Biology Reference
In-Depth Information
and on the Great Barrier Reef (One Tree Reef) and found very sub-
stantial changes in assemblage structure over time in both localities,
despite the differences in taxonomic composition. Conclusions were
based on monitoring the fish populations over 10 years at One Tree
Reef and over 5 years at St. Croix. A recent study of early recruitment of
coral reef fish in the tropical eastern Pacific, at a locality (Gorgona Island)
where tidal amplitude reaches 4.4m, has shown that lunar and tidal factors
contribute to recruitment dynamics. In species with sporadic and aperiodic
recruitment pulses, stochasticity in weather conditions and in oceano-
graphic events may be the most important factor determining recruitment
variability (Lozano and Zapata
2003
).
Robertson and co-workers made thorough studies of reef fish assem-
blages and arrived at conclusions somewhat different from those of Sale.
For example, Robertson (
1995
) doubted the existence of a lottery
mechanism at least for the Caribbean damselfish Stegastes diancaeus and
S. dorsopunicans. The former species is larger, grows faster, and lives longer
than the latter, with which it shares its primary habitat, and from smaller
individuals of which it often takes over habitat. There was no evidence
that the competitive advantage due to larger body size was offset by other
competitive advantages. Asymmetric competition between other closely
related species of the same genus with similar ecological requirements was
also shown to limit abundances of species (Robertson
1996
). Robertson
and Gaines (
1986
) demonstrated the important role of interspecific com-
petition in surgeon fish at the outer edge of the barrier reef of Aldabra,
Indian Ocean. When meeting, 38 pairs interacted rarely and 27 pairs
always interacted. With the exception of one pair, all pairs had highly
asymmetric dominance relations. Subordinate species took over habitats
vacated by previously agonistically dominant species, but the reverse was
rare. The authors concluded that interference competition for food plays a
role in structuring reef fish assemblages: 60-80% of habitat use relationships
in the area of study may be affected. Competition may also occur between
taxonomically totally different species. In 1983/84, 95 % of the sea urchin
Diadema antillarum in Atlantic Panama died off, which led to a sharp
increase in soft corals, some of which are also eaten by reef fish. Three
herbivorous fish species, Acanthurus spp., were monitored between 1978
and 1990 on six patch reefs. The two fish species that feed largely on reef
substrata, increased by 250 and 160 %, respectively. The third species,
which often feeds off the reefs, was not affected (Robertson
1991
).
Robertson (
2001
) demonstrated that taxonomically and biologically,
endemic reef fish from seven small islands are broadly representative of the
