In situ measurement of meiobenthic grazing rates on sediment bacteria and edaphic diatoms

Abstract

A radioactive tracer technique was used to measure meiofaunal grazing on bacteria and diatom communities in natural sediments. Radioactive '4C-glucose and 14C-bicarbonate were used to label heterotrophs (bacteria) and autotrophs (diatoms), respectively. The labeled compounds were added to undisturbed sediment cores and incubated for 4 h at in situ temperatures. After incubation, radioactivity was determined for the sediment (microbes) and the major meiofaunal taxa. To quantify meiofaunal grazing on microbes, a 3-compartment model was used where: available label is not limiting, microbial uptake is linear, and meiofaunal uptake is hyperbolic. The formula to calculate meiofaunal grazing rate (k) is: k = 2f/t, where f = fraction of meiofaunal radioactivity (DPM) relative to microbial radioactivity at time t. Although microbial actlvity was greater in summer than winter, there were no differences between meiofaunal grazing rates in winter and summer Total meiofaunal ingestion of microbes was dominated by polychaetes. Preliminary results suggest that, on the average, 3 % of the bacteria and 1 % of the diatom communities were removed per hour Thus turnover times of approximately 30 h for bacteria and 6.5 d for diatoms are apparently sufficient to maintain the microbial community in steady state under the meiofaunal grazing regime. This meiofaunal grazing pressure (60 pg bacterial C and 27 pg diatom C ingested 10 cm-2 h-') probably represents a significant stimulatory effect on the microbial community.

Carbon and nitrogen sources for juvenile blue crabs Callinectes sapidus in coastal wetlands

“…These results are in agreement with bulk-isotope studies which have shown that planktonic and benthic algae are important contributors of carbon for the dominant meiofaunal taxa like nematodes, harpacticoid copepods and ostracods (e.g. Gleason & Zimmerman 1984, Montagna 1984, Riera et al 1996. In contrast, Couch (1989) reported 6I3C values for the meiofauna (-13.9 to -15%0) intermediate between the benthic algae (-12 to -13.5%0) and Spartina alterniflora detritus (-15.9 to -16.7%) and concluded that detrital S. alterniflora may be the main source of C for the meiofaunal populations in the North Inlet Estuary, South Carolina.…”

Benthic communities along a littoral of the Central Adriatic Sea (Italy)

“…These three components are closely linked by numerous types of interactions and a vast literature concerning them exists, but only the relationships between macrofauna and meiofauna or between meiofauna and bacteria are commonly considered. In particular, the predation pressures of macrofauna upon meiofauna and, reciprocally, of meiofauna upon macrofaunal juveniles are well known (Bell and Coull 1980;Gee 1987) and there is also evidence of a regulatory impact of meiofauna upon bacteria (Montagna 1984;Nilson et al 1991). Furthermore, previous findings within the literature do not only suggest nutritional interactions or competition, but also the presence of some synergistic relationships (Tenore and Rice 1980;Reise 1985;Tita et al 2000).…”

Interactions between sediment-feeders and microalgae on coral reefs: grazing losses versus production enhancement

“…In contrast, holothurians and other sediment-feeders feed on material and organisms spanning 3 orders of magnitude (approximately from bacteria <1 µm up to diatoms >1 mm), and thus their function in such a food web is very difficult to grasp. Generally, grazing on a microbial food source in the benthos may increase productivity by preventing bacteria from reaching self-limiting densities (Johannes 1965, Gerlach 1978, Montagna 1984. A similar mechanism was suggested for gastropod grazing on bacteria in temperate (Bianchi & Levington 1981 and coral reef sediments (Hansen & Skilleter 1994), and the feeding activity of detritivores may stimulate bacterial decomposition of detritus (Fenchel 1971, Kristensen et al 1992).…”

“…Montagna 1984, Moriarty et al 1985, Hansen & Skilleter 1994. The effects that grazers have on plant production are composed of negative feedback effects by consumption, and of a variety of potential positive feedback effects.…”