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Light Penetration (light + penetration)
Selected AbstractsCompetitive effects of grasses and woody plants in mixed-grass prairieJOURNAL OF ECOLOGY, Issue 4 2001Duane A. Peltzer Summary 1,Variation in the competitive ability of plant species may determine their persistence and abundance in communities. We quantified the competitive effects of grasses and woody plants in native mixed-grass prairie on the performance of transplant species and on resources. 2,We separated the effects of grasses, shrubs and intact vegetation containing both grasses and shrubs by manipulating the natural vegetation using selective herbicides to create four neighbourhood treatments: no neighbours (NN), no shrubs (NS), no grasses (NG) and all neighbours (AN). Treatments were applied to 2 × 2 m experimental plots located in either grass- or shrub-dominated habitats. The effects of grasses and shrubs on resource availability (light, soil moisture, soil available nitrogen) and on the growth of transplants of Bouteloua gracilis, a perennial tussock grass, and Elaeagnus commutata, a common shrub, were measured over two growing seasons. 3,Resource availability was two- to fivefold higher in no neighbour (NN) plots than in vegetated plots (NS, NG, AN) with grasses and shrubs having similar effects. Light penetration declined linearly with increasing grass or shrub biomass, to a minimum of about 30% incident light at 500 g m,2 shoot mass. Soil resources did not decline with increasing neighbour shoot or root mass for either grasses or shrubs, suggesting that the presence of neighbours was more important than their abundance. 4,Transplant growth was significantly suppressed by the presence of neighbours, but not by increasing neighbour shoot or root biomass, except for a linear decline in Bouteloua growth with increasing neighbour shoot mass in plots containing only shrubs. Competition intensity, calculated as the reduction in transplant growth by neighbours, was similar in both grass- and shrub-dominated habitats for transplants of Bouteloua, but was less intense in shrub-dominated habitats for the shrub Elaeagnus. Variation in the persistence and abundance of plants in communities may therefore be more strongly controlled by variation in the competitive effects exerted by neighbours than by differences in competitive response ability. [source] Experimental sponge fishery in Egypt during recovery from sponge diseaseAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2005J. Castritsi-Catharios Abstract 1.A survey was undertaken (1995) on the Mediterranean coast of Egypt that investigated four sponge fishing grounds. These fishing banks suffered from sponge disease between 1987 and 1990, causing a mass mortality of commercial sponges in the eastern and central Mediterranean. 2.Adult commercial sponges (length >10 cm) were harvested by divers in the infralittoral zone (depth range 17,36 m). The substratum at most of the sampling stations was hard, consisting mainly of plaques, rocks and heavy stones, sometimes covered by Posidonia oceanica. 3.Two commercial sponge species were detected, Hippospongia communis and Spongia cfr zimocca; the former was more prevalent and abundant. Light penetration in the area surveyed was high. The two commercial sponge species detected seemed to be well adapted to these conditions, as indicated by the colour of their external membranes, which were almost black due to enhanced pigment formation. The absence of Spongia officinalis, in the area surveyed may also be related to light penetration, since S. officinalis is a more sciaphilous species. 4.The shape of H. communis was almost spherical, and the average dimensions (length, width, height, circumference) increased with increasing depth of the fishing grounds. At shallower depths (<30 m), adult H. communis occurred in lower densities, whereas young commercial sponges were abundant. No signs of sponge disease were found. 5.It is concluded that the recovery of the four sponge fishing grounds was in progress, and that the repopulation of commercial sponges in the infralittoral zone showed a gradient from deeper to shallower waters. It is recommended to prohibit destructive fishing methods in the deeper waters in order to protect the population and its ability to regenerate. Copyright © 2005 John Wiley & Sons, Ltd. [source] NEW APPLICATION OF NARROW BAND IMAGING FOR CHOLANGIOPANCREATOSCOPYDIGESTIVE ENDOSCOPY, Issue 2007Mitsuhiro Kida The usefulness of narrow band imaging (NBI), which is based on the principle that the depth of light penetration depends on its wavelength, has been accepted for evaluating malignant or benign lesions in the pharynx, the upper, and lower gastrointestine. The purpose of the present paper was to investigate NBI for diagnosing biliopancreatic disease. Using NBI it has become easy to detect the surface microstructure of biliary mucosa and subjacent vascular network of the bile duct, and inflammatory scarring stenosis is visualized as a whitish scar and multiple inflammatory red spots. However, bile duct cancer was detected as a stenosis with abnormal subjacent vessels and irregular surface. Concerning pancreatic duct, NBI has clearly shown vascular network and spreading of branch-type intraductal papillary mucinous neoplasm to the main pancreatic duct. In contrast, bile juice has been detected as red fluid and bleeding as black red. Therefore, it is important to flush the biliary system before observing with NBI. [source] Weedbeds and big bugs: the importance of scale in detecting the influence of nutrients and predation on macroinvertebrates in plant-dominated shallow lakesFRESHWATER BIOLOGY, Issue 3 2010ANGELA L. BERESFORD Summary 1. The scale of investigations influences the interpretation of results. Here, we investigate the influence of fish and nutrients on biotic communities in shallow lakes, using studies at two different scales: (i) within-lake experimental manipulation and (ii) comparative, among-lake relationships. 2. At both scales, fish predation had an overriding influence on macroinvertebrates; fish reduced macroinvertebrate biomass and altered community composition. Prey selection appeared to be size based. Fish influenced zooplankton abundance and light penetration through the water column also, but there was no indication that fish caused increased resuspension of sediment. 3. There were effects of nutrients at both scales, but these effects differed with the scale of the investigation. Nutrients increased phytoplankton and periphyton at the within-lake scale, and were associated with increased periphyton at the among-lake scale. No significant effect of nutrients on macroinvertebrates was observed at the within-lake scale. However, at the among-lake scale, nutrients positively influenced the biomass and density of macroinvertebrates, and ameliorated the effect of fish on macroinvertebrates. 4. Increased prey availability at higher nutrient concentrations would be expected to cause changes in the fish community. However, at the among-lake scale, differences were not apparent in fish biomass among lakes with different nutrient conditions, suggesting that stochastic events influence the fish community in these small and relatively isolated shallow lakes. 5. The intensity of predation by fish significantly influences macroinvertebrate community structure of shallow lakes, but nutrients also play a role. The scale of investigation influences the ability to detect the influence of nutrients on the different components of shallow lake communities, particularly for longer lived organisms such as macroinvertebrates, where the response takes longer to manifest. [source] Benthic metabolism in two turbid dryland riversFRESHWATER BIOLOGY, Issue 2 2009CHRISTINE S. FELLOWS Summary 1.,Australian dryland rivers have among the most variable discharge of any rivers worldwide and are characterized by extended periods of no flow during which aquatic habitat contracts into isolated waterholes. Despite naturally high turbidity, benthic primary production is known to be the main source of carbon to waterhole food webs. The objective of this study was to quantify rates of benthic metabolism and identify factors influencing these rates in two Australian dryland rivers, the Cooper Creek and the Warrego River. 2.,Both rivers have similar variable hydrology and high levels of turbidity (photic depths < 0.4 m), but fish abundance in Cooper Creek is 10 times than that of the Warrego River. Therefore, an additional aim of the study was to determine if fish abundances reflected underlying differences in benthic primary production. 3.,Benthic gross primary production (GPP), benthic respiration, nutrient concentrations and light penetration were measured immediately after flow had ceased (,post-flow') and after at least 2 months of zero flow (,no-flow') in 15 waterholes from each river. A subset of four waterholes from each river was sampled on two additional occasions to determine if patterns were consistent over time. 4. Cooper Creek generally had higher rates of GPP and a more autotrophic benthic zone than the Warrego River. As a result, the expected positive relationship between fish abundance and GPP was generally observed at a broad catchment scale. 4.,Light was the major control in benthic GPP in both rivers, as nutrient concentrations were high on all sampling occasions. However, for similar values of photic depth, GPP was greater in Cooper Creek than in the Warrego River. This suggests that more frequent disturbance of the littoral zone may inhibit biofilm development in waterholes of the Warrego River. 5.,Although flow variability in dryland rivers is extreme compared with other rivers worldwide, cycles of expansion and contraction of aquatic habitat in these two rivers were associated with a shift in the dominance of regional scale (subcatchments contributing to river flow) versus local scale (waterhole morphology) influences on ecosystem functioning, similar to floodplain rivers in tropical and temperate regions. [source] Effects of sediment resuspension on phytoplankton production: teasing apart the influences of light, nutrients and algal entrainmentFRESHWATER BIOLOGY, Issue 2 2004Marc Schallenberg Summary 1. Wind-induced sediment resuspension can affect planktonic primary productivity by influencing light penetration and nutrient availability, and by contributing meroplankton (algae resuspended from the lake bed) to the water column. We established relationships between sediment resuspension, light and nutrient availability to phytoplankton in a shallow lake on four occasions. 2. The effects of additions of surficial sediments and nutrients on the productivity of phytoplankton communities were measured in 300 mL gas-tight bottles attached to rotating plankton wheels and exposed to a light gradient, in 24 h incubations at in situ temperatures. 3. While sediment resuspension always increased primary productivity, resuspension released phytoplankton from nutrient limitation in only two of the four experiments because the amount of available nitrogen and phosphorus entrained from the sediments was small compared with typical baseline levels in the water column. In contrast, chlorophyll a entrainment was substantial compared with baseline water column concentrations and the contribution of meroplankton to primary production was important at times, especially when seasonal irradiance in the lake was high. 4. Comparison of the in situ light climate with the threshold of light-limitation of the phytoplankton indicated that phytoplankton in the lake were only likely to be light-limited at times of extreme turbidity (e.g. >200 nephelometric turbidity units), particularly when these occur in winter. Therefore, resuspension influenced phytoplankton production mainly via effects on available nutrients and by entraining algae. The importance of each of these varied in time. 5. The partitioning of primary productivity between the water column and sediments in shallow lakes greatly influences the outcome of resuspension events for water column primary productivity. [source] The balance between photosynthesis and grazing in Antarctic mixotrophic cryptophytes during summerFRESHWATER BIOLOGY, Issue 11 2002William Marshall SUMMARY 1. Grazing and photosynthetic contributions to the carbon balance of planktonic, mixotrophic cryptophytes in Lakes Fryxell and Hoare in the Taylor Valley, Antarctica were measured during November and December 2000. 2. The cryptophytes never became entirely photosynthetic, although carbon derived from grazing decreased in December. Individual grazing rates ranged between 5.28 and 10.08 bacteria cell,1 day,1 in Lake Fryxell and 0.36,11.76 bacteria cell,1 day,1 in Lake Hoare. Grazing rates varied temporally and with depth in the water column. In Lake Fryxell, which is a meromictic lake, highest grazing occurred just above the chemocline. Individual photosynthetic rates ranged from 0.23 to 1.35 pg C cell,1 h,1 in Lake Fryxell and 0.074 to 1.08 pg C cell,1 h,1 in Lake Hoare. 3. Carbon acquisition by the cryptophyte community gained through grazing ranged between 8 and 31% during November in Lake Fryxell, dropping to between 2 and 24% in December. In Lake Hoare grazing contributed 12,21% of the community carbon budget in November and 1,28% in December. Around 4% of the carbon acquired from grazing and photosynthesis was remineralised through respiration. 4. Mixotrophy is probably a major survival strategy for cryptophytes in the extreme lakes of the Dry Valleys, because perennial ice-cover severely limits light penetration to the water column, whereas these phytoflagellates are not normally mixotrophic in lower latitude lakes. The evidence suggests that mixotrophy may be a mechanism for supplementing the carbon budget, as well as a means of acquiring nutrients for growth. [source] Effects of Plant Population Density and Intercropping with Soybean on the Fractal Dimension of Corn Plant Skeletal ImagesJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 2 2000K. Foroutan-pour Three-year field experiments were conducted to determine whether the temporal pattern of fractal dimension (FD) for corn (Zea mays L.) plant structure is altered by plant population density (PPD) or intercropping with soybean [Glycine max. (L.) Merr.], and how changes in the FD are related to changes in other canopy characteristics. Plants in monocropped corn and intercropped corn,soybean plots were randomly sampled and labelled for later identification. Corn plant structure was photographed from the side that allowed the maximum appearance of details (perpendicular to the plane of developed leaves) and from two fixed sides (side 1: parallel to the row and side 2: perpendicular to the row). Images were scanned and skeletonized, as skeletal images provide acceptable information to estimate the FD of plant structure two-dimensionally by the box-counting method. Differences in the FD estimated from images taken perpendicular to the plane of developed leaves were not significant among competition treatments. An adjustment of corn plants to treatments, by changing the orientation of the plane of developed leaves with respect to the row, was observed. Based on overall FD means, competition treatments were ranked as: high > normal , intercrop , low for side 1 and intercrop > low , normal > high for side 2. Leaf area index (LAI) and plant height had a positive correlation with FD. In contrast, light penetration had a negative correlation with FD. In conclusion, FD provides a meaningful and effective tool for quantifying corn plant structure, measuring the structural response to cultural practices, and modelling corn plant canopies. Zusammenfassung Folgende Ziele der Untersuchungen wurden berücksichtigt: 1) Eine geeignete Methode für die Abschätzung der Anteile (FD) 2-dimensional für Pflanzen mit einer einfachen dreidimensionalen Vegetationsstruktur wie z. B. Mais (Zea mays L.) zu bestimmen; 2) der Frage nachzugehen, ob die zeitlichen Muster von FD bei der Maispflanzenstruktur durch die Bestandesdichte verändert wird (PPD: low, normal und hoch) oder in Mischanbau mit Sojabohnen (Glyzine max. L.) Merr.); und 3) in welcher Beziehung Änderungen in der FD in der Maispflanzenstruktur zu Änderungen in anderen Bestandeseigenschaften stehen. Pflanzen im Reinanbau von Mais und im Mischanbau in Mais-Sojabohnen-Parzellen wurden randomisiert gesammelt und für die spätere Identifikation gekennzeichnet. Die Maispflanzenstruktur wurde von der Seite fotografiert, so dai eine maximale Darstellung der Details (perpendiculär zu der Ebene der entwickelten Blätter) und von zwei festgelegten Seiten (Seite 1: parallel zur Reihe und Seite 2 perpendikulär zur Reihe) verfügbar war. Die Abbildungen wurden gescannt und skelettiert; Skelettabbildungen geben eine akzeptierbare Information zur Abschätzung von FD Pflanzenstrukturen in zweidimensionaler Form über die Box-counting-Methode. Unterschiede in der FD, die sich aus Bildern mit einer perpendikulären Aufnahme zu der Ebene der entwickelten Blätter ergaben, waren nicht signifikant innerhalb der Konkurrenzbehandlungen. Eine Anpassung der Maispflanzen an die Behandlungen durch Änderungen der Orientierung zur Ebene der entwickelten Blätter im Hinblick auf die Reihe, wurde beobachtet. Auf der Grundlage von gesamt FD-Mittelwerten ergab sich, dai Konkurrenzbehandlungen in folgender Reihe auftraten: Hoch (1,192) > (1,178) , zu Mischanbau (1,177) , zu gering (1,170) für Seite 1 und bei Mischanbau (1,147) > gering (1,158) , (1,153) > hoch für Seite 2. Der Blattflächenindex (LAI) und die Pflanzenhöhe hatten eine positive Korrelation zu FD. Im Gegensatz dazu wies die Lichtpenetration eine negative Korrelation zu FD auf. Es kann festgestellt werden, dai FD eine aussagekräftige und zweckmäiige Methode ist, die Maispflanzenstruktur zu quantifizieren, Strukturreaktionen zum Anbauverfahren zu messen und Maispflanzenbestände zu beschreiben. [source] A test of the indirect facilitation model in a temperate hardwood forest of the northern French AlpsJOURNAL OF ECOLOGY, Issue 6 2003Jean-Philippe Pages Summary 1We tested the hypothesis that the more frequent occurrence of tree seedlings below the adult trees than in canopy openings might be explained by indirect facilitation. In a temperate hardwood forest, we compared the performance of five target tree seedlings (Picea abies, Abies alba, Fagus sylvatica, Acer pseudoplatanus and Quercus petraea), transplanted with or without a herbaceous competitor (Molinia caerulea), either within the forest or into experimentally created gaps. 2We quantified changes in understorey biomass, light penetration and available forms of soil nitrogen during three growing seasons. 3Photosynthetic photon flux density and total biomass of Molinia were significantly higher in the gap treatment than within the forest. Total available nitrogen was higher in the gaps in the absence of Molinia, but higher in the forest in the presence of Molinia. 4Quercus survival was very low within the forest because of fungal infection, whereas survival was very high for the four other tree species in all combinations of the two treatments. 5Although the competitive effect of Molinia on the growth of the tree seedlings was much greater in the gap treatment, seedling growth was lower within the forest. We conclude that the tree canopy imposed strong light competition, and that this direct negative influence was much greater than any indirect positive effect of increased availability of nutrients to tree seedlings, due to reduced nutrient uptake by Molinia. 6Target species responses to treatments were similar, despite strong differences in nitrogen requirements between species. This may be due to the overwhelming negative influence of the tree canopy in our experiment. [source] Hardness of Three Resin-Modified Glass-Ionomer Restorative Materials as a Function of Depth and TimeJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 4 2009HOWARD W. ROBERTS DMD ABSTRACT Statement of the Problem:, The polymerization of bulk-placed resin-modified glass-ionomer (RMGI) restoratives is compromised when penetration of the curing light is limited because of the materials' thickness. It is unknown if additional post light-curing resin polymerization and/or glass-ionomer setting occurs over time to ensure adequate polymerization. Purpose:, The primary objective was to evaluate the depth of cure of various thicknesses of RMGI restorative products over 1 year using Knoop hardness (KH) testing. Materials and Methods:, The materials were placed in Delrin molds having an internal diameter of 5.0 mm and heights of 2, 3, 4, and 5 mm and were photopolymerized with a halogen light-curing unit. Five specimens of each depth were prepared for each time period evaluated. Specimens were stored in darkness at 37 ± 2°C and 98 ± 2% humidity until being tested at 24 hours, 1 week, and 1, 3, 6, 9, and 12 months after fabrication. Mean KH values were calculated for the bottom and top surfaces of each thickness group and used to determine bottom/top hardness ratios. Data were compared using two-way analysis of variance (factors of time, thickness) at a 0.05 significance level with Scheffé's post hoc analysis, where required. Results:, The materials had relatively stable top surface KH, which permitted valid assessment of changes in bottom surface KH over time. The bottom surface KH of some RMGIs changed significantly over time (p < 0.001), but degrees of change were material dependent. Certain RMGIs demonstrated a potential for statistically significant post light-activation hardening; however, that too was material dependent. As compared with top surface KH, deeper layers of the thicker RMGI specimens consistently failed to achieve an adequate degree of polymerization. Conclusion:, Although certain RMGI materials demonstrate a potential for post light-activation chemically initiated resin polymerization and/or polyalkenoate acid/base reaction, these reactions may not be sufficient to ensure that the material is adequately polymerized for long-term success. This is particularly true when RMGI materials are placed in thicker layers where curing light penetration may be compromised. CLINICAL SIGNIFICANCE RMGI materials should not be placed in bulk but photopolymerized in layers to ensure adequate light activation. The results of this study suggest that Photac-Fil Quick be placed in layers no thicker than 2 mm while Fuji II LC and Vitremer may be placed in layers up to 3 mm in thickness. [source] Comparison of red and green laser doppler imaging of blood flowLASERS IN SURGERY AND MEDICINE, Issue 3 2004Andrea K. Murray PhD Abstract Background and Objectives Laser Doppler imaging (LDI) of perfusion has been performed with a novel green wavelength (532 nm) for comparison with a HeNe laser (633 nm), the aim being validation of the green laser wavelength as a research tool. Study Design/Materials and Methods The effect of wavelength and power on images was investigated and perfusion response following both finger occlusion and local heating of the dorsum were examined as reproducible stimuli for clinical studies. Results The most striking difference between red and green LDI is the absence of veins on green LDI, which are seen with red LDI. Differences have been quantified using vein LDI profiles. Differences were found between blood flow responses imaged by red and green LDI (3 and 5 mW, respectively) for occlusion and heat stimuli. Results are discussed in the context of light penetration. Conclusions Red and green wavelengths appear to image different components of the microcirculation. Lasers Surg. Med. 35:191,200, 2004. © 2004 Wiley-Liss, Inc. [source] Functional ecology of a blue light photoreceptor: effects of phototropin-1 on root growth enhance drought tolerance in Arabidopsis thalianaNEW PHYTOLOGIST, Issue 1 2007Candace Galen Summary ,,The blue light photoreceptor phototropin-1 has been shown to enhance fitness in Arabidosis thaliana under field conditions. Here, we ask whether performance consequences of phototropin-1 reflect its impact on root growth and drought tolerance. ,,We used a PHOT1-GFP gene construct to test whether phototropin-1 abundance in roots is highest at shallow soil depths where light penetration is greatest. We then compared root growth efficiency and size at maturity between individuals with and without functional phototropin-1. Comparisons were made under wet and dry conditions to assess the impact of phototropin-1 on drought tolerance. ,,Phototropin-1 was most abundant in upper root regions and its impact on root growth efficiency decreased with soil depth. Roots of plants with functional phototropin-1 made fewer random turns and traveled further for a given length (higher efficiency) than roots of phot1 mutants. In dry (but not wet) soil, enhancement of root growth efficiency by phototropin-1 increased plant size at maturity. ,,Results indicate that phototropin-1 enhances performance under drought by mediating plastic increases in root growth efficiency near the soil surface. [source] Determination of Wavelength-Specific UV Protection Factors of Sunscreens in Intact Skin by EPR Measurement of UV-Induced Reactive Melanin RadicalPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Leslie Lund ABSTRACT There remains an unmet need for skin tissue-based assays for the measurement of the UVA protection and efficacy of sunscreens. Here we describe development of a novel electron paramagnetic resonance assay that uses the photogeneration of reactive melanin radical as a measure of UV light penetration to melanocytes in situ in skin. We have used areas of focal melanocytic hyperplasia in the skin of Monodelphis domestica to model the human nevus. We show that we are able to use this assay to determine the monochromatic protection factors (mPF) of research and commercial sunscreens at specific narrow wavebands of UVB, UVA and blue visible light. Both commercial sunscreens, a sun protection factor (SPF) 4 and an SPF 30 product, had mPFs in the UVB range that correlated well with their claimed SPF. However, their mPF in the UVA ranges were only about one-third of claimed SPF. This technique can be used to design and assay sunscreens with optimally balanced UVA and UVB protection. [source] Ultrastructural changes induced in cutaneous collagen by ultraviolet-A1 and psoralen plus ultraviolet A therapy in systemic sclerosisTHE JOURNAL OF DERMATOLOGY, Issue 2 2008Noriyuki SAKAKIBARA ABSTRACT In the present study, we examined the ultrastructural alterations in collagen fibrils clinically softened by ultraviolet-A1 (UVA1, 340,400 nm) therapy and psoralen plus long-wave ultraviolet (PUVA) therapy and compared collagen fibril diameters in four patients with systemic sclerosis (SSc). In skin sclerosis, the dermis is compacted from the epidermal layer to the sweat glands, and the collagen bundles are thicker with decreased space between them. We obtained skin specimens before and after UVA1 or PUVA therapy, and compared cutaneous alterations in one diffuse-type patient and one limited-type patient following UVA1 therapy, and in two diffuse-type patients following PUVA treatment. Ultramicroscopic analysis revealed that UVA1 treatment decreased the diameter of the broad collagen fibrils, mainly in the upper reticular layer. PUVA induced similar alterations in the collagen fibrils, extending to the upper and middle reticular layers. PUVA therapy induced alterations in collagen fibril diameter in deeper layers than did UVA1 therapy, which might be related to the direct action of UV light and the depth of the light penetration. In three of four patients, collagen fibril diameter decreased, collagen fibril thickness equalized, and new, thin fibrils developed among the collagen fibrils, suggesting that collagen degradation and synthesis underlie the alterations induced by UVA1 and PUVA phototherapies. [source] Conservation of natural wilderness values in the Port Davey marine and estuarine protected area, south-western TasmaniaAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2010Graham J. Edgar Abstract 1.Port Davey and associated Bathurst Harbour in south-western Tasmania represent one of the world's most anomalous estuarine systems owing to an unusual combination of environmental factors. These include: (i) large uninhabited catchment protected as a National Park; (ii) ria geomorphology but with fjord characteristics that include a shallow entrance and deep 12-km long channel connecting an almost land-locked harbour to the sea; (iii) high rainfall and riverine input that generate strongly-stratified estuarine conditions, with a low-salinity surface layer and marine bottom water; (iv) a deeply tannin-stained surface layer that blocks light penetration to depth; (v) very low levels of nutrients and low aquatic productivity; (vi) weak tidal influences; (vii) marine bottom water with stable temperature throughout the year; (viii) numerous endemic species; (ix) strongly depth-stratified benthic assemblages exhibiting high compositional variability over small spatial scales; (x) deepsea species present at anomalously shallow depths; (xi) no conspicuous introduced taxa; (xii) a predominance of fragile sessile invertebrates, including slow-growing fenestrate bryozoans; and (xii ) sponge spicule- and bryozoan-based sediments that are more characteristic of deep sea and polar environments than those inshore. 2.Although this region has historically been protected by its isolation, seven major anthropogenic stressors now threaten its natural integrity: boating, fishing, dive tourism, nutrient enrichment, introduced species, onshore development, and global climate change. These threats are not randomly distributed but disproportionately affect particular habitat types. 3.For management of environmental risk, the Port Davey,Bathurst Harbour region is subdivided into six biophysical zones, each with different ecological characteristics, values, and types and levels of potential threat. In response to the various threats, the Tasmanian Government has enacted an adaptive management regime that includes a multi-zoned marine protected area and the largest ,no-take' estuarine protected area in Australia. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||