DISSERTATION RESEARCH: Testing carbon limitation of cave stream ecosystems via a whole-reach detritus addition

University Of Alabama Tuscaloosa, Tuscaloosa AL

Investigators

Abstract

The overall goal of this study is to determine whether the availability of energy limits biological activity in cave stream ecosystems. In cave ecosystems, the resource at the base of the food web, and thus the resource that potentially controls overall biological activity, is dead organic matter (e.g. dead leaves, twigs, and logs, hereafter referred to as detritus). Because there are few physical openings into cave systems, the amount of detritus washed into caves is typically very low, so cave communities are assumed to be energy-limited. However, this energy-limitation hypothesis has never been tested, despite it being central to scientific understanding of cave ecology, evolution, and conservation. This study has been designed to be the first rigorous test of this hypothesis. The study design is elegantly simple: corn litter (leaves, stalks, and husks leftover from corn harvest) were added to a 100-m reach of a cave stream (Bluff River Cave, Jackson Co., AL) beginning in February 2010. The response of the stream community to this addition of energy will be followed for one year relative to that of a reference reach upstream (which will receive no litter). Additionally, over one year of pre-manipulation data (October 2008 to February 2010) has already been collected from both reaches. Samples will be collected monthly to track changes in species composition, abundance, and growth, as well as the incorporation of corn-derived material into animal tissue. This study will examine the response of the entire food web of the cave stream, from the most basal consumer (the bacteria and fungi that consume natural detritus and the added corn litter) to top predators (cave crayfish and salamanders). Thus, not only is this study the first to test the energy-limitation hypothesis, but it is also the first to characterize a cave stream's food web over an extended period of time. The results from this study will be valuable to various individuals and organizations. Conservation personnel and cave conservation groups will use the life history information (growth rates and time to maturity) obtained for the critically threatened Tennessee cave salamander (Gyrinophilus palleucus) and cave crayfishes (Cambarus tenebrosus and the imperiled Cambarus hamulatus). Cave systems are a window through which groundwater systems can be studied and monitored. Thus the general scientific community and society at large will benefit because groundwater systems are poorly understood but contain about 99% of all liquid freshwater on the planet, and provide important ecological services, including sustaining surface aquatic ecosystems, natural purification of water supplies, and maintenance of many highly endemic and endangered species. Results from this study will be shared both through scientific (journal articles, reports, and oral presentations) and public avenues (interactions with caving groups, landowners, state and federal agencies, and K-12 educators). As part of this project, a lesson plan for local high-school students has been developed, which teaches basic principles of cave and groundwater ecology, illustrates how ecology and evolution interact to structure cave communities, and introduces the concept of detritus-based food chains. To increase the number of students exposed to this material, the entire lesson plan (i.e., instructions, lectures, and activities) will be disseminated to local high-school teachers.