Development of habitat suitability criteria for macroinvertebrate community metrics for use in habitat restoration projects

Community-based macroinvertebrate habitat suitability criteria are needed for two reasons: (1) community-based criteria, such as with macroinvertebrates, are a better measure of ecosystem health than single-species habitat suitability criteria (HSC); and (2) if food rather than physical habitat is the limiting factor for juvenile salmonids, it is better to evaluate habitat restoration projects based on macroinvertebrate habitat than juvenile habitat. The goal of this study was to generate habitat suitability criteria for macroinvertebrates in the Sacramento River. Habitat suitability criteria were derived for three macroinvertebrate community metrics. One of the metrics (biomass of baetids, chironomids and hydropsychids) was selected to represent food supply for juvenile salmonids, while the other two metrics (total biomass and diversity) were selected as measures of ecosystem health. Baetidae, Chironomidae and Hydropsychidae were chosen because they are the dominant taxa present in stomach contents samples of Sacramento River juvenile Chinook Salmon Oncorhynchus tschawytscha. Habitat suitability criteria were developed using data from 75 macroinvertebrate samples stratified by season, mesohabitat type, depth, velocity, and substrate. The criteria for depth, velocity and substrate were developed taking into account several potential confounding variables, and using a polynomial regression for depth and velocity, and analysis of variance for substrate (a categorical variable). The criteria showed no effect of substrate on baetid/chironomid/hydropsychid biomass or diversity. Criteria for total biomass showed a higher suitability for larger cobbles, versus other substrates, for total biomass. The optimum depths for baetid/chironomid/hydropsychid biomass, total biomass and diversity were, respectively, 0.82–0.85 m, 0.61–0.67 m and 1.16–1.19 m. The optimum velocities for baetid/chironomid/hydropsychid biomass, total biomass and diversity were, respectively, 0.73–0.79 m/sec, 0.61–0.67 m/sec, and 0.61–0.73 m/s. Suggestions for development of future macroinvertebrate HSC include: (1) stratifying sampling by depth, velocity and substrate; (2) measuring the amount of organic matter in samples for use as an additional potential confounding factor; and (3) sampling a large area (0.84 m2) with a sampler with a rubber foam lining on the bottom of the sampler.