Estuarine benthic invertebrates of Indian river and Rehoboth Bays,Delaware

From 1968 to 1970, 273 quantitative samples of macroscopic benthic invertebrates were collected seasonally (winter and summer) from Indian River and Rehoboth Bays, Delaware. A total of 103, 485 individuals representing 11 phyla and 149 species was taken. Mobile carnivores comprised 30.9% (46 species) of the fauna, selective deposit feeders 28.2% (42 species), sedentary suspension feeders 18.1% (27 species), nonselective deposit feeders 3.4% (5 species), and sessile carnivores 2.7% (4 species). In terms of number of individuals, selective deposit feeders and sedentary suspension feeders comprised 49.2% (51,442 individuals) and 43.7% (44,647 individuals), respectively. The average density (no./m²) was generally significantly higher in Indian River than Rehoboth Bay. Maximum density for the former was 106,871/m² and for the latter 60,192/m². Evenness diversity was normally slightly higher in summer than winter and higher in Rehoboth Bay than in Indian River Bay. The top three species, ranked by density and frequency of occurrence, were Ampelisca abdita, Gemma gemma, and Tellina agilis. Annual and seasonal changes in density and dominance (exclusive of the top three species) were substantial. Biomass patterns were very similar to areas north (Moriches Bay, New York) and south (Beaufort, North Carolina). It was suggested that larger invertebrates have been deemphasized in biomass estimates in past studies. It was concluded that Rehoboth and Indian River Bays contained an Ampelisca — bivalve (Gemma gemma, Tellina agilis, Mercenaria mercenaria) community.     

Sewage pollution and the infaunal benthos of Victoria Harbour,Hong Kong

Victoria Harbour, Hong Kong, receives 800 million litres · day^?1 of untreated sewage from 3.6 million people, but is flushed by tidal currents at velocities up to 1.1 m · s^?1. Two replicate Smith-McIntyre grab samples were collected at 66 stations in August 1979, yielding a total of 5797 animals belonging to 68 species. Agglomerative hierarchical classification was used to delineate five station groups; a sixth group contained four stations where no fauna were found. All but one of the groups inhabited fine sediments (> 70% silt-clay) and could be placed along a gradient conforming to the typical pattern of organic pollution effects found in boreal and temperate waters. Abiotic areas, found in enclosed typhoon shelters, were successively replaced by a very poor fauna, a peak of opportunists, an ecotone point and a transition to normal fauna. The peak of opportunists was dominated by the oligochaete Thalassodrilidesgurwitschi (Hrabe); the polychaetes Capitella capitata (Fabricius) and Minuspio cirrifera (Wiren) were also numerous. Overall abundance was low (784 individuals · m^?2) compared with opportunists in boreal and temperate waters. The remaining station group was found in coarser sediments (<40% silt-clay) and an inflexion was observed in the log-normal distribution of individuals per species. Dominant species included the bivalve Tapes philippinarum (Adams & Reeve) and the polychaete Minuspio cirrifera; overall abundance was high (1103 individuals · m^?2). In general, pollution was assessed by the pattern of changes in number of species, abundance, biomass, diversity and evenness, by log-normal distributions of individuals per species, and by the indicator species M. cirrifera. When compared with earlier (1976) data, community conditions were generally similar but the abundance of individual species varied greatly and M. cirrifera was absent. The severely polluted area was ≈ 15 km²; this is similar in extent to offshore discharge sites and indicates the importance of tidal flushing in this inshore channel.     

Die Weichbodengemeinschaft vor der Elbemündung unter dem Einfluß der Klärschlammverklappung. II. Die Gemeinschaftsstruktur im saisonalen Wechsel

Macrobenthic fauna and sediment parameters were studied at 40 stations representing a 494 km² survey area in the eastern part of the German Bight and encompassing the sewage sludge dumping site. Data were taken in July 1980, one month after dumping ended, and in April 1981. pH-value, redox potential of the interstitial water, amount of sand in the sediment as well as total number of species and diversity were lower in the dumping area than outside, whereas alkalinity and water content of the sediment were higher. Due to mass development of a few species around the dumping site, biomass and number of individuals were high in July. Abundance and biomass values were lower in April. 2 communities are described and related to abiotic parameters such as sediment structure. Due to disturbance effects of sewage sludge, 2 stages of the second successional phase (Pearson & Rosenberg, 1978) were ascertained, described by one of these communities each time. The first faunal community, characterized by anAbra alba assemblage, describes an early stage of the second successional phase. In summer (July) theAbra alba community showed a wider spatial range than in spring. The other, dominated byNucula nitida, indicated a later stage of the second succession phase that was passing to the third phase.      

Sediments in Marsh Ponds of the Gulf Coast Chenier Plain: Effects of Structural Marsh Management and Salinity

Physical characteristics of sediments in coastal marsh ponds (flooded zones of marsh associated with little vegetation) have important ecological consequences because they determine compositions of benthic invertebrate communities, which in turn influence compositions of waterbird communities. Sediments in marsh ponds of the Gulf Coast Chenier Plain potentially are affected by (1) structural marsh management (levees, water control structures and impoundments; SMM), and (2) variation in salinity. Based on available literature concerning effects of SMM on sediments in emergent plant zones (zones of marsh occasionally flooded and associated with dense vegetation) of coastal marshes, we predicted that SMM would increase sediment carbon content and sediment hardness, and decrease oxygen penetration (O₂ depth) and the silt-clay fraction in marsh pond sediments. Assuming that freshwater marshes are more productive than are saline marshes, we also predicted that sediments of impounded freshwater marsh ponds would contain more carbon than those of impounded oligohaline and mesohaline marsh ponds, whereas C:N ratio, sediment hardness, silt-clay fraction, and O₂ depth would be similar among pond types. Accordingly, we measured sediment variables within ponds of impounded and unimpounded marshes on Rockefeller State Wildlife Refuge, near Grand Chenier, Louisiana. To test the above predictions, we compared sediment variables (1) between ponds of impounded (IM) and unimpounded mesohaline marshes (UM), and (2) among ponds of impounded freshwater (IF), oligohaline (IO), and mesohaline (IM) marshes. An a priori multivariate analysis of variance (MANOVA) contrast indicated that sediments differed between IM and UM marsh ponds. As predicted, the silt-clay fraction and O₂ depth were lower and carbon content, C:N ratio, and sediment hardness were higher in IM than in UM marsh ponds. An a priori MANOVA contrast also indicated that sediments differed among IF, IO, and IM marsh ponds. As predicted, carbon content was higher in IF marsh ponds than in ponds of other impounded marsh types. In contrast to our predictions, C:N ratio and sediment hardness were lowest and silt-clay fraction and O₂ depth were highest in IO and IM marsh ponds. Our results indicated that SMM has affected physical properties of sediments in coastal marsh ponds. Moreover, sediments in IF marsh ponds were affected more so than were those in IO and IM marsh ponds. Our results, in conjunction with those of previous studies, indicated that sediments of marsh ponds and emergent plant zones differed greatly. We predict that changes in pond sediments due to SMM will promote greater epifaunal macroinvertebrate biomass, which in turn should attract larger populations of wintering waterbirds. However, waterbirds that filter or probe soft sediments may be negatively affected by SMM because of the expected decrease in infaunal invertebrate biomass.     

Sediment toxicity in lakes along the river Kolbäcksån,central Sweden

The River Kolbäcksån system is located in a historical mining and steel works district of central Sweden. Ten years ago, intensive limnological studies indicated that the sediments in many of the lakes of this system were contaminated with metals and oil (grease). More recently a very high toxicity was found in the sediments from some of these lakes in tests with Daphnia magna and Tubifex tubifex. The objective of this study was to determine the toxicity to Daphnia magna of surficial sediments from representative locations (N = 39) within this system of lakes and to look for possible correlations with concentrations of metals (Cd, Cr, Cu, Hg, Ni, Pb, Zn) and oil (total) analysed in parallel samples. These results were also compared with spiked sediment toxicity data generated for these metals and with the bottom fauna at 8 of the 39 locations. Among the metals analyzed, only Cd, Pb and Zn were correlated with whole sediment toxicity. Only for Zn and Cr did the maximum concentrations approach those that were toxic in the spiked sediments. Correlations using single and combined metal contamination and toxicity (additive models) explained 16% of the sediment toxicity (r ² = 0.16; N = 39). Significant correlations with the bottom fauna in situ (gross abundance, biomass and species richness) were found for whole sediment toxicity, but not for metal contamination (N = 8). The use of the sediment quality triad approach for assessment of sediment quality is exemplified with a numerical normalization procedure for the latter 8 sites.     

Alien dominance of the parasitoid wasp community along an elevation gradient on Hawai’i Island

Through intentional and accidental introduction, more than 100 species of alien Ichneumonidae and Braconidae (Hymenoptera) have become established in the Hawaiian Islands. The extent to which these parasitoid wasps have penetrated native wet forests was investigated over a 1,765 m elevation gradient on windward Hawai’i Island. For >1 year, malaise traps were used to continuously monitor parasitoid abundance and species richness in nine sites over three elevations. A total of 18,996 individuals from 16 subfamilies were collected. Overall, the fauna was dominated by aliens, with 44 of 58 species foreign to the Hawaiian Islands. Ichneumonidae was dominant over Braconidae in terms of both diversity and abundance, comprising 67.5% of individuals and 69.0% of species collected. Parasitoid abundance and species richness varied significantly with elevation: abundance was greater at mid and high elevations compared to low elevation while species richness increased with increasing elevation, with all three elevations differing significantly from each other. Nine species purposely introduced to control pest insects were found, but one braconid, Meteorus laphygmae, comprised 98.0% of this assemblage, or 28.3% of the entire fauna. Endemic species, primarily within the genera Spolas and Enicospilus, were collected almost exclusively at mid- and high-elevation sites, where they made up 22.1% and 36.0% of the total catch, respectively. Overall, 75.9% of species and 96.0% of individuals are inferred to parasitize Lepidoptera larvae and pupae. Our results support previous data indicating that alien parasitoids have deeply penetrated native forest habitats and may have substantial impacts on Hawaiian ecosystems.     

Habitat preferences and species associations of shallow-water marine Tubificidae (Oligochaeta) from the barrier reef ecosystems off Belize,Central America

The marine tubificid oligochaete fauna of Belize is the most diverse that has been described for the Caribbean Sea, with records for over 50% of all known Caribbean species. Tubificids were sampled at 77 stations around the outer barrier of the coral reefs off the Belize mainland. A total of 1,529 individuals representing 52 species were collected. Species distribution patterns were controlled mainly by sediment type and the presence or absence of mangroves. Six species (Phallodrilus molestus, Tubificoides bermudae, Inanidrilus leukodermatus, Heterodrilus flexuosus, Bathydrilus formosus, Smithsonidrilus hummelincki) with diverse life history characteristics were common and had broad habitat preferences being found in various types of heterogeneous sandy sediments. Heterodrilus flexuosus was the only common species in these samples known only in Belize. The other five common species range from Belize to Florida or Bermuda. Most other species have narrower habitat preferences and are limited to specific habitats. For example, one group of gutless species was restricted to organically enriched fine to medium sands, a group of Limnodriloidinae occurred only in mud around mangrove cays, and a group of meiofaunal species were restricted to saline groundwater.     

Spatial dispersion of an estuarine benthic faunal community

By means of a box-sampler 20 moderately undisturbed sediment samples were obtained, which were subsampled on board the ship. The fauna in the upper 0–5 cm of the sediments was compared to that in the 5–10 cm layer; almost all species collected in both strata were found in the upper 0–5 cm. About 64% of the individuals and 74% of the biomass were restricted to this upper layer. A sample area of 0.5 m² (depth 0–10 cm) was found to be sufficient to make a quantitative evaluation of the benthic community. The horizontal dispersion of the macrobenthic community was studied using the variance/mean ratio and its dependence on sample size is discussed. The abundant species occurred in patches larger than 0.06 m² and high densities were correlated with aggregation.     

Vertical movements through subsurface stream sediments by benthic macroinvertebrates during experimental drying are influenced by sediment characteristics and species traits

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Are arctic soft-sediment macrobenthic communities impoverished?

 Samples of the macrobenthic fauna of soft sediments were collected from around Svalbard during the 1991 Arctic EPOS cruise of RVPolarstern. Although faunal variability could be related to sediment granulometry and depth, all stations to the south and east of the Archipelago lay within the broadly defined central Barents Sea community. In this community, α-diversity was variable and sampled between 77 and 337 m showed no clear relationship to depth. Diversity in the area close to the polar front was notably high, rarefaction predicting that 43±5.5 species might occur in a sample of 201 individuals. k-Dominance plots suggested that muddy sand communities around Svalbard were no less diverse than similar assemblages in the North Sea. Received: 27 March 1995/Accepted: 30 July 1995     

Pliensbachian gastropods from Venetian Southern Alps (Italy) and their palaeobiogeographical significance

Abstract: The Pliensbachian gastropods described by De Toni in 1912, coming from an isolated boulder at the foot of Mt Vedana (eastern margin of Trento Platform, Venetian Southern Alps, Italy) are revised. The fauna consists of 13 species representing nine families and eight superfamilies. Despite the low number of species, the assemblage represents the most diverse Early Jurassic gastropod fauna known for the Venetian Southern Alps. The boulder yielding the material was thought to derive from the upper part of the Early Jurassic Calcari Grigi Group, a carbonate platform unit extensively cropping out in the Mt Vedana area. The sedimentological analysis indicates a prevalently bioclastic wackstone‐floatstone, reflecting a lime‐muddy deposit undergone to an early consolidation. This and the high content of ammonoids, which is unusual for the Calcari Grigi Group, are typical aspects of a condensed pelagic sediment, presumably a fissure filling at the top of the carbonate platform succession. Palaeobiogeographical comparisons show that the fauna is composed of species occurring exclusively in pelagic limestones of the western Tethys. By contrast, it shows no relationships with the coeval faunas of the adjacent Trento platform and of the other western Tethyan carbonate platforms. These lines of evidence and the facies analysis would testify to the Pliensbachian drowning of the eastern margin of the Trento platform. In the wider context of the palaeobiogeographical history of Early Jurassic western Tethyan gastropods, the species from Vedana belong to a faunal stock which is typical for pelagic, mainly postdrowning sediments. Thus, appearance and diffusion in space and time of this stock were probably regulated by the direction, rate and pattern of the Neotethyan rifting. A new subgenus, Proarcirsa (Schafbergia) subgen. nov., and three new species, namely Ataphrus (Ataphrus) cordevolensis sp. nov., Guidonia pseudorotula sp. nov. and Proarcirsa (Schafbergia) zirettoensis sp. nov. are erected.     

Selective feeding by the aquatic oligochaete Tubifex tubifex (Tubificidae,Clitellata)

The particle size distribution of faecal pellets produced by the tubificid worm Tubifex tubifex in laboratory culture, was measured with a Coulter® Multisizer. The faecal material from worms cultured in a range of sediments was composed of particles with a mean diameter of less than 63 m, and only a few isolated larger particles were found by microscopic analysis. This suggests that this species actively selects the silt-clay fraction, avoiding larger sand particles. A more detailed analysis of faeces revealed that about 75%, by volume, was composed of particles with a mean diameter < 25m, and the mode was < 10m. T. tubifex fed selectively on the organic rich particles of the sediment, and this feeding was independent of particle size. Measurement of the organic content of faeces (measured as % loss on ignition) showed that they had a consistently higher organic content than the sediment, considered as whole sediments or the <63 m sieved fraction. On the basis of these results, we hypothesise that this species exhibits two levels of selectivity in its feeding behaviour. Thus selection is primarily based on particle size, avoiding the ingestion of sand particles and also, on the preferential selection of particles associated with organic material, within the fine (silt-clay) fraction of the sediment.     

Influence of quantity and lability of sediment organic matter on the biomass of two isoetids,Littorella uniflora and Echinodorus repens

1. Despite real improvement in the water quality of many previously eutrophic lakes, the recovery of submerged vegetation has been poor. This lack of recovery is possibly caused by the accumulation of organic matter on the top layer of the sediment, which is produced under eutrophic conditions. Hence, our objective was to study the combined effects of quantity and lability of sediment organic matter on the biomass of Echinodorus repens and Littorella uniflora and on the force required to uproot plants of L. uniflora. 2. Lake sediments, rich in organic matter, were collected from four lakes, two with healthy populations of isoetids and two from which isoetids had disappeared. The four lake sediments were mixed with sand to prepare a range of experimental sediments that differed in quantity and lability of sediment organic matter. Two isoetid species, E. repens and L. uniflora, were grown in these sediments for 8 weeks. Sediment quality parameters, including elemental composition, nutrient availability and mineralisation rates, were determined on the raw sources of sediment from the lakes. Porewater and surface water were analysed for the chemical composition in all mixtures. At the end of the experiment, plants were harvested and their biomass, tissue nutrient concentration and (for L. uniflora) uprooting force were measured. 3. For both species, all plants survived and showed no signs of stress on all types of sediment. The biomass of E. repens increased as the fraction of organic matter was increased (from 6 to 39% of organic content, depending upon sediment type). However, in some of the sediment types, a higher fraction of organic matter led to a decline in biomass. The biomass of L. uniflora was less responsive to organic content and was decreased significantly only when the least labile sediment source was used to create the gradient of organic matter. The increase in shoot biomass for both species was closely related to higher CO₂ concentrations in the porewater of the sediment. The force required to uproot L. uniflora plants over a range of sediment organic matter fitted a Gaussian model; it reached a maximum at around 15% organic matter and declined significantly above that. 4. Increasing organic matter content of the sediment increased the biomass of isoetid plants, as the positive effects of higher CO₂ production outweighed the negative effects of low oxygen concentration in more (labile) organic sediments. However, sediment organic matter can adversely affect isoetid survival by promoting the uprooting of plants.     

Preliminary study of the development of the subfossil chironomid fauna (Diptera) of Lake Taylor,South Island,New Zealand,during the younger Holocene

The composition and succession of the subfossil chironomid fauna has been studied in a sediment core from Lake Taylor. The sediments of the core are all within the Nothofagus phase of the last 3000 years within the Aranuian. In the older sediments of the core the chironomid fauna was dominated by Tanytarsini and Orthocladiinae whereas Chironomini dominated in the more recent sediments. The species diversity is very high compared with the results of other studies of the recent chironomid fauna of lakes in the South Island. The most abundant head capsules belong to the taxa Chironomus zealandicus, Tanytarsus vespertinus, Corynocera sp., and Eukiefferiella sp. Several additional taxa which have not yet been described also occurred in large numbers. It is not possible to correlate any definite changes in the composition of the subfossil chironomid fauna with a change in climatic conditions or the trophic status of the lake.     

Influence of natural amphipod (<Emphasis Type="Italic">Victoriopisa</Emphasis><Emphasis Type="Italic">australiensis</Emphasis>) (Chilton, 1923) population densities on benthic metabolism,nutrient fluxes,denitrification and DNRA in sub-tropical estuarine sediment

The influence of natural populations of the sub-surface deposit-feeding amphipod Victoriopisa australiensis on sediment biogeochemistry was assessed by randomly collecting 21 sediment cores in a zone of Coombabah Lake, southern Moreton Bay, Australia, where the benthic infauna was dominated by this species. Cores were incubated sequentially to determine sediment–water column fluxes of oxygen, dissolved inorganic carbon and inorganic N species, followed by incubations to determine rates of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) using the isotope pairing technique. Finally, each core was sieved in order to determine the population and biomass of amphipods present. Whilst all measures of overall benthic metabolism (sediment oxygen demand, and effluxes of inorganic carbon and nitrogen) showed increased with amphipod density, with rates being stimulated 70–220% at the highest categorised density range of 2,500–3,500 ind m⁻², only the correlation with dissolved inorganic carbon was statistically significant. In contrast, there were no discernable trends between amphipod densities and any of the N-cycle processes with the slopes of all correlations being very close to zero. These results highlight the differences in mesocosm simulations of fauna effects, which primarily relate to shifts in rates of organic matter turnover, compared to natural sediments where fauna effects relate more to induced changes in rates of organic matter deposition. Therefore, while mesocosms represent a powerful tool to investigate the mechanisms by which fauna influences microbial metabolism in the sediment, only studies of natural sediments can determine to what extent these mechanisms function in situ. Handling editor: Pierluigi Viaroli     

Predation,sediment stability and food availability as determinants of the benthic invertebrate fauna in two shallow lakes

The sedimentary benthos of a series of shallow, eutrophicated lakes, the Norfolk Broads is, in general, low not only in number of species but unexpectedly in number of individuals. In two of the lakes, Hudsons Bay and Hoveton Great Broad, chironomids and oligochaetes dominated the fauna. Hudsons Bay has an extensive stand of water lilies (Nuphar lutea); Hoveton Great Broad does not. There were significant relationships between number of chironomids and of Potamothrix hammoniensis with organic content of the sediments, but these were due not to food availability but to the structure imparted to the otherwise fluid sediment by the organic matter. Sediment stabilised in plastic bowls developed much larger populations of oligochaetes than found in the unrestricted sediment. Protection of the community from fish predation resulted in a further major increase in numbers. Sediment stability and predation rather than food supply were the major determinants of these benthic populations.     

Subtropical coral-reef associated sedimentary facies characterized by molluscs (Northern Bay of Safaga, Red Sea, Egypt)

Summary The shallow marine subtropical Northern Bay of Safaga is composed of a complex pattern of sedimentary facies that are generally rich in molluscs. Thirteen divertaken bulk-samples from various sites (reef slopes, sand between coral patches, muddy sand, mud, sandy seagrass, muddy seagrass, mangrove channel) at water depths ranging from shallow subtidal to 40m were investigated with regard to their mollusc fauna >1mm, which was separated into fragments and whole individuals. Fragments make up more than 88% of the total mollusc remains of the samples, and their proportions correspond to characteristics of the sedimentary facies. The whole individuals were differentiated into 622 taxa. The most common taxon,Rissoina cerithiiformis, represented more than 5% of the total mollusc content in the samples. The main part of the fauna consists of micromolluscs, including both small adults and juveniles. Based on the results of cluster-, correspondence-, and factor analyses the fauna was grouped into several associations, each characterizing a sedimentary facies: (1) “Rhinoclavis sordidula—Corbula erythraeensis-Pseudominolia nedyma association” characterizes mud. (2) “Microcirce sp.—Leptomyaria sp. association” characterizes muddy sand. (3)”Smaragdia spp.-Perrinia stellata—Anachis exilis—assemblage” characterizes sandy seagrass. (4) “Crenella striatissima—Rastafaria calypso—Cardiates-assemblage” characterizes muddy seagrass. (5) “Glycymeris spp.-Parvicardium sueziensis-Diala spp.-assemblage” characterizes sand between coral patches. (6) “Rissoina spp.-Triphoridae —Ostreoidea-assemblage” characterizes reef slopes. (7) “Potamides conicus—Siphonaria sp. 2—assemblage” characterizes the mangrove. The seagrass fauna is related to those of sand between coral patches and reef slopes with respect to gastropod assemblages, numbers of taxa and diversity indices, and to the muddy sand fauna on the basis of bivalve assemblages and feeding strategies of bivalves. The mangrove assemblage is related to those of sand between coral patches and the reef slope with respect to taxonomic composition and feeding strategies of bivalves, but has a strong relationship to those of the fine-grained sediments when considering diversity indices. Reef slope assemblages are closely related to that of sand between coral patches in all respects, except life habits of bivalves, which distincly separates the reef slope facies from all others.     

Inhibition of Chara vulgaris oospore germination by sulfidic sediments

The germinability of Chara vulgaris oospores collected from the sediments of four Ontario lakes varies considerably, ranging in germination percentage from 7% to 54%. Chemical analysis of the interstitial water of the sediments indicated that oospores with low germination occurred in lakes which have high acid volatile sulfides (H₂S, FeS, HS⁻) and high soluble Fe²⁺. The inhibitory effects of sediment on oospore germination were demonstrated by transplant experiments, and suggested that sulfide was the toxic agent. Exposure of high-germinating sedimentary oospores to free sulfide concentrations greater than 2.0 mM caused a greater than 30% reduction in oospore germination. The presence of sulfide in sediments was shown to result from sulfate reduction by bacteria in sediment pore water of those lakes where oospore viability was lowest. Differences in oospore germination percentage appear, therefore, to be due to the toxicity of H₂S produced in the sediment, either by a direct effect on the oospore, or on the parent plants.     

The role of sediment type in growth and fecundity of mud snails (Hydrobiidae)

Summary We test the hypothesis that body size and population density of the deposit-feeding gastropod, Hydrobia truncata, are greater in muddy than in sandy habitats as a result of faster growth on fine- compared to coarse-grained sediments. We refute this hypothesis using a combination of field measurements and laboratory experiments. Three out of three populations tested had higher maximal growth rates and two of three populations approached their asymptotic size more quickly on sand than on silt-clay fractions of natural sediment. Growth decreased with increasing snail density and was as high or higher on sand as on silt-clay at all densities. Two populations were more fecund on sand than on silt-clay, and fecundity of the third population was not affected by sediment type. We show that the smaller body sizes observed in snails from the sandiest habitat result from late recruitment of these snails, relative to the other populations.     

Distribution and diversity of sipunculan fauna in high Arctic fjords (west Svalbard)

Sipuncula is a relatively species poor and generally rarely investigated phylum; nonetheless, it may play a considerable role in the ecosystem. During this study sipunculan species distribution patterns in four fjords of west Spitsbergen (Kongsfjorden, Hornsund, Isfjorden and van Mijenfjorden) were examined. Material was collected during ten cruises undertaken from 1997 to 2006. A total of 381 samples were taken at 132 stations located in the four fjords and, a total number of 920 sipunculans specimens were found in 114 of those samples. The highest sipunculan species richness was observed in Hornsund (six species), followed by Kongsfjorden and Isfjorden (five species in each fjord). Sipunculan fauna in all fjords was strongly dominated by Golfingia vulgaris (80% of all sipunculan individuals in Kongsfjorden), and Golfingia margaritacea (84% in van Mijenfjorden and 40% in Hornsund) or Nephasoma diaphanes (54% in Isfjorden). Locally, sipunculans were found in high densities (max. 62 ind. 0.1 m⁻² and up to 11% of macrobenthic densities) and biomass (max. 110.87 g 0.1 m⁻² and up to 80% of total fauna biomass). At such sites, sipunculans may play an important role in bioturbation of sediments and as a food source for higher trophic levels. Sipunculans did not occur within close proximity of the glacier where they might be eliminated due to high sedimentation rate and low amounts of organic matter. Because of their importance in benthic systems, a need to include sipunculans in routine macrobenthic surveys is emphasized.