Sedimentation and benthic mineralization of organic detritus in a Norwegian fjord

The supply of particulate material to the sea-bed as well as the oxygen consumption and the redox potential of the sea-bed were measured during a one-year period (1979/1980) at 60 and 90 m depth in the inner part of a west Norwegian fjord, Fanafjorden. At both sites, uniform sedimentation rates of total particulate material (825 and 885 g m^-2 yr^-1, respectively) and particulate inorganic material (576 and 616 g m^-2 yr^-1, respectively) were found. The sedimentation rates of particulate organic carbon (96 and 107 g m^-2 yr^-1, respectively) and particulate organic nitrogen (10 and 12 g m^-2 yr^-1, respectively) were low in winter, higher in summer and autumn, with maxima in May/June, reflecting similar maxima in the phytoplankton biomass in the area, with 6 to 8 wk delay. The oxygen consumption of the sea-floor was lowest in winter/spring and highest in summer. Thirtytwo and 38 g C m^-2 yr^-1 (respiration quotient=0.85) were metabolized by the sediment at 60 and 90 m, respectively. The simultaneous measurements of sedimentation rates and sediment oxygen uptake throughout a whole year demonstrated that the benthic mineralization is governed by the sedimentation over a longer time-scale, but that seasonal imbalances do occur. A box-model of the flux of particulate organic carbon to the sediment surface is presented, and includes the relevant processes and some quantitative estimates.     

Brood size and chemical composition of Pareuchaeta norvegica (Crustacea: Copepoda) in Loch Etive,Scotland

Brood size and chemical composition (carbon, nitrogen, and ash) of Pareuchaeta norvegica in Loch Etive, Scotland have been determined. From 23 to 37 eggs were found in each egg mass (mean=30 eggs). The eggs are oval; the mean size of the longer axis is 438 m. Variation in egg mass (as dry weight) is related to increase in dry weight of the maternal body. an increase of 1 mg in maternal body dry weight produces an increase of 0.03 mg dry weight in the egg mass. Carbon content increases with increasing body dry weight both in pre-spawning and spent females, but nitrogen content decreases with increasing body weight. Thus, the carbon:nitrogen ratio increases with increasing body dry weight. The carbon content of an egg mass ranges from 61.4 to 65.3%, and nitrogen content from 9.6 to 13.2% of the total dry weight. Some examples of partitioning of chemical components of the maternal body into the egg mass are also described.     

A link between biologically imported particulate organic nutrients and the detritus food web in reef communities

Previous work with planktivorous fishes has shown that they import particulate organic and inorganic material to reefs in the form of fecal pellets, which, in part, are deposited in crevices on the reef where these fishes shelter during their inactive period. Since these feces do not accumulate in fish shelters, we predicted that some of the feces could be rapidly consumed by reef detritivores. We examined the attractiveness of fish feces to potential reef detritivores by placing traps baited with planktivorous fish feces, along with unbaited control traps, in crevices on rocky reefs at Santa Catalina Island, California, USA, between June 1982 and November 1983, and on coral reefs at St. Croix, U.S. Virgin Islands, during June 1983. Significantly more animals (the majority being crustaceans) were trapped in the baited traps compared to the unbaited controls on both reefs. There was also a significant association between the presence of trapped animals and fish feces at Santa Catalina Island (p = 0.009); this association was not quite as strong in St. Croix (p = 0.069). The consumption by shrimp of feces marked with carmine particles and, in turn, the predation on these shrimp by a reef fish demonstrates the links between this type of imported particulate organic and inorganic material and the food web of the reef community.Please address all correspondence and requests for reprints to Dr. Miller at California State University, Long Beach     

Ingestion and incorporation of coral-mucus detritus by reef zooplankton

The copepod Acartia tonsa and the reef mysid Mysidium integrum ingest stained coral mucus. Ingestion rates determined with radioisotope-labeled mucus ranged from 4 to 81% body carbon · 24 h^-1 for the copepods and I to 70% body carbon · 24 h^-1 for the mysids. Incorporation was measured by comparing the organic composition of fecal material and by the incorporation of isotope-labeled mucus. A. tonsa incorporated 47% of ingested ash-free material, 68% of carbon and 36% of nitrogen. M. integrum incorporated 44% of ingested ash-free matter, 57% of carbon and 55% of nitrogen. Incorporation estimates using ¹⁴C-labeled mucus were 65% and 39% for incorporation by A. tonsa and M. integrum respectively. A. tonsa and M. integrum incorporated both the mucus substrate and the epiphytic bacteria of the mucus-detritus.     

The role of isopods and amphipods in the initial fragmentation of eelgrass detritus in Nova Scotia,Canada

Daytime observations on the isopods Idotea phosphorea and I. baltica and the amphipod Gammarus oceanicus held in laboratory microcosms showed that I. phosphorea and G. oceanicus spent 45% and 30% respectively, of their active time feeding on dead, intact eelgrass leaves which had been recently released from plants. I. baltica spent 41% of its active time consuming intact green leaves. The shredding of intact dead leaves by I. phosphorea and G. oceanicus resulted in production of small detrital particles which were liberated from the faeces of the invertebrates and this type of feeding led to the breakdown of whole leaves. Field experiments which separated the effects of shredding by invertebrates and grinding by waves and ice on the loss of weight from leaf packs showed that relative to controls isopods significantly increased weight loss from dead leaves. Loss of weight from leaf packs exposed to both biotic and physical shredding forces was not significantly different from that found on those exposed only to shredding by isopods. However, trends in the data indicated that fragmentation of whole, dead leaves in the field probably is a result of the synergistic effects of shredding by invertebrates and physical factors, particularly ice grinding. The role played by invertebrates in fragmenting intact, dead leaves is discussed in the light of energy flow and nutrient cycling within seagrass systems.     

Topographically generated fronts,very nearshore oceanography,and the distribution of chlorophyll,detritus, and selected diatom and dinoflagellate taxa

At four sites (Sunset Bay, Miller's Cove, and Shore Acres 43° 20.13 N; 124° 22.40 W, Nellies Cove 42° 44.75 N; 124° 29.75 W) along the Oregon coast, USA, relationships between fronts associated with shore-parallel foam lines and the distributions of chlorophyll, selected phytoplankters, and detritus were investigated. Sampling dates at the study sites were as follows: Sunset Bay, 1 August 1997, 25 June 1999 and 20 July 1999; Miller's Cove, 24 August 2000; Shore Acres, 19 July 1999 and 16 August 2000; Nellies Cove 17 August 2000 and 31 August 2000. Conductivity, temperature and depth data were used to describe the water masses on either side of the fronts, and vertical plankton tows with a 53-m mesh net were used to describe the distribution of selected phytoplankters and detritus. At the cove sites during upwelling, fronts marked the presence of warm water within the bay and cooler water offshore. Chlorophyll a (Chl a) and phytoplankton concentrations were generally lower within the coves than seaward while detritus concentrations were higher. From 3 July 2000 to 15 September 2000, a period when upwelling winds from the north prevail, a time series of samples was collected at Sunset Bay. The front was only present during periods of upwelling favorable winds. During these periods there were significantly higher concentrations of Chl a, Pseudo-nitzschia spp., and Protoperidinium spp. seaward of the front than landward. During downwelling winds the front was absent and there were no significant differences in the concentrations inside and outside the mouth of the bay. At Shore Acres, an exposed, relatively straight stretch of shoreline, the shore-parallel front appears to be formed by boundary mixing. Chl a and phytoplankton from the coastal ocean spread well shoreward of the boundary-mixing front. When present, the front at the mouth of the coves and bay indicated the presence of water masses with distinct physical and biological characteristics, but not at Shore Acres. Alongshore differences in the very nearshore oceanography, by altering the availability of continental shelf phytoplankton production, may affect both the growth rates of intertidal benthic suspension feeders and community structure.Electronic Supplementary Material Supplementary material is available in the online version of this article at .Communicated by J.P. Grassle, New Brunswick     

A rapid method of extracting meiobenthic nematodes and copepods from mud and detritus

The extraction of nematodes and harpacticoid copepods from muddy sediments or sediments containing a large amount of organic detritus can be achieved through a series of centrifugations or the material in a saccharose solution of at least 900 g/l. The number of individuals appearing in the supernatant after each centrifugation forms a geometric series, with a ratio which is dependent on the amount of material, the concentration of the saccharose solution, and the acceleration of the centrifuge. Knowledge of this ratio allows an estimation of density after only one centrifugation. More than 90% of the animals present in the sample can be extracted after only two centrifugations.     

Dispersion of Tellina tenuis from Kames Bay,Millport, Scotland

The dispersion of Tellina tenuis da Costa in the laboratory was analysed by the Clark and Evans nearest-neighbour test and by the Kolmogorov-Smirnov one-sample test. The dispersion was random, with a slight tendency toward aggregation that was independent of density. In the field, the dispersion was analysed by the Clark and Evans nearest-neighbour test and by the X² approximation to Fisher's coefficient of dispersion. The dispersion was again random, this time with a slight tendency toward spacing out that was independent of density. The tendency toward aggregation displayed in the laboratory was independent of the dispersion pattern shown at the start of the experiment, and also unaffected by the edge of the container. The apparent randomness suggests that T. tenuis is primarily a suspension feeder, but may be a deposit feeder under certain environmental conditions.     

Chemistry and adsorption-desorption properties of manganese oxides deposited in Forehill Water Treatment Plant,Grampian, Scotland

Manganese oxide coatings on sand particles within filtration beds from a water treatment plant in Grampian, Scotland were examined to determine their control on metal mobility. This study first sought to characterise the oxides, notably their mineralogy and metal content, to provide a foundation for studies on the adsorption of dissolved metals from the treated water by the oxides. The oxides were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and analysed by flame atomic absorption spectrophotometry (AAS). These techniques showed the oxide coatings were amorphous but uniformly distributed over each sand grain. The oxides were selectively removed from the sand grains prior to analysis by AAS using a hydroxylamine hydrochloride selective leaching method. The compositional range of the extracts was 100–150 mg L⁻¹ Mn; 30–55 mg L⁻¹ Fe; 17–56 mg L⁻¹ Ca; 4.6–7.0 mg L⁻¹ Ni; 4.6–6.8 mg L⁻¹ Zn and 1.3–5.7 mg L⁻¹ Mg. When these results are expressed as mg of metal per mg of Mn, the metal content of the oxides is remarkably uniform: 0.25–0.37 mg Fe; 0.14–0.35 mg Ca; 0.035–0.042 mg Ni; 0.035–0.040 mg Zn; 0.01–0.04 mg Mg. The greatest metal concentrations were consistently found in the upper 3 cm of the filtration bed, and these decrease with increasing depth. After the beds are cleaned a more uniform distribution of metals occurs throughout the bed. The metals taken up by the manganese coating are retained over a wide pH range with the exception of Ca and Mg which desorb to a significant extent. The percentage of calcium and magnesium lost from the coating ranges from 30–94%, the amount being dependent on the final pH of the solution. The presence of manganese oxide in the filtration beds appears to be advantageous in terms of removal of transition metals from the treated water.     

Is kelp detritus a good food for suspension feeders? Effects of kelp species, age and secondary metabolites

The food quality of detrital particles derived from three species of kelps was evaluated in a laboratory feeding experiment utilizing two species of suspension feeders, the serpulid polychaete Pseudochitonopomaoccidentalis and the mussel Mytilustrossulus. Fresh and aged kelp particles were also evaluated, and growth in all treatments was compared to growth on ad libidum phytoplankton rations. Fresh particles from Laminariagroenlandica, aged particles from Agarumfimbriatum and Alariamarginata, and mixed phytoplankton promoted the highest growth rates in both consumers. Growth was inversely related to total polyphenolic concentration in the fresh kelp particles. The increase in quality of both Agarumfimbriatum and Alariamarginata particles with age corresponded with a rapid loss of polyphenolic secondary metabolites and an increase in total nitrogen. Received: 26 November 1996 / Accepted: 9 January 1997     

Growth and collapse of a spring phytoplankton bloom in the Firth of Clyde,Scotland

A range of physical and chemical parameters were measured through the water column at two previously unstudied shallow-water sites in the Firth of Clyde, Scotland, in the spring of 1991. Sediment traps were also deployed at one of the sites. The results of this survey are presented and discussed. A bloom of Skeletonema costatum was observed at one site through March and into April, when it collapsed completely, the phytoplanktonic cells sedimenting out of the water column. No significant bloom or sedimentation was observed at the second study site.     

Recycle of buried macroalgal detritus in sediments: use of dual-labelling experiments in the field

In intertidal sediments, burial and decomposition of macroalgal detritus can fuel the sediment of carbon (C) and nitrogen (N), which can be either promptly mineralised or assimilated to enter the food web. This study investigates the transfer of algal-derived C and N to the sediment and to the infauna feeding primarily on benthic diatoms. Thalli of Ulva spp. were ¹³C- and ¹⁵N-labelled in the mesocosm and frozen to create detritus. Thawed macroalgae were, then, buried in the sediment of an intertidal sand-flat forming a mosaic of small patches (50 × 50 cm²) enriched with the macroalgae interspersed with bare sediment. The area was dominated by Corophium volutator and Hydrobia ulvae. The uptake of ¹³C and ¹⁵N was measured in the residual macroalgae, in the sediment and in those animals. Decomposition of detritus was rapid and after 4 weeks the residual biomass was 3% the amount added. Algal-derived ¹³C and ¹⁵N were moved to the sediment. The total amount of ¹³C and ¹⁵N retained in the sediment after completing the decomposition was 3.4 ± 0.5% ¹³C and 2.7 ± 0.6% ¹⁵N the amount decomposed. During the first 2 weeks more N than C was assimilated (1.7% ¹³C and 13.5% ¹⁵N). During the remaining two weeks, N was released from the sediment, while there was little accumulation of C (+6.4 ± 2.0 % ¹³C and −7.7 ± 3.8% ¹⁵N). At the end of the decomposition, animals were ¹⁵N- and ¹³C-labelled. Considering the total accumulation of label in the sediment, they accounted for 3.5 ± 1.8% ¹³C and 25.8 ± 12.9 % ¹⁵N. Similarly, considering the mass of the heavy isotopes gained (¹³C) or lost (¹⁵N) during the remaining 2 weeks, the animals accounted for 4.7 ± 2.1% of the ¹³C in excess and for 18.6 ± 9.1% of the ¹⁵N loss. The transfer of C and N to the sediment and to the surface deposit-feeders can be a relevant mechanism to remove the excess of detritus from the sediment.     

The composition and biosynthesis of lipids in Thysanoessa raschi from the Clyde Estuary,Scotland

The lipid composition and biosynthesising activity of Thysanoessa raschi collected from the Clyde Estuary, Scotland, in May 1981 were examined. Triacylglycerols were the major lipid class present, although 16.7% of the total lipid were wax esters in which phytol was the dominant fatty alcohol. The thoracic contents (hepatopancreas) of the krill were capable of biosynthesising lipids in vitro from various labelled substrates. Radioactivity from [1-¹⁴C] palmitic acid was incorporated into lipids in the order phospholipids>triacylglycerols>wax esters; the bulk of the radioactivity was present in all cases in the fatty acyl moieties of the lipids. [U-¹⁴C] glucose labelled lipids in the order phospholipids>triacylglycerols>free fatty acids> was esters; in the first two lipids the radioactivity was mainly in the glycerol moieties, whereas in was esters it was solely in the fatty acyl moieties. The extent of labelling of these lipids from [U-¹⁴C] alanine was less than that from [U-¹⁴C] glucose, but the pattern of labelling was generally similar. More than 90% of the radioactivity incorporated into total lipid from ³H₂O was present in free fatty acids from which it was calculated that the hepatopancreas of T. raschi can synthesise 2.5 g of fatty acid per hour at 15°C. This value is approximately three times lower than that previously determined for T. inermis from Balsfjorden, northern Norway. The results are discussed in terms of the sources of the dietary lipids of krill and the role of endogenous biosynthesis in contributing to its lipid reserves.     

The modified niche model: Including detritus in simple structural food web models

Food webs are constructed as structural directed graphs that describe “who eats whom,” but it is common to interpret them as energy flow diagrams where predation represents an energy transfer from the prey to the predator. It is the aim of this work to demonstrate that food webs are incomplete as energy flow diagrams if they ignore passive flows to detritus (dead organic material). While many ecologists do include detritus in conceptual and mathematical models, the detrital omission is still commonly found. Often detritus is either ignored or treated as an unlimited energy source, yet all organisms contribute to the detritus pool, which can be an energy source for other species in the system. This feedback loop is of high importance, since it increases the number of pathways available for energy flows, revealing the significance of indirect effects, and making the functional role of the top predators less clear. In this work we propose the modified niche model by adding a detritus compartment to the niche model. We demonstrate the effect of structural loops that result from feeding on detritus, by comparing empirical data sets to five different assembly models: (1) cascade, (2) constant connectance, (3) niche, (4) modified niche (original in this work), and (5) cyber-ecosystem. Of these models, only the last two explicitly include detritus. We show that when passive flows to detritus are included in the food web structure, the structure becomes more robust to the removal of individual nodes or connections. In addition, we show that food web models that include the detritus feedback loop perform better with respect to several structural network metrics.     

Modelling the long-term morphological evolution of the Clyde Estuary,Scotland, UK

The long-term morphodynamic response of the Clyde Estuary to any possible change in environmental forcing associated with global climate change and human interference is examined here using a model based on a systems approach. The model, which uses Boolean Algebra as its formal mathematical language, provides a qualitative insight into the long term morphodynamic behaviour of the estuarine system, at this level without the need for detailed and quantitative hydrodynamic and morphodynamic process knowledge or extensive data resources. The model predictions suggest that the long-term morphological changes in the Clyde Estuary largely depend on the fluvial flow of the River Clyde. Salt marshes in the upper reaches of the estuary were found to be the most vulnerable morphological feature of the estuary. In the event of increased river flow in the future, a likely situation according to climate change scenarios, saltmarshes will deplete or disappear altogether, irrespective of the sediment influx into the estuary. Changes to waves and tides will also contribute to the evolution by taking the estuary through significantly different intermediate morphological states whilst evolving towards a stable end state.     

An unusual case of failure in old oil-shale workings at Pumpherston,West Lothian,Scotland

This paper discusses the result of a drilling exercise in the Camps Shale, at the base of the Upper Oil Shale Group which lies in the Lower Carboniferous. One borehole, later duplicated, indicated that the stooped out area had failed in a manner totally unexpected and unpredicted. The site investigated lies to the east of Livingston New Town, in an area being considered for an extension of Livingston's industrial area in West Lothian District. The work was supervised by the author, funded by the Scottish Development Agency, and the contract let by the Derelict Land Rehabilitation Unit of Lothian Regional Council.     

Diet of copepods (Scopalatum vorax) associated with mesopelagic detritus (giant larvacean houses) in Monterey Bay,California

The feeding structures or houses of the giant larvacean Bathochordaeus sp. serve as both habitat and food for the calanoid copepod Scopalatum vorax. Gut contents of S. vorax include both microbial and metazoan associates of larvacean houses, and possibly the house-mucus matrix itself. Copepods were observed and collected from larvacean houses between 100 and 500 m in Monterey Bay, California, using a submersible ROV (remotely operated vehicle) from the Monterey Bay Aquarium Research Institute. Gut contents were compared to potential food items on the houses and in the open water (not associated with the house). Copepods were generalist feeders, with amorphous detritus, diatoms, and copepods or other crustacean parts dominating gut contents. Protozoans and algae other than diatoms were rarer in guts. Houses contained a diverse assemblage of microplankton and metazoans, both intact specimens and detrital remains of these. Numbers of diatoms and fecal pellets were enriched by 1 to 3 orders of magnitude on houses compared to numbers in surrounding water. Many of the abundant species of diatoms and copepods on houses occurred in S. vorax guts. This observation coupled with S. vorax feeding habits observed in situ and in the laboratory provide evidence for feeding on houses. S. vorax appears to possess special adaptations to living in a resource-limited environment, such as gorging as a feeding adaptation, chemosensory structures to help locate houses, and the ability to change feeding modes. Consumption of detritus at depth by S. vorax provides evidence that metazoans contribute to remineralization of particulate organic carbon in the mesopelagic zone.     

Individual- and Assemblage-Level Effects of Anthropogenic Sedimentation on Snails in Lake Tanganyika

Abstract:  Human impacts on aquatic biodiversity are often measured at the assemblage or community level, although it has been suggested that individual-level measures are more sensitive. We evaluated the effects of anthropogenic sedimentation on endemic snails in Lake Tanganyika, East Africa, by comparing assemblage-level (i.e., species richness, evenness, and abundance) and individual-level (i.e., frequencies of predation and parasitism, fecal organic content, life history) data between sediment-disturbed and reference sites. Previous studies have indicated that sedimentation kills snails and reduces mollusc diversity in this system, but we found little evidence of changes in species richness, evenness, or snail abundance at the levels of sedimentation recorded. In contrast, individual-level data revealed a variety of differences associated with sedimentation. Frequencies of shell scarring by predatory crabs and castration by parasitic trematodes were significantly lower at disturbed sites, indicating shifts in interspecific interactions. Snails ingested large amounts of inorganic sediments at disturbed sites, suggesting a reduction in food quality. In addition, sedimentation was associated with a large downward shift in size distribution within some species and reproduction at smaller size. These strong patterns in individual-level data contrast with the lack of effects at the assemblage level. We argue that incorporating individual-level measures will often enhance the sensitivity of impact surveys and may reveal effects of disturbance on important interspecific interactions.     

Short-term patch dynamics of macroinvertebrate colonization on decaying reed detritus in a Mediterranean lagoon (Lake Alimini Grande,Apulia, SE Italy)

In aquatic ecosystems, the ecology of macrophytal detritus aggregations has been investigated over a range of temporal scales. Yet, no attempts have been made to minimize the temporal resolution of the analysis, thus neglecting the occurrence of short-term colonization and decay dynamics for these ephemeral patches of high biological activity. The present study was carried out at two sampling sites in Lake Alimini Grande, a brackish lagoon in South-East Italy. The abundance of macroinvertebrate taxa colonizing prepared packs of reed leaf detritus and the ash-free dry mass of the packs were monitored daily for 40 days. Spectral analysis was used to investigate the fine-scale temporal dynamics of invertebrates colonization and leaf pack mass variations. The macrobenthos found on leaf packs was dominated at both sites by few taxa (i.e., the vagile Lekanesphaera monodi, Microdeutopus gryllotalpa, Neanthes caudata and the sessile Balanus sp.), whose general colonization patterns were described by unimodal curves. At a daily temporal resolution Balanus sp. was characterized by random short-term density variations, while vagile taxa showed non-random, highly site- and species-specific fluctuations generally characterized by an oscillation period comprised between 2 and 3 days. In addition, leaf packs were characterized by non-random, short-term mass oscillations, coherent and in phase with L. monodi abundance fluctuations. Our results highlight the occurrence of short-term, non-random density variations of invertebrate colonizers on leaf detritus patches. In addition, they emphasize a previously unexplored, fine-scale linkage between abundance patterns of invertebrate consumers and short-term mass variations of decaying detritus.