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REEF ACCRETION

F10

What

What Is It?

BENCHMARK

Reef accretion or long-term reef "net growth"

To

To be developed.

represents the continual battle between constructive

and destructive processes on the reef. The reef

TA R G E T

framework is created through the construction

processes of biological accretion by corals and

To be developed.

calcareous algae and by sediment accumulation, but

is counteracted by destructive processes such as

RED FL AG

bioerosion and net sediment export.

Reef accretion should not be confused with the

To be developed.

growth of individual reef organisms. Coral growth

and calcification occur at the organismal level, while

reef accretion and bioerosion occur at the ecosystem

level.

How Do We Measure It?

Why Do We Measure It?

Why

This indicator is under development.

This indicator helps with assessments of a reef's

Reef accretion can be directly measured from dated

ability to maintain itself. Long-term reef sustainability

core samples taken through the reef substrate36.

could be threatened by a shift in the balance between

accretion and erosion or by a shift in the balance

Potential accretion rates can also be estimated in

between calcifying organisms (e.g., corals) and non-

terms of gross production (that is, the total amount

calcifying organisms (e.g., fleshy macroalgae).

of carbonate produced on a reef during a specified

period of time). Productivity and calcification profiles

Reef accretion is the "bottom line" of the reef's

can be developed from measurements of seawater

ecological balance sheet -- although it receives little

pH and oxygen concentration37.

to no attention in most monitoring programs.

Usefulness

Usefulness

For a coral reef to persist, its rate of accretion must

equal or exceed deconstruction losses due to biological

Techniques are available to estimate accretion by

and physical erosion and transport of sediment away

measuring primary productivity and calcification by

from reef framework. A reduction of the populations

corals plus respiration of the reef community. However,

of corals and coralline/calcareous algae may result

these methods require equipment and expertise not

in a reef becoming dominated by non-calcifying

widely available in the region.

organisms (macroalgae, some sponges), thus shifting

the carbonate budget from one of net construction

Cores of individual corals provide useful data for

to one of net erosion. A decline in the population

studying one coral colony's growth (see Indicator F8 ­

of calcifiers and/or an increase in the population of

Coral Growth), but more information is needed on the

bioeroders can result in a shift to a state of no net

correlation (if any) of core data to the reef community

accumulation of reef framework. In the long term, the

level and studies of reef accretion.

reef framework itself may potentially be lost.

In addition, if accretion rates decrease (due, for

example, to higher nutrient concentrations or lower

pH), a reef's ability to keep up with sea level rise may

decrease, and its susceptibility to bioerosion and

physical damage may increase.

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