Fish assemblages in tropical estuaries of northeast Brazil: A multi-component diversity approach

Highlights

• Environmental changes and human activities can impact biodiversity in estuaries.

• We assessed the diversity of exploited fish communities within four estuaries, Brazil.

• Diversity indices, abundance models and a recent multivariate analysis were used.

• Assemblage diversity of the largest estuary of wide mangrove differed from the others.

• This multi-facet approach is useful for an ecosystem-based fisheries management.

Abstract

Biodiversity in estuarine ecosystems suffers from the impact of environmental changes and human activities. This mainly involves changes in temperature, salinity, pollution, habitat degradation or loss and fishing activities. The diversity of species communities is traditionally assessed on the basis of their species richness and composition. However, there is growing interest in taking into account complementary components dealing with species differences (e.g. taxonomic relatedness). In spite of their social, ecological and economic importance, the diversity of tropical estuarine fish assemblages has rarely been monitored by means of a multi-component approach under different human pressure and environmental conditions. We analysed the diversity of exploited fish communities (both target and non-target species) sampled during scientific surveys within four estuarine complexes in the state of Pernambuco, Brazil: Itapissuma, Suape, Sirinhaém, and Rio Formoso. A total of 122 species were collected within 34 samples. Overall, diversity indices and species models fitting dominance-evenness profiles mainly revealed differences between assemblages from Itapissuma, being the largest estuary with wide areas of mangrove, and the other estuaries. While assemblages from Itapissuma generally encompassed more species and individuals than the other estuaries, species were more closely related from a taxonomic point of view. In addition, a Double Principal Coordinate Analysis (DPCoA) established a typology of assemblages, useful for management purposes, and linked to particular fish families: it highlighted differences between Itapissuma, Suape, Sirinhaém and Rio Formoso. This method combines matrices of species abundances and differences (here taxonomic distances according to the Linnean classification). It was particularly accurate with a first factorial plane explaining 73% of the total inertia, while only 17% was achieved by a traditional Principal Component Analysis (PCA). Overall, this study provides an assessment of the state of fish assemblage diversity in Pernambuco estuaries where contrasted human and environmental conditions occur. It underscores the accuracy of using a multi-component diversity approach, with a multivariate analysis that is not yet widely used, for monitoring the diversity of estuaries for ecosystem-based fisheries management purposes.

Introduction

Estuaries, interfaces between land and sea, are the site of a range of hydrological (e.g. river discharge), oceanographic and anthropogenic processes. These complex processes create habitats with intense thermal and salinity gradients and variable nutrient and pollutant concentrations (Wolanski, 2007). They notably drive fish patterns of distribution in space and time, and shape the diversity of assemblages (Elliott et al., 2007, Potter et al., 2015). Estuaries are ecologically essential as feeding and breeding grounds, providing appropriate habitats for different stages of the fish life cycle. In addition, they are a migratory pathway for both anadromous and catadromous species (Elliott et al., 2007, Potter et al., 2015). Furthermore, the high socio-economic value of their products, especially as a source of income and food, is widely recognized (Glaser and Diele, 2004, Isaac et al., 2009). However, global environmental change and direct human pressures impact the water quality and biodiversity of estuarine ecosystems (Garcia et al., 2003, Halpern et al., 2008, Borja et al., 2010, Li and de Jonge, 2015). Notably, major changes in fish diversity from the effects of mangrove removal, shrimp farming and agricultural development have been recently documented for estuaries worldwide in terms of assemblage composition, decrease in number of species, feeding groups and larger fishes (Blaber, 2008, Blaber, 2009, Blaber, 2013, Weerts and Cyrus, 2002, Singkran and Sudara, 2005, Oribhabor and Ogbeibu, 2010, Viana et al., 2010, Viana et al., 2012).

Aquatic resources are of fundamental importance for human food and for the development of Brazil, which has one of the longest coastlines in the world (9th longest worldwide) (Burke et al., 2001). Recently, Pinheiro et al. (2015) stated that the Brazilian aquatic biodiversity is in peril, notably with regard to fishes, in many cases due to habitat degradation. However, it is widely acknowledged that the success of many fisheries resources is dependent on the quantity and quality of the habitat (Lindall and Thayer, 1982; Auster et al., 1996). The northeast is one of the most densely populated coastal regions in Brazil. In Pernambuco state, the degradation of coastal ecosystems is most severe around the main urban centre, Recife, mainly due to domestic pollution, industrial activity and habitat degradation and loss. These coastal ecosystems are also threatened by fishing (Elfes et al., 2014) because of the impact on the habitat (Turner et al., 1999) and/or fishes at the top of the trophic networks (e.g. trophic downgrading, Estes et al., 2011). Along the Pernambuco coast are located 34 fishing communities, with ca. 12 000 fishermen (Lessa et al., 2006). To supply food and satisfy economic needs, aquatic resources are intensively exploited using multiple techniques and multispecies artisanal fisheries (Frédou et al., 2006, Frédou et al., 2009a, Frédou et al., 2009b). The majority of stocks are either fully or over-exploited, and there is little room for expansion into new fisheries (MMA, 2006). Despite all these threats, the degree of dependency on and use of estuarine ecosystems, even in urban areas, remains very high (MMA, 2002).

The diversity of the threats and their intensification in the Pernambuco estuaries (Lira et al., 2010a, Lira et al., 2010b) highlight the need to monitor fish biodiversity for management and sustainable use purposes. While several studies dedicated to the diversity of fish assemblages have been carried out in this area (Paiva et al., 2009, Paiva and Araújo, 2010), there is still a need to assess and quantify their state in the main estuaries subjected to contrasting human pressure and environmental conditions. For this purpose, the diversity of fish assemblages can be monitored more exhaustively by a multi-component diversity approach (e.g. Wilsey et al., 2005; Mérigot et al., 2007, Gaertner et al., 2010, Lefcheck et al., 2014). This approach consists in assessing different components, or facets, such as species number and evenness, and also components that explicitly take into account the degree of difference among species. This reflects the taxonomic relatedness between species, on the basis of which diversity indices can be more sensitive to environmental and/or human drivers (Clarke and Warwick, 1998). Monitoring a single diversity component using one or few diversity indices leads to an incomplete description of the diversity of assemblages, and in turn important responses in the face of environmental and/or human drivers could be missed (e.g. Stuart-Smith et al., 2013, D’agata et al., 2014).

In this context, the aim of this work is to investigate the fish diversity assemblages on the basis of a multi-component approach, comparing tropical estuaries subjected to contrasting environmental conditions and human pressure. Firstly, complementary diversity indices were quantified for each estuary. Secondly, the typology of fish assemblages among these estuaries was characterized using a recent multivariate analysis, the Double Principal Coordinates Analysis (DPCoA), that explicitly takes into account species differences (here, taxonomic relatedness). Overall, this study provides an assessment of the state of assemblages among the studied tropical estuaries of northeast Brazil, and demonstrates that a multi-component approach of this kind can be useful for ecosystem-based fishery management in estuarine ecosystems.