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Antarctic krill reproductive development: Is climate change krilling the vibe?

Updated: Aug 17

By Katie Coates, W.A. Franke College of Forestry and Conservation, University of Montana


Hello! My name is Katie Coates, and I am a rising senior at the University of Montana studying Wildlife Biology with a concentration in Aquatic Ecology. Perhaps because I grew up in the deserts of Arizona, I have always felt drawn to the ocean, and I hope to study marine ecosystems in my future career. I was able to apply my passion for marine ecology this summer through the CEOAS REU program, and was lucky enough to work on a  project concerning Antarctic krill, the adorable superheroes of the Southern Ocean!


Figure 1: Katie working on data analysis.

I am fascinated by Antarctic krill (Euphausia superba) because of their instrumental role in the Antarctic ecosystem. They are major consumers of phytoplankton, prey for apex predators like blue whales (Nicol et al., 2008), the target of a quickly growing fishing industry (Nicol et al., 2012), and regulators of carbon storage in the Southern Ocean (Cavan et al. 2019). As one of the most abundant animals on earth (more than 300 million metric tons of biomass and an annual production of up to 500 million metric tons, Atkinson et al. 2009), in one year, Antarctic krill can remove the equivalent amount of carbon from the atmosphere that is produced by two million school buses!


Figure 2: Euphausia superba. Photo by the British Antarctic Survey. Taken onboard RRS James Clark Ross cruise JR230.

Antarctic krill populations fluctuate on a five to seven-year cycle, with large recruitment events being key to their abundance. Recruitment events occur when juvenile krill that survived the winter join the population in the spring. These new additions increase the number of individuals available for reproduction and help offset the negative effects of harsh winter conditions on larval krill survival (Ross et al., 2014). As climate change continues to negatively affect winter survival rates of larval krill (Flores et al., 2012), reproductive output is increasingly important in maintaining healthy krill populations.


The reproductive output of Antarctic krill is largely driven by the quality and availability of their food (Quetin & Ross, 2007). Their diet includes ice algae, diatoms, copepods, and protozoans (Schmidt et al. 2014), all of which vary due to environmental conditions such as the timing of sea ice retreat, or climate oscillations like the Southern Annular Mode (Steinke et al. 2021). However, the Southern Ocean is one of the fastest-warming places on the planet (Ducklow et al., 2012), causing changes in the food web that exceed natural variability (Atkinson et al., 2022). These changes pose unknown consequences for the reproductive development and output of mature female krill.


The reproductive cycle of Antarctic krill includes a resting stage in autumn-winter (March-August), during which mature females and males regress to their immature forms. Sexual development resumes towards the end of winter in preparation for the spring reproductive season (November-February) and the summer spawning season (March-August) (Cuzin-Roudy, 2000). 


Figure 3: Reproductive cycle in female Antarctic krill. (Figure adapted by Bernard, K. S., from Ross & Quetin, 2000). 

In the spawning season, females are capable of  very high reproductive output, as they can spawn 3-9 times in one season, releasing around 8,000 eggs each time (Ross & Quetin 2000). Because sexual development and spawning takes so much energy, changes in the food available to female Antarctic krill during critical stages of reproductive development (such as regression in the winter and development in the spring) can impact how many times a female can spawn and how many eggs are released each spawning event (Steinke et al. 2021).


Little is known about how shifts in the type and quantity of food available to female krill during critical stages of their reproductive development impact their reproductive fitness beyond natural variability. My project aims to understand how climate change may be impacting the reproductive development of mature female Antarctic krill, enabling us to better predict changes in their populations and the ecosystems they support. Using preserved samples of female Antarctic krill collected at the Antarctic Peninsula, I am assessing the effects of oceanic and climatic conditions on their reproductive output.


Figure 4: Map of the study area, with sampling stations represented by points with their corresponding region names shown. 

I am thrilled to work on such an important and exciting project with significant implications for a vital species and part of the world. I am excited to continue this research for my undergraduate thesis during my final undergraduate year, giving me the ability to investigate more environmental variables than I initially had time for this summer. I would like to thank the CEOAS REU program, my mentors Kim Bernard and Rachel Kaplan, and my REU peers for their support!



References


Atkinson, A., Siegel, V., Pakhomov, E.A., Jessopp, M.J., Loeb, V. (2009). A re-appraisal of the total biomass and annual production of Antarctic krill. Deep-Sea Research I, 56, 727740.


Atkinson, A., Hill, S. L., Reiss, C. S., Pakhomov, E. A., Beaugrand, G., Tarling, G. A., Yang, G., Steinberg, D. K., Schmidt, K., Edwards, M., Rombolá, E., & Perry, F. A. (2022). Stepping stones towards Antarctica: Switch to southern spawning grounds explains an abrupt range shift in krill. Global Change Biology, 28, 1359–1375. https://doi.org/10.1111/gcb.16009


Cavan, E. L., Belcher, A., Atkinson, A., Hill, S. L., Kawaguchi, S., McCormack, S., Meyer, B., Nicol, S., Ratnarajah, L., Schmidt, K., Steinberg, D. K., Tarling, G. A., & Boyd, P. W. (2019). The importance of Antarctic krill in biogeochemical cycles. Nature communications, 10(1), 4742. https://doi.org/10.1038/s41467-019-12668-


Cuzin-Roudy, J., (2000). Seasonal reproduction, multiple spawning, and fecundity in northern krill, Meganyctiphanes norvegica, and Antarctic krill, Euphausia superba. Canadian Journal of Fisheries and Aquatic Sciences. 57(S3): 6-15. https://doi.org/10.1139/f00-165


Ducklow, Hugh & Clarke, Andrew & Dickhut, Rebecca & Doney, Scott & Geisz, Heidi & Huang, Kuan & Martinson, Douglas & Meredith, Michael & Moeller, Holly & Montes, Martin & Schofield, Oscar & Stammerjohn, S. & Steinberg, Debbie & Fraser, William. (2012). The Marine Ecosystem of the West Antarctic Peninsula. 


Flores H, Atkinson A, Kawaguchi S, Krafft BA and others (2012). Impact of climate change on Antarctic krill. Mar Ecol Prog Ser 458:1-19. https://doi.org/10.3354/meps09831


Nicol, S., Foster, J. and Kawaguchi, S. (2012), The fishery for Antarctic krill – recent developments. Fish and Fisheries, 13: 30-40. https://doi.org/10.1111/j.1467-2979.2011.00406.x


Nicol, S.,Worby, A., Leaper, R., (2008). Changes in the Antarctic sea ice ecosystem: potential effects on krill and baleen whales. Marine and Freshwater Research 59, 361-382.


Quetin, L. B., R. M. Ross, C. H. Fritsen, and M. Vernet., (2007). Ecological Responses of Antarctic Krill to Environmental Variability: Can We Predict the Future? Antarctic Science, 19:1–14.

Ross, R. M., Quetin, L. B.. Baker, K. S., Vernet, M., Smith, R. C. (2000), Growth limitation in young Euphausia superba under field conditions, Limnology and Oceanography, 1, doi: 10.4319/lo.2000.45.1.0031.


Ross RM, Quetin LB, Newberger T, Shaw CT, Jones JL, Oakes SA, Moore KJ. (2014), Trends, cycles, interannual variability for three pelagic species west of the Antarctic Peninsula 1993-2008. Mar Ecol Prog Ser 515:11–32.


Schmidt, Katrin & Atkinson, Angus & Pond, David & Ireland, Louise. (2014). Feeding and overwintering of Antarctic krill across its major habitats: The role of sea ice cover, water depth, and phytoplankton abundance. doi:10.4319/lo.2014.59.1.0017. 


Steinke, K. B., Bernard, K. S., Ross, R. M., Quetin, L. B. (2021) Environmental drivers of the physiological condition of mature female Antarctic krill during the spawning season: implications for krill recruitment. Mar Ecol Prog Ser 669:65-82. https://doi.org/10.3354/meps13720


“Beaver Research Champion - Kim Bernard.” YouTube, uploaded by Oregon State University, 17 November 2017,  https://youtu.be/ZPOeok-bQuM?si=pMZ0mG3Z-6e7BQNd.






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