Week 2
10 July 2006

In Pursuit of Polar Plankton:
What Is It? Who Needs It?

What is it? Plankton are organisms that drift in ocean currents. In the Southern Ocean, large areas of green, brown, or red colored water are actually plankton. Plankton are an essential link in the Antarctic food chain. Krill, a type of zooplankton, feed on phytoplankton. Krill are consumed by baleen whales which consume up to 150 metric tons per year. (See Weekly Wildlife #3 – Cetaceans.) The high mineral content (especially iron) in parts of the Southern Ocean and Scotia Sea combined with low ocean temperatures produces an environment highly conducive to plankton growth.

Question: Why would phytoplankton grow better in colder water? (Hint: the answer has something to do with water density.)

Where are plankton found? One area where more plankton is found is in the East-Wind Drift region. This is an area of weaker wind and more stable water that is close to the shore of the continent. The other area is one that is being sampled on this cruise. (See the Chlorophyll Concentrations illustration). The scientists want to document what occurs as the water passes through the Shackleton Gap and how it affects the plankton blooms to the east. (Read the Science in the Spotlight articles for further details.)

The Oceanic Biological Pump Link

What kinds of plankton are there?

Phytoplankton are the smallest plant plankton. Most of them found in the Antarctic region are diatoms. Diatoms are single celled plants contained within a box of silica and are either brown or green. Some of them have long thin shapes that form chains. They have whiskers or bristles that allow them to remain near the surface. These chains of diatoms can stain the edges of ice floes red brown. Dinoflagellates are also a unicellular green plant. These plants are the food for zooplankton.

Zooplankton are organisms such as krill (a crustacean), other crustaceans such copepods and protozoa, and larval fishes. Krill are small crustaceans of the group Euphousiacea, (luminescent shrimp).

Phytoplankton Genus: Genus Dactyliosolen Photo by: Chris Hewes, Scripps Institution of Oceanography	Phytoplankton A typical antarctic diatom: Genus Corethron, Species Criophilum Photo by: Chris Hewes, Scripps Institution of Oceanography

Zooplankton Antarctic krill, Euphausia superba, the second step in the Antarctic food chain and the most common food for the penguins and baleen whales that visit Antarctica. Image courtesy of Langdon Quetin and Robin Ross, UCSB researchers. Link

Question: What is luminescence?

Krill is the principal food for baleen whales, Crabeater seals, and tubenoses (birds such as petrels with a tube-like beak. For more on petrels, see Weekly Wildlife #1 – Seabirds.)

Krill are extremely abundant in cold polar oceans. Of the 85 known species of krill, 11 are restricted to Antarctic waters. Antarctic krill are 3-6 cm long.

Baleen whale - Humpback feeding on krill Photo by: Heather McRae Link

Baleen whales do not have teeth. They have baleen, which is made of Keratin, the same material as our fingernails or hair. These teeth are arranged like the teeth of a comb, The whales open their mouths to fill it with water. Then they force the water out of their mouths, and the mat on the inside of the baleen teeth catches plankton.

A Southern Giant Petrel Photo by: Dan Grossman Link	Petrels in general, feed extensively on Antarctic krill. The contribution percentage of krill to their diet varies depending on the species, but seems to be very high in smaller petrel species. Photo by: Dan Grossman Link

Question: How many centimeters are in an inch?

Seasonal variations

The lowest populations of phytoplankton occur from April through July when the days are very short. During the austral winter the sun is very low in the sky and it is often cloudy.

Question: What does austral mean? What is the meaning of the name Australia?

Phytoplankton Genus Thalassiosiria, Species Antarcticus Photo by: Chris Hewes, Scripps Institution of Oceanography

Question: Why are populations of phytoplankton low during the winter?

The population begins to increase in August, but remains low until September and October when phytoplankton return to the surface and begin to bloom. Zooplankton follows a similar pattern.

Question: Why would the zooplankton growth pattern be similar to the phytoplankton growth pattern?

What’s for dinner? And breakfast? And lunch? PLANKTON!

• Seabirds eat 40 million metric tons of krill per year. All of the seabirds, including penguins, are dependent on plankton.
• The Crabeater Seal eats 100 million metric tons annually of planktonic arthropods.
• Some baleen whales eat up to 1 metric ton per day when they are in Antarctic waters.
• Fish and squid eat up 150-200 million metric tons per year.

Crabeater seals NMML Photo Gallery Link	Crabeater seal with its mouth open, The teeth are designed to filter krill out of the water. Photo by: Dr. Mike Cameron, NMML Link

Question: What does the word part “arthr” mean? Hint: What is arthritis?

Today’s final plankton question submitted by Greg Mitchell, chief scientist on board the Nathaniel B. Palmer:

Microscopic phytoplankton in the ocean produce about 50% of the oxygen in the atmosphere that we breathe, and land plants produce about 50%. However, land plants are about 99.5% of all plant biomass on Earth, and phytoplankton about 0.5%.

Question: Why do you think that land plants have so much more mass compared to their photosynthetic capacity?