Who’s at the bottom of the food chain?

Who’s at the bottom of the food chain? | Marine Biology

April 25, 2021

We’ve talked about how it all started, ending on the last universal common ancestor, more commonly known as LUCA. Today’s topic is about a microorganism that just floats along with the ocean current, an organism that is very much overlooked when we talk about marine life however, if removed from the equation, would end up collapsing the entire ecosystem. I’m talking about Planktons.

So, the word Plankton literally translates to “drifter” in Greek, since their only form of locomotion is to be carried by the current. Plankton are usually microscopic, often less than one inch in length, but they also include larger species like some crustaceans and jellyfish. Some planktons stay planktons their whole life, for example; krill, that are the main source of food for Blue whales.

Scientists have divided planktons into 3 groups; Phytoplankton, Zooplankton and Bacterioplankton.

Phytoplankton

Phytoplankton are microscopic plants that play a huge role in the food web. Like plants on land, phytoplankton perform photosynthesis to convert the sun’s rays into energy to sustain themselves. Most phytoplankton are buoyant and float in the upper part of the ocean, where sunlight penetrates the water to be able to carry out photosynthesis.

The two main classes of phytoplankton are dinoflagellates and diatoms. Dinoflagellates are a group of unicellular protists that can be identified using the light microscope, and are recognized by their golden-brown plastids, assimilative cell with indented waist and relatively large nucleus that contains visible chromosomes. Diatoms are single celled algae that live in houses made of glass. They are the only organism on the planet with cell walls composed of transparent, opaline silica. Diatom cell walls are ornamented by intricate and striking patterns of silica.

Zooplankton

Zooplankton are a type of heterotrophic plankton that range from microscopic organisms to large species, such as jellyfish. Zooplankton are found within large bodies of water, including oceans and freshwater systems. There are 2 types of zooplankton; holoplankton, or animals that spend their entire lives as plankton like copepods and rotifers, and meroplankton, or animals that are only planktonic for a short time like larval fish and crustaceans.

Bacterioplankton are typically assumed to be limited by the availability of organic carbon and, since algal carbon appears to be the preferred substrate for bacterial metabolism, bacterial production should be closely linked to algal production and/or biomass.

Bioluminescent Plankton

One of my personal favourite types of plankton are bioluminescent plankton (mainly because they glow and make the water look so mesmerizing). Luciferase is an enzyme. The interaction of the luciferase with oxidized luciferin creates a by-product, called oxyluciferin. More importantly, the chemical reaction creates light. Bioluminescence is used to evade predators and acts as a defence mechanism. They produce light when disturbed and will give a light flash lasting a fraction of a second. The flash is meant to attract a predator to the creature disturbing or trying to consume them.

Bioluminescent Plankton

So, the big question is, why should we care about planktons? They are so microscopic; they seem insignificant to us… right? Well, the whole ecosystem is a chained system, so if you take one of the working members out of the chain, the whole system collapses.

We all know phytoplankton photosynthesise; they account for about 50% of the oxygen in our air. With no phytoplankton to clear up the waste, the zooplankton have nothing to eat. So, both types of plankton are removed from the picture. With no plankton, the diet of smaller predators like dolphins, whales and sharks are compromised, they will soon perish. The whole food web that is so delicately balanced, fully collapses.

It’s now discovered that plankton account for 20% of all photosynthesis on Earth, and around 95% of the recycling of organic matter in the ocean. Without planktons, the ocean would just be a vast emptiness of water.

With the base of the food web gone, seabirds will have no fish to feed on, since these small fish survive off of planktons. Along with sea birds, seals and polar bears also go down.

With there being a lack of fish, it would affect over 3.2 billion people. 3.2 billion people all around the world eat fish, but its not just them who will be affected, it’s the fishing industry as well and that accounts for about an additional 59.5 million people! (20.5 million people were employed in aquaculture and 39.0 million in fisheries). So, if you think planktons are just marine creatures that wouldn’t affect us if they were to disappear, then think again. The absence of these tiny organisms would be a global catastrophe which most of us wouldn't survive.

If you enjoyed reading this, check out my previous post on how it all started, check it out!

https://musings-of-a-musical-biologist.blogspot.com/2021/04/how-it-all-started-marine-biology.html

Citations:

What are plankton?

https://oceanservice.noaa.gov/facts/plankton.html

https://www.nationalgeographic.org/encyclopedia/plankton/

https://oceanconservancy.org/blog/2019/08/09/plankton-small-organism-big-role/

Phytoplankton-

https://oceanservice.noaa.gov/facts/phyto.html

Dinoflagillate-

https://www.sciencedirect.com/topics/earth-and-planetary-sciences/dinoflagellate

Diatoms-