Is phytoplankton an algae?

Most phytoplankton are algae — diatoms, dinoflagellates, green algae, and golden-brown algae are all algae. The exception is cyanobacteria (blue-green algae), which are technically photosynthetic bacteria, not algae. So phytoplankton is a functional ecological group, not a taxonomic one: it includes algae plus a few bacteria that live the same way.

Where do phytoplankton live?

Phytoplankton live in the euphotic (sunlit) zone of any body of water — typically the top 0–200 meters of the open ocean, and just a few meters in murky lakes. They cannot survive below the depth at which sunlight is too dim to power photosynthesis.

How are phytoplankton different from zooplankton?

Phytoplankton are autotrophs — they make their own food via photosynthesis. Zooplankton are tiny drifting animals (heterotrophs) that eat phytoplankton or each other. Phytoplankton are the producers; zooplankton are the first consumers in the marine food chain.

What Is Phytoplankton?

Q: What are phytoplankton?

Phytoplankton are microscopic, plant-like organisms that drift in the sunlit layer of oceans, lakes, and rivers. They are not true plants but a diverse mix of single-celled algae and cyanobacteria — including diatoms, dinoflagellates, coccolithophores, green algae, and blue-green algae — that turn sunlight, CO2, and nutrients into food via photosynthesis.

Q: Why are phytoplankton important?

Phytoplankton produce roughly half of the oxygen in Earth's atmosphere, fix tens of billions of tonnes of carbon each year, and sit at the base of nearly every marine food web — from krill and small fish all the way up to whales. Without them, the ocean would collapse and atmospheric oxygen and CO2 would be drastically different.

Table of Contents (click to expand)

What Are Phytoplankton?
Why Are Phytoplankton Important?
Do They Cause Any Problems?

Phytoplankton are a group of microorganisms consisting of about 5,000 known species. They are known as ‘the grasses of the sea’. Most of them are buoyant in nature and float near the surface of the water. The major types of phytoplankton are diatoms, golden-brown algae, blue-green algae, green algae and dinoflagellates. They live in the euphotic (sunlit) zone of the ocean, the upper layer that extends from the surface down to a maximum of about 200 meters.

When we think of oxygen sources, the first thing that we think of are plants. However, does the sea or ocean immediately come to mind? No, it usually does not, but what if I told you that one particular inhabitant of the ocean is responsible for 50% of the photosynthesis carried out across the world. That sounds insane, right? This inhabitant isn’t even something that we can see by taking a dive into the ocean; in fact, it can’t be seen with the naked eye. It is microscopic in nature. The organism that I am talking about is phytoplankton.

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What Are Phytoplankton?

Phytoplankton are a group of microorganisms consisting of about 5,000 known species. They are known as ‘the grasses of the sea’. Most of them are buoyant in nature and float near the surface of the water. The major types of phytoplankton are diatoms, golden-brown algae, blue-green algae, green algae and dinoflagellates. They live in the euphotic (sunlit) zone of the ocean — the upper layer that extends from the surface down to a maximum of about 200 meters, and often much shallower. Although microscopists have studied phytoplankton for over a century, their global distribution only became visible from space in 1978, when NASA launched the Coastal Zone Color Scanner (CZCS) and started mapping ocean color from orbit.

Diatoms through the microscope — Phytoplankton (Photo Credit : Prof. Gordon T. Taylor, Stony Brook University / Wikimedia Commons)

Why Are Phytoplankton Important?

Phytoplankton carry out photosynthesis, using carbon dioxide and water to generate food for themselves, while giving out oxygen as a waste product. This reduces CO₂in the water and allows water to take in more from the atmosphere. This also provides the ocean with organic carbon, making phytoplankton a major factor in the Carbon cycle. The carbon is transferred to other levels of the ocean after being eaten by various sea creatures. The rest goes to the bottom of the ocean after the phytoplankton die. This system of phytoplankton helps to transfer 10 gigatons of carbon to the deep ocean every year, which greatly helps to keep the climate system in check.

What Are Phytoplankton?

The group is even important to the biogeochemical cycle. Through this cycle, a chemical substance moves through the biotic and abiotic cycle. Phytoplankton take up many elements from the ocean, which they transform and recycle so that other organisms can take them. One such substance is vitamins. The ocean is nutrient poor, so Phytoplankton take up vitamins and micronutrients that help other marine life.

Phytoplankton is also the foundation of almost all food cycles in the ocean. A number of sea creatures like krill, shrimp and jellyfish feed on them, which in turn become food for crustaceans and fish. In addition, we all know that those two are major parts of our own diet. Even larger organisms, such as whales and turtles, include phytoplankton as a part of their diet – sometimes a major part! This clearly indicates that the survival of major food chains is linked to the presence of phytoplankton.

Food chain. (Photo Credit : Siyavula Education / Flickr)

Do They Cause Any Problems?

After finishing their nutrients, phytoplankton die and begin decomposing. This leads to the loss of oxygen in the surrounding regions. The levels of oxygen drop and affect marine life. Such oxygen-depleted areas are called ‘dead zones’. Animals in the region die or move to areas that are more suitable for life.

Some phytoplankton even produce toxins that can be lethal to marine life and even humans if the growth occurs in coastal areas. Fortunately, few types of phytoplankton form Harmful Algal Blooms (HABs). These blooms cause respiratory problems for animals due to extreme oxygen depletion. Seafood, restaurant, and tourism industries take a serious financial hit from HABs — a Woods Hole Oceanographic Institution analysis pegs average direct US costs at around $50 million per year, while individual events can dwarf that: the 2018 Florida red tide alone is estimated to have cost tourism-related businesses about $2.7 billion.

Phytoplankton bloom in Lake Ontario. (Photo Credit : NASA Goddard Space Flight Center / Wikimedia Commons)

It is obvious that Phytoplankton are necessary for the survival of life as we know it. From climate cycles to food cycles, they are at the foundation of everything. It’s funny how highly developed organisms, including humans, are so dependent on single-celled organisms floating blindly in the vast ocean!

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