Wave Splash Research Articles

Multidimensional Transport Experiment and Simulation of Chloride Ions in Concrete Subject to Simulated Dry and Wet Cycles in a Marine Environment.

Chloride ion erosion is an important factor affecting the durability of marine engineering concrete. In particular, concrete structures in wave splash and tidal zones are subjected to dry and wet cycles and multidimensional diffusion of chloride ions. To investigate the intricate diffusion of chloride ions within concrete under these dynamic conditions, we devised a comprehensive experiment. This experiment encompasses multiple dimensions, involving dry and wet cycles, as well as static immersion. The experiment intends to reveal how chloride ions are distributed in the concrete and clarify the changes that occur in its microstructure. Based on Fick's second law, the multidimensional diffusion model of chloride ions in concrete under the dry and wet cycles and static immersion was established by comprehensively considering the effects of chloride ion exposure time, environment temperature, relative humidity, and the action of dry and wet cycles. The results show that, under the same conditions, the chloride content in concrete decreases with the increase in penetration depth but increases with the increase in the chloride diffusion dimension and exposure time. Dry and wet cycles and multidimensional diffusion of chloride ions increase the development of cracks and pores in the concrete structure and generate large quantities of C3A·CaCl2·10H2O, which will exacerbate the chloride ion transport rate and penetration depth of concrete. Under the same exposure time and penetration depth, the chloride ion content in concrete under two-dimensional (2D) and three-dimensional (3D) diffusion under dry and wet cycles was 1.09~4.08 times higher than that under one-dimensional (1D) diffusion. The correlation coefficients between the simulation results of the multidimensional transport model of chloride ions in concrete under multi-factor coupling and the experimental results were all greater than 0.95, and the model can be utilized to predict the distribution of chloride ion concentration in concrete.

Effect of Metakaolin on the Microstructural and Chloride Ion Transport Properties of Concrete in Ocean Wave Splashing Zones

In order to address the problem of the durability deficiency of concrete in wave splash zones in a harsh marine environment, this paper investigates the effects of coupled carbonation, sulfate, and chloride salts on the strength, capillary water absorption, and ion migration properties of cement concrete incorporated with metakaolin, and characterizes the pore structural changes with the mercury-pressure method and AC impedance technique. The results show that, compared with a single chloride salt environment, the improvement in mortar strength and impermeability with carbonation coupling is almost positively correlated with the calcium content in the specimen, and renders its pore structure more refined and denser. In contrast, the presence of sulfate reduces mortar strength and increases the ion migration coefficient. When the three factors of sulfate, carbonation, and chloride salt were coupled, damage to the strength and pore structure of the specimens was the most significant, but the specimen incorporated with 30% metakaolin had its strength improved compared with the blank group specimen; from the perspective of pore structural parameters and transport coefficient, the microstructure was denser, and the impermeability was significantly improved.

Optical flow based measurement of flow field in wave-structure interaction

Accurate measurement of the flow field in the wave-structure interaction, which is fundamental to the study of flow mechanism, is still a challenging task to date. The widely used Particle Image Velocimetry (PIV) technique is a promising approach to measure the flow field. However, it requires having the laser sheet to highlight the artificial particles seeded in the water and is only suitable for the clear water condition. It is incapable for the scenario of wave impacting on the structure, since a large number of bubbles interfere the tracking of particles. In this study, a computer vision-based method, i.e. the Optical Flow (OF) based method, is proposed and adopted to measure the flow field, and further to explore the underlying flow mechanism in wave-structure interaction. Firstly, the OF method is validated by comparing with the direct numerical simulation (DNS) and PIV measured results, involving the simple case of open-channel flow and complicated case of vortex flow. It is shown that the OF method can reasonably capture the primary flow features, as well as obtain the velocity with comparable accuracy of PIV method. Then, the OF method is used to study the flow field in the process of wave impacting on a rectangular structure. From the OF measured flow field around the structure, it is found that some typical flow phenomena, e.g. wave splash, jet flow, air entrainment, and wake vortex, exist at different phases during the wave-structure interaction. It also demonstrates that the flow acceleration and kinetic energy of wave impacting on the structure are increased with the increase of wave height due to the increase of flow velocity. Therefore, the OF method could be a useful non-intrusive approach for flow measurement in the wave-structure interaction.

Kompleksnoye issledovaniye volnovykh i litodinamicheskikh protsessov v beregovoy zone p. Morskoye (Vostochnyy Krym)

Wind waves can have a significant impact on the coastal infrastructure. The paper aims at a comprehensive study of regional characteristics of wind waves near the village of Morskoye (south-eastern coast of Crimea), which are necessary to develop a project of reconstruction of the highway adjacent to the coastal area. Space images and cartographic information were used to study the beach dynamics in the studied area. It is shown that before construction of the coast protection structures the beach width in the studied area was 25–30 m, whereas after the construction it narrowed down to 15–25 m. Based on the wind wave reanalysis data obtained using SWAN spectral model and ERA-Interim surface wind fields for 1979–2017, regime characteristics of waves in the coastal zone of Morskoye were calculated. It was found that waves with average periods of 3.0–3.5 s have the maximum recurrence (over 16 %). Wind waves coming from SE-SSE sector have the highest recurrence rate. Estimates were obtained for the extreme characteristics of wind waves that may occur once in a given number of years. The SWASH hydrodynamic model was used to perform mathematical modelling of wave run-up on the coastal area. In their calculations the authors used a regular grid of the coastal relief with high spatial resolution based on the interpolation of topo-geodetic and bathymetric survey results. An incoming wave was given as a soliton of 2.0; 3.0 and 3.4 m high. It was found that with the incoming wave height of 2.0 m, the vertical wave splash in the studied area varies within 1.7–2.2 m. At a height of 3.4 m, the splash reaches 1.8–2.9 m. In this case the beach is flooded completely. During the run-up, wave current velocity amounts up to 5 m/s. Along the lower boundary of the cliff the bottom maximum current velocity reaches 1.5–1.75 m/s. At such velocities near the cliff, the beach consisting of material with the grain size up to 60–90 mm can be eroded.

Monitoring Total Suspended Sediment Concentration in Spatiotemporal Domain over Teluk Lipat Utilizing Landsat 8 (OLI)

Total suspended sediment (TSS) is a water quality parameter that is used to understand sediment transport, aquatic ecosystem health, and engineering problems. The majority of TSS in water bodies is due to natural and human factors such as brought by river runoff, coastal erosion, dredging activities, and waves. It is an important parameter that should be monitored periodically, particularly over the dynamic coastal region. This study aims to monitor spatiotemporal TSS concentration over Teluk Lipat, Malaysia. To date, there are two commonly used methods to monitor TSS concentration over wide water regions. Firstly, field sampling is known very expensive and time-consuming method. Secondly, the remote sensing technology that can monitor spatiotemporal TSS concentration freely. Although remote sensing technology could overcome these problems, universal empirical or semiempirical algorithms are still not available. Most of the developed algorithms are on a regional basis. To measure TSS concentration over the different regions, a new regional algorithm needs to develop. To do so, two field trip was conducted in the study area concurrent with the passing of Landsat 8. A total of 30 field samples were collected from 30 sampling points during the first field trip and 30 samples from 30 samplings from the second field trip. The samples were then analyzed using an established method to develop the TSS algorithm. The data obtained from the first field trip were then used to develop a regional TSS algorithm using the regression analysis technique. The developed algorithm was then validated by using data obtained from the second field trip. The results demonstrated that TSS in the study area is highly correlated with three Landsat 8 bands, namely green, near-infrared (NIR), and short-wavelength (SWIR) bands, with R2 = 0.79. The TSS map is constructed using the algorithm. Analyses of the image suggest that the highest TSSs are mainly observed along the coastal line and over the river mouth. It suggested that the main contributing factors over the study area are river runoff and wave splash.

Experimental Study on Mechanical Properties of Q690 High Strength Steel in Marine Corrosive Environment

In order to study the mechanical property degradation rule of Q690 high-strength steel in the ocean wave splash area, the rusted specimen is obtained by indoor damp heat surrounding soaking environment corrosion test. The scanning electron microscopy, uniaxial tensile and cyclic loading tests of corroded steel are performed. This paper analyzes the steel from elastic modulus, yield strength, ductility and law of hysteresis degradation under different corrosion cycles and establishes the constitutive model of HSS. The results show that the appearance of HSS is obviously affected by the corrosion cycle. With the increase of the corrosion cycle, reddish-brown flaky corrosion products are formed on the surface of the steel and there are obvious corrosion pits. After 100 days of corrosion, the corrosion rate of steel reached 7.21%; the elastic modulus and yield strength under uniaxial tension load decreased by 10.2% and 4.9%. Under the effect of cyclic reciprocating load, the hysteretic energy is reduced by 15.3%; at the same time, the test curve is fitted by the secondary plastic flow model and the Ramberg–Osgood model and it is found that the shape parameter S1 and the cyclic strengthening coefficient K' are reduced by 20.1% and 10.2%, While the shape parameter S2 and the cycle strengthening index n' have no obvious changes.

Half-hourly changes in intertidal temperature at nine wave-exposed locations along the Atlantic Canadian coast: a 5.5-year study

Abstract. Intertidal habitats are unique because they spend alternating periods of submergence (at high tide) and emergence (at low tide) every day. Thus, intertidal temperature is mainly driven by sea surface temperature (SST) during high tides and by air temperature during low tides. Because of that, the switch from high to low tides and vice versa can determine rapid changes in intertidal thermal conditions. On cold-temperate shores, which are characterized by cold winters and warm summers, intertidal thermal conditions can also change considerably with seasons. Despite this uniqueness, knowledge on intertidal temperature dynamics is more limited than for open seas. This is especially true for wave-exposed intertidal habitats, which, in addition to the unique properties described above, are also characterized by wave splash being able to moderate intertidal thermal extremes during low tides. To address this knowledge gap, we measured temperature every half hour during a period of 5.5 years (2014–2019) at nine wave-exposed rocky intertidal locations spanning 415 km of the Atlantic coast of Nova Scotia, Canada. This data set is freely available from the figshare online repository (Scrosati and Ellrich, 2020a; https://doi.org/10.6084/m9.figshare.12462065.v1). We summarize the main properties of this data set by focusing on location-wise values of daily maximum and minimum temperature and daily SST, which we make freely available as a separate data set in figshare (Scrosati et al., 2020; https://doi.org/10.6084/m9.figshare.12453374.v1). Overall, this cold-temperate coast exhibited a wide annual SST range, from a lowest overall value of −1.8 ∘C in winter to a highest overall value of 22.8 ∘C in summer. In addition, the latitudinal SST trend along this coast experienced a reversal from winter (when SST increased southwards) to summer (when SST decreased southwards), seemingly driven by alongshore differences in summer coastal upwelling. Daily temperature maxima and minima were more extreme, as expected from their occurrence during low tides, ranging from a lowest overall value of −16.3 ∘C in winter to a highest overall value of 41.2 ∘C in summer. Daily maximum temperature in summer varied little along the coast, while daily minimum temperature in winter increased southwards. This data set is the first of its kind for the Atlantic Canadian coast and exemplifies in detail how intertidal temperature varies in wave-exposed environments on a cold-temperate coast.

КРУПНЫЙ ОПОЛЗЕНЬ И ВЫЗВАННОЕ ИМ ЦУНАМИ В БУРЕЙСКОМ ВОДОХРАНИЛИЩЕ

The structure, parameters, causes and consequences of a large landslide with a volume of 24.5 million cubic meters on the steep slope of the Bureysky Reservoir in its narrow mountain region (Khabarovsky Krai) were established. The displacement of the earth masses occurred on December 11, 2018 at an air temperature below minus 30°C. It was revealed that the cause of the landslide was a combination of factors, such as high steepness of the slope, the presence of highly fractured rocks in a zone of tectonic crushing, melting permafrost and the flooding of the soil at the bottom of the slope. As a result of the displacement of the landslide, a dam with a length of 800 m and a height of up to 47 m above the water level was formed, dividing the reservoir into two isolated parts. Heterogeneity of the composition of the deposits of the landslide body, a significant part of which is permafrost, was revealed. The landslide caused a tsunami wave, which spread along the reservoir for 11 km in in both directions along the Bureya River valley and for 3.2 km along the valley of the Sr. Sandar river located opposite the landslide. The maximum height of the wave splash reached 90 m in the narrow part of the valley in the middle reaches of the river Sr. Sandar. The wave completely destroyed the forest on an area of 300 hectares and washed away slope deposits at an area of about 100 hectares. On the slopes, numerous erosion furrows were formed up to 20 m long and up to 1.2 m deep. Now on a wall of failure collapses and small landslides became more active. The role of anthropogenic factors in the formation of landslides is the warming effect of water on the frozen rocks at the base of the steep slope of the valley as a result of rising water levels when filling the reservoir Bureyskaya HPP.

Splash zone lowering analysis of a large subsea spool piece

Lifting operation though the wave splash zone is challenging. Careful numerical analysis in the design phase is needed to minimize associated risks. This study addresses numerical modeling and analysis of the splash zone lowering of a large subsea spool. A typical offshore construction vessel is used for the operation. The objective is to compare the effects from different numerical methods and parameters on the allowable sea states and the operability. These methods and parameters include wave short-crestedness, shielding effects from the vessel, wave direction and wave seed number. A coupled numerical model of the spool-vessel system is established in SIMO program, which is a simulation tool for marine operations. Slamming and submergence-dependent loads on the spool during the transient lowering process are calculated. A large number of time-domain simulations has been performed to derive the allowable sea states. The operational criteria for assessment of the sea states include slack sling, snap loads in wires and clearance between spool and the vessel. Operability analysis of the operation at one reference site in the Barent Sea is established using 50-year hindcast data. The influences from different methods on the allowable sea states and the operability are compared and discussed in detail.

Analysis of generation and arrival time of landslide tsunami to Palu City due to the 2018 Sulawesi earthquake

Tsunami waves severely damaged the densely populated coast of Palu City immediately after the 2018 Mw 7.5 Sulawesi earthquake. Among the several tsunami waves that arrived to the city, the two initial waveforms were most likely generated by a landslide at the south-western shore of Palu Bay, about 5 km away from one of the city’s shopping malls. The authors accurately identified the arrival time and direction of the waves by comparing multiple videos taken by a pilot from the cockpit of a plane and local people who witnessed waves approaching the coast. Although the authors’ bathymetric survey only covered a limited area of 0.78 km2, it was found that about 3.2 million m3 of mass disappeared from it, causing a maximum decrease in the seabed elevation of 40 m. A landslide scarp up to 5 m height was also investigated in the southwestern shore of the bay, which seems to be relatively minor compared to the submarine mass failure. Visible clue for liquefaction was not observed at this particular site. A simplified numerical model suggests that the landslide tsunami propagated as an edge wave and split into two separate waves due to the presence of an underwater shallow area just north of Palu City. Both waves arrived to the coast of this city within several minutes: one from North-West and the other from the North. Three major waves were witnessed by residents, who felt horizontal and vertical ground movements and heard the sound of an explosion just after the earthquake. Wave splash exceeded the height of trees on the beach. Given the results, the authors conclude that any modern early warning system is unlikely to work well against such short-warning time tsunamis, and thus, it is necessary for disaster risk managers to consider a way to help people quickly become aware of the potential disaster and evacuate.

High‐energy inundation events versus long‐term coastal processes – room for misinterpretation

AbstractCoastal boulder deposits and chevrons are two features whose origin have triggered controversial discussions. Boulders are often used as indicators of past tsunamis and storms, with the former interpretation in many cases preferred due to the clast size. Chevrons, defined as large parabolic sand bodies, were previously attributed to (mega‐)tsunami, potentially caused by oceanic impacts, because of their dimensions, height above sea level and alignment of the central axis. This study documents that chevrons along the Quobba coast in Western Australia are parabolic dunes and not related to tsunami inundation; their age is consistent with an arid period at about 3·9 to 2·3 ka when the sea level was 1 to 2 m higher than today. The internal age distribution proves an inland migration. Weakly developed soil horizons represent phases of intermittent dune stabilization and later reactivation. The calculated velocities required for wind transport and the prevailing wind directions are consistent with on‐site meteorological parameters. The boulders at Quobba are most likely to be remnants of in situ platform denudation that produces shell hash, coral clasts and boulders. An unknown portion of the boulders was certainly moved by tropical cyclones. A previously proposed tsunami origin is unsustainable because the observed features can be explained by processes other than tsunamis. Boulders were tilted during gravitative platform collapse, standing water caused dissolution of the boulder bottoms, creating ‘pseudo‐rockpools’, consequently not applicable as upside‐down criteria, and ages of attached encrusting organisms document their colonization at higher sea level and (sub)recent frequent inundation by wave splash during rough seas.

Experiments of Floatable UAV for Wave Dissipating Block Inspection

In this paper, we present our modification experience of making a UAV watertight and floatable. Then we present several experiments on taking pictures considering ocean monitoring in the sea near our campus. The watertight experiments are done from our school’s pier. In these experiments, we repeated to start flying the UAV from the sea surface and fall it down into the water several times. Using this UAV, we tested several experiments to take pictures of wave dissipating blocks at MIHO Island where beach line erosion is critical and many blocks are arranged to prevent waves from washing the shore. We can see the shoreline very clearly from more than 200m height as a macro image and also we can inspect the blocks looking around its stacks as well as approaching near the sea surface where waves break and wave splash washes the UAV.

Macro- and meso-fabric structures of peritidal tufa stromatolites along the Eastern Cape coast of South Africa

Stromatolites are rare in modern ecosystems due to factors associated with seawater chemistry or biological competition that restrict their formation. Actively calcifying stromatolites, near the Kei Mouth in the Eastern Cape, South Africa, were discovered in the early 2000s. Similar deposits were later described along a 200km stretch on the south coast of Port Elizabeth. This study aims to describe the environmental setting, the macro- and meso-structures, as well as the evolution of the deposits near Port Elizabeth compared to other similar formations. Results show that the general environmental setting is consistent amongst peritidal stromatolites, including those described in this study. In all instances stromatolite growth occurs on a wave-cut rocky platform in and around rock pools. Growth is maximal within the intertidal to supratidal zone, as a result of freshwater inflow via emerging mineral springs at the base of landward slopes, and the periodic intrusion of seawater via storm surges or wave splash. In comparison with other systems, the South African stromatolite formations exhibit an additional macro-structure (beachrock/conglomerate) and four previously undescribed meso-structures: wrinkled laminar, laminar flat, rhizoliths, and blistered types. The South African stromatolites are also larger and more concentrated than other peritidal stromatolites, which could be due to this area having more suitable growth conditions.

Seasonal variation in Chironomid emergence from coastal pools

Understanding the phenology of emergences can be useful in determining seasonal chironomid life cycle patterns, which are often influenced by ice cover and temperature in cold climates. Lake Superior is the largest lake in North America and with a mean surface temperature of 3.9 °C influences regional climate. Coastal pools at Isle Royale, a wilderness archipelago in the northern part of the lake, occur in dense patches on low-gradient volcanic bedrock between the lakeshore and forest, creating variable microhabitats for Chironomidae. Four sites were sampled monthly from April to October, 2010. Surface-floating pupal exuviae were collected from a series of pools in two zones: a lower zone near the lake influenced by wave splash, and an upper zone near the forest and influenced by upland runoff. We used Jaccard’s and Whittaker’s diversity indexes to test community similarity across months. Temperature loggers in pools collected hourly readings for most of the study. Assemblage emergences were stable in upper pools, with significant similarity across late spring and summer months. Assemblages were seasonally variable in lower pools, with significant dissimilarity across spring, summer, and fall months. Few species in either zone were unique to spring or fall months. However, many summer species in the splash zone had a narrow emergence period occurring during calm weather following distinct increases in mean water temperature. Regardless of input of cold lake water to the lower zone, pools from both zones generally had corresponding temperature trends.

Estimating coseismic coastal uplift with an intertidal mussel: calibration for the 2010 Maule Chile earthquake (Mw = 8.8)

Coseismic coastal uplift has been quantified using sessile intertidal organisms after several great earthquakes following FitzRoy's pioneer measurements in 1835. A dense survey of such markers may complement space geodetic data to obtain an accurate distribution of fault slip and earthquake segmentation. However, uplift estimates based on diverse intertidal organisms tend to differ, because of few methodological and comparative studies. Here, we calibrate and estimate coastal uplift in the southern segment of the 2010 Maule, Chile earthquake (Mw = 8.8) using >1100 post-earthquake elevation measurements of the sessile mussel Perumytilus purpuratus. This mussel is the predominant competitor for rocky shores all along the Pacific coast of South America, where it forms fringes or belts distinctively in the middle intertidal zone. These belts are centered at mean sea level and their width should equal one third of the tidal range. We measured belt widths close to this value at 40% of the sites, but overall widths are highly variable due to the unevenness in belt tops; belt bases, in turn, are rather regular. Belt top unevenness apparently results from locally-enhanced wave splash, whereas belt base evenness is controlled by predation. According to our measurements made beyond the earthquake rupture, the belt base is at the bottom of the middle intertidal zone, and thus we propose to estimate coastal uplift using the belt base mean elevation plus one sixth of the tidal range to reach mean sea level. Within errors our estimates agree with GPS displacements but differ from other methods. Comparisons of joint inversions for megathrust slip suggest combining space geodetic data with estimates from intertidal organisms may locally increase the detail of slip distributions.

Hidden signals of climate change in intertidal ecosystems: What (not) to expect when you are expecting

One of the most significant biological impacts of global climate change is through alterations of organismal body temperature, which ultimately drives almost all physiological processes. Using a simple heat budget model ground-truthed using ~ 5 years of in situ temperature data collected using biomimetic sensors, we explored the sensitivity of aerial (low tide) mussel body temperature at three tidal elevations to changes in air temperature, solar radiation, wind speed, wave height, and the timing of low tide at a site in central California, USA (Bodega Bay). Results suggest that while increases in air temperature and solar radiation can significantly alter the risk of exposure to stressful conditions, especially at upper intertidal elevations, patterns of risk can be substantially reduced by convective cooling such that even moderate increases in mean wind speed (~ 1 m s −1) can theoretically counteract the effects of substantial (2.5 °C) increases in air temperature. Simulations further suggest that shifts in the timing of low tide (+ 1 h), such as occur moving to different locations along the coast of California, can have very large impacts on sensitivity to increases in air temperature. Depending on the timing of low tide, at some sites increases in air temperature will primarily affect animals in the upper intertidal zone, while at other sites animals will be affected across all tidal elevations. Field measurements and model predictions show that animal temperatures are often high even when air temperatures are not, confirming the importance of solar radiation in the heat budgets of intertidal ectotherms. Conversely, body temperatures are not always elevated even when low tide air temperatures are extreme due to the combined effects of convective cooling and wave splash. The results of these simulations, coupled with ongoing field measurements, suggest that the timing and magnitude of warming will be highly variable at coastal sites, and can be driven to a large extent by local oceanographic and meteorological processes. Moreover, they strongly caution against the use of single environmental metrics such as air temperature as indicators of past, current and future physiological stress on the west coast of North America, and instead advocate for approaches that consider the interactive roles of multiple physical drivers.

Predicting patterns of stress and mortality in intertidal invertebrates: applications of biophysical ecology in a changing world

Abstract Background , Questions and Methods Recent studies have emphasized that local and geographic patterns of species distributions can be set by a variety of factors related to weather and climate, including exposure to lethal environmental conditions, indirect effects on consumers and competitors, and sublethal effects of physiological stress on growth and reproduction. Predicting where, when and with what magnitude these impacts are most (and least) likely to occur is imperative if we are to effectively plan for (i.e. adapt to) the effects of climate change.We developed a series of methods for translating patterns of environmental “signals” into organismal responses in intertidal ecosystems. Importantly, “organismal climatologies” – long term patterns of organism temperature measured using in situ biomimetic sensors - show distinct differences from patterns based on environmental temperature (air or water temperature). Similarly, we explored the use of dynamic energy budget models, linked to heat budget models of animal temperature, to examine temporal and spatial patterns of sublethal stress and growth. Results and Conclusions Comparisons of four different metrics of stress- seasonal averages, extreme temperatures, number of “stressful days” (>32°C) and return time of stress events – show that temporal and spatial patterns of sublethal stress do not always track patterns of lethal exposure. In other words, simply knowing average temperature often tells us very little about exposure to extremes and vice versa. These results are consistent with the idea that extreme events can occur during the temporal synchrony of multiple “normal” events- for example low wave splash, extreme low tides and high solar radiation. Results also suggest that the combination of heat budget models with dynamic energy budgets are potentially an effective way to predict spatial patterns of intertidal organisms, but that we still need more physiological data regarding the role of aerial body temperature in driving growth and reproduction.

Knowing when to stop: Rhythms of locomotor activity in the high-shore limpet, Cellana grata Gould

The high shore limpet, Cellana grata, forages whilst awash, moving upshore with the rising tide and retreating downshore on the ebbing tide to become inactive in refuges. Spraying inactive, emersed individuals with seawater at low tide invokes a locomotory response, with limpets moving up the shore. Controlled laboratory experiments under continuous white or red light (to simulate light or dark periods respectively) and continuous emersion, immersion or seawater spray showed that C. grata possesses a free-running endogenous rhythm of locomotor activity. This rhythm was maintained over 30 days in continuous seawater spray and white light. Maximum entropy spectral analysis (MESA) revealed two major components to this rhythm, at 7.2 h and 12.4 h. The 12.4 h component is of a circatidal nature and appears to initiate activity, allowing individuals to anticipate immersion by the incoming tide, although this clock can be over-ridden by strong wave splash or spraying vigorously with seawater. The 7.2 h period, however, was the most significant component and is suggested to act as a stopwatch enabling the limpet to assess the duration of each foraging excursion in order to prevent being stranded at the wrong height on the shore. The environmental stimulus for both components of the endogenous rhythm in C. grata appears to be the time of first exposure to wave wash from the incoming tide. C. grata, therefore, has behavioural rhythms entrained to initiate and also terminate activity, which play a role in the limpet maintaining a fixed vertical level on the shore when inactive.

Salinity responses of halophytic and non-halophytic bryophytes determined by chlorophyll fluorometry

The mosses Schistidium maritimum and Tortella flavovirens are halophytes growing in the supralittoral zone of rocky shores, where they are exposed to wave splash, occasional tidal immersion and desiccation. We investigated their recovery from desiccation and their metabolic activity when moistened by seawater and distilled water, taking the non-halophytes Atrichum undulatum and Eurhynchium striatum for comparison, and using chlorophyll fluorescence to monitor photosynthetic efficiency. All the species, regained photosynthetic capacity after rewetting with seawater, although the maximum quantum efficiency (Fv/Fm) attained in seawater was lower than in distilled water. Switching the treatments indicated that the depression of Fv/Fm was probably an osmotic effect. Under ambient laboratory lighting 17 days' seawater treatment had little effect on S. maritimum but brought about some decline of Fv/Fm in A. undulatum. At ca 350 μmol m–2 s–1 PPFD, 10 days' seawater treatment caused a rapid and severe decline of Fv/Fm in A. undulatum, and a lesser decline in S. maritimum. Isotonic PEG 6000 caused a reduction in Fv/Fm comparable to that in seawater. This suggests that osmotic stress increases susceptibility to photo-injury. In all species RETR was lower in seawater; 1-qP increased in seawater in all the species but only slightly in S. maritimum. NPQ was lower in seawater than in distilled water in the non-halophytes A. undulatum and E. striatum, but higher in seawater in the halophytes, in which it increased steeply with irradiance, suggesting a higher capacity for harmless dissipation of excess excitation energy in the halophytes.

Experimental Study on Damage to Wave Splash Barrier for a Coastal Road

National Route E is a coastal road where overtopping waves cause frequent traffic disturbances. High waves resulting from a storm surge damaged the wave splash barrier for length of 78m out of 400m in October 2006. Impulsive wave pressure, acted on sections that were rendered incomplete due to scattering of wave-dissipating blocks as a result of the high waves and abnormal tide level, caused the damage of the wave splash barrier. The results of experiments revealed that the ratio of the critical wave force to the wave force acting on the barrier ranged from 2.6 to 3.0 in the damaged section, while the corresponding value in the undamaged section was 1.7 to 2.2