Coral community structure and sedimentation at different distances from the coast of the Abrolhos Bank, Brazil

Abstract

Sedimentation has previously been considered an important source of impact in coral reefs. We compared 3 sites on the Abrolhos Bank, Brazil, regarding sedimentation rates, carbonate sediment composition, coral cover, and colony size for the commonest local coral species (Mussismilia braziliensis, Siderastrea stellata, and Favia gravida). The sites are located at different distances from the mainland: Pedra de Leste (14 km), Pontas Sul (26 km), and Parcel dos Abrolhos (58 km). Sedimentation was higher in winter (p <0.05), but no difference among sites was noted. Sites differed in sediment type (P <0.05), with Parcel dos Abrolhos showing nearly 90% of carbonate in sediment composition, Pontas Sul nearly 65%, and Pedra de Leste only nearly 50%. The farther from the mainland, where the zoanthid cover was smaller, the higher was the coral cover (p <0.01). Differences in colony sizes were found only for M. braziliensis, with smaller colonies occurring at Pedra de Leste (p <0.05). It is suggested that terrigenous sediment distribution and turbidity may be the main factors controlling reef development at the Abrolhos Reefs.

Brazilian coral reefs in a period of global change: A synthesis

“…In the northeastern region, for example, the sediments on the reefs of Rio do Fogo and Sioba, on the coast of the state of Rio Grande do Norte, have more than 55% of relict siliciclastic constituents (TESTA, 1997). Along the entire coast of the state of Bahia (the eastern region), on the nearshore reefs, 40 to 80% of the perireefal sediments have terrestrial sources (NOLASCO; LEÃO, 1986), particularly in the Abrolhos area (LEÃO; GINSBURG, 1997; BARROS; , DUTRA et al, 2006aCASTRO, 2011). All of these siliciclastic sediments are unconsolidated muddy sands derived from ancient deposits that cover most of the hinterland and outcrops along the coast, mostly of the Tertiary Barreiras Formation that can also occur submerged on the inner shelf and, to a minor degree, from river outputs that are carried out to the reefs during winter storms.…”

“…In the northeastern region, for example, the sugar cane monoculture forms a belt that is approximately 60 km wide and nearly 100 km long and located a few kilometers inland in the area in which the nearshore reefs are more numerous (MAIDA; FERREIRA, 1997). Along the eastern region, the effects of the increasing sedimentation rates are negatively correlated with the biotic parameters of the reef biota (DUTRA et al, 2006a, b;SEGAL et al 2008;CASTRO, 2011), and the increase in the deposition of terrigenous mud near the inshore reefs over the last decades may significantly affect the reefs on the short term, even though the Brazilian coral fauna has already been surviving in turbid waters for a long time (SILVA et al, 2013).…”

Looking at the soft-bottom around a coastal coral reef: the impact of terrigenous input on Polychaeta (Annelida) community

“…The sediment between the coast and the Coastal Arc is terrigenous (siliciclastic), whilst around the reefs it is carbonate, and a mix of both types occurs between the reef arcs (LEÃO, 2002;CASTRO, 2011;AMADO-FILHO et al, 2012). Sedimentation rates are higher during winter and spring, when they may attain more than 10 mg cm -2 day -1 in the coastal arc CASTRO, 2011;CASTRO et al, 2012). The Sebastião Gomes reef complex is located in the Coastal Arc of the Abrolhos Bank, close to the Caravelas river mouth, and is part of the Ponta da Baleia/Abrolhos Marine Protected Area.…”

“…We have also sought to answer the question as to whether the distribution of total polychaetes corresponds to that of the total macrofauna, in order to verify the viability of the use of Polychaeta as a good indicator of the macrofaunal patterns in reef sediments. The focus on sediment characteristics was chosen because Abrolhos Bank is a unique reef area where sedimentation rates may be higher than the maximum of 10 mg cm -2 day -1 CASTRO, 2011;CASTRO et al, 2012), a limiting rate usually used to consider the reef healthy (ROGERS, 1990). Studies of the statistical modelling of marine communities are mainly undertaken for fishery resources (REISS et al, 2011;ROBINSON et al, 2011), but spatial and temporal patterns in benthic communities are well suited to statistical modelling too.…”

Looking at the soft-bottom around a coastal coral reef: the impact of terrigenous input on Polychaeta (Annelida) community

“…The reefs of the Abrolhos Bank are situated in two arcs: the Coastal Arc (10 to 20 km from the coast) and the Outer Arc (60 to 70 km from the coast) (LEÃO, 1996) (Figure 1a). The sediment between the coast and the Coastal Arc is terrigenous (siliciclastic), whilst around the reefs it is carbonate, and a mix of both types occurs between the reef arcs (LEÃO, 2002;CASTRO, 2011;AMADO-FILHO et al, 2012). Sedimentation rates are higher during winter and spring, when they may attain more than 10 mg cm -2 day -1 in the coastal arc (DUTRA el al., 2006;CASTRO, 2011;CASTRO et al, 2012).…”