Surprisingly, Ocean Acidity Benefits Vital Crustacean

Science is clear that the excess carbon dioxide produced by humans will have increasingly devastating effects on the planet, but some organisms may benefit as the Earth changes. New research by Bigelow Laboratory for Ocean Sciences shows that the increasing acidity of the ocean can actually support the growth of a tiny crustacean that serves as a vital food source for a myriad of species across northern oceans.

“As carbon dioxide builds up in the ocean and makes water more acidic, it's generally accepted that this is going to be damaging to marine life,” said Senior Research Scientist David Fields, lead author on the study published in Limnology and Oceanography. “That isn’t the case all-around. This study shows the opposite for this particular copepod.”

The study examined Calanus finmarchicus, a keystone copepod species in the North Atlantic. Researchers determined that they were bigger and more robust when living in more acidic waters. The results can help scientists reveal specific mechanisms that contribute to ideal growth for one of the region’s most important animals.

Calanus finmarchicus are energy rich and help form the foundation of many food webs – providing nutrition to juvenile fish and all the species that feed on them. They are also the primary food source of the critically endangered North Atlantic right whale. Changes that happen to these tiny creatures ripple out across ecosystems.

The new research built on a 2016 study where Fields and his team conducted experiments to see how the animals responded to different temperature and acidity conditions. The results suggested that increased acidity may be beneficial to their growth.

While the implications caught their attention, the researchers could not verify the accuracy of the unexpected results. They had studied adult copepods but did not know exactly how old each one was, which could make a significant difference in developmental metrics.

“It would be like studying human babies in their first year of growth, but you didn't know if they were two days old or 300 days old.” Fields said. “Instead, we wanted to see how these environmental factors impacted copepods at specific times in their development.”

The team repeated a similar experiment, but they isolated the copepods right before they started to go through their biggest growth spurt. This allowed them to accurately measure developmental metrics like body fat percentage, weight, and size.

“So we knew exactly how old they were and how long they had been growing,” Fields said. “That was an extremely novel approach. Nobody has done that kind of age-specific monitoring of copepod species to look at how fast they grow. By doing that, we were able to quantify their response.”

Their new study showed that Calanus finmarchicus were significantly larger and fattier in more acidic environments. This was especially the case in colder water, where they naturally thrive. However, the excess carbon dioxide that will make the ocean pleasantly acidic for copepods will eventually lead to harsher environmental conditions overall.

“If you heat up the globe, the ramifications of warmer water are going to overpower any positive effect of acidity,” Fields said. “There may be a moment when these copepods are incredibly happy with the changes in the ocean, but that time is likely to quickly pass – if it hasn’t already.”