Date of Award

Spring 2012

Document Type

Legacy Thesis

Degree Name

Master of Science in Coastal Marine and Wetland Studies

Department

Coastal and Marine Systems Science

College

College of Science

First Advisor

Kevin S. Godwin

Second Advisor

John J. Hutchens, Jr.

Third Advisor

Brent L. Lewis

Abstract

The goal of my project was to conduct the first limnological investigation of Laguna de Cube, Ramsar site 1143, linking hydrogeologic landscape setting to local condition (i.e., water quality and nekton composition). Laguna de Cube, a rare lacustrine wetland within the Choco Darien biodiversity hotspot, performs critical ecosystem functions and services in a region recognized for its extraordinary biodiversity, rarity, and increasing human interference. Abiotic gradients (i.e., thermocline, pH, conductivity, dissolved oxygen (DO)) and hydrochemical parameters (i.e., plant limiting nutrients, herbicides and fecal coliform threshold levels) were quantified in vertical profile and related to nekton composition and habitat utilization. Direct (i.e., flag and caste nets, unbaited fish traps) sampling utilized 20 paired sampling sites and quantified nekton richness, abundance and diversity. Acoustic sonar surveys were used to assess fish abundance, aquatic vegetation, substrate, and lake bathymetry. Nonparametric statistics (e.g., Chi2, Kruskal Wallis), with an a priori p:5 0.10, were used for comparisons Using sonar, depth at Laguna de Cube, ranged from 0.3914 to 31.72 meters (mean 14.41 m) had a total volume of 3,000,000 m3, with a distinct thermocline at 2m. Conductivity, pH, and DO concentrations were significantly different above and below the thermocline (i.e., p=0.089, 3.2e-8, 1.2e-7 respectively). DO, in vertical profile, exhibited elevated concentrations between 8-12m. Plant limiting nutrients (total N and P), fecal coliforms, herbicides (atrizine and simazine) all exceeded US EPA safe drinking water standards. Nekton sampling resulted in 228 individuals representing 5 taxa of IUCN (2012) east concern, dominated by exotic tilapia ( Oreochrontis niloticus niloticus) that represented the majority of nekton biomass. Fish assemblages preferred edge habitats (abundance p=6.1e-7, Shannon-Wiener Diversity p=0.0015) and acoustic surveys showed variations in diurnal distributions with more fish below the therrnocline during the day, and more above the thermocline at night. Likely the oldest and deepest lacustrine feature in Ecuador, the volume, exceeding poor quality, and the potential for deadly toxic algal blooms, derived from metalimnetic cyanobacteria residing in the lake, suggests eutrophication and bioaccumulation will increase, immediately threatening human health. While no historic nekton composition data are available for Laguna de Cube, the extremely low diversity I report is likely a result of the combination of anthropogenic impacts and the presence of an exotic invasive species. The ecological importance of Laguna de Cube is not manifested in conventional measures of conservation. This floodplain lake buffers human threats to biodiversity and its location at the headwaters of the Mache Chindul Ecological Reserve makes its conservation vital. Implementation of clear and transparent conservation management plans that improve water quality, halt the range expansion of tilapia and other invasive species, and promote ecologically sound sustainable agriculture at Laguna de Cube is necessary to protect the down-gradient biodiversity of the region.

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