C. Zilberberg et Pj. Edmunds, Competition among small colonies of Agaricia: the importance of size asymmetry in determining competitive outcome, MAR ECOL-PR, 221, 2001, pp. 125-133
Scleractinian corals may experience competition at early life history stage
s, particularly where aggregated settlement decreases the space available f
or growth, The outcome of such interactions can affect post recruitment suc
cess and the relative abundance of coral species, The purpose of this study
was to determine the importance of competition among small colonies (less
than or equal to 4 cm diameter) of Agaricia on shallow (less than or equal
to 10 m depth) reefs in St. John (US Virgin Islands) and Jamaica. The assoc
iation between the density of small Agaricia and the frequency of congeneri
c encounters was examined, together with the relationship between density o
f Agaricia and reef rugosity (topographic complexity). Rugosity was analyze
d because it indirectly affects competitive interactions by providing crypt
ic habitats that promote aggregated settlement and coral-coral interactions
. To test one possible mechanism determining the outcome of such interactio
ns, the relationship between size asymmetry of competing colonies and compe
titive outcome was assessed. The results demonstrate that competition among
small Agaricia is common, particularly where aggregated settlement is favo
red by high topographic complexity. In other words, competitive interaction
s among small Agaricia are affected by both physical (e.g. topographic comp
lexity) and biological (e.g., settlement patterns) factors. The outcome of
such interactions is influenced by the difference in size of competing colo
nies, with dominant colonies generally being larger than subordinate coloni
es. Further research is required to identify the mechanistic basis of domin
ance, but currently the most likely hypotheses are that large colonies are
dominant because they have greater energy resources than small colonies, or
intrinsically faster growth rates. The high frequency of competition among
Agaricia colonies in St. John and Jamaica suggests that further studies of
congeneric competition within the Scleractinia may prove valuable in under
standing the population biology of this taxon.