Dried leaves of Thalassia testudinum and Syringodiurn filiforrne released 12.6 % and 19.4 %, respectively, of their organic carbon as dissolved organic carbon (DOC) dunng 3 d of axenic leaching. When inoculated with microbes, the DOC was rapidly converted to bacterial aggregates of a size that could be ingested by macroconsumers. Large populations of ciliates and flagellates also developed, presumably feeding on the unaggregated bacteria. In treatments containing the residual macroparticulate organic carbon (MPOC), 75-95 % of the bacteria present were attached to the leaves, and suspended aggregates were not observed. The protozoan community was dominated by freeswimming flagellates that grazed on the suspended bacteria and were thus responsible for the absence of those forms. Total microbial populations in the DOC treatments were 10-12 times greater per unit of seagrass carbon originally added than in the MPOC containing flasks. These results show that seagrass DOC may rapidly be made available to higher consumers through processes that produce suitable sized food particles-viz., growth of protozoans on bacteria and formation of bacterial aggregates.

Microbial (bacterial and fungal) biomass associated with decaying Thalassia testudnum, Syringodium fdiforme, Halodule wnghtii, and Rhizophora mangle, incubated in litter bags in Florida Bay, was estimated from direct microscopic determinations of microbial abundance and cell volume. Bacterial biomass predominated throughout decomposition, with fungi usually constituting 0 to 20 % of the total microbial biomass. Total microbial biomass was never greater than 1.2 % of detrital mass, and in most cases was substantially less than 1.0 %. Based on these results, it is unlikely that detritivores that feed by ingestion of detrital particles can rely solely on microorganisms as an energy source.

Microbial O2 consumption and bacterial growth associated with decaylng Zostera marina increased rapidly in the first 24 h of incubation at the sediment surface. Dunng this period, the detrital complex lost 20 O/o of its initial dry weight. An additional 20 % of the original dry weight was lost in the next 13 d , and 73 % was lost over the entire 6 wk incubation period; changes in the rate of weight loss were consistent w t h changes in the patterns of bacterial activity While the initial response of the detritus-associated bacteria was rapid and substantial, less than 7.5 % of the detrital carbon lost during the first 48 h of incubation was metabolized (assimilated plus respired), although 52 6 "/o was metabolized during the 28 d to 42 d period. Of the plant carbon metabolized, over 80 O/O was m~neralized to CO?. The results suggest that if bacterial transformation of plant litter is an important link in the transfer of primary production to aquatic food webs, water column bacteria function as a link and not the bactena associated with detrital part~cles.

ABSTRACT. Bacterial biornass, abundance, and product~vity were greater in 3 tidal marsh creeks on the Chesapeake Bay side of the lower Delmarva Peninsula than in nearby creeks of the seaside coastal lagoon complex (biomass: 462 and 71 n g C ml-'; abundance: 12 X 10' and 3.8 X 106 cells ml-l; productivity: 46 and 7.3 ng C rnl-' h-'; bayside and seaside respectively). Bacterial cell-size distributions were also significantly different between the seaside and bayside creeks, with a larger proportion of smaller cells dominating samples from the seaside creeks. Bayside and seaside concentrat~ons of total suspended solids (TSS) and dissolved organic carbon (DOC) were similar (approximately 49 m g 1.' TSS and 3.5 mg I-' DOC) The amount of organic matter (OM) and chlorophyll a was higher in the bayside creeks, while inorganic N and P concentrations were higher in the seaside creeks (OM. 9 0 a n d 3.4 mg 1 -l ; chlorophyll a. 6 0 and 4.1 g 1.'; PO," 0.2 and 1.2 FM; NH,' 0.6 and 1.2 ubI; bayside and seaside respectively). The high inorganic nutrient pools combined with the low levels of bacterial productivity suggest that bacterial production is not l~nlited by N or P in the seaside creeks and that the amount of carbon moving through the bacterial loop is much less than on the bayside. In fact, DOC turnover times were much longer for the seaside (22 d ) than for the bayside (6 d ) . Reasons for the observed differences in bacterial dynamics for the bay and seasides are not known specifically, but may be related to differences in the source of the DOC (marsh grass vs phytoplankton), grazlng on the bacterial cells, or bacterial community structure

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