Coral recruitment is the process by which drifting planulae (tiny coral larvae) attach and establish themselves as members of the reef community.Some species tend to settle close to their “mother colony”;others drift for great distances before settling down.The greater a reef’s recruitment success, the greater its potential for future growth and recovery after disturbance.Reef recruitment rates depend upon many factors, some of which have been changing recently in the MAR:
- How many adults are reproducing, and what species
- What is the fecundity of the adults (that is, how fruitful
are they in producing offspring)?
- How many larvae survive the treacherous early life
phase of drifting?
- How well connected are the larval source sites and
the settlement sites?
- How hospitable are the settlement sites, and how
many larvae survive after attachment?
Stressful conditions such as bleaching (D14) or exposure to harmful chemicals (D7) can lower a reef’s reproductive output and recruitment. Areas with high recruitment potential tend to have abundant crustose coralline algae and little fleshy macroalgae (F13)—an indication of the importance of herbivorous fishes (F11) and urchins (F12) in helping to keep a reef hospitable to new recruits.
The late 1990s—with the triple blow of coral bleaching (D14), Hurricane Mitch, and Diadema die-off aftereffects (F12)—was a tough time for MAR recruitment. Between 1998 and 1999,coral recruitment plummeted 53% on one well-studied patch reef in Belize.1
We recommend monitoring coral recruitment with well-defined,standardized methods for surveying and classifying recruits.2 These methods—of which several are available3—all require a moderate to highlevel of expertise. Currently,few MPAs have the time and money to routinely monitor recruitment.
A promising sign of interim (Benchmark) reef recovery would be a regional average of 5 recruits/
- The MAR averaged 3 recruits/m 2.
- Most recruits were brooding species (species whose
larvae settle close to the mother colony). Recruits of major
reef-building corals were rare.