Source: CSIRO

There are huge numbers of small ocean-roaming plants and animals, collectively called plankton. The word plankton comes from the Greek planktos meaning ‘to drift’. Trillions of plankton inhabit our seas and they are a lot of the food that supports life in the ocean.

Plankton is sensitive to changes in temperature, acidity and nutrients. The amount, growth and composition of plankton is critical. How much plankton there is, and where it is, determines how many fish, marine mammals and turtles are in the sea. They can even live inside the tissue of the organism (corals, giant clams, and some jellyfish) and provide them with nutrient. The tiny algae zooxanthellae live inside tropical corals and provide most of their energy.

Plankton also produce about half of the oxygen we breathe too. Plankton can also influence the pace of climate change. Through photosynthesis, plankton suck carbon from the atmosphere. It has contributed to the ocean sucking up 40% of the carbon dioxide people have produced – it would be a much warmer world without plankton.

Our oceans are changing and plankton can show us how. Warming Australian ocean temperatures have altered the distribution of many plankton species. Researchers have found that on the east coast of Australia, plankton have moved southward by 300 km over the past 30 years. For example, he ‘red tide’ species Noctiluca scintillans, once only found around Sydney, is expanding throughout Australian waters and into the Southern Ocean. This species can cause problems for aquaculture farms.

Off Tasmania’s east coast at Maria Island, there has been a shift from cold-water to warm-water species. Warm-water plankton is smaller and some fish, seabirds and marine mammals won’t eat those new species.

Ironically, it is the zooplankton bodies that settled on the sea floor over millions of years has formed the oil we now burn.