C OR AL RECRUITMENT
ORITY ON
F1
RI
RE
TH
EF
S FOR HEAL
What Is It?
What
BENCHMARK
Recruitment is the process by which planulae (tiny,
(Very Preliminary) No decline from
swimming "baby corals") establish themselves as
2000 values: Regional average of 3
members of the reef community. Coral recruits are
recruits per m2 (for recruit size < 2 cm)
typically quantified in terms of the number of small
stony corals per unit area. ("Small" in this case is
More data are needed on settlement
defined as up to 2 cm, although some studies have
rates (i.e., plate data).
used up to 10 cm maximum diameter, depending on
TA R G E T
objectives.)
(Very Preliminary) On par with ~2000
Coral planulae require specific conditions in order to
Caribbean average: At least 4.5
settle and survive (i.e., recruit into the population).
recruits per m2 (for recruit size < 2 cm).
Areas with high recruitment potential tend to have
abundant crustose coralline algae and little fleshy
More data are needed on settlement
macroalgae.
rates (i.e., plate data).
RED FL AG
Recruitment rates ("success" rates) depend upon the
number and species distribution of reproducing adult
(Very Preliminary) A regional average of
corals; their fecundity (ability to produce offspring);
less than 3 recruits per m2 (for recruit
survival of the larvae (planulae) during their open-
size < 2 cm).
ocean swimming phase; linkages between larval
sources and settlement sites, which depend in part
on poorly understood, small-scale current patterns;
placed every 2 meters along a 10-meter transect line.
and larval survival after settlement, which depends in
This method generally covers approximately 3 m2 per
part on habitat conditions.
site. Other studies have used larger (50 cm x 50 cm)
and more numerous quadrats or belt transects to
Corals under stress may have lower reproductive
attain the minimum recommended sample area per
output and/or lower recruitment rates. Examples of
site4,5,6.
potentially stressful conditions might include high
partial coral mortality, disease, coral bleaching,
Some researchers in the region (e.g., the Global
contaminants (e.g., heavy metals, agrochemicals
Environment Facility (GEF) / World Bank Targeted
or sewage) or physical abrasions from storms and
Research & Capacity Building Program) are using
hurricanes.
settlement plates (square tiles that offer larvae a well-
defined place to "land") to study recruitment rates7.
Why
Why Do We Measure It?
Recruitment is one of the most critical processes
Suzanne Arnold
governing reef communities. The abundance of
recruits is an important indication of a reef's potential
for growth and recovery after major disturbances.
Recruitment also includes particularly sensitive life
phases (i.e., macroalgae and contaminants interfere
in settlement). Healthy reef ecosystems depend on
replenishment of populations and connectivity among
reefs.
How Do We Measure It?
Most recruitment data for the MAR region are based on
the AGRRA method3. To quantify coral recruits, a diver
counts the number of stony coral recruits (up to 2 cm
maximum diameter) within a 25 cm x 25 cm quadrat
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