Interference between the macroalga Caulerpa prolifera and the seagrass Halodule wrightii

A field experiment was conducted to examine interactions between the seagrass Halodule wrightii and the macroalga Caulerpa prolifera in the Indian River Lagoon, FL, USA, and further if the outcome of the interactions between the two species was influenced by water depth. The experiment involved the manipulation of neighbor presence in plots established at the shallowest (50 cm) and deepest (80 cm) depths at which the two species co-existed at adequate densities to perform removal experiments. Shoot and frond densities were measured at the beginning (April), middle (July) and end (October) of the 6-month growing season, and above- and below-ground biomass values were determined at the end of the experiment (October). In the middle of the growing season H. wrightii had higher shoot densities and greater biomass in plots where C. prolifera had been removed at both water depths. This same pattern in shoot density and biomass for H. wrightii also occurred at the end of the growing season at the 80 cm depth. C. prolifera occurred at higher densities and greater biomass in the 80 cm depth range, but was generally unaffected by the presence of H. wrightii at either depth.     

Linking clonal growth patterns and ecophysiology allows the prediction of meadow-scale dynamics of seagrass beds

Seagrasses are a group of 12 genera of monocotyledonous plants in four families that have successfully colonised shallow coastal seas, probably since the Cretaceous. Variations in light availability and water movement are prime environmental factors for the growth of these marine angiosperms. An overall similarity in growth form and modular clonal architecture allows the generalisation that small species have short-lived shoots with rapidly elongating rhizome axes, whilst the larger species have longer-lived shoots that do not expand rapidly with rhizomes. Annual rhizome elongation rates range between 2 cm and 4 m among species. This range in expansion capacity is correlated with rhizome diameter in an allometric fashion (y=191x^?1.5, r²=0.58, p<0.05). Rhizomes with a wider diameter also allow the storage of larger quantities of reserve carbohydrates to be mobilized during the adverse winter season at higher latitudes or for flowering. Repeated branching and the basal positioning of the meristems allow the formation and maintenance of seagrass meadows, and these are a prominent feature creating spatial heterogeneity on the sea floor down to a mean colonisation depth of 15.1±1.3 m (median 8 m, range 0.7–90 m, n=150). Spatial complexity is highest in multi-species seagrass beds, such as those of the Indo-Pacific region and Australia. Seagrass beds function as important coastal filters for nutrients and pollutants and display high carbon sequestration rates. Due to the recalcitrant nature of seagrass detritus, it forms a disproportionally high contribution (12%, but only 1% of productivity) to the carbon stored in ocean sediments. The services provided by these ecosystems to human society range from water quality improvement via nursery and feeding grounds for economically important fish to storm buffering and recreative amenity.     

Germination characteristics of the grass weed Digitaria nuda (Schumach.)

The effect of various pre-treatments and their interaction with temperature on cumulative percentage and the rate of germination were evaluated for Digitaria nuda. Stored and fresh seeds were pre-treated with either 0.02 M KNO₃, soaked in water for 24 h (priming), sterilized with 0.5% NaOCl or heat treated at 60 °C. Seeds were germinated at constant temperatures of 25 and 30 °C and fluctuating temperature regimes of 25/10 and 30/15 °C. The effect of pre-chilling on germination of stored and fresh seed was evaluated at 30/15 °C, and seed emergence in two soil types at different burial depths (0, 0.5, 1, 2, 3, 4, 5 and 6 cm) was also determined. The pre-treatment of stored seed with KNO₃ resulted in the highest germination percentage (100%), whereas the pre-treatment of fresh seed with water for 24 h gave the best germination (99%), at constant temperatures of 25 and 30 °C. Pre-chilling of seed increased germination by more than 30%. Emergence from clay loam soil was greater compared with the emergence from sandy loam soil. Total seedling emergence decreased exponentially with increasing burial depths with only 5% of seed germinating from a burial depth of 6 cm. Results from this study showed that germination requirements are species specific and knowledge of factors influencing germination and emergence of grass weed seed can assist in predicting flushes in emergence allowing producers to implement control practices more effectively.     

Morphological variations,biomass and ion accumulation of the aboveground shoots of Desmostachya bipinnata (L.) Stapf

The present study aimed to evaluate the morphological characteristics and biomass of Desmostachya bipinnata and their relation to the environmental variables in three main habitats (canal banks, railway and roadside shoulders) where it is found in Egypt. In addition, the ability of this plant is evaluated to accumulate nutrients and heavy metals in its aboveground shoots. Twenty five quadrats (1 m × 1 m per quadrat) were selected along five sites representing the different habitats of D. bipinnata for this study. The aboveground shoots displayed considerable morphological variations, differing in the different habitats. The above ground biomass, number of spikes and leaves, rachis length and diameter, leaf length, width and area, leaf sheath length, and spike length and diameter were in the order: road sides > canal banks > railway shoulders. A regression equation: biomass = (67.37 × density) + 108.2, was used to estimate the shoot biomass from the plant growth density. Metal uptake capability from soil to grass is in the order Fe > Zn > Cu > Mn, and all of them are in safe concentration ranges. These heavy metals had a transfer factor more than unity, which indicates that D. bipinnata is a powerful accumulator for heavy metals. In addition, the plant shoots exhibit high accumulation of inorganic and organic nutrients.     

Environmental driving factors affecting plant biomass in natural grassland in the Loess Plateau,China

Plant biomass is a key parameter for estimating terrestrial ecosystem carbon (C) stocks, which varies greatly as a result of specific environmental conditions. Here, we tested environmental driving factors affecting plant biomass in natural grassland in the Loess Plateau, China. We found that above-ground biomass (AGB) and below-ground biomass (BGB) had a similar change trend in the order of Stipa bungeana > Leymus secalinus > Artemisia sacrorum > Artemisia scoparia, whereas shoot ratio (R/S) displayed an opposite change trend. There was a significantly positive linear relationship between the AGB and BGB, regardless of plant species (p < 0.05). Furthermore, more than 50% of the AGB were found in 20–50 cm of plant height in Compositae plants (A. sacrorum, A. scoparia), whereas over 60% of the AGB were found in 20–80 cm of plant height in Gramineae plants (S. bungeana, L. secalinus). For each plant species, more than 75% of the BGB was distributed in 0–10 cm soil depth, and 20% was distributed in 10–20 cm soil depth, while less than 5% was distributed in 20–40 cm soil depth. Further, AGB and BGB were highly affected by environmental driving factors (soil properties, plant traits, topographic properties), which were identified by the structural equation model (SEM) and the generalized additive models (GAMs). In addition, AGB was directly affected by plant traits, and BGB was directly affected by soil properties, and soil properties associated with plant traits that affected AGB and BGB through interactive effects were 9.12% and 3.59%, respectively. However, topographic properties had a weak influence on ABG and BGB (as revealed by the lowest total pathway effect). Besides, soil organic carbon (SOC), soil microbial biomass carbon (MBC), and plant height had a higher relative contribution to AGB and BGB. Our results indicate that environmental driving factors affect plant biomass in natural grassland in the Loess Plateau.     

Morphological and reproductive acclimations to growth of two charophyte species in shallow and deep water

We investigated the distribution of two charophyte species, Chara fibrosa var. fibrosa (A. Br.) and Nitella hyalina (DC.) Ag., in Myall Lake, a shallow lake in New South Wales, Australia, in an attempt to elucidate the factors causing their distribution patterns. The field study was carried out from July 2003 to May 2005 and charophytes were sampled together with bottom sediments at 20 sampling locations in the lake on 13 occasions. Charophyte biomass (0–321 g DW m⁻²) displayed an optimum curve with depth and maximum biomass occurred between 1 and 2.5 m depth. In deeper water, shoots were longer (i.e., around 30 cm at 1 m depth to 60–90 cm between 2 and 4 m depth). Oospore and antheridia densities were higher in shallower water with a maximum around 80 cm. Plants growing in shallow depths had shorter internodes implying a short life cycle of shoots, and nodal spacing was relatively regular in contrast to its deep water counterparts although spacing tended to increase at locations farther from the apex. The present study also reports that there is an apparent decline in sexual propagule production rates with increasing water depth, further highlighting the different morphological and reproductive acclimations of charophytes in shallow and deep water.     

Epibiosis of Calpensia nobilis (Esper) (Bryozoa: Cheilostomida) on Posidonia oceanica (L.) Delile rhizomes: Effects on borer colonization and morpho-chronological features of the plant

Shoots of the Mediterranean seagrass Posidonia oceanica (L.) Delile can be overgrown with a thick encrustation of the bryozoan Calpensia nobilis (Esper) (Chelostomida) particularly under high hydrodynamic conditions. We compared shoots with and without this encrustation and assessed whether it affected shoot morphology and production, and incidence of polychaete borers. The borers collected were represented by three species of polychaete Eunicidae (Lysidice ninetta, Lysidice collaris and Nematonereis unicornis). Shoots affected by overgrowth of C. nobilis showed a significantly lower borer frequency (17% versus 49%), lower values of both yearly biomass of the rhizome (mean 6.3 mg/year in shoot with C. nobilis versus 8.3 mg/year in shoot without) and biomass/elongation (B/E) ratio, and lower mean sheath thickness (0.25 mm versus 0.30 mm), while the mean width of the leaves was slightly higher (1.0 mm versus 0.7 mm). Significant Spearman coefficient's values were estimated between carbonate mass of C. nobilis and rhizome length, muff length and rhizome length, and maximum thickness of the muff and rhizome length. Plant and bryozoan morphometrics allowed to estimate between 5 and 10 years the colonization age of C. nobilis on the living shoots studied.     

Trace amounts of nickel in belowground rhizomes of Vaccinium myrtillus L. decrease anthocyanin concentrations in aerial shoots without water stress

Nickel (Ni) may impair plant water balance through detrimental effects on the belowground level. Bilberry (Vaccinium myrtillus L.) plants were grown in a mesic heath forest-type soil and subjected to Ni sulphate (NiSO₄·6H₂O) concentrations of 0, 10, 50, 100 and 500 mg m⁻² during an entire growing season in northern Finland (65°N). Biomass of belowground rhizomes, and tissue water content (TWC) and anthocyanin concentrations of aerial shoots were determined from mature plants in order to study rhizospheric Ni stress, and its possible long-distance effects on aerial shoots. As the major proportion of biomass of bilberry is invested in belowground parts, it was hypothesised that Ni-induced rhizospheric disturbance causes water stress in aerial shoots and increases their anthocyanin concentrations for osmotic regulation. Uptake of Ni from the soil to the rhizome and aerial shoots was measured with X-ray fluorescence spectrometry. Ni concentrations in the soil and rhizome exhibited a dose–response relationship, but the concentrations in the rhizome were about 10-fold lower (<3 mg Ni kg⁻¹) than those in the soil (<30 mg Ni kg⁻¹). Translocation of Ni from the rhizome to aerial shoots did not occur, as Ni concentrations in shoots remained at 1 mg Ni kg⁻¹. Although Ni concentrations in the rhizome were below the threshold values of Ni toxicity (i.e. 10–50 mg Ni kg⁻¹), Ni decreased the rhizome biomass. Anthocyanins decreased in aerial shoots along with the Ni accumulation in the rhizome, while TWC was unaffected. The result suggests that anthocyanins are not involved in osmotic regulation under Ni stress, since anthocyanins in aerial shoots responded to the Ni concentrations in the rhizome despite the lack of water stress.     

Effects of dwarf bamboo (Fargesia denudata) density on biomass, carbon and nutrient distribution pattern

Dense dwarf bamboo population is a structurally and functionally important component in many subalpine forest systems. To characterize the effects of stem density on biomass, carbon and majority nutrients (N, P, K, Ca and Mg) distribution pattern, three dwarf bamboo (Fargesia denudata) populations with different stem densities (Dh with 220 ± 11 stems m^?2, Dm with 140 ± 7 stems m^?2, and Dl with 80 ± 4 stems m^?2, respectively) were selected beneath a bamboo-fir (Picea purpurea) forest in Wanglang National Nature Reserve, Sichuan, China. Leaf, branch, rhizome, root and total biomass of dwarf bamboo increased with the increase of stem density, while carbon and nutrient concentrations in bamboo components decreased. Percentages of below-ground biomass and element stocks to total biomass and stocks decreased with the increase of stem density, whereas above-ground biomass and element stocks exhibited the opposite tendency. Moreover, more above-ground biomass and elements were allocated to higher part in the higher density population. In addition, percentages of culm biomass, above-ground biomass and element stocks below 100 cm culm height (H₁₀₀) increased with the increase of stem density, while percentages of branch and leaf biomass below H₁₀₀ decreased. Pearson’s correlation analyses revealed that root biomass, above-ground biomass, below-ground biomass and total biomass significantly correlated to leaf biomass in H_100?200 and total leaf biomass within high density population, while they significantly correlated to leaf biomass in H_50?150 within low density population. The results suggested that dwarf bamboo performed an efficient adaptive strategy to favor limited resources by altering biomass, carbon and nutrients distribution pattern in the dense population.     

Phenotypic plasticity in Phragmites australis as a functional response to water depth

We have performed investigations to see if the emergent macrophyte Phragmites australis (Cav.) Trin. ex Steud. exhibits phenotypic plasticity as a response to water depth and if such responses in biomass allocation pattern and morphology are functional responses, improving the performance of the plant. In greenhouse experiments plants were grown in deep or shallow water to evaluate plastic responses. Allometric methods were used to handle effects caused by size differences between treatments. To evaluate if phenotypic responses to water depth are functional, the relative growth rate (RGR) of plants acclimatised to shallow or deep water, respectively, were compared in deep water, and the growth of plants in fluctuating and constant water level were compared.When grown in deep (70 or 75 cm), compared to shallow (20 or 5 cm) water, plants allocated proportionally less to below-ground weight, made proportionally fewer but taller stems, and had rhizomes that were situated more superficially in the substrate. Plants acclimatised to shallow water had lower RGR than plants acclimatised to deep water, when they were grown in deep water, and plants in constant water depth (40 cm) grew faster than plants in fluctuating water depth (15/65 cm). In an additional field study, the rhizomes were situated superficially in the sediment in deep, compared to shallow water.We have shown that P. australis acclimatises to deep water with phenotypic plasticity through allocating more resources to stem weight, and also by producing fewer but taller stems, which will act to maintain a positive carbon balance and an effective gas exchange between aerial and below-ground parts. Furthermore, the decreased proportional allocation to below-ground parts probably results in decreased nutrient absorption, decreased anchorage in the sediment and decreased carbohydrate reserves. Thus, in deep water, plants have an increased risk of becoming uprooted and experience decreased growth and dispersal rates.     

Study on ascending and descending vertical dispersal behavior of third instar larvae of Chrysomya megacephala (Fabricius) (Diptera:Calliphoridae): An evidence that blowflies survive burial

Although the pupation behavior of blowflies has been widely studied, this preliminary study was done on the vertical dispersal behavior (both ascending and descending) and fly emergence rate of third instar larvae of Chrysomya megacephala (Fabricius) to evaluate weather immature stages of blowflies survive burial and emerge out as adult. Third instar larvae of Chrysomya megacephala were placed at three different depths (5 cm, 25 cm and 45 cm) of soil under laboratory conditions to determine the impact of soil depth on the ascending and descending vertical dispersal behavior and the subsequent emergence of adults. The results of this study, although preliminary, but valuable to the field of forensic entomology because they provide new information about both ascending and descending vertical dispersal behavior of Chrysomya megacephala forensically important species of blowfly. In all the cases, maximum number of pupae recovered at the depth of 0 to 5 cm are 35.5 ± 4.5, 34 ± 1, 25 ± 5, when food was located at 5 cm, 25 cm and 45 cm depth respectively. This means that maximum no of larvae reached to the depth of 0 to 5 cm by ascending dispersal irrespective of at which depth they are placed. Paramount pupae were recovered from shallow burial depth of 0–5 cm in ascending dispersal and showed highest eclosion success i.e. 90.1% followed by 25 cm and 45 cm i.e. 71.7% and 55% respectively. While the number of pupae recovered as well as eclosion success was less in descending dispersal with an average of 62.8%, 39.25% and 33.9% at depths of 5, 25 and 45 cm respectively. This manifest if larvae disperse ascendingly, it increases their chance of survival.     

Seasonal abundance and activity of pill millipedes (Arthrosphaera magna) in mixed plantation and semi-evergreen forest of southern India

Seasonal occurrence and activity of endemic pill millipedes (Arthrosphaera magna) were examined in organically managed mixed plantation and semi-evergreen forest reserve in southwest India between November 1996 and September 1998. Abundance and biomass of millipedes were highest in both habitats during monsoon season. Soil moisture, conductivity, organic carbon, phosphate, potassium, calcium and magnesium were higher in plantation than in forest. Millipede abundance and biomass were about 12 and 7 times higher in plantation than in forest, respectively (P < 0.001). Their biomass increased during post-monsoon, summer and monsoon in the plantation (P < 0.001), but not in forest (P > 0.05). Millipede abundance and biomass were positively correlated with rainfall (P = 0.01). Besides rainfall, millipedes in plantation were positively correlated with soil moisture as well as temperature (P = 0.001). Among the associated fauna with pill millipedes, earthworms rank first followed by soil bugs in both habitats. Since pill millipedes are sensitive to narrow ecological changes, the organic farming strategies followed in mixed plantation and commonly practiced in South India seem not deleterious for the endangered pill millipedes Arthrosphaera and reduce the risk of local extinctions.     

Trade-offs among growth, clonal, and sexual reproduction in an invasive plant Spartina alterniflora responding to inundation and clonal integration

The purpose of this article was to study the trade-offs among vegetative growth, clonal, and sexual reproduction in an aquatic invasive weed Spartina alterniflora that experienced different inundation depths and clonal integration. Here, the rhizome connections between mother and daughter ramets were either severed or left intact. Subsequently, these clones were flooded with water levels of 0, 9, and 18 cm above the soil surface. Severing rhizomes decreased growth and clonal reproduction of daughter ramets, and increased those of mother ramets grown in shallow and deep water. The daughter ramets disconnected from mother ramets did not flower, while sexual reproduction of mother ramets was not affected by severing. Clonal integration only benefited the total rhizome length, rhizome biomass, and number of rhizomes of the whole clones in non-inundation conditions. Furthermore, growth and clonal reproduction of mother, daughter ramets, and the whole clone decreased with inundation depth, whereas sexual reproduction of mother ramets and the whole clones increased. We concluded that the trade-offs among growth, clonal, and sexual reproduction of S. alterniflora would be affected by inundation depth, but not by clonal integration.     

Strong regeneration ability from rhizome fragments in two invasive clonal plants (Solidagocanadensis and S. gigantea)

The two rhizomatous perennials Solidago canadensis and S. gigantea belong to the most widespread alien plants in Europe. Anecdotal observations suggest that they disperse also by rhizome fragments. For testing their resprouting ability, rhizome fragments of different sizes from both species were buried at four different soil depths (0, 5, 10 and 20 cm, respectively) in a common garden. Rhizome fragments of S. canadensis ranged 3–6 cm in length, those of S. gigantea 5–20 cm in length. Resprouting plants were harvested after 3 months and growth related traits measured to assess their vitality. Resprouting rate in S. gigantea was far higher than in S. canadensis (85 and 19%, respectively). In S. gigantea, fragments of all sizes resprouted from all soil depths whereas none rhizome of S. canadensis emerged from 20 cm burial depth. In S. gigantea, size related traits showed significant interactions between fragment size and burial depth, but not relative shoot growth rate. At all burial depths, vitality of plants emerging from small rhizomes was lower than plants emerging from large rhizomes. Effects of rhizome size became stronger with increasing burial depth. The results show that both species are able to resprout from buried rhizome fragments, and that succesful regeneration is more likely to occur in S. gigantea. Managing these species should avoid any activities promoting rhizome fragmentation and dispersal of fragments.     

Abundance and biomass of planktonic ciliates in the sea area around Zhangzi Island,Northern Yellow Sea

We investigated the abundance and biomass of planktonic ciliates in the sea area around Zhangzi Island, Northern Yellow Sea, from July 2009 to June 2010. Ciliates were sampled monthly from surface to bottom with a 10 m depth interval at 13 sample stations along three transects. A 1 L sample of water from each depth was collected with a 2.5 L Niskin water sampler and fixed in 1% acid Lugol’s iodine solution. Water samples were pre-concentrated using the Utermöhl method and observed using an Olympus IX51 inverted microscope at 100× or 200x. The dimensions of the ciliates were measured and the cell volume of each species was estimated using appropriate geometric shapes. The carbon:volume ratio used to calculate biomass was 0.19 pg C/μm³. Abundance and biomass of the ciliate in water column were calculated as the integral of the abundance and biomass from bottom to surface, respectively. The classification of tintinnids was based on taxonomic literature. The average abundance of non-loricate ciliates was 3066 ± 2805 ind/L, ranging from 165 ind/L (50 m depth of St. B6 in July) to 26,595 ind/L (surface of St. C1 in September). The average biomass of non-loricate ciliates was 2.88 ± 2.68 μg C/L, ranging from 0.05 μg C/L (10 m depth of St. A6 in July) to 20.51 μg C/L (surface of St. A5 in August). The average tintinnid abundance was 142 ± 273 ind/L, ranging from 0 ind/L (monthly) to 2756 ind/L (surface of St. A1 in July). The average tintinnid biomass was 0.84 ± 2.19 μg C/L, ranging from 0.00 μg C/L (every month) to 37.64 μg C/L (20 m depth of St. C5 in July). The results showed that the average abundance of total ciliates was 3208 ± 2828 ind/L, ranging from 166 ind/L (10 m depth of St. A6 in July) to 26,625 ind/L (surface of St. C1 in September); the average biomass of total ciliates was 3.73 ± 3.55 μg C/L, ranging from 0.05 μg C/L (10 m depth of St. A6 in July) to 38.29 μg C/L (20 m depth of St. C5 in July). Abundance and biomass were vertically homogeneous in February, November and December, but decreased dramatically from the surface down to the bottom in other months. 23 tintinnid species were identified, 12 of which were in genus Tintinnopsis. Tintinnid species were more abundant in February, July and August. Tintinnids occupied 6.6 ± 10.2% and 19.7 ± 23.3% of the total ciliate abundance and biomass, respectively, which increased during the warm season and at coastal stations, and decreased during the cold season and at offshore stations. Large non-loricate ciliate species were prevalent in spring, while smaller species dominated in summer and autumn. The average abundance of total ciliates in water column was 132 ± 72 × 10⁶ ind/m², with increases during spring and autumn. The average biomass of total ciliates in water column was 152.57 ± 93.10 mg C/m², with increases during spring and summer. The average abundance and biomass of total ciliates in water column were greater at offshore stations than at coastal stations during spring and autumn, and were lower during summer and winter. Non-loricate ciliates, tintinnids and total ciliates showed significant positive correlation with temperature and significant negative correlation with salinity (p < 0.01). Non-loricate ciliates and total ciliates showed significant positive correlation with Chl a concentration (p < 0.01); however, relationship between Chl a concentration and tintinnids was not significant.     

Decomposition of Phragmites australis rhizome in a shallow lake

Decomposition of Phragmites australis (Cav. Trin ex Steudel) rhizome was studied at Lake Fertő/Neusiedler See using the litter bag technique. Samples were analysed for rhizome dry mass, fibre (cellulose, hemicellulose, lignin) and nutrient content (C, N, P and S), litter-associated fungal biomass, potential microbial respiration (electron transport activity: ETS) and cellulolitic bacteria. The mass loss of decomposing rhizome was rapid in the initial period and only 13.6% of the dry mass remained at the end of the experiment during 953 days. Substantial quantities of C, N, S and P were lost during 99 days; only 18% C, 19% N, 14% S and 6.4% of the P remained after 953 days. Hemicellulose degraded more rapidly than the other fibres whilst the lignin had the slowest rate of decomposition. Bacteria were found to be the primary colonizers of plant detritus, which was followed by fungal growth. An antagonistic relationship was observed between bacteria and fungi. Fungal biomass as determined by ergosterol concentrations ranged between 4.1 and 420 μg g⁻¹ and peaked every year in September. The number of cellulolitic bacteria varied from 0 to 22 MPN g⁻¹ with higher values in summer. The ETS-activity ranged between 0.1 and 1.6 mg O₂ g⁻¹ h⁻¹. The changes in ETS-activity varied almost in parallel with the in situ temperature of the lake water.     

Gambierdiscus (Dinophyceae) species diversity in the Flower Garden Banks National Marine Sanctuary,Northern Gulf of Mexico,USA

Globally, ciguatera fish poisoning (CFP) is the principal cause of non-bacterial illness associated with seafood consumption. The toxins (ciguatoxins) responsible for CFP are produced by dinoflagellates in the genus Gambierdiscus, which are endemic to tropical and sub-tropical areas. Ciguatoxins are lipophilic and bioaccumulate in marine food webs, typically reaching their highest concentrations in fish. Following a CFP event in 2008, the U.S. Food and Drug Administration (USFDA) issued a ciguatera toxin alert that included fish harvested in the northern Gulf of Mexico in and near the Flower Garden Banks National Marine Sanctuary (FGBNMS). The East Flower Garden Bank (EFGB) and West Flower Garden Bank (WFGB) are characterized by thriving coral communities that support Gambierdiscus growth. This study was undertaken specifically to document the diversity of Gambierdiscus species present in the sanctuary that may be sources of ciguatoxins entering the food web. Samples collected from the FGBNMS over a three year period were screened using species-specific polymerase chain reaction assays. A diverse assemblage of Gambierdiscus species was distributed to depths of >45 m, a new depth record for Gambierdiscus. Gambierdiscus belizeanus, Gambierdiscus caribaeus, Gambierdiscus carolinianus, Gambierdiscus carpenteri and Gambierdiscus ribotype 2 were all found on both East and West FGB with Gambierdiscus ruetzleri also recorded from the WFGB. The most common species was G. carolinianus, originally identified from samples collected between 35 and 40 m off the coast of NC, USA. Our findings are consistent with recent physiological studies showing that some Gambierdiscus species can grow year round at the temperatures and salinities at the FGBNMS and at light levels as low as 10 μmol photons m⁻² s⁻¹. Such irradiances are estimated to occur in the FGBNMS at depths of ∼70–80 m. The consistent recovery of Gambierdiscus species from deep sampling sites in areas known to produce ciguatoxic fish signals a substantial change in our concept of suitable habitats for Gambierdiscus to include depths greater than 50 m.     

Seasonal and spatial distribution of ciliates in the sandy hyporheic zone of a lowland stream

The seasonal and spatial distribution of abundance and biomass as well as the taxonomic composition of ciliates inhabiting the sandy hyporheic zone of a lowland stream were studied. The mean abundances varied between 0 and 895 cells ml⁻¹ sediment, and the mean ciliate biomass ranged between 0 and 5.3 μg C ml⁻¹ sediment. Ciliate numbers and biomasses were greatest at the sediment surface and declined significantly with increasing sample depth. Abundance and biomass varied seasonally, with maximum values in late autumn and early winter and minimum values in early summer. The community was dominated by small representatives of the Hymenostomatia and Peritrichia. Ciliate community composition changed with depth from a very diverse community at the sediment surface to a less diverse one at greater sediment depths. Ciliate abundance and biomass were two orders of magnitude lower in the channel water than in the hyporheic zone. Although representatives of all sediment taxa could also be found in the channel water, the greatest concentrations of Peritrichia and Suctoria were in the hyporheic zone. The species of the sandy Ladberger Mühlenbach sediment were ubiquitous; there was no single ciliate fauna that proved to be typical for this kind of freshwater biotope.     

Effects of nitrogen and phosphorus supply on growth and flowering phenology of the snowbed forb Gnaphalium supinum L.

The warming-induced increase in nutrient mineralization and the further increase in atmospheric nitrogen depositions raise the topic of whether and how alpine plants will react to enhanced nutrient availability. Despite several studies have shown the effects of fertilization on primary production of alpine plants, only few studies have considered the influences of nutrients on reproduction. Here, we investigated the effects of nitrogen (N) and phosphorus (P) amendments on cover, number of ramets, flowering effort and phenological timing of Gnaphalium supinum, an arctic-alpine widespread snowbed species. We set up an experimental design with four fertilization treatments (low N, P without additional N, low N + P, and high N + P) and an unfertilized control for three years (2003–2005), within a late snowbed located in the Italian Alps (Gavia Pass, 2700 m a.s.l.). The cover of Gnaphalium supinum was recorded at the peak of the aboveground biomass development in the three years, while the temporal dynamic of ramet density and reproductive phenophases were monitored during the 2005 growing season. The clonal growth of G. supinum resulted to be co-limited by N and P, while the flowering effort was stimulated by P. Flowering date was advanced by P supply, while N alone did not show any significant effect on phenology. In a warming scenario, with a predicted increase in N and P availability by nutrient mineralization and atmospheric deposition, this species should probably experience some benefits for its growth and reproduction if not limited by other factors such as the length of the growing season or interspecific competition.     

Response of Potamogeton crispus root characteristics to sediment heterogeneity

Plant growth, biomass allocation, root distribution and plant nutrient content were investigated in the submerged macrophyte Potamogeton crispus growing in heterogeneous sediments. Three experimental sediments heterogeneous in nutrient content and phosphorus release capacity were used: sandy loam with low nutrient content (A), clay with intermediate nutrient content (B), and clay with high nutrient content (C). Biomass accumulation was significantly affected by the sediment type, and was highest in clay C (1.23 mg per plant dry weight) but lowest in sandy loam (0.69 mg per plant dry weight). The root:shoot ratios in treatments A, B and C were 0.30, 0.14 and 0.09, respectively. P. crispus allocated more biomass to roots in sandy loam compared with the other sediments. The average root numbers in sediments A, B and C were 16, 19 and 20, respectively, and the total root lengths in sediments A, B and C were 238.84, 200.36 and 187.21 cm, respectively. Almost 90% of the root biomass was distributed in the 0–15 cm depth in sediments B and C, compared with 64.53% in sediment A. The rank order of plant nitrogen and phosphorus concentrations in the sediment types was C > B > A. These results indicate that both sediment structure and nutrient availability influence the growth and distribution of the root system of P. crispus.