Phytoplankton are microscopic organisms that live in water and perform photosynthesis. These tiny plants are a vital part of the marine food chain, providing food and oxygen for fish, shellfish, and other sea creatures. Phytoplankton also play an important role in the global carbon cycle by absorbing atmospheric carbon dioxide and releasing oxygen into the atmosphere.
There are two main types of phytoplankton: diatoms and dinoflagellates. Diatoms are single-celled algae that have a hard, glass-like shell made of silicon dioxide. Dinoflagellates are also single-celled algae, but they do not have a hard shell. Both types of phytoplankton float in the water column and are able to move using tiny appendages called flagella.
Phytoplankton populations can fluctuate rapidly in response to changes in environmental conditions such as temperature, light intensity, nutrient availability, and salinity. These fluctuations can have major impacts on marine ecosystems since many animals rely on phytoplankton for food. For example, large blooms of dinoflagellates can sometimes occur which can lead to harmful algal blooms (HABs). HABs can cause fish kills and make shellfish unsafe to eat due to the accumulation of toxins in their bodies.
climate change is causing ocean temperatures to rise which is having negative impacts on phytoplankton populations around the world. Warmer ocean waters can cause phytoplankton blooms to occur earlier in the year than they normally would which disrupts the timing of the marine food web. Additionally, rising CO2 levels are making oceans more acidic which makes it harder for some species of phytoplankton to build their shells or skeletons properly leading to lower populations overall.