Nursery Habitat Shifts in an Estuarine Ecosystem: Patterns of Use by Sympatric Catfish Species David Valença Dantas & Mario Barletta & André Ricardo Araújo Lima & Jonas de Assis Almeida Ramos & Monica Ferreira da Costa & Ulrich Saint-Paul Received: 30 September 2010 / Revised: 22 June 2011 / Accepted: 2 October 2011 / Published online: 1 November 2011 # Coastal and Estuarine Research Federation 2011 Abstract The seasonal and spatial distribution (density and biomass) of five size classes of two catfish species (Cathorops spixii and Cathorops agassizii) were studied along an estuarine ecocline to test the relative importance of the nursery function of each habitat. Seasonal vs. area interactions were significant for all size classes of both species. During the early rainy season, the middle estuary is an important nursery habitat for juveniles of both species. When environmental conditions change during the late rainy season, the C. spixii primary nursery habitat shifts to the lower estuary. During this period, juveniles of C. agassizii remain in the middle estuary. Another important ecological area is the upper estuary, which becomes a breeding, spawning and hatchery area during the late dry season for both species. The nursery function of habitats shifts accord- ing to the seasonal fluctuation of salinity and dissolved oxygen, and each species responds differently to this change. Keywords Spatial-temporal variability . Fish movement . Nursery role . Estuary . Water quality Introduction The distribution of estuarine fishes and the migration of juveniles into adult populations are subject to a number of biotic (e.g. predation, food availability, recruitment), abiotic (e.g. salinity, dissolved oxygen, temperature) and landscape factors (e.g. habitat size and habitat connectivity) (Beck et al. 2003; Barletta et al. 2005, 2008). Patterns of fish distribution in coastal and estuarine ecosystems, being subject to seasonal fluctuation of environmental variables, are of ecological and socioeconomic interest (Lugendo et al. 2007; Nakamura and Tsuchiya 2007; Barletta et al. 2008; Dantas et al. 2010). However, observation and modelling of movements and studies of habitat use by different ontogenetic phases of ecologically important fish species in tropical estuaries remain scarce. On occasions, the movement from juvenile to adult habitats has been studied in attempts to determine the particular value of a habitat as nursery grounds, but these efforts have principally been aimed at coral reefs and their adjacent habitats (Nagelkerken and van der Velde 2002; Mellin et al. 2007). According to Beck et al. (2003), a habitat is a nursery for juveniles of a particular species if its contribution per unit area to the production of individuals that recruit to adult populations is greater, on average, than the production from other habitats in which juveniles occur. The nursery function of habitats in estuarine and coastal ecosystems (e.g. seagrass meadows, mangrove forests, wet- lands and sandy beaches) for fishes and invertebrates has been generally accepted among scientists (Perkins-Visser et al. 1996; Nagelkerken et al. 2000; Sheridan and Hays 2003; Jenkins and King 2006), conservation groups and the general public as fundamental to species development and survival. However, there is an ongoing need to test the nursery hypothesis (Beck et al. 2003) for particular estuarine habitats D. V. Dantas : M. Barletta (*) : A. R. Araújo Lima : J. de Assis Almeida Ramos : M. F. da Costa Laboratório de Ecologia e Gerenciamento de Ecossistemas Costeiros e Estuarinos, Dept. Oceanografia, Universidade Federal de Pernambuco, Cidade Universitária, Recife, Pernambuco, Brazil 50740-550 e-mail: mario.barletta@pq.cnpq.br D. V. Dantas : M. Barletta : M. F. da Costa : U. Saint-Paul Instituto de Ecologia e Gerenciamento de Ecossistemas Aquáticos (IEGEA), P.O. Box: 8132, Recife, Pernambuco, Brazil 51020-970 U. Saint-Paul Leibniz Center for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany Estuaries and Coasts (2012) 35:587–602 DOI 10.1007/s12237-011-9452-0