Tide Mark Research Articles

Functional traits of common New Zealand foredune species at New Brighton, Canterbury

The introduction of exotic plant species to the sand dunes of New Zealand has displaced native dune species. To examine our hypotheses that: (1) exotic species have functional traits that allow them to outcompete native species; and (2) that traits of exotic species vary across the dune environment, we measured specific leaf area, leaf dry matter content, leaf area and plant height in five common fore-dune taxa of New Brighton, Christchurch. The native species Spinifex sericeus, Ficinia spiralis and Poa billardierei had traits indicative of a more conservative growth strategy compared with the exotic tussock grass Ammophila arenaria and the exotic succulent Carpobrotus spp., suggesting that natives would be less competitive. In exotics, leaf size was larger at greater distances from the high tide mark, as was plant height in A. arenaria. These differences in traits across the dune environment point to phenotypic plasticity across short, but sharp, environmental gradients.

Nitrogen transformations within a tropical subterranean estuary

A detailed geochemical groundwater survey was conducted within a carbonate sand subterranean estuary (STE) system on the tropical island of Rarotonga, Cook Islands, to identify N sources and transformation along the groundwater flow paths. There were two distinct sources of N to the STE: (1) local organic material which produced NH4+ in the anoxic deeper groundwater (3.5–4m below the aquifer surface), and (2) an NO3− rich upper saline plume located in the shallow groundwater near the high tide mark of the STE. Ammonium concentrations decreased away from the organic source and the δ15N-NH4+ signature became increasingly enriched. The calculated kinetic fractionation factor for NH4+ loss was much less than that reported for nitrification in other systems, implying that mixing was important in reducing concentration. A simple fractionation/mixing model showed that NH4+ loss via nitrification increased towards the surface where it contributed up to 80% of the observed decrease in NH4+ concentration. A fast moving (~2md−1) upper saline plume of shallow NO3− rich groundwater was a major feature of the studied STE. Denitrification was estimated to account for up to 88% of the decrease in NO3− concentration in this plume. The potential denitrification rate based on an isotope tracer addition experiment was 270μmolL−1d−1. Assuming that similar NO3− rich plumes occur all along the foreshore of the studied lagoon, we estimate that groundwater can contribute 4–15% of the daily lagoon N standing stock. We conclude that submarine groundwater discharge of shallow N rich porewater into the studied lagoon system is strongly regulated by denitrification within the STE.

Behavioural adaptations of two sympatric sandhoppers living on a mesotidal European Atlantic sandy beach

Behavioural adaptations of supralittoral species on sandy beaches are expressed as responses to environmental changes and constitute a key factor in their survival and evolution. Two sympatric talitrid amphipods (Talitrus saltator and Britorchestia brito) from a mesotidal exposed sandy beach on the European Atlantic coast (Portugal) were compared as regards orientation and littoral zonation patterns under natural conditions. Orientation experiments were carried out during spring and summer 2011 and 2012 at Quiaios beach, a highly dynamic exposed sandy beach. Multiple regression models were fitted to the angular data and the environmental effects on orientation were investigated for each species. Both talitrids were shown to be well orientated towards the shoreline and finely adapted to the mesotidal environment but a different use of local cues and climatic features between the two species was apparent. T. saltator showed a lower precision in the orientation performance (with a bimodal distribution sea- and land-wards), with less dependence on the sun cues and higher dependence on climatic features. In addition, the zonation of T. saltator was across the land–sea axis during both seasons. For B. brito the landscape vision, sun visibility and the tidal range enhanced the orientation to the shoreline. On this mesotidal Atlantic beach, T. saltator appeared to have a more flexible orientation with respect to B. brito, which appeared to be more dependent on the conditions offered by the intertidal zone, a behaviour confirmed by its restricted zonation below the high tide mark. Consequently, T. saltator showed a more flexible behaviour that may be considered an important evolutionary adaptation to dynamic and mesotidal sandy beaches.

Regional scale impact of tidal forcing on groundwater flow in unconfined coastal aquifers

summary This paper considers the impact of tidal forcing on regional groundwater flow in an unconfined coastal aquifer. Numerical models are used to quantify this impact for a wide range of hydrogeological conditions. Both a shallow and a deep aquifer are investigated with regard to three dimensionless parameter groups that determine the groundwater flow to a large extent. Analytical expressions are presented that allow for a quick estimate of the regional scale effect of tidal forcing under the same conditions as used in the numerical models. Quantitatively, the results in this paper are complementary to previous studies by taking into account variable density groundwater flow, dispersive salt transport and a seepage face in the intertidal area. Qualitatively, the results are in line with previous investigations. The time-averaged hydraulic head at the high tide mark increases upon a decrease of each of the three considered dimensionless parameter groups: R (including the ratio of the hydraulic conductivity and the precipitation excess), a (the slope of the intertidal area) and AL (the ratio of the width of the fresh water lens and the tidal amplitude). The relative change of the location and the hydraulic head of the groundwater divide, which together characterize regional groundwater flow, increase as a and AL decrease, but decrease as R decreases. The difference between the analytical solutions and numerical results is small. Therefore, the presented analytical solutions can be used to estimate the bias that is introduced in a numerical model if tidal forcing is neglected. The results should be used with caution in case of significant wave forcing, as this was not considered.

Pyrite-coated granite cobbles at Lee Bay, Stewart Island

On the west side of Lee Bay on the northeast coast of Stewart Island, ventifact cobbles of pyrite-coated granite occur on the beach near the high tide mark and appear to be derived from a sand-cemented gravel deposit that forms a low bank at the back of the beach. The pyrite coat (up to 1 mm thick) completely covers the granitic cobbles and is zoned, with an inner zone of fine-grained colloform pyrite and an outer framboidal zone. Framboidal pyrite is typically formed in anoxic sedimentary environments. Subrounded grains of hematite, ilmenite with hematite blebs, magnetite, feldspar, biotite, quartz and zircon are present in the outer framboidal zone, with some ilmenite and hematite grains being partially replaced by pyrite. The assemblage of ilmenite-hematite-magnetite-biotite-zircon is similar both in mineralogy and size range to that found in heavy mineral beach sands. Sulphur isotope values of the pyrite coat are consistent with formation of the pyrite by microbial sulphate reduction of seawater sulphate. The framboidal texture together with the presence of grains of beach sand in the pyrite coating indicate that it was deposited in a low-temperature sedimentary environment.

Deleterious effects of osteoarthritis on the structure and function of the meniscal enthesis

The ability of menisci to prevent osteoarthritis (OA) is dependent on the integrity of the complex meniscal entheses, the attachments of the menisci to the underlying subchondral bone (SB). The goal of this study was to determine mechanical and structural changes in meniscal entheses after the onset of OA. Healthy and osteoarthritic meniscal entheses were evaluated for changes in histomorphological characteristics, mineralization, and mechanical properties. Glycosaminoglycans (GAG) and calcium in the insertion were evaluated with histological staining techniques. The extent of calcium deposition was assessed and tidemark (TM) integrity was quantified. Changes in the mineralized zone of the insertion were examined using micro-computed tomography (μCT) to determine bone mineral density, cortical zone thickness, and mineralization gradient. Mechanical properties of the entheses were measured using nano-indentation techniques to obtain material properties based on viscoelastic analysis. GAG thickness in the calcified fibrocartilage (CFC) zone and calcium content were significantly greater in osteoarthritic anterior meniscal entheses. TM integrity was significantly decreased in OA tissue, particularly in the medial anterior (MA) enthesis. The mineralized zone of osteoarthritic meniscal entheses was significantly thicker than in healthy entheses and showed decreased bone mineral density. Fitting of mineralization data to a sigmoidal Gompertz function revealed a lower rate of increase in mineralization in osteoarthritic tissue. Analysis of viscoelastic mechanical properties revealed increased compliance in osteoarthritic tissue. These data suggest that significant changes occur at meniscal enthesis sites with the onset of OA. Mechanical and structural changes in meniscal entheses may contribute to meniscal extrusion, which has been shown to increase the progression of OA.

The ecology of freshwater wrack along natural and engineered Hudson River shorelines

Organic matter that is washed onto shore, or “wrack,” is an important component of shoreline ecosystems, providing habitat for macroinvertebrates and organic matter and nutrients to both the upland terrestrial communities and aquatic ecosystems. While marine wrack has been studied extensively, wrack along freshwater shorelines has received less attention. In this article, we report on the standing stocks, mobility, decomposition rates, and macroinvertebrate communities of wrack on different types of Hudson River shorelines (natural: sand, rock, bedrock; and engineered: riprap, cribbing, and bulkhead). Standing stocks of wrack sometimes exceeded 1 kg dry mass/m2, and were the highest on shorelines having flat slopes. Artificial wrack (hay) placed below the high tide mark was rarely retained for more than a few tidal cycles, particularly on highly exposed shores. Wrack on cribbing shorelines decayed significantly faster than on other shoreline types. Macroinvertebrate abundance and diversity were significantly different among shoreline types, with the lowest abundance found on cribbing, along with significantly lower diversity. Consequently, if managers use structures such as cribbing and bulkheads to rebuild or reinforce shorelines, then certain ecological functions may be lost.

Differential accumulation of lead and zinc in double-tidemarks of articular cartilage

Long-term exposure to increased lead (Pb) concentrations is associated with several chronic diseases. The divalent cation zinc (Zn) is essential for numerous enzymes. In a recent study we found remarkably elevated concentrations of Pb and Zn in the tidemark (TM), which is the mineralization front of human articular cartilage. Duplication or multiplication of TMs occurs with advancing age or degeneration. We hypothesized that trace elements accumulate in TMs as a function of time. Thus, in cases of double TMs, the deep (older) TM should contain higher Pb and Zn concentrations than the superficial (younger) TM. Undecalcified tissue from articular cartilage and subchondral bone of femoral heads and patellae was examined by synchrotron radiation induced confocal micro X-ray fluorescence analysis and by quantitative backscattered electron imaging to determine the local distribution of Ca, Zn, and Pb in this tissue. The evaluation of X-ray fluorescence intensities in double TMs revealed in average a 2.6-fold higher Pb level in the deep TM compared to the superficial TM while Zn concentrations were similar. Pb and Zn contents were significantly enhanced in the deep TM (Pb: 35-fold, Zn: five-fold) and in the superficial TM (Pb: 12-fold, Zn: five-fold) compared to the bone level. For the first time a differential accumulation of Pb and Zn is documented in regions with double TMs revealing various timescales for the accumulation of these elements. Increased amounts of Pb are present in the TMs (up to the 62-fold of the bone level) featuring a potential source of internal Pb release if the TM region is destroyed.

A comparison of the post-storm recovery of two sandy beaches on Hong Kong Island, southern China

Typhoon Hagupit was one of six tropical cyclones that affected Hong Kong in 2008. When the typhoon made landfall, the combined effect of the waves, storm surge and seasonal high tides resulted in a maximum sea level of 3.53 m at the nearest tide gauge to the study site, the highest since 1962. The event caused considerable damage to coastal infrastructure and large-scale erosion on many sandy beaches in Hong Kong. To study the degree of erosion and recovery of Hong Kong beaches, we surveyed two sandy beaches: Tai Long Wan (TLW), a relatively high-energy exposed beach system, and To Tei Wan (TTW), a relatively low-energy Sheltered beach system. We examined the two beaches for changes in their beach profiles and sediment properties. TLW recovered quickly, with significant post-storm accretion of fine- to medium-grained sand. Within four months after the typhoon, TLW regained >700 m3 sand, forming a new, ∼1.0 m high, berm, with the beach face prograding approximately 5.0 m seaward. In contrast, within the same four months after the typhoon, TTW showed little evidence of sand accretion or recovery, with only minor changes in the beach profile. In fact, instead of post-storm sand accretion, the landward migration of the high tide mark shown in the pre- and post-storm satellite images suggested that the post-storm beach elevation at TTW decreased. The results, which reflect the different background energy regimes of each beach, indicate that different coastal management strategies should be applied. In the case of relatively high-energy beaches of Hong Kong, we suggest not interfering with their natural state. In contrast, in the case of relatively low-energy beaches of Hong Kong, which appear unlikely to recover rapidly from erosion during storms, we suggest further investigation before applying any long- to medium-term management strategies.

ST. IVES, CORNWALL, TIDAL EQUATIONS, 2012

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Spatial Distribution of Uca sindensis (Crustacea, Ocypodidae) along the coast of Pakistan

Spatial distribution of Uca sindensis was studied along the coast of Pakistan. The density, size distribution, population structure, sex ratio and handedness were investigated. U. sindensis crabs were collected through quadrate (0.5 m2 quadrates were placed during low tide periods) and transect (low tide mark to high tide mark) method from nine different sites along the coast. Results indicated that the substratum properties (organic content, size,and heterogeneity) were of primarily importance for the distribution of U. sindensis. The spatial variation was observed in the density distribution and was ranged from 4 to 48 m-2. The overall sex ratio was differed significantly from the expected 1:1 (χ2 =22.4; P = 0.004). The sizes of the male and female crabs were significantly different at all studied sites. The carapace (CW) of males ranged from 8.3 to 17.3 mm and of females from 6.2 to 14.4 mm indicating sexual dimorphism. The occurrence of dextral and sinistral males was overall in the 1:1 ratio.

Anti-inflammatory effect of chondromodulators in experiment

Background. There are a few data about the systemic influence of drugs, used in osteoarthritis. A hind limp arthropathy is characterized by progressive cartilage destruction and develops spontaneously in MRL/Mp-lpr/lpr (MRL/l) mice. These mice are a good model for assessment of drugs with chondro-reparitive activity. The aim of our investigation was to study healing effect of intramuscular injection (IMJ) of chondroitin sulphate (CS) on joint cartilage and tissue lesions. Material and methods. The age of all animals (60 mice - 30males and 30 females) at the experiment beginning was 5 months. Cartilage, heart, kidney and liver were studied in two groups as follows: the placebo group received 3 times per week 25 IMJ of 0,2 ml isotonic solution, CS group - received 3 times per week 25 IMJ of 0,2 ml 10% solution CS. After euthanasia tissues were fixed for 24 hours in 10% neutral buffered formaldehyde. Kidney, heart and liver were investigated by histological and histochemical methods. The material was studied by blind method. Results. At the end of the experiment only 5 males survived in placebo group, in the CS group - 15males and 10 females. The alive animals were decapitated. In placebo group fibrocartilage articular surface was destroyed and remodelled. Tide mark was absent. Acid glycosaminoglycanes (GAG) depletion and collagen network fragmentation have been estimated. Severe vasculitis in all organs were found. There were severe nephritis, myocarditis and hepatitis too. In the CS group cartilage was uniform, with normal thickness and layer differentiation. Cartilage reparation processes have been estimated as follows - the number of double-nuclear chondrocytes increased and accumulated in groups. GAG increased too. Collagen structure re-established. Tide mark was safe. Dystrophy and mild vasculitis in heart and liver, severe alteration in kidney were found. There was significant difference between the group results (p<0,05). Conclusion. Not only cartilage, but organic lesions, such as vasculitis, nephritis, myocarditis and hepatitis are influenced after chondromodulators’ treatment of MRL/l mice. These results provide some insight into the anti-inflammatory mechanism of CS action.

Mangrove litter fall: Extrapolation from traps to a large tropical macrotidal harbour

Mangrove litter is a major source of organic matter for detrital food chains in many tropical coastal ecosystems, but scant attention has been paid to the substantial challenges in sampling and extrapolation of rates of litter fall. The challenges arise due to within-stand heterogeneity including incomplete canopy cover, and canopy that is below the high tide mark. We sampled litter monthly for three years at 35 sites across eight mapped communities in the macrotidal Darwin Harbour, northern Australia. Totals were adjusted for mean community canopy cover and the occurrence of canopy below the high tide mark. The mangroves of Darwin Harbour generate an estimated average of 5.0 t ha −1 yr −1 of litter. This amount would have been overestimated by 32% had we not corrected for limited canopy cover and underestimated by 11% had we not corrected for foliage that is below the high tide mark. Had we made neither correction, we would have overestimated litter fall by 17%. Among communities, rates varied 2.6-fold per unit area of canopy, and 3.9-fold among unit area of community. Seaward fringe mangroves were the most productive per unit of canopy area but the canopy was relatively open; Tidal creek forest was the most productive per unit area of community. Litter fall varied 1.1-fold among years and 2.0-fold among months though communities exhibited a range of seasonalities. Our study may be the most extensively stratified and sampled evaluation of mangrove litter fall in a tropical estuary. We believe our study is also the first such assessment to explicitly deal with canopy discontinuities and demonstrates that failure to do so can result in considerable overestimation of mangrove productivity.

Change of Diffusion Tensor Imaging Parameters in Articular Cartilage With Progressive Proteoglycan Extraction

To investigate changes of diffusion tensor imaging (DTI) parameters (mean apparent diffusion coefficient [ADC], fractional anisotropy [FA], and first eigenvector) with increasing proteoglycan (PG) extraction of articular cartilage. Twelve cylindrical cartilage-on-bone samples were drilled from 4 human patellae (3 per patella). Each sample was divided into 2 pieces. One piece underwent histologic examination to assess the PG content of the native sample by safranin-O staining and its collagen architecture by polarized light microscopy. The other underwent magnetic resonance imaging (MRI) at 17.6 T for DTI measurement. After MRI, 2 of the 3 samples from each patella were immersed in a dilute trypsin solution (0.1 mg/mL), whereas the third sample was kept as a negative control in physiological saline. After incubation (6, 48, 72, and 96 hours), the samples were reimaged, stained for PG content and for the collagen orientation. Maps of ADC, FA, and the orientation of the first eigenvector as well as histology were available for each sample before and after incubation. PG loss led to increased ADC and reduced safranin-O staining from the articular surface to the bone-cartilage interface. A significant correlation (r(2) = 0.86, P < 0.01) was observed between the change in bulk ADC and PG loss. Regional analysis from the articular surface to the tide mark demonstrated depth dependent significant correlations of ADC and PG loss. FA and first eigenvector as well as polarized light microscopy showed only small changes in the order of magnitude of measurement errors, not correlating with PG loss. Mean diffusivity evidence by the ADC is linearly correlated to progressive PG extraction in articular cartilage. FA and the first eigenvector seem to be specific to the collagen architecture of cartilage. DTI has the potential to become a valuable biomarker for the workup of cartilage degeneration in osteoarthritis, since evaluation of the PG content and collagen architectural properties of cartilage can be performed with a single, non–contrast-enhanced proton-based MRI measurement.

Distribution and species composition of the littoral interstiticial free living nematodes in the northern Red Sea, Egypt

ree living nematodes represent the most abundant and diversified group of the interstitial meiobenthos in the northern Red Sea, where their contribution ranged between 38 and 100% of total count of all interstitial organisms. Nematodes distribution, abundance and species composition in the Egyptian Red Sea were studied during winter, 2006. Nematodes abundance ranged between 8 and 163 organisms/10 cm 2 . The intertidal zonation was investigated and showed increasing in the average density of nematodes toward low tide mark (sublittoral zone). A total of 79 nematode species were recorded; xyalid and oncholaimid were the most abundant families contributing 12% for each of total nematodes count. Densities of nematodes were affected by the grain size of the sediment, TOMs and redox potential (Eh). Also, pollution and landfilling have the most drastic effect on their abundance and diversity.

Effect of salinity and PEG-induced water stress on water status, gas exchange, solute accumulation, and leaf growth in Ipomoea pes-caprae

This study was designed to evaluate the response of I. pes-caprae, a pantropical species growing down to the high tide mark on the beach, under low and high drought and saline stresses and under both stresses applied simultaneously. Leaf water relations, gas exchange parameters, and leaf expansion and production rates were evaluated using NaCl and Polyethylene glycol 6000 to adjust the iso-osmotic potential in the nutrient solution to −0.5 and −1.0 MPa. Additionally, both osmotica were combined in the quantities required to allow that both solutes contribute in the same proportion to the total reduction in the solution water potential. The leaf osmotic potential decreased more rapidly at low stress levels and was always lower in plants growing under salinity. At long term, the osmotic adjustment was reached in all treatments, but under high stress, the osmotic adjustment was delayed and plants experimented eventual turgor loss. The simultaneous addition of NaCl and PEG accelerated turgor recovery after the induction of osmotic stress, compared with both agents applied individually. Na + accumulation was enhanced in plants by salt addition, while proline content per leaf water unit increased significantly only at high stress levels. In all treatments maximum assimilation rate and stomatal conductance decreased the first day after addition of salt and/or PEG, and thereafter progressively increased throughout the treatment. At short term and at high stress level, the leaf expansion rate (LER) decreased compared with control plants. When both stresses were applied simultaneously, the effects on LER and leaf area were less detrimental when compared with each stress separately. The results suggest that I. pes-caprae is more susceptible to high water limitations than to soil salinity, while the water and carbon balance were always enhanced when both stresses were applied simultaneously. Thus, although salinity and drought stress are physiologically related and the tolerance mechanisms overlap, some aspect of plant physiology and metabolism may differ when the plant experiments single saline and water or both stresses simultaneously.

Erratum to: Responses of Uniola paniculata L. (Poaceae), an Essential Dune-Building Grass, to Complex Changing Environmental Gradients on the Coastal Dunes

Coastal dunes are well known for plant species zonation but less is known about species-specific responses to underlying environmental gradients. We investigated variation in morphological traits and tissue nutrient concentration in Uniola paniculata, along a shoreline-to-landward gradient (transects spanning from the dunes directly behind the high tide mark to 40–100 m inland) in the southeast USA. Several environmental factors decreased with distance from the shoreline (soil B, K, Mg, Na; salinity, pH, and sand accretion), and differences were most pronounced between the 10 m closest to the shoreline and the remainder of the transect. In the 10 m closest to the shoreline, 94% more sand accumulated, which was 31% more saline. Additionally, plants here were taller, contained higher aboveground tissue N and K, and a higher percentage tended to flower. This contrasts with patterns found in salt marshes and saline desert dunes, where plant size is often negatively correlated with salinity. During the 2 years following the planned study, storms washed out ≤25 m of the transects. Resampling of the remaining sites demonstrated that even after erosion of the dune profile, a higher percentage of the plants in the 10 m closest to the shoreline plants tended to flower, relative to populations located further from the shore. Our findings suggested that the environment and plant response in the shoreward 10 m can re-establish relatively quickly.

Optical imaging of mouse articular cartilage using the glycosaminoglycans binding property of fluorescent-labeled octaarginine

The aim of the current study was to examine the cartilage-specific binding property of polyarginine peptides (R4, 8, 12, and 16) and specifically to test octaarginine peptides for the optical imaging of articular cartilage in experimentally induced arthritis in mice. Four rhodamine-labeled polyarginine peptides each with a different-length arginine chain (R4, 8, 12, or 16) were injected into the knee joints of C57BL/6J mice (n=20). The joints were excised 1h later and the fluorescent signal intensity in cartilage cryosections was compared for the four peptides. To examine the substrate of R8 in cartilage, femoral condyles obtained from another set of mice were treated with chondroitinase ABC (Ch'ase ABC), keratanase or heparitinase then immersed in R8-rhodamine. Fluorescent signals were examined by fluorescent microscopy. Next, R8-rhodamine was injected into the right knee joints of three control and three collagen antibody-induced arthritis (CAIA) mice, and fluorescent intensity in normal and degenerative cartilage was semi-quantitatively analysed on the histological sections using image software. Finally, femoral condyles from normal mice (n=2) and CAIA mice (n=2) were immersed in R8-rhodamine and calcein, then imaged using optical projection tomography (OPT). Fluorescent signals were specifically detected in the cartilage pericellular matrix from the surface to the tide mark but were completely absent in the calcified layer or bone marrow. The number of arginine residues significantly influenced peptide accumulation in articular cartilage, with R8 accumulating the most. The fluorescent signal in the femoral condylar cartilage diminished when it was treated with Ch'ase ABC. R8 accumulation was significantly decreased in the degenerative cartilage of CAIA mice, and this was demonstrated both histologically and in three-dimensional (3D)-reconstruction image by OPT. R8 may be a useful new experimental probe for optical imaging of normal and arthritic articular cartilage.

Ecophenotypic variation in the Flat Tree Oyster, Isognomon alatus (Bivalvia: Isognomonidae), across a tidal microhabitat gradient

Isognomon alatus is a sessile intertidal bivalve species that attaches to hard substrata. Within the Florida Keys, where tidal ranges are usually less than 1 m, settlement sites only a few centimetres apart experience drastically different tidal microhabitats. These varying conditions may create morphological gradients that can complicate taxonomic designations. To quantify and characterize the conchological effects of this microhabitat gradient and estimate the degree to which these effects can confuse species identification, I. alatus was studied in relation to tidal position using geometric morphometrics. Isognomon alatus was only found at positions 0.4 m below the highest tide mark, positions exposed to air less than 80% of the time. Below this limit specimen size, immersion time, and area available all covary. Shape differences due to ontogeny were removed using regression and the remaining phenotypic variation within these specimens is significantly correlated with the measured habitat conditions, immersion time being the more robust predictor. The observed phenotype effects are small but can influence species identification. Species assignment tests between I. alatus and the morphologically similar Indo-Pacific I. ephippium ranged in accuracy from 98 to 90% across microhabitat conditions.

Cartilage Collagen Matrix Reorientation and Displacement in Response to Surface Loading

An investigation of collagen fiber reorientation, as well as fluid and matrix movement of equine articular cartilage and subchondral bone under compressive mechanical loads, was undertaken using small angle X-ray scattering measurements and optical microscopy. Small angle X-ray scattering measurements were made on healthy and diseased samples of equine articular cartilage and subchondral bone mounted in a mechanical testing apparatus on station ID18F of ESRF, Grenoble, together with fiber orientation analysis using polarized light and displacement measurements of the cartilage matrix and fluid using tracers. At surface pressures of up to approximately 1.5 MPa, there was reversible compression of the tangential surface fibers and immediately subjacent zone. As load increased, deformation in these zones reached a maximum and then reorientation propagated to the radial deep zone. Between surface pressures of 4.8 MPa and 6.0 MPa, fiber orientation above the tide mark rotated 10 deg from the radial direction, with an overall loss of alignment. With further increase in load, the fibers "crimped" as shown by the appearance of subsidiary peaks approximately +/-10 deg either side of the principal fiber orientation direction. Failure at higher loads was characterized by a radial split in the deep cartilage, which propagated along the tide mark while the surface zone remained intact. In lesions, the fiber organization was disrupted and the initial response to load was consistent with early rupture of fibers, but the matrix relaxed to an organization very similar to that of the unloaded tissue. Tracer measurements revealed anisotropic solid and fluid displacement, which depended strongly on depth within the tissue.