Macro-algae affect corals by competing with them for space by
overgrowth, allelopathy, shading and whiplash; inducing physiologi-
cal stress, reducing growth and fecundity, increasing mortality by
direct competition or indirectly via increased microbial contamina-
tion, and reducing coral recruitment [32–35]. Recruitment-failure of
corals, following phase-shifts to macro-algae or other weedy species,
plays a key role inmaintaining the resilience of alternate assemblages
on degraded reefs [25]. Increases in the amount of macro-algal can
cause a disproportionate decline in coral recruitment, especially if
corals or other occupiers of space (sponges, clonal anemones
zoanthids, etc.) are also abundant, leaving limited room for new
recruits. For example, in Jamaica, coral recruitment decreased by
more than 80% within two years of the die-off of the sea urchin
Diadema antillarum(froman average of 31 to 5 recruitsm2
per year),
when macro-algal abundance increased from 2 to 20% cover [98].