Download The Diversity of Ningaloo Reef

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NINGALOO: Australia’s Untamed Reef
3. Life on the Reef
Ningaloo Reef is one of the most diverse and exciting regions of Western Australia’s coast. The incredible diversity
of life that is sustained by Ningaloo brings with it the need for a wide variety of interactions between the various
organisms. Each individual is required to communicate a range of messages to a number of others in order to
survive and reproduce. Predators, prey, competitors, partners and symbiotic associates all need to receive the right
signals at the right time. To achieve this, reef organisms have evolved the most amazing (and sometimes bizarre)
anatomical structures, colouration or behaviours. The result is an enormously complex and fascinating ecosystem
full of alliances and struggles, tranquillity and terror, beauties and beasts.
The Diversity of Ningaloo Reef
Ningaloo Reef is part of the Indo-Pacific region,
renowned for the highest biodiversity in the world’s
oceans (Topic Box 7)52,53. The centre of this
biodiversity hotspot lies closer to the equator, where
reefs have survived for hundreds of millions of years,
and it is linked to Ningaloo Reef through the
presence of the Leeuwin Current. The major part of
Ningaloo Reef’s biodiversity is a direct result of this
link and consists of tropical organisms that over the
past 8,000 years or so have established themselves in
the region alongside a minority of subtropical and
temperate organisms. About 220 species of hard
corals, 120 species of octocorals (e.g. soft corals,
gorgonians and sea pens), 650 species of molluscs
(e.g. mussels, abalone, snails, squid and octopus),
140 species of echinoderms (e.g. sea stars and
urchins) and 500 species of fish have, so far, been
reported to inhabit Ningaloo6,22. These residents
share the reef with a series of spectacular seasonal
visitors such as: whale sharks, manta rays, dugongs,
four species of marine turtles and up to 20 species of
cetaceans (i.e. dolphins and whales)6.
The significant biodiversity of Ningaloo,
and coral reefs in general, is largely a result of its
motley environment consisting of a wide range of
habitats, each of which is packed with specific
creatures (Topic Box 8). Traversing the reef some of
the more basic habitats can be easily recognised.
From north to south
Along Cape Range peninsula the continental shelf is
exceptionally narrow, which places the northern
section of Ningaloo Reef in the path of the Leeuwin
Current. The increased influence of the Leeuwin
Current on this part has resulted in an enormous
tropical biodiversity that is unequalled elsewhere on
the reef. The southern section, in contrast, lies about
four times further from the edge of the shelf and
misses out on some of the tropical species found at
the reefs adjacent to the Cape Range peninsula and
the Muiron Islands. But part of what the southern
end lacks in tropical diversity it gains in temperate
and sub-tropical species as numerous organisms
reach the northern limit of their distribution here6.
In the central region of Ningaloo Reef, i.e.
between Point Edgar and Coral Bay, the lagoon is 3-7
km wide, much wider than at the northern and
southern parts54. Here large patches of sandy habitats
are interspersed with seagrass beds, limestone macro-
algae habitats and patches of coral reef6. The soft
sediment habitats are characterised by coarse sand
and, occasionally, coral rubble. The sandy bottom is
often overlain by a film of microalgae and other
organisms that provide food for a very diverse range
of invertebrates, such as grazing molluscs, polychaete
worms and crustaceans that live on or under the
surface. These, in turn, attract numerous other
invertebrates, rays and fish that prey on burrowers.
The sandy substrate is also perfect for seagrasses,
forming the basis of yet another type of community
where juveniles of many fish and crustaceans find
shelter and food. In other places within the lagoon,
limestone structures are ideal foundations for algal
communities. Like seagrasses, algae contribute to
primary production and provide shelter for many
invertebrate and vertebrate animals. Algae and, in
particular, seagrasses attract some extraordinary
grazers including the elusive dugong and the
endangered green turtle.
Life on the Reef
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Moorish idols (Zanclus cornitus, Family Zanclidae) are ‘generalists’ – feeding on a wide range of algae
and invertebrates – and are found in many different habitats. (Photo: Craig Kitson)
One of the numerous growth
forms of Acropora corals
(Family Acroporidae). (Photo:
Craig Kitson)
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NINGALOO: Australia’s Untamed Reef
Top: Orca’s (Orcinus orca, Family
Delphinidae) are seasonal visitors
at Ningaloo – coming in to feed on
prey including dolphins, manta
rays and young whales. (Photo:
Andrew Morgan)
Right: One of the most famous
and charismatic seasonal visitors
at Ningaloo Reef: the whale shark
(Rhincodon typus). (Photo: Craig
Kitson)
Life on the Reef
Right: A school of seapike
(Sphyraena sp., Family
Sphyraenidae) in the lagoon north
of Mangrove Bay. (Photo: Blue
Office / MIRG Australia)
Below: Whereas most sea
cucumbers (Class Holothuroidea)
are freeliving and crawl over the
bottom, this species (Pentacta sp.,
Order Dendrochirotida) buries
itself and uses its large, branched
‘tentacular crown’ to filter organic
material from passing water.
Each oral tentacle in turn is bent
into the oral cavity to deliver food.
(Photo: Craig Kitson)
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