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Neira, C, Levin LA, Grosholz ED.  2005.  Benthic macrofaunal communities of three sites in San Francisco Bay invaded by hybrid Spartina, with comparison to uninvaded habitats. Marine Ecology-Progress Series. 292:111-126.   10.3354/meps292111   AbstractWebsite

A hybrid cordgrass, formed from a cross between Spartina alterniflora (Atlantic cordgrass) and S. foliosa (Pacific cordgrass), has recently spread within the intertidal zone of south San Francisco Bay. Sediment properties and macroinfaunal community structure were compared in patches invaded by Spartina hybrid and adjacent uninvaded patches at 3 sites in San Francisco Bay (2 tidal flats and 1 Salicornia marsh). We hypothesized that (1) sediments vegetated by Spartina hybrid would have reduced sediment grain size, higher organic matter content, lower redox potential, lower salinity and reduced microalgal biomass relative to adjacent unvegetated tidal flat sediments, and (2) that differences in the sediment environment would correspond to changes in the infaunal invertebrate community structure and feeding modes. We observed 75 % lower total macro-faunal density and lower species richness in Spartina-vegetated sediments at Elsie Roemer (30 yr old invasion) than in an adjacent unvegetated tidal flat. This was due to lower densities of surface-feeding amphipods, bivalves, cirratulid and spionid polychaetes. The proportional representation of subsurface-deposit feeders was greater in Spartina patches than in unvegetated sediments. At a more recently invaded site (Roberts Landing; 15 yr invasion), Spartina patches differed from tidal flat sediments in composition, but not in abundance. Native (Salicornia) and Spartina patches exhibited similar sediment properties at San Mateo, where the Spartina hybrid invaded 8 to 10 yr earlier. No differences were detected in densities or proportions of surface- or subsurface-deposit feeders, but the proportion of carnivores/omnivores and grazers increased in the hybrid-invaded patches. These studies suggest that the invasive Spartina hybrid in south San Francisco Bay can have differing effects on sediment ecosystems, possibly depending on the location, age, or type of habitats involved.

Levin, LA, Blair NE, Martin CM, Demaster DJ, Plaia G, Thomas CJ.  1999.  Macrofaunal processing of phytodetritus at two sites on the Carolina margin: in situ experiments using (13)C-labeled diatoms. Marine Ecology-Progress Series. 182:37-54.   10.3354/meps182037   AbstractWebsite

Tracer experiments using (13)C-labeled diatoms Thalassiosira pseudonana were carried out at two 850 m sites (I off Cape Fear and III off Cape Hatteras) on the North Carolina, USA, slope to examine patterns of macrofaunal consumption of fresh phytodetritus. Experiments examined the influence of taxon, feeding mode, body size and vertical position within the sediment column on access to surficial organic matter. delta(13)C measurements were made on macrofaunal metazoans and agglutinating protozoans from background sediments and from sediment plots in which (13)C-labeled diatoms were deposited and then sampled 0.3 h, 1 to 1.5 d, 3 mo and 14 mo later. Significant between-site differences were observed in background delta(13)C signatures of sediments, metazoans, and large, agglutinating protozoans, with values 2 to 3 parts per thousand lower at Site III than at Site I. Background delta(13)C signatures also varied as a function of taxon and of vertical position in the sediment column at Site III. The background delta(13)C value of carnivores was higher than that of surface-deposit feeders among Site I annelids, but no annelid feeding-group differences were observed at Site III. delta(13)C data from short-term (1 to 1.5 d) experiments revealed rapid diatom ingestion, primarily by agglutinated protozoans and annelids at Site I and mainly by annelids at Site III. Selective feeding on diatoms was exhibited by paraonid polychaetes, especially Aricidea spp. Exceptionally high uptake and retention of diatom C also was observed in the maldanid Praxillella sp., the nereid Ceratocephale sp. and several other surface-deposit feeding polychaetes. After 14 mo, little of the diatom (13)C remained at Site III, but high concentrations of the tracer were present in annelids and agglutinating protozoans at Site I. At both sites, nonannelid metazoans and subsurface-deposit feeding annelids exhibited the least uptake and retention of diatom C. Our hypotheses that large-bodied taxa and shallow-dwelling infauna should have greatest access to freshly deposited organic matter were not borne out. Some small, deep-dwelling taxa acquired label more readily than large or near-surface forms. Differences in tracer fates between sites reflected greater vertical mixing at Site III. These results indicate heterogeneity in benthic processes along the Carolina margin. but suggest that labile organic matter is consumed quickly at both sites. Because most of the taxa found to consume freshly deposited diatoms in these experiments are typical of bathyal settings, we infer that phytodetritus reaching the seabed in margin environments is rapidly processed by protozoan and metazoan components of the benthic fauna.