Benthic meiofauna responses to five forest harvest methods

Benthic meiofauna were collected from the pools of minute (0 order) streams in the Ouachita National Forest, Arkansas during March 21–23, 1996 to see if benthic communities responded to forest harvest methods in a similar manner as plankton communities collected two years prior. The study streams and their watersheds (2–6 ha) were located in 14–16 ha forest stands that were selected for comparability of stands. Five treatment stands were paired with adjacent undisturbed reference stands (10 total). Treatment stands were subjected to one of five harvest methods listed in order of decreasing severity of harvest disturbance to the stands: (1) clearcut; (2) pine seed-tree; (3) pine shelterwood; (4) pine-hardwood group selection; and (5) pine single-tree selection. The mean number of taxa per site was 14 with a range of 9–20 taxa including rotifers, copepods, nematodes, dipterans, ostracods and `other' meiofauna. Densities of total meiofauna (mean=2449 No. l ^–1) were significantly higher (p= 0.002) in treated sites. Highest densities occurred in single-tree and clearcut treatments. Rotifers were significantly more numerous at the single-tree treatments (p=0.03) and nematodes were significantly greater at the clearcut treatments (p=0.03). We conclude that benthic meiofauna in these headwater streams are sensitive to silviculture practices and that the impact of forest harvest persists for at least 2.5 years.     

Carbon sources of Antarctic nematodes as revealed by natural carbon isotope ratios and a pulse-chase experiment

δ¹³C of nematode communities in 27 sites was analyzed, spanning a large depth range (from 130 to 2,021 m) in five Antarctic regions, and compared to isotopic signatures of sediment organic matter. Sediment organic matter δ¹³C ranged from −24.4 to −21.9‰ without significant differences between regions, substrate types or depths. Nematode δ¹³C showed a larger range, from −34.6 to −19.3‰, and was more depleted than sediment organic matter typically by 1‰ and by up to 3‰ in silty substrata. These, and the isotopically heavy meiofauna at some stations, suggest substantial selectivity of some meiofauna for specific components of the sedimenting plankton. However, ¹³C-depletion in lipids and a potential contribution of chemoautotrophic carbon in the diet of the abundant genus Sabatieria may confound this interpretation. Carbon sources for Antarctic nematodes were also explored by means of an experiment in which the fate of a fresh pulse of labile carbon to the benthos was followed. This organic carbon was remineralized at a rate (11–20 mg C m⁻² day⁻¹) comparable to mineralization rates in continental slope sediments. There was no lag between sedimentation and mineralization; uptake by nematodes, however, did show such a lag. Nematodes contributed negligibly to benthic carbon mineralization.     

Hydro-morphologically related variance in benthic drift and its importance for numerical habitat modelling

Numerical fish-habitat modelling on various scales is considered to be state of the art in river management. However, most of the concepts applied use steady-state hydraulic parameters such as flow velocity and water depth. Herein we present analysis and discussion of the possibility of including a drift-feeding parameter (SI_F) into habitat evaluations based on multiplying suitability indices. “Sources” and “sinks” of benthic drift were identified according to both the zero-crossing and hydraulic-threshold methods in an alpine gravel-bed river. Minor differences could be determined between the two methods in a well-developed riffle–pool section. Macroinvertebrates, used for simulating benthic drift, were collected by multi-habitat sampling and appraised according to their critical threshold (τ _cr) for motion on the bed surface and sinking velocity (v _s). The findings of the calculation of drift rates using one- (1D) and two-dimensional (2D) hydrodynamic numerical models highlight a specification of best feeding position for drift-feeding fish (i.e. brown trout, grayling) considering the SI_F parameter. Riffle–pool sequences are characteristic of pristine alpine streams; our findings underline their importance as production (riffles) and consumption areas (pools) in terms of holistic river function. Moreover, the results indicate that (artificial) lateral obstruction (e.g. dams) may lead to a reduced transport rate of benthic organisms due to low bottom shear stress (<0.25 N m⁻²). Thus, deposition of drifting macroinvertebrates occurs in backwaters, with downstream impacts on benthic and fish communities.     

Abundance and colonization potential of artificial hard substrate-associated meiofauna

Meiofauna are known to live on hard substrates in association with periphytic and epiphytic algae and attached epibiota; however, the abundance, diversity and colonizing abilities of hard-substrate meiofauna have been poorly documented. We quantified meiofauna living on microalgal-covered pilings associated with a wood pier in a shallow (<2 m deep) estuarine embayment with the use of a suction sampler, and compared colonization of pier-piling and sediment-dwelling meiofauna onto collectors that capture suspended meiofauna from the water column. Collectors were small mesh pads (159 cm³) suspended at mid-water depth, and their size and structural complexity were similar to floating or drifting masses of macroalgae that may be colonized by meiofauna. Sediment was collected by coring, and copepod (to species) and nematode (to genera) colonists on mesh pads were compared with pier-piling and sediment communities. Abundance of total meiofauna averaged 124±13.6 (S.E.) on pier pilings, compared to 2092±274.6 individuals 10 cm⁻² in surrounding sediment. Phytal copepods (free-living copepods with prehensile first legs and dorsoventrally and laterally compressed body forms) and copepod nauplii dominated pier-piling collections, but nematodes were dominant on faunal collectors and in sediment. Phytal copepods also were abundant on faunal collectors but were rare in sediments. Copepod and nematode diversities were similar, but species composition was largely nonoverlapping, in pier pilings and sediments. Net recruitment of meiofauna to faunal collectors averaged about 900 individuals collector⁻¹ day⁻¹ during the 1-week experiment. Nematode and copepod colonists on faunal collectors were both much more similar to pier-piling than to sediment assemblages. These data suggest that meiofauna are abundant and diverse on algal-covered pier pilings, and they may become more important to marine ecology as artificial hard substrates increase with increasing urbanization. Furthermore, pier-piling meiofauna appear to readily migrate into the water column and probably contribute to a rapidly dispersing pool of meiofauna in estuaries.     

Metazoan meiofauna dynamics and pelagic–benthic coupling in the Southeastern Beaufort Sea,Arctic Ocean

Pelagic–benthic coupling is relatively well studied in the marginal seas of the Arctic Ocean. Responses of meiofauna with regard to seasonal pulses of particulate organic matter are, however, rarely investigated. We examined the dynamics of metazoan meiofauna and assessed the strength of pelagic–benthic coupling in the Southeastern Beaufort Sea, during autumn 2003 and spring–summer 2004. Meiofauna abundance varied largely (range: 2.3 × 10⁵ to 5 × 10⁶ ind m⁻²), both spatially and temporally, and decreased with increasing depth (range: 24–549 m). Total meiofauna biomass exhibited similar temporal as well as spatial patterns as abundance and varied from 25 to 914 mg C m⁻². Significant relationships between sediment photopigments and various representatives of meiofauna in summer and autumn likely indicate the use of sediment phytodetritus as food source for meiofauna. A carbon-based grazing model provided estimates of potential daily ingestion rates ranging from 32 to 723 mg C m⁻². Estimated potential ingestion rates showed that meiofauna consumed from 11 to 477% of the sediment phytodetritus and that meiofauna were likely not food-restricted during spring and autumn. These results show that factors governing the distribution and abundance of metazoan meiofauna need to be better elucidated if we are to estimate the benthic carbon fluxes in marginal seas of the Arctic Ocean. This paper is dedicated to the memory of our dear friend and colleague Gaston Desrosiers who contributed so much to benthic ecology. We will continue in his spirit.     

Arctic cyanobacteria and limnological properties of their environment: Bylot Island, Northwest Territories, Canada (73°N, 80°W)

Cyanobacteria were a major constituent of phototrophic communities in the lakes, ponds and streams of Bylot Island, in the Canadian high Arctic. The waters spanned a range of temperatures (1.8–16.8°C in late July), pH regimes (6.2–9.2) and conductivities (1.5–1700 μS cm⁻¹) but nutrient concentrations were consistently low (< 1 μg dissolved reactive P l⁻¹ at all sites; < 10 μg NO₃-N l⁻¹ at most sites). Picoplanktonic species (Synechococcus spp.) were often the numerical dominants in the plankton, and periphytic filamentous species (Oscillatoriaceae) commonly formed thick (5–50 mm) benthic mats. Bloom-forming species of cyanobacteria were either absent or poorly represented even in Chla-rich ponds. The total community biomass ranged from 0.1 to 29.8 μg Chla l⁻¹ in the plankton and from 1.1 to 34.8 μg Chla cm⁻² in the benthos. The in vivo absorbance characteristics of isolates from these environments indicated a genetically diverse range of species in each group of Arctic cyanobacteria. Growth versus irradiance relationships were determined for each of the isolates and similarly revealed large genetic differences (maximum growth rates from 0.17 to 0.61 day⁻¹), even between morphologically identical taxa. A comparison of nutrients, pigment concentrations and species composition underscores the strong similarities between freshwater ecosystems in the north and south polar zones. Received: 3 June 1996 / Accepted: 3 November 1996     

Seasonal and microhabitat influences on diatom assemblages and their representation in sediment traps and surface sediments from adjacent High Arctic lakes: Cape Bounty,Melville Island,Nunavut

The spatial (i.e. microhabitat) and temporal (i.e. seasonal) characteristics of diatom assemblages in adjacent High Arctic lakes were studied intensively June–August 2004. These baseline data are used to improve understanding of modern diatom community dynamics, as well to inform paleoenvironmental reconstructions. Diatoms were collected approximately weekly through the melt season from each principal benthic substrate (moss/macrophyte, rock scrapes, littoral sediment), plankton, and sediment traps, and were compared to the uppermost 0.5 cm of a surface core obtained from the deepest part of the lake where sediment cores are routinely collected. Water samples were collected concurrently with diatom samples to investigate species–environment relationships. The lakes share approximately half of their common taxa, the most abundant overall in both lakes being small Cyclotella species. Results of detrended correspondence analysis (DCA) indicate that the largest gradient in species turnover existed between benthic and planktonic communities in both lakes, and that sediment trap and the surface core top samples most closely resemble the planktonic assemblage, with an additional contribution from the lotic environment. Our results indicate clear micro-spatial controls on species assemblages and a degree of disconnection between the benthos and deep lake sediments that manifests as an under-representation of benthic taxa in deep lake surface sediments. These findings are particularly relevant in the context of interpreting the paleoenvironmental record and assessing ecosystem sensitivity to continued climate change.     

Drifting Algae as a means of Re-Colonizing Defaunated Sediments in the Baltic Sea. A Short-Term Microcosm Study

We conducted a microcosm experiment to evaluate the capability of fauna inhabiting or being transported by drifting filamentous algae to colonize defaunated sediment. We expected meiofauna would perform a quicker and more effective re-colonization of disturbed areas by means of the algal mats than their macrofaunal counterparts. Similarly, within meiofauna, we expected more mobile taxa such as ostracods and harpacticoids to colonize the sediment more readily than other more sedentary ones such as nematodes. Naturally drifting algae were collected from the field and placed in 1 l aquaria on top of 5 cm of defaunated sediment. After 3 and 6 days, one core sample (5 cm deep) was taken from each aquarium; the first 2 cm were sliced into 2 mm layers, and the remaining fraction into 1 cm layers. The sediment remaining in the aquaria was sieved through a 0.5 mm sieve to collect the re-colonizing macrofauna. The dominant macrofaunal taxa inhabiting the algae were juvenile bivalves and gastropods, with Cerastoderma glaucum accounting for the majority of the bivalves and Hydrobia sp. for most of the gastropods. After 3 and 6 days, the most abundant macrofaunal taxa colonizing the sediment were Cerastoderma glaucum, Hydrobia sp. and gammarid amphipods. Higher abundances were found after 6 days than after 3, though differences were not significant for any of the major taxa. Meiofauna inhabiting the algae were dominated by rotifers, nematodes, ostracods, chironomid larvae and harpacticoid copepods. Contrary to our predictions, nematode and harpacticoid species inhabiting the drifting algae were not driven to sediment re-colonization but remained in the algae. Our results indicate that some benthic animals may indeed benefit from drifting algal mats as a means of dispersal and re-colonization of previously defaunated sediments in relatively short periods of time. Also, they may contribute to explain some of the trends found in other studies, regarding species increase under drifting algae and the recovery patterns found in areas often exposed to algal conglomerates.     

Food of an endangered cyprinodont (Aphanius iberus): ontogenetic diet shift and prey electivity

Synopsis We studied the ontogenetic diet shift and prey electivity of an endangered cyprinodontid fish endemic to the Iberian Peninsula, the Spanish toothcarp (Aphanius iberus). The toothcarp’s diet was omnivorous, dominated by harpacticoid copepods (Mesochra lilljeborgi and Tisbe longicornis), copepod nauplii and detritus. Diet composition varied greatly among habitats, depending on prey availability. In a rarely inundated habitat (glasswort), there was more consumption of the isopod Protracheoniscus occidentalis and the harpacticoid copepod Mesochra lilljeborgi, while in algal mats another harpacticoid (Tisbe longicornis), chironomid dipterans and invertebrate eggs were more important in diet. Although a benthic feeding habitat has previously been suggested, in our study the diet was based rather on water column organisms for both glasswort and algal mat habitats. There was also an ontogenetic diet shift, with an increase of mean prey length with fish length, clearly linked to a microhabitat change. Smaller fish showed positive electivity and greater reliance on planktonic prey (e.g. copepod nauplii, the harpacticoid copepods Mesochra lilljeborgi and Tisbe longicornis, the rotifer Brachionus plicatilis, and ostracods), while larger fish elected and preyed on more benthic organisms (e.g. Canuella perplexa, Mesochra rapiens, and ephydrid dipterans).     

Chemo-enzymatic preparation of copolymeric polythioesters containing branched-chain thioether groups

Branched-chain copolymeric polythioesters (PTE) were formed in good yield (∼87%) by chemoenzymatic reactions including thiyl radical-induced addition of 1,6-hexanedithiol to the >C=C< double bond of dimethyl 1,18-octadec-9-enedioate and transthioesterification of polyfunctional dimethyl 1,18-octadec-9-enedioate with bifunctional 1,6-hexanedithiol catalyzed by immobilized lipase from Rhizomucor miehei. The reactions were performed in vacuo at 80°C without a solvent. PTE was extracted from the reaction mixture using methyl-t-butylether and precipitated from i-hexane. The polymer structure of the i-hexane-insoluble PTE precipitate was elucidated by GPC/SEC showing an average molecular mass (M _w) of 1,857 Da corresponding to a molecular weight range of up to 24,000 Da and a maximum degree of polymerization of up to 50 monomer units. Chemical derivatization with TMSH demonstrated the formation of up to ∼58 mol% of a branched-chain thio(S)ether, i.e., dimethyl S-9-(6-mercaptohexylthio)-1,18-octadecanedioate, and small proportions (∼8 mol%) of a dimeric disulfide formed therefrom. The chemical structures of various low-molecular weight (<900 Da) reaction products formed by transthioesterification, addition reaction or disulfide formation of the reactants or reaction intermediates, e.g., 1,18-octadec-9-enedioic acid methyl(O)ester 6′-S-mercaptohexyl thio(S)ester, dimethyl S-9-(6-mercaptohexylthio)-1,18-octadecanedioate, were elucidated by GC–MS. Similarly, dimethyl S-9-(6-S-methylthiohexylthio)-1,18-octadecanedioate and dimethyl 11,18,19,26-tetrathia-10,27-di-(7-carboxymethyl-heptyl)hexatriacontane-1,36-dioate were detected in the reaction mixtures after derivatization with trimethylsulfonium hydroxide.     

Long-term changes in a benthic assemblage associated with artificial reefs

The aim of the study was to evaluate the long-term development of a hard bottom benthic assemblage over a period of 20 years in an area off the mouth of a large river. The artificial reef of Fregene was selected because benthic assemblage data were available for the period 1981–1992. This artificial reef is located in the mid Tyrrhenian Sea, 5 nautical miles north of the two mouths of the Tevere River (Latium, Italy) and 1.5 nautical miles offshore from Fregene (Rome, Italy). The artificial reef was deployed in March 1981 for fisheries enhancement in 10–14 m of water on a sandy-silty seabed. The Tevere River carries suspended materials and a heavy load of organics since it transports Rome’s effluent, resulting in the eutrophic state of area waters. Benthic sampling was conducted in 2001 by SCUBA diving; two standard surfaces of 400 cm² were scraped from the vertical walls of the same uppermost block in four different periods. All organisms were identified and counted. The methodology used is the same as that adopted in the previous periods, so that the 2001 data could be compared with past collected data. The benthic assemblage was analysed by cluster analysis using the Bray-Curtis index and clustered using the group average clustering algorithm. The SIMPER procedure was used to identify those taxa that characterize each station group identified by cluster analysis. Changes in benthic assemblages and hydrological trends of the Tevere River were investigated using the cumulative sum series method. The 20-year development of the benthic community, starting from the new substratum, is composed of different phases characterised by different benthic assemblages. In particular five different phases were distinguished: 1. Pioneer species recruitment (May 1981–June 1981); 2. Mytilus galloprovincialis (mussel) dominance (August 1981–November 1983); 3. M. galloprovincialis regression (July 1984–October 1985); 4. M. galloprovincialis absence (91–92); 5. Bryozoans bioconstruction dominance (2001). The dynamic succession of the observed benthic assemblages exhibited a good relation with the Tevere River flow. The Tevere River flow, and the subsequent sedimentation process, seems to have strongly influenced the benthic assemblage succession of the Fregene artificial reef. Guest editors: G. Relini & J. Ryland Biodiversity in Enclosed Seas and Artificial Marine Habitats     

Diverse communities of active Bacteria and Archaea along oxygen gradients in coral reef sediments

Microbial communities inhabiting highly permeable sediments of Checker Reef in Kaneohe Bay, Hawaii, were characterized in relation to porewater geochemistry (O₂, NO₃ ⁻, NO₂ ⁻, NH₄ ⁺, phosphate). The physiologically active part of the population, assessed by sequencing cDNA libraries of 16S rRNA amplicons, was very diverse, with an estimated ribotype richness ≥1,380 in anoxic sediment. Quantitative analysis of community structure by rRNA-targeted fluorescence in situ hybridization (FISH) indicated that the archaeal population (9–18%) was dominated by marine Crenarchaeota (5–9%). Planctomycetales were the most abundant group in the oxic and interfacial habitat (17–19%) but were a minority (<5%) in anoxic reef sediment, where γ-Proteobacteria were numerically dominant (18%). Another 9–14% of the microbial benthos belonged to β-Proteobacteria, predominantly within the order Nitrosomonadales, many cultured representatives of which are NH₄ ⁺ oxidizers. The results of this study contribute to the phylogenetic characterization of benthic microbial communities that are important in organic matter degradation and nutrient recycling in coral reef ecosystems.     

Spring-to-summer changes and regional variability of benthic processes in the western Canadian Arctic

Seasonal dynamics in the activity of Arctic shelf benthos have been the subject of few local studies, and the pronounced among-site variability characterizing their results makes it difficult to upscale and generalize their conclusions. In a regional study encompassing five sites at 100–595 m water depth in the southeastern Beaufort Sea, we found that total pigment concentrations in surficial sediments, used as proxies of general food supply to the benthos, rose significantly after the transition from ice-covered conditions in spring (March–June 2008) to open-water conditions in summer (June–August 2008), whereas sediment Chl a concentrations, typical markers of fresh food input, did not. Macrobenthic biomass (including agglutinated foraminifera >500 μm) varied significantly among sites (1.2–6.4 g C m⁻² in spring, 1.1–12.6 g C m⁻² in summer), whereas a general spring-to-summer increase was not detected. Benthic carbon remineralisation also ranged significantly among sites (11.9–33.2 mg C m⁻² day⁻¹ in spring, 11.6–44.4 mg C m⁻² day⁻¹ in summer) and did in addition exhibit a general significant increase from spring-to-summer. Multiple regression analysis suggests that in both spring and summer, sediment Chl a concentration is the prime determinant of benthic carbon remineralisation, but other factors have a significant secondary influence, such as foraminiferan biomass (negative in both seasons), water depth (in spring) and infaunal biomass (in summer). Our findings indicate the importance of the combined and dynamic effects of food supply and benthic community patterns on the carbon remineralisation of the polar shelf benthos in seasonally ice-covered seas.     

Parasite transfer from crustacean to fish hosts in the Lübeck Bight,SW Baltic Sea

Four helminth parasites out of 19 species found in the Lübeck Bight, Baltic Sea, were chosen for investigations on the transfer from invertebrate to small-sized fish hosts: larvae of the tapewormsSchistocephalus sp. andBothriocephalus sp. (Cestoda) living in planktonic copepods as primary hosts;Podocotyle atomon (Digenea) andHysterothylacium sp. (Nematoda) were found in benthic crustaceans, especiallyGammarus spp. These hosts were the prey of 3 gobiid fishes,Gobiusculus flavescens (feeding mainly on plankton),Pomatoschistus minutus (preferring benthos), andP. pictus (feeding more on plankton than benthos). Because the fishes selected smaller sizes of crustaceans, they ingested all stages of the copepods but only the smaller-sized groups of gammarids which were often less infested by parasites. In order to evaluate the probability for a fish to be parasitized by a helminth, an infestation potential index (IP) was calculated.Podocotyle atomon andHysterothylacium sp. revealed an IP which was far lower in gobies than expected when the prevalences of the previous hosts were taken into consideration. The IP of tapeworm larvae was mainly influenced by the feeding pressure of the gobiid predators, which might change with developmental stage and season. It is concluded that parasite transfer to the next host decreases when sizes of prey and predator differ only moderately. This mechanism can reduce the numbers of parasites transferred to less suitable or wrong hosts.     

Long-term change in limnology and invertebrates in Alaskan boreal wetlands

Climate change is more pronounced at high northern latitudes, and may be affecting the physical, chemical, and biological attributes of the abundant wetlands in boreal forests. On the Yukon Flats, located in the boreal forest of northeast Alaska, wetlands originally sampled during 1985–1989 were re-sampled for water chemistry and macroinvertebrates in summer 2001–2003. Wetlands sampled lost on average 19% surface water area between these periods. Total nitrogen and most metal cations (Na, Mg, and Ca, but not K) increased between these periods, whereas total phosphorus and chlorophyll a (Chl a) declined. These changes were greater in wetlands that had experienced more drying (decreased surface area). Compared with 1985–1989, densities of cladocerans, copepods, and ostracods in both June and August were much higher in 2002–2003, whereas densities of amphipods, gastropods, and chironomid larvae were generally lower. In comparisons among wetlands in 2002–2003 only, amphipod biomass was lower in wetlands with lower Chl a, which might help explain the decline of amphipods since the late 1980s when Chl a was higher. The decline in Chl a corresponded to greatly increased zooplankton density in June, suggesting a shift in carbon flow from scrapers and deposit-feeders to water-column grazers. Declines in benthic and epibenthic deposit-feeding invertebrates suggest important food web effects of climate change in otherwise pristine wetlands of the boreal forest. Handling editor: R. Bailey     

Interspecific differences in drift behaviour between the native <Emphasis Type="Italic">Gammarus pulex</Emphasis> and the exotic <Emphasis Type="Italic">Gammarus roeseli</Emphasis> and possible implications for the invader’s success

“Drifting” is known to subject aquatic invertebrates to intense predation by drift feeding fish. Consequently, interspecific variations in drifting behaviour could lead to differences in predation pressure between coexisting prey species. Predation being an important factor determining the success of invaders, differences in drift patterns could advantage either native or exotic invertebrates through differential predation by native fish predators. The exotic freshwater amphipod (Gammarus roeseli) has now largely colonized Western Europe where it is often found in sympatry with a native species (Gammarus pulex). Here we documented interspecific differences in drifting behaviour that might have favored the invader’s success through differential predation. Benthic and drifting amphipods were sampled three times at the same site to compare the proportion of each species within and between sample types (benthos or drift) across time. Compared with the benthos, where the invader (G. roeseli) was significantly less abundant than the native (G. pulex), G. roeseli was proportionally overrepresented in the drift but displayed a very different drifting pattern. While G. pulex drift rates remained roughly constant over a 24 h period, G. roeseli showed a marked diel periodicity with low diurnal and high nocturnal drift rates. Such drifting behaviour could procure this species with a competitive advantage regarding predation as most drift feeding fish are diurnal. As a result, the native appears more disadvantaged with respect to drift. This may partly explain the ability of G. roeseli to coexist with G. pulex in a habitat more suitable to the native.     

Identification and production of 3-hydroxy-Δ9-cis-1,18-octadecenedioic acid by mutants of Candida tropicalis

 The transformation of oleic acid by mutants of Candida tropicalis was studied in fed-batch cultures. Besides Δ⁹-cis–1,18-octadecenedioic acid, 3-hydroxy-Δ⁹-cis–1,18-octadecenedioic acid was detected as the main fermentation product. Here we describe the production, isolation and the complete chemical characterization of the purified 3-hydroxy-Δ⁹-cis–1,18-octadecenedioic acid. The geometric configuration of the double bond was not changed during bioconversion. The enantiomeric excess of the compound was 76%. Mutagenesis of C. tropicalis DSM 3152 with N-methyl-N-nitro-N′-nitrosoguanidine and selection with oleic acid as the sole carbon source led to mutant M 25, which produced the 3-hydroxy-Δ⁹-cis–1,18-octadecenedioic acid at a 1.8-fold higher concentration in the medium as compared to the parent strain. The maximum concentration of the hydroxy dioic acid was 19.4 g/l after 223 h fermentation. Received: 24 August 1995/Received revision: 21 September 1995/Accepted: 4 October 1995     

Benthos structure on tropical tidal flats of Australia

General features of benthos communities of tropical tidal flats are defined from northeast Australia, based on surveys from 1988 to 1991 in Hinchinbrook Channel and in the Haughton River estuary. A zonation of benthic communities is described. Total abundances for macrofauna averaged 31 individuals 200 cm⁻², mesofauna (defined as infauna smaller than 0.5 mm and retained on a 0.25 mm sieve) averaged 16 individuals 10 cm⁻² and meiofauna averaged 231 individuals 5 cm⁻². The two study sites were similar in their abundance structures, but species due to a higher diversity of polychaeta in the Channel (120 species, H′=3.80 vs. 29 species and H′=1.78 in the Haughton estuary). Species densities were comparable at both sites and rather low (6 species 177 cm⁻², 2–7 species 10 cm⁻² and 5 meiobenthic Plathelminth species 5 cm⁻²). Over 50% of the species encountered were represented by less than three individuals. Deposit feeders, dominated the assemblages both in terms of individuals as well as species numbers. Tropical tidal flats are compared with their temperate counterparts and approaches for future research in tropical benthos communities are recommended.     

Vertical distribution of benthic community responses to fish predators, and effects on algae and suspended material

The vertical positioning of benthic invertebrates should be a trade-off between the risky, but productive, sediment surface and the safer, but physiologically harsher, conditions deeper down in the sediment. This is because the foraging efficiency of benthic fish decreases with sediment depth, whereas the sediment surface is generally better oxygenated and has a higher resource quality than lower layers. We studied how two benthic fish predators, bream (Abramis brama) and ruffe (Gymnocephalus cernuus), affected the community composition and vertical distribution of benthos, and their indirect effects on algae and suspended material, in field enclosures. Whereas bream had significant effects on the density, composition and distribution of the benthos, ruffe had no such effects. The total benthos biomass in bream treatments was an-order of magnitude lower in the upper sediment layer (0–1 cm) and three times lower in the middle layer (1–3 cm) than in the controls, whereas there were no significant effects in the deepest layer (3–10 cm). Bivalves persisted in the deepest layer although their density was reduced in shallow sediment, whereas gastropods faced the risk of local extinction in the presence of bream. As indirect effects, small-bodied cladocerans, phytoplankton, periphyton and both organic and inorganic suspended material were higher in the bream treatments. We␣conclude that the impact of bream diminished substantially with increasing sediment depth, enabling invertebrates to survive in the sediment and to persist in the presence of bream. However, there were␣no␣indications of any group adjusting their vertical position behaviourally as a response to predation threat.     

Meiobenthic stocks and benthic activity on the NE-Svalbard shelf and in the Nansen Basin

Summary High Arctic meiofaunal distribution, standing stock, sediment chemistry and benthic respiratory activity (determined by sediment oxygen consumption using a shipboard technique) were studied in summer 1980 on the NE Svalbard shelf (northern Barents Sea) and along a transect into the Nansen Basin, over a depth range of 240–3920 m. Particulate sediment proteins, carbohydrates and adenylates were measured as additional measures of benthic biomass. To estimate the sedimentation potential of primary organic matter, sediment bound chloroplastic pigments (chlorophylls, pheopigments) were assayed. Pigment concentrations were found comparable to values in sediments from the boreal and temperate N-Atlantic. Meiofauna, which was abundant on the shelf, decreased in numbers and biomasses with increasing depth, as did sediment proteins, carbohydrates, adenylates and sediment oxygen consumption. Meiofaunal abundances and biomasses within the Nansen Basin were comparable with those observed in abyssal sediments of the North Atlantic. Nematodes clearly dominated in metazoan meiofauna. Protozoans were abundant in shelf sediments. Probably in response to the sedimentation of the plankton bloom, meiofauna abundance and biomass as well as sediment proteins, carbohydrates and adenylates were significantly correlated to the amount of sediment bound chloroplastic pigments, stressing the importance of food quantity to determine benthic stocks. Ninety-four percent of the variance in sediment oxygen consumption were caused by chloroplastic pigments. Benthic respiration, calculated per unit biomass, was 3–10 times lower than in the East Atlantic, suggesting low turnover rates in combination with a high standing stocks for the high Arctic benthos.