High dissolved C : P excretion ratios for large benthic marine invertebrates

Abstract

CO, respiration and P excretion were measured in 13 species of large benthic invertebrates. Wet weight, dry weight, and C, N. P content for each species was determined. CO2 respiration per dry weight and P excretion per dry weight decreased as animal size increased. A closer relation was found between CO, respiration and P excretion than between either CO, respiration or P excretion and dry weight: P = 1.13 cO,'.~~ (P in nmoles gDW-' h-' and CO, in pmoles gDW-' h-'). The mean C : P excretion ratio. 609 : 1, is higher than 0 : P ratios for zooplankton, probably reflecting detritus or macrophyte food sources which have substantially higher C : P ratios than phytoplankton or bacteria. In the surface oceans nutrient excretion by zooplank-ton is a major source of inorganic nutrients for phyto-plankton growth. Consequently the nutrient excretion rates of zooplankton are studied in relation to animal size, food availability, feeding activity, environmental conditions, and respiration (Corner and Davies, 1971). Nutrient excretion rates, usually N or P, and respiration rates, as measured by C production or 0 consumption , are ratioed to one another. Redfield et al. (1963) showed that the net removal of dissolved N and P from the surface oceans matched the average N : P composition of plankton, and the decomposition of these organisms in deep water resulted in the production of N : P in the same ratio. It has been a common working hypothesis that, because zooplankton generally feed on other plankton, zooplankton might metabolize 0 , C, N and P in the Redfield ratio. However, planktonic animals tend to excrete N and P relative to 0 consumption or C production in a range of ratios that usually only approximate the Redfield ratio.