The Abrolhos Reefs of Brazil
93
colonies of Favia gravida and Siderastrea stellata, and sporadic growth
of Agaricia agaricites. Montastrea cavernosa occupies the deepest part
of these reefs. Millepora alcicornis and M. nitida grow among the hard
corals. Crustose coralline algae often cover the dead parts of reefs and
branching types are common. An encrusting community that is comprised
of reef-building organisms, however, covers most island slopes, though
limestone formations do not exceed a few centimeters and a reef flat is
absent.
6.4.3 Outer Arc
A reef area (Parcel dos Abrolhos, about 5 x 15 km), composed of abundant
coral pinnacles (Figs. 6.1A, 6.3C}, extends to the east of the Abrolhos Archipelago. Contrary to the Coastal Arc of reefs, the isolated pinnacles of the
Outer Arc do not coalesce to form bank reefs and are not exposed during
low tides. Depth differences between coastal reef arc (15m) and outer reef
arc areas (25m), common reef growth initiation at around 7,000 years B.P.,
and similar growth rates may explain why reefs of the Coastal Arc reached
the sea surface earlier than those of the Outer Arc. However, the morphology and the distribution of coral species on the reef walls follow a similar
pattern in coastal and outer reefs. At the top of"chapeir6es" large columns
of Mussismilia braziliensis are common and some may reach heights of up
to 2m and may be topped by a living colony of approximately 1m in diameter. Smaller colonies of Favia leptophylla and Siderastrea stellata occur
between the columns. On the top of these reefs Millepora alcicornis surrounds central areas of corals. The vertical distribution of corals on pinnacle walls follows zonation from photophile forms in the upper portions
to shade-loving species (sciaphile) which attain maximum development
under overhangs in lower zones.
6.5 Environmental Impacts and Management
Natural disturbances of the Abrolhos reef environment are limited to millennia! sea level oscillations, water temperature fluctuations, and episodic
input of fine sediments. Holocene sea level oscillations had a profound
effect on the evolution of Abrolhos coral reefs. Lower sea levels during
regression periods exposed reef tops to marine erosion, dissolution, and
to extensive bioerosion (Leao 1982), as well as approximated reefs to the
coast, thus subjecting them to increased influence by siliciclastic sedi-
93
colonies of Favia gravida and Siderastrea stellata, and sporadic growth
of Agaricia agaricites. Montastrea cavernosa occupies the deepest part
of these reefs. Millepora alcicornis and M. nitida grow among the hard
corals. Crustose coralline algae often cover the dead parts of reefs and
branching types are common. An encrusting community that is comprised
of reef-building organisms, however, covers most island slopes, though
limestone formations do not exceed a few centimeters and a reef flat is
absent.
6.4.3 Outer Arc
A reef area (Parcel dos Abrolhos, about 5 x 15 km), composed of abundant
coral pinnacles (Figs. 6.1A, 6.3C}, extends to the east of the Abrolhos Archipelago. Contrary to the Coastal Arc of reefs, the isolated pinnacles of the
Outer Arc do not coalesce to form bank reefs and are not exposed during
low tides. Depth differences between coastal reef arc (15m) and outer reef
arc areas (25m), common reef growth initiation at around 7,000 years B.P.,
and similar growth rates may explain why reefs of the Coastal Arc reached
the sea surface earlier than those of the Outer Arc. However, the morphology and the distribution of coral species on the reef walls follow a similar
pattern in coastal and outer reefs. At the top of"chapeir6es" large columns
of Mussismilia braziliensis are common and some may reach heights of up
to 2m and may be topped by a living colony of approximately 1m in diameter. Smaller colonies of Favia leptophylla and Siderastrea stellata occur
between the columns. On the top of these reefs Millepora alcicornis surrounds central areas of corals. The vertical distribution of corals on pinnacle walls follows zonation from photophile forms in the upper portions
to shade-loving species (sciaphile) which attain maximum development
under overhangs in lower zones.
6.5 Environmental Impacts and Management
Natural disturbances of the Abrolhos reef environment are limited to millennia! sea level oscillations, water temperature fluctuations, and episodic
input of fine sediments. Holocene sea level oscillations had a profound
effect on the evolution of Abrolhos coral reefs. Lower sea levels during
regression periods exposed reef tops to marine erosion, dissolution, and
to extensive bioerosion (Leao 1982), as well as approximated reefs to the
coast, thus subjecting them to increased influence by siliciclastic sedi-