6 - Spatial and Temporal Variations′ of Habitat Suitability for Fish: A Case Study in Abras de Mantequilla Wetland, Ecuador

Abstract

A central component of predictive ecology in wetlands is the analysis of species distribution as a function of their biotic and abiotic environment. Decision-makers in biodiversity conservation, species monitoring, and environmental planning, among others, normally use this analysis. Habitat suitability modeling is a major component of the process of making the analysis; however, temporal and spatial variations of hydrological, hydrodynamic, and environmental variables are normally not well known and overall values are estimated. In Abras de Mantequilla wetland (Ecuador) we find a tropical situation where the hydrodynamics of inflows seem to play an important role in the stability of the ecosystem. Habitat suitability in wetlands is driven by hydrodynamic, physical, and biological interactions that are not fully understood. This research explores the habitat changes in space and time for the overall fish community in this tropical wetland, by formulating a Habitat Suitability Index (HSI) from a combination of hydrodynamic model variables. The main goal was to quantify the extension of the habitat areas where the HSI was high enough to be considered as suitable for the fish community. The analysis was based on the hydrodynamic features and spatiotemporal variations of the habitat index. The hydrodynamic variables water depth and velocity were modeled with a 2D flow representation and information from hydrological model simulations at the inflows of the wetland. Different hydrological conditions were simulated to evaluate the natural variability of this river/wetland system: a typical dry year, an extreme wet year (el Niño), the sampling years of the present study, and the minimum and maximum historical conditions. The hydrodynamic model for each of the different conditions was built in Delft3D-FLOW software. A habitat assessment tool was built in the MATLAB environment. Results from the hydrodynamic models were used as input for the habitat tool. Our findings revealed a high natural variability of the percentage of suitable areas according to the different hydrological conditions simulated. Despite this high variability, all habitat simulations determined that a higher percentage of suitable areas occurred during periods of high flows (middle of the wet season), given the hydrodynamic variables selected. Spatial analysis determined that areas located close to the main inflow were the ones that contribute more to the overall suitability of the wetland. From the historical perspective, and considering the whole wetland area, HSI scores were not lower than 0.4, even in the most unfavorable conditions. The combination of hydrodynamic variables proved to be useful for an initial habitat assessment. However, we acknowledged that other physical, chemical, and biotic variables play an important role in defining habitat preferences and therefore should be gradually included for an integrated ecological habitat assessment.