The structure of aquatic macro-invertebrate communities within cave streams
Email: tnwatson@hotmail.com 1
Abstract
Cave aquatic macroinvertebrate communities are structured by a host of abiotic and biotic factors unique to their environment resulting in variations between cave and surface aquatic communities. Primarily, cave stream invertebrate communities are presumed to be resource limited with a dependence upon surface-derived energy resources, such as FPOM and CPOM. This dependence upon surface derived energy was assessed down a longitudinal gradient within a cave stream using stable isotopes of carbon and nitrogen, pre-conditioned replicate algal tiles, and leaf packs. Furthermore, I investigated the potential for cave aquatic communities to subsidise subterranean terrestrial communities. Resource additions and stable isotopes confirmed that cave aquatic communities were resource limited and dependent upon surface derived materials, with an isotopic signature similar to that of C3 plants. Seston, benthic FPOM, and epilithon (i.e. bacterial, fungal, and diatom communities) were the most important basal resources within the cave, compared with seston, benthic FPOM, and filamentous algae outside of the cave. CPOM did not appear to be readily incorporated into the food-web. Furthermore, in the absence of an alternative carbon source aquatic derived energy would seem to support subterranean terrestrial predators, such as glow-worms, harvestmen, and spiders. Therefore, both aquatic and terrestrial cave invertebrate communities, including the iconic glow-worm populations, were supported by surface originating organic material, intricately linking their health to that of the surface system, leaving cave communities vulnerable to surface land-use changes.