Production, Predation, and Decomposition in a Low-Salinity Hibiscus Marsh

Abstract

The rates of production, leaf grazing, and stem decomposition associated with Hibiscus moscheutos were quantified to contrast the ecology of this brackish herbaceous perennial with fresh and salt marsh species. Average net aerial primary production (NAPP) during 1978 and 1979 was estimated to be slightly over 1200 g°m—2°yr—1, which was calculated by summing: peak standing crop (49%); leaf mortality and litter production (36%); and losses to herbivores (15%). Three species of herbivorous insects were found to be important grazers: Atomacera decepta, Chionodes hibiscella, and Althaeus hibisci. Herbivore consumption was far greater than previously reported in salt marsh systems and rivals that of terrestrial communities. The root: shoot ratio (2.3) is comparable to many fresh marsh species but lower than most high—salinity species. The decomposition rate of Hibiscus stem material was estimated to be on the order of 7—8 yr, or up to five times slower than stems and leaves of other typical brackish marsh species (Typha, Scirpus, and Phragmites). The export potential of detritus from decaying stems is apparently minor because of this slow rate of decomposition combined with the diminished tidal action typical of Hibiscus—dominated marshes. We hypothesize that this unusual marsh dominant differs from Spartina in salt marsh systems by nourishing a more robust grazing food chain and by not exporting significant quantities of detrital material.