Genetic evolution among selected members of the genus Naso (Nasinae), "unicornfishes" from Guam

A species-level phylogeny of selected surgeonfishes in the genus Naso (Acanthuridae: subfamily Nasinae) was constructed using allozyme data and found to be concordant with previous inferences drawn from morphological data. Naso spp. examined from waters surrounding Guam between 1992 and 1994 were: N. caesius (Randall and Bell, 1992), N. hexacanthus (Bleeker, 1855), N. lituratus (Schneider, 1801), N. thynnoides (Valenciennes, 1835), and N. unicornis (Forskål, 1775). Acanthurus lineatus (Linnaeus, 1758) (Acanthuridae: subfamily Acanthurinae) and Zanclus cornutus (Linnaeus, 1758) (Zanclidae) were included for the purpose of outgroup comparison. Analyses of the allozyme data set generated from 16 presumptive loci using both cladistic and phenetic tree-constructing techniques identified the sibling species N. caesius and N. hexacanthus as the most genetically similar taxa among the Naso species surveyed. The pair shared the most synapomorphic alleles and the lowest degree of genetic divergence with respect to other species studied. The unweighted pair-group method using the arithmetic mean (UPGMA) and the neighbor-joining (NJ) topologies, along with two synapomorphic alleles (Aat-2 and Gpi-A), characterize N. caesius, N. hexacanthus, N. lituratus, and N. unicornis as a monophyletic group. Many allelic autapomorphies were detected in N. thynnoides, a member of the subgenus Axinurus. This supports the morphological data, which suggest that one-plated unicornfishes form a monophyletic group. The proposed partial phylogeny inferred from the allozyme data is concordant with the morphological differences (i.e. dentition, osteology, and myology) that have been used to support the partition of the genus Naso into the subgenera Axinurus and Naso.     

Genetic divergence of Maldivian and Micronesian demes of the damselfishes Stegastes nigricans,Chrysiptera biocellata,C. glauca and C. leucopoma (Pomacentridae)

Samples representing the damselfishes (Perciformes: Pomacentridae) Stegastes nigricans, Chrysiptera biocellata, C. glauca, and C. leucopoma from North Male Atoll, Republic of Maldives, and Guam, Southern Marianas, were surveyed electrophoretically. A sample representing C. leucopoma from Ngemelis Island, Republic of Palau, was included in the analysis to provide a within-Micronesia comparison. On average, products of 23 presumptive protein-coding loci were examined in each sample. In comparisons of Maldivian and Guamanian samples, absolute or virtually fixed allelic differences were detected at: (1) ADA ^* and PEPS ^* for Stegastes nigricans; (2) ADA ^*, AAT-1 ^*, AAT-2 ^*, and mMDH ^* for C. biocellata, and; (3) ADA ^*, AAT-1 ^*, and AAT-2 ^* for C. glauca. At three polymorphic loci, ADA ^*, sMDH-1 ^*, and sMDH-2 ^*, similar allele frequencies were found in Palauan and Guamanian samples representing C. leucopoma, suggesting that these samples share a gene pool. Significantly different allele frequencies at ADA ^* and sMDH-1 ^* and a virtually fixed allelic difference at sMDH-2 ^* were detected between the Maldivian samples and each of the Micronesian samples representing C. leucopoma. The observed patterns of allele frequency differentiation suggest that Maldivian and Micronesian samples of each of the four study species represent separate demes.     

Fixed allele frequency differences among Palauan and Okinawan populations of the damselfishes Chrysiptera cyanea and Pomacentrus coelestis

A survey of intraspecific allozymic variation among samples of the damselfishes Chrysiptera cyanea and Pomacentrus coelestis collected from Palau and Okinawa revealed levels of genetic divergence far in excess of estimates reported previously for populations of coral reef fishes. Absolute or nearly fixed differences in allele frequencies were detected at ADA ^*, sMDH-2 ^*, MEP-1 ^*, PEPB ^*, PEP-LT ^* and sSOD ^*, and at sAAT ^*, GPI-A ^*, LDH-1 ^*, and PEPB ^*, among the geographic samples of C. cyanea and P. coelestis, respectively. Examination of allele frequencies at most other loci (26 for C. cyanea; 24 for P. coelestis) revealed slight differentiation or identical fixation among the geographic samples. The observed patterns of allele frequency distribution suggest the existence of localized demes of these fishes: these demes may be cryptic and/or incipient species. Whether or not speciation is incipient, the observed patterns of allozymic and isozymic variability suggest that natural selection is a factor in the maintenance of population substructuring of the study species. Pronounced allelic differences were highly concentrated at a small number of loci: strongly bimodal frequency distributions of loci relative to their genetic identities (I) were observed for among-population comparisons in both study species. Allozymes encoded by the PEPB ^* locus in samples of the noncongeners from Palau exhibited identical electrophoretic mobilities. In Palauan P. coelestis, mSOD ^* is expressed but sSOD ^* apparently is not, whereas in Okinawan P. coelestis, both mSOD ^* and sSOD ^* are expressed.     

Allozyme and mitochondrial DNA variation in yellowfin tuna (Thunnus albacares) from the Pacific Ocean

Samples of yellowfin tuna (Thunnus albacares) collected in 1991 and 1992 from the western, central and eastern regions of the Pacific Ocean were examined for genetic variability. Four polymorphic allozyme loci (ADA ^*, FH ^*, GPI-S ^* and GPI-F ^*) were examined in all samples and a fifth polymorphism (GDA ^*) was examined in western and central samples only. Samples were also screened for mitochondrial DNA variation following restriction analysis by two enzymes (BcII and EcoRI) detecting polymorphic cut sites. Eighteen mtDNA haplotypes were revealed, with an overall nucleon diversity of 0.678. A subset of individuals screened for eight restriction enzymes had an overall nucleon diversity of 0.724 and a mean nucleotide diversity per sample of 0.359%. No significant spatial heterogeneity was detected for alleles at the ADA ^*, FH ^*, GPI-S ^* and GDA ^* loci nor for the mtDNA haplotypes. Significant heterogeneity was detected for GPI-F ^*. At this locus, the two eastern samples (southern California and northern Mexico) were not significantly different from each other but were significantly different (P<0.001) from the five western/central samples (Philippines, Coral Sea, Kiribati, Hawaii-91 and Hawaii-92). GPI-F ^* 100 was the most common allele in western and central regions, GPI-F ^* 75 the most common in eastern samples.     

Assessing the Leakage Rates from Punctured Submerged Vessels

The leakage of fluid leaving a puncture in a pressurized vessel immersed in a quiescent, miscible medium is studied under steady flow conditions. This problem has engineering applications in submerged pipelines and hazardous gas lines. The leakage rate for the puncture is characterized as functions of various hydrodynamic and geometric conditions. Dimensional analysis shows that the leakage percent, Q*, is a function of the Reynolds number, the pressure ratio between the center of the tube and the external hydrostatic pressure, P^*, and the hole-to-main tube diameter ratio, D^*. The effect of puncture shape is also examined, rectangular and circular. A 3-D finite volume computational model is constructed for laminar flow of a Newtonian fluid under steady conditions and validated with supporting experiments. The results show that the fractional leakage rate Q* increases with P^* and approaches a constant value at high P^* for a fixed Reynolds number. In addition, it is found that the leakage rate increases with decreasing Reynolds number at a fixed pressure ratio. The geometric effect of the diameter ratio is shown to have a more pronounced effect near a pressure ratio of two with more fluid exiting the puncture for larger diameter ratios. The results of the shape analysis show that the circular puncture has the largest fractional leakage when compared to a rectangle with an equivalent cross-sectional area.     

Influence of sediment nitrogen-availability on carbon and nitrogen dynamics in the seagrass Thalassia testudinum

Variations in tissue carbon (C), nitrogen (N) content, and non-structural carbohydrate (NSC) reserves in the turtle grass Thalassia testudinum Banks ex König were examined in relation to changes in sediment-N availability in Corpus Christi Bay (CCB) and lower Laguna Madre (LLM), Texas, USA, from May to October 1997. Under natural conditions, sediment pore-water NH⁺ ₄-concentrations were higher at CCB (100?μM) than at LLM (30?μM); this difference was reflected in a significantly higher leaf and rhizome N-content at CCB than at LLM. However, sediment NH⁺ ₄-enrichment using a commercial fertilizer resulted in significantly higher tissue N-content relative to controls at both sites. N enrichment also influenced plant carbon metabolism, as reflected by distinct increases in leaf C-content at both sites. Significant decreases in rhizome NSC-content was recorded during the first two months of the experiment, suggesting that C was reallocated from rhizomes to leaves to support stimulated leaf growth at both sites. At LLM, leaf growth-rates increased and leaf turnover-time decreased as a result of sediment NH⁺ ₄-enrichment. With respect to chlorophyll, concentrations did not change significantly at CCB, but increased steadily at LLM after the first month following fertilization. In general however, chlorophyll concentrations in control plots were significantly higher at CCB than that at LLM. These observations suggest that leaf function related to C-fixation is enhanced under higher sediment N conditions, as reflected in higher leaf growth-rates and increased blade chlorophyll-content. In contrast, under low-N conditions, below-ground tissue production is enhanced at the expense of the above-ground shoots and leaves, resulting in the high below: above-ground biomass ratios often observed in seagrass beds of oligotrophic environments.     

Genetic population structure of southern bluefin tuna (Thunnus maccoyii )

Samples of southern bluefin tuna, Thunnus maccoyii (Castelnau), taken from off the coasts of South Africa, Western Australia, South Australia and Tasmania from 1992 to 1994 were analysed for six polymorphic allozyme loci (ADA ^*, GDA ^*, GPI-A ^*, MPI ^*, PGDH ^* and PGM-1 ^*, n = 595 to 733 per locus) and for mitochondrial DNA variants revealed by three restriction enzymes (Bam HI, Bcl I and Eco RI) detecting polymorphic cut sites (n = 555). No significant spatial heterogeneity was detected. There were no sex-related differences in allele or mtDNA haplotype frequencies. Juveniles (30 to 35 cm and 46 to 54 cm) from what are thought to be two temporally-separated spawning peaks showed no significant genetic differentiation. There were also no significant differences in allele or haplotype frequencies between fish smaller than 70 cm and those larger than 70 cm. These data are consistent with the null hypothesis of a single unit stock of southern bluefin tuna, with a single spawning area. This is located to the south of Java and off the north-west coast of Australia. Received: 28 August 1996 / Accepted: 30 September 1996     

Bacterial community structure and microorganism inactivation following water treatment with ferrate(VI) or chlorine

Drinking water disinfection plays a critical role in protecting humans from waterborne pathogens. Ferrate(VI) (Fe^VIO₄ ^2?) has also been proposed as a disinfectant. This is the first study investigating the bacterial microbiomes of ferrate(VI)-treated water compared to chlorinated water. Tested water was collected after sand filtration and before disinfection from a drinking water treatment plant at Jiaxing, Zhejiang Province, China. A culture-independent method utilizing propidium monoazide was used with quantitative polymerase chain reaction and pyrosequencing of 16S rRNA genes to distinguish between the viable and nonviable bacterial populations. The operational taxonomic units and α-diversity indexes of the live bacterial phylotypes in the samples were determined. Viable bacteria remained in all samples following chlorination or ferrate treatment. However, the genera Vibrio, Salmonella, Shigella, Escherichia, Campylobacter, Yersinia, Plesiomonas, Legionella, and Helicobacter, which contain important human pathogens, were not present among the 25 dominant genera seen in these samples. The profiles of the bacteria remaining after treatment with either chlorine or ferrate differed. The ferrate-treated samples showed a reduced percent relative abundance of operational taxonomic units of the class Alphaproteobacteria within the total remaining viable bacteria. The genera Flavobacterium and Duganella were relatively resistant to treatment by either chlorine or ferrate(VI). At the highest doses of chlorine and ferrate(VI), the genus Sphingobium represented a greater percentage of live bacteria in the chlorinated sample than in the ferrate(VI)-treated sample. The results suggest that ferrate(VI) and chlorine could inactivate slightly different sets of bacteria and could have different mechanisms of bacterial inactivation.     

Relation between respiration,excretion (ammonia and inorganic phosphorus) and activity of amylase and trypsin in different species of pelagic copepods from an Indian Ocean equatorial area

The relationship between respiration, nitrogen and phosphorus excretion and specific activity of amylase and trypsin was investigated from shipboard experiments with several species of copepods from the equatorial divergence area of the Indian Ocean, in June 1978. Statistical analysis of O:N ratios in 6 of the most common species revealed three main groups: a group displaying low O:N (Pontella fera, Candacia pachydactyla); a group with high O:N (Undinula darwini, Euchaeta marina, Temora discaudata); and a species displaying an intermediate O:N ratio: Scolecithrix bradyi. O:P and N:P did not differ significantly between species. There was a direct relationship between average O:N and the ratios of specific activity of the digestive enzymes amylase and trypsin. Species displaying low O:N and/or A:T ratios such as P. fera, C. pachydactyla and Oncaea venusta probably metabolize proteins more efficiently than they do plant carbohydrates (high nitrogen excretion and low amylase activity). Species displaying high O:N and A:T ratios, such as U. darwini, E. marina and T. dicaudata (low nitrogen excretion and high amylase activity) were assumed to use carbohydrates (starch) and proteins with equal efficiency. S. bradyi showed a large range of variations in trypsin activity and low amylase activity, resulting in a low average A:T ratio, but its O:N ratio was intermediate. Variations in O:N and O:P ratios were related to differences in the nutritional strategy of the different species, based on literature data concerning the anatomy of their mouth parts and their selectivity for animal material in mixed-food experiments.     

UV absorption by mycosporine-like amino acids in Phaeocystis antarctica Karsten induced by photosynthetically available radiation

Mycosporine-like amino acids (MAAs), which occur in diverse taxonomic groups, exhibit in vivo absorption maxima between 310 nm and 360 nm and may play a photoprotective role against ultraviolet (UV) exposure. Using cultures of colonial Phaeocystis antarctica, we examined the relationship between MAA concentration, in vivo UV absorption, photoprotective (carotenoid) and photosynthetic pigments, and photosynthetically available radiation (PAR, 350–700 nm). UV absorption was high; chlorophyll-specific absorption, a ^* _ph, at 330 nm ranged from 0.06 to 0.41 m²/mg chlorophyll a. Values of a ^* _ph (330) were 4–13 times greater than a ^* _ph (676). Mycosporine-glycine, shinorine, and mycosporine-glycine valine are responsible for the strong in vivo UV absorption. The sum of all MAAs increased with irradiance when normalized to chlorophyll a or carbon concentrations, whereas individual MAAs varied independently from each other. Mycosporine-glycine concentrations showed no statistically significant change over the range of light intensities, whereas mycosporine-glycine and shinorine concentrations increased at higher irradiances. The relative fluorescence yield for chlorophyll a was low in the UV region compared to the visible region, implying that absorbed UV radiation (<375 nm) is transferred inefficiently to chlorophyll a in the reaction center. Quantitative estimates of UV screening by MAAs are attributed to elevated MAA concentrations and increased diameter at high light. Received: 31 March 1999 / Accepted: 13 July 2000     

Geographical patterns of variability at allozyme loci in the European oyster Ostrea edulis

The variability of 14 enzyme-coding genes has been analysed in samples from 19 populations of the oyster Ostrea edulis L., collected along the Atlantic and Mediterranean coasts of Europe. We found an abundance of clines, which appeared at 8 loci, including the most polymorphic (AP-2 ^*, ARK ^*, EST-4 ^*, MDH-2 ^*, ME-1 ^*, 6PGH ^*, PGI ^* and PGM ^*). Another 6 loci (ALDH ^*, EST-3 ^*, EST-5 ^*, IDH-2 ^*, MDH-1 ^*, ME-2 ^*) exhibited V-shaped patterns of gene-frequency variation, with clines at one or both sides of the Straits of Gibraltar. The observation of coincident clines at many loci can be explained by a model of secondary intergradation. The geographical location of the midpoints of the clines and V-shaped patterns suggests the existence of two ancient Atlantic and Mediterranean oyster stocks which became differentiated in allopatry and subsequently merged. Clines observed along Atlantic and/or Mediterranean coasts at the loci with V-shaped patterns must have arisen independently. The large heterogeneity observed in the levels of gene differentiation (G _ST ) across loci (G _ST ranged from 0.008 to 0.290) and important differences in estimates of gene flow obtained by different methods suggest that the populations of O. edulis are not in genetic equilibrium. Lack of population equilibrium can be due to natural selection and/or restrictions to gene flow. The average among-population variability was higher than in other oyster species that do not show incubatory habits, and represented 8.8% of the total heterozygosity. Levels of intrapopulation variability were lowest in populations from the North Atlantic, suggesting low population sizes in that area.     

Photometrische Bestimmung der Zytotoxizität von Chemikalien

Two test methods are presented to assess the cytotoxicity of chemicals. On one hand the protozoonTetrahymena pyriformis and on the other the bacteriumPseudomonas aeruginosa is cultured in defined media containing the test chemicals. Test parameter is the quantity of living cells surviving exposure. The conversion of the tetrazolium salt MTT into formazan is equivalent to cell viability. A mixture of detergent and isopropanol is used to dissolve the blue formazan which is not soluble in water, prior to photometric measurement. For cetyltrimethylammonium bromide, benzyldimethyldodecylammonium chloride, dodecylbenzenesulfonic acid sodium salt, potassium dichromate, 4-toluenesulfonic acid sodium salt, and 4-nitrophenol the EC50-values (mol/l) in theTetrahymena pyriformis- (Pseudomonas aeruginosa) test system were: 10^?5,81 (10^?5,08); 10^?4,68) (10^?3,80; 10^?4,50 (10^?4,14); 10^?3,97 (10^?5,11); 10^?2,71 (10^?2,50) and 10^?4,00 (10^?3,64). — With the assays described here it is possible to measure a large number of samples by quick and simple means.     

Estimating photophysiological condition of endosymbiont-bearing Baculogypsina sphaerulata based on the holobiont color represented in CIE L*a*b* color space

Symbiont-bearing large benthic foraminifers (LBFs) are widely distributed around coral reefs. If the physiological responses of LBFs to environmental changes can be recognized at an individual level, LBFs could serve as highly accurate bioindicators. In this study, chlorophyll a, respiration, and photosynthesis of Baculogypsina sphaerulata individuals were measured, and whether these physiological traits could be estimated based on the color of the holobiont (foraminifera and the diatom symbionts) was examined. Chlorophyll a content was estimated using a* and b* values of holobiont color represented in CIE L*a*b* color space. Photosynthetic performance decreased significantly with increasing whiteness (L*). These results indicated chlorophyll content as well as photosynthetic performance of Baculogypsina could be directly estimated using the holobiont color. The increased whiteness in color and decreased photosynthetic performance were mainly observed under low-light environment, possibly indicating symbiotic algae were shrunk into the central part of the host shell due to prolonged exposure to adverse conditions.     

Effects of nitrogen addition on the growth of the salt marsh grassElymus athericus

Effects of nitrogen addition on the growth of the salt marsh grassElymus athericus were studied under greenhouse conditions. The addition of inorganic nitrogen (in the form of nitrate or ammonium and ranging from 0–24 g N/m²) stimulated the growth ofElymus athericus at the highest addition. Addition of nitrogen led to an increase of the soil nitrate concentrations both in the nitrate and ammonium treated soil in the first period of the experiment, whereas no differences were present at the end of the experiment. Ammonium in the ammonium treatments was transformed to nitrate within 15 days. In another experiment the values of the stable isotope nitrogen-15—expressed as δ¹⁵N-in nitrogen compounds used as fertilizer, in salt marsh soil and ofElymus athericus were measured. The δ¹⁵N of the N-compounds added (between ?3.2 and +2.6‰) were lower than the soil (ca.+10‰) and plants (ca.+8‰). During growth in water culture the δ¹⁵N of the leaves, stems and roots ofElymus athericus decreased from +9‰ to ?1‰. The latter value was close to the °¹⁵N of the N-compounds used in the water solution. Addition of N-compounds in soil culture, however, did not lead to such a decrease of the °¹⁵N ofElymus athericus. The difference in δ¹⁵N between soil nitrogen and the N-compounds added may be too small to be used successfully in ecological studies of nitrogen fluxes in the salt marsh environment.     

Primary production and heterotrophy of a pennate and a centric salt marsh diatom

Radionuclide labeled sodium bicarbonate and glucose were used to measure the rates of primary production and glucose uptake by Nitzschia obtusa var. undulata and Cymbella pusilla. The presence of glucose in the medium enhanced primary production in both diatom species. Uptake of glucose in C. pusilla was photoinhibited. A maximum of 9.3 nmol C mg dry wt^-1 h^-1 of glucose was taken up in the light without the presence of NaHCO₃ in the medium and with NaHCO₃ present the value was 18 nmol C mg dry wt^-1 h^-1. The ratio of inorganic carbon fixed to the total carbon budget (autotrophy and heterotrophy) was 0.51 for N. obtusa var. undulata and 0.62 for C. pusilla.     

Strong population differentiation of softshell clams (Mya arenaria) sampled across seven biogeographic marine ecoregions: possible selection and isolation by distance

Twenty-two Mya arenaria samples spanning seven marine ecoregions mostly situated in the Cold Temperate Northwest Atlantic (CTNA) biogeographic province were collected between 2001 and 2010 and genotyped at seven highly polymorphic microsatellite loci to test for population differentiation. Results showed strong regional differentiation with six genetic clusters: (1) Northern Gulf of St. Lawrence (GSL), (2) Magdalen Archipelago, (3) Southern GSL, (4) Lower Atlantic Canada, (5) US Coasts and (6) Northern Europe. Population structure was supported no matter the statistical approach and generally does not reflect the geographical limits of marine ecoregions. A latitudinal cline in allelic richness provides evidence for a northward post-glacial expansion range for this species. While geographical distance explains the genetic variation detected in southern CTNA, increased heterogeneity observed in northern CTNA can be explained by isolation by distance, marine landscaping and presumable selective processes acting at the Mar5 locus. Exclusion of Mar5 from analyses resulted in the detection of three genetic clusters instead of six.     

On the parameterization of the roughness length for the air-sea interface in free convection

The roughness length at the air-sea interface during free convection (z_0fc) is mainly related to the convective velocity (w_*) rather than the friction velocity (u_*). The parameterization of z_0fc with w _* ² /g as proposed by Abdella and DAlessio in 2003 is evaluated. It is shown that their proposed formula is consistent with field measurements. In order to avoid self-correlation by using u_*, a new parameterization of w_* with wind speed (U_z) at height z and stability parameter (z/L, where L is the buoyancy length) is proposed. This new formula for w_* is in agreement with an independent field result.     

Evidence for benthic primary production support of an apex predator–dominated coral reef food web

Five hundred and ninety-nine primary producers and consumers in the Papahānaumokuākea Marine National Monument (PMNM) (22°N–30°N, 160°W–180°W) were sampled for carbon and nitrogen stable isotope composition to elucidate trophic relationships in a relatively unimpacted, apex predator–dominated coral reef ecosystem. A one-isotope (δ¹³C), two-source (phytoplankton and benthic primary production) mixing model provided evidence for an average minimum benthic primary production contribution of 65 % to consumer production. Primary producer δ¹⁵N values ranged from ?1.6 to 8.0 ‰ with an average (2.1 ‰) consistent with a prevalence of N₂ fixation. Consumer group δ¹⁵N means ranged from 6.6 ‰ (herbivore) to 12.1 ‰ (Galeocerdo cuvier), and differences between consumer group δ¹⁵N values suggest an average trophic enrichment factor of 1.8 ‰ Δ¹⁵N. Based on relative δ¹⁵N values, the larger G. cuvier may feed at a trophic position above other apex predators. The results provide baseline data for investigating the trophic ecology of healthy coral reef ecosystems.     

Hydrodynamics,diffusion-boundary layers and photosynthesis of the seagrasses Thalassia testudinum and Cymodocea nodosa

Photosynthetic rates of aquatic plants frequently increase with increasing current velocities. This is presumably due to a reduction in the thickness of the diffusion boundary-layer which allows for a higher carbon availability on the plant surface. Blades of the seagrasses Thalassia testudinum and Cymodocea nodosa exposed to different current velocities under controlled laboratory conditions, showed increased photosynthetic rates with increasing flow only at low current velocities (expressed as blade friction velocities, u _*). Carbon saturation of photosynthetic processes occurred at a relatively low u _* level (0.25 cm s^-1) for T. testudinum collected from a calm environment compared to C. nodosa (0.64 cm s^-1) collected from a surf zone. No further enhancement of photosynthetic rates was observed at higher u _* levels, suggesting limitations in carbon diffusion through the boundary layer below critical u ^* levels and possible limitations in carbon fixation by the enzymatic system at higher u _* levels. These results, as well as those of previous theoretical studies, assumed the flow on the immediate seagrass-blade surface to be hydrodynamically smooth. The presence of epiphytes and attached debris causes the surface of in situ seagrass blades to be exposed to flows ranging from smooth to rough-turbulent. As a consequence, the boundary-layer thickness on moderately epiphytized blades under medium to high flow-conditions is not continuous, but fluctuates in time and space, enhancing carbon transport. In situ u _* levels measured directly on blades of seagrasses indicate that T. testudinum and C. nodosa can be exposed to conditions under which the boundary layer limits photosynthesis during short periods of time (milliseconds) during low-energy events. As waves cause the thickness of the diffusion boundary-layer to fluctuate constantly, carbon-limiting conditions do not persist for prolonged periods.     

Nitrogen limitation in the coastal heath at Anholt,Denmark

The purpose of the study was to investigate, whether the coastal grey dune vegetation at Anholt, Denmark, is limited by nitrogen or phosphorus. The island Anholt (22,37 km²) is situated in the centre of Kattegat A two factor fertilization experiment with nitrogen as NH₄NO₃ (N-addition) and phosphorus as KH₂PO₄ (P-addition) was carried out in the coastal grey dune vegetation of Anholt. The N-addition corresponded to 40 kg N ha^?1 year^?1 and the P-addition to 7 kg P ha^?1 year^?1 The experiment included N-, P-, N + P-addition and control. Lichens (genera: mainly Cladonia, Stereocaulon, Cetraria, Hypogymnia) and bryophytes (genera: Polytrichum, Racomitrium) cover most of the surface. Only two plant species, Corynephorus canescens and Empetrum nigrum, constitute nearly all vascular plant cover and biomass of this calcium poor coastal heath community. Corynephorus and Empetrum increased their cover significantly following N and N + P addition. No effect was observed by P addition alone. N limitation of this coastal heath vegetation remote from agricultural and industrial activities was evident. The effect on the plant species of the single application was short-lived. After two-three years of enhanced cover, the Corynephorus and Empetrum cover had returned to their level before the experiment. The lichen vegetation, however, changed more permanently, and after 12 years the subplots with N + P addition was dominated by rich growth of Cladina and Cetraria species. The results are discussed in relation to anthropogenic nitrogen deposition and conservation of this high priority ecosystem.