Monday, 17 June 2013

16 - The Scoop on Poop

The amphipod Themisto compressa
seen under the microscope.
Our group of three scientists (myself, Christina Thiele, and Rebekah Newstead) are here on-board the RRS James Cook  to collect information on the community structure of mesozooplankton (zooplankton in between 0.2- 2 mm) from the surface through the twilight zone to 1000m. We are also interested in how zooplankton may be influencing the transport of carbon through the twilight zone and into the deep sea where it can stay for thousands of years.

Faecel pellets produced by Themisto sp.
Image credit© Staphanie Wilson
One of the ways that zooplankton can influence this is by feeding on smaller plankton and marine snow and packaging them into faecal pellets which can sink faster than the smaller particles. Yes, pretty much every animal in the ocean poops, and zooplankton produce a lot of poop! Zooplankton also come in many shapes and sizes and so does their poop. Understanding how these characteristics differ from region to region can help us learn more about carbon flux and transformations of marine snow throughout the oceans.

The pelagic harpacticoid copepod Microsotella  sp.
seen under the microscope.
Species such as salps produce really big pellets which sink close to 1000 m per day. Large amphipods, currently common at the Twilight station also produce large, quickly sinking pellets. Some other taxonomic groups produce tiny pellets which may degrade before they sink too far. For example harpacticoid copepods (an order of copepods) most of which are benthic. But when found living in the water column like the genus Microsotella  sp., they colonise particles such as, you guessed it, poop.

Another one of our tasks was to measure rates of faecal pellet production by some of the dominant mesozooplankton in the region. We are specifically looking at the larger species that will be producing faecal pellets which may be transported out of the surface waters. This can be done by either passive sinking of large pellets or a more active transport during a zooplankton’s daily migration from the surface at night (where they feed) to the deeper and darker twilight zone at dawn (where they stay until dusk to avoid visual predators). On their way, they produce faecal pellets.

The amphipod Themisto  caught
in a "poop trap" jar.
Image credit© Staphanie Wilson
These pellets have within them the remnants of past meals and are an important mechanism for the transport of carbon to the deep sea. The three groups we chose to look at here on the cruise were salps, the large amphipod Themisto, and the daily migrating copepod Pleuromamma. We collect them, put them in special “poop trap” jars that will separate out the poop (because they like to eat the poop too), and count how many pellets they produce per hour.

By looking at the community structure as well as the faecal pellet production rate we can calculate potential carbon fluxes for some of the zooplankton species. Then we can compare these rates to what we find in the sediment traps and see which species are contributing the most to carbon transport through the twilight zone. This part of our project will be highly collaborative as we all share our data to create an interesting story about poop and marine snow in the twilight zone.

By Stephanie Wilson

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