Showing papers by "Peter A. Jumars published in 1995"

Bioavailable amino acids in sediments: A biomimetic, kinetics-based approach

Abstract: We developed a biomimetic approach, based on direct incubation with proteolytic enzymes, to measure bioavailable amino acids in sediments. The kinetics of release of monomers and oligopeptides, which are amenable to absorption by cells, is measured as either individual or total amino acids. Microbial proteases incubated with fresh sediments yield amino acids at a similar rate as gut juices from a deposit-feeding holothuroid. Amino acid release from fresh sediment was dominated by a slow hydrolysis step from a refractory substrate, which can be described with a first-order rate law. Typical rate constants for release were in the range 0.15-0.52 h-l, consistent with gut residence times of deposit feeders. The bioavailable pool of peptides had a composition resembling that of average biological tissue, but comparisons with tissue composition suggested dietary deficiency of some essential amino acids. The early stages of release exhibited significant contributions from osmolytes (e.g. glutamic acid and taurine), while a larger, more slowly released pool was anomalously low in methionine, suggesting a contribution from microbial coat proteins. Freezing the sediment led to greater yields of amino acids, which reduced the simulation of a deposit feeder’s gut but indicated a larger pool of potentially bioavailable substrate protected by some kind of matrix. This larger pool of peptide substrate was usually dominated by higher molecular weight polypeptides as measured by the Coomassie Blue method.

Influences of turbulence on suspension feeding by planktonic protozoa; experiments in laminar shear fields

Abstract: Laminar shear below the turbulence microscale can create relative motion between protozoan suspension feeders and their prey, potentially influencing encounter and retention. Theory suggests that ingestion rate may rise sigmoidally with increasing turbulence strength, although interference with feeding mechanisms might occur at some turbulence levels. We measured rates of feeding on fluorescently labeled prey at concentrations below feeding saturation in a survey of cultured bacterivorous and herbivorous flagellates, ciliates, and a helioflagellate over a wide range of shear rates produced in rotating Couette flows. Shears of 0.1-10 s-l (corresponding to moderate to extremely strong marine and estuarine turbulence) enhanced clearance rates by the aloricate choanoflagellate, Monosiga sp., up to 2.7 x the mean rate in still water. Shears of l10 s- l enhanced clearance rates by the helioflagellate, Ciliophrys marina, up to 7.0 x the mean in still water. The data are consistent with a sigmoidal response to increasing shear rate. In contrast, clearance rates of the tintinnid, Helicostomella sp., were suppressed at 10 s-l to as low as 0.42 x the still-water rate. Several other flagellates and ciliates (Paraphysomonas sp., two unidentified chrysomonads, Diaphanoeca grandis, Favella sp., and an unidentified heterotrich) showed no significant effects. We hypothesize that the protozoa most susceptible to an influence of turbulence are nonmotile (e.g. Heliozoa, Foraminifera, Radiolaria) or are weak swimmers (e.g. some flagellates and ciliates). Current methods for measuring feeding rates in still-water incubations may underestimate grazing by these taxa under strong turbulence in the field. Through speciesspecific influences on feeding rates, spatial and temporal variations in turbulence may have very selective effects on microbial food-web dynamics.