessile filter feeder, the species is Clavelina lepadiformis, is an example of a more typical tunicate. Compare with the salps.
Sea squirts are small barrel-shaped creatures often living in clusters. They have a ‘tadpole larva’ dispersal phase with a notochord, absent in adults. An incurrent siphon, see os above, brings seawater into a slitted pharynx which filters food; excurrent exits at ats. These two siphons have been adapted in some species for locomotion: see salps.

15. “A propulsive jet for locomotion is created by rhythmic compression of muscle bands encircling the barrel-shaped body. Fluid enters the anterior oral siphon to fill the mostly hollow body of the salp. ...oral lips close and circular muscle bands contract, decreasing the volume of the jet chamber so that fluid is accelerated out of the posterior atrial siphon.” [antagonists?] “...unique in possessing incurrent and excurrent siphons on opposite ends of the body allowing for unidirectional flow and reverse swimming during escape” (Sutherland et al. 2010).
Some tunicates called salps are Pelagic: living in the open ocean and swimming by ejecting seawater.
Pelagic: any water in a sea or lake that is neither close to the bottom or the shore (Wikki) ‘open ocean’
See: Sutherland K.R., Madin L.P Comparative jet wake structure and swimming performance of salps. J. exp. Biol. 213:
Peter J. Bryant

16. Sutherland Fig. 3
‘Oral lips close and circular muscles contract, decreasing chamber volume so that fluid is accelerated out of the posterior atrial siphon.’ [antagonists?]
“...unique in possessing incurrent and excurrent siphons on opposite ends of the body allowing for unidirectional flow and reverse swimming during escape”.
“A propulsive jet for locomotion is created by rhythmic compression of muscle bands encircling the barrel-shaped body. Fluid enters the anterior oral siphon to fill the mostly hollow body of the salp.”

17. Salp chains: individuals (zooids) strung together in colonies
Colonial tunicates
I wonder if vortex-assisted locomotion (vortex-ring propulsion) is not universal in jetting animals?
Are there any fish that employ jet propulsion? Flounders (flatfish) use their ‘offside’ operculum. See Brainerd E.L., Page B.N., Fish F.E Opercular jetting during fast-starts by flatfishes. J. exp. Biol. 200:
Kenneth Kopp
Assigned reading:
Sutherland K.R., Madin L.P Comparative jet wake structure and swimming performance of salps. J. exp. Biol. 213:

18. Jellyfish Jetting locomotion
Assigned reading:
Dabiri J. O., Colin S.P., Costello J.H., Gharib, M Flow patterns generated by oblate medusan jellyfish: field measurements and laboratory analyses. Journal of experimental Biology 208: in which they demonstrate the stopping vortex ring which contributes to medusa swimming.
Yong, Ed Why a jellyfish is the ocean’s most efficient swimmer. Nature doi: /nature
JELLYFISH FORM AND FUNCTION Website by John H. Costello & Sean P. Colin, Roger Williams University. See this website for information about jellyfish swimming form from specialists: >fox.rwu.edu/jellies/index.html<

19. Medusae can be bullet-shaped (prolate) or plate-shaped (oblate)
Medusae can be bullet-shaped (prolate) or plate-shaped (oblate). Velum has to do with directing the jet?
Oblate medusae have smaller velums than prolate, contract more slowly when swimming and throw larger amounts of water behind them.
Prolate
Torpedo/bullet
shaped
More ‘streamlined’
oblate
Swimming cycle: power stroke (contraction of subumbrellar circular muscles) followed by a recovery stroke (mesoglea returns its elastic force of distortion). Two vortex rings are formed in relation to this cycle.

20. Jetting by Jellyfish

21. Schematic of a jetting prolate medusa with vortex rings in the wake.
Jetting medusa with vortex rings in wake
Periodic bell contractions decrease volume of subumbrellar cavity, displacing out the high bulk modulus (incompressible) water as a jet: jet propulsion.
Swimming cycle: fluid efflux emerges during bell contraction: a toroidal volume of rotating fluid known as the power stroke starting vortex ring. This travels downstream – is shed -- behind the forward progress of the medusa. There are two things in the wake: this vortex and a central jet (D).
The cycle continues with a second fluid efflux shed during bell relaxation and recovery, a recovery stroke stopping vortex ring as mesoglea returns its elastic force. of distortion, elastic force). Prolate drawn here is jetting other oblate is Rowing.
Dabiri J O et al. J Exp Biol 2005;208:
©2005 by The Company of Biologists Ltd

22. solid arrows: direction of vortex rotation ambient: surrounding
Kinematics of the starting, stopping and co-joined lateral vortex structures from Dabiri et al..
Dye used to visualize the behaviour of the fluid in the wake of the swimming medusa.
Starting vortex ring involves fluid originating from ‘regions inside the subumbrellar volume’, but also from outside the bell via ‘entrainment of ambient fluid’ [flow induced by vortex rotation]; motion of this ring is oriented at an angle away from the bell margin toward the central axis of the bell and downstream (broken arrows).
solid arrows: direction of vortex rotation
ambient: surrounding
Kinematics of the starting, stopping and co-joined lateral vortex structures. (A) Image of medusa vortex wake. (B) Corresponding schematic of medusa vortex wake. P, power stroke starting vortex ring; R, recovery stroke stopping vortex ring; L1/L2, adjacent lateral vortex superstructures. (C) Flow paths in vortex wake. Solid arrows indicate directions of vortex rotation; broken arrows, flow induced by vortex rotation.
Starting vortex pulls in ambient water, some of it up under the bell and some of it (broken arrows) behind the animal and toward the axis. ‘motion of this ring is oriented at an angle?? how do you change the angle of a toroid to affect the direction of entrainment?
Dabiri J O et al. J Exp Biol 2005;208:
©2005 by The Company of Biologists Ltd

23. Kinematics of the starting, stopping and co-joined lateral vortex structures.
Stopping vortex ring: bell circular muscle fibres relax and bell opens (mesoglea returns energy for this that originated with the coronal muscle) . This bell recoil makes a stopping vortex initially within the subumbrellar cavity. But fluid originating from outside the bell is also entrained: it is drawn toward the subumbrellar cavity.”
Kinematics of the starting, stopping and co-joined lateral vortex structures. (A) Image of medusa vortex wake. (B) Corresponding schematic of medusa vortex wake. P, power stroke starting vortex ring; R, recovery stroke stopping vortex ring; L1/L2, adjacent lateral vortex superstructures. (C) Flow paths in vortex wake. Solid arrows indicate directions of vortex rotation; broken arrows, flow induced by vortex rotation.
“the stopping vortex ring from the preceding lateral vortex structure persists in the bell and contributes to the formation of the subsequent starting vortex”
“The stopping vortex remained in the subumbrellar cavity during the beginning of the contraction phase of the next swimming cycle. As the bell contracted [the next cycle beginning], a part of the [first cycle] stopping vortex ring was ejected from the subumbrellar cavity and interacted with the starting vortex of the new cycle. In the interaction, a portion of the fluid from the stopping vortex co-joined with the starting vortex ring, completing formation of the downstream lateral vortex superstructure.”
The ‘lateral vortex structure’ is confusing.

24. The quote below comes from Nature’s promotion blurb (Ed Yong) of contained articles (He is referring to Gemmell 2013).
They “…contract their umbrella-shaped bells, [and] create two vortex rings – doughnuts of water that are continuously rolling into themselves. The creature sheds the first ring in its wake, propelling itself forward. As the bell relaxes, the second vortex ring rolls under it and starts to spin faster. This sucks in water which pushes up against the centre of the jellyfish and gives it a secondary boost...” I think this simplification helps understanding. The stopping vortex, which Dabiri et al. discovered, is created by the motion of the jellyfish through the fluid (just as the motion of a spore mass in sphagnum moss). In the case of the spores there is no expanding bell. The expansion of the bell in the jellyfish adds some complexity to how the stopping vortex is visualized.

25. My first attempt to make these ‘kinematics’ comprehensible
to make the information my own. Drawings, scribbles are important to me in this process. I recommend something like this for both learning and for testing.
L1/L2, adjacent lateral vortex superstructures
created between the two toroids.
I issue a challenge to the students in this course to better resolve the description of what is happening here. The question is: how does the second vortex, the ‘so-called’ stopping vortex successfully enhance the forward locomotion of the jellyfish during the recovery stroke of the swimming cycle. Right now the description given by myself (and perhaps authors in the literature) is not very clear. Perhaps close reading of Dabiri et al. will help. Perhaps the entrainment of ambient fluid into the stopping vortex is important?
Stopping vortex lateral
structure contributes
to advance of swimmer
during recovery cycle.

26. Velella: By-the-wind sailor: using the wind for locomotion
Wilson, E.O Sociobiology. Harvard, Cambridge Mass.
Wikkipedia
from Meglitsch P.A. Invertebrate Zoology
Colonial cnidarians create “a complex metazoan body by making organs out of individual organisms” (p 386, E.O. Wilson, Sociobiology)
gastrozooid, gonozooid, dactylozooid, pneumatophore, etc.

27. Physalia: Portuguese Man ‘o War
Pneumatophore a zooid modified into a gas-filled float giving buoyancy to the colony below and also enabling sailing.
Sailing
locomotion
Pneumatophore
They use stinging cells nematocysts
to capture fish prey.
Zooids: nectophores: squirt out jets of seawater to propel the colony.
gastrozooids are sac-like, specialized for ingestion and distribution of nutrients to rest of colony dactylozooids with batteries of nematocysts etc.
Order Siphonophora (Cnidaria) are pelagic colonies of polypoid and medusoid individuals within the Class Hydrozoa, ~300 spp living in open ocean [pelagic]. (Hydrozoans are typically colonial, but those in other orders are sessile.) Moving in the water column near the surface of the sea they trail long ‘fishing stems’ with batteries of nematocysts catching small fish as prey.
Fishing
Stems
trail