Britta Culbertson: The Beat of the Bongo (Part 2) – Catching Zooplankton, September 12, 2013

NOAA Teacher at Sea
Britta Culbertson
Aboard NOAA Ship Oscar Dyson
September 4-19, 2013

Mission: Juvenile Walley Pollock and Forage Fish Survey
Geographical Area of Cruise: Gulf of Alaska
Date: Wednesday, September 12th, 2013

Weather Data from the Bridge (for Sept 12th, 2013 at 9:57 PM UTC):
Wind Speed: 23.05 kts
Air Temperature: 11.10 degrees C
Relative Humidity: 93%
Barometric Pressure: 1012.30 mb
Latitude: 58.73 N              Longitude: 151.13 W

Science and Technology Log

Humpback Whale

A humpback whale. (Photo credit: NOAA)

We have been seeing a lot of humpback whales lately on the cruise.  Humpback whales can weigh anywhere from 25-40 tons, are up to 60 feet in length, and consume tiny crustaceans, plankton, and small fish.  They can consume up to 3,000 pounds of these tiny creatures per day (Source: NOAA Fisheries).  Humpback whales are filter feeders and they filter these small organisms through baleen.  Baleen is made out of hard, flexible material and is rooted in the whale’s upper jaw.  The baleen is like a comb and allows the whale to filter plankton and small fish out of the water.

Baleen

This whale baleen is used for filter feeding. It’s like a small comb and helps to filter zooplankton out of the water. (Photo credit: NOAA)

I’ve always wondered how whales can eat that much plankton! Three thousand pounds is a lot of plankton.  I guess I felt that way because I had never seen plankton in real-life and I didn’t have a concept of how abundant plankton is in the ocean. Now that I’m exposed to zooplankton every day, I’m beginning to get a sense of the diversity and abundance of zooplantkon.

In my last blog entry I explained how we use the bongo nets to capture zooplankton.  In this entry, I’ll describe some of the species that we find when clean out the codends of the net.  As you will see, there are a wide variety of zooplankton and though the actual abundance of zooplankton will not be measured until later, it is interesting to see how much we capture with nets that have 20 cm and 60 cm mouths and are towed for only 5-10 minutes at each location.  Whales have much larger mouths and feed for much longer than 10 minutes a day!

Cleaning the codends is fairly simple; we spray them down with a saltwater hose in the wet lab and dump the contents through a sieve with the same mesh size as the bongo net where the codend was attached.  The only time that this proves challenging is if there is a lot of algae, which clogs up the mesh and makes it hard to rinse the sample.  Also, the crab larvae that we find tend to hook their little legs into the sieve and resist being washed out.  Below are two images of 500 micrometer sieves with zooplankton in them.

Zooplankton

A mix of zooplankton that we emptied out of the codend from the bongo.

Crab larvae

Crab larvae (megalopae) that we emptied out of the codend.

Some of the species of zooplankton we are finding include different types of:

  • Megalopae (crab larvae)
  • Amphipods
  • Euphausiid (krill)
  • Chaetognaths
  • Pteropods (shelled: Limasina and shell-less: Clione)
  • Copepods (Calanus spp., Neocalanus spp., and Metridea spp.)
  • Larval fish
  • Jellyfish
  • Ctenophores

The other day we had a sieve full of ctenophores, which are sometimes known as comb jellies because they possess rows of cilia down their sides.  The cilia are used to propel the ctenophores through the water.  Some ctenophores are bioluminescent.  Ctenophores are voracious predators, but lack stinging cells like jellyfish and corals. Instead they possess sticky cells that they use to trap predators (Source:  UC Berkeley).  Below is a picture of our 500 micrometer sieve full of ctenophores and below that is a close-up photo of a ctenophore.

Ctenophores

A sieve full of ctenophores or comb jellies.

Ctenophore

A type of ctenophore found in arctic waters. (Photo credit: Kevin Raskoff, MBARI, NOAA/OER)

It’s fun to compare what we find in the bongo nets to the type of organisms we find in the trawl at the same station.  We were curious about what some of the fish we were eating, so we dissected two of the Silver Salmon that we had found and in one of them, the stomach contents were entirely crab larvae! In another salmon that we dissected from a later haul, the stomach contents included a whole capelin fish.

Juvenile pollock are indiscriminate zooplanktivores.  That means that they will eat anything, but they prefer copepods and euphausiids, which have a high lipid (fat) content. Once the pollock get to be about 100 mm or greater in size, they switch from being zooplanktivores to being piscivorous. Piscivorous means “fish eater.”  I was surprised to hear that pollock sometimes eat each other.  Older pollock still eat zooplankton, but they are cannibalistic as well. Age one pollock will eat age zero pollock (those that haven’t had a first birthday yet), but the bigger threat to age zero pollock is the 2 year old and older cohorts of pollock.  Age zeros will eat small pollock larvae if they can find them.  Age zero pollock are also food for adult Pacific Cod and adult Arrowtooth Flounder.  Older pollock, Pacific Cod, and Arrowtooth Flounder are the most voracious predators of age 0 pollock.  Recently, in the Gulf of Alaska, Arrowtooth Flounder have increased in biomass (amount of biological material) and this has put a lot of pressure on the pollock population. Scientists are not yet sure why the biomass of Arrowtooth Flounder is increasing. (Source: Janet Duffy-Anderson – Chief Scientist aboard the Dyson and Alaska Fisheries Science Center).

The magnified images below, which I found online, are the same or similar to some of the species of zooplankton we have been catching in our bongo nets.  Click on the images for more details.

Personal Log (morning of September 14, 2013)

I’m thankful that last night we had calm seas and I was able to get a full eight hours of sleep without feeling like I was going to be thrown from my bed.  This morning we are headed toward the Kenai Peninsula, so I’m excited that we might get to see some amazing views of the Alaskan landscape.  The weather looks like it will improve and the winds have died down to about 14 knots this morning.  Last night’s shift caught an octopus in their trawl net; so hopefully, we will find something more interesting than just kelp and jellyfish in our trawls today.

Did You Know?

I mentioned that we had found some different types of pteropods in our bongo nets.  Pteropods are a main food source for North Pacific juvenile salmon and are eaten by many marine organisms from krill to whales.  There are two main varieties of pteropods; there are those with shells and those without.  Pteropods are sometimes called sea butterflies.

Pteropod

A close-up of Limacina helicina, a shelled pteropod or sea butterfly. (Photo credit: Russ Hopcroft/University of Alaska, Fairbanks)

Unfortunately, shelled pteropods are very susceptible to ocean acidification.  Scientists conducted an experiment in which they placed shelled pteropods in seawater with pH and carbonate levels that are projected for the year 2100.  In the image below, you can see that the shell dissolved slowly after 45 days.  If pteropods are at the bottom of the food chain, think of the implications of the loss of pteropods for the organisms that eat them!

Pteropods

Shelled pteropods after being exposed to sea water that has the anticipated carbonate and pH levels for the year 2100. Notice the degradation of the shell after 45 days. (Photo credit: David Liittschwager/National Geographic Stock)

Read more about ocean acidification on the NOAA’s Pacific Marine Environmental Laboratory (PMEL) website. Also, check out this press release from November 2012 by the British Antarctic Survey about the first evidence of ocean acidification affecting marine life in the Southern Ocean.

Teacher’s Corner

In my last blog entry on the bongo, I talked about using the “frying pan” or clinometer to measure wire angle.  If you’re interested in other applications of clinometers, there are instructions for making homemade clinometers here and there’s also a lesson plan from National Ocean Services Education about geographic positioning and the use of clinometers this website.

If you are interested in teaching your students about different types of plankton, here is a Plankton Wars lesson plan from NOAA and the Southeast Phytoplankton Monitoring Network, which helps students to understand how plankton stay afloat and how surface area plays a role in plankton survival.

If you would like to show your students time series visualizations of phytoplankton and zooplankton, go to NOAA’s COPEPODite website.

Zooplankton time series

Zooplankton time series visualization from the COPEPODite website.

For more plankton visualizations and data, check out NOAA’s National Marine Fisheries Service website.

If you are interested in having your students learn more about ocean acidification, there is a great ocean acidification module developed for the NOAA Ocean Data Education Project on the Data in the Classroom website.