Effects of industrial outfalls on tropical macrobenthic sediment communities in Reunion Island (Southwest Indian Ocean) Lionel Bigot a, * , Chantal Conand a , Jean Michel Amouroux b , Patrick Frouin a , Henrich Bruggemann a , Antoine Gre ´mare b a Laboratoire d’Ecologie marine (ECOMAR), Universite ´ de La Re ´union, BP 7151, 97715 Saint-Denis, La Re ´union, France b Observatoire Oce ´anologique de Banyuls, Laboratoire d’Oce ´anographie Biologique de Banyuls, UMR 7621, CNRS-UPMC, BP 44, 66651 Banyuls Cedex, France Abstract Temporal changes in the composition of soft bottom macrobenthic assemblages at Reunion Island (Southwest Indian Ocean) were studied in the context of a long-term environmental monitoring programme studying the impacts of effluents of industrial sugar cane refin- eries that are transferred to shallow and deep coastal environments by different pathways: surface discharge and deep underground injec- tion. Seven stations (between 20 and 160 m depth) were surveyed between 1994 and 2003 on the industrial zone. One additional station was surveyed on a reference site. Spatio-temporal changes in the composition of macrobenthic communities were assessed using several diversity indices, ABC curves, MDS and associated ANOSIM tests and biotic indices. Among the 171 taxa recorded, polychaetes were dominant (89 species), followed by crustaceans and molluscs. The analysis of spatial changes in the composition of macrobenthos showed the existence of distinct benthic communities along the depth gradient. Temporal changes in macrobenthos composition were most pro- minent at the shallowest station. They mainly corresponded to the decline of several initially dominant taxa and the increase of the Eunicid polychaete Diopatra cuprea. This station further showed increasing macrofaunal abundance, biomass and sediment organic con- tent over time, concomitant with decreasing sediment grain sizes. In deeper environments, temporal changes were much smaller. Macro- faunal abundance and species richness increased progressively, suggesting a moderate impact on benthic ecosystems resulting from slight enrichments due to effluents rich in organic matter. Our results highlight an original response to disturbance pattern involving opportu- nistic Eunicidae species (D. cuprea) not previously described. Moreover, they allow for the comparison of the impact on macrofauna caused by industrial effluents exported by two distinct and different pathways in a tropical coastal high-energy marine environment. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Macrobenthic communities; Temporal change; Sediments; Industrial wastewater; Environmental impact; Organic matter; Pollution; Tropical shores (non-reef); Indian Ocean; Reunion Island 1. Introduction Human disturbance in marine ecosystems can be assessed directly from physical and chemical parameters (Daskalakis and O’Connor, 1995), or indirectly using com- munities of macrobenthic organisms that characterize the ecological quality of their habitats (Pearson and Rosen- berg, 1978; Lindegarth and Hoskin, 2001; Cruz-Motta and Collins, 2004; Currie and Isaacs, 2005). Macrobenthic species are of special interest in this context because: (1) most of them are sessile or have a limited mobility (Olsgard and Gray, 1995; Rosenberg, 2001; Shin et al., 2004) and are thus directly depending on environmental conditions, and (2) they show marked responses to environmental changes depending on their species-specific sensitivity/tolerance lev- els (Ferraro and Cole, 1995; Paiva, 2001; Mendez, 2002; Lancellotti and Stotz, 2004). Moreover, macrobenthic com- munity analysis provides an instantaneous both snapshot assessment of current disturbance effects, much as most chemical and physical analyses can provide, as well as an 0025-326X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2005.11.021 * Corresponding author. Tel.: +33 262 93 86 90; fax: +33 262 93 86 85. E-mail address: lionel.bigot@univ-reunion.fr (L. Bigot). www.elsevier.com/locate/marpolbul Marine Pollution Bulletin 52 (2006) 865–880