On 21 November, Surviving the Century at the Zoological Society of London (ZSL) asks how dependent human health is on the health of the animal populations around us. Four speakers will each put the case for an animal species that we simply can’t survive without. Here Richard Kirby puts the case for plankton. What do you think? Add your comments at the bottom.
Zooplankton are the myriad animals drifting at the sunlit surface of the sea. Although the largest plankton – the jellyfish – may be familiar, most live unseen, with many no bigger than a grain of rice. Despite their small size, however, the zooplankton are the unsung heroes of life on Earth. They influence almost every aspect of our lives, from the food that we eat to the petrol in our cars, and, most importantly, they play a central part in the global carbon cycle.
Foodchain providers. The plankton food web underpins the marine food chain, a web of life providing an annual harvest of over 115 million tonnes of seafood. Although this food web begins with the phytoplankton (plant-like cells that harness sunlight to convert carbon dioxide into organic carbon compounds that form the tissues of their bodies), it is the zooplankton (a great array of animals ranging from copepods and krill to the juvenile planktonic stages of creatures that live on the sea floor, such as crabs, shrimps, cockles and mussels) that make the plankton food chain. This plankton food chain provides the food for all of the other animals in the sea, from fish to baleen whales, from sharks to dolphins, seals and polar bears, and from penguins to every other seabird. It would be hard to contemplate a world without all these creatures or to imagine how their absence might alter life on Earth. Although pirates would have had less to fear from keel hauling without any barnacles, what would a childhood holiday at the beach be like without crabbing from the pier, or a southern ocean be without its evocative wandering albatross ?
Carbon converters. While the sea would be a barren wilderness without the plankton food web, what often goes untold is how, over millions of years, the zooplankton have shaped life on Earth through their role in the global carbon cycle. The organic carbon in oil and gas is, largely, the dead remains of plankton and their faecal pellets, which settled to the seabed over tens or hundreds of millions of years. Since this carbon originated in the atmosphere as carbon dioxide gas – fixed first by phytoplankton photosynthesis, before being transferred up the food web by the zooplankton – its removal represents the biological sequestration of this greenhouse gas. The burial of this organic carbon also serves to maintain the oxygen content of our atmosphere. For every organic carbon atom that enters the sediment reservoir, the oxygen freed during its formation by phytoplankton photosynthesis has not been reused by respiration of decomposition and returned to the atmosphere as carbon dioxide gas.
Climate regulators. The plankton have been central to the evolution of life on Earth. Now, by burning oil and gas, we are returning carbon to the atmosphere far faster than it is removed by the plankton food web. This is leading to rising levels of atmospheric carbon dioxide and warmer air and sea surface temperatures. Today, as their habitat warms, the plankton are changing in their abundance, seasonality and distribution with consequences for the marine food chain and the ecology of our planet. Arguably, it has never been a more important time to pay attention to the unsung heroes of life on earth, the zooplankton that live at the sunlit surface of the sea.
Richard Kirby‘s initial interest in animals led into a zoology degree at Exeter University, after which he obtained a PhD from UCL in 1992. He worked subsequently in the USA, first at Hopkins Marine Station and then at the Belle W Baruch Institute of Marine Science. Between 2003 and 2001 he held a Royal Society Research Fellowship. A molecular geneticist, his research interests focus on the plankton, primarily understanding their diversity, biogeography and evolution, and how their communities are influenced by current climate change. Richard is currently a Marine Institute Research Fellow at Plymouth University.