Quality Of Detritus Research Articles

Paradoxical selective feeding on a low-nutrient diet: why do mangrove crabs eat leaves?

Sesarmid crabs dominate Indo West-Pacific mangroves, and consume large amounts of mangrove litter. This is surprising, since mangrove leaves have high tannin contents and C/N ratios that far exceed 17, normally taken as the maximum for sustainable animal nutrition. This paradox has led to the hitherto untested hypothesis that crabs let leaves age in burrows before consumption, thereby reducing tannin content and C/N ratio. We excavated burrows of Neosarmatium meinerti within high-shore Avicennia marina mangroves, and investigated whether burrow leaves had C, N or C/N values significantly different from those of senescent leaves. Leaves were found in <45% of burrows, mostly only as small fragments, and N concentrations and C/N ratios of burrow leaves never varied significantly from senescent leaves. The leaf-ageing hypothesis was therefore not supported. In the field N. meinerti and Sesarma guttatum fed on sediment in 76% and 66-69% of observations, respectively, and on leaves in <10% of observations. Sediments from two A. marina mangroves had a mean C/N ratio of 19.6. Our results, and the literature, show that mangrove leaves are unlikely to fulfil the N requirements of crabs, whether or not leaf ageing takes place. Sediment detritus could be a richer source of N, as shown by lower C/N ratios and regular ingestion by crabs. By fragmenting leaves crabs may be elevating the nutritional quality of the substrate detritus.

Multiscale habitat associations of detrivorous blennies (Blenniidae: Salariini)

The distribution and habitat associations of detrivorous blennies on a tropical coral reef were investigated at several spatial scales and compared with other fish that feed on the epilithic algal matrix to assess density and biomass contributions of small detrivorous fishes to these assemblages. At broad spatial scales total blenny abundance and biomass were highest on the tops of reefs exposed to prevailing winds. On the finer scale of microhabitat use, all species showed a preference for non-living corals, although the type of coral utilised differed between species. The high abundance of blennies on reef tops and non-living corals may be partially related to the quality and availability of detritus in these habitats. Comparisons of total blenny abundance and biomass with other territorial detrivores found that blennies accounted for approximately 60% of this functional group's density and 21% of their biomass on exposed reef tops. Overall, territorial detrivores were found to constitute approximately 37% of the density and 26% of the biomass of the detrivorous/herbivorous fish assemblage on exposed reef tops. Small detrivorous fish therefore represent a substantial proportion of fish assemblages that feed on epilithic algae and associated detritus on coral reefs.

Feeding Ecology of Three Omnivorous Fishes in Lake Texoma (Oklahoma-Texas)

Feeding Ecology of Three Omnivorous Fishes in Lake Texoma (Oklahoma-Texas)

Compensatory Restoration of Mangrove Habitat Following the Tampa Bay Oil Spill

ABSTRACT In 1993, an incident involving three vessels near the entrance to Tampa Bay, near St. Petersburg, Florida, resulted in a discharge approximately 300,000 gallons of No. 6. fuel oil into the waters off Egmont Key. The oil contacted the shores from Egmont Key to locations approximately 14 miles to the north. Oil also entered Boca Ciega Bay through John's Pass and impacted four small islands that supported mature overwash mangrove forest. A cooperative damage assessment process was developed between the Responsible Parties (RPs) and the trustees for the natural resources: the state of Florida, the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Fish and Wildlife Service (USFWS). Through the cooperative process, several alternatives for primary and compensatory restoration were developed. In considering alternatives to compensate for impacts to epibenthic communities, fish and bird habitats, wetlands, and mangrove communities, the trustees and the RPs considered purchase of shoreline habitat and restoration of mangrove forest at several sites. The RP developed a proposal to purchase and deed into public ownership in perpetuity, a 10.67-acre parcel of land on the west bank of Cross Bayou in Boca Ciega Bay that had been used as a disposal site for dredge spoil in the past. This site consisted of approximately 5.0 acres of uplands, 4.4 acres of mangrove forest, and 1.4 acres of nonmangrove intertidal and subtidal habitat. The objective of the project was to establish a typical Tampa Bay mangrove forest and a roadside buffer free of exotic plant species. The secondary goals were to establish a typical Tampa Bay salt marsh dominated by smooth cordgrass (Spartina spp.) as a successional precursor to mangrove recruitment by seeds and seedlings. Tidal exchange through the site was reestablished to improve water quality and increase export of mangrove detritus and import of high-quality tidal waters. The project was designed and constructed by the RPs with the approval and supervision of the trustees. The project was completed and title transferred to Pinellas County, Florida in summer 1999. A monitoring program was developed and performance criteria established by trustee representatives and the RPs. The monitoring program currently is being conducted and has met performance criteria to date. This project demonstrates the positive result of trustees and the RPs working together to provide compensation to the environment.

Seasonal dynamics of macroinvertebrate assemblages in the benthos and associated with detritus packs in two low-order streams with different riparian vegetation

Summary 1 The seasonal dynamics of the benthic macroinvertebrate assemblage, and the subset of this assemblage colonising naturally formed detritus accumulations, was investigated in two streams in south-west Ireland, one draining a conifer plantation (Streamhill West) and the other with deciduous riparian vegetation (Glenfinish). The streams differed in the quantity, quality and diversity of allochthonous detritus and in hydrochemistry, the conifer stream being more acid at high discharge. We expected the macroinvertebrate assemblage colonising detritus to differ in the two streams, due to differences in the diversity and quantity of detrital inputs. 2 Benthic density and taxon richness did not differ between the two streams, but the density of shredders was greater in the conifer stream, where there was a greater mass of benthic detritus. There was a significant positive correlation between shredder density and detritus biomass in both streams over the study period. 3 Detritus packs in the deciduous stream were colonised by a greater number of macroinvertebrates and taxa than in the conifer stream, but packs in both streams had a similar abundance of shredders. The relative abundance of taxa colonising detritus packs was almost always significantly different to that found in the source pool of the benthos. 4 Correspondence analysis illustrated that there were distinct faunal differences between the two streams overall and seasonally within each stream. Differences between the streams were related to species tolerances to acid episodes in the conifer stream. Canonical correspondence analysis demonstrated a distinct seasonal pattern in the detrital composition of the packs and a corresponding seasonal pattern in the structure of the detritus pack macroinvertebrate assemblage. 5 Within-stream seasonal variation both in benthic and detritus pack assemblages and in detrital inputs was of similar magnitude to the between-stream variation. The conifer stream received less and poorer quality detritus than the deciduous stream, yet it retained more detritus and had more shredders in the benthos. This apparent contradiction may be explained by the influence of hydrochemistry (during spate events) on the shredder assemblage, by differences in riparian vegetation between the two streams, and possibly by the ability of some taxa to exhibit more generalist feeding habits and thus supplement their diets in the absence of high quality detritus.

Effects of leaf litter species on macroinvertebrate community properties and mosquito yield in Neotropical tree hole microcosms.

Detritus quality and quantity affect macroinvertebrate productivity and distribution in many freshwater ecosystems. This study experimentally investigated the effects of leaf litter from Ceiba pentandra, Dipteryx panamensis, Ficus yoponensis, and Platypodium elegans on macroinvertebrate species composition, richness, and abundance in artificial water-filled tree holes in a lowland moist forest of Panama. Species composition was similar among treatments, but species richness and longevity differed among litter types and were consistently highest with Platypodium litter. Similar patterns were observed in natural tree holes of the focal tree species. The mosquito Culex mollis was the most abundant species in the field experiment. Average conductivity and dissolved oxygen concentration differed among leaf species, but pH did not. Leaf toughness was positively correlated with mean macroinvertebrate abundance and cumulative species richness. A laboratory experiment measured C. mollis yield and pupation time in tree hole microcosms containing the four litter species. Cumulative mosquito mass and time to pupation differed among leaf litter species, with Platypodium litter supporting the greatest yield. Pupation was slowest on Ceiba litter. Grazing by mosquito larvae facilitated leaf decomposition in all treatments. Results suggest that differences in macroinvertebrate species richness and mosquito yield can be attributed to differences in nutritional quality among litter species.

Global change, soil biodiversity, and nitrogen cycling in terrestrial ecosystems: three case studies

AbstractThe relative contribution of different soil organism groups to nutrient cycling has been quantified for a number of ecosystems. Some functions, particularly within the N‐cycle, are carried out by very specific organisms. Others, including those of decomposition and nutrient release from organic inputs are, however, mediated by a diverse group of bacteria, protozoa, fungi and invertebrate animals. Many authors have hypothesized that there is a high degree of equivalence and flexibility in function within this decomposer community and thence a substantial extent of redundancy in species richness and resilience in functional capacity. Three case studies are presented to examine the relationship between soil biodiversity and nitrogen cycling under global change in ecosystem types from three latitudes, i.e. tundra, temperate grassland and tropical rainforest.In all three ecosystems evidence exists for the potential impact of global change factors (temperature change, CO2 enrichment, land‐use‐change) on the composition and diversity of the soil community as well as on various aspects of the nitrogen and other cycles. There is, however, very little unequivocal evidence of direct causal linkage between species richness and nutrient cycling efficiency. Most of the changes detected are shifts in the influence of major functional groups of the soil biota (e.g. between microflora and fauna in decomposition). There seem to be few data, however, from which to judge the significance of changes in diversity within functional groups. Nonetheless the soil biota are hypothesized to be a sensitive link between plant detritus and the availability of nutrients to plant uptake. Any factors affecting the quantity or quality of plant detritus is likely to change this link. Rigorous experimentation on the relationships between soil species richness and the regulation or resilience of nutrient cycles under global change thus remains a high priority.

MUSMOD ©, a production model for bottom culture of the blue mussel, Mytilus edulis L.

A mussel production model, MUSMOD © was developed to seed bottom culture lease sites in Maine to their carrying capacity. The process of model development is demonstrated with three models: (a) an initial conceptual model, (b) an aggregated model driven by the tidal exchange of food particles and (c) MUSMOD ©, the final model driven by food supplied in the tidal flow of water across a site. The final model predicts mussel production using the concentrations of phytoplankton and detritus in the surface water, detritus quality, tidal current speed, water depth and temperature. Field measurements of several quantities (e.g., clearance, respiration, growth rates for shell and meat, food concentration gradient, and temporal feeding pattern, (Newell et al., 1997, Development of the mussel aquaculture lease site model, MUSMOD ©: a field program to calibrate model formulations, J. Exp. Mar. Biol. Ecol., this volume) were obtained to evaluate and calibrate the final model. Model refinement using iterations of modeling and field work demonstrated the importance of food quantity and quality in explaining the observed patterns of mussel growth. Food quantity explained the first-order growth pattern, but it was necessary to account for the quality of the food to explain the second-order details of growth. Vertical mixing supplied the majority of new food particles, however, particles settling over the mussel bed during slack water accounted for 33% of the phytoplankton and 45% of the detritus entering the feeding layer from above. A sensitivity analysis of the effects of seed density on mussel growth using MUSMOD © identified the optimum carrying capacity for three Maine lease sites. Seeding mussels during the optimum time period (May to early July) resulted in the harvest of marketable mussels from 40 mm seed in 8 months for a high food year and in 13 months when the food supply was low. Characterizing the food supply using particulate organic matter, POM, alone was not sufficient to explain mussel growth in the detail necessary to answer many farm management questions.

Development of the mussel aquaculture lease site model MUSMOD ©: a field program to calibrate model formulations

Field observations were used along with mathematical modelling to develop model formulations to represent mussel ( Mytilus edulis) growth at several shallow subtidal study sites along the Maine coast, USA. In order to match predicted growth from the model MUSMOD © (D.E. Campbell, C.R. Newell, 1997. MUSMOD ©: A mussel production model for use on bottom culture lease sites. J. Exp. Mar. Biol. Ecol., in press.) with observed growth rates in the field, modifications were made in the model with respect to: (a) factors affecting the supply of food to the mussel feeding zone (vertical mixing, settling, resuspension and particle depletion); (b) short-term variability in mussel feeding and respiration over a tidal cycle; (c) the effects of seasonal variations in food quality on assimilation, scope for growth, and observed growth. Surface and bottom water samples taken from 1989 to 1991 revealed daily fluctuations in SPM, POM, chlorophyll a, particulate carbon and nitrogen, and phytoplankton carbon which were similar to annual ranges. Maine waters are typified by a spring diatom bloom, followed by a rise in detritus in early summer. Successful representation of mussel growth was obtained when food concentration was expressed as phytoplankton and detrital carbon, and assimilation was modelled as a function of food type (phytoplankton or detritus), and detritus quality (as percent of maximum annual N/C ratio of the detritus). By expressing particle depletion as a percent reduction from conditions at the edge of the lease site, scope for growth was modelled over an annual period. Observations with a time-lapse benthic video monitor (TLBVM) and flow-through physiological chambers demonstrated tidal variations in filtration rate, respiration rate and shell gape in subtidal mussels, with periods of valve closure correlated with low particle concentrations. These observations support the hypothesis that mussel energy gain is maximized during fluctuating food availability by the control of pumping rate via the shell gape response. This may explain why field observations of filtration rate are sometimes lower than maximum published values, and allows the mussels to maintain a slightly positive scope for growth by reducing respiratory losses when food particles are limiting. The settling flux of phytoplankton and detritus, while poorly characterized in coastal New England waters, provides over 30% of the estimated food supply to subtidal mussel cultures and may explain, in part, the patterns of shell gape observed in this study.

Variability of Dissolved Organic Carbon in Sediments of a Seagrass Bed and an Unvegetated Area within an Estuary in Southern Texas

Pore-water dissolved organic carbon (PWDOC) concentrations were examined in vegetated and bare sediments of aHalodule wrightii seagrass bed, and in a mud bottom sediment of a southern Texas estuary. Temporal variability was examined at diel (dawn and noon) and bimonthly time scales. Distribution patterns of PWDOC were compared with physical, chemical, and biological factors thought to exert control on PWDOC. Concentration of PWDOC, bacterial production, and resultant PWDOC turnover times displayed statistically significant spatial and temporal variability. Concentration of PWDOC ranged from 14 mg C 1−1 to 107 mg C 1−1 of pore water, or 9–71 μg C cm−3 wet sediment. PWDOC was more variable and was approximately 5 times higher than DOC concentrations in the water column. Low PWDOC concentrations (mean = 14.6 μg C cm−3) and high bacterial production rates (mean = 1.92 μg C cm−3 h−1) were observed at the mud station, whereas PWDOC concentrations were high (mean = 24.6 μg C cm−3) and bacterial production rates were low (mean = 0.43 μg C cm−3 h−1) at the bare station. PWDOC turnover times (Tt), assuming 50% bacterial growth efficiency (1–840 h) were shortest at the mud station (mean=13 h) and longest at the bare station (mean=180 h). In the overlying water column, Tt values were longer, ranging from 1,000–10,000 h. PWDOC concentrations were 25% higher in vegetated sediments than in neighboring bare sediments. This difference was probably due to inputs of labile photosynthetic excretia, since bacterial production rates in vegetated sediments displayed significant diel variability and were 4 times greater than that of bare sediments. Based upon the entire data set, PWDOC was significantly related to macrofaunal biomass, sediment POC, sediment C:N ratios, and oxygen metabolism, but was significantly correlated only to the latter two variables in stepwise multiple regression. Our findings suggest that organism activities and detrital quality are the major determinants controlling variability in PWDOC.

Benthic infauna and organism-sediment relations in a shallow, tropical coastal area: influence of outwelled mangrove detritus and physical disturbance

Sediment infauna and sedimentary structures within the shallow ( S 15 m depth) inshore of the central Great Barrier Reef lagoon were examined seasonally for 1 yr to relate benthic fauna1 abundance, community composition and biogenic activity to outwelling of mangrove detritus and natural physical disturbance. Standing amounts of mangrove litter exceeded 4000 g dry weight (DW) m'2 in a semi-enclosed area and declined to 3.5 g DW m-' at the inshore-middle shelf boundary. Macroinfaunal densities (mean = 1452; range = 308 to 3950 ind.m-2) and biomass (ash-free dry weight = 0.17 to 6.31 g m-2) varied greatly among sites and seasons, with densities correlating negatively with detritus standing stocks; biomass did not relate to outwelling. Total meiofaunal densities (mean = 715; range = 295 to 1568 ind.10cm-*) varied significantly among sites and seasons, but only turbellarians correlated positively to standing amounts of mangrove litter. Classification and ordination of nematode communities separated stations mainly on the basis of detntal loading. Species diversity (H') and evenness (J') correlated negatively with detritus standing stocks and extractable tannins derived from the litter. X-radiographs of sediment cores revealed sedimentary facies characterized by low to moderate rates of sedimentation, large patches of buried litter and bioturbation mainly in the upper 5 to 6 cm at the muddiest sites. X-radiographs also showed that these inshore sediments are devoid of large, equilibrium species, but subjected to episodes of scouring and resuspension by large tides and climatic disturbances. The poor nutritional quality of mangrove detritus and intermittent physical disturbances appear to be the major factors preventing the establishment of equilibrium communities and perpetuating the dominance of pioneering infaunal assemblages in this shallow, tropical inshore region.

Nitrogen assimilation from amorphous detritus by two coastal consumers

The food value of recognizable pieces of dead vegetation, morphous detritus, has been the focus of many studies in coastal systems. In contrast, the nutritional quality and formation process of amorphous detritus, aggregates of dissolved organic matter (DOM), is poorly studied. We created 15N-labelled aggregates from the leachate of four macrophytes, a marsh grass and three macroalgae common in New England coastal waters. We fed the labelled aggregates to two coastal consumers, the grass shrimp Palaemonetes pugio and the sheepshead minnow Cyprinodon variegatus. Fish and shrimp fed each of the labelled aggregates became labelled with 15N. This study provides direct evidence for nitrogen assimilation from amorphous detritus by marine consumers. In addition, fish fed amorphous marsh grass detritus assimilated 10–40 times more nitrogen from this detritus than from morphous grass detritus. Therefore, amorphous aggregates may be higher-quality food than morphous detrital fragments for coastal consumers.

Epibenthos of mangrove waterways and open embayments: Community structure and the relationship between exported mangrove detritus and epifaunal standing stocks

The epibenthos inhabiting creek-bottoms in a tidally influenced mangrove forest, a mangrove-lined estuary and several sites in two open embayments, was sampled on four occasions between August 1986 and June 1987. The inshore (mangrove habitats)-offshore (embayment) patterns in total faunal taxonomic richness (means ranging from 0 to 32·5 taxa per trawl) and density (range of means, −2 ) were generally complex, with patterns across the gradient changing seasonally. Patterns in total biomass (range of means 0–740 mg.m −2 ) were clearer, with highest biomasses recorded in May (post-wet season) and lowest in February (mid-wet season), with no significant cross-habitat gradient in biomass. Densities and biomasses were lower than those recorded in other studies, probably owing to the physically harsh conditions available to epibenthos and to the low quality of mangrove detritus as a food source. The significant difference in the structure of epibenthic communities in mangrove and embayment habitats in the dry season months (August and October) was likely due to the longer residence time of water in mangrove water-ways at that time of the year. Greater tidal amplitudes and increased tidal current velocities in February transported mangrove detritus and many faunal taxa into embayments. Variation in the quantities of exported mangrove detritus in nettings explained significant proportions of the variance in total (and component taxa) epibenthic standing stocks in mangrove and embayment habitats. Several factors may be important in causing the positive response of different groups within the epibenthos to mangrove detritus. For penaeid shrimps it seems likely that clumps of exported mangrove detritus provide refuges from predatory fish in both mangrove and embayment habitats.

Enzymic and chemical analysis of particulate organic matter from a boreal river

SUMMARY. 1. Benthic particulate organic matter (POM) was collected from a shallow pool of a fourth order boreal stream and sorted into seven size fractions ranging from 63 to &gt;4000μm. Each size fraction was analysed for fibre, total phosphorus, and total Kjeldahl nitrogen. Microbial activity was measured by oxygen consumption and characterized by assaying for eleven classes of exoenzymes including cellulase, phenol oxidase, peroxidase, phosphatase and sulphatase.2. Indices of detritus quality such as C/N, C/P, percent lignin, and microbial respiration showed improvement with decreasing particle size. Three covarying exoenzyme groups were identified: a carbohydrase‐phosphatase group that included eight enzymes, a phenol oxidase‐peroxidase group, and sulphatase. The activity of the carbohydrase‐phosphatase group, was significantly correlated with microbial respiration and the carbohydrate content of the POM. Phenol oxidase‐peroxidase activity was correlated with lignin content for POM greater than 250 μm, but activity increased markedly in the two smallest size fractions even though the lignin content of the POM continued to decline, Sulphatase activity was inversely related to particle size over the entire range.3. The changes in microbial activity with particle size were attributed to the increasing surface area to volume ratio of smaller particles and to an ecological succession in the microbial community.

Chemical Composition and Microbial Activity of Seston in a Southern Appalachian Headwater Stream

Chemical composition and microbial activity of seston (i.e., fine particulate organic matter and associated inorganic material in transport) in a southern Appalachian headwater stream were evaluated to determine whether changes in microbial activity associated with decreasing particle size were related to changes in seston surface area and/or chemical composition. As seston particle size decreased from 500 to 10 μm, organic content measured as ash free dry mass decreased from 72.5% to 36.7%. Simultaneously, the nutritional quality of the organic fraction declined, as evidenced by increases in lignin and cellulose content and corresponding reductions in acid-detergent-soluble materials (simple carbohydrates, proteins, and lipids). Microbial activity, measured as mass-specific ¹⁴C-glucose mineralization and ³H-thymidine incorporation rates, increased significantly as particle size decreased, despite the reduced nutritional quality of smaller particles. Microbial biomass (ATP) and activity (glucose mineralization) per unit seston surface area were proportional to particle size over the 10-250-μm particle size range. Smaller particles of lower nutritional quality supported lower area-specific microbial biomass and activity. Production: biomass ratios of microorganisms associated with seston were low (1.21 to 6.08 × 10^-9/hr), suggesting that these microorganisms may have become inactive in response to the gradual decline in quality of detritus as it decomposed.

Kinetics of microbial degradation of vascular plant material in two wetland ecosystems.

Vascular plant decomposition was followed during two different years in one freshwater and one marine wetland in southeastern Georgia, USA, using a modified litterbag technique. Chemical analysis of plant material revealed different rates of decomposition for different components of the plant material (soluble components, α-cellulose, hemicellulose, and lignin) and, further, that rates of decomposition of each component changed over time, such that the specific rate of decay for each fraction decreased as decomposition proceeded. Three mathematical models which differen in their treatment of the biochemical heterogeneity of vascular plant detritus were investigated with regard to their relative abilities to describe decomposition kinetics from the field incubations as well as from laboratory microcosm studies with radiolabeled plant material. A decaying coefficient model, which treats plant detritus as a single component but allows for a decreasing specific decomposition rate as material ages, was most successful in describing kinetics of decomposition. This model accomodates the changes in quality of vascular plant detritus resulting from preferential decomposition of more labile components (e.g., non-lignocellulosic material and holocellulose) and the relative accumulation of more refractory components (e.g., lignin) observed with time. The model also accomodates the potential transformation of various plant components into more refractory compounds (humification) during the decomposition process.

Effects of sediment organics, detrital input, and temperature on demography, production, and body size of a deposit feeder

In spring, organic detritus enters temperate marine nearshore habitats during a penod of changing temperature and often shifbng detrital quality. We investigated the lnteractlng roles of sedimentary orgamc matter, detrital quality (Sparbna versus Ulva input), and varymg temperature on the population dynamics and blomass productivity of the common nearshore oligochaete Paranais htoralis. Dunng the phase of population increase, detrital input had the same positive effect on population size, Irrespective of the specific detrltal type or temperature. Later, however, the populations overexploited available resources, and crashes occurred in the order: high temperature-Spartina, low temperature-Spart~na, h ~ g h temperatureUlva, low temperatureUlva. In contrast, b~omass productivity was negatively affected by temperature. Carbon and nitrogen analyses of the sed~ment , detritus, and worms were used to calculate the nutnt~onal value of the sedimentary carbon and nitrogen. At 15C, 0.8% of the nitrogen in the sediment was usable by the worms, while the conversion efficiency on detntus was 20 to 30 %. For carbon, about 0.2 % of the sediment was converted, whereas about 5 % of detrital carbon was converted. These numbers are somewhat lower at 25°C. Results suggest that the overwhelming majonty of carbon and nitrogen in the sediment 1s useless for depos~ t feeder nutrition. The large absolute amount, however, stlll may s u b s ~ d ~ z e considerable deposit feeder production. In effect, a small percentage conversion, mulbphed by a large availabihty, results in a considerable yleld from the sedimentary organic matter. Pulses of detrital addition, however, may be nutritionally more valuable.

Use of ATP and carbon: nitrogen ratio as indicators of food quality of stream detritus

SUMMARY. 1. Differences in food quality of suspended and benthic organic detritus, as measured by ATP content and C/N ratio, were assessed along three contrasting headwater streams in southern Ontario.2. Large differences in ATP content of sediments between cooler upstream reaches and warmer downstream reaches were detected. Sediment ATP content was highly correlated with stream temperature, presumably as a result of faster microbial growth, and with stream gradient. C/N ratios of sediments showed much the same pattern of differences as ATP, but were less variable.3. By contrast, the ATP content (or BIOC/POM ratio) and C/N ratios of suspended organic matter showed no systematic variation between upstream and downstream or between warmer open and cooler shaded areas, probably due to the very short residence time of suspended particles.

The invertebrate fauna of a forest stream and its association with fine particulate matter

Abstract The invertebrate fauna colonising wooden blocks placed in a beech forest stream was studied over a period of 1 year. At least 31 species were taken during the course of the study, with 3 species of Chironomidae predominating numerically. Most species were associated principally with fine particulate matter (FPM) deposited on the upper surfaces of blocks, although a stonefly, Spaniocerca zelandica, was most abundant on the barer surfaces. Of the Chironomidae, Paucispinig‐era approximata and Polypedilum canum had clearly defined life history patterns with emergence from February to April and October to January, respectively. Psectrocladius sp. had a poorly defined life history. Gut contents of 16 insect species showed that 4 were predominantly predatory, and the remainder were detritivores. The latter could be categorised as shredders (large particle detritivores) or collector‐browsers which mainly ingested particles in the dominant (<50 μm) size range. Oxygen consumption by fine stream sediments was similar at different times of year which suggests that the food quality of detritus may tie relatively constant at all times.

Effect of detrital nutritional quality on population dynamics of a marine nematode (Diplolaimella chitwoodi)

The quantity and nutritional quality of detritus significantly affected the population growth rate (r) and carrying capacity (K) of Diplolaimella chitwoodi (Nematoda) in laboratory cultures. The rate of increase (r) was roughly constant for cultures fed Ulva fasciata, Pablum, Gracilaria foliifera and one Spartina alterniflora detritus, but was lower for Thalassia testudinum detritus and another S. alterniflora detritus. Rate of increase was unaffected by amount of food supplied except for seaweed detritus where r was lower for lower ratios. Carrying capacity (K) was strongly affected by both detrital type and rate of food supply. The best predictor of K was the rate of nitrogen supply to these cultures implying that natural populations may be N-limited. The nitrogen content of detritus appears to be the best measure of its nutritional quality.