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The marine organism that supports all others They make up 98% of the biomass of the world’s oceans. They supply more than half the world’s oxygen. They are the major processors of the world's greenhouse gases and our greatest hope for mitigating the effects of climate change. They are the cause of diseases which are suspected to be spreading due to global warming, yet paradoxically they may hold a cure for cancer and the solutions for combating known diseases.
It is only recently that science has developed the technology to conduct large-scale (more than a few litres of seawater) studies on these tiny creatures. Even today, researchers can only grow between 0.1-10% percent of what exists in the oceans. In fact, we know more about distant stars and planets than we do about the microbes living in our oceans.
Marine microbes – the final frontier for marine science While marine science has historically focused its efforts on large charismatic marine creatures (such as seals, whales, coral reefs), or economically important food species (rock lobster, fish, abalone), we need to know more about the invisible creatures of the sea that provide the living backdrop against which all these species and their ecosystems hang in balance – and we need to know now. Today’s top marine scientists are warning that life under the sea is changing as a result of human activities on land which lead to global warming, pollution, overfishing and other threats to marine life. Evidence of these impacts has been seen in the decline of world fisheries, loss of coastal biodiversity, and increased outbreaks of marine diseases which lead to mass species die-off. However, the effect of such changes on the marine microbial community, the greatest biological component of all marine systems, remains unknown. Marine microbes may act as early warning indicators of stress in marine systems and are likely to be the best indicators of ocean health, yet we have not managed to harness their predictive capabilities. Pioneering work focusing on tropical marine microbial ecology by the Australian Institute of Marine Science is helping researchers and resource managers to better understand the critical role marine microbes play in ocean processes.
What is a microbe? The term ‘microbe’ generally encompasses all living organisms that are invisible to the naked human eye. Marine microbes include bacteria, fungi, algae, and various types of plankton. Although they are considered non-living, viruses may also be referred to by some scientists as microbes.
Microbial Partnerships Living with corals Zooxanthellae (like plants) use photosynthesis to provide the coral with nutrition. In exchange, the coral provides them with a safe home and some essential nutrients. Several studies have shown that the particular type of zooxanthellae a coral possesses, may determine the coral’s physiological characteristics. For example, corals hosting one type of zooxanthellae might grow fast while corals with another type may be able to tolerate more extreme temperatures. Some corals have been shown to host multiple types of zooxanthellae that can be "shuffled" according to varying environmental conditions. These corals are particularly resilient to bleaching. Increased stress to corals caused by increasing sea surface temperatures and other human impacts can cause the delicate coral/algal relationship to deteriorate which increases the coral’s vulnerability to disease. Mass coral die offs have been recorded in the Caribbean and AIMS researches are studying the coral/algal relationship in an effort to understand the potential impacts of climate change on coral reefs and the prospective threat of disease outbreaks to the Great Barrier Reef.
Living with sponges The partnerships between sponges and microbes appear to be highly complex associations where both organisms benefit. By working together, both sponges and their live-in microbes are better able to withstand environmental conditions, disease and predation. The sponge (like corals) can receive nutrients from the microbe with some sponges actually ‘farming’ bacteria inside their tissues. The sponge may use defensive chemicals created by the bacteria (a subject of much medical research) to defend its own tissue from predators. In exchange, the microbe gets a comfortable home inside the sponge.
Drug discovery and disease The sponge/microbe combination is a rich source of chemicals and more than 30 compounds are currently undergoing clinical trials as anti-cancer drugs. The compounds appear to be generated by the animals as natural defences against fungal or bacterial infections and cell mutation. In addition to holding potential cures for human disease, marine microbes are also the cause of many pathogenic infections. For example, the bacteria responsible for causing cholera and related diseases (Vibrio cholerae and Vibrio vulnificus) are widespread in our oceans. These microbes erupt in blooms (which are expected to increase in frequency with global warming) and spread disease. Understanding marine microbes and tracking algal blooms is providing scientists with ways of predicting where and when disease outbreaks are likely to occur. Other marine micro-organisms produce toxins when they bloom. For example, blooms of toxic algae are consumed by tiny crustaceans which are in turn consumed by fish and then by humans. Researchers from AIMS are working to develop biosensors to detect harmful compounds in food. Marine microbes are also known to cause mass outbreaks of disease in corals and sponges - two key marine animals. In Australasian aquaculture, viral infections have lead to mass death of pilchards in southern Australia and throughout New Zealand. Outbreaks of white spot (another viral infection) are devastating prawn farms worldwide. AIMS research has also shown that filamentous bacteria residing within hatchery tanks can become tangled around the mouthparts of baby lobsters, preventing them from feeding and making the larvae susceptible to bacterial infections which lead to death. New ventures in Australia’s aquaculture industry will be focused on understanding the role of microbes in the life cycles of aquaculture animals. Climate change: The microbial perspective Changes in temperature, nutrient availability and environmental pH could alter microbial processes. Any change in microbial cycles that determine ocean chemistry could have an influence on the earth’s climate. These small organisms could ultimately become the biggest players in efforts to mediate climate change. AIMS scientists are attempting to better understand the role of marine microbes in climate change in order to develop early warning indicators of environmental health in tropical marine ecosystems. While microbes can live without humans, we are totally dependent upon them for our continued survival.
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