Juvenile fish condition in estuarine nurseries along the Portuguese coast R.P. Vasconcelos a, * , P. Reis-Santos a , V. Fonseca a , M. Ruano a , S. Tanner a , M.J. Costa a, b , H.N. Cabral a, b a Instituto de Oceanografia, Faculdade de Cieˆncias da Universidade de Lisboa, Campo Grande,1749-016 Lisboa, Portugal b Departamento de Biologia Animal, Faculdade de Cieˆncias da Universidade de Lisboa, Campo Grande,1749-016 Lisboa, Portugal article info Article history: Received 18 September 2008 Accepted 5 January 2009 Available online 9 January 2009 Keywords: juvenile fish estuarine nurseries habitat quality condition RNA:DNA Fulton’s K abstract Connectivity between estuarine fish nurseries and coastal adult habitats can be affected by variations in juvenile growth and survival. Condition indices are renowned proxies of juvenile nutritional status and growth rates and are valuable tools to assess habitat quality. Biochemical (RNA:DNA ratio) and morphometric (Fulton’s condition factor K) condition indices were determined in juveniles of Solea solea, Solea senegalensis, Platichthys flesus, Diplodus vulgaris and Dicentrarchus labrax collected in putative nursery areas of nine estuaries along the Portuguese coast (Minho, Douro, Ria de Aveiro, Mondego, Tejo, Sado, Mira, Ria Formosa and Guadiana) in the Spring and Summer of two consecutive years (2005 and 2006) with distinct climatic characteristics. Individual condition showed significant variation amongst species. The combined use of both condition indices highlighted the low correlation between them and that RNA:DNA had a higher sensitivity. RNA:DNA varied between years but overall the site relative patterns in condition were maintained from one year to the other. Higher RNA:DNA values were found in Spring than in Summer in most species. Intra-estuarine variation also occurred in several cases. Species specific trends in the variability of condition amongst estuaries were highlighted. Some estuaries had higher juvenile condition for more than one species but results did not reveal an identical trend for all species and sites, hindering the hypotheses of one estuarine nursery promoting superior growth for all present species. Significant correlations were found between condition indices, juvenile densities and environmental variables (water temperature, salinity and depth) in the estuarine nurseries. These influenced juvenile nutritional condition and growth, contributing to the variability in estuarine nursery habitat quality. Management and conservation wise, interest in multi-species approaches is reinforced as assessments based on a single species may not reflect the overall nursery habitat quality. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Numerous fish species rely on estuarine and coastal adjacent areas as nursery grounds (Beck et al., 2001; Able, 2005). Juveniles in estuarine nursery areas tolerate and overcome some of the occur- ring environmental constraints, benefiting from favourable condi- tions for growth, such as high food availability, water temperature and refuge from predators (Haedrich, 1983; Gibson, 1994; Beck et al., 2001). Estuarine nurseries are associated with high juvenile densities and enhanced survival and growth rates, which likely contribute towards maximizing juvenile export and recruitment to coastal adult habitats. Small differences in growth and mortality rates in the first year of life are known to result in large differences in the number of individuals entering the reproductive stage annually (Houde, 1987; Cushing and Horwood, 1994; Gibson, 1994; Van der Veer et al., 1994). The relevance of increased juvenile survival and growth is reflected in the nursery role concept of Beck et al. (2001), according to which a nursery is an area or habitat that produces relatively more adult recruits per area unit than other juvenile habitats used by a particular species. Therefore, understanding sources of variation in juvenile growth is an important step in recognizing the overall nursery role status of an estuary and its influence on coastal stock replenishment. This knowledge is particularly relevant considering that not all estuaries are equal and the quantity or quality of their available habitats for juveniles of marine fish species is not necessarily the same. Moreover, habitat quality and its possible implications on connectivity are not only dependent on the natural features of the estuary but also on the effects of anthropogenic factors that are conspicuous in most * Corresponding author. E-mail address: rpvasconcelos@fc.ul.pt (R.P. Vasconcelos). Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss 0272-7714/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2009.01.002 Estuarine, Coastal and Shelf Science 82 (2009) 128–138