92
Z.M.A.N. Leao and R.K.P. Kikuchi
patches of the prolific green alga Penicillus sp. and isolated laminated
cyano-algal structures (soft oncolites).
The reef edge is a 2- to 3-m-thick irregular overhang which projects
from the pinnacle. At the border of reef structures, small isolated pinnacles
will eventually become part of the main reef body through lateral growth
and trapping of sediment in open spaces. An irregular rim which rises
about 30 em above the flat top of bank reefs is constructed by encrusting
organisms at the windward side where it tends to dissipate the energy of
waves (Leiio 1982). Coralline algae and encrusting mollusks (i.e. Spiroglyphus = Dendropoma) are major components of northern windward reef
rims, while millepores (Millepora alcicornis) are also an important constituent of windward edges of southern reefs. Millepora braziliensis is located
immediately below the zone of Millepora alcicornis (Laborel1969b ). Large
colonies of Millepora alcicornis (<10m depth) are sometimes followed
by gorgonians (Plexaurella grandiflora, Phyllogorgia dilatata, Muriceopsis
sulphurea). Several species of hard corals, mostly Mussismilia braziliensis,
M. hispida and Siderastrea stellata, are also present (Castro 1994).
On upper reef walls Mussismilia braziliensis, Millepora sp. and gorgonians dominate, at about 2m depth Mussismilia harttii, gorgonians and
millepores are the major organisms, and at deeper reef walls millepores
dominate. At greater depths, only small sciaphile forms (e. g. black corals
and the octocoral Carijoa riisei) thrive in darker environments which are
protected by the overhangs. On the leeward side of reefs, large colonies of
Montastrea cavernosa, Scolymia wellsi and Carijoa riisei are common and
large clumps of Mussismilia harttii occur close to the bottom sediments on
the windward side (Castro 1994). On muddy bottoms (10-20 m depth) between pinnacles, prolific sea grass growth alternates with calcareous green
algae (Penicillus, Halimeda, Udotea) and the free form of the coral Meandrina braziliensis.
6.4.2 Fringing Reefs of the Abrolhos Archipelago
Rather than a reef structure, fringing reefs of the five Abrolhos Islands are
a veneer of reef organisms on stable volcanic or sedimentary rocks
(Figs. 6.1B, 6.3C). They are formed by the growth of corals, cementation
by coralline algae and other encrusting organisms, and the filling of cavities with cemented sediment. The reef flat extends about 50-60 m from
the shore and does not exceed 5 m from the bottom to low water level
(Fig. 6.3C). In protected areas (i.e., around Redonda Island), the shallow
part of fringing reefs is composed of coral colonies (Mussismilia braziliensis, M. hispida, Favia leptophylla), bushes of Mussismilia harttii, small
Z.M.A.N. Leao and R.K.P. Kikuchi
patches of the prolific green alga Penicillus sp. and isolated laminated
cyano-algal structures (soft oncolites).
The reef edge is a 2- to 3-m-thick irregular overhang which projects
from the pinnacle. At the border of reef structures, small isolated pinnacles
will eventually become part of the main reef body through lateral growth
and trapping of sediment in open spaces. An irregular rim which rises
about 30 em above the flat top of bank reefs is constructed by encrusting
organisms at the windward side where it tends to dissipate the energy of
waves (Leiio 1982). Coralline algae and encrusting mollusks (i.e. Spiroglyphus = Dendropoma) are major components of northern windward reef
rims, while millepores (Millepora alcicornis) are also an important constituent of windward edges of southern reefs. Millepora braziliensis is located
immediately below the zone of Millepora alcicornis (Laborel1969b ). Large
colonies of Millepora alcicornis (<10m depth) are sometimes followed
by gorgonians (Plexaurella grandiflora, Phyllogorgia dilatata, Muriceopsis
sulphurea). Several species of hard corals, mostly Mussismilia braziliensis,
M. hispida and Siderastrea stellata, are also present (Castro 1994).
On upper reef walls Mussismilia braziliensis, Millepora sp. and gorgonians dominate, at about 2m depth Mussismilia harttii, gorgonians and
millepores are the major organisms, and at deeper reef walls millepores
dominate. At greater depths, only small sciaphile forms (e. g. black corals
and the octocoral Carijoa riisei) thrive in darker environments which are
protected by the overhangs. On the leeward side of reefs, large colonies of
Montastrea cavernosa, Scolymia wellsi and Carijoa riisei are common and
large clumps of Mussismilia harttii occur close to the bottom sediments on
the windward side (Castro 1994). On muddy bottoms (10-20 m depth) between pinnacles, prolific sea grass growth alternates with calcareous green
algae (Penicillus, Halimeda, Udotea) and the free form of the coral Meandrina braziliensis.
6.4.2 Fringing Reefs of the Abrolhos Archipelago
Rather than a reef structure, fringing reefs of the five Abrolhos Islands are
a veneer of reef organisms on stable volcanic or sedimentary rocks
(Figs. 6.1B, 6.3C). They are formed by the growth of corals, cementation
by coralline algae and other encrusting organisms, and the filling of cavities with cemented sediment. The reef flat extends about 50-60 m from
the shore and does not exceed 5 m from the bottom to low water level
(Fig. 6.3C). In protected areas (i.e., around Redonda Island), the shallow
part of fringing reefs is composed of coral colonies (Mussismilia braziliensis, M. hispida, Favia leptophylla), bushes of Mussismilia harttii, small