Effects of sediment organics, detrital input, and temperature on demography, production, and body size of a deposit feeder

Abstract

In spring, organic detritus enters temperate marine nearshore habitats during a penod of changing temperature and often shifbng detrital quality. We investigated the lnteractlng roles of sedimentary orgamc matter, detrital quality (Sparbna versus Ulva input), and varymg temperature on the population dynamics and blomass productivity of the common nearshore oligochaete Paranais htoralis. Dunng the phase of population increase, detrital input had the same positive effect on population size, Irrespective of the specific detrltal type or temperature. Later, however, the populations overexploited available resources, and crashes occurred in the order: high temperature-Spartina, low temperature-Spart~na, h ~g h temperature-Ulva, low temperature-Ulva. In contrast, b~omass productivity was negatively affected by temperature. Carbon and nitrogen analyses of the s e d ~m e n t , detritus, and worms were used to calculate the nutnt~onal value of the sedimentary carbon and nitrogen. At 15"C, 0.8% of the nitrogen in the sediment was usable by the worms, while the conversion efficiency on detntus was 20 to 30 %. For carbon, about 0.2 % of the sediment was converted, whereas about 5 % of detrital carbon was converted. These numbers are somewhat lower at 25C. Results suggest that the overwhelming majonty of carbon and nitrogen in the sediment 1s useless for d e p o s ~t feeder nutrition. The large absolute amount, however, stlll may s u b s ~d ~z e considerable deposit feeder production. In effect, a small percentage conversion, mulbphed by a large availabihty, results in a considerable yleld from the sedimentary organic matter. Pulses of detrital addition, however, may be nutritionally more valuable.