Four-year monthly sediment deposition on turbid southwestern Atlantic coral reefs, with a comparison of benthic assemblages

Abstract

A B S T R A C THigh sedimentation is often related to stress in coral reef communities. Most southwestern Atlantic reefs are characterized by high sedimentation. However, there are no temporal series of sediment deposition rates. We evaluated sediment deposition, the sediment carbonate composition and coral and zoanthid covers on six reefs in Brazil over four-years. Sediment deposition rates varied from near zero to 233 mg cm -2 day -1 , with peaks between August and December, and yearly averages ranging from nine to 104 mg cm -2 day -1 . Deposition rates presented site-specific correlations with wind, indicating that resuspension must be a major factor. The presence of carbonates varied from 38% to 90%, with two sites showing seasonal differences. Benthic communities were fairly similar among sites, but the analyses suggested particular frequencies at each site. There was no significant correlation between sediment and benthic communities. However, Palythoa caribaeorum usually occur in high sediment deposition areas. Our results did not corroborate previous data that suggested that a 10 mg cm -2 day -1 would be a "critical limit for coral survival". Some coral reefs may be associated with high sedimentation environments including carbonatic fractions, but which does not per se hinder the development of southwestern Atlantic coral reef communities. R E S U M OA sedimentação é freqüentemente relacionada a estresse em recifes de coral. Os recifes do Atlântico sul ocidental possuem grande sedimentação, entretanto carecem de séries temporais das taxas de deposição de sedimento. Foram avaliadas estas taxas e a composição carbonática do sedimento, além da cobertura de corais e zoantídeos em seis recifes brasileiros durante quatro anos consecutivos. A deposição variou de zero a 233 mg cm -2 dia -1, com picos entre agosto e dezembro e médias anuais variando de nove a 104 mg cm -2 dia -1. As taxas de deposição apresentaram correlação com o vento, indicando que a ressuspensão deve ser o fator preponderante. A contribuição do carbonato variou de 38% a 90%, com dois locais apresentando diferenciação sazonal. As comunidades bênticas foram similares entre locais, entretanto as análises sugerem freqüencias diferenciadas para cada local. Não houve correlação significativa entre sedimentação e a comunidade bêntica. Entretanto, maior cobertura de Palythoa caribaeorum normalmente ocorreu em áreas de maior sedimentação. Nossos resultados não corroboraram resultados prévios sugerindo que 10 mg cm -2 dia -1 seria "limite crítico para sobrevivência" dos corais. Recifes brasileiros podem estar associados a ambientes de alta deposição de sedimento com elevadas frações carbonáticas, o que não impede o desenvolvimento das comunidades recifais do Atlântico sul ocidental.

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

“…The climate is characterized by two main seasons, summer and winter. During summer, winds are N/NE and mean water surface temperature is about 27.5°C, while in the winter, wind direction changes to S/SE due to the Atlantic Polar Front, that resuspends sediment (BITTENCOURT et al, 2000;LEÃO, 2002;SEGAL et al, 2008;CASTRO et al, 2012).…”

“…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.…”

“…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. This reef was chosen because it lies inside the area with the highest sedimentation rate of the bank (PATCHINEELAM; SMOAK, 1999;CASTRO et al, 2012) and its island-like format facilitates observation of a possible edge effect of the reef on the polychaete community.…”

“…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.…”

Cyanobacterial and microeukaryotic profiles of healthy, diseased, and dead Millepora alcicornis from the South Atlantic

“…The colonial fire coral Millepora alcicornis (Cnidaria, Hydrozoa, Milleporidae), an important component of some coral reefs that may be abundant around the world (Edmunds 1999, Castro et al 2012, is one of the most important and abundant builders of shallow reefs in Brazil. M. alcicornis is also widely distributed in the Western Atlantic, and diseases in this group of corals should be viewed with great concern.…”