Uncovering Seasonal Changes in the Algae Our Oceans Depend On


NSF Intern Emily Spiegel hybridizes RNA samples for analysis

Emily Spiegel, Bryn Mawr College

A study conducted in the Hollings Marine Laboratory under Dr. Peter Lee recently discovered evidence on the impact of the seasons on our oceans. Diatoms, highly productive and important photosynthetic algae, form the base of the marine food web. Their interaction with the wide range of environments they live in is incredibly interesting to marine biologists because so much may be garnered from these studies in the way of understanding the marine ecosystems at large.

This study focused on a polar diatom, F. cylindrus, and despite the harsh temperatures of its home habitat, this diatom is awesomely productive. It can form blooms under sea ice so thick, it looks like grass! Marine organisms feed on these blooms which allows the entire ecosystem to survive. The poles are subject to constant change: in temperature, in ice formation, even in light exposure. Since they are situated at the ends of the Earth, light ranges in the poles from continuous light to continuous darkness. How are photosynthetic organisms like F. cylindrus able to adapt to this stressful change? Their ability to produce is dependent on light levels: too much and these cells can be overwhelmed, too little and there may not be enough light to sustain the population.

Researchers found that at the low light exposure of polar autumn (6h light: 18h darkness), F. cylindrus begins to reproduce sexually, instead of asexually. This was found through analysis of RNA expression, which is an indicator for how much a certain gene is being transcribed into proteins to do work within the cell. Sexual reproduction leaves behind a trace in the RNA, based on the particular genes necessary to pull of this mode of reproduction. As opposed to the primary form of diatom reproduction (asexual), sexual reproduction conserves resources and produces fewer cells. So the population does not grow to the same extent as populations reproducing asexually, but it’s also able to survive in stressful conditions better than asexual populations.

Interestingly, scientists also found that stress could reduce the ability of F. cylindrus to remove carbon dioxide from the atmosphere, in a process known as carbon fixation. This could have major implications for our well the polar oceans remove CO2 from the atmosphere throughout the year. Could autumnal months in the poles show dramatically decreased carbon fixation rates? What does this mean for current global carbon models? Further research must be conducted in the poles themselves to determine whether this relationship exists in nature, and how it is affecting the carbon flux within the polar oceans.

This research was conducted in the lab of Dr. Peter Lee at Hollings Marine Laboratory in collaboration with the Medical University of South Carolina. Many thanks to all members of the lab, particularly Nicole Schanke, MSc.