Importance of detrital algae, bacteria, and organic matter to littoral microcrustacean growth and reproduction

Abstract

Cumulative incorporation of radiolabeled algal (NaH14CO3) and bacterial (14C‐acetate) carbon associated with benthic organic matter (BOM) was measured at timed intervals to determine the relative importance of algal, bacterial, and detrital components of BOM to the growth and reproduction of Eurycercus vernalis (Chydoridae). Five times more algal than bacterial carbon was incorporated, which corresponded to relative amounts of algal and bacterial carbon quantified from the BOM. Algal and bacterial carbon provided 38% and 8% of the carbon required for Eurycercus growth and reproduction, respectively. Approximately 54% of the carbon required for Eurycercus growth was presumably provided by nonlabeled microbes (e.g., fungi, protists) or detritus. Parallel studies were conducted to measure the growth and reproduction for Eurycercus fed diets varying in amounts of algae, bacteria, and detritus. Effects of diet were especially noticeable in early instar growth and reproduction. Individuals fed diets with high algal and bacterial biomass relative to detrital content exhibited higher maximum somatic growth rates (75‐89% d21) than those fed aggregate and particulate detritus (51‐60%). Egg production and net reproductive rate were highest for females fed nutrient‐supplemented algae and corresponded to increased survivorship, early reproduction, and larger clutches. Survivorship was highest for females fed aggregate detritus; however, the percentage of total growth allocated toward egg production was similar for individuals fed aggregate detritus and cultured algae (67‐82%). Relative trophic importance of algae and bacteria as constituents of BOM likely depends on their relative abundance, but the two in combination can be substantially more important than the detritus alone.