Fish metacommunity structure in Caño Maraca, an important nursery habitat in the Western Llanos of Venezuela

Kirk O Winemiller,Carmen G Montaña,Friedrich W Keppeler,Donald C Taphorn,Edwin O López-Delgado,Leslie C Kelso-Winemiller

doi:10.1590/1982-0224-20180074

Abstract

ABSTRACT We investigated spatial and seasonal variation of fish assemblages of Caño Maraca, a creek in Venezuela’s Western Llanos, a region with strong wet-dry seasonality. Fishes were surveyed over a 19-year period at three sites along the longitudinal gradient: a headwater site with a narrow channel, a middle site with shallow channels traversing a seasonal wetland, and a lower site where the channel has higher banks. Assemblage composition and presence of species with juveniles and various life history strategies were compared during wet and dry seasons. Overall, fish species richness was lowest at the headwater site and highest at the downstream site. During the wet season, however, species richness is greatest at the middle site, a pattern associated with migration into the site for reproduction and use of the wetland as a nursery. During the dry season, species richness is greater at the downstream site where habitat quality is sufficient to provide suitable habitat for many species. Fish movements and population dynamics in Caño Maraca respond to seasonal environmental changes, and the fish metacommunity appears influenced by species sorting (habitat selection), mass effects (source-sink dynamics), patch dynamics (interspecific differences in colonization and species interaction) as well as random factors (dry-season strandings).

Highlights

Headwater streams typically make up two thirds or more of the total channel length within a drainage network, and small streams are important for maintenance of biodiversity and ecosystem services at regional scales (Freeman et al, 2007)
Understanding of stream ecology in the tropics continues to lag behind knowledge from north temperate regions (Winemiller et al, 2008), recent years have seen a great increase in research on fish ecology in Neotropical streams, especially in Brazil (e.g., Abes, Agostinho, 2001; Casatti, 2005; Almeida, Cetra, 2016; Juen et al, 2016)
When all available data for each site were combined and species richness values adjusted for survey effort via rarefaction, species richness varied according to the longitudinal fluvial gradient, with lowest richness at the headwater site (Naciente) and highest richness at the site located furthest downstream (Puente) (Fig. 2)

Summary

Introduction

Headwater streams typically make up two thirds or more of the total channel length within a drainage network, and small streams are important for maintenance of biodiversity and ecosystem services at regional scales (Freeman et al, 2007). As for any organism, stream fishes undergo changes in population abundance and spatial distribution as a function of reproduction, mortality and dispersal These processes are influenced by temporal and spatial variation in habitat quantity and quality, disturbance regime (e.g., flash floods, desiccation, aquatic hypoxia), primary production, inputs of allochthonous materials, predation, and landscape connectivity as affected by local precipitation and hydrology. Headwater streams in flatlands have meandering channels, slow water currents, and sandy or silty substrates. These sluggish streams often accumulate large amounts of detritus and in semiarid and arid climates may have reaches that periodically become dry, leaving series of isolated pools. Fish assemblages in low-gradient streams often support fish assemblages that are more taxonomically and functionally diverse compared to those found in higher-gradient streams of the same region (Gonçalves, Braga, 2012; Wolff, Hahn, 2017)

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Conclusion