Science for sustainable reefs

Glossary

atoll. Circular shaped coral islands that either partly or completely surround a central lagoon.  Atolls form around submerged volcanic islands. They are typically low lying, so their human populations are susceptible to rising sea levels due to climate change.

biodiversity. Biological diversity. A measure of the variety of life. It is usually calculated from the number of species of organisms – although genera, families, classes and phyla can all be counted too. For more information see Biodiversity and its value (Australian Government Department of the Environment, Water, Heritage and the Arts).

bivalve. A mollusc with the shell in two parts hinged together as in mussels, scallops or clams. Bivalves are bilaterally symmetrical, have a reduced head and large gills that are used for gas exchange and filter feeding.

coral bleaching. Loss of colour of corals due to an environmental stress from such causes as increased water temperature, pollution or sedimentation. Environmental stress can cause corals to expel microscopic algae from their tissues. These symbiotic algae provide up to 90 per cent of the coral’s energy needs. Loss of these algae results in the bleached appearance of corals as they provide most of the coral’s colour. Bleached corals often starve then die if the stress persists. For more information see Coral bleaching – will global warming kill the reefs? (Nova: Science in the news).

diatom. Microscopic, single-celled algae that have a silica-based skeleton. Diatoms are found in a range of aquatic environments including freshwater, marine and moist soils.

El Niño-Southern Oscillation (ENSO). A sporadic climatic phenomenon that occurs because of changes in the usual atmospheric pressure patterns and in the sea surface temperature in parts of the Pacific Ocean. The results include the substantial reduction of the normal upwelling off the Peruvian coast, failure of the anchovy fishery in the same area, excessive rain in western South America, and droughts in Australia, parts of Asia and southern Africa.
 
ocean acidification. The lowering of the pH of oceans due to increasing levels of carbon dioxide. Ocean acidification affects the growth, structure and health of certain types of microscopic algae (phytoplankton), corals and other marine organisms with calcium carbonate skeletal structures. For more information see Acid test for the seas (Nova: Science in the news).

phase-shift. A shift from one type of ecosystem to another. Each has a distinctive set of species, and each can be highly persistent. A common example is a shift from ecosystems dominated by corals to degraded systems that are characterized by large amounts of seaweeds or other weedy species. Overfishing and pollution undermine the resilience of coral-dominated ecosystems, making phase-shifts more likely to occur.

phytoplankton. Microscopic, photosynthetic algae that live in water. Plant-like plankton.
 
resilience. The ability of an ecosystem, such as a coral reef, to cope with repeated external disturbances (such as a major warming of the ocean or a large storm) without fundamentally changing. Resilience is an aspect of ecosystem dynamics that prevents phase-shifts. Ecosystems with greater biodiversity are usually more resilient to disturbances.

rising sea levels. Increasing height of sea levels due to global warming. A warmer world will have a higher sea level because as the land and atmosphere warm, heat is transferred into the oceans. When materials are heated they expand (thermal expansion). So the heat that is transferred causes sea water to expand, which then results in a rise in sea level. In addition, water from land-based ice such as glaciers and ice sheets may enter the ocean, thus adding to the rise. For more information see Getting into hot water – global warming and rising sea levels (Nova: Science in the news).
 
sustainable. An activity that is capable of being maintained at a steady level without depleting natural resources or causing excess damage to an ecosystem. A sustainable yield in fisheries is achieved when the number of fish removed does not eventually cause the fish stock to collapse.

symbiotic. Describes a relationship between two species that live together, to the benefit of at least one of them. Some symbiotic species are unable to live without each other. Algae (called zooxanthellae) live within corals. The zooxanthellae gain protection, access to sunlight for photosynthesis and nutrients from the nitrogen waste that the coral produces. The coral benefits from the removal of wastes and from the sugars produced by the zooxanthellae.

turbidity. A measure of the suspended solids or cloudiness of water. Turbidity can be increased by sediment, often fine clay or silt that is discharged into the sea by rivers. Turbidity can also be caused by floating micro-organisms such as in an algal bloom. Increased turbidity reduces the penetration of light through water, reducing the growth of aquatic plants and corals. For more information see Turbidity (Waterwatch, Australian Government).

zooxanthellae. Symbiotic algae that live in a range of marine animals such as corals. In corals, the zooxanthellae gain protection, access to sunlight for photosynthesis and nutrients from the nitrogen waste that the coral produces. The coral benefits from the removal of wastes and from the sugars produced by the zooxanthellae, which make up over 90 per cent of the coral's food.


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Posted September 2009, edited August 2012.