//
you're reading...

Behavior

The Efficiency of Nautili

Neil, T. R., & Askew, G. N. (2018). Swimming mechanics and propulsive efficiency in the chambered nautilus. Royal Society open science5(2), 170467.

Background:

Imagine if you could function just as well at the top of Mt. Everest (where the air is super thin) as you do at sea level; you’d probably be considered pretty special.  Well, nautiluses (Figure 1) can do that, except they do it in the water at depths where there are low supplies of dissolved oxygen.

Figure 1: Nautilus shell (source: A.M. Hartwell)

During the day, nautiluses either rest around 600 ft. or forage around 2100 ft., whereas at night, they continuously travel between the two depths.  Moving up and down through the water column is a challenge because of variable oxygen conditions.  In the deeper depths where the nautiluses forage, the oxygen availability is low (hypoxic) relative to the shallow depths.

Nautiluses can function normally in the low oxygen environment because their blood contains a protein called haemocyanin that basically enables it to store a lot of oxygen.  Additionally, they can use oxygen stored in the chambers of their shell (Figure 2).  It is also thought that their method of movement, pushing water from their funnels (Figure 3), a mechanism known as ‘jet propulsion’, is advantageous in low oxygen environments. This makes nautiluses unique.

Figure 2: Chambers in a nautllus shell (source: https://en.wikipedia.org/wiki/Nautilus)

Figure 3: Diagram of a Nautilus (source: https://en.wikipedia.org/wiki/Nautilus#/media/File:Nautilus_diagram-en.svg)

Jet propulsion swimming is generally less efficient then undulatory swimming (moving like a wave- think fish or snake) because of the size and velocity of the displaced water differs. In jet propulsion swimming, a small mass of water is moved quickly, whereas in undulatory swimming, a large mass of water is moved slowly.

Puzzled by this unique advantage to nautiluses, researchers looked at and measured the wake structure of swimming nautiluses to get insight into the benefits of using jet propulsion in low oxygen environments.

 

Methods:

Drs. Neil and Askew at the University of Leeds used observation tanks to observe the swimming behavior of nautiluses and visually analyze the wakes made from their movements.  The researchers had to incentivize the nautiluses to swim by placing shrimp for them to eat in the observation tank. While the nautiluses swam for the shrimp, their wakes were videotaped so that the wake structure could be quantified.  A green laser was used to illuminate the wake structure so that it could be captured on video.  The illuminated structure enabled Neil and Askew to isolate the movement of water in only the area that bisected the nautilus’ funnel.  Between video-frames they tracked the movement of each particle to reconstruct the wake structure (i.e. the movement of the jetted water).

The researchers used their observations of the animals and fluid to determine the ‘jet thrust’ and ‘whole cycle propulsive efficiency’. Jet thrust is the force propelling the animal and was calculated from the density of seawater, the velocity of the water in the wake, and the cross section of the funnel opening. Whole cycle propulsive efficiency is ratio of useful power to the sum of useful power and wasted power and was calculated from the velocity of the nautilus, the mass of the water being moved, the velocity of the fluid refilling the mantle.  (Check out the paper for details of the equations and calculations!)

Results:

The nautiluses swam in two orientations: anterior-first (frontend first) or posterior-first (backend first).   Backend-first swimming accounted for 77% of the observations and was 15-20% faster than that frontend-first swimming.  Additionally, during backend-first swimming, the funnel opened 4-times its normal diameter compared to 7-times its normal size during frontend-first swimming.

Two, asymmetric wake structures were observed. One was characterized has having an isolated ring structure and the other was characterized as having an elongated structure.  Both wake structures had similar whole cycle propulsive efficiency and thrust generation.

For nautiluses swimming backend-first, both the isolated ring and elongated wake structures were observed at all speeds.  For nautiluses swimming frontend-first, the isolated ring wake structure was observed at slower speeds and the elongated wake structure was observed at higher speeds, with some overlap in-between.  The transition between wake structures is a function of the ratio of funnel length to diameter.

Neil and Askew found that the most efficient swimming orientation was frontend-first swimming with an isolated ring wake structure (slow moving).  The second more efficient orientation was the backend-first swimming with an elongated wake structure.

Take away:

All in all, the whole cycle propulsive efficiency of nautiluses agrees with previous observations of jet propulsion animals: efficiency comes at the expense of swimming speed.  The nautilus is unique in that at slower speeds its efficiency is up to 30% greater than other propelled animals, such as squid and jellyfish.  The bulbous shape of the nautilus does impact the swimming performance at high speeds compared to the slender physique of squid bodies.

Having the capability to move efficiently is important because it translates to a low cost of locomotion, meaning there are few metabolic demands that consume oxygen when in hypoxic environments.

check out this musical video of swimming nautiluses on YouTube!

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 2 weeks ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 2 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 2 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 4 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 4 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 4 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 6 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 7 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 7 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 8 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 8 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 9 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 9 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 10 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com