If you can read this, thank a plankton!

By Anthony Mott, Charles Darwin University

Sure, the bumper sticker says, “If you can read this, then thank a teacher”.  And that is true, you should probably thank a primary school teacher.

But in the six seconds it took you to read to this point you breathed three times, and microscopic plankton produced around two-thirds of the oxygen you breathed into your lungs. In fact, you have been reliant on plankton for much of your oxygen since you were born. This is not to say that the trees, plants and large intact forests such as the Amazon are unimportant, but marine studies since the 1980’s revealed that the tiny microorganisms that photosynthesise like plants and float around in the ocean are much, much more important than anyone realised. Collectively they contribute more oxygen into the atmosphere than any other living species. Plankton matter much more than your science teachers knew when they were trying to pique your interest.

RV Investigator sits at the wharf in Hobart, Tasmania before departing on the 2019 CAPSTAN voyage providing 18 students from across Australia hands-on training in marine science
RV Investigator sits at the wharf in Hobart before the voyage

This week eighteen postgraduate University students interested in the marine environment boarded CSIRO’s RV Investigator and sailed from Hobart on a slow trip to Fremantle to better understand Australia’s marine estate, which is actually larger than all the land Australia is responsible for. Along the way they have undertaken studies of plankton at various locations and at various depths, guided by another 20 senior scientists and technicians.  They also filled in some poorly defined spots by mapping the ocean floor, collected and examined samples of often ancient mud, gravel and ooze from undersea canyons, and measured different currents from the surface all the way to the ocean floor. But breathing is important, so arguably the plankton studies matter the most.

CAPSTAN student Anthony Mott stands on one of the outside decks of RV Investigator as the ship departs Hobart for 10 days of at-sea marine science training
Enjoying the deck of RV Investigator

Plankton are a broad category of tiny, often microscopic organisms that live mostly by drifting around in the water and include both plants and animals.  Some generate energy by acting like plants, and others devour other plankton. Plankton exist in both fresh and seawater, but marine plankton outnumber the rest simply by sheer number. The plankton that generate the oxygen we rely on are the plant-like plankton which photosynthesise just like plants on land – taking in CO2 and water, and releasing oxygen. They can have very short life cycles and can reproduce really quickly when conditions are right – often producing massive natural blooms in response to a sudden increase in nutrients, such as runoff from land or agricultural areas following a major storm.  Most marine plankton are made up of single cells and their small size means they are highly efficient and are an important mechanism for soaking up CO2 from the atmosphere, so plankton are an important part of the global carbon cycle.

CTD rosette with 36 niskin bottles is recovered from the ocean on board RV Investigator as part of CAPSTAN's hands-on marine science training
The niskin bottles on the CTD rosette can be seen coming out of the water

Once the RV Investigator neared the Victorian coast near Portland it positioned itself at the head of three undersea canyons to investigate their role in channelling coastal soil and sand down onto the undersea continental slope-looking at how they funnel cool, nutrient rich deeper water up from the depths up onto the continental shelf. This concentrated source of nutrients underpins a broad marine food web – with plankton being the first organisms to capitalise on the nutrient supply.  Very fine nets were dropped to capture the plankton populations at different depths.  Water samples were collected at the top, sides and bottom of the canyon systems. Collecting samples at different depths and locations provided important information on which conditions best suit different species, as well as provided some insights as to how widely certain species are distributed.  Nutrient rich waters close to the surface may contain up to a million microscopic plankton in one litre of water, whereas similar locations can yield completely different results with variations in factors such as temperature or nutrients. The Southern Ocean that circles just above Antarctica seems particularly important. And 40-odd marine scientists and students want to know why because any change in the mix and number of plankton may have significant implications for oxygen supply and the changing climate.

Deployment of the bongo nets for plankton sampling from RV Investigator as part of the CAPSTAN hands-on marine science training program.
RV Investigator’s crew and support staff deploy the Bongo nets to recover a vertical tow plankton sample

The southern Australian coast is home to many marine species not found anywhere else in the world. This region also attracts much travelled species like Southern Bluefin Tuna that spawn south of Indonesia and migrate south down the WA coast and across the Great Australian Bight to SA and Victoria; Southern Right Whales come here t0 breed and calve. The area also attracts rare and endangered marine mammals like Sperm, Killer, Blue, Minke, and Humpback Whales. It’s easy to be distracted by the big things, but they are all dependent on a sustainable food web that starts with the microscopic things that are easily overlooked. And that’s why 40-odd scientists braved forecasts of 12 metre swells and unpredictable weather to head into remote oceans to study the little, poorly understood, strange, but often beautiful creatures that make an under-recognised contribution to global oxygen and carbon cycles.

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