Compartments of the pelagic system and material exchange at the Abrolhos Bank coral reefs, Brazil

Increase of human activities in the coastal zone of the Abrolhos Bank, Brazil, gave rise to the opinion that its reef environments may be threatened by eutrophication and insilting. This study, conducted in austral summer from January 14th to 20th, 1995, presents a first insight into the current regime, distribution of water properties and material exchange at the land-sea interface of the Abrolhos reef system. Specific tracers, such as particle mineralogy and phytoplankton pigments, were employed to discern the impact of material sources upon the system. Patterns of the current regime and water properties were largely controlled by topography and revealed the presence of distinct inshore, coastal, open reef, and inner shelf realms of the pelagic system. The inshore realm was mesotrophic with typical estuarine phytoplankton and the others, fed by the Brazil Current, were oligotrophic with oceanic phyto- and zooplankton. Foreshore shoals, governed by terrigenous resuspended material, were the main source of matter to the coastal realm. The seaward transport of material was hampered by a hydrodynamic barrier set-up by strong shore-parallel currents and the inner arc of the reefs. Land impact upon the reef waters was mitigated due to efficient flushing by the Brazil Current.