Ecological Indicators 18 (2012) 11–19 Contents lists available at SciVerse ScienceDirect Ecological Indicators journal homepage: www.elsevier.com/locate/ecolind Vulnerability of Portuguese estuarine habitats to human impacts and relationship with structural and functional properties of the fish community Susana Franc ¸a a,∗ , Rita P. Vasconcelos a , Patrick Reis-Santos a , Vanessa F. Fonseca a , Maria José Costa a,b , Henrique N. Cabral a,b a Centro de Oceanografia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal b Departamento de Biologia Animal, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal article info Article history: Received 25 March 2011 Received in revised form 25 October 2011 Accepted 30 October 2011 Keywords: Estuary Habitat Saltmarsh Mudflat Anthropogenic threats Vulnerability Portugal abstract Estuaries are extremely productive ecosystems, providing habitat for numerous species and considered essential nurseries for many marine species. However, environmental changes caused by anthropogenic threats affect the quantity and quality of estuarine habitats. Habitat loss and degradation, conspicuous in estuaries worldwide, is considered a major threat to the function of estuaries. Information on threat- ening processes leading to habitat loss and degradation and on relative vulnerability of different habitats is imperative for conservation planning. The vulnerability of estuarine habitats (saltmarsh, mudflat and subtidal) from five Portuguese estuaries (Ria de Aveiro, Tejo, Sado, Mira and Guadiana) to the major anthropogenic threats affecting them was assessed through a threat ranking approach developed with basis on expert’s judgment. Simultaneously, fish communities in these habitats (in two sites per estu- ary) were sampled seasonally in 2009, in order to relate habitat vulnerability and habitat use by fish communities. Experts ranked threats such as nutrient input, changes in river flow and land reclama- tion as having stronger impacts on estuarine habitats, making them more vulnerable to destruction or degradation. Averaging all threats, vulnerability scores were higher in mudflats, followed by subtidal and saltmarsh habitats. Overall, habitats in the Tejo and Sado estuaries were ranked as the most vul- nerable and in the Mira estuary as the least vulnerable. Relationships between vulnerability values and fish community indicators in sampled habitat types and areas evidenced similarities between intertidal habitats (saltmarsh and intertidal mudflats), highlighting their priority in conservation and management contexts. The presented approach provides a useful tool as it allows prioritizing threat mitigation and identifies the most vulnerable habitats to potential degradation and destruction. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Estuaries are important coastal ecosystems; they represent transition systems between freshwater and marine environments and are among some of the most biologically productive areas on Earth (Costanza et al., 1997; Kennish, 2002). Estuarine systems are essential to the renewal of fisheries resources, as they provide nursery grounds for many marine fish species (Beck et al., 2001; Able, 2005). These species’ juveniles may find in estuaries potential advantages for their growth and survival, namely high prey avail- ability, refuge from predators and good environmental conditions (Haedrich, 1983; Lenanton and Potter, 1987; Beck et al., 2001). Despite their high productivity, estuaries are ranked amongst the most anthropogenically degraded habitat types on Earth ∗ Corresponding author. Tel.: +351 21 750 08 26; fax: +351 21 750 02 07. E-mail address: sofranca@fc.ul.pt (S. Franc ¸ a). (Hodgkin, 1994; Blaber et al., 2000; Edgar et al., 2000). Human activities jeopardize estuary’s functioning, and in many cases have caused large scale changes in natural communities (Edgar et al., 2000). Environmental problems in these systems are invariably related with overpopulation and uncontrolled development in coastal watersheds, as well as human activities in the estuarine embayment (Kennish, 2002). These strong human impacts collide with the important ecological function of estuarine systems, which might threat these ecosystems’ viability and health namely with decrease in natural productivity, change in ecosystem stability and loss of biodiversity (Vasconcelos et al., 2007). Fisheries have always been considered one of the most threaten- ing anthropogenic factors to fish populations’ viability (Boreman, 1997; Johnson et al., 1998). Nevertheless, recent studies showed that activities such as reclamation of wetlands, dredging of shipping channels, construction of port facilities and introduction of alien species have caused large scale habitat loss and degradation (Edgar et al., 2000; Vasconcelos et al., 2007; Goberville et al., 2011). Many of these endangered habitats have been considered essential for 1470-160X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecolind.2011.10.014