In Structuring Fish Assemblages in Lakes of a Neotropical Floodplain
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Hydrobiologia (2010) 651:115–126 DOI 10.1007/s10750-010-0281-0 PRIMARY RESEARCH PAPER The role of the predatory trahira (Pisces: Erythrinidae) in structuring fish assemblages in lakes of a Neotropical floodplain Ana Cristina Petry • Luiz Carlos Gomes • Pita´goras Augusto Piana • Angelo Antonio Agostinho Received: 8 June 2009 / Revised: 19 April 2010 / Accepted: 26 April 2010 / Published online: 15 May 2010 Ó Springer Science+Business Media B.V. 2010 Abstract We performed an experimental manipu- assemblages and were more pronounced at the end of lation of trahira Hoplias aff. malabaricus in a series of the experiment within macrophyte-covered areas of isolated lakes of the upper Parana´ River floodplain to the lakes where H. aff. malabaricus was removed. In evaluate its short-term impact on the structure of fish these lakes, the number of fish was also significantly assemblages. The effects of trahira density (treatment smaller and evenness was significantly higher than in groups: addition, removal, and reference) in two those in which trahira were added or maintained at habitat categories (open and macrophyte-covered natural densities. The increase of the relative abun- areas) on attributes of the fish assemblage structure dance of all size classes over the first 60 days on the were evaluated (using rm-ANOVA) over 120 days. assemblages where trahira was present, and the Reductions in species richness were recorded in all decrease of the small-sized fish where trahira was absent contributed to the lack of pronounced altera- tions in total biomass. The absence of the predator Electronic supplementary material The online version of from its preferred habitat was found to negatively this article (doi:10.1007/s10750-010-0281-0) contains affect the less abundant species, which seemed to be supplementary material, which is available to authorized users. highly sensitive to the effects of interspecific compe- Handling editor: D. Dudgeon tition among prey species. In addition to the well- known effects of hydrological seasonality, the role A. C. Petry (&) played by native predators might be important in Universidade Federal do Rio de Janeiro, Nupem, determining the persistence of local species in the fish R. Rotary Club, sn, CP: 119331, Macae´, RJ 27910-970, Brazil assemblages of Neotropical floodplains. e-mail: [email protected] Keywords Hoplias aff. malabaricus Á Predation Á L. C. Gomes Á A. A. Agostinho Whole-lake experiment Universidade Estadual de Maringa´, Nupe´lia, Av. Colombo, 5790, Maringa´, PR 87020-900, Brazil e-mail: [email protected] A. A. Agostinho Introduction e-mail: [email protected] The identification of mechanisms through which P. A. Piana some species can assume greater importance within Universidade Estadual do Oeste do Parana´,R.da Faculdade, 2550, Toledo, PR 85903-000, Brazil their assemblages has been the basis for research e-mail: [email protected] aiming conservation of species and ecosystems, 123 116 Hydrobiologia (2010) 651:115–126 especially in temperate regions (Power et al., 1996a; H. aff. malabaricus, which appears to play an Creed, 2000). For example, predators may affect prey important role in structuring fish assemblages either in several ways, such as on its number, habitat use, in temporary disconnected lakes of the upper Parana´ period and intensity of foraging, with direct effects on River floodplain over time. There, densities of trahira intra- and inter-specific dynamics (e.g., growth, were used to explain variations in the density of prey reproduction, and interactions) (Werner et al., 1983; species in recent studies, especially in macrophyte- Fraser & Gilliam, 1992; Miyasaka et al., 2003). Paine covered areas (Okada et al., 2003; Piana et al., 2006). (1969) used the term keystone to identify species, This study evaluated the short-term impact of the such as the sea star Pisaster ochraceus, that, when strong piscivore trahira in modifying the dynamics of present, promoted the coexistence of a larger number fish assemblage structure of isolated lakes in the upper of species than expected relative to its abundance Parana´ River floodplain. The ichthyofauna of these (Paine, 1966, 1969; Power et al., 1996b). In tropical lakes is essentially composed of sedentary, small-sized regions, however, factors such as high environmental species whose life history characteristics [e.g., short complexity, high species diversity, high potential life span, early maturation (\12 months)] reflect in interactions among species, and a limited understand- high population growth rates (Winemiller, 1989; ing of food web dynamics (Lowe-McConnell, 1987; Vazzoler, 1996; Okada et al., 2003; Froese & Pauly, Flecker, 1992) have hampered investigations of the 2008). The expected reduction in consumption and the keystone concept. simplification of food webs during droughts (from Based on the conclusions of several descriptive autumn to spring) suggests that, if competition exists, studies, a strong candidate for this status is the trahira it should be more intense during these periods. Aquatic Hoplias aff. malabaricus (Bloch, 1794), an opportu- macrophytes play an important role in floodplain lakes nistic and sedentary predator that is widespread in by increasing habitat heterogeneity, providing food Neotropical aquatic environments (Oyakawa, 2003). resources and refuge for prey species, and lessening Controlled investigations of the trahira’s effects on the forage efficiency of pelagic and aerial predators other species are restricted to those which experi- (Agostinho et al., 2007), but not reducing predation mentally examined only one (Mazzeo et al., 2010)or from trahira (Piana et al., 2006). Therefore, we tested two prey species (Fraser & Gilliam, 1992; Gilliam the hypothesis that by piscivory, trahira determines et al., 1993; Fraser et al., 1999; Gilliam & Fraser, assemblage structure and, therefore, is able to mediate 2001). However, other fish and some invertebrate fish species coexistence. If the hypothesis is true, the taxa, e.g., the crab Pseudothelfusa garmani, appear to addition and removal of H. aff. malabaricus will alter undergo behavioral shifts in their habitat use patterns species richness, abundance, evenness, biomass, and in the presence of this strong predator (D.Fraser, pers. body size structure of the fish assemblages. We also comm.). Alterations in the distribution patterns of tested whether any effects depended upon habitat small-sized fish species in Caribbean streams, structure, once trahira may be successful in capturing increasing fishery yields in large northeastern Brazil- fish in macrophyte-covered areas. ian reservoirs, and strong cascading effects in subtropical mesocosms have been associated with the presence of trahira (Fraser & Gilliam, 1992; Paiva Materials and methods et al., 1994; Mazzeo et al., 2010). H. aff. malabaricus represents a species complex in several Brazilian The biology of the trahira H. aff. malabaricus riverbasins, since at least seven cytotypes have been identified (Bertollo et al., 2000). In the upper Parana´ Hoplias aff. malabaricus is commonly found in the River floodplain, trahira are found in almost all upper Parana´ River floodplain (Bialetzki et al., 2002; biotopes, such as river channels, secondary channels, Petry et al., 2003b), where it is the main predator. The permanent and temporary lakes (Petry et al., 2003a). absence of pronounced floods in recent years has Despite the unsolved taxonomic problems, and the prevented access for other large piscivores (Petry et al., fact that ecological reports may involve more than 2003b; Agostinho et al., 2004). The species exhibits one species, all trahiras studied have strong impacts multiple spawning and an extended reproductive in their local communities, which is also true for period (from September to February) (Bialetzki et al., 123 Hydrobiologia (2010) 651:115–126 117 2002; Suzuki et al., 2004). The sedentary and solitary lakes (HM- treatment). Despite the fact that the trahira preferentially inhabits macrophyte-covered experimental removal did not assure complete pred- areas that favor its ambush feeding strategy (Almeida ator exclusion, the trahira density was kept near zero et al., 1997; Luz-Agostinho et al., 2008), and as larvae, in these lakes. Predator density manipulation was juveniles, and adults, respectively, feeds on plankton, carried out 2 days after the first sampling. At the insects, and primarily fishes (Oliveros & Rossi, 1991; beginning of the experiment, SL did not differ Hahn et al., 2004). Although there is evidence of a significantly between HM? treatment lakes (Student positive relationship between trahira and prey size, t test, t(52) = 0.53, P = 0.60). small-sized fish are the trahira’s most important food All samplings (before and after the manipulations) resource (Loureiro & Hahn, 1996). were carried out bimonthly (from April to August) during the morning (from 07:00 to 11:00). Seine nets Whole-lake experiment (50 m 9 2.4 m, 0.5 cm mesh) were used to isolate ca. 112 m2 in two selected sampling areas (open and The experiment was conducted over 120 days during macrophyte-covered) in every lake. These nets were autumn and winter of 2002. This period was selected set on the bottom and were attached to the edges 24 h based on the low water levels of the Parana´ River, prior to sampling. Immediately before each sampling, which caused the lakes to remain isolated (no fish the nets were raised to completely enclose the areas movement between lakes). The experimental design in order to block fish passage, and fish were collected consisted of six lakes (Canal do Meio, Carioca, inside the areas by seine nets (open area) (5 mm Cida˜o, Ze´ Marinho, Genipapo, and Tia˜o), all with mesh) and a sieve (macrophyte-covered area) until open and macrophyte-covered areas (herein named successive five sweeps did not capture any fish. The habitats) and a single initial disturbance (manipula- large sieve consisted of a rectangular metal frame tion of trahira density). We opted to test habitat effect with a 1 mm mesh sized net, dimensions of 1.5 m 9 because trahira has behavioral adaptations to thrive in 1.0 (1.5 m2) following Nakatani et al.