Analyses of the biota in the aquatic habitats of Montezuma Castle National Monument

Blinn, Dean; Oberlin, Gaye

A cooperative study between Northern Arizona University and the National Park Service was initiated in 1992 with the intent to better understand and document the water-related biotic resources in the Montezuma Castle National Monument (MOCA). Included in the objectives for this three year project were a review of existing literature, an intensive inventory of the Park's aquatic habitats, and an assessment of the habitat requirements of these aquatic organisms, especially the endemic species. Montezuma Castle National Monument contains three interconnected but distinctly different aquatic ecosystems. While they are geographically in close proximity and influenced by the same climatic and seasonal patterns, their morphology and hydrology differ enough to create physicochemical conditions that vary significantly between habitats. Superimposed on these spatial gradients in environmental conditions, these aquatic systems also represent extremes in temporal change, ranging from the near-constant lentic environment of Montezuma Well to the frequently disturbed lotic environment of Beaver Creek. In between, the contiguous cave and irrigation canal provide a rapidly changing gradient of physicochemical conditions over a short distance (1.5 km). This range of environmental conditions in such close proximity offers a unique opportunity to study the response of aquatic invertebrates to spatial and temporal change. The organization of this report will follow a journal format to expedite the preparation of parts of this document for submission to scholarly journals for publication. It consists of a general introductory chapter, three manuscript chapters, and a conclusion chapter. Some redundancy may occur as a result of combining journal articles in this format. This report will examine invertebrate response to environmental gradients at three levels of resolution. Chapter 2, "Distribution of Aquatic Invertebrates in Montezuma Castle National Monument, Arizona, in Response to Physicochemical Gradients," summarizes the inventory of all aquatic habitats within Montezuma Castle National Monument and relates invertebrate distributional patterns to the physicochemical properties of their respective environments. A comprehensive literature review is also included. Chapter 3, "Spatial and Temporal Patterns Among Invertebrates Following Disturbance in a Southwestern Desert Stream," focuses on the impact of disturbance on the invertebrate communities in Beaver Creek. Frequency and intensity of disturbance events is one of the major hydrological differences between these aquatic systems and can have tremendous impacts on invertebrate community composition and abundance. If disturbance is infrequent, biotic interactions will be an important determinant of community structure. In Montezuma Well, for example, densities may vary seasonally in response to changes in the algal food base but community structure is relatively constant. In contrast, invertebrate densities and community structure in the frequently disturbed Beaver Creek are constantly changing in response to successional and recolonization events. Chapter 4, "Metabolic Oxygen and Temperature Requirements of the Endemic Amphipod, Hyalella montezuma, in a Thermally Constant Aquatic Environment," examines the impact of temperature on the physiology and distribution of an endemic amphipod in Montezuma Well. Hyalella montezuma is a "keystone" species within this community because it has extremely high production rates and is the major prey item for most predators, including two other endemic species. Therefore, its distribution in response to physicochemical gradients may have significant effects on all trophic levels within Montezuma Well. (Introduction copied verbatim from the report.)

Analyses of the biota in the aquatic habitats of Montezuma Castle National Monument

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