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1(b) Marine Habitats

Within Queensland there are several major ecosystem types that are sometimes referred to as biomes. A biome is a region of interacting ecosystems with a similar climate, and plant and animal species. The community of living organisms, the physical environment that affects it, including the flow of energy and cycling of nutrients, is called an ecosystem. The term habitat is used for the place where a given species lives, including its food, water, shelter and the conditions suitable for its survival and reproduction.

Biomes may be freshwater, marine, desert, forest, grassland or tundra. Marine biomes cover about 75 percent of the Earth's surface and comprise oceans and coral reefs. They differ from freshwater biomes as they have high levels of salts in the water. In some areas such as estuaries, where rivers meet the sea and fresh water mixes with seawater, organisms have to cope with changes in salt concentration.

Organisms that live in marine habitats have specific abiotic (or physical) factors to contend with, such as:

  1. Buoyancy – the force or upthrust that assists in supporting the weight of an organism.
  2. Viscosity – the resistance to movement of the medium - in this case, the seawater.
  3. Temperature variation – of lesser extremes as compared to land habitats.
  4. Light Penetration – to only the first 20 metres or so from the ocean surface. Red light gets absorbed first by the water and blue light penetrates the farthest.
  5. Salts – giving marine waters a high concentration of salts in solution with 3.5% being the average salt content in seawater.
  6. Gases in solution – less oxygen is dissolved in seawater as compared to air.
  7. Density of the Water – which increases with depth, due to the weight of water above.

There are several activities that investigate these Physical Factors of Marine Environments in the For Teachers Section.

the Great Barrier Reef

The Great Barrier Reef.
Image: Dr. John Hooper, QM.

The biotic components of marine habitats refer to the organisms that live within them and the relationships that exist between them. Some interesting sessile marine organisms can be found on the sea floor. Sessile organisms are ones that remain fixed in place and generally don’t move about in the adult stage, although most have motile larval stages. Some examples are sponges, corals, giant clams, sea anemones and ascidians (tunicates and sea squirts). Sponges and ascidians are of special interest for research purposes as they produce many bioactive chemicals.

Ascidian, Sycozoa pulchra
Ascidian, Sycozoa pulchra.
Image: QM.
Sponge, Haliclona nematifera
Sponge, Haliclona nematifera. Image: Dr. John Hooper, QM.

Scientists from the Queensland Museum have been investigating some sessile sea creatures for possible biochemicals. Biodiscovery refers to the collection of small amounts of native biological resources (plants, animals, fungi and micro-organisms) and screening them to identify any bioactive compounds that may be used for commercial purposes, such as pharmaceuticals and insecticides.

Dr. John Hooper, Head of Biodiversity and Geosciences at the Queensland Museum, has been researching sponges and other sessile marine invertebrates for years. Through his collaborations, it was found that certain chemicals extracted from these organisms have the potential to:

  • combat different cancers
  • treat inflammatory and cardiovascular diseases
  • reduce the progression of osteoporosis
  • prevent or treat stomach ulcers and stomach cancers.

The benefits of these chemicals for human health are obvious.

Many of the organisms on the Reef live in special relationships with other organisms. Some types of relationships between organisms are:

  • Commensalism – one organism benefits and the other is not affected. For example, a remora (or sucker fish) which attaches to a shark and feeds on the remains of the shark’s meal.
  • Mutualism – both organisms benefit from the association. For example: clownfish and sea anemones; cleaner fish and giant grouper fish. In some cases the organisms must live together to survive. For example: zooxanthellae algae and hermatypic coral polyps; some sponges and cyanobacteria.
  • Parasitism – one organism (the parasite) benefits at the expense of the other (the host). The host is harmed in some way. For example: QX disease and oysters. Normally, a parasite doesn’t kill its host.
  • Predation – one organism (the predator) benefits by killing the other (the prey) for food. For example, the Crown of Thorns starfish eating coral polyps.
  • Competition – both organisms have the same needs or requirements. These could be for food, space, territory or mates. This may involve the same species (intra-specific competition) or different species (inter-specific competition). For example: sponges competing for space with corals.
Remora (sucker fish) attached to the side and belly of a Leopard shark.
Commensalism: Remora (sucker fish) attached to the side and belly of a Leopard shark. Image: Richard Ling, Creative Commons.
Clownfish Premnas biaculeatus, shown amongst the tentacles of a sea anemone.
Mutualism: Clownfish Premnas biaculeatus, shown amongst the tentacles of a sea anemone. Image: Leonard Low, Creative Commons.
Crown of Thorns starfish on dead coral.
Predation: Crown of Thorns starfish on dead coral. Image: Dr. John Hooper, QM.

You may like to try the Animal Adaptations and Marine Food Webs activities in the For Teachers section.

Useful web link: Diving the Gold Coast with Ian Banks

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