You have probably heard that more and more polar ice is disappearing due to climate change. We have all seen the depressing clips of malnourished polar bears, right? However, some optimistic scientists thought that there might be at least one upside to reduced seasonal polar ice. They believed that the types of algae blooms occurring in open water where ice had previously formed were beneficial because they could help trap carbon in the ocean and prevent it from being released into the atmosphere. But, a study published in Biogeosciences on April 4 suggests that replacing seasonal ice with open water may have negative implications for marine polar species.
Antarctic krill have long been studied for their key role in the Antarctic food web and their commercial value. However, the population has decreased significantly as seasonal sea ice has decreased. Researchers believed that this may have been related to decreasing amounts of the specific algae that grow in icy areas and the marginal ice zone (MIZ), a seasonal zone of ice that partially melts over the summer, but they did not have a way of measuring this algae easily. Algae blooms in open water are typically measured by looking at satellite images, where they show up as green patches due to chlorophyll. However, algae blooms in icy areas cannot be measured in this way because they cannot be seen through the ice.
In order to determine how the types of algae found in icy areas and the MIZ were related to krill growth, the researchers looked for two biomarkers in krill populations. Krill eating a type of algae that grows in ice, Berkeleya adeliensis, would contain a compound called IPSO25, while krill eating the algae most common in the MIZ would contain a compound called HBI III. The researchers collected and tested krill from 47 sites in the Scotia Sea for these compounds.
They found that IPSO25 was present in krill from 21 of the sites, HBI III was present in krill from all 47 and overall krill with high concentrations of both IPSO25 and HBI III were healthier than other krill. This means that krill feeding on algae from icy areas and the MIZ were healthier than those feeding primarily on open-water algae. The researchers believe this is because the ice protects the algae that grow in icy areas and the MIZ and allows them to photosynthesize more effectively and produce more nutrients than algae in open water, which are subject to wind and constantly churning seas.
They also found that the positive effects of seasonal ice could be seen for some time after it melted. Krill in areas where seasonal ice had been present showed high concentrations of IPSO25 and HBI III up to a month after its melting. Researchers believe this is because the water remained relatively calm and some of the algae associated with icy areas and the MIZ remained. Krill from areas previously occupied by seasonal ice that fed on remaining MIZ algae, indicated by high HBI III levels, were heavy for their size. After feeding there for two weeks, their growth matched that of krill that had fed on open-water algae for 16 weeks.
So why does it matter if krill need algae associated with seasonal ice to thrive in the Antarctic? Well, krill are a key food source for other Antarctic sea life, the bottom of the food chain. And, if you remove the bottom of a food chain, everything above it comes crashing down. It is one more serious issue we will be forced to confront if climate change is not addressed, and with this year being the second worst for seasonal Arctic ice in the last 39, according to the National Snow & Ice Data Center, we do not have time to waste.
Abbey Bigler is a fourth-year student majoring in English with minors in business and technical writing, communications studies and biology. ✉ AB842693@wcupa.edu.