Abstract
We have studied seven symbiont-bearing foraminiferal species to evaluate the condition of sedimentary reef areas (Pirangi, Maracajaú, and Açu) in Rio Grande do Norte (RN, Brazil). The species are: Amphisorus hemprichii, Amphistegina gibbosa, Archaias angulatus, Borelis schlumbergeri, Heterostegina antillarum, Peneroplis carinatus, and Laevipeneroplis proteus. This paper focuses on the quantitative distributions of the first two species in Maracajaú and Pirangi, considering micro-habitat variation, shelf zonation, and anthropogenic disturbances. Amphistegina gibbosa, which is more abundant than A. hemprichii, is prevalent in coral or coral-rubble substrates, whereas Amphisorus hemprichii is better represented in seagrass habitats. Our dataset from Pirangi and Maracajaú is based on 123 samples collected over three years through diver collection, grab samples, and underwater videographic surveys. Compared to other Brazilian reefs, species diversity at Pirangi is low, and the community is impoverished near tourism sites. These areas, especially Pirangi, may also be affected by pollution from domestic sewage and industrial waste. In Maracajaú, the community appears healthier, except in sites heavily impacted by tourism. Data from 84 foraminiferal samples from Açu show well-preserved symbiont-bearing foraminifera (SBF), indicating good water quality, with microhabitat variations likely due to natural factors. A quantitative examination of the foraminiferal species revealed the presence of a Caribbean-type reef community, including Amphisorus hemprichii, Amphistegina gibbosa, Archaias angulatus, Heterostegina antillarum, Homotrema rubra, Peneroplis carinatus, and Laevipeneroplis proteus. Additionally, among 65 species, living Buccella peruviana were found with a very restricted distribution in organic-rich sediments associated with upwelling wind events, highlighting areas of cold water upwelling on the outer shelf. The spatial distribution of this species indicates that cold waters are bringing nutrients through tidal currents perpendicular to the shelf edge, likely using canyons and valleys to transport nutrients and cold water masses into the partially filled incised valley of the ancient Açu River. Changes in diversity appear to be primarily induced by anthropogenic influences on the inner shelf rather than the outer shelf.