Bacterial mediation in the utilization of carbon and nitrogen from detrital complexes by Crassostrea virginica

Abstract

Unattached, cellulolytic bacteria isolated from a salt marsh were cultured on [LSN]ammonium sulfate and ['Qglucose and fed to the American oyster Crassostrea virginica. Oysters were able to digest and assimilate bacterial C with an assimilation efficiency of 52.5%. We estimate that freeliving bacteria may be capable of supplying up to -9.5% of the total C requirements of oysters in their natural habitat. Cellulolytic bacteria were also cultured on 14C-labeled refractory Spartina alternlyora particles as the sole C source and [rSN]ammonium sulfate as a source of N. These labeled bacteria, together with the S. a/terniforu, were fed to the oysters. The refractory C from these detrital complexes was assimilated by the oysters with an efficiency of 10.3%. It was significantly (P = 0.0007) greater than the assimilation efficiency of 2.7% measured in a previous study for oysters feeding on the refractory S. alterniflora substrate alone. This result provides direct experimental evidence that cellulolytic bacteria in the environment can contribute to the transfer of C from refractory detritus to an ecologically important suspension-feeding macroinvertebrate.We calculated that C. virginica, when fed detrital complexes, assimilated bacterial N with an efhciency of 57.2% but that assimilation of total N present in the detrital complexes was only 3.4%. We speculate that this low assimilation efficiency was due to most (94%) of the N being in the form of condensation products such as humic geopolymers and extracellular polymeric substances secreted by bacteria which could not be digested and absorbed by the oysters. Calculations show that detrital complexes in the natural environment may provide a significant contribution to an oyster's C demand. The magnitude of this contribution can increase from 1.3 to 60% as both absolute bacterial abundance and proportion of bacteria attached to detrital particles increase, raising the oysters' efficiency of filtration for these substrates.The trophic relationship between filterfeeding bivalves and detrital complexes in the seston is poorly understood, although the potential value of the detrital complex as a food source for estuarine organisms is well recognized (Darnell 1967;Frankenberg and Smith 1967). Detrital-based food webs may add stability to ecosystems by making energy fixed seasonally in primary production available to consumers over extended periods (Riley 1963; Heinle and Flemer

Use of dual‐labeled microcapsules to discern the physiological fates of assimilated carbohydrate, protein carbon, and protein nitrogen in suspension‐feeding organisms

“…respiration, incorporation). For example, the energy budget of suspensions-feeders has been assessed by means of 14C-labeled natural diets, such as microalgae (Mathers 1972;Lampert 197 5;Hawkins and Bayne 198 5), bacteria (Crosby et al 1990;Chalermwat et al 199 1;Douillet 1993), and detritus (Newell and Langdon 1986;Kreeger et al 1988;Crosby et al 1989), and the N budget has been summarized with 15N-labeled diets (Hawkins and Bayne 1984;Hawkins 1985).…”

Variability in responses to nutrients and trace elements, and transmission of stressor effects through an estuarine food web

“…The oyster is a key epifaunal species throughout Chesapeake Bay, occurring on and forming hard substrate. It is a suspension-feeder feeding principally on phytoplankton but capable of ingesting other food such as detritus and attached bacteria Crosby et al 1990;Baldwin and Newell 1991;Kennedy et al 1996). Macoma is an infaunal species found in both muddy and sandy environments.…”

Ingestion and assimilation of carbon from cellulolytic bacteria and heterotrophic flagellates by the mussels Geukensia demissa and Mytilus edulis (Bivalvia, Mollusca)

“…Consequently, unattached bacteria meet only about 10% of the C requirements of suspension-feeding bivalves , except perhaps in eutrophic estuaries where bacterial abundances can exceed 1 X 107 ml-' (Crosby et al 1990). However, the gill of the ribbed mussel Ceukensia demissa (Dillwyn), which is a dominant organism in salt marshes of North America (Odum & d e la Cruz 1967, Jordan & Valiela 1982, Bert-(Kreeger et al 1988, it has been postulated that ness 1984), can retain small bacteria-sized particles bacteria and bacterivorous flagellates may make this with a greater efficiency (e.g.…”

“…There is no information available, before and after washing. however, on the di.gestibility of bacterivorous nanoflaBacteria: We used a cellulolytic strain of unidentified gellates by adult bivalves, and hence the nutritional bacteria originally isolated from Canary Creek salt value of such microheterotrophs in the diet of bivalve marsh, lower Delaware Bay, USA (Crosby et al 1990, molluscs is still largely unknown.…”

“…Langdon & Newel1 1990), purified twice on agar plates In this study we examined grazing and utilization of containing only cellulose as the C source, and propamlcroheterotrophs by adults of 2 common species of gated in the laboratory for more than 8 yr on cellulosebivalve mussels-the ribbed mussel Geukensia debased medium as described by Crosby et al (1990). For missa and the blue mussel Mytilus edulis.…”