Understanding the Impact and Causes of Phytoplankton Blooms

Have you ever wondered why some parts of the ocean suddenly turn vibrant green or blue, transforming the waters overnight? These stunning colour shifts are caused by phytoplankton blooms. Recently, scientists reported that more than half of our oceans are turning green, a sign that they may contain more phytoplankton. Along the coast of California, hundreds of sea lions and dolphins fell ill or died due to exposure to toxic algal blooms triggered by harmful phytoplankton.

The rapid increase or accumulation of populations of algae (usually microscopic) in an aquatic system is considered an 'algal bloom'. Plankton are the foundation of life in oceans and freshwater, helping to support all kinds of aquatic life. They also play a big role in balancing gases in Earth's atmosphere. But due to the changing climate, the water and air of the planet are changing rapidly and this affects the plankton. Some of these effects are not good. Here's a look at what plankton is and their interactions with the climate.

What are plankton?

The word “plankton” is derived from Greek, with phyto meaning plant and plankton meaning wanderer or drifter. Phytoplankton are mostly microscopic, single-celled organisms that live in both salty and fresh water environments. Plankton are grouped into two types: phytoplankton, which are tiny plants, and zooplankton, which are tiny animals.

Some of the phytoplankton are cyanobacteria (also known as blue-green algae); and dinoflagellates, which have appendages that help them move. All algae are a type of phytoplankton, but not all phytoplankton are algae. Zooplankton includes krill, copepods, small shrimp-like crustaceans, and animals such as jellyfish. They usually eat phytoplankton and are then eaten by fish and other bigger animals.

Like land plants, phytoplankton contain chlorophyll, which they use to capture sunlight and convert it into chemical energy through photosynthesis. They consume carbon dioxide and release oxygen. While all phytoplankton photosynthesize, some also gain extra energy by consuming other organisms.

Causes of phytoplankton blooms

The growth of phytoplankton depends on the presence of carbon dioxide, sunlight and essential nutrients. Phytoplankton, similar to land plants, need nutrients like nitrate, phosphate, silicate, and calcium in varying amounts depending on the species. Some phytoplankton can fix nitrogen and grow in areas where nitrate concentrations are low. They also require small amounts of iron which limits the growth of phytoplankton in large areas of the ocean because the concentration of iron is very low. The growth rate of phytoplankton is influenced by various factors, including water temperature, salinity, depth, wind conditions, and the presence and type of predators grazing on them.

Why they are so important?

Plankton forms the essential base of the entire marine food web. Phytoplankton are microscopic plants floating in marine and aquatic ecosystems that produce 50–80% of the world's oxygen and contribute significantly to Earth's carbon cycle. When phytoplankton die, a portion of the carbon they absorb during photosynthesis sinks to the ocean floor, where it becomes sequestered away from the atmosphere. This process, known as the biological pump, allows the ocean to act as Earth's largest carbon sink, moving 10 billion metric tons of carbon from the atmosphere to the ocean's depths every year.

Protein-rich phytoplankton can serve as a sustainable alternative to fishmeal in aquaculture and as a supplement for meat and soy-based animal feeds. Planktonic enzymes are utilized in the production of pharmaceuticals and food products. Fats obtained from plankton are added to cosmetics and food supplements. They can also used as fertilizers in place of chemical-based products. Organic compounds produced by plankton can be used to treat Alzheimer's, cancer, diabetes, AIDS, osteoporosis, and other diseases.

Consequences of phytoplankton bloom

Phytoplankton can also cause death or disease. Some species of phytoplankton produce powerful biotoxins, making them responsible for so-called "red tides" or harmful algal blooms (HABs). These harmful blooms can kill marine life and people who eat contaminated seafood. Cyanobacteria and dinoflagellates are the most common toxin-producing groups of phytoplankton in fresh and marine waters, respectively.

Cyanobacteria produces a wide variety of cyanotoxins including hepatotoxic (liver-damaging) microcystins, nodularins, and cylindrospermopsins, neurotoxic (nerve-damaging) saxitoxins and anatoxins, and dermatoxic (skin-damaging) Lyngbya toxins. The two most common ways humans, pets, and livestock are exposed to toxins are through drinking contaminated water and skin contact during recreational activities.

Red tide dinoflagellate blooms of Karenia brevis produce brevetoxin that kills fish and other marine life and, when aerosolized by wave action, can cause respiratory irritation in humans. The decomposition of phytoplankton reduces oxygen levels in the water, creating hypoxic (low oxygen) areas where aquatic life cannot survive.

How to control phytoplankton bloom?

Bloom formation can be controlled by nutrient concentration and/or controlling the light and temperature. The following are a few practiced processes by which bloom can be controlled:

Biological and chemical controls-

Inoculation of cyanophage (virus that insects cyanobacterial cells) for controlling cyanobacterial bloom is a common phenomenon. Algaecides can be used to control phytoplankton blooms. Copper-based algaecides can effectively kill most phytoplankton groups, and algaecides containing hydrogen peroxide can be equally effective on cyanobacteria, without potentially unintended toxic effects at higher trophic levels.

Light shielding-

Light is the major factor for bloom formation. Light shielding is therefore an easy process for bloom control. Shielding can be done by covering with some dark sheet or by floating agiospermic plants like Eischornia and Lemna.

Monitoring and Early Detection-

Remote sensing technologies, such as satellite imagery and in situ monitoring, help detect blooms early, enabling timely interventions.

Public Awareness and Education-

Educating communities on the causes and risks of HABs encourages responsible behaviors, like minimizing fertilizer use and reporting unusual water discoloration. Public awareness campaigns also promote safety measures for individuals who may be exposed to harmful blooms.

This article highlights that while blooms can support marine life and fisheries, harmful algal blooms (HABs) can also release toxins or damage the environment in other ways. By implementing these strategies, we can help protect water resources and reduce harmful phytoplankton blooms.