13 – Biodiversity
123
BOX 13.1 MAJOR SOURCES OF SPATIAL AND TEMPORAL VARIATION
IN SPECIES RICHNESS
Spatial variation
Among tropical seas and oceans (e.g. Caribbean v. Pacific)
With distance from diversity hot-spots (e.g. Indonesia, Philippines triangle)
With increasing latitude (e.g. along the Great Barrier Reef)
Cross shelf (e.g. from mainland to the shelf break of the GBR)
Among seascapes (e.g. reefs v. inter-reefal areas)
Among habitats within reefs
Over depth ranges
Temporal Variation
Evolutional time (speciation, extinction)
Climate change (e.g. changes species ranges)
ENSO and Pacific Decadal Oscillations events (e.g. bleaching causing local extinctions)
Seasonal change (especially at higher latitudes)
Pulse events (e.g. storms)
Spatial and temporal variation
Anthropogenic effects (fisheries, eutrophication, climate change, introductions)
Natural perturbations (cyclones, tsunami, COTS, productivity)
Many factors are responsible for the high diversity
of biota found on coral reefs but in part it is due to the
diversity of habitats found within coral reefs—ranging
from soft sediments (both vegetated and unvegetated),
various reefal habitats, and pelagic and coastal habitats
that include mangroves and salt marsh. Habitats are
usually characterised by particular habitat-forming organisms and variation in geomorphology. For example,
Isopora cylindrica is a habitat-forming coral with spur
and groove geomorphology, creating a shallow habitat
(see Chapter 5).
For all groups of organisms associated with coral
reefs, the highest number of genera occurs in the triangle
of diversity delineated by Indonesia and the Philippines
(the so-called ‘coral reef triangle’) with numbers declining both eastward and westward as well as north and
south of this area. For example, while a total of 70 coral
genera occur in the Indo-Pacific, most of these occur in
the triangle with numbers declining across the Pacific
with 10 in Hawaii and only two on the Pacific coast of
America. The decline is smaller across the Indian Ocean
with 50 genera present on the eastern Indian Ocean reefs.
The Indo-Pacific is much richer than the Caribbean
where only 20 coral genera occur with only Acropora, Favia, Leptoseris, Madracis, Montastrea, Porites, Scolymia and
Siderastrea (Fig. 13.1) being shared between these two
coral realms, and no species of corals occur in both
realms. Similarly, as one moves north or south of this
triangle, numbers of genera decline, with only 30 genera
found at Lord Howe Island and 50 at Ningaloo on the
West Australian coast, and numbers continuing to decline southwards down to two genera at Rottnest Island
in the far south-west corner of Australia. If we now consider species of corals we find similar patterns. The genus Acropora represents the largest extant group of
reef-building corals and over 370 species have been
123
BOX 13.1 MAJOR SOURCES OF SPATIAL AND TEMPORAL VARIATION
IN SPECIES RICHNESS
Spatial variation
Among tropical seas and oceans (e.g. Caribbean v. Pacific)
With distance from diversity hot-spots (e.g. Indonesia, Philippines triangle)
With increasing latitude (e.g. along the Great Barrier Reef)
Cross shelf (e.g. from mainland to the shelf break of the GBR)
Among seascapes (e.g. reefs v. inter-reefal areas)
Among habitats within reefs
Over depth ranges
Temporal Variation
Evolutional time (speciation, extinction)
Climate change (e.g. changes species ranges)
ENSO and Pacific Decadal Oscillations events (e.g. bleaching causing local extinctions)
Seasonal change (especially at higher latitudes)
Pulse events (e.g. storms)
Spatial and temporal variation
Anthropogenic effects (fisheries, eutrophication, climate change, introductions)
Natural perturbations (cyclones, tsunami, COTS, productivity)
Many factors are responsible for the high diversity
of biota found on coral reefs but in part it is due to the
diversity of habitats found within coral reefs—ranging
from soft sediments (both vegetated and unvegetated),
various reefal habitats, and pelagic and coastal habitats
that include mangroves and salt marsh. Habitats are
usually characterised by particular habitat-forming organisms and variation in geomorphology. For example,
Isopora cylindrica is a habitat-forming coral with spur
and groove geomorphology, creating a shallow habitat
(see Chapter 5).
For all groups of organisms associated with coral
reefs, the highest number of genera occurs in the triangle
of diversity delineated by Indonesia and the Philippines
(the so-called ‘coral reef triangle’) with numbers declining both eastward and westward as well as north and
south of this area. For example, while a total of 70 coral
genera occur in the Indo-Pacific, most of these occur in
the triangle with numbers declining across the Pacific
with 10 in Hawaii and only two on the Pacific coast of
America. The decline is smaller across the Indian Ocean
with 50 genera present on the eastern Indian Ocean reefs.
The Indo-Pacific is much richer than the Caribbean
where only 20 coral genera occur with only Acropora, Favia, Leptoseris, Madracis, Montastrea, Porites, Scolymia and
Siderastrea (Fig. 13.1) being shared between these two
coral realms, and no species of corals occur in both
realms. Similarly, as one moves north or south of this
triangle, numbers of genera decline, with only 30 genera
found at Lord Howe Island and 50 at Ningaloo on the
West Australian coast, and numbers continuing to decline southwards down to two genera at Rottnest Island
in the far south-west corner of Australia. If we now consider species of corals we find similar patterns. The genus Acropora represents the largest extant group of
reef-building corals and over 370 species have been