Antarctic Krill and Salps Trophic Cascades can Bring an Increase in Productivity.
What is Trophic Cascades?
Trophic cascade is an ecological concept of side effects when the trophic level of the ecosystem is reduced or removed, which is one of the problematic phenomena in ocean ecosystems. It is important to be aware of because it can either increase or decrease the population of both upper predator and prey species which is also known as top-down control. For example, if the population number of mackerel decreases due to overfishing, the number of shark population which prey on those to live will decrease, while the number of small fish or shrimp population will increase because there are fewer predators.
Krill and Salps Population
Due to climate change and the melting of sea ice in the Southern Ocean, the research from Nature by Atkinson et al. called “Long-term decline in krill stock and increase in salps within the Southern Ocean”, assumed that the density of the Antarctic Krill population will decrease because krill prefer cool temperatures and tend to be around regions with sea ice. They collected the data of annual krill population and sea ice duration and extents, and finally, researchers could find a positive correlation between krill density and sea ice.
While krill prefer cool temperatures, salps like to live in warmer temperatures than krill do. This difference in preference creates segregation between them. With that correlation between krill and sea ice, researchers could also assume that the population density of salps in the Southern Ocean will increase because of the ice melting and climate change.
Impacts on the ocean productivity
With this trophic cascade of krill and salps in the Southern Ocean, researchers also want to figure out how could this affect ocean productivity. The scientific paper from Current Biology by Bockmann et al. called “Salp fecal pellets release more bioavailable iron to Southern Ocean phytoplankton than krill fecal pellets”, developed a two steps incubation experiment at the Western Antarctic Peninsula named Elephant Island, which has undergone growing salps and declining krill numbers in the past 5 decades to explore the influence of salps and krill fecal pellets on the Southern Ocean Iron (Fe) biogeochemistry because iron is the key limiting resource for phytoplankton growth in several sections of the Southern Ocean. As a result, salps fecal pellet material released more iron per microgram of carbon than krill, according to researchers. Furthermore, we discovered that the iron produced by salps’ fecal pellets was more bioavailable for phytoplankton than that released by krill pellets.
Why should we care?
The Southern Ocean is critical for our climate’s future because its huge expanses of water have the ability to absorb or release massive amounts of carbon dioxide from or into the atmosphere. And this trophic cascade could also bring a huge impact on this ecosystem. When sea ice meltdown, more sunlight can be absorbed, and collaboration with bioavailable fecal pallets could dramatically increase the production of phytoplankton. Thus studying and expecting the consequences of the trophic cascade can help to understand that it is a powerful indirect interaction that can control entire ecosystems.