- Phytoplankton are microscopic, photosynthetic organisms that float freely in the upper layers of oceans, lakes, and other bodies of water. Often referred to as the “grass of the sea,” phytoplankton form the base of the aquatic food web, supporting nearly all marine life. Despite their small size, they play an outsized role in global ecological balance, climate regulation, and oxygen production.
- Phytoplankton include a wide variety of organisms, such as diatoms, dinoflagellates, cyanobacteria, and coccolithophores. These organisms contain chlorophyll and other pigments that enable them to perform photosynthesis, the process by which they convert sunlight, carbon dioxide (CO₂), and nutrients into organic matter and oxygen. Through this process, phytoplankton contribute at least 50% of the Earth’s atmospheric oxygen—rivaling the productivity of all terrestrial plants combined.
- Phytoplankton are critical to the carbon cycle, as they absorb vast quantities of CO₂ from the atmosphere. When they die or are consumed by other organisms, some of this carbon is transferred to deeper ocean layers, contributing to the biological pump—a natural mechanism that sequesters carbon and helps regulate Earth’s climate. Additionally, they produce dimethylsulfoniopropionate (DMSP), a compound that leads to the formation of cloud-condensing particles, which can influence global weather and temperature patterns.
- These microscopic plants also sustain the marine food chain. Herbivorous zooplankton feed on phytoplankton, and in turn, become prey for larger predators such as fish, whales, and seabirds. The abundance and diversity of phytoplankton directly affect the productivity and health of fisheries and marine ecosystems.
- Phytoplankton populations are sensitive to environmental changes. Factors such as light availability, nutrient concentration, temperature, and pH levels determine their growth and composition. For example, nutrient-rich upwellings in the ocean support large phytoplankton blooms, which can drive seasonal cycles of productivity. Conversely, warming waters, acidification, and pollution can cause declines or harmful shifts in phytoplankton communities. In some cases, certain species may proliferate excessively, resulting in harmful algal blooms (HABs) that release toxins and deplete oxygen in the water, threatening marine life and human health.
- Phytoplankton are also important indicators of ocean health and climate change. Scientists monitor their abundance and diversity using satellite imagery (based on chlorophyll concentrations) and in-situ measurements to assess ecosystem productivity and detect changes in oceanic conditions.
