Anthropogenic perturbation of coral reef environments near Natal, Brazil: Clues from symbiont-bearing benthic foraminifera

Abstract:

Besides global stressors such as temperature rise and acidification, local anthropogenic disturbances, especially those connected with tourism, affect many Atlantic patch reefs off the Brazilian shore. Using reef-inhabiting foraminifera with algal symbionts as environmental indicators, we confirmed this problem in coastal reefs near Natal, Rio Grande do Norte. The foraminiferal community is particularly depauperate in the small reefs of Pirangi, about 25 km south of Natal (~6^o S, water depth <5-m), showing the result of numerous tourists trampling or otherwise damaging the reef substrate. Shells of Amphistegina gibbosa, the characteristic reef foraminifer of tropical America, have an exceptionally patchy distribution here, with rare living individuals. A few other symbiont bearers, e.g. Archaias angulatus, Amphisorus hemprichii, and Heterostegina antillarum, are present, but in extremely small numbers. In general, the dominant species is Quinqueloculina lamarckiana, a eurytopic, small miliolid (without symbionts), but many specimens are brown or black, indicating a mixing of relict and living populations. Compared to known foraminiferal communities in other Brazilian reefs, species diversity at Pirangi is remarkably low. About 77 km north of Pirangi, in the more extensive patch reef system of Maracajaú, the foraminiferal community is apparently healthier, except in an area targeted for tourism. However, living Amphistegina is still rare, and the only living Amphisorus is found in seagrass habitats. In contrast, many symbiont-bearing taxa, including peneroplids (virtually absent in Pirangi and Maracajaú) exist in sizeable populations northwest of Maracajaú, in the small patch reefs of the drowned Açu river valley (~4^o 50’ S).