Macroinvertebrate inventory of the Caspar Creek watershed

A macroinvertebrate assessment was conducted on the Caspar Creek Experimental Watershed in northwestern California using a functional feeding group (FFG) classification. The approach, developed over 30 years ago (Cummins 1973), has been tested, modified, and employed in many studies (e.g. Cummins and Klug 1979, Cummins and Wilzbach 1985), Merritt and Cummins 2006). The approach categorizes macroinvertebrates based on their morphological and behavioral mechanisms by which they acquire one or more of six general food types: coarse particulate organic matter (CPOM), fine particulate organic matter (FPOM), periphytic, non-filamentous algae and associated bio-film, invertebrate prey organisms, and filamentous algae (Table 1). The morpho-behavioral adaptations of stream macroinvertebrates for acquiring food are easily observed in the field on live specimens. An example is the large eyes, bright color patterns, and active movement that characterize the three predaceous stonefly families (setipalpian Plecoptera). The abundance (especially expressed as biomass) of any FFG is an indicator of the relative availability of its food resource category. The method has the advantage that the survey crew leaves the field with the data as well as with preserved samples that can be analyzed in taxonomic data, and measured for biomass conversion calculations in the lab, if (and this is almost always the problem) funds are available for the very time-consuming process of microscope analysis. The point is, that a great deal of information about the status of a stream ecosystem can be obtained in the field using the FFG approach, but it does not for close the ability to analyze the samples in the lab.

The field numbers can be converted to biomass using length-mass regressions, or to calculate any of the commonly used indices of stream condition (e.g. % Ephemeroptera, Plecoptera, and Trichoptera in a sample). Ecological tables in Merritt et al. (2008) provide information of the functional feeding group categorization of essentially every genus of North American aquatic insect. Information in Pennak (1989) can be used to assign non-insect invertebrates to functional groups.