Despite their minute size, the tiny organisms known as plankton hold significant sway in our ocean’s ecosystems. Plankton, derived from the Greek word “planktos,” meaning ‘drifter’ or ‘wanderer,’ cannot swim against the water current. These tiny organisms are essential to life on Earth for many reasons that we will explore in this article.
Types of Plankton
Plankton can be divided into different categories based on their trophic level, function, and size:
- Phytoplankton: These are microscopic plants that form the base of the aquatic food web. Via photosynthesis, they utilize sunlight to convert water and carbon dioxide into glucose, which is energy for themselves and for those who consume them. They produce half of the world’s oxygen[^1^].
- Zooplankton: These are small animals and animal-like organisms, including larval forms of fish, crab, and other marine species. Zooplankton feed on phytoplankton and bacteria.
- Bacterioplankton: Responsible for recycling compounds that other marine life need to survive, these organisms play a significant role in the nitrogen and sulfur cycles.
Role of Plankton in the Ecosystem
Marine ecosystems largely depend on phytoplankton. They are foundational to the aquatic food web, feeding an array of creatures—from zooplankton to whales. While phytoplankton represents the food, the zooplankton are the primary consumers. The healthier the phytoplankton population is, the healthier the rest of the ocean will be.
Plankton also plays a significant role in carbon sequestration. Their photosynthesis process takes in carbon dioxide and releases oxygen. When they die, they sink to the ocean floor, carrying the absorbed carbon to the depths, often storing it there for centuries[^2^].
Impact of Climate Change on Plankton
Increasing ocean temperatures significantly affect plankton populations. Warmer water temperatures can stimulate plankton growth in some areas, but they can also alter ocean currents and nutrient availability, resulting in less predictable blooms.
Ocean acidification, another impact of climate change, is detrimental to many phytoplankton species, especially those that create shells or skeletons like coccolithophores. A decrease in pH makes it more difficult for these organisms to form their calcium carbonate exteriors, leading to reduced populations and a shift in species composition[^3^].
Monitoring Plankton for Ocean Health
Scientists monitor plankton populations to assess the ocean’s health and make predictions about its future. Changes in phytoplankton populations can indicate broader changes in their environment.
For example, by examining plankton data, scientists were able to identify the Pacific Decadal Oscillation in the early 1990s – a large-scale climate phenomenon that impacts Pacific Ocean ecosystems. This ability to “read” the state of the oceans by studying their smallest inhabitants is a powerful tool in the race to understand and combat climate change.
Plankton: The Unsung Heroes
In these times of growing concern over climate change, the significance of these seemingly insignificant organisms is increasingly acknowledged by the scientific community. The fragile balance of marine biodiversity hangs heavily on the wellness of the plankton population. Acting as the backbone of our ocean’s ecology and a significant weapon in combatting carbon dioxide emissions, they truly are the unsung heroes of the underwater world.
[^1^]: Falkowski, P., & Raven, J. A. (2013). Aquatic Photosynthesis (2nd ed.). Princeton University Press.
[^2^]: Passow, U., & Carlson, C. A. (2012). The biological pump in a high CO2 world. Marine Ecology Progress Series, 470, 249–271.
[^3^]: Riebesell, U., Zondervan, I., Rost, B., Tortell, P. D., Zeebe, R. E., & Morel, F. M. M. (2000). Reduced calcification of marine plankton in response to increased atmospheric CO2. Nature, 407(6802), 364-367.
