El Ni ~ no induced local extinction of coral reef bryozoan species from Northern Bahia, Brazil Francisco Kelmo a,b , Martin J. Attrill a, * , Rilza C.T. Gomes c , Malcolm B. Jones a a School of Biological Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK b Brazilian Research Council, CNPq Brazil & Departamento de Zoologia, Instituto de Biologia, Universidade Federal da Bahia, Campus Universit ario de Ondina, Salvador, Bahia 40210-340, Brazil c Regional Council for Protection of the Environment, CRA, Bahia, Brazil Received 25 March 2003; received in revised form 25 September 2003; accepted 12 October 2003 Abstract The 1997–1998 El-Ni~ no Southern Oscillation was the most severe on record and dramatically impacted corals worldwide. However, the effect of this event on the associated community of reef organisms has received much less attention. The composition of the bryozoan assemblage from the coral reefs of Northern Bahia, Brazil were monitored annually from 1995 to 2000, allowing the investigation of the effects of this large-scale stressor on an important, diverse, yet understudied component of the coral reef system. Bryozoan samples (35 replicates/reef) were collected during April/May from four shallow bank reefs (10–40 m depth) located a few kilometres off the coast, together with measurements of the associated environmental parameters. Currently 157 species have been recorded from the study area, but significant reductions in density and diversity were apparent between pre- and post El-Ni ~ no Southern Oscillation (ENSO) years, multivariate analysis denoting significant changes in assemblage composition. A total of 61 species were unrecorded following the 1997–1998 ENSO event (22 species from 1997; 25 further species from 1998 and 14 more from 1999). These included several species endemic to Brazil, suggesting that the 1997–1998 ENSO has had a marked influence on the reef bryozoan community, resulting in the local extinction of several species. Bryozoan mortalities were probably initiated by elevated temperatures, but continued disappearance of species for 2 years after ENSO suggests other indirect factors are also influential. These results demonstrate that ENSO events can have severe long-term impacts on the biodiversity of coral reefs, with important conservation consequences. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: ENSO; Bryozoa; Environmental impact; Global warming 1. Introduction The Bryozoa is a relatively poorly known group of eurytopic sessile invertebrates recorded worldwide at all depths (Soule et al., 1995). Such a wide distribution is closely associated with the particular morphology and growth form of the colony, which are directly influenced by environmental variables such as hydrodynamics, depth, temperature, sedimentation rate, substrate, lu- minosity and oxygen availability (Souza, 1986; McKin- ney and Jackson, 1989; Harmelin, 1988). Consequently, these organisms can play an important role in ecological and palaeoecological investigations (e.g. Anstey, 1986; Moissette, 1991; Smith, 1995). To investigate the response of these organisms to environmental changes, a long-term monitoring study was started in 1995 throughout the coral reefs of northern Bahia, Brazil, where little is known of the bryozoan fauna (but see, for example, Marcus, 1941; Souza and Barbosa, 1994). Such quantitative monitor- ing was designed to record spatial and temporal patterns in bryozoan biodiversity and assemblage structure from four shallow-bank reefs: Aba  ı, Guarjuba, Itacimirim and Praia do Forte. However, the monitoring period subsequently included the severe 1997–1998 El-Nino Biological Conservation 118 (2004) 609–617 www.elsevier.com/locate/biocon BIOLOGICAL CONSERVATION * Corresponding author. Tel.: +44-1752-232916; fax: +44-1752- 232970. E-mail address: m.attrill@plymouth.ac.uk (M.J. Attrill). 0006-3207/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2003.10.010