Small in size, but mighty in impact

Salps, barrel-shaped marine primitive vertebrate animals found alone or in string-like colonies, and krill, small crustaceans that are the main food source for many ocean creatures, are fascinating organisms that have a huge impact on the planet’s ability to manage climate change.

In late spring of 2018, a German led research expedition travelled to the Southern Ocean near Antarctica, where salps and krill are most abundant (though they are found throughout the world’s ocean), to study these creatures. Over 50 scientists from around the globe boarded the German icebreaker RV Polarstern to participate in this unique voyage, including UBC Institute for the Oceans and Fisheries Professor and Director, Dr. Evgeny Pakhomov.

Dr. Pakhomov’s research on this voyage was concentrated mainly on salp ecophysiology, to understand how much they eat and how important they are in the downward carbon flux. In addition, a special emphasis was given to the basic salp biology. Along with the other scientists, he helped gather samples from various locations and depths around the Antarctic Peninsula, and documented salp numbers, weight, sex, stage of development, and stomach content. Scientists also collected samples to perform DNA, carbon nitrogen, and stable isotope analyses of salps and their stomachs. Much of this was concentrated on the composition of salp fecal pellets, including their size, composition, and drop rate, which is indicative of their effect on carbon flux.

“Salps are like little ‘vacuum cleaners’ that come to the surface, generally at night, to feed, digest and produce fecal pellets. These pellets then drop through the water, typically at a rate of about 400-1,000 metres per day. They break apart, some being consumed by various zooplankton, including krill, or defragmented into smaller pieces that fall at slower rates than the larger pellets,” said Pakhomov. “With my colleagues, we discovered the rate of fecal pellet degradation per day, and were able to discern how efficient salps are at removing organic carbon.”
 

Salps are known to be important for their abilities to increase downward carbon flux. However, their neighbour, the krill, are just as important. The main prey food source for larger ocean predators – whales, seals, penguins, squid, and fish – krill are an integral element in the food web. Both creatures compete for the same phytoplankton and small zooplankton food source, and researchers were also focused on this tension. “In earlier research we undertook in 2002 and 2004, we found that salps had also shifted their distribution further south and we were catching them closer to the Antarctic Continent in areas that were traditionally dominated by krill. We need to know more about how this movement would affect the krill. Would their populations start to decrease? Or even disappear? If that happened how it would affect top predators eating krill?” Pakhomov dismissed the idea that predators could simply switch their diet. “Salps are not good for top predators; it is like eating jellyfish – mostly water. Thus, any decreases in krill population could cause a negative ripple effect up the food chain.” It is even more critical because whales are still recovering from overexploitation in 1950s and 1960s and any krill declines could jeopardize this.

“Furthermore, we need to know what will happen if, as the Southern Ocean warms due to climate change, salps continue to move south into krill areas. What will happen not just to the krill population, but to the whole pelagic ecosystem and overall biogeochemical cycling? And how will the role of the Southern Ocean change in the anthropogenic carbon dioxide absorption?”

Pakhomov is currently reviewing his datasets and preparing to publish the research that was generated during the expedition. “We are gathering for a workshop in November at the Alfred Wegener Institute for Polar Research in Bremerhaven, Germany, to go over the findings and draft the results, some of which are quite unique.”

One such finding is that while salps had been considered to be sequential hermaphrodites; changing to male after completing a female cycle, Pakhomov says they were able to document that salps may be true hermaphrodites because “some were already functional males before they had completed their female cycle.”

For those more interested in the climate change implications, Pakhomov indicated that they did find areas in the Southern Ocean where salps and krill were actually co-existing – still distinctly separated by depth or by small horizontal distances (i.e. one on shelf break and the other on shelf slope), but able to interact. “The implications of that require more research, but could be quite paradigm changing,” Pakhomov stated.