Y. Letourneur et al., MASS SETTLEMENT AND POSTSETTLEMENT MORTALITY OF EPINEPHELUS-MERRA (PISCES, SERRANIDAE) ON REUNION CORAL-REEFS, Journal of the Marine Biological Association of the United Kingdom, 78(1), 1998, pp. 307-319
An unusual mass settlement event of the grouper Epinephelus merra occu
rred on the fringing coral reefs of Reunion Island (south-western Indi
an Ocean) in April 1994. This major event coincided with stormy condit
ions associated with the new moon period. The abundance of new settler
s was surveyed for 45 days following settlement on both the reef flat
and the back reef area of the coral reefs of St Gilles, La Saline and
St Leu. Mean densities of settlers were higher on reef flats (maximum
474 ind/20 m(2) at La Saline) than on back reef areas (maximum 156 ind
/20 m(2) at La Saline). Seven weeks later, densities of settled E. mer
ra had drastically decreased, and did not differ with site and zone (1
8.5 ind/20 m(2)). Percentages of post-settlement mortality at that per
iod ranged from 85 to 88% in back reef areas and from 93 to 95% on ree
f flats. A strong correlation between density of recruits and per capi
ta mortality suggests density-dependent early postsettlement mortality
for E. merra. The limitation of food resources and shelters, perhaps
combined with an increase of diseases due to high population densities
of settlers, was probably the main cause of mortality just after the
mass settlement. Predation by reef fish, including cannibalism between
settlers, is probably responsible for most subsequent mortality.