The Great Barrier Reef is the largest and most complex reef system in the world. It stretches more than 2000 km along the north-east coast of Australia and is one of the only natural structures that can be seen from the moon.
Australians and tourists alike are well acquainted with the Great Barrier Reef as one of the world's great natural wonders. What they are not so familiar with is the importance of the surrounding bluewater zone to the survival of the Great Barrier Reef. Compared to the colourful and highly visible reef these clear blue waters look empty and barren, but on closer inspection they are teeming with life - Plankton.
The word Plankton comes from the Greek word planktos, which means 'wandering' or 'drifting'.
The animals (zooplankton) and plants (phytoplankton) that make up the plankton either float passively in the water, or have such limited powers of swimming that they are carried from place to place by the currents.
Phytoplankton are tiny, photosynthetic organisms, that manufacture their own food using the energy from sunlight and produce oxygen as a by-product. They are often referred to as tiny plants because of this ability to photosynthesise, but many species are more closely related to protists and bacteria than true plants. hytoplankton produce more oxygen than all other plant life on earth and are vital in maintaining the earth's atmosphere. They are also the organisms most likely to be affected by gobal warming and climate change.
Zooplankton are floating or weakly swimming animals that rely on water currents to move any great distance. Zooplankton includes both holoplankton - animals that spend their entire lives as part of the plankton, as well as meroplankton - those that only spend a larval or reproductive stage as part of the plankton.
To most people the jellyfishes are probably the most visible and best known of the holoplankton. The tropical waters around the Great Barrier Reef contain a huge diversity of jellyfishes, all of which are predatory, securing their prey using stinging cells (nematocysts) or sticky cells (colloblasts).
Meroplankton includes the animals that spend only the early stages of their life as part of the plankton, and later move to the reef. Some, like polychaete worms, will then revisit the plankton during their reproductive stages.
Many of the common, well-known animals found on the Great Barrier Reef spend their early lives as free-swimming meroplankton, bearing little or no resemblance to the animal they will become. The differences between the appearance and behaviour of larval and adult stages has led to much confusion in the past when larval forms were often believed to be completely different species than the adults.
Plankton range in size from tiny microbes, invisible to the naked eye, to jellyfish that are metres long. Apart from the bacteria, planktonic organisms are the most abundant life form on earth and play a crucial role in the marine food chain. Plankton are food for animals ranging from barnacles and sea squirts, to large fish and whales. The largest fish in the world, the Whale shark, is a plankton feeder as are many of the largest whales. Without plankton, there would be few living organisms in the world, and certainly no Great Barrier Reef.
Beyond the Reef is an Australian Museum exhibition about these fascinating and often overlooked creatures and their lives spent suspended in the deep blue waters surrounding the Great Barrier Reef. The exhibition will feature stunning photographs from world famous English documentary makers,
Image Quest, including several three-dimensional images. It will also feature specimens from the Australian Museum's vast collections and a short film produced by Richard Smith of the ABC about ground-breaking research carried out in this field by Australian Museum Scientists.
Brooke Carson-Ewart
An Australian Museum Website
Copyright © Australian Museum 2003
