Don't Hold Your Breath...
Updated: Apr 11, 2020
...The Respiration Blog is here!
First, you may have a few questions, such as ... How does something as simple as breathing play a role in juvenile krill physiology? OR... Why should we study patterns in respiration rates?
Well… understanding krill respiration rates allows us to have insights into metabolic activity and we can use the patterns from these respiration rates to infer changes in energy expensive behaviors.
Our main project here at Palmer Station, “The Omnivore’s Dilemma,” is based on understanding overwintering krill physiology. If you refer back to Kim’s blog http://kimsbernard.wixsite.com/zoop-lab/post/why-do-we-care-so-much-about-krill-poo, Kim explains our project in the context of this energy budget equation:
Growth = Ingestion – Respiration – Egestion
In short, each part of this equation is used to understand the overall physiology of juvenile krill, using the food they eat is their energy source. By measuring ingestion (how much they eat), respiration (metabolic activity), and egestion (how much they poop), we can calculate growth (how much energy/food they are using to grow). As you can see, respiration plays a key role in helping us understand juvenile krill’s overwinter physiology.
To do these respiration experiments, each time-point we place 16 krill (4 from each treatment) into 20L buckets filled with particle-free seawater (PFSW), and keep them in an Environmental Room (set at -1˚C and constant darkness). PFSW is finely filtered sea water and contains no organic material. We use PFSW because, unlike the ingestion and egestion experiments, during the respiration experiments we do not want the krill to be eating or pooping. This is because in order to get accurate assessment of resting metabolic activity, we don't want the krill to be digesting anything and we also don't want any bacteria in the water, because they respire too. Thus, placing the krill in buckets with PFSW for about 24 hours, allows them to clear their guts prior to being placed in their respiration chambers.
Once the krill have cleared their guts, we transfer each individual krill into their own respective 500mL Nalgene respiration bottle. Using more PFSW (and many, many, hand warmers), we submerge the bottle into the water and close the cap, simultaneously making sure all air bubbles have been released and the krill remain inside the bottle. A rather cold and challenging task..
Each respiration bottle is fitted with a PyroScience oxygen sensor spot on the inside of the bottle. Once all 16 krill have been placed into their experimental bottles, we hook up a fiber-optic cable to the outside of the bottle targeted at that oxygen sensor spot on the inside. The fiber-optic cable, once activated, uses Red-Light Excitation and Near Infrared (NIR) Light Emission to calculate oxygen inside the bottle and records the data at every second.
These experiments last for at least 48 hours, long enough for us to calculate an overall trend in the data signifying a respiration rate, as well as pick up daily peaks in respiration to analyze circadian respiration patterns.
My senior thesis is based on understanding these circadian respiration patterns in juvenile krill, and offer suggestions as to the reasons behind the timing of the peaks we find. Peaks in the data signify an increase in respiration over time and we may be able to attribute these peaks to energy expensive behaviors such as Diel Vertical Migration and feeding.
Diel Vertical Migration (DVM) is a migration to the surface within a 24 hour period (Diel = 24 hours, Vertical Migration = migrating up or down). This behavior is known to occur in many zooplankton species across the world’s oceans. Some major DVM theories include a migration to the surface at night to feed, and retreating to the depths during the day to avoid predation at the surface.
If you can imagine a small krill swimming up the water column, and compare it to what it is like for us (humans) to run or hike uphill, you can easily picture that respiration rates will increase during these activities. Krill also increase our respiration rates when feeding and processing food, again, just like us. Thus, we can infer that the peaks in our juvenile krill respiration experiments may suggest ingrained circadian behaviors such that of feeding and DVM.