Diagenesis in subrecent marine sediments in the Eastern Scheldt,Southwest Netherlands

The diagenesis in fine-grained sediments from a 300 to 400-years-old Dunkirk deposit, exposed on the intertidal flat, was studied at a site in the Eastern Scheldt. A new in situ pore water sampling technique that allowed repeated sampling at exactly the same place was used to monitor the seasonal fluctuations in interstitial water composition.Concentrations of organic carbon (1.5 to 2%), nitrogen (C/N = 19), phosphorus (500 μg·g⁻¹) and manganese (250 μg·g⁻¹) in the subrecent anoxic sediments were low, probably because they had already been depleted during earlier stages of diagenesis. Rates of organic carbon mineralization by sulphate reduction (0.1 Mole·m⁻²·y⁻¹) and rates of nutrient regeneration were 1 to 2 orders of magnitude lower than in recent fine-grained sediments elsewhere in the Eastern Scheldt.Pore water NH₄⁺ and ΣPO₄ concentrations were controlled by mineralization, uptake by Zostera noltii and sediment-seawater exchange. During the summer the uptake exceeded the mineralization rate at 0 to 5 cm. Mineralization and diffusional processes dominated the changes in the NH₄⁺ and ΣPO₄ profiles in the other seasons.Dissolved manganese and iron concentrations showed a typical subsurface maximum at 0 to 3 cm, and low (<5 μMole) concentrations below this depth. Dissolved iron concentrations were probably controlled by the solubility of iron sulphides, and manganese probably by the solubility of Mn, Ca-carbonate.     

Distribution of chroococcoid cyanobacteria and size-fractionated chlorophyll a biomass in the central and southern north sea waters during June/July 1989

The spatial and vertical distribution of phycoerythrin(PE)-containing chroococcoid cyanobacteria and the contribution of the <3 μm size fraction to overall phytoplankton chlorophyll a biomass were investigated in the central and southern North Sea during June and July 1989. PE-containing chroococcoid cyanobacteria cell numbers ranged between 6×10⁵ and 4.4×10⁷ cells·dm⁻³ and was typically between 0.5×10⁷ and 3×10⁷ cells·dm⁻³, lowest numbers being recorded near the British coast in central North Sea waters. The vertical distribution of these cyanobacteria showed no evidence to suggest a preferential accumulation deep in the euphotic zone. The <3 μm size fraction accounted for 6.6 to 57.5% of the total phytoplankton chlorophyll a biomass (mean 19.7%). In general, the relative significance of the <3 μm size fraction decreased with increasing total chlorophyll a biomass.     

Impact of a decontamination step with peroxyacetic acid on the shelf-life,sensory quality and nutrient content of grated carrots packed under equilibrium modified atmosphere and stored at 7 °C

Peroxyacetic acid (PAA) is a strong oxidizer and exerts antimicrobial properties. The effect of a decontamination step with 80 and 250 mg L⁻¹ PAA on shelf-life of grated carrots stored under equilibrium modified atmospheric packaging at 7 °C was determined and compared with the shelf-life of unwashed and water-washed carrots. Microbial parameters, including total aerobic plate count, numbers of lactic acid bacteria, Lactobacillae and yeasts, and sensory quality were evaluated. Next to these parameters, atmospheric gas composition, pH and nutrient content were also monitored. The suggested packaging configuration prevented CO₂ accumulation, but at the end of the study anoxic conditions were reached for unwashed carrots and carrots washed with 80 mg L⁻¹ PAA. The microbial shelf-life of water-washed carrots was 4 d based on the yeast count, whereas the flavour was not acceptable after 5 d. The total aerobic plate count and the yeast count determined the shelf-life of carrots treated with 80 mg L⁻¹ PAA on 5 d, whereas the flavour was unacceptable after 7 d. None of the microbial parameters determined the shelf-life of carrots washed with 250 mg L⁻¹ PAA. However, this treatment had already a pronounced adverse effect on the initial sensory quality. Water washing already decreased the content of all individually studied nutrients (−16 to −28%), except for lutein content and the antioxidant capacity. Additional losses after adding PAA on day 0 were found for α-tocopherol and phenols. Regardless of the applied treatment, α- and β-carotene remained stable during storage, whereas ζ-carotene, lutein and α-tocopherol were unstable. The phenol content and the antioxidant capacity of unwashed, water-washed and 80 mg L⁻¹ PAA-treated carrots increased significantly at the end of the storage period, whereas no changes were found in carrots treated with 250 mg L⁻¹ PAA.On the condition that carrots were packed under an adequate EMA, the 80 mg L⁻¹ PAA treatment showed possibilities for extending shelf-life without pronounced effects on nutrient content.     

The uptake and distribution of copper in the lugworm,Arenicola marina (annelida,polychaeta)

The uptake and distribution of copper in the polychaetous worm Arenicola marina (L.) have been studied both under experimental conditions and in a natural environmental situation, by analyzing the whole body and three body-compartments; body-wall, intestine and blood.No relationship between the copper concentrations in various fractions of the sediment and any of the body-compartments could be found.Under experimental conditions, the copper concentrations in the blood were higher than in the intestine and the body-wall. Uptake of dissolved copper occurred directly from the water. Copper uptake also occurs via sediment at high copper concentrations of the silt fraction of the habitat sediment.The data obtained from the field showed small differences in copper concentrations between blood, intestine and body-wall. The copper concentrations in the blood varied from 1 to 4 μ·cm⁻³, in the inetestine from 2 to 6μg·g⁻¹, and in the body-wall from 1 to 3 μg·g⁻¹ wet weight.A significant correlation existed between blood cooper concentration and body weight: small (young) individuals had higher copper concentrations in their blood than larger (older) ones. This means that young animals will encounter more stress at similar environmental copper levels than older animals.The concentration in the different body-compartments appears to be dependent on the season the samples were taken. The copper concentration in the intestine and the body decreased from April to November, whereas the blood copper concentration increased.     

Distribution and abundance of the zooplankton of the Ems estuary (North Sea)

From 1974 to 1977 a study was made of the abundance and the distribution of the zooplankton species of the Ems estuary (The Netherlands and the Federal Republic of Germany), an area of about 500 km² with extensive tidal flats.The most important component of the zooplankton consisted of holoplanktonic calanoid copepods with, during the summer, a significant contribution of meroplankton, mainly consisting of polychaete and cirripede larvae. Zooplankton abundance showed a marked seasonality, with a pronounced spring peak and a smaller late summer/autumn peak. In the low salinity area the spring bloom was dominated by Eurytemora affinis, which persisted in the salinities below S=5 upriver during the whole year. In the polyhaline area Acartia bifilosa was the main component of the spring bloom. The late summer maximum from August to October was dominated by Acartia tonsa in the meso- and polyhaline area and by A. discaudata and Centropages hamatus in the euhaline part of the estuary bordering on the Wadden Sea proper. The number of abundant (> 1000 ind·m⁻³) species increased from the inner, fresher part of the estuary towards the Wadden Sea but, except for April, average zooplankton density in salinities <18 was similar (2768 ind·m⁻³) to the density in salinities >18 (2817 ind·m⁻³).The distribution patterns show that there are only a few autochthonous species and that the majority of species is allochthonous and penetrates more or less deeply into the estuary from the Wadden Sea and North Sea, varying with species and season.     

Production and consumption of tropical seagrass fields in Eastern Indonesia measured with bell jars and microelectrodes

During the Indonesian-Dutch Snellius-II Expedition the production and consumption of tropical seagrass species were measured with bell jars at four sampling stations in eastern Indonesia. Applying a conversion factor of 0.29, the amount of carbon fixed and mineralized was calculated from the recorded oxygen evolution. The gross production of the different seagrass communities was found to be between 1230 and 4700 mg C·m⁻²·d⁻¹. The consumption lay between 860 and 3860 mg C·m⁻²·d⁻¹. From these data a relatively low net production of 60 to 1060 mg C·m⁻²·⁻¹ could be calculated. At one sampling station incubations were carried out at different depths in a sloping Halodule uninervis (Forssk.) Aschers meadow, which indicated that seagrasses above a depth of about 2 m may become subject to photoinhibition. A linear correlation between biomass and measured production was found for Thalassia hemprichii (Ehrenb.) Aschers. Above a biomass of 100 g DW·m⁻² the production per unit of biomass decreased due to self shading.Using microelectrodes the oxygen production of epiphytes was found to be 230 mg C·m⁻² leaf surface·d⁻¹. at 1900 μE·m⁻²·s⁻¹ assuming an epiphyte coverage of 40%. This indicated that up to 36% of the primary production in a seagrass community may be attributed to epiphytes.The seagrass fields in Indonesia were found to be healthy ecosystems with a high primary production, but organisms within the communities use the abundance of organic matter very efficiently, creating net production rates of 100 to 300 mg C·m⁻²·d⁻¹ which are similar to barren areas.     

An experiment on the relative importance of denitrification,nitrate reduction and ammonification in coastal marine sediment

Simultaneous determinations of ¹⁵N-nitrogen gas production, ¹⁵N-ammonia formation by nitrate reduction and ammonia production from organic nitrogen were carried out after addition of ¹⁵N-nitrate to anaerobically incubated sediment slurries from a location in the Dutch Wadden Sea. The rate of nitrogen gas production was 1.57 μmol N·cm⁻³ wet sediment·d⁻¹, nitrate reduction to ammonia occurred at a rate of 0.79 μmol N·cm⁻³·d⁻¹ and ammonification at 1.17 μmol N·cm⁻³·d⁻¹. At the end of the incubation experiment (after 30 h) 63% of the originally added ¹⁵N-nitrate was present as nitrogen gas, 32% ended up as ammonia and ∼4% as particulate organic nitrogen. Ammonia production by degradation of organic nitrogen compounds was the most important process in building up the ammonia pool in the anaerobic sediment incubation.     

In situ fluctuations of oxygen and sulphide in marine microbial sediment ecosystems

Laminated microbial ecosystems (microbial mats) on the island of Schiermonnikoog (The Netherlands) were studied with respect to variation in oxygen and sulphide profiles, depth distributions of photopigments and viable number and cell volume of purple sulphur bacteria. Cyanobacteria occurred in the top 2 mm, the dominant species being Microcoleus chthonoplastes. The blooming of purple sulphur bacteria below the cyanobacterial layer was observed in autumn, the dominant species being the immotile Thiocapsa roseopersicina. Cell volume of this species is indicative of its growth rate.In situ measurements showed strong diel fluctuations in oxygen and sulphide profiles. Frequently, cyanobacteria and purple sulphur bacteria were exposed to oxygen during the day, and to anoxic conditions at night. Sulphide sometimes reached the layer of the cyanobacteria. The cyanobacteria and the purple sulphur bacteria both are very well adapted to these diel fluctuations. In addition, strong seasonal variations were observed, whereas short-term fluctuations of oxygen occurred due to changing light-climate and rainfall.Attention was paid to the unusual occurrence of microbial mats on the North Sea beach during the autumn of 1987.     

Seasonal variation in growth and biomass of an intertidal Zostera noltii stand in the Dutch wadden sea

To assess relationships between the life cycle of the seagrass Zostera noltii and light conditions in its habitat, the seasonal dynamics of a seagrass-dominated community on a tidal flat off Terschelling were studied. The main components of this community were seagrass, periphyton and the periphyton grazing mudsnail Hydrobia ulvae. Total biomass of the seagrass stand showed a unimodal curve with a maximum of more than 110 gADW·m⁻² in August and a minimum of less than 10 gADW·m⁻² in January. Chlorophyll density of periphyton on the seagrass leaves followed a more or less similar pattern, ranging from 0.4 μg chlorophyll·cm⁻² in May to more than 3 μg chlorophyll·cm⁻² at the end of August. Periphyton biomass was, however, already maximal in May with almost 1.6 mgADW·cm⁻² and subsequently decreased to less than 0.6 mgADW·cm⁻² in August. The total weight of H. ulvae was more or less stable, varying between more than 150 and less than 400 gDW·m⁻², although significant changes were observed within size classes.Light is assumed to be the primary limiting factor for seagrass distribution in the Wadden Sea. The light conditions of seagrass in the study area were influenced by periphyton and mudsnails. Leaf growth rates and biomass development appeared to be related with light conditions in the seagrass habitat. Shading caused by periphyton during the growing season was estimated at 10 to 90% of incident light, resulting in a reduction of about 2 to 80% of the yearly period during which the light compensation point (LCP) of the seagrass is exceeded. The mudsnails were found to be theoretically able to ingest daily 25 to 100% of the standing stock of periphyton and microphytobenthos. It is concluded that shading by periphyton and grazing by mudsnails play an important role in the seasonal biomass development and survival of Z. noltii in the seagrass-dominated community on a tidal flat off Terschelling.     

Organic carbon in the upper 100 m and downward flux in the banda sea; monsoonal differences

Organic carbon was measured in the upper 100 m and its downward flux from the euphotic zone recorded, as part of a multidisciplinary study in the Banda Sea on monsoonal differences in the upper water layers.All 35 stations occupied showed on average 1.5 times higher POC values in August 1984 (4.9 g·m⁻², SE monsoon, upwelling period) than in February/March 1985 (3.3 g·m⁻², NW monsoon, downwelling period) for the 0 to 100 m water column. Monsoonal variation in POC was confined to the surface layer and related to a variation in phytoplankton content; it can be explained by — local— upwelling during the SE monsoon. At 100 m no seasonal variation occurred.Contrary to POC, average figures for DOC in February/March were almost twice the average observed in August (66.5 against 37.5 g·m⁻² for the 0 to 100 m water column). In February/March spatial variation was more pronounced than in August with highest values occurring in the NE part (>100 g·m⁻², 0 to 100 m), with a subsurface maximum. In this period the NW monsoon causes a surface current to the east. This might cause a westward subsurface countercurrent of Arafura Sea water rich in riverine or benthic layer DOC, influencing the eastern Banda Sea.At 100 m depth daily sedimentation amounted to ∼50 mg C·m⁻². The limited number of data do not indicate a difference between the 2 periods. On average the daily downward flux at 100 m depth amounted to 1.2% of POC and 0.8% of chlorophyll present in the 0 to 100 m water column, and equalled 5% of the daily primary production.     

The determination of the sizes and settling velocities of estuarine flocs by an underwater video system

The in situ underwater video system VIS is described. VIS determines sizes and settling velocities of suspended mud flocs without destroying the large fragile aggregates. The settling process of the flocs and aggregates can be observed directly on a screen on board the research vessel. Analysis of the videorecordings was possible up to 600 mg·dm⁻³, which is of importance in turbid estuarine systems. Experiments with VIS in the Ems estuary showed macroflocs with settling velocities of 0.5 to 2.0 mm·s⁻¹ and sizes of 200 to 500 μm. These flocs were observed at relatively low suspended-sediment concentrations (20 to 50 mg·dm⁻³). During certain phases of the tidal cycle (around mid-tide) even larger aggregates were observed with dimensions in the range of 400 to 1100 μm and settling velocities of 1 to 7 mm·s⁻¹, surviving relatively high current velocities. The large aggregates are shown to play an essential role in the phenomenon of rapid settling, as observed in various estuaries.     

Effects of river discharge and vertical circulation on aquatic primary production in a turbid Louisiana (USA) estuary

Aquatic primary production was measured in stationary and moving bottles with the light/dark oxygen method at two sites in Fourleague Bay, a shallow, turbid estuary on the central Louisiana coast receiving flow from the Atchafalaya River. Riverflow strongly influenced spatial and seasonal patterns of production. Annual net production increased from 382.5 g O₂·m⁻² (119.5 g C·m⁻²) at an upper bay site near the river mouth to 1015.7 g O₂·m⁻² (317.4 g C·m⁻²) at a lower bay site distant from the river. Net production was negatively correlated with seasonal changes in riverflow at both sites. Maximum production rates occurred at intermediate salinities. At low sainities, production was apparently light-limited because of the extreme turbidity of the riverwater. At high salinities, production declined despite greater water clarity, apparently due to nitrogen limitation. At the upper bay areal production estimates from moving incubations were significantly lower than estimates from stationary incubations, but no consistent differences were found at the lower bay and in the bay as a whole. This is the first report of moving incubations yielding significantly lower estimates most of the time. The productivity differences between moving incubations and stationary incubations were significantly correlated with relative light penetration and we suggest that this was because of at least two distinct time-dependent production-versus-irradiance phenomena whose influences varied as conditions changed.     

Biomass and activity of benthic fauna on the fladen ground (northern North Sea)

During May 1983 the abundance and biomass of macrobenthos and meiobenthos populations, as well as the metabolic activity (shipboard incubated and in situ measured respiration, and potential respiration activity by ETS) were studied in the Fladen Ground area.Macrofauna showed an abundance of 4500 specimens per m²; the corresponding biomass was 10.7 g ash-free dry weight per m². The bivalve Arctica islandica, with 12 specimens per m² contributed 7.2 g to this biomass. Average meiofauna numbers, 0.9·10⁶ per m² were low; a meiofaunal biomass of only 0.3 g was estimated. Depending on the method applied, large variations in metabolic activity were found. Results from shipboard incubation experiments probably present a large underestimate. The in situ bell-jar experiments showed an average oxygen uptake of 1010 μmol O₂·m⁻²·h⁻¹, equalling a carbon demand of 7.3 gC·m⁻²·month⁻¹ in May. ETS measurements gave a 3 times higher estimate. Taking into account that macrofaunal and meiofaunal abundance and biomass, as well as bottom temperatures, show minimum values in spring, an annual carbon mineralization by the benthic system of 50 to 70 gC·m⁻² is suggested. This would mean that about one third of the total primary produced organic matter is channelled into the benthic system.     

Primary production and nitrogen assimilation in the North sea during July 1987

An extensive survey of the whole of the North Sea, carried out in July 1987, is described. The study concentrated on the measurement of surface water inorganic nutrient concentrations and concomitant rates of primary production (¹⁴C) and nitrogen assimilation (¹⁵N). Primary production was investigated using size fractionation techniques. Three vertical profiles of primary production and nitrogen assimilation were also investigated.Much of the North Sea exhibed thermal stratification. Surface nutrient concentrations were low and chlorophyll concentrations typically <1 mg m⁻³. More than 75% of the primary production was attributable to cells <5 μm in diameter. Ammonium assimilation accounted for most of the nitrogen assimilation.The water column was vertically well mixed in the coastal zones. Here, inorganic nitrogen concentrations were high (e.g. up to 25 μmol NO₃⁻ with chlorophyll concentrations up to 10 mg⁻³, and organisms >5 μm diameter accounted for most of the primary production. As in offshore regions ammonium accounted for the major part of the nitrogen assimilated.A 115 km section obtained using an undulating oceanographic recorder showed that in certain regions of the North Sea physical features acted to increase the dependence of the phytoplankton on nitrate.     

Temporal and lateral fluctuations in production and biomass of bacterioplankton in the western Dutch Wadden Sea

To contribute to the validation of a recently developed ecosystem model of the western Wadden Sea (EON, 1988), data on bacterial biomass and production were acquired. Seven field stations, spread over the two main basins of the estuarine system, were sampled monthly in 1986. Between these basins significant differences were found in counts, biovolume, biomass and production of bacteria (measured by the ³H-thymidine method) with consistently higher mean values of bacterial variables in the Vlie basin. Bacterial production rates of 2 to 175 mg C· m⁻³· d⁻¹ were obtained for the Vlie basin, with an annual production of 10 to 11 g C· m⁻³, while the production in the Marsdiep basin did not exceed 45 mg C·m⁻³ ·d⁻¹, with an annual production of g C·m⁻³. Bacterial biomass varied over the year from 2 to 140 mg C·m⁻³ in the study area, with a mean biomass of 39 mg C·m⁻³ in the Vlie basin and 23 mg C·m⁻³ in the Marsdiep basin. Blooms of bacteria occurred in May and July–August. Spatial and temporal fluctuations in bacterial variables are discussed, taking into account different environmental factors and the availability of food for bacteria in relation to transport and exchange of water masses between the two basins and the North Sea. Results are compared with the results as simulated by the ecosystem model.     

Control of postharvest grey mould (Botrytis cinerea Per.: Fr.) on strawberries by glucosinolate-derived allyl-isothiocyanate treatments

The vapours of allyl-isothiocyanate (AITC) were evaluated in in vitro and in vivo trials against Botrytis cinerea, a severe pathogen of strawberries. In in vitro trials AITC activity was assayed on conidial germination and mycelial growth of the fungus. The mycelium appeared less sensitive to AITC than conidia (EC₅₀ values of 1.35 mg L⁻¹ and 0.62 mg L⁻¹, respectively). In addition, AITC had a fungistatic effect against the pathogen, since the values of EC₅₀, for both parameters, increased by around 30% after AITC removal. In in vivo trials, ‘Tecla’ and ‘Monterey’ strawberries (spring-bearing and day-neutral cultivars, respectively) obtained from organic production and naturally infected by B. Cinerea, were exposed for 4 h in an atmosphere enriched by pure AITC or derived from defatted seed meals of Brassica carinata (0.1 mg L⁻¹, in a 0.1 m³ treatment cabinet). After 2 days at 0 °C and another 3–4 days at 20 °C, the fruit were evaluated for grey mould infections. The AITC treatment reduced the decay caused by the pathogen by over 47.4% up to 91.5%, significantly different from the untreated fruit. No significant differences were found between synthetic and glucosinolate-derived AITC. Residue analysis performed on fruit at the end of storage (7 d after treatment) showed values lower than 1 mg kg⁻¹. Total phenolic content and antioxidant capacity estimated in treated and untreated strawberries showed no significant difference between control and AITC treated fruit. Our results show it is possible to reduce the incidence of postharvest grey mould on strawberries with a treatment of AITC (0.1 mg L⁻¹) for 4 h, opening a potential application of biofumigation in the postharvest control of B. cinerea in strawberry.     

Essential oils and silver nanoparticles (SNP) as novel agents to extend vase-life of gerbera (Gerbera jamesonii cv. ‘Dune’) flowers

The aim of this study was to evaluate the efficacy of silver nanoparticles (SNP) and essential oils as novel antimicrobial agents in extending the vase-life of gerbera (Gerbera jamesonii cv. ‘Dune’) flowers. The vase-life of flowers held in a solution containing 5 mg L⁻¹ SNP plus 6% sucrose was found to be significantly higher than with 8-HQC (8-hydroxyquinoline citrate) or control treatments. However, the vase-life was not different to that of flowers held in similar concentrations of silver nitrate. All gerbera flowers held in SNP solutions showed significantly higher relative fresh weight than the control. Vase-life of gerbera flowers was extended by addition of either 50 or 100 mg L⁻¹ carvacrol and either 1 or 2 mg L⁻¹ SNP from 8.3 to 16 d. In addition, the relative fresh weight and solution uptake of gerbera flowers were increased by addition of 100 mg L⁻¹ essential oils and 1 or 2 mg L⁻¹ SNP as compared to that of control flowers. Our results suggest the potential application of essential oils or SNP as novel alternatives to common chemicals used in preservative solutions for gerbera flowers.     

Increased phytoplankton primary production in the Marsdiep area (Western Dutch Wadden Sea)

Annual phytoplankton primary production in the Marsdiep tidal inlet increased from ca 150 gC·m⁻² in the period 1964 to 1976, to ca 300 gC·m⁻² in 1981/1982 and 1985. This increase is considerable, but comparable to that observed in the outer Ems estuary, eastern Wadden Sea, from 240 gC·m⁻²a⁻¹ in 1972/1973 to 400–500 gC.m⁻².a⁻¹ in 1976/1980. Although the increase is most probably due to eutrophication, as illustrated by the regular increase in phosphate in the Marsdiep area since 1950, it is difficult to explain why this affected primary production not earlier than the late seventies. Primary production has probably not increased in the more turbid inner parts of the Wadden Sea, where light is the limiting factor, and P values were already higher than in the inlet areas.     

Free-living plathelminthes in sheep-grazed and ungrazed supralittoral salt marshes of the North Sea: Abundance,biomass, and their significance in food chains

The supralittoral salt marshes of the North Sea are marked by high halophyte primary productivity. The environmental factors are strongly fluctuating. Despite these features the metazoan meiofaunal abundance is equal to that found in other littoral habitats. On average 1250 marine metazoans are found per 10 cm² in ungrazed and 770 per 10 cm² in sheep-grazed supralittoral salt marshes. Nematoda dominate in numerical abundance, Oligochaeta in biomass. Plathelminthes account for 15% of marine metazoans in ungrazed and 5% in grazed salt marshes.Total plathelminth abundance increases with halophyte density, whereas the abundance of diatom-feeding Plathelminthes decreases. In ungrazed marshes on average 104 Plathelminthes are found per 10 cm², accounting for a biomass of 0.65 g DW·m⁻². In sheep-grazed marshes the average abundance is only 32 individuals per 10 cm², accounting for a biomass of 0.1 g DW·m⁻². Average individual weight is 3.2 μg DW or 2.5 μg AFDW.In grazed salt marshes, 30% of plathelminthes feed on diatoms, 66% are predators, and 4% feed on bacteria (gut analysis). In ungrazed salt marshes only 3% are diatom-feeders, and 90% are predators feeding on Nematoda, Copepoda, Oligochaeta, and smaller Plathelminthes. Presumably plathelminthes are top predators on the salt marsh meiofauna.