Montoya Ceballos, Jose Vicente (2008-12). Influence of hydrological seasonality on sandbank benthos: algal biomass and shrimp abundance in a large neotropical river. Doctoral Dissertation. Thesis uri icon

abstract

  • In this study, I examined the influence of hydrological seasonality on
    spatiotemporal variation of algal biomass and shrimp abundance on sandbanks of the
    Cinaruco River in southwestern Venezuela. Seasonal variations of abiotic and biotic
    variables in the Cinaruco were driven by the hydrological regime. During the highwater
    periods, river sites in the main channel and lagoon sites were similar in water
    physicochemical variables and algal biomass. In contrast, physicochemical variables
    and algal biomass differed between river and lagoon sites during the low-water period.
    The absence of flow in lagoons and consistently low algal biomass on river sandbanks
    were the most important features of the spatial variability between main-channel and
    lagoon sandbanks during low-water phases. Benthic algal biomass was highly uniform
    at small spatial scales and significantly heterogeneous at large spatial scales. In the
    second major part of this dissertation, I found a relatively species-rich shrimp
    assemblage with seven species inhabiting the sandbanks of the Cinaruco. I also
    observed clear patterns of temporal and spatial variation in shrimp abundance on the
    Cinaruco sandbanks. Abundance of shrimp on the sandbanks presented remarkable diel variation, showing almost exclusive use of this habitat at nights. Seasonally, shrimp
    were more abundant during rising- and falling-water periods, when rapid changes of
    environmental conditions occur. Shrimp abundance was high on those sandbanks with
    absence of troughs and presence of submerged vegetation. These environmental features
    presumably promote colonization/establishment and survival/persistence of shrimp in
    the sandbanks. In a patch-dynamic view of communities, a mobility control model
    seems to apply to shrimp of the sandbanks in the Cinaruco during the period of rapid
    changes in hydrology and habitat structure. During low-water periods, when habitat
    structure of sandbanks is relatively constant, low shrimp abundance appears to be
    heavily controlled by high fish predation. The annual flood regime of the Cinaruco,
    which drives the concentrations of dissolved materials, affects material interchanges
    between aquatic and terrestrial systems, and modifies aquatic habitat structural
    complexity, is responsible for creating strong patterns of seasonal and spatial variation in
    benthic algal crops and shrimp abundance on the sandbanks of this large floodplain
    river.

publication date

  • December 2008