Showing papers by "Peter A. Jumars published in 1993"

Enhanced deposition to pits: a local food source for benthos

Abstract: Particle deposition experiments using mimics of biogenous negative relief (“pits”) and low-excess-density particles in a small annular flume indicate a significantly enhanced deposition rate (number of particles per time) compared to smooth, flat patches of the same diameter. This study included flow visualizations as well as observations of particle residence times, particle concentrations in the pits, and particle fluxes to the pits from the main flow. Experimental conditions of particle concentration, shear velocity, and particle settling velocity mimicked the dynamic characteristics (low excess density and large size) of organic-rich floes and flow conditions in the subtidal and deep sea where biogenous pits are common features. Results suggest that pits provide benthic organisms an important capture mechanism for such floes. Flow visualizations concur qualitatively with previously reported results for twodimensional cavity flow, with unique features due to the conical shape of the pits. When the Rouse number (settling velocity/shear velocity) was much less than 1, pit deposition rate increased with increasing pit aspect ratio (AR = depth/diameter; ranging from 0.25 to 2) and always exceeded deposition to a flat patch of comparable diameter. For the single aspect ratio tested (AR = 0.5) under conditions of increasing turbulence, deposition to the pit increased under transitional flow, but then decreased to near zero when conditions reached fully rough flow. Relative enhancement of deposition to this pit decreased with increased ambient bed roughness since grave1 beds also effectively collect particles. Particle concentration inside pits decreased weakly with pit aspect ratio but greatly increased with increasing roughness Reynolds number. Particle residence time increased somewhat with pit aspect ratio but decreased significantly with increasing roughness Reynolds number. Particle flux into pits from the main flow increased with both increasing aspect ratio and increasing roughness Reynolds number. Enhancement of food supply to pit inhabitants thus depends on the flow regime.

Low-density particles as potential nitrogenous foods for benthos

Abstract: The demonstrated bias of both macrobenthos and fluids to mobilize low-density particles leads to their potential importance as nutritional materials in benthic systems. We fractionated sediments from three coastal regions into low- and high-density separates, and examined both their organic geochemical characteristics and effects on ingestion rates of a deposit feeder. The low-density separates were highly enriched in total organic matter relative to the high-density phases. Enzymatically hydrolyzable protein concentrations in low-density separates were as much as 57-fold higher than the corresponding high-density separates, though some samples from Puget Sound and the Mediterranean Sea showed no enrichment at all. Low-density phases without nutritional enrichments were usually composed of woody debris. In spite of the organic richness of the low-density phase, it makes up no more than a minor fraction of either total sedimentary organic matter or its nutritional component. Addition of anomalously high concentrations of low-density materials to sediments caused a deposit-feeding spionid polychaete to reduce ingestion rates.

Concepts in Biological Oceanography: An Interdisciplinary Primer

Abstract: Introduction 1. Ecological Principles (with marine examples) 2. Central Issues in Biological Oceanography 3. Intersections of biological oceanography with other disciplines

Immunofluorescence assay for effects on field abundance of a naturally occurring pseudomonad during passage through the gut of a marine deposit feeder, Abarenicola pacifica.

Abstract: In a seasonal study we used immunofluorescence to follow a specific bacterial population, as well as total numbers, through the fore-, mid-, and hindgut of a deposit feeder, Abarenicola pacifica. We chose a pseudomonad because of its high ambient abundance. On five dates, we collected A. pacifica gut contents, with concurrent measurements of sedimentary food quality (chlorophyll a, protein, bacterial abundance), animal egestion rates (inversely proportional to gut residence time), and temperature. Increasing bacterial numbers from ingested sediment to foregut contents, and decreases from foregut to midgut indicate significant selection and digestion, respectively, of both the pseudomonad and the total bacterial community. Inverse correlations between egestion rate and digestive removal of bacteria offer some support for the prediction that digestion of bacteria is proportional to time spent exposed to digestive enzymes, although the significance of the associated statistical tests is marginal. No hindgut growth of the pseudomonad was observed, likely due to the short gut residence time of A. pacifica. The pseudomonad showed variation of less than a factor of 3 in its ambient sedimentary abundance over the year.