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13. Biodiversity
P. A. Hutchings & M. J. Kingsford
Biodiversity generally refers to species richness (i.e.
number of species), but other definitions are also common. It is critical that biodiversity is defined carefully as
it is sometimes considered synonymous with genetic diversity, habitat diversity, structural diversity, the diversity of functional groups (e.g. trophic groups of life
history stages) or even life history traits (e.g. feeding
type, growth forms, reproductive strategy, longevity).
Some definitions can be a proxy for species richness. For
example, species representation and abundance are
known to vary among habitats. Habitat richness, therefore, can be especially relevant where the taxonomy of
organisms in the various habitats is poorly known and
there are concerns to protect species richness. A critical
component of the zoning plan of the GBR (the Representative Areas Program, see Chapter 12) was partly based
on the protection of different habitats and used these as
surrogates to conserve species diversity as the biota on
the GBR is poorly known apart from the corals and fish.
In this chapter we focus on patterns of species richness at
different spatial and temporal scales. We also note that
descriptions of biodiversity and an understanding of
processes influencing biodiversity (e.g. the impact of human activities) are critical for ecosystem management.
Coral reefs occur in a broad band around the equator, wherever suitable depths occur, between latitudes
of 30°N and 30°S, see Chapter 7, although some coral
reef development occurs further south and north where
water currents ensure that for most of the year water
temperatures do not drop below 18°C. For example,
the gyre from the East Australian Current diverges
eastwards south of the GBR and enables coral reefs to
be developed on the east coast of Lord Howe Island at
31°30S. This is the southernmost coral reef in the
world. Species richness varies at scales that range from
ocean basins and seas to habitats on reefs (Box 13.1 and
Box 13.2). The richest reefs in the world in terms of
number of species occur in the triangle that includes
the northern tip of the Philippines and eastern and
western tips of Indonesia, although today many of
these reefs have been damaged by human activities,
including dynamite fishing, overfishing and coastal
developments.
An illustration of this diversity is the recent intensive survey of all the coral reef environments within an
area of 295 km
2 in New Caledonia, which resulted in the
collection of over 2700 species of molluscs. This is much
larger than the number of species recorded from similar
areas anywhere else in the world. Of these molluscs
32% were found only at one site and 20% of species
were only represented by a single individual, indicating
that rare species make up a considerable proportion of
the fauna. In addition, many of the species were undescribed. In the entire Indo-Pacific, in the well known
group of opisthobranchs (nudibranchs) it is estimated
that at least 30% remain to be formally described. In
other invertebrate groups much of the fauna remains
even to be collected, let alone formally described.
13. Biodiversity
P. A. Hutchings & M. J. Kingsford
Biodiversity generally refers to species richness (i.e.
number of species), but other definitions are also common. It is critical that biodiversity is defined carefully as
it is sometimes considered synonymous with genetic diversity, habitat diversity, structural diversity, the diversity of functional groups (e.g. trophic groups of life
history stages) or even life history traits (e.g. feeding
type, growth forms, reproductive strategy, longevity).
Some definitions can be a proxy for species richness. For
example, species representation and abundance are
known to vary among habitats. Habitat richness, therefore, can be especially relevant where the taxonomy of
organisms in the various habitats is poorly known and
there are concerns to protect species richness. A critical
component of the zoning plan of the GBR (the Representative Areas Program, see Chapter 12) was partly based
on the protection of different habitats and used these as
surrogates to conserve species diversity as the biota on
the GBR is poorly known apart from the corals and fish.
In this chapter we focus on patterns of species richness at
different spatial and temporal scales. We also note that
descriptions of biodiversity and an understanding of
processes influencing biodiversity (e.g. the impact of human activities) are critical for ecosystem management.
Coral reefs occur in a broad band around the equator, wherever suitable depths occur, between latitudes
of 30°N and 30°S, see Chapter 7, although some coral
reef development occurs further south and north where
water currents ensure that for most of the year water
temperatures do not drop below 18°C. For example,
the gyre from the East Australian Current diverges
eastwards south of the GBR and enables coral reefs to
be developed on the east coast of Lord Howe Island at
31°30S. This is the southernmost coral reef in the
world. Species richness varies at scales that range from
ocean basins and seas to habitats on reefs (Box 13.1 and
Box 13.2). The richest reefs in the world in terms of
number of species occur in the triangle that includes
the northern tip of the Philippines and eastern and
western tips of Indonesia, although today many of
these reefs have been damaged by human activities,
including dynamite fishing, overfishing and coastal
developments.
An illustration of this diversity is the recent intensive survey of all the coral reef environments within an
area of 295 km
2 in New Caledonia, which resulted in the
collection of over 2700 species of molluscs. This is much
larger than the number of species recorded from similar
areas anywhere else in the world. Of these molluscs
32% were found only at one site and 20% of species
were only represented by a single individual, indicating
that rare species make up a considerable proportion of
the fauna. In addition, many of the species were undescribed. In the entire Indo-Pacific, in the well known
group of opisthobranchs (nudibranchs) it is estimated
that at least 30% remain to be formally described. In
other invertebrate groups much of the fauna remains
even to be collected, let alone formally described.