Why are phytoplankton important? Take a deep breath and fill up your chest. Feels good, doesn’t it? Where do you suppose that oxygen comes from? Everyone remembers learning about photosynthesis in high school biology…it’s the trees and grass, right? Sure, terrestrial plants do their part, but the true workhorses in global oxygen production are phytoplankton. These microscopic organisms account for only 1-2% of all plant matter, but are responsible for a staggering 50-70% of worldwide oxygen production!
Phytoplankton, from the Greek phytos meaning ‘plant’, and planktos meaning ‘wanderer’, are a diverse group of algae that produce food for themselves using photosynthesis–exchanging carbon dioxide for oxygen and sugar–just like plants on land. These organisms rapidly spread by the billion in warm, nutrient rich waters around the globe. According to Phytoplankton Ecologist Mike Behrenfeld, ‘If you were to take an empty coke can and go scoop up some water from the [ocean] shore, you’d have an order of 75 to 100 million phytoplankton in that coke can’.
Phytoplankton blooms form the foundation of the marine food chain, feeding everything from zooplankton, shrimp, small fish, to whales weighing hundreds of tons. As all food chains start with energy from the sun, and algae are the primary producers upon which all successive levels depend on, it can not be overstated their importance to all aquatic life . Remove these wanderers from the ocean, and you’d see starvation epidemics in coastal communities worldwide, as empty nets cause the seafood industry to collapse.
These little guys are also responsible for 95% of the recycling of organic matter in the world’s oceans, and are the most important agents for sequestering carbon to the deep. As plankton die off and decompose, much of the organic matter sinks to the ocean floor and collects in layers, a process known as ‘Marine Snow’. It has been estimated that this process successfully transfers over 10 gigatons of C02 from the atmosphere to the ocean floor every year. Add heat, pressure, and let it sit for a couple million years…you’ve got yourself a recipe for petroleum. Ever wonder where the oil comes from in off-shore rigs?
Things Are Heating Up…
Let’s get to it: what effect, if any, does global warming have on phytoplankton populations and distribution? Research isn’t extensive, but it’s safe to say we aren’t making things easy for them.
Algae thrive in warm waters and live close to the surface, but they also depend on cool, nutrient-rich waters to cycle up from the deep. Generally speaking, as surface water temperatures get warmer, buoyancy increases, and cold, dense water doesn’t mix as well. This causes further stratification of ocean waters. Deprived of nutrients, phytoplankton are unable to reproduce or perform essential life functions. Ocean stratification causes plankton blooms to trend towards increasingly polar waters, or fail to bloom at all. It has been estimated that warming ocean waters have reduced global populations by 1% every year; that’s an overall decrease of about 40% since 1950.
And things can get much worse. After a certain increase in ocean temperature (~5-6 degrees Celsius), the balance tips, and phytoplankton shift from net producers to consumers of oxygen. This leads to marine anoxia (oxygen deprivation), and large dead zones. Even scarier, It has been argued that ’Whenever the oxygen production rate falls below a certain critical value, sustainable dynamics becomes impossible, and the system experiences a free fall to the extinction/depletion state’. To be perfectly clear: we do not want this to happen under any circumstances.
Iron It Out…
Instead of treading water, oceanographers have developed several creative ways to try and restore phytoplankton populations.
Perhaps the best-known is a process known as Iron Fertilization. Iron is a necessary nutrient for algae to reproduce, and its absence precludes blooms in many areas of the Southern Ocean. The basic idea is to spread iron sulphate en masse into nutrient deprived waters either directly from a ship, or released as dust from a plane. Ultimately, these blooms would form a carbon pump that would help offset greenhouse gas emissions. As revered Oceanographer John Martin once quipped: ‘give me a half tanker of iron, and I will give you an ice age.’
While multiple expeditions have been undertaken to test the effectiveness of Iron Fertilization to varying degrees of success, the process remains controversial. Violation of global dumping treaties, the potential to create toxic ‘red blooms’, and questions of other unforeseen ecological impacts all hinder large scale fertilization projects.
Another more ambitious proposal is a startup that seeks to genetically engineer phytoplankton to become a more efficient carbon pump. In theory, these GMO algae would band together to form columns that reach the ocean floor, whereby nutrients can be cycled to the surface, and carbon dioxide can be deposited. While this concept is still in its infancy and leaves a lot of question marks, it’s nonetheless commendable that groups of engineers and ecologists are devoting time and resources to seek pathways to protect and develop phytoplankton populations.
Sometimes, Less Is More…
Human activity can also lead to excess blooms in areas that when left unchecked, disrupt habitats and can create marine dead zones.
In coastal areas, agricultural runoff often deposits a surplus of nutrients in surrounding waters. This in turn makes for perfect breeding conditions for algal blooms, whose thick surface cover block sunlight from reaching the sea bed, causing plants at the bottom to wither and die. The bacteria which decompose this decaying plant matter exhaust oxygen levels, and animals which inhabit the sea bottom either suffocate, or are driven from the area. The microbes that are able to withstand these low oxygen conditions typically produce lots of nitrous oxide, a greenhouse gas which is 300x more harmful to our atmosphere than carbon dioxide. This chain reaction, known as Eutrophication, is endemic to well populated coastal areas worldwide.
Marine dead zones are increasing in size and frequency. It’s been calculated that there has been a tenfold increase in dead zones since 1950, from 50 to 500 locations worldwide.
Clean Up Your Act
The rise of marine dead zones should alarm all of us, but fortunately there’s ample evidence proving that if we curb agricultural runoff, these zones can be revitalized.
Perhaps the best example of this is the Chesapeake Bay, the largest estuary in the United States. Once a dumping ground of agriculture and industrial runoff, animal populations were dwindling by the early 2000’s, and much of the bay contained zero-oxygen water. Key legislation restricting dumping, coupled with a reduction in commercial fishing and more efficient agricultural practices have spurred a boom in animal populations. As of 2017, ecologists recorded that dissolved oxygen had returned to Chesapeake waters to the point that it could no longer be classified as a dead zone. Other undertakings, such as the multilateral efforts made to clean up The Black Sea, have also proven successful.
You may have never given phytoplankton a thought, but if they up and disappeared, it’d only be a matter of time before you did too. These powerhouses put more oxygen into the atmosphere than any other organism, form the basis of the marine food chain, and safely sequester carbon to the abyss. Their numbers have been steadily decreasing because of human activity, and this should concern each and every one of us.
Want to do something? Support efforts to limit greenhouse gas emissions, reduce your own carbon footprint, donate to organizations like Oceana, contact your representatives about ocean conservation efforts, get involved, and perhaps most importantly, use your vote!