59
7. Primary Production, Nutrient
Recycling and Energy Flow
through Coral Reef Ecosystems
O. Hoegh-Guldberg & S. Dove
Corals reefs provide a spectacular contrast to the oceanic ecosystem that surrounds them. While coral reefs
are ablaze with thousands of species living within a
highly productive ecosystem, the surrounding ocean is
usually devoid of particles and has a low rate of primary production. Whereas coral reefs are often likened
to the ‘rainforests of the sea’, the surrounding waters
are often referred to as ‘nutrient deserts’ due to the low
quantities of essential inorganic nutrients such as
ammonium and phosphate ions. How a marine ‘rainforest’ exists in an oceanic ‘desert’ was one of the grand
puzzles that faced the early workers on coral reefs, including Charles Darwin.
In this chapter, the various drivers of the energy flow
through coral reefs are explored. After investigating
which physical and chemical factors define corals and
the reefs that they build, we describe some of the fundamental biological relationships that lead to the capture
of energy and nutrients by coral reefs, and how these
essential requirements of life flow through coral reef
ecosystems. As we will see, while primary production is
similar to that of other shallow marine ecosystems, coral
reefs have a high proportion of pathways that involve
the recycling of nutrients between closely associated
primary producers and consumers. We will also see that
the highly productive nature of coral reefs is deceptive
in that it is accompanied by the rapid and efficient recycling of nutrients and energy such that overall rates of
accumulation of organic carbon as reef growth are low.
This theme lies at the heart of the puzzle of how highly
productive and diverse coral reefs can exist in the
‘nutrient deserts’ of tropical and subtropical oceans.
N ENVIRONMENTAL FACTORS DRIVING
THE DEVELOPMENT OF CORAL REEFS
Coral reefs grow in shallow, sunlit waters of tropical
and subtropical oceans and are built from the activities
of many types of calcifying organisms. Globally, coral
reefs occupy 284 300 square kilometres, which is less
than 1% of the global ocean. They dot oceans and line
coasts within a band between 30° north and south of the
equator. In Australia, coral reefs stretch northwards
along continental shelves, from northern NSW on the
east coast, from Rottnest Island in the south-west to the
north-west coast of Australia and along the western
edge of the Gulf of Carpentaria. Throughout this range
there is a tremendous variability in the structure of coral
7. Primary Production, Nutrient
Recycling and Energy Flow
through Coral Reef Ecosystems
O. Hoegh-Guldberg & S. Dove
Corals reefs provide a spectacular contrast to the oceanic ecosystem that surrounds them. While coral reefs
are ablaze with thousands of species living within a
highly productive ecosystem, the surrounding ocean is
usually devoid of particles and has a low rate of primary production. Whereas coral reefs are often likened
to the ‘rainforests of the sea’, the surrounding waters
are often referred to as ‘nutrient deserts’ due to the low
quantities of essential inorganic nutrients such as
ammonium and phosphate ions. How a marine ‘rainforest’ exists in an oceanic ‘desert’ was one of the grand
puzzles that faced the early workers on coral reefs, including Charles Darwin.
In this chapter, the various drivers of the energy flow
through coral reefs are explored. After investigating
which physical and chemical factors define corals and
the reefs that they build, we describe some of the fundamental biological relationships that lead to the capture
of energy and nutrients by coral reefs, and how these
essential requirements of life flow through coral reef
ecosystems. As we will see, while primary production is
similar to that of other shallow marine ecosystems, coral
reefs have a high proportion of pathways that involve
the recycling of nutrients between closely associated
primary producers and consumers. We will also see that
the highly productive nature of coral reefs is deceptive
in that it is accompanied by the rapid and efficient recycling of nutrients and energy such that overall rates of
accumulation of organic carbon as reef growth are low.
This theme lies at the heart of the puzzle of how highly
productive and diverse coral reefs can exist in the
‘nutrient deserts’ of tropical and subtropical oceans.
N ENVIRONMENTAL FACTORS DRIVING
THE DEVELOPMENT OF CORAL REEFS
Coral reefs grow in shallow, sunlit waters of tropical
and subtropical oceans and are built from the activities
of many types of calcifying organisms. Globally, coral
reefs occupy 284 300 square kilometres, which is less
than 1% of the global ocean. They dot oceans and line
coasts within a band between 30° north and south of the
equator. In Australia, coral reefs stretch northwards
along continental shelves, from northern NSW on the
east coast, from Rottnest Island in the south-west to the
north-west coast of Australia and along the western
edge of the Gulf of Carpentaria. Throughout this range
there is a tremendous variability in the structure of coral