Fecal coils of Mesochaetopterus taylori exhibiting two distinct sections, differing in color and composition (reprinted from Busby and Plante 2007 with permission). 

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... with overlapping distributions. Surprisingly few studies have directly compared microbial community structure of suspended particles to the underlying seabed, although Shimeta et al. (2002) demonstrated contrasts in microeukaryotic community structure due to dif- ferences in resuspension susceptibility among benthic diatoms and other protists. Suspended particulate matter in coastal salt marshes is composed of a variety of par- ticles originating from a multitude of sources. e contribution of resuspended sedi- ment is highly variable, both spatially and temporally (Huang et al. 2003), but was a likely contributor in our samples given the overlap in microbial populations. Further, grain size analysis of these nepheloid samples reveal that > 15% of the mass of these samples were of grain size diam > 63 μm and appreciable fractions (> 6%) over 180 μm, despite a median grain size of ~50 μm (Busby and Plante 2007). Determination of the provenance of ingested material by examining the contents of the egesta of detritivorous animals is complicated by selective feeding, digestion, and, potentially, growth of ingested microbes. Numerous studies have shown that heterotrophic bacteria can be stimulated and increase in numbers during or imme- diately following gut transit (Plante et al. 1989, Lucas et al. 2003), likely due to readily accessible digestive products and/or mixing within the gut (Dade et al. 1990, Plante et al. 1990). Microalgae may also be stimulated in this way (Porter 1976), although mechanisms for elevated provision of limiting factors (inorganic nutrients, light) are less apparent. Despite these caveats, qualitative and quantitative characteristics of the associated microbiota suggest that the brown portion of M. taylori fecal coils is derived from the nepheloid layer and surficial deposits. Microalgal biomass in brown coils was higher than that found in deep sediments, but lower than concentrations in surface sediments or the nepheloid layer. is suggests that seston, surficial sediments, or both were consumed by M. taylori during immersion and that chlorophyll was lost during gut transit. Grain size analysis and field behavioral observations corrobo- rate these findings (Busby and Plante 2007). However, diatoms in brown fecal coils were qualitatively distinct from both nepheloid and surface sediment diatoms ac- cording to ANOSIM, indicating that relative compositions of various diatom spe- cies were altered with gut passage. Prior studies have likewise demonstrated loss of BMA biomass and compositional changes with passage through the guts of marine detritivores (Smith et al. 1996, Sommer 2000). at bacterial abundances were high- est in the brown portions of egesta suggests that selective feeding and/or bacterial growth occurred as well. DGGE banding patterns suggest a strong input of bacteria into egesta from the gut itself, likely representing rapid growth of select populations within the gut. Alternatively, these bands could represent inoculation from true gut symbionts; however, it is di ffi cult to imagine that such a high level of loss to the ex- ternal environment could be sustained. Diatom DGGE banding patterns suggest that gray fecal materials are derived from a diversity of sources, with the diatom assemblage in gray coils indistinguishable from either surface or deep sediments, but seemingly more similar to deeper sedi- ment. Both total bacterial numbers and BMA biomass also suggest that surface sedi- ments contribute because deep sediments are lower than gray coils on both counts. Grain size analysis also suggests that both surface and deeper sediments are con- sumed because median grain size is intermediate between subsurface and shallow sediments, and 4.8% silt/clay in gray coils is also intermediate between deep (2.8%) and surface (17.2%) sediments, but clearly closer to that of deep samples (Busby and Plante 2007). Observation of palp feeding at low tide suggests surficial sediments as the primary food source linked to gray coils, and would seem to preclude suspended seston as a contributor; however, the gray color of these coils reinforces the idea that deeper sediments make the greater contribution to the diet when M. taylori is deposit feeding. Although most chaetopterids can reverse position in their tubes (Barnes 1965), feeding at the tube bottom has not been recorded for M. taylori to our knowledge. More likely, the worm uses its palps to deposit-feed while in normal body orientation, but probes to depths below the surficial layer of fine, lighter-colored sed- iments. Unfortunately, our subsurface samples taken from ~5 cm depth do not allow us to distinguish between these possibilities. Besides the obvious color distinction between the egesta associated with deposit- and suspension-feeding in M. taylori , that portion of the egesta associated with sus- pension feeding also di ff ers structurally in that the “coil” consists of small, elongated pellets within a mucus string (Fig. 1). is observation raises the question of why M. taylori pelletizes egesta when suspension-feeding, but not while deposit-feeding. Some suspension feeders are thought to pelletize fecal wastes to more readily clear their foraging area of previously processed ingesta (e.g., using a mucous sling in Am- phicteis scaphobranchiata Moore, 1906; Nowell et al. 1984). Because large mucus- bound pellets were commonly observed at the tube end of M. taylori , this does not appear to be an e ffi cient means to void egesta in this species. Besides coloration, the most obvious di ff erence in the coil types is grain size distribution, with median grain size slightly smaller, but both spread in grain size (quartile deviation 0.43 vs 0.25 for gray egesta) and % silt/clay much greater in brown egesta (Busby and Plante 2007). Grain size and sorting both influence permeability, such that the brown egesta should be substantially less permeable than the gray (Shepherd 1989, Fetter 2001). us, in this case, pelletization may be a means to overcome limitations on di ff usion of enzymes and digestive products in the gut (Penry and Jumars 1990, Jumars 2000). Spatial distributions of benthic invertebrates often have been explained according to the paradigm that the suspension-feeding guild dominates where water velocity and the flux of suspended matter is relatively high, whereas deposit feeders should be more abundant where flow is reduced and organic particulates are deposited on the seabed (Jumars and Nowell 1984, Snelgrove and Butman 1994). Ample evidence for plasticity in feeding behavior has lead to predictions that switching between feed- ing modes should occur in hydrodynamically variable benthic habitats (Taghon et al. 1980, Turner and Miller 1991), for instance, when flow is oscillatory or when the average rate of flow varies significantly through time. is capacity to both suspen- sion- and deposit-feed noted here in M. taylori is not novel, having previously been described in at least one species, S. oculatus , of the same polychaete family (Chae- topteridae), and is even more familiar among spionid polychaetes, tellinid bivalves, and various crustaceans. is behavior in M. taylori is unusual in that the switch is not due to change in water velocity, but rather to fluctuations in tidal height (i.e., emersion), although this has been recorded in at least one prior study [in Macoma balthica (Linnaeus, 1758) , Brafield and Newell 1961]. In addition, switching in some facultative feeders may not represent a fundamental switch in diet, i.e., the same materials are thought to be ingested, simply suspended or deposited depending on flow (e.g., Taghon et al. 1980, Kamermans 1994). In contrast, in M. taylori , finer par- ticulates are ingested during tidal immersion, with concomitant di ff erences in mi- crobiota and granulometric characteristics. e capacity of M. taylori to continue feeding after emersion, employing an al- ternative mechanism of food acquisition, is an adaptation to intertidal life. Because most suspension feeders cease feeding during aerial exposure (Newell 1972), this ability likely confers competitive advantages in this habitat. Perhaps more impor- tantly, the disparate dietary components (with respect to both provenance and com- position) of M. taylori should supply a broad range of essential nutrients, and thus remedy the nutritional deficiencies of specific detrital components (Phillips 1984, Marsh and Tenore 1990). For instance, fatty acids, sugars, amino acids, and other dietary components di ff er among di ff erent bacterial types (Dobbs and Guckert 1988, Bobbie and White 1980) and among di ff erent species of microalgae (Chuecas and Riley 1969, Nichols et al. 1993). More directly, fatty acids in near-bottom seston dif- fer compositionally from that of sediments (Budge and Parrish 1998), and sugars likewise di ff er (Bergamaschi et al. 1999). Deposit feeding has been shown in prior studies to alter sedimentary microbial communities, through translocation of sediments (Plante and Wilde 2004), digestive removal (Dobbs and Guckert 1988, Plante and Wilde 2004), and stimulation (Plante et al. 1989, Grossi et al. 2006). It has not yet been established if the quantitative or qualitative e ff ects of various deposit-feeding species are unique or are generally similar among diverse taxa, although the few studies of this nature point to species- specific imprints (Plante and Shriver 1998, Plante and Wilde 2004). e compositional impacts on the microbiota of bulk sediment by M. taylori are likely distinctive and particularly great, in that it both translocates deeper sediments to the surface during deposit feeding and deposits fine, suspended materials ingested while filter feeding. A ...