ABSTRACT AQUATIC CONSERVATION BIOLOGY IN ARID ECOSYSTEMS

Aquatic conservation in arid ecosystems is a pressing concern for the public and land managers in the Southwest. This study focuses on aquatic conservation issues in 2 sites – 1 international site, Cuatro Ciéneags, México and 1 Arizona site, Fossil Creek which was the focus of a collaborative, multi-faceted stream restoration project. In Cuatro Ciénegas, we conducted an experiment manipulating fish access to stromatolites. We manipulated 2 fish species that occur with stromatolites, the polymorphic Herichthys minckleyi, and the pupfish Cyprinidon bifasciatus. We used a trophic cascade index as an indicator of cascade strength, and only molariform morphs were responsible for a trophic cascade, reducing snail densities so that stromatolite algal biomass was positive. The papilliform morph treatments, in contrast, allowed snail densities to increase, resulting in stromatolite algae declines indicating loss of stromatolite formation. Our results show that modern stromatolite formation requires the presence of a specific keystone morph of an endemic threatened cichlid. Our results are also consistent with the hypothesis that metazoan grazing could have been responsible for ancient stromatolite declines, and modern stromatolites should be studied in the contex