Plankton

Planktons are freshwater or marine organisms that currents and tides carry since they are too weak or too small to swim against these forces. The term originates from the Greek word planktos, meaning ‘wanderer’ or ‘drifter.’ It shows that these organisms typically drift for their entire lifetime. However, some only drift when they are young and are classified as plankton during this period, but they grow large enough to swing against tides and currents with time.

While most of them are microscopic, less than an inch in length, you can find larger ones. There are two common ways to classify these organisms. These are zooplankton (animals) and phytoplankton (plants).

This article delves deeper into this subject to understand its significance to the environment. It shall pay close attention to issues like these organisms’ appearance, diet, habitat, reproduction, and threats.

Appearance

The term generally refers to a diverse collection of plants and animals. So, the term doesn’t refer to any single organism.  

They come in many shapes, including spheres, rods, chains, stars, and intricate geometric patterns. While many phytoplankton contain chlorophyll and appear green, others exhibit hues of brown, red, or golden due to additional pigments. Some even possess flagella (whip-like structures) for movement. Others have intricate shells made of silica (glass-like material) or calcium carbonate.

Some great examples of plankton are:

• Protozoa
• Algae
• Bacteria
• Archaea
• Fish eggs
• Crab larvae
• Dinoflagellates
• Radiolarians

Scientists confuse them with large floating seaweeds like Sargassum and many related multicellular algae. It is distinguished from nekton, strong swimming animals, and benthos, which refers to plenty of burrowing organisms on the seafloor.

In short, any animal or plant that is too weak or too small to swim is a plankton.

Types of Plankton

1. Holoplankton: Organisms that spend their entire life cycle as plankton. They do not transform into another form that would remove them from the planktonic state.
   
   Examples of holoplankton include many species of diatoms, dinoflagellates, copepods, amphipods, and jellyfish.
   
   These organisms are adapted to a life spent drifting or swimming weakly in the water column, relying on ocean currents for dispersal.
   
   
2. Meroplankton: Organisms that are planktonic for only part of their life cycle, typically during their larval or juvenile stages. After a period of time, these organisms undergo a metamorphosis which transitions them to a non-planktonic adult stage.
   
   Common examples of meroplankton include the larvae of most marine crustaceans, fishes, sea stars, sea urchins, and many bivalves.
   
   After they mature, they settle down as part of the benthic (bottom-dwelling) or nektonic (actively swimming) community.
   
   
3. Phytoplankton: Microscopic plant-like organisms that photosynthesize, forming the base of the aquatic food chain.
   
   
4. Zooplankton: Tiny animal-like organisms that feed on phytoplankton and other smaller particles.

Habitat

Planktons are available in large numbers in saltwater and freshwater. That’s why most people call them freshwater and marine drifting organisms.

However, there is enough evidence that some also spend part of their lives drifting in the atmosphere, for example, plant spores, pollens, and lightweight seeds.

According to the National Geographic Society, they are usually less in clear water than in brownish or greenish water.

Diet 

Phytoplankton make their food through photosynthesis. These plant-like living things contain chlorophyll, the green coloring matter found in plants, and use it to convert sunlight into energy. Once this process is over, they combine water and carbon dioxide to create a form of simple sugar known as glucose.

Phytoplankton store glucose as carbohydrates, which they rely on for survival. They also depend on nutrients they find in their surroundings, such as calcium and phosphate.

The zooplanktons also feed to survive and reproduce. However, unlike their counterparts that manufacture their food, these animal-like organisms prey on other planktonic creatures.

Reproduction

Many planktonic organisms reproduce sexually. Some use specialized appendages to prevent their partners from drifting away during copulation.

Studies have also shown that some planktonic organisms release sperm into the water column near their female counterparts. Once that’s done, the females take up the sperm, and the reproduction process moves on to the next step.

Some of these organisms release eggs and sperm simultaneously to increase the probability of fertilization. Chemical, environmental, and environmental cues often trigger this simultaneous reaction.

Asexual reproduction is not common in these invertebrates.

Significance

Plankton, though minuscule, play a monumental role in the Earth’s ecosystems, particularly in the oceans. Here’s a deeper dive into their significance:

As a Food Source

Plankton are the foundation of the aquatic food chain. They are crucial as a primary food source for a wide variety of marine organisms, from tiny krill to massive whales. Zooplankton, in particular, feed on microscopic phytoplankton and then themselves become prey for larger marine animals, including fish and squid, which in turn support commercial fisheries and other marine life higher up the food chain.

Part of the Biological Carbon Pump

Phytoplankton plays a significant role in climate regulation. They absorb carbon dioxide from the atmosphere, much like terrestrial plants, and produce oxygen. This process not only contributes to atmospheric oxygen but also helps mitigate the impacts of climate change by removing CO2. When phytoplankton die, they often sink to the ocean floor, sequestering carbon away from the atmosphere for millennia, a process crucial in controlling Earth’s carbon cycle.

Oxygen Production

Plankton contributes to over half of the world’s oxygen production. Through the process of photosynthesis, phytoplankton releases oxygen into the water, which is then exchanged with the atmosphere. This makes them critical not just to marine life but to all life on Earth, reinforcing the fact that the health of ocean ecosystems is tightly linked to the overall health of the planet.

Influence on Weather and Climate Patterns

Plankton also influences weather and climate patterns. The distribution and density of plankton in the world’s oceans can affect sea surface temperatures, which in turn influence climatic phenomena such as El Niño and the distribution of nutrients in the ocean.

Ecosystem Health Indicators

Plankton populations are sensitive to changes in environmental conditions, including water temperature, salinity, and pollution levels. As such, they are often used as indicators of ecological health for marine environments. Fluctuations in plankton populations can signal shifts in environmental conditions and can be early indicators of broader changes within the ecosystem.

Threats 

Like many animals, the rising sea temperature, ocean acidification, and climate change pose a great risk to them. Experts have also pointed out that plastic pollution is killing them in large numbers every day.

When environmental conditions change, often triggered by too much of a nutrient—such as nitrogen or phosphorus from fertilizer runoff—populations of some types of phytoplankton grow rapidly.

They play a primary part in the food chain in the sea, they are highly valuable for the ocean ecosystem. Crustaceans, whales, and fish are some sea creatures that thrive by feeding on them.

While it isn’t endangered currently, a combination of the factors presented in this section could lead to their extinction in the future.

6 Facts About Plankton

1. Besides energy from photosynthesis, phytoplanktons depend on nutrients available in the ocean, like nitrite, calcium, and phosphate, to thrive.
2. Most sea animals and large marine animals like whales eat zooplankton.
3. Blue whales can eat approximately 12,000 pounds of krill in a single feeding session.
4. They don’t swim independently— tides and currents carry them and determine where they go.
5. Many types of phytoplankton, such as copepods and diatoms, produce oil to keep them afloat.
6. Blue-green algae or cyanobacteria are also planktons, although they have unique characteristics.

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