Recently in Sea Life Category

While here in Antarctica, I am trying to grow copepods.  Copepods are small crustaceans that are part of the zooplankton, a word for all animals whose movement in the sea is mainly due to the movement of their liquid surroundings.  Their sizes range from less than one millimeter to several.  They have complex life histories, involving both naupliar and copepodite stages, before reaching maturity.  Copepod growth rates are thought to be primarily controlled by food availability, while their development rates are likely linked more to temperature.  Therefore, under different temperature conditions, it is likely that copepods will mature at different sizes.  I would like to find out what the relationship is between copepod egg development and temperature; eggs are interesting in this respect because they do not require food from the environment outside of the egg.  

I began by collecting live copepods in a net, selecting out mature females, carefully placing them in glass petri dishes.  I placed trays of petri dishes into two incubators at two different temperatures (0 and approximately 4 degrees Celsius).  The first time I did this, the copepods lived for about four days and that was it; nothing happened.  I was a little discouraged.

The second time I tried the experiment, I had better luck.  The copepods I selected laid eggs within a couple days in the warmer incubator and within a couple more days in the colder one!  The eggs have yet to hatch and may have stopped developing.  The copepods that laid eggs were a Calanus species, the ones with the red antennae, which I have yet to identify to a species level.  

Calanus sp. used in my experiment

Editor's note: Notice the shiny sack of  oil filling out the copepod's carapace.  This is why everyone wants to eat Calanus.  

There is incredible copepod diversity here; it is both exciting and a little overwhelming trying to learn the different species.

A copepod of the genus Candacia, distinguishable by its frilly black legs.  When Candacia are floating around in a tub with lots of other zooplankton, all you can see is their legs because their bodies are transparent.

Editor's note: I think Candacia would be an excellent candidate for the next stuffed copepod.

A mature female Paraeuchaeta antarctica, with a spermatophore attached to her uromsome (tail).

Editor's note: Paraeuchaeta is a voracious predator.  Not quite in the same league as a honey badger, but close.

The setae on the posterial corners of a Paraeuchaeta antarctica: a feature that helps distinguish this copepod from other species.

I am still working on definitively identifying the Calanus species that I used in my experiment; they may be Calanus propinquus.  You can tell the difference between Calanus spp. and Calanoides spp. by a serrated upper, inner edge of the most rear swimming legs.  Try seeing that in a microscope on a moving ship!  It's a great challenge.

One of the zooplanktonic critters that we catch in our nets from time to time is salps.  The species seen most commonly here in large numbers is Salpa thompsoni.  Salps have received a lot of attention in marine science lately due to the nature of their poop.  Compared with the fecal pellets of other marine zooplankton, the poop produced by salps is denser and in a larger pellet-like form.  Krill on the other hand produce a long strand of poop.  Copepod fecal pellets are much smaller.  The result of having such dense, large turds is that salp poop sinks faster and is not broken down as quickly as others as it sinks, making it a first-rate organic matter transporter from the surface waters where it is generated, to depth where it eventually settles.  This process is one mechanism that naturally sequesters carbon (organic matter) in the ocean.  Futher, salps are thought to thrive in relatively nutrient-poor waters, making them able to proliferate where other organisms, such as krill, may not.  

Salp species are found in the ocean world-wide.  They have two different adult life-cycle forms: aggregate and solitary.  Aggregates can form long chains, up to several meters in length.  

Salpa Thompsoni in aggregate form- note its pointy ends, characteristic of aggregates.  Also, note the lighter muscle bands and bright orange gut.  

Solitary salps are more barrel-shaped than aggregates, and in our net tows are less common.  Their poops are larger than aggregate poops, in fact, Kate, a scientist conducting fecal pellet production experiments on this cruise, nearly collapsed a large hard plastic carboy while trying to filter a solitary salp's poop, though she had filter plenty of aggregate salps' poop before with no problems.  Solitary salps reproduce asexually by budding off chains of tens to hundreds of clones, whereas aggregate salps reproduce sexually.  Younger chains of salps produce the female gametes, which are fertilized by male gametes from older chains.  Eventually, embryos are released and grow in the solitary form.  We sometimes catch salp embryos.

When we collect net tows in an area rich with salps, it's a big mess and takes a long time to sort though to find other non-salp zooplankton. This tends to happen at our offshore stations, rather than inshore; we have only had this situation once thus far.

The weather on this cruise has been (typical of Antarctica) highly variable.  The majority of the time has been overcast.  We have had a few snow storms, and just yesterday we had to cancel science for the day because it was blowing 50 knots with 15 foot seas.  However, we have also had several beautiful days, with nice sun and moon rises and sets.

This entry is really an excuse to wow you with pretty pictures of seals.  Elephant seals are one of the species commonly seen around the Antarctic Peninsula and they were fairly abundant around Palmer Station.  Other seal species that live here include: leopard seals, Weddell seals, crab-eater seals and fur seals.  Elephant seals live in harems of females, for which male individuals fight.  It is therefore common to see one large male with several females.    

At the moment, little work is being done on seals in Antarctica.  Researchers opportunistically survey their populations for numbers and distribution.  Moms and pups are surveyed for their respective weights.  A study that ended a few years ago sought to understand the lipid (fat) transfer from mother Weddell seals to their pups; this work was conducted out of McMurdo Research Station.  I wonder what the trends are in different seal populations and whether each species is susceptible to different environmental factors, perhaps related to their respective food sources.  I also wonder how much the animals' distributions change over time- do the seals use one habitat for an amount of time and then shift to another?  Does this happen on the scale of one animal's lifetime?  Multiple generations?  Just some food for thought...so to speak.

This research cruise is part of a Long Term Ecological Research Program (LTER), an NSF-funded project to study long-term change in a diverse set of ecosystems.  Palmer Station and the LTER cruise are the primary components of the Antarctic LTER.  Long-term research is expensive to support and does not turn out a lot of results in the short-term.  However, without it, people would have no way of knowing how the world is changing over time.  It is therefore exceedingly important.

LTER science covers many aspects of the ecosystem.  There are people studying gases and trace metals in the ocean, bacteria, phytoplankton (plant plankton), zooplankton (animal plankton), birds and whales.  Carbon flux is a major focus that crosscuts many of the different project teams.  

The group that I work with studies zooplankton and their role in the Antarctic carbon cycle.  Dr. Deborah Steinberg, from the Virginia Institute of Marine Science (VIMS), runs the project.  We conduct different kinds of net tows to sample the zooplankton at different locations and at different depths around the peninsula.  In addition, some of us are conducting experiments to look at fecal pellet production, gut evacuation rates and development rates.  Each of these aspects of zooplankton ecology directly relates to carbon cycling.

Carbon cycling is important because carbon is one of three primary elements that simulate the growth of life in the sea; the other two are nitrogen and phosphorus.  In addition, carbon in the ocean can exist as carbon dioxide (CO2), a major player in greenhouse gas warming.  It is therefore of utmost importance to understand how carbon moves in the marine system, and under what conditions it remains in the sea versus exits into the atmosphere.  

The way we catch zooplankton is with large nets that are towed behind the boat.  We use nets made of different sized meshes to catch different sized organisms.  

picture:

Once we have our zooplankton samples onboard, we sort, identify and count all of the animals that we have caught; this takes quite a long time!  Some examples of animals that we typically catch include: krill, salps, amphipods, copepods and chaetognaths.  We also occasionally catch larval and juvenile fish and squid.

We are not the only ones out here trying to catch zooplankton; whales are a great indicator of large numbers of krill in the area.  In fact, when we do a net tow in the presence of whales, we usually find big healthy-looking krill in the sample.

The zooplankton community changes with the oceanographic conditions in different areas.  Nearshore, the water contains more phytoplankton, while offshore, the waters are less phytoplankton-rich.  We tend to find large schools of krill inshore, where phytoplankton is most abundant.  Offshore, less krill are seen but we also catch more salps, a type of gelatinous zooplankton.  Salps tend to be found in nutrient-poor waters, potentially indicating ecosystem niche-differentiation from krill.  

While tiny, zooplankton are an incredibly important component of the Antarctic ecosystem.  They are the link between the organisms converting sunlight into useable energy, and all higher trophic levels here. ¬ There is evidence that as the climate warms and ice conditions change, major changes in the zooplankton community will follow.  LTER scientists are seeking to describe and understand these changes, as they occur. 

The video was developed for the Radiolab.  You can see the original video here, and there is also a link to the podcast, which features Dr. Smith, that inspired the animation.  I'll be listening to the podcast on my next drive to Orono.

You can clearly see the rows of reflective cilia called "ctenes" that give the phylum it's name.  You can also see one of the tentacles dangling down to the left.  It uses these sticky threads to entangle zooplankton.  The stomach is in the middle of the ball, and the bald thing with the snorkel is me.  I'm not a jelly expert, but I'm pretty sure this guy is Pleurobrachia, a known copepod predator.

(in photo above: dorsal fin extended, anal fin pointing towards the camera)


(in this picture, the dorsal fin is at the surface bent toward us, and the anal fin is extended downward)