Detritus-based Food Webs Research Articles

Production ecology of eelgrass ( Zostera marina L.) in a cape cod salt marsh-estuarine system, Massachusetts

Primary production and biomass loss of Zostera marina L. were estimated at two sites within the Nauset Marsh system, Cape Cod, Massachusetts. Maximum live leaf-blade biomass at the Nauset Harbor (305 g dry weight (DW) m −2) and Town Cove (199 g DW m −2) sites peaked in mid-August. Maximum leaf-blade productivities, estimated by a leaf-marking technique, were 10.8 g DW m −2 day −1 and 5.5 g DW m −2 day −1, respectively. Leaf-blade production occurred throughout winter, but at much reduced rates (<0.2 g DW m −2 day −1, both sites). Net annual aboveground (leaf blades, reproductive shoots, sheaths) primary production was estimated at 987 g DW m −2 year −1 and 444 g DW m −2 year −1, respectively. Peak rates of leaf-blade biomass loss occurred in early September (Nauset Harbor, 8.5 g DW m −2 day −1; Town Cove, 4.7 g DW m −2 day −1), corresponding to a period of high eelgrass-wrack accumulation on New England shorelines. Annual leaf-blade biomass loss was 577 g DW m −2 year −1 and 303 g DW m −2 year −1, respectively. These loss rates, coupled with leaf-crop turnover rates of 6 crops year −1, stress the role of eelgrass meadows in the support of estuarine detritus-based food webs.

Carbon conversion efficiency for bacterial growth on lignocellulose: Implications for detritus-based food webs

Carbon conversion efficiency for bacterial growth on lignocellulose: Implications for detritus-based food webs

Microbial Biomass and Utilization of Dissolved Organic Matter in the Okefenokee Swamp Ecosystem

The Okefenokee Swamp exhibited levels of microbial biomass and aerobic glucose uptake comparable to those of other organically rich, detritus-based aquatic ecosystems. In contrast to other peat-accumulating systems, this acidic (pH 3.7), low-nutrient environment does not show diminished water column or surface sediment microbial biomass or heterotrophic activity. The total particular ATP varied between 0.03 and 6.6 mug liter (mean, 1.6 mug liter) in water and between 1 and 28 mug g (dry weight) (mean, 10.0 mug g [dry weight] in sediments. The turnover times for dissolved d-glucose were 1.26 to 701.25 h (mean, 110.25 h) in aerobic waters and 2.4 to 72 min (mean, 10.2 min) in aerobic surface sediments. Water column bacterial secondary production, measured as the incorporation of [H]thymidine into cold-trichloroacetic acid-insoluble material, ranged from 0.06 to 1.67 nmol liter day (mean, 0.45 nmol liter day). The kinetics of d-glucose uptake by water column microflora are multiphasic and suggest the presence of a diverse microbial population capable of using labile substrates at nanomolar concentrations and at substantial rates. The presence of a large and active aerobic microbial community in the Okefenokee Swamp is indicative of an important role for microbes in swamp geochemistry and strongly suggests the existence of a detritus-based food web.

Dieback of Salt-water Cordgrass (Spartina alterniflora Loisel.) in the Lower Cape Fear Estuary of North Carolina: An Experimental Approach to Re-establishment

Spartina alterniflora is the dominant endemic saltmarsh angiosperm along the East and Gulf coasts of the United States. Dieback of S. alterniflora became evident through aerial surveys of the Lower Cape Fear Estuary of North Carolina. The areas affected varied in size, the largest being greater than 40 ha in areal extent. As S. alterniflora productivity losses can subsequently affect the productivity of the estuarine detritus-based food-web, studies were initiated in 1975 to examine the dieback phenomenon, follow successional trends, and determine the recolonization potential of S. alterniflora in dieback-affected salt-marshes.Three S. alterniflora dieback sites in the Lower Cape Fear Estuary were selected for study. Two of the sites, both above mean high-water, were recolonized by Salicornia europaea, Distichlis spicata, Scirpus robustus, Spartina patens, and S. alterniflora. At a third site, found to be below mean high-water, all volunteer plants were of S. alterniflora. Final stabilization of all three sites was mainly by S. alterniflora, with the living standing-crop biomass ranging from 341 to 1,565 g/m2 in September of 1978.Experimental plots within each of the three dieback sites were sprigged with S. alterniflora plants from three sources: (i) sandy dredge-material, (ii) volunteer plants within affected sites, and (iii) unaffected sites near the dieback areas. The success of these sprigs was strongly site-dependent. It is suggested that the plants used for revegetation of dieback sites should be obtained from areas similar to the site that is being transplanted and/or plants which have large rhizome systems.

Microbial degradation of Rhizophora mangle leaves immersed in the sea

The leaching and degradation of senescent leaves of red mangrove ( Rhizophora mangle) immersed in the water column adjacent to a mangrove stand on Virginia Key, Florida were investigated. During the first 70 days the carbon content decreased from 46·2 to 36·2% while the nitrogen content increased from 0·51 to 0·89%. This represented a decrease in the carbon: nitrogen ratio from 90·6 to 40·7. Readily leachable carbohydrates and tanninlike compounds were lost from the leaf material by the 14th and 28th days, respectively. These leachable organic compounds contribute to the dissolved organic matter in the water. A microbial population slowly built up on the leaf surface after the tannin was lost and the degradation of the structural material was observed using scanning electron microscopy. Changes in the caloric content of the mangrove leaves reflected their microbial degradation. Earlier reports emphasizing the role of micro-organisms in a detritus-based food web in an estuarine mangrove community are confirmed.

The community structure of a tropical marine lagoon

The structure of the benthic community in a nearshore tropical marine lagoon, in the upper Florida Keys, was examined in early spring and mid-summer in 1973 and 1974. Eight environmental parameters (water depth, tidal range, current flow, water temperature, salinity, pH, sediment depth and particle size) were monitored. The biota was compared along an intertidal-subtidal environmental gradient. The amount of vegetation present and the stability of the sediment modified the abundance and diversity of the benthic macrofauna. The results of this study are compared with those from other areas in the tropical Western Atlantic Ocean. The uniqueness of the lagunar environment made it possible to examine the changes in species abundance and diversity as a detritus-based food web graded into a phytoplankton based-food web.

DDT Residues in Benthic Invertebrates and Demersal Fish in St. Margaret’s Bay, Nova Scotia

Organochlorine residues (p,p′-DDT and its metabolites) were measured in samples of benthic invertebrates and demersal fish taken from St. Margaret’s Bay, Nova Scotia. No other organochlorine compounds were present in detectable amounts. ΣDDT levels in whole organisms, excluding lipid-rich tissues, grouped as benthic epifauna, infauna, and demersal fish were not significantly different and thus no accumulation occurs in this food chain. Atmospheric supply is probably the major source of low levels of contamination and a detritus-based food web may equalize residue concentration between various feeding types.