you're reading...

Biological oceanography

Southern Ocean diatoms: while they’re small, they are mighty!

Citation: Strzepek, R.F., Boyd, P.W., Sunda, W.G., 2019. Photosynthetic adaptation to low iron, light, and temperature in Southern Ocean phytoplankton. Proceedings of the National Academy of Sciences 116, 4388–4393. https://doi.org/10.1073/pnas.1810886116

Note: This post was originally posted in April 2019 but was lost due to server issues so it is being re-posted.

Why study phytoplankton?

Phytoplankton are tiny organisms at the base of the marine food web that fuel the productivity of marine life. They are key players in the biological pump, the biologically fueled part of the carbon cycle. The carbon cycle describes how carbon is used, transformed, and recycled in Earth processes and is a process that occurs in all ocean basins. In the carbon cycle, phytoplankton within the sunlit region of the ocean take up carbon dioxide from the atmosphere and convert it into organic carbon.

The biological pump is fueled by tiny organisms called phytoplankton. These cells take in carbon dioxide from the atmosphere and produce oxygen. Image credit: NASA

The organic carbon produced by phytoplankton help fuel the carbon cycle by either: 1) getting eaten by zooplankton, a type of larger planktonic organism 2) sinking out to the deep ocean after dying or 3) contracts a marine virus that causes the cellular content (organic carbon) to leak out. The contribution that phytoplankton make to the carbon pump differs between ocean regions as the types and abundance of phytoplankton vary. Phytoplankton species vary between different ocean regions depending on specific environmental conditions, such as light, nutrients and temperature. The Southern Ocean (SO) surrounding Antarctica is home to a particular type of phytoplankton called diatoms.

Variety of diatoms on a slide (detail). Image Credit: Wipeter, Creative Commons

How do light, temperature and iron affect diatoms? Primary production, or the amount of carbon dioxide that phytoplankton take up in a given amount of time, is limited in the SO by light, temperature, and iron availability. Diatoms, like other types of phytoplankton, are photosynthetic, so they require light to produce energy (food). Many regions of the SO do not receive enough sunlight because of ice coverage. Ice-cold water temperatures in the SO further hinder diatom productivity because of a reduction in their cellular efficiency, such that more energy is required to take up carbon dioxide. The lack of available iron in the SO also limits production. The main mechanism for iron deposition into the ocean is through dust transport via atmospheric winds that do not often reach the SO. For phytoplankton, iron is a required nutrient for their photosystems (PS) (the main iron containing part of the cell and make up the foundation of the photosynthetic machinery). Despite these challenges of darkness, coldness and lack of iron, SO diatoms have adapted. These adaptations are explored by Strzepek et al (2019).

How the study was done:

An example of phytoplankton cultures in a laboratory setting. Image credit: University of New England

To understand how SO diatoms have adapted to extreme conditions, Strzepek et al (2019) studied the diatoms’ photosystems to measure the use efficiency of both their PS’s in iron-rich versus iron- limited conditions. The team examined cultures of three different SO diatom species and two warmer water (temperate) species. They grew the diatom cultures in two different conditions: one with plenty of iron and the other with low iron (to mimic SO conditions). To reflect the different environmental conditions in the SO compared to temperate oceanic regions, SO diatom cultures were grown at a lower light intensity and a lower temperature than the temperate diatom cultures. The cellular carbon content of the SO and temperate diatom species were normalized by determining the photosynthetic iron to carbon ratio for each diatom species so that scientists could accurately compare the PS use efficiency across species.

What did the study find?

Strzepek et al. (2019) determined that SO diatoms have higher PS efficiencies than temperate species due to their larger photosystems compared to temperate diatoms. It is usually disadvantageous for diatoms to have larger photosystems because increased surface area results in increased energy loss as heat. However, in the cold environment, such as in the Southern Ocean, the larger size means that heat loss decreases and more energy remains in the photosystems to drive photosynthesis. SO diatoms have adapted to have larger photosynthetic antennae, or in other words, larger photosynthetic machinery to be able to harvest more light in light-limited regions. In fact, the authors describe how the adaptation of these larger photosynthetic antennae are among the largest ever recorded in marine phytoplankton! This economical adaptation for SO diatoms results in higher production rates than the frigid, dark and low iron Southern Ocean environment should permit.

A phytoplankton bloom in the Southern Ocean reflects light back toward a NASA satellite. Credit: NASA

This research shows that SO diatoms have adapted quite well to the harsh conditions found in their environment. However, with environmental changes, such as a warming ocean, expected to continue, how will increased water temperatures influence SO diatoms? Will they be able to adapt to warmer water, less ice and more sunlight? How will iron concentrations in the SO fluctuate with climate change? Understanding the adaptations of SO diatoms, helps improve predictions about the overall productivity of the Southern Ocean and its impact on global carbon cycles as the ocean continues to change.


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