Ecological quality assessment of small estuaries from the Portuguese coast based on fish assemblages indices Inês Cardoso a,⇑ , Miguel Pessanha Pais a , Sofia Henriques a , Luís Cancela da Fonseca b,c , Henrique N. Cabral a a Centro de Oceanografia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal b Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal c Centro de Oceanografia, Laboratório Marítimo da Guia, Faculdade de Ciências da Universidade de Lisboa, Av. N. Sra. do Cabo, 939, 2750-374, Portugal article info Keywords: Fish assemblages Small estuaries Ecological integrity Fish-based multimetric indices Portuguese coast abstract The importance of establishing the ecological quality of estuarine systems has been widely acknowledged and led to the development of several fish community-based multimetric indices. Nevertheless, a question rose about the accuracy of these tools when natural disturbance is acting upon the organization of the systems’ communities. Four multimetric indices were used to examine their ability to differentiate the ecological status of five small estuarine systems (southern Portugal), and also to test if they reflected the level of anthropogenic pressures. Fish assemblages from Mira, Odeceixe and Aljezur (in the Southwest coast), Gilão and Bensafrim (in the South coast) estuaries were sampled seasonally for one year, and anthropogenic sources of pressure were identified and quantified. We found that although the applied indices provided information on ecological condition differentiation among systems, they are unable to explain different classes of ecological status in systems with equivalent pressure levels. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Estuarine ecosystems are among the most valuable in the World because of their high productivity and their fundamental role con- cerning ecosystem services (Costanza et al., 1997). Nevertheless, this widely accepted statement is actually coupled with the knowl- edge that these ecosystems are facing increasing and significant human-induced impacts, which include physical and chemical transformation, habitat destruction and changes in biodiversity (Halpern et al., 2007). The ultimate challenge of scientists and pol- icy makers is to manage estuarine systems in order to improve their ecological quality, prevent further deterioration, and ensure the progressive reduction of pollution. These are the main objec- tives of the water framework directive, developed for the European context, which has the final goal of achieving a ‘‘good ecological quality status’’ for all water bodies by 2015 (EC, 2000; Borja et al., 2006). This directive urged the development of consistent tools to assess the ecological status of estuarine systems. The task of evaluating ecosystems health is far from simple mainly because of the complexity of the systems, and the conse- quent articulation of a number of interacting components. In gen- eral, these components vary in type, structure and function within the whole system (Costanza and Mageau, 1999). This complexity lead to a biological criterion of ecosystem integrity, where biological indicators are used to increase the probability that an assessment program will detect degradation due to anthropogenic influences (Karr, 1991; Nip and Udo de Haes, 1995; Whitfield and Elliott, 2002). The general idea is that, when ecosystems are not suffering from unusual external perturbations, we observe certain well-defined developmental trends (Odum, 1985). Thus, ecological integrity indicates the divergence from natural conditions, which is attributable to human activities (Karr, 1991). Along with other biological components of aquatic systems, fish-based indicators have been considered a good way of evaluat- ing the environmental status of the ecosystem (e.g. Brind’Amour and Lobry, 2010). In this regard, several multimetric indices have been developed (e.g. Karr, 1991; Deegan et al., 1997; Harrison and Whitfied, 2004; Harrison and Whifield, 2006; Breine et al., 2007; Coates et al. 2007; Breine et al., 2010; Delpech et al., 2010), all attempting to meet the assumptions that the ideal index would be sensitive to all human-generated stresses exerted on bio- logical systems, while also having limited sensitivity to natural variation in physical and biological environments. At this point it is clear that we have to be able to distinguish deviations induced by human activities from the ones resulting on changes of the ecosystems’ equilibrium state originated by nat- ural processes. This is especially difficult in the case of estuaries, since they are naturally stressed and highly variable ecosystems that are at the same time, exposed to high degrees of anthropo- genic stress, a problem recently termed as ‘‘Estuarine Quality Par- adox’’ (Dauvin et al., 2007; Elliott and Quintino, 2007). The 0025-326X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2011.02.037 ⇑ Corresponding author. Tel.: +351 217500826; fax: +351 217500207. E-mail address: ipcardoso@fc.ul.pt (I. Cardoso). Marine Pollution Bulletin 62 (2011) 992–1001 Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul