Effect of detritus supply on trophic relationships within experimental benthic food webs. I. Meiofauna-polychaete (capitella capitata (Type I) Fabricius) interactions

In a long-term (40–55 wk) microcosm experiment, the presence of the polychaete Capitella capitata (Type I) Fabricius reduced population densities and trophic transfer efficiencies (detritivore production per amount of detritus supplied) of the nematode Diplolaimella chitwoodi Gerlach at high (150 mg N · m^?2 · day^?1) detritus ration and of the harpacticoid copepod Tisbe holothuriae Humes at low (50 mg N · m^?2 · day^?1) detritus supply. The rarer nematodes Theristus ostentator Wieser & Hopper and Paracyatholaimus pesavis Wieser & Hopper fed at depth on fungal hyphae attached to polychaete fecal pellets thereby minimizing contact with the other metazoa.In a series of short-term (4-day) growth experiments, the presence of either Diplolaimella chitwoodi or Tisbe holothuriae reduced daily weight-specific growth (g increase · g worm^?1 · day^?1) of Capitella capitata on separate diets of mixed cereal and red seaweed, Gracilaria foliifera (Harvey) Taylor, detritus.Both sets of experiments suggest that Capitella capitata competes for food with Diplolaimella chitwoodi and Tisbe holothuriae. Meiofauna-polychaete interactions were dependent, in part, upon the degree of similarity among species in food requirements and habitat preferences, and may incorporate a variety of regulatory mechanisms other than competition or predation.     

Replacement of native seagrass with invasive algal detritus: impacts to estuarine sediment communities

Biological invasions modify the quality and supply of detrital subsidies to aquatic and terrestrial ecosystems. Where the invader has very different traits to native species, major changes in associated consumer communities may result, as a consequence of differences in their nutritional value and effects on the sedimentary habitat. We assessed how the replacement of seagrasses with the invasive alga Caulerpa taxifolia in modified Australian estuaries influences invertebrate communities of mudflats that are subsidized by detritus from submerged aquatic vegetation. Two months after experimental enrichment of sediments with high (60?g dry weight per 0.25?m² plot) or low (30?g dry weight) quantities of either non-native C. taxifolia or native Posidonia australis or Zostera capricorni detritus, there were positive effects of detrital addition on invertebrate abundance that occurred irrespective of the resource added. By 4?months after addition, however, detritus from invasive C. taxifolia had produced effects on benthic communities that could not be replicated by detritus from either of the native seagrasses. Plots receiving the high loading of C. taxifolia detritus contained fewer invertebrates than plots of the other treatments, perhaps due to the induction of sediment hypoxia. The pattern, however, reversed at low detrital loading, with the plots receiving 30?g of C. taxifolia containing more invertebrates and more taxa than the other plots, presumably due to the greater resource availability for detritivores. Our results demonstrate that replacement of native seagrass with invasive algal detritus can have large impacts on sediment-dwelling communities.     

Effects of aquatic vegetation type on denitrification

In a microcosm ¹⁵N enrichment experiment we tested the effect of floating vegetation (Lemna sp.) and submerged vegetation (Elodea nuttallii) on denitrification rates, and compared it to systems without macrophytes. Oxygen concentration, and thus photosynthesis, plays an important role in regulating denitrification rates and therefore the experiments were performed under dark as well as under light conditions. Denitrification rates differed widely between treatments, ranging from 2.8 to 20.9 ??mol N m^?2 h^?1, and were strongly affected by the type of macrophytes present. These differences may be explained by the effects of macrophytes on oxygen conditions. Highest denitrification rates were observed under a closed mat of floating macrophytes where oxygen concentrations were low. In the light, denitrification was inhibited by oxygen from photosynthesis by submerged macrophytes, and by benthic algae in the systems without macrophytes. However, in microcosms with floating vegetation there was no effect of light, as the closed mat of floating plants caused permanently dark conditions in the water column. Nitrate removal was dominated by plant uptake rather than denitrification, and did not differ between systems with submerged or floating plants.     

Some structural and functional aspects of the epiphytic component of four seagrass species (Cymodoceoideae) from Papua New Guinea

The epiphytic component of four monospecific seagrass beds from Papua New Guinea was studied structurally and functionally. The floristic composition and abundance of the epiphytes on leaves of four seagrass species (Cymodoceoideae) showed considerable variation, but on all four seagrass species, the same algae were among the five quantitatively most important epiphytes: encrusting coralline algae, Cyanophyta, Ceramium gracillimum (Harv.) Mazoyer, Polysiphonia savatierii Hariot and Audouinella spp. The temporal pattern of the epiphytic algae showed more or less the same features on the four seagrass species.Annual mean biomass of epiphytes and seagrass leaves ranged from 54 g ADW m^?2 in a community of Cymodocea rotundata Ehrenb. and Hempr. ex Aschers. to 169 g ADW m^?2 in a community of Syringodium isoetifolium (Aschers.) Dandy. The contribution of the epiphytic component to the total above-ground biomass ranged from 22 to 24%. Productivity of epiphytes was highest on leaves of Halodule uninervis (Forssk.) Aschers. (2.12 g ADW m^?2 sediment surface day^?1) and the epiphytic community contributed 35–44% of the total above-ground production of these four seagrass communities.     

A quantitative diving survey of benthic vegetation and fauna in Lake Kariba, a tropical man-made lake

SUMMARY. 1. The biomass distribution of submerged vascular vegetation and benthic fauna were investigated by diving in Lake Kariba. The vegetation was well correlated with transparency of the water. Maximum biomass (1400 g dryweight m^?2) and a depth penetration of 6 m were found in areas little influenced by river inflow, while these were only 110 g m^?2 and 2 m, respectively, in the basin receiving water from the Zambezi river. 2. The lake is mesotrophic-oligotrophic. The total biomass for the lake was 101,000 tons dryweight of rooted vegetation composed of Lagarosiphon ilicifolius Oberm. (52%), Najas pectinata (Parl) Magnus (33%), Vatlisneria aethiopica Frenzl (11%), Ceratophyllum demersum L. (3%) and Potamogeton octandrus L. (0.5%). Average plant biomass for the potentially colonizable depth zone of 0-12 m and for the total lake amounted to 79.9 g m^?2 and 18.8 g m^?2, respectively. 3. The distribution of the benthic fauna generally followed that of the vegetation. The total animal biomass of 118,840 tons dryweight. including shells, consisted of mussels (95.8%), snails (4.1%) and insect larvae (0.1%). Four species of mussels were found: Caelatura mossambicensis (von Martens) (81% of mussel biomass), Corbicula africana (Krauss) (9%). Mutela dubia (Gmelin) (5%) and Aspatharia wahlbergii (Krauss) (5%). Among the snails Melnoides tuberculuta (Müller), Cleopatra spp. and Bellamya capillata (Frauenfeld) dominated. 4. The average animal biomass was high compared to most other lakes perhaps due to lack of predators. For the colonizable 0-12 m depth interval and the total lake it was 96.2 g m^?2 including shells (15.0 g m^?2 shell-free dryweight) and 22.6 g m^?2 including shells (3.4 g m^?2 shell-free dryweight). respectively. Biomass of plants and animals was even higher prior to the recent lowering of the water level by 7 m, which was estimated to have stranded 84,000 tons of mussels on the shore.     

Meiofauna and macrofauna communities in a mangrove from the Island of Santa Catarina, South Brazil

The composition and abundance of the meiofauna and macrofauna were studied in a survey carried out within 6 locations in a mangrove at the Island of Santa Catarina, South Brazil. Nine meiofaunal taxa were registered with densities ranging between 77 and 1589 inds.10 cm^?2. The nematodes, composed by 94 putative species (86 genera), largely dominated the meiofauna. The most abundant genera were Haliplectus (Haliplectidae), Anoplostoma (Anoplostomatidae) and Terschillingia (Linhomoidae). Contrary to the meiofauna, the macrofauna showed a low number of taxa (only 17 recorded) and abundance (up 7250 inds.m^?2). The macrofauna was mainly composed by deposit feeders, and numerically dominated by oligochaetes and capitellid polychaetes. For both components, differences in the composition and abundance along the sampling sites were significant but not primarily related to the typical variations along estuaries, such as salinity. The results of the stepwise multiple regression analyses showed that the detritus biomass (ash-free dry weight) was the most important predictor of faunal densities and diversity. The clear relationship between detritus and fauna, together with the contrasting community structure of the two component of the benthos suggest that the meiofauna showed a high efficiency in exploiting the micro-habitat created by the presence of the detritus. Yet the macrofauna, potentially the main consumer of the debris, is negatively affected by their low palatability and poor nutritive value.     

Above- and belowground dynamics of plant community succession following abandonment of farmland on the Loess Plateau, China

Aboveground and belowground changes during vegetation restoration and vegetation successions need to be characterized in relation to their individual responses to changes in soil resources. We examined above- and belowground vegetation characteristics, soil moisture, and nutrient status at the end of the growing season in 2006 in plots with vegetation succession ages of 2, 4, 6, and 8 years (two replicates each) that had been established on abandoned cropland, where potatoes had been grown for 3 years, using hoe and plow cultivation, immediately prior to vegetation clearance and subsequent natural plant colonization. A plant community comprising pioneer species [e.g., Artemisia capillaries, (subshrub)] was characterized by low levels of species richness (7.5?±?1.4 species m^?2), plant density (35.7?±?4.2 stems m^?2), fine root length density (940.1?±?90.1 m m^?2), and root area density (2.3?±?0.3 m² m^?2) that increased rapidly with time. Aboveground and belowground characteristics of both A. capillaries and the later successional species, Stipa bungeana (C3 perennial grass), increased in the first 6 years, but in the following 2 years A. capillaries declined while S. bungeana thrived. Thus, the fine root length density of A. capillaries, 812.4 m m^?2 after 2 years, changed by a factor of 1.7, 2.0, and 0.4 in the 4th, 6th, and 8th years, whereas that of S. bungeana changed from 278.4 m m^?2, after 4 years, and by 1.7 and 23.3 times in the 6th and 8th years, respectively. Secondary vegetation succession resulted in reduced soil moisture contents. Soil available P and N mainly influenced aboveground characteristics, while soil moisture mainly influenced belowground characteristics. However, soil moisture had no significant affect on S. bungeana belowground characteristics at the population level in this semiarid region.     

Flux of lead in submerged plants and its relevance to a freshwater system

The fluxes of lead in submerged freshwater angiosperms, mosses and benthic algae were investigated by laboratory and field observations. Laboratory experiments showed that the initial uptake of lead by angiosperm shoots and Navicula sp. was rapid (up to 0.07 mg Pb g^?1 dry weight min ^?1 from a solution containing 1.0 mg Pb l^?1), and over-whelmingly passive. Mosses were especially efficient at sorbing lead from solutions containing less than 1.0 mg Pb l^?1 . Rates of uptake increased with rising external concentrations, but decreased with time. Anatomical and morphological characteristics of plant tissues affected metal flux and an epiphytic covering of Navicula (i.e., an Aufwuchs community) sorbed metal and reduced uptake into tissues by a third. Up to 90% of the lead sorbed in the first hour by shoots of Elodea canadensis Michx from a solution containing 1.0 mg Pb l^?1 was released within 14 days of transfer into a lead-free medium; 10% was irreversibly bound.Moss monitors placed in Ullswater, a lake with sediments containing up to 26 mg Pb g^?1 dry weight, confirmed that the metal is brought into circulation during turbulence, but not in periods of calm. Shoots of Elodea collected from the lake contained up to 0.3 mg g^?1 dry weight non-exchangeable lead. Young shoots tended to contain less than older shoots (0.12 compared with 0.3 mg Pb g^?1), and leaf more than stem tissues. The fluxes of lead from the environment through Aufwuchs and submerged plants are discussed.     

Resource dynamics and detritivore production in an acid stream

1. Life history patterns and production of eight shredder‐detritivore species were studied in relation to the detritus dynamics of a small acidic stream in England. Mean annual detritus inputs (direct and lateral sources combined) were approximately 400 g m^?2 year^?1 and showed significant seasonal and annual variation. 2. Detritus standing stock did not increase significantly during times of high input, reflecting low retention efficiency. However, the mean detritus standing stock was relatively large (108 g m^?2) reflecting a slow decomposition rate typical of acid streams. 3. Four species were univoltine with highly synchronous patterns of emergence and recruitment (Leuctra inermis, Leuctra hippopus, Capnia vidua and Amphinemura sulcicollis). Two species were univoltine with extended patterns of emergence and recruitment (Nemoura cinerea, Potamophylax cingulatus). Leuctra nigra was apparently semivoltine, while Protonemura meyeri showed two successive cohorts in the second year of the study, suggesting either bivoltinism or cohort splitting. 3. Secondary production of the dominant shredders was 1.67 g m^?2 year^?1 in 1997 and 1.99 g m^?2 year^?1 in 1998, which is low compared with other small European streams. This was probably because of an impoverished invertebrate community and poor food quality associated with acid conditions. Food availability probably did not account for the low production as the detritus standing stock far exceeded the estimated shredder ingestion of 42–50 g m^?2 year^?1. 4. Despite low overall shredder production, species‐specific production was high, possibly because of competitive release in this species‐poor acid stream. Periods of high production and growth showed no relationship with detritus availability but were closely related to life history.     

Epiphytes of the St. Lucia Estuary and their response to water level and salinity changes during a severe drought

St. Lucia is the largest estuary in South Africa with extensive areas of submerged macrophytes that fluctuate rapidly in response to water level and salinity changes. Epiphytes associated with submerged macrophytes were sampled during a severe drought between November 2004 and October 2005 when very low water level and high, variable salinity characterised the estuary. Potamogeton pectinatus and Ruppia cirrhosa were the dominant submerged macrophytes throughout the estuary, with P. pectinatus occurring at relatively low salinity (∼10 ppt) and R. cirrhosa at higher salinity (9–33 ppt). Zostera capensis, normally the other dominant submerged macrophyte, was conspicuously absent under the prevailing conditions. Epiphytic biomass, estimated as chlorophyll a, varied greatly between sites and over the 12 month sampling period, ranging from 10.9 to 71.7 mg Chl a m⁻² leaf area for P. pectinatus and 16.9–165.0 mg Chl a m⁻² leaf area for R. cirrhosa. Epiphytic biomass was twice as high in the Southern Lake where R. cirrhosa occurred, probably because the dominant epiphytes were macroalgae. An assessment of the diatom species composition of the epiphytic community indicated the dominance of only six species throughout the estuary. Neither epiphytic biomass nor diatom species composition showed strong statistical relationships with the environmental variables measured and it is believed that biological factors may be more important than the physico-chemical environment in determining epiphyte biomass distribution. Because epiphyte biomass is dependent on the presence of host surface area it will only contribute substantially to overall system biomass and productivity when submerged macrophyte area cover is high. In the St. Lucia Estuary this will occur when the water level is high and the upper level of the salinity gradient does not increase above that of seawater.     

SHADE ADAPTED BENTHIC DIATOMS BENEATH ANTARCTIC SEA ICE1

A dense community of shade adapted microalgae dominated by the diatom Trachyneis aspera is associated with a siliceous sponge spicule mat in McMurdo Sound, Antarctica. Diatoms at a depth of 20 to 30 m were found attached to spicule surfaces and in the interstitial water between spicules. Ambient irradiance was less than 0.6 μE · m^?2· s^?1 due to light attenuation by surface snow, sea ice, ice algae, and the water column. Photosynthesis-irradiance relationships determined by the uptake of NaH¹⁴CO₃ revealed that benthic diatoms beneath annual sea ice were light-saturated at only 11 μE·m^?2·s^?1, putting them among the most shade adapted microalgae reported. Unlike most shade adapted microalgae, however, they were not photoinhibited even at irradiances of 300 μE·m^?2·s^?1. Although in situ primary production by benthic diatoms was low, it may provide a source of fixed carbon to the abundant benthic invertebrates when phytoplankton or ice algal carbon is unavailable.     

Biodiversity of settled material in a sediment trap in the Gulf of Trieste (northern Adriatic Sea)

Phytoplankton succession and sinking rates were studied from January to December 2003 at a coastal station in the Gulf of Trieste (northern Adriatic Sea), 200 m offshore, in a relatively undisturbed area. A conical sediment trap, moored at 15 m depth (water depth 17 m), was used. The hypothesis if the presence of benthic and epiphytic diatoms can lead to an overestimation of the vertical fluxes was tested. To evaluate primary and secondary sedimentation contributions, planktonic, benthic and epiphytic diatoms were distinguished. Benthic species abundance varied throughout the year and it was related to resuspension that strongly influenced sinking rates. All over the year, diatoms were the prevailing class in the trap material accounting for 75.32% of the settled cells, while flagellates represented 24.11%. Dinophyceae and resting cells constituted minor components, accounting for 0.43% and 0.14%, respectively. The gross sedimentation rates ranged from 0.006 × 10⁸ cell m⁻² d⁻¹ in the second week of May to 6.30 × 10⁸ cell m⁻² d⁻¹ in the third week of January with a mean annual value of 1.09 ± 1.43 × 10⁸ cell m⁻² d⁻¹. To the primary sedimentation rate Pseudo-nitzschia seriata of the group “Nitzschia seriata complex” contributed for 49.77% followed by Chaetoceros spp. (23.88%). The major contributor to the secondary sedimentation rate was the diatom Paralia sulcata, accounting for 24.76%. Epiphytic diatoms contributed for 11.19% and 12.27% on annual average gross abundance and biomass, respectively, reaching even 72.04% of gross abundance and 56.06% of gross biomass in the second week of August. The correlation between temperature and the logarithm of the epiphytic biomass was statistically significant, with r = 0.66 and P < 0.001. Both in the cluster analysis and in the PCA four main groups were formed, where benthic and epiphytic species were separately gathered. Planktonic, benthic and epiphytic forms accounted for 50.78%, 36.95% and 12.27%, respectively, calculated on the annual average biomass. Therefore, vertical fluxes can be overestimated of 50% or more if benthic and epiphytic species are not rejected.     

Effect of detritus supply on trophic relationships within experimental benthic food webs. II. Microbial responses,fate and composition of decomposing detritus

The dynamics of bacterial, protozoan and fungal populations were examined in a long-term (40–55 wk) microcosm experiment designed to assess the effects of detritus supply on meiofauna-polychaete (Capitella capitata (Type I) Fabricius) interactions. Bacterial and protozoan numbers and bacterial growth rates were inversely correlated with population fluctuations of the polychaete at low (50 mg N · m^?2 · day ^?1) detritus supply, but did not correlate with fluctuating polychaete densities at two higher (100 and 150 mg N · m^?2 · day^?1) ration levels of detritus. Bacterial and protozoan numbers and bacterial growth rates did not correlate with standing amounts of detritus or with fungi or meiofauna at any of the detritus rations. Fungi were associated primarily with aggregates of detritus particles and fecal pellets produced by C. capitata.Labile (fiber-free) organic matter did not correlate with microbes or meiofauna, but was inversely correlated with population fluctuations of the polychaete C. capitata at all three ration levels of detritus. Polychaete fecal pellets accounted for most of the refractory matter in the tanks with C. capitata and did not accumulate in the sediments, suggesting that fecal pellets were continually being produced, broken apart and decomposed.Our experiments suggest that contradictions in previous studies on the effects of macroconsumers on microbes, especially bacteria, can be explained as a failure to consider the effects of detritus supply on microbial growth rates.     

Particulate organic matter in a mountain stream in the south-western Cape,South Africa

The quality and quantity of allochthonous inputs and of benthic organic matter were investigated in a second-order, perennial mountain stream in the south-west Cape, South Africa, between April 1983 and January 1986. Although the endemic, riparian vegetation is sclerophyllous, low and evergreen, inputs of allochthonous detritus to the stream (434 to 500 g m^–2y^–1) were similar to those recorded for riparian communities worldwide, as were calorific values of these inputs (9548 to 10 032 KJ m^–2y^–1). Leaf fall of the riparian vegetation is seasonal, occurring in spring (November) as discharge decreases, resulting in retention of benthic organic matter (BOM) on the stream bed during summer and early autumn (maximum 224 g m^–2). Early winter rains (May) scoured the stream almost clean of benthic detritus (winter minimum 8 g m^–2). Therefore, BOM was predictably plentiful for about half of each year and predictably scarce for the other half. Coarse BOM (CBOM) and fine BOM (FBOM) constituted 46–64% of BOM standing stock, ultra-fine BOM (UBOM) 16–33% and leaf packs 13–24%. The mean annual calorific value of total BOM standing stock was 1709 KJ m^–2. Both standing stocks and total calorific values of BOM were lower than those reported for streams in other biogeographical regions. Values of C:N ratios decreased with decrease in BOM particle size (CBOM 27–100; FBOM 25–27; UBOM 13–19) with no seasonal trends. The stream is erosive with a poor ability to retain organic detritus. Its character appears to be dictated by abiotic factors, the most important of which is winter spates.     

Export of invertebrates and detritus from fishless headwater streams in southeastern Alaska: implications for downstream salmonid production

1. We examined the export of invertebrates (aquatic and terrestrial) and coarse organic detritus from forested headwaters to aquatic habitats downstream in the coastal mountains of southeast Alaska, U.S.A. Fifty‐two small streams (mean discharge range: 1.2–3.6 L s^?1), representing a geographic range throughout southeast Alaska, were sampled with 250‐μm nets either seasonally (April, July, September) or every 2 weeks throughout the year. Samples were used to assess the potential subsidy of energy from fishless headwaters to downstream systems containing fish. 2. Invertebrates of aquatic and terrestrial origin were both captured, with aquatic taxa making up 65–92% of the total. Baetidae, Chironomidae and Ostracoda were most numerous of the aquatic taxa (34, 16 and 8%, respectively), although Coleoptera (mostly Amphizoidae) contributed the greatest biomass (30%). Mites (Acarina) were the most numerous terrestrial taxon, while terrestrial Coleoptera accounted for most of the terrestrial invertebrate biomass. 3. Invertebrates and detritus were exported from headwaters throughout the year, averaging 163 mg invertebrate dry mass stream^?1 day^?1 and 10.4 g detritus stream^?1 day^?1, respectively. The amount of export was highly variable among streams and seasons (5–6000 individuals stream^?1 day^?1 and <1–22 individuals m^?3 water; <1–286 g detritus stream^?1 day^?1 and <0.1–1.7 g detritus m^?3 water). Delivery of invertebrates from headwaters to habitats with fish was estimated at 0.44 g dry mass m^?2 year^?1. We estimate that every kilometre of salmonid‐bearing stream could receive enough energy (prey and detritus) from fishless headwaters to support 100–2000 young‐of‐the‐year (YOY) salmonids. These results illustrate that headwaters are source areas of aquatic and terrestrial invertebrates and detritus, linking upland ecosystems with habitats lower in the catchment.     

EFFECT OF SEASONAL SEA ICE BREAKOUT ON THE PHOTOSYNTHESIS OF BENTHIC DIATOM MATS AT CASEY,ANTARCTICA1

Photosynthesis of marine benthic diatom mats was examined before and after sea ice breakout at a coastal site in eastern Antarctica (Casey). Before ice breakout the maximum under‐ice irradiance was between 2.5 and 8.2 μmol photons·m^?2·s^?1 and the benthic microalgal community was characterized by low E_k (12.1–32.3 μmol photons·m^?2·s^?1), low relETR_max (9.2–32.9), and high alpha (0.69–1.1). After breakout, 20 days later, the maximum irradiance had increased to between 293 and 840 μmol photons·m^?2·s^?1, E_k had increased by more than an order of magnitude (to 301–395 μmol photons·m^?2·s^?1), relETR_max had increased by more than five times (to 104–251), and alpha decreased by approximately 50% (to 0.42–0.68). During the same time interval the species composition of the mats changed, with a decline in the abundance of Trachyneis aspera (Karsten) Hustedt, Gyrosigma subsalsum Van Heurck, and Thalassiosira gracilis (Karsten) Hustedt and an increase in the abundance of Navicula glaciei Van Heurck. The benthic microalgal mats at Casey showed that species composition and photophysiology changed in response to the sudden natural increase in irradiance. This occurred through both succession shifts in the species composition of the mats and also an ability of individual cells to photoacclimate to the higher irradiances.     

The role and contribution of the seagrass Posidonia oceanica (L.) Delile organic matter for secondary consumers as revealed by carbon and nitrogen stable isotope analysis

The δ¹³C and δ¹⁵N values of primary producers and consumers were studied to obtain information on the trophic role of Posidonia oceanica L. Delile, the dominant primary producer, in a Mediterranean shallow environment (the Stagnone di Marsala, western Sicily). δ¹³C strongly discriminated between pelagic and benthic pathways, with the former based on phytoplankton and the latter on a mixed pool of seagrass detritus, epiphytes and benthic algae as carbon sources. A particularly important trophic role appears to be performed by the vegetal epiphytic community on seagrass leaves (δ¹³C = –14.9 ± 0.1‰), which supports most of the faunal seagrass community (i.e. Amphipoda, Isopoda, Tanaidacea; δ¹³C = –14.9 ± 0.1‰, –12.5 ± 0.1‰ and –14.8 ± 1.0‰, respectively). Although P. oceanica (δ¹³C = –11.3 ± 0.3‰) does not seem to be utilised by consumers via grazing (apart from a few Palaemonidae species with δ¹³C value of –10.8 ± 1.8‰), its trophic role may be via detritus. P. oceanica detritus may be exploited as a carbon source by small detritivore invertebrates, and above all seems to be exploited as a nitrogen reservoir by both bottom and water column consumers determining benthic–pelagic coupling. At least three trophic levels were detected in both the pelagic (mixture of phytoplankton and cyanobacteria, zooplankton, juvenile transient fish) and benthic (sedimentary organic matter and epiphytes, small seagrass-associated invertebrates, larger invertebrates and adult resident fish) pathways.     

Urea Transformation of Wetland Microbial Communities

Transformation of urea to ammonium is an important link in the nitrogen cycle in soil and water. Although microbial nitrogen transformations, such as nitrification and denitrification, are well studied in freshwater sediment and epiphytic biofilm in shallow waters, information about urea transformation in these environments is scarce. In this study, urea transformation of sedimentary, planktonic, and epiphytic microbial communities was quantified and urea transformation of epiphytic biofilms associated with three different common wetland macrophyte species is compared. The microbial communities were collected from a constructed wetland in October 2002 and urea transformation was quantified in the laboratory at in situ temperature (12°C) with the use of the ¹⁴C-urea tracer method, which measures the release of ¹⁴CO₂ as a direct result of urease activity. It was found that the urea transformation was 100 times higher in sediment (12–22 mmol urea-N m⁻² day⁻¹) compared with the epiphytic activity on the surfaces of the submerged plant Elodea canadensis (0.1–0.2 mmol urea-N m⁻² day⁻¹). The epiphytic activity of leaves of Typha latifolia was lower (0.001–0.03 mmol urea-N m⁻² day⁻¹), while urea transformation was negligible in the water column and on the submerged leaves of the emergent plant Phragmites australis. However, because this wetland was dominated by dense beds of the submerged macrophyte E. canadensis, this plant provided a large surface area for epiphytic microbial activity—in the range of 23–33 m² of plant surfaces per square meter of wetland. Thus, in the wetland system scale at the existing plant distribution and density, the submerged plant community had the potential to transform 2–7 mmol urea-N m⁻² day⁻¹ and was in the same magnitude as the urea transformation in the sediment.     

Biomass and element pools of understory vegetation in the catchments of Čertovo Lake and Plešné Lake in the Bohemian Forest

This paper presents data on species composition, biomass, and element pools (C, N, P, Ca, Mg, Na, K, Al, Fe, Mn) of the understory vegetation of spruce forests in the catchments of lakes ?ertovo jezero (CT) and Ple?né jezero (PL) in the Bohemian Forest (?umava, Czech Republic). Calamagrostis villosa was the most abundant species in the CT catchment, while Vaccinium myrtillus was the most abundant species in the PL catchment. The catchments weighted mean (CWM) of above-ground biomass of the understory vegetation was 288 and 723 g m^?2 in the CT and PL catchments, respectively. The significant difference in the biomass between the catchments was caused by the much higher abundance of V. myrtillus in the PL catchment. The CWM of below-ground biomass of the fine roots was 491 and 483 g m^?2 in the CT and PL catchments, respectively. The respective CWM element pools of biomass in the CT and PL catchments were: C (33 and 51 mol m^?2), N (0.8 and 1.0 mol m^?2), P (24 and 34 mmol m^?2), Ca (53 and 113 mmol m^?2), Mg (24 and 41mmol m^?2), Na (3.7 and 6.5 mmol m^?2), K (83 and 109 mmol m^?2), Al (50 and 42 mmol m^?2), Fe (13.3 and 7.3 mmol m^?2), and Mn (4.2 and 8.8 mmol m^?2).     

A new well-preserved ostracod fauna from the middle Burdigalian (lower Miocene) of the North Alpine Foreland Basin

The marine middle Burdigalian sediments of the North Alpine Foreland Basin (NAFB) or Molasse Basin are well known for abundant occurrences of benthic foraminifers and ostracods. However, taxonomic studies of ostracod assemblages are comparatively rare and, given its abundance, the group remains heavily understudied. Here we report a new, rich and well-preserved ostracod fauna from the middle Burdigalian Neuhofen Formation at Mitterdorf, in the northeastern part of the NAFB. The material comprises a total of 3029 ostracod specimens. We identified 44 species; all species are described and, with one exception, illustrated. Our material reveals the presence of 17 ostracod species that were previously unknown from the middle Burdigalian in the NAFB, i.e., Cytherella aff. vulgatella, Cytherella aff. méhesi, Bairdoppilata aff. subdeltoidea, Paranesidea? sp., Paracypris aff. aerodynamica, Parakrithe dactylomorpha, Pseudopsammocythere sp., Callistocythere daedalea, Costa aff. reticulata, Ruggieria aff. longecarenata, Heliocythere aff. vejhonensis, Heliocythere sp., Loxocorniculum hastatum, Neocytherideis cypria, Cytheretta cf. tenuipunctata dentata, Cytheropteron cf. ruggierii, and Semicytherura resecta. The palaeobiogeography of the ostracods indicates a relatively open marine Burdigalian connection between the NAFB and the Mediterranean Sea, in agreement with previous work. Our data also suggest that a significant degree of endemism existed in the middle Burdigalian sea of the NAFB, of which previous studies yielded only sparse signs. Moreover, our results indicate that some ostracod species survived the late Burdigalian sea retreat from the NAFB by dispersing eastward into the adjacent regions (Vienna Basin, Carpathian Foredeep), where marine conditions still prevailed. A compilation of all known middle Burdigalian ostracod faunas from the NAFB documents a high species diversity, with over 120 species. Their spatial distribution, with many species being restricted to a single site, suggests heterogenous microhabitats, possibly influenced by small-scale differences in water depth, nutrient availability and oxygenation.