Journal of Coastal Research SI 39 633 - 638 ICS 2004 (Proceedings) Brazil ISSN 0749-0208 DUTRA, L.X.C. KIKUCHI, R.K.P. and LE��O, Z.M.A.N., 2006. Effects of sediment accumulation on reef corals from Abrolhos, Bahia, Brazil. Journal of Coastal Research, SI 39 (Proceedings of the 8 International Coastal Symposium), 633 - 638. Itaja��, SC, Brazil, ISSN 0749-0208. This paper evaluates the effects of sediment accumulation on reef corals from the Abrolhos area, at the southern coast of the state of Bahia, Brazil. Sediment accumulation rate was measured with sediment traps that were fixed in five reef stations during the months of October/2001 and March/2002. Live coral cover, diameter of the coral colonies and species diversity were measured in the same stations according to theAGGRA(Atlantic and Gulf Rapid Reef Assessment) protocol, along six belt transects (10 m x 1 m), and the number of recruits were counted in five quadrats (25 cm) located at every 2 m along the transects. Pearson's correlation was used in order to confirm the relationship between biotic and abiotic parameters. Sediment accumulation rate of 10 mg.cm .day seems to constitute a critical limit for coral survival. Bellow it, there is a significant inverse relationship between sedimentation rate and the measured biotic parameters such as live coral cover, average diameter of colonies, the total number of recruits and of the recruits of In places where sedimentation rate is higher than this value, there is a considerable decline in the coral community health indicators. Morphological and distribution variations of the reefs structures are, most probably, the major factors that expose the corals to the effects of sediment influx. The stations located at the top of the bank reefs closest to mainland show the highest values for the rate of sediment accumulation and the highest percentage of siliciclastic sediments, which also seems to influence reef vitality. Negative impact of terrigenous sediment content is shown by the inverse relationship among its content, which decrease relative to carbonate sediments from near shore to offshore, and reef vitality indicators, which increase from the inner to the outer reefs. th -2 -1 Millepora alcicornis Siderastrea stellata. Coral reefs, sedimentation, Abrolhos. ADDITIONALINDEXWORDS: ABSTRACT Effects of SedimentAccumulation on Reef Corals FromAbrolhos, Bahia, Brazil L. X. C. Dutra��� R. K. P. Kikuchi��� and Z. M.A. N. Le��o��� INTRODUCTION Sediment influx in coastal waters is one of the main factors that affect reef distribution, community structure, growth rates and coral recruitment. Increasing rates of sedimentation can be the result of natural and anthropogenic phenomena. Natural processes include fluvial discharge, terrigenous run-off after strong rain periods, erosion of the coastline and ressuspension of bottom sediments after storms ( 1976 1990). The anthropogenic impacts may result from nearshore dredging and the unplanned human occupation of the coastal zone ( and 1993 and 2000 1993). These processes will affect reef corals through several mechanisms, and some of them can be lethal and/or sublethal to the reef corals, such as: asphyxia, reduction on growth rates, abrasion, recruitment inhibition, reduction on live coral cover, changes on coral zonation, greater abundance of branching corals or the dominance of colonies with small sizes ( and 1988 1992 and 1999). References about Brazilian reefs suggest that the probable increasing of sediment influx in the coastal zone is due to natural sources caused by the sea level regression, which occurred since the end of Quaternary period, approaching reefs to the coastline ( and 1998 1996 and 1999 ., 1997 2001).These references also suggest that this process has been increasing in the Present due to deforestation in coastal areas causing negative effects to the reef vitality. In the present work we tested if the parameters of reef corals vitality, such as coral cover, number of coral colonies, among others, can be related with the increment of sediment accumulated in the reef tops. The studied area is located at the south coast of the State of Bahia, where there are the largest and richest coral reefs in the whole South Atlantic Ocean. Five reefs were selected and they are located at varied distances from the coastline: Pedra de Leste Reef (LES, 12 km), Timbebas Reef (TIM, 18 km), Lixa Reef (LIX, 20 km), Pedra Grande Sul Reef (PGS, 32 km) and Parcel dosAbrolhos Reefs (PAB, 60 km) (Figure 1). Climate in the region is characterized by summer temperatures (December to April) ranging from 25 to 27��C and an average winter temperature (June to August) of 23��C. Average annual precipitation is 1392 mm and monthly averages range from 66 mm (February and August) to 175 mm (November) ( 2003). The main oceanic current influencing the study area is the Brazil Current, which flows to south with an annual average speed of 0.7 knots (DHN, 1993). Tidal currents have average speeds of 1.0 to 1.5 knots ( 2001) and tidal range varies from about 2 m during spring tide to 0.5 m during neap tide (DHN, 1993). The Abrolhos region has the most developed reefs of the whole Brazilian coast ( and 2001 1969 1982). They are mainly constituted by bank reefs parallel to the coastline forming an inner arc, which is affected by the processes acting in the mainland, and an outer arc, shorter, and about 60 km off the coast, which is influenced by the waters of the Brazil Current ( 1999). According to (2003), the coral reefs of this region LOYA, ROGERS, DODGE VAISNYS, 1977 HODGSON HODGSON DICKSON, VAN KATWIJK ABDEL-SALAM PORTER, ROGERS, 1990 TE, WOOLFE LARCOMBE, KIKUCHI LE KIKUCHI, CANALDOTEMPO.COM, NATIONAL IMAGERY AND MAPPING AGENCY, CASTRO PIRES, LABOREL, KNOPPERS et al., et al et al., et al., et al. ��O, LE O, LE LE O LE LE LE �� ��O �� ��O ��O, ��O The Coral Reefs ofAbrolhos ���Centre for Ecological Economics and Water Policy Research University of New England Armidale NSW 2351 Australia tel: +61 2 6773 3986 fax:+61 2 6773 3237 leo.dutra@une.edu.au Journal of Coastal Research Special Issue 39, 2006 ,

can be classified in four types: (i) bank reefs adjacent to the coastline, which are discontinuous with varied shapes but always elongated and usually parallel to the coastline (ii) bank reefs detached from the coast, whose horizontal dimensions range from about 50 m up to some tens of kilometers and their heights from the sea floor varies from 10 m (shallower banks) to more than 20 m (deeper banks). They have varied shapes (irregular, elongated, circular, arc-like) and are flat topped, emergent during low tides, what favors their lateral growth instead of a vertical development. Submerged bank reefs, few meters high, are found in depths up to 10 m, and (iii) fringing reefs, quite continuous, formed by incrustation of calcareous organisms in the rocky outcrops that border the islands present in the region, and (iv) coral pinnacles, which can be of two types: 1) columnar, where the base is equally as wide as, or wider than the top of the reef, and 2) chapeir��o where the flat top is wider, sometimes over three times larger than its base (Figure 2B). Chapeir��o (from the Spanish ���chaperon���, pl. in Portuguese ���chapeir��es���) is a term introduced by Charles F. Hartt in 1870 1870), which alludes to hats with broad brims. It refers to the coral growth form unique of the Brazilian reefs and consists of isolated narrow pillars whose tops are expanded laterally, resembling flat topped mushrooms. The studied reefs are classified in two of the described types. LES and LIX stations are located in an area of isolated bank reefs with dimensions in the order of kilometers.They are located less than 20 km away from the shoreline, and their position in relation to the coast may function as a barrier, blocking the water flux towards the open ocean and thus acting as sediment traps (Fig. 2A). The other reef stations (TIM, PGS and PAB) are located in an area of isolate coral pinnacles, where water circulates more freely (Figure 2B). The bottom intereefal sediments of Abrolhos are characterized by a transition from dominant siliciclastic components along and near the coastal zone to pure carbonate sediments in the middle and outer shelves ( 1982). Near the coastline the bottom sediments are constituted by 30 to 70% of quartz grains, rare micas, and terrigenous mud. In Parcel dos Abrolhos reefs (PAB station) siliciclastic sediments represent less than 10% (Figure 3).According to and (1997), these sediments are originated from two main sources: (i) reworked material from erosion of the coastal cliffs (Tertiary sediments of the Barreiras Group) and (ii) fluvial discharges transported to reef area by longshore currents.At the base of the reefs, carbonate sand and mud dominate, representing more than 50% of the grains ( 2001). The coexistence of reef growth and an active muddy sedimentation in Abrolhos is discussed by (1982) and and (1997), who suggest that this fact is related to: (a) the absence of great fluvial flows facing the reefs, (b) the short term events of ressuspension of fine sediments from the sea bottom, during winter storms, and (c) a probable functional adaptation of the coral fauna to the presence of turbid waters. The coral community parameters were measured according to the AGRRA (Atlantic and Gulf Rapid Reef Assessment) protocol ( 1998). Six belt transects (10 m x 1 m) were extended in the top of the reefs, where all coral colonies were identified. Colonies larger than 20 cm were measured for the maximum height and diameter, and dead coral cover was evaluated. Living coral cover was estimated along a line of 10 m. Recruits (coral colonies with less than 2 cm of diameter) were counted in five quadrats (25 cm), 2 m apart from each other along each transect. (HARTT, LE LE GINSBURG LE LE O LE GINSBURG GINSBURG Intereefal Sediments METHODS Coral Community ��O, ��O ��O �� ��O et al., et al., Figure 1. Location of studied reefs. Figure 2. Top, major reef types in the study area. A) Large bank reefs from the coastal arc where the LES and LIX stations were located. B) The isolated chapeir��es that form the reefs of the TIM, PGS and PAB stations. Bottom, the average sediment accumulation rates measured in each reef station. Figure 3. Distribution of the intereefal bottom sediment in the area of theAbrolhos reefs (Modified from 1982). LE ��O, Dutra et al. Journal of Coastal Research Special Issue 39, 2006 , 634