Influences of benthic boundary‐layer flow on feeding rates of ciliates and flagellates at the sediment‐water interface

Abstract

Heterotrophic protists are integral to sedimentary food webs, but influences on their activities are poorly understood, especially the role of benthic boundary-layer flow. Effects of flow on ingestion rates were measured for bacterivorous protists at the sediment surface in a flume. Results from four common, benthic suspension-feeding ciliates were species specific. Mean clearance rates of the scuticociliates Cohnilembus sp. and Paranophrys magna and the hypotrich Euplotes minuta increased by factors of two to three as friction velocity (u*) increased from 0 to 1.0 cm s Ϫ1. Above u* ϭ 1.0 cm s Ϫ1 , clearance rates of Cohnilembus sp. and P. magna were constant, whereas the clearance rate of E. minuta was reduced by 40% at u* ϭ 1.5 cm s Ϫ1 . E. minuta thus revealed an optimal flow regime for feeding. In contrast, the mean clearance rate of the scuticociliate, Cyclidium sp., was unrelated to u*. In experiments with sediment cores from a subtidal, silty sand site, the mean clearance rate of the bacterivorous ciliate community of the sediment-water interface increased by a factor of five between u* ϭ 0 and 0.9 cm s Ϫ1. The effects of flow were likely due to enhanced advection of prey to the ciliates. In contrast, the clearance rate of the nanoflagellate community in sediment cores was unrelated to u*. Tidal currents at the field site were estimated to increase the ciliate community's daily integrated feeding by a factor of 3.2 compared to still water. Epibenthic ciliates create a dynamic link between planktonic and benthic food webs, mediated strongly by benthic boundary-layer flow.Heterotrophic protists play important roles in marine sedimentary food webs as consumers, facilitators of organicmatter decomposition, and as links to higher trophic levels (Fenchel 1987;Patterson et al. 1989; Epstein 1997a,b). An understanding of the factors that influence feeding rates, growth rates, and trophic interactions of benthic heterotrophic protists, however, is at an early stage of development, especially when compared to knowledge of planktonic protistan ecology (Fenchel 1987;Caron and Finlay 1994). Some of the clearest influences on distributions and activities of 1 Previously Cheryl Ann Butman. Present address: Department of Biology, University of California Los Angeles, Los Angeles, California 90095-1606. AcknowledgmentsWe thank N. Trowbridge, J. Sisson, and M. Gould for help in the field and/or lab; the director of the Rinehart Coastal Research Center (WHOI) for use of facilities; W. McGillis and J. S. Fries for assisting with particle-imaging velocimetry; J. Grant for advice on calibrating the hot film; D. Caron for providing a culture of H. halodurans; and two anonymous reviewers for comments that improved the manuscript.

Calcification acidifies the microenvironment of a benthic foraminifer (Ammonia sp.)

“…The Petri dish was filled with natural seawater of reduced salinity (to about 26) and contained >30 individuals. The friction velocity at the bottom of the Petri dish was adjusted to 0.2 cm s − 1 by measuring particle movement over the bottom and directing an air jet onto the water surface, to emulate natural flow conditions of tidal flat sediment surfaces (Huettel and Gust, 1992;Shimeta et al, 2001). Temperature and pH (total scale) in the bulk seawater were measured using a micro-thermometer and a handheld pH meter (WTW pH 330i), respectively.…”

Resuspension of benthic protists at subtidal coastal sites with differing sediment composition

“…The hypotrichs at Round Hill were dominated by a small Euplotes sp. (likely the E. minuta isolated there by Shimeta et al 2001), whereas at Weepecket they were predominantly larger euplotid species. The fact that diatoms had higher resuspension thresholds at Round Hill may be related to the higher threshold for bulk sediment erosion, because at each site most diatom thresholds (as well as chl a) generally matched the threshold for bulk sediment.…”

“…1 m above the sea bottom during spring tides with the moon in perigee. An abbreviated portion of Weepecket data set was published in a different form in Shimeta & Sisson (1999), and Round Hill friction velocity is from Shimeta et al (2001). Light transmittance was corrected (detrended) for fouling of the instrument over time trends (Fig.…”

“…These cells are known to be integral to microbial food-webs in the water column, and they may be similarly important in benthic food-webs as consumers of microbes, sources of regenerated nutrients, and food for higher trophic levels (Fenchel 1987, Patterson et al 1989, Caron & Finlay 1994, Epstein 1997a. Recent studies have documented resuspension of protozoa in coastal systems and the importance of benthic boundary-layer flow in both their distributions and feeding rates (Wainright 1987, 1990, Shimeta & Sisson 1999, Garstecki et al 2000, Garstecki & Wickham 2001, Shimeta et al 2001. It is unknown whether protozoan resuspension is a widespread phenomenon in coastal systems, or what the roles are of physical-environmental factors (e.g.…”

“…Weepecket Station and nearby locations have been sites for numerous studies of sediment geochemistry, resuspension, and infauna (Sanders 1958, Rhoads 1973, Rhoads et al 1975, Roman 1978, 1980, Roman & Tenore 1978, McNichol et al 1988, 1991, Banta et al 1995. Round Hill Station is near Stn S (Sanders 1958) and Stns 79 and 80 (Moore 1963), and was also the site where sedimentary protozoa were collected for feeding studies by Shimeta et al (2001).…”