The stable isotope compositions (C and N) of plants and animals of a marsh dominated by Spartina alterniflora in the Delaware Estuary were determined. The study focused on the juvenile stage of the Atlantic blue crab, Callinectes sapidus, and the importance of marsh-derived diets in supporting growth during this stage. Laboratory growth experiments and field data indicated that early juvenile blue crabs living in the Delaware Bay habitat fed primarily on zooplankton, while marsh-dwelling crabs, which were enriched in C relative to bay juveniles, utilized marsh-derived carbon for growth. In laboratory experiments, the degree to which juvenile blue crabs isotopically fractionated dietary nitrogen, as well as the growth rate, depended on the protein quality of the diet. The range of δC of amino acids in laboratory-reared crabs and their diets was almost 20‰, similar to the isotopic range of amino acids of other organisms. In laboratory studies, the δC of nonessential and essential amino acids in the diet were compared to those in juvenile crabs. Isotopic fractionation at the molecular level depended on diet quality and the crabs' physiological requirements. Comparison of whole-animal isotope data with individual amino acid C isotope measurements of wild juvenile blue crabs from the bay and marsh suggested a different source of total dietary carbon, yet a shared protein component, such as zooplankton.

We used fluorescence in situ hybridization to examine the spatial and temporal variation in the abundance of major bacterial groups in the Delaware Estuary. The abundance of alpha-and beta-proteobacteria and Actinobacteria varied systematically in the estuary and mirrored the pattern seen in lakes and oceans. Beta-proteobacteria and Actinobacteria were abundant in the Delaware River but were less so in the marine waters of the Delaware Bay. In contrast, alpha-proteobacteria, including the SAR11 clade, were most abundant in the Bay and rare in the Delaware River. Actinobacteria were active in assimilating thymidine and leucine and appeared to contribute substantially to bacterial production in the Delaware River. Among the several biogeochemical parameters we examined, only salinity accounted for a substantial portion of the variation in abundance of these bacterial groups. However, relative abundance of these groups often varied independently of salinity. Cytophaga-like bacteria were often abundant throughout the estuary, but they did not vary systematically over the estuarine gradient, unlike the other dominant bacterial groups. We hypothesize that this estuary-wide high abundance occurs because Cytophaga-like bacteria are very diverse, more so than other groups. Data on 16S rRNA sequences are consistent with this hypothesis. The consistent biogeographic patterns suggest that some bacterial groups, even at a broad phylogenetic level, operate as ecologically meaningful units for examining some processes, whereas the Cytophaga-like bacteria as now defined might be too diverse to be useful for ecological studies.

This study examined the abundance, cell size, and activity of Bacteria and Archaea in the Chukchi Sea and the Canada Basin of the western Arctic Ocean in the spring (May-June) and summer (July-August) of 2002 and 2004. Data from fluorescence in situ hybridization (FISH) analyses indicate that bacterial abundance as a percent of total prokaryotes decreased with depth, whereas in contrast, Crenarchaeota increased from about 10% of prokaryotes in surface waters to as much as 40% in samples from 100 to 200 m. Euryarchaeota were detectable in only a few samples. Relative abundance of Crenarchaeota, expressed as a percent of total prokaryotes, correlated with ammonium concentrations, but relative bacterial abundance did not. Crenarchaeota cells were significantly larger than Bacteria by 1.5-to 2-fold in the upper 200 m. Data collected from a combination of FISH and microautoradiography indicate that often the fraction of both Bacteria and Crenarchaeota assimilating organic compounds was high (up to 55%), and both microbial groups were more active in assimilating amino acids than other compounds. However, Crenarchaeota were usually less active than Bacteria in assimilating amino acids and glucose, but were nearly as active as Bacteria in assimilating protein and diatom extracellular polymers. The fraction of Bacteria and Crenarchaeota assimilating CO 2 in surface waters was higher than expected by anaplerotic fixation alone, suggesting that many of these microbes are chemoautotrophic. These data add to a growing body of evidence indicating how the roles of Archaea and Bacteria differ in biogeochemical cycles of the oceans.The abundances of Archaea and Bacteria vary differently with depth in the oceans examined to date, and these differences provide one of the first clues that the two prokaryotic domains are regulated by different factors in marine environments. Data from fluorescence in situ hybridization (FISH) studies indicate that Archaea make up a larger fraction of total prokaryote abundance in the mesopelagic and bathypelagic zones than in surface waters of the North Pacific Ocean (Karner et al. 2001). In fact, Crenarchaeota are nearly as abundant as Bacteria at about 1,000-m depth in the North Pacific but are near detection limits in surface waters where Bacteria dominate (Karner et al. 2001). There is some evidence of a similar depth distribution for Archaea and Bacteria in the North Atlantic Ocean (Herndl et al. 2005;Teira et al. 2006).Unlike temperate oceans, Archaea may be abundant even in the surface layer of the polar oceans (DeLong et al. 1994). Probing of ribonucleic acid (RNA) blots has suggested that Archaea make up, depending on the season and location, 1-17% of the picoplankton in surface waters around Antarctica (Massana et al. 1998;Murray et al. 1999). FISH studies with polyribonucleotide probes have confirmed the high abundance of Archaea, mainly Crenarchaeota, especially in winter surface waters near the Antarctic Peninsula (Church et al. 2003). Total archaeal abundance also appears to ...