Everything You Ever Wanted to Know About Plankton

Plankton is seriously underrated. This diverse group of microorganisms is the fundamental bedrock upon which ocean ecology is built, as well as the sole food source for the largest animals ever to grace planet Earth. Planktonic creatures also play a major role in the global carbon cycle, yet despite their keystone status, we know next to nothing about them relative to the countless animals that depend on them—humans included.

Fortunately, a new wave of plankton research is featured in the latest issue of the journal Science, representing years of research from the Tara Oceans expedition. This plankton-centric infodump will consist of five comprehensive new studies authored by multinational teams of scientists, based on specimens collected aboard the Tara ocean schooner.

"This is the largest DNA sequencing effort ever done for ocean science," said genomics expert Patrick Wincker in a statement. "[A]nalyses revealed around 40 million genes, the vast majority of which are new to science, thus hinting towards a much broader biodiversity of plankton than previously known.

The Tara schooner visited 210 sites in every major oceanic region between 2009 and 2013, and collected roughly 35,000 samples of planktonic life. "We have so much to learn about the microbiota in the upper ocean […] and the effect that this added heat will have on them is entirely unknown." said Science editor-in-chief Marcia McNutt in the issue's opening editorial.

"It is likely to have deleterious impacts on fisheries already stressed from overharvesting," she noted. "And yet, if it were not for the large amount of heat that the oceans absorb, the amount of global warming we would otherwise experience would be truly intolerable."

The five studies delve deep into individual issues associated with the behavior and diversity of planktonic life, as well as their massive ecological effect on the environments around them. The first paper was led by plankton expert Colomban de Vargas, who assembled dozens of specialists to assess the diversity of these tiny creatures. The results were spectacular.

"In terms of eukaryotes, we sequenced nearly a billion genetic barcodes, and found that there is a greater variety of single-cell eukaryotes in plankton than was thought," said de Vargas in a statement. "They appear to be much more diverse than bacteria or animals, and most belong to little-known groups."

The second study, led by computational biologist Shinichi Sunagawa, created a colossal gene catalog based on the Tara expedition's samples, which further confirmed the mind-boggling diversity of planktonic life. Sunagawa's team also found that plankton are sensitive to temperature shifts, and could be significantly disrupted by anthropogenic climate change.

"These microorganisms, and the communities they form, drive and respond to changes in the environment, including climate change–associated shifts in temperature, carbon chemistry, nutrient and oxygen content, and alterations in ocean stratification and currents," Sunagawa and his authors said.

The third study tackled the role of viruses in planktonic ecosystems, and was headed up by microbial oceanographer Jennifer R. Brum. "We established a means to study viral populations within more complex communities and found that surface ocean viruses were passively transported on currents and that population abundances were structured by local environmental conditions," said study co-author and ecologist Matthew Sullivan in a statement.

Bacteriologist Gipsi Lima-Mendez led the fourth study, which focused on how different kingdoms of plankton interact with each other on a global scale, marking the first time such a comprehensive map of oceanic microbe relationships has ever been made. "We identified interactions among grazers, primary producers, viruses, and (mainly parasitic) symbionts," Lima-Mendez's team said. "We have thus provided a resource to support further research on ocean food webs and integrating biological components into ocean models."

Finally, the last study, led by microbiologist Emilie Villar investigated the role of ocean currents and circulation in plankton transport and distribution, especially in the Indian Ocean.

Any one of these studies would have been a boon to plankton research, but taken together, they have significantly advanced our awareness about these abundant yet mysterious organisms. The lives of these tiny creatures might not be as bombastic as those of larger animals, but given that they produce half the world's oxygen and support countless species both in and outside of the oceans, it's past time we understood their world.