you're reading...

Biological oceanography

Put your cilia in the air and wave ‘em like you just don’t care

Jiang, H. and Johnson, M. D. (2017), Jumping and overcoming diffusion limitation of nutrient uptake in the photosynthetic ciliate Mesodinium rubrum. Limnol. Oceanogr., 62: 421–436. doi:10.1002/lno.10432

Phytoplankton are the microscopic organisms at the base of the marine food web. As their name suggests, they need light to produce energy. They also need nutrients, such as nitrogen and phosphorous, to grow. Since sunlight is generally plentiful in the upper ocean, scientists refer to phytoplankton as nutrient limited organisms. So in any given area of the ocean, the presence or absence of a particular nutrient regulates the growth of plankton.

Figure 1 – A scanning electron micrograph of a single M. rubrum. Notice the cilia, or arms, around the middle of the organism. (Courtesy of the Florida Fish and Wildlife Research Institute)

At an individual level, a phytoplankter gets its nutrients via diffusion — the process by which molecules move from an area of high to low concentration. Imagine an idealized spherical plankton sitting in a nutrient rich area. Over time, the organism will deplete the nutrient in the area immediately surrounding it. Once the system reaches a steady state, the rate at which nutrients reach the organism is regulated by diffusion.

Life in the real ocean, however, does not fit nicely into the simple diffusive model of nutrient uptake. In fact, many studies have observed plankton growth rates far exceeding those predicted under this regime. For decades, scientists have hypothesized mechanisms that might explain how the micro-biota of our world circumvent the physical limitations imposed by diffusion. One popular theory suggests that some plankton might swim to escape the nutrient depleted region around their bodies. But demonstrating experimentally that plankton do this is a challenge.

Drs. Houshuo Jiang and Matthew Johnson of the Woods Hole Oceanographic Institution were able to do just that. They used a creative combination of high-speed imaging and computational fluid models to examine the swimming behavior of a ciliate called Mesodinium rubrum (fig. 1). These cosmopolitan phytoplankton can be found all over the world. In fact, Jiang and Johnson used samples from both Antarctica and the Chesapeake Bay in their experiments.

Figure 2 – A video clip of a M. rubrum during a 1-beat jump. (Adapted from Jiang and Johnson, 2017)

The team cultured both kinds of M. rubrum in the lab. Samples of the organism were then placed under a microscope fitted with a 2000 frame-per-second video camera. Besides being mesmerizing, the videos are also quantitative; the high frame rate allowed the researchers to compute accurate estimates of an individual’s swim speed and distance traveled (fig. 2).

Jiang and Johnson observed two distinct behaviors in both the Antarctic and temperate strains of M. rubrum. Each type had a short distance swim motion; dubbed 1-beat short jumps and tumbles respectively. Both strains displayed similar multiple-beat long jumps. In all cases, a “beat” refers to a single cycle of the organism’s cilia, or arms. The videos revealed that the peak jump speed for each behavior was quite close. The major difference was the distance the organism covered.

The team used their experimentally derived speeds and distances to simulate how these jumps affect nutrient uptake. The physics based model started with a stationary cell in a nutrient depleted area. The cell is then allowed to move, constrained by the measured values for speed and distance. Jiang and Johnson repeated this process for each of the observed jumps.

Figure 3 – Simulation of nutrient concentration of a moving cell. On the left is a M. rubrum after a short jump. The right is after a multiple-beat long jump. The color scale represents the ratio between the nutrient concentration near the cell to the concentration very far away. Red indicates lots of nutrients, blue means there is nothing there. The green color near the cell depicts a depleted area. (Adapted from Jiang and Johnson, 2017)

Using the model results, the researchers demonstrated that M. rubrum can escape to more nutrient rich waters using a multiple-beat long jump. The shorter jumps do not get the organism to fresh water, suggesting a different behavioral stimulus (fig. 3). While the long jump takes longer, both motions take less than a second. Jiang and Johnson point out that it takes a couple of seconds for the organism to deplete nutrients in new water. They argue that means that frequent long jumps substantially enhance the ciliates’ ability to take up nutrients.

M. rubrum is just one of many types of marine phytoplankton. But, the species is remarkably successful in a variety of environments. Jiang and Johnson believe that mechanistic experiments on other organisms can start to illuminate why certain phytoplankton thrive in a given environment. Such studies are not purely academic; the behavior of these organisms has real world, ecological consequences. The more we understand about how they function, the better we can understand how aquatic ecosystems function as a whole.


No comments yet.

Post a Comment


  • by oceanbites 3 months 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 4 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 5 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 6 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 6 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 7 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 7 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 8 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 8 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 8 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 8 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 9 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 9 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 9 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 10 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 11 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 11 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 12 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 12 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 1 year 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