Tidal Patterns Research Articles

Temporal variation of zooplankton on a tropical Amazonian beach

Pinheiro, S.C.C., Magalhães, A., Costa, V.B. da, Pereira, L.C.C. and Costa, R.M. da, 2013. Temporal variation of zooplankton on a tropical Amazonian beach.To assess the spatial and temporal variation in zooplankton populations at Ajuruteua Beach, northern Brazil, monthly samples were taken between August, 2004, and July, 2005, at three fixed stations, during the spring (flood/ebb) tide. The zooplankton community was characterized by the absence of any significant spatial or seasonal variation in density, diversity or evenness. However, density was significantly higher during the ebb tides, with mean values ranging from 4,967±670.0 ind.m−3 in July (flood tide) to 38,213±15,157 ind.m−3 in April (ebb tide). A similar tidal pattern was recorded for the density of copepods. The dominant copepod species were Euterpina acutifrons (47.0±30.5 to 18,313±2,431 ind.m−3) and Paracalanus quasimodo (420.0±60.0 to 11,260±7,203 ind.m−3) and, together with Oithona hebes and O. oswaldocruzi, were responsible for the peaks in zooplankton density recorded in April. Monthly zooplankton diversity (1.8±0.2 to 3.0±0.1 bits.ind−1) was relatively high overall, whereas evenness varied from 0.4±0.0 to 0.8±0.0, with both indices presenting significantly lower values in November. The absence of any significant seasonal trend in total zooplankton during the present study may have been related to atypical precipitation patterns during the study period, when surface waters were abnormally warm (~1.5°C). Overall, zooplankton community structure at Ajuruteua Beach was indirectly related to the local rainfall regime, which affected the physical, chemical, and biological parameters of the water, influencing the temporal dynamics of these organisms.

Analysis of the Respiratory Dynamics During Normal Breathing by Means of Pseudophase Plots and Pressure–Volume Loops

This paper reports on the analysis of tidal breathing patterns measured during noninvasive forced oscillation lung function tests in six individual groups. The three adult groups were healthy, with prediagnosed chronic obstructive pulmonary disease, and with prediagnosed kyphoscoliosis, respectively. The three children groups were healthy, with prediagnosed asthma, and with prediagnosed cystic fibrosis, respectively. The analysis is applied to the pressure-volume curves and the pseudophase-plane loop by means of the box-counting method, which gives a measure of the area within each loop. The objective was to verify if there exists a link between the area of the loops, power-law patterns, and alterations in the respiratory structure with disease. We obtained statistically significant variations between the data sets corresponding to the six groups of patients, showing also the existence of power-law patterns. Our findings support the idea that the respiratory system changes with disease in terms of airway geometry and tissue parameters, leading, in turn, to variations in the fractal dimension of the respiratory tree and its dynamics.

Residency and behavioural rhythmicity of ballan wrasse (Labrus bergylta) and rays (Raja spp.) captured in Portelet Bay, Jersey: implications for Marine Protected Area design

We monitored the long-term residency of reef-associated ballan wrasse and sand-dwelling rays captured at the site of a potential future Marine Protected Area (MPA: Portelet Bay, Jersey) by implanting them with small transmitters and deploying underwater receivers inside the bay. Individual fish were detected at Portelet Bay for up to 618 days, but there were species-specific differences in residency and detection patterns. Ballan wrasse were year-round residents at the study site where they exhibited distinct, rhythmic, diel, tidal and seasonal patterns of behaviour, whereas rays were occasional visitors to Portelet Bay with no discernible pattern to their visits. Results indicate relatively small MPAs (<0.5 km2) that with suitable habitat could provide effective, long-term protection for ballan wrasse, but would likely be of little conservation benefit for rays. Our findings emphasize the importance of quantifying fish movements when planning MPAs which intend to protect multi-species assemblages of coastal fishes.

Contemporary hydrodynamics and morphological change of a microtidal estuary: a numerical modelling study

Contemporary hydrodynamics and morphological change are examined in a shallow microtidal estuary, located on a wave-dominated coast (Port Stephens, NSW, Australia). Process-based numerical modelling is undertaken by combining modules for hydrodynamics, waves, sediment transport and bathymetry updates. Model results suggest that the complex estuarine bathymetry and geometry give rise to spatial variations in the tidal currents and a marked asymmetry between ebb and flood flows. Sediment transport paths correspond with tidal asymmetry patterns. The SE storms significantly enhance the quantities of sediment transport, while locally generated waves by the westerly strong winds also are capable of causing sediment entrainment and contribute to the delta morphological change. The wave/wind-induced currents are not uniform with flow over shoals driven in the same direction as waves/winds while a reverse flow occurring in the adjacent channel. The conceptual sediment transport model developed in this study shows flood-directed transport occurs on the flood ramp while ebb-directed net transport occurs in the tidal channels and at the estuary entrance. Accretion of the intertidal sand shoals and deepening of tidal channels, as revealed by the model, suggest that sediment-infilling becomes advanced, which may lead to an ebb-dominated estuary. It is likely that a switch from flood- to ebb-dominance occurs during the estuary evolution, and the present-day estuary acts as a sediment source rather than sediment sink to the coastal system. This is conflictive to the expectation drawn from the estuarine morphology; however, it is consistent with previous research suggesting that, in an infilling estuary, an increase in build-up of intertidal flats/shoals can eventually shift an estuary towards ebb dominance. Thus, field data are needed to validate the result presented here, and further study is required to investigate a variety of estuaries in the Australian area.

Ion-neutral coupling during deep solar minimum

The equatorial ionosphere under conditions of deep solar minimum exhibits structuring due to tidal forces. Data from instruments carried by the Communication/Navigation Outage Forecasting System (C/NOFS) which was launched in April 2008 have been analyzed for the first 2 years following launch. The Planar Langmuir Probe (PLP), Ion Velocity Meter (IVM) and Vector Electric Field Investigation (VEFI) all detect periodic structures during the 2008–2010 period which appear to be tides. However when the tidal features detected by these instruments are compared, there are distinctive and significant differences between the observations. Tides in neutral densities measured by the Gravity Recovery and Climate Experiment (GRACE) satellite were also observed during June 2008. In addition, Broad Plasma Decreases (BPDs) appear as a deep absolute minimum in the plasma and neutral density tidal pattern. These are co-located with regions of large downward-directed ion meridional velocities and minima in the zonal drifts, all on the nightside. The region in which BPDs occur coincides with a peak in occurrence rate of dawn depletions in plasma density observed on the Defense Meterological Satellite Program (DMSP) spacecraft, as well as a minimum in radiance detected by UV imagers on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) and IMAGE satellites.

Tidal Wetland Vegetation in the San Francisco Bay-Delta Estuary

We analyzed tidal wetland vegetation patterns in the San Francisco Bay–Delta estuary (Bay–Delta) and discuss their significance for future conservation. Our objective was to conduct a balanced, random sample of six historic “remnant” tidal wetlands along a salinity gradient that ranged from southern San Pablo Bay to the lower Delta. We also wanted to compare diversity among these sites at five different scales, ranging from small subplots to total species per site. We randomly established twenty 0.1-ha plots at each site, and sampled ten 7-m2 circular subplots (subplot scale) in each plot for species presence and cover. We calculated total species per plot (plot scale) and total species per site (site scale) based on these subplot data. We calculated importance values for each species found in subplots based on frequency of occurrence and proportion of total cover at each site. In addition, we recorded species found within the 0.1-ha plot but not sampled in subplots (plot_all scale), and calculated the total species for each site based on these plot_all data (site_all scale). Thus, richness at each site was evaluated at five different scales that ranged from 7 m2 to 20,000 m2. We conducted a one-way ANOVA that compared mean richness among three scales with continuous data: subplot, plot, and plot_all. At lower estuary (San Pablo Bay) sites, richness values at these three scales were significantly lower than upper estuary (Suisun–Delta) sites. In Suisun–Delta sites, significant differences in richness varied, depending on sampling scale. Rush Ranch, a brackish wetland, had the highest average number of species per plot, whereas Sand Mound Slough, a freshwater wetland, had the highest average number of species at the subplot scale and the most total species at the site_all scale. Sand Mound Slough also had the highest number of unique species (22) compared to the other sites. We found a strong negative correlation (r2 = 0.99) between total species number and salinity (the most in the Delta at the lowest salinity, and the least at China Camp with the greatest salinity). Our analysis suggests the following conservation recommendations: (1) restore habitat for freshwater plant species diversity in the Delta; (2) restore transitional brackish wetland habitat in salt marshes of the San Pablo Bay and San Francisco Bay; and (3) focus on control of pepperweed (Lepidium latifolium) in brackish marshes.

Holocene evolution of bottom sediment distribution on the continental shelves of the Bohai Sea, Yellow Sea and East China Sea

Coastline shifts due to transgression and regression can remodel tidal fields of continental shelves, and this can control transport of sediments and modulate sediment distribution accordingly. Tidal currents have become the dominant hydrodynamic processes on the continental shelves of the Bohai Sea, Yellow Sea and East China Sea (BYECS) since the transgression after the Last Glacial Maximum (LGM). To examine the evolution of the bottom sediment distributions on the continental shelves of the BYECS, we simulated patterns of tides and tidal currents, sediment transport, and bottom sediment types (sand, mud and mixed sediments) for five periods, corresponding to sea level lowstands of 80m, 52m and 30m below present, the Holocene transgression maximum (HTM), and the present. The simulation shows that both sediment transport and shelf sediment distribution patterns were controlled by the strength, type and asymmetry of tidal currents in the BYECS since the LGM. Evolution of shelf sediment distribution patterns occurred in two stages: (1) sediment emplacement and formation stage before the HTM, and (2) local adjustment after the HTM. The marked changes in coastline configuration since the LGM are the dominant factor controlling tide and tidal current evolution. Distribution of shelf sediment types in the BYECS is closely related to tidal current fields during transgression after the LGM.

In situ thermal dynamics of shallow water corals is affected by tidal patterns and irradiance

We studied the diel variation of in situ coral temperature, irradiance and photosynthetic performance of hemispherical colonies of Poriteslobata and branching colonies of Poritescylindrica during different bulk water temperature and tidal scenarios on the shallow reef flat of Heron Island, Great Barrier Reef, Australia. Our study presents in situ evidence that coral tissue surface temperatures can exceed that of the surrounding water under environmental conditions typically occurring during low tide in shallow reef or lagoon environments. Such heating may be a regular occurrence on shallow reef flats, triggered by the combined effects of high irradiance and low water flow characteristic of low Spring tides. At these times, solar heating of corals coincides with times of maximum water temperature and high irradiance, where the slow flow and consequent thick boundary layers impede heat exchange between corals and the surrounding water. Despite similar light-absorbing properties, the heating effect was more pronounced for the hemispherical P. lobata than for the branching P. cylindrica. This is consistent with previous laboratory experiments showing the evidence of interspecific variation in coral thermal environment and may result from morphologically influenced variation in convective heat transfer and/or thermal properties of the skeleton. Maximum coral surface warming did not coincide with maximum irradiance, but with maximum water temperature, well into the low-tide period with extremely low water flow in the partially drained reef flat, just prior to flushing by the rising tide. The timing of low tide thus influences the thermal exposure and photophysiological performance of corals, and the timing of tidally driven coral surface warming could potentially have different physiological impacts in the morning or in the afternoon.

A Case Study on Curtailed Tidal Hydrodynamic Modeling along UAE Coast

A curtailed numerical model has been developed to assess the tidal hydrodynamics of entrance of a navigational channel in Abu Dhabi coast, United Arab Emirates. The curtailed model is developed using a finite element based numerical scheme, RMA2 (Donnell et al., 2006). The boundary conditions for the model were extracted from a large scale numerical model covering entire Abu Dhabi coast, developed using TELEMAC (Hervouet, 2000) modeling software. The hydrodynamic results of the curtailed model are validated with that of large scale model. The comparisons of water levels and current velocities obtained from the two models are found to be in agreement, demonstrating the efficiency and accuracy of the curtailed numerical model. The features of the tidal current pattern in the vicinity of the entrance of the navigational channel are also discussed. The details of the numerical scheme, model setup and methodology are presented and discussed in this paper.

The Possible Observation of Slow Slip Events Prior to the Occurrence of the 1999 Chi-Chi Earthquake

Possible short-term precursors several days before the Taiwan Chi-Chi earthquake (M(subscript w) = 7.6) on 20 September 1999 were observed by examining crustal deformation that were directly integrated from broadband velocity seismograms. Significant deviations of the vertical displacement from a normal Earth tidal pattern on 15-19 September show some tiny surface crustal deformation having taken place several days in advance of the earthquake on 20 September. A series of slow slip events on the nearly horizontal plane (or decollement) at depths between 10 and 12 km provide a possible explanation for generating the anomalous crustal deformations before the earthquake. Although those slow slip events are not well constrained owing to limited observations at only two broadband seismic stations, their possibility is acceptable from a geological standpoint if the decollement beneath central Taiwan can be evidenced from both geological and geodetic studies. However, no matter what the exact mechanism was which generated the irregular earth tidal deformation several days before the 1999 Taiwan Chi-Chi earthquake, these anomalous crustal deformations might be considered to be possible short-term earthquake precursors.

Visual plumes coastal dispersion modeling in south-west Sabah

The visual plumes model encompassing the DKHW (Davis, Kannberg, Hirst model for Windows) and Update Merge (UM3) sub-models were utilized in the modeling exercise. In theory, the dilution capacity of open waters, particularly coastal areas, straits and oceans are enormous. This means that for surface and sub-merged point source discharges, the effluent concentration (C e ) will cause insignificant change in the overall ambient water quality. Instead, C e will eventually reach C a (ambient concentration) over a spatial distance (vertical and horizontal). This distance is of interest with regards to water quality preservation efforts as the macro level distribution effects of the pollutant species in question can be determined. The travel distance (l t ) is a main function of ambient current velocity (m/s) and direction. Prior to the modeling exercise, field data pertaining to ambient water quality, hydraulic characteristics and tide patterns were collected. The modeling results indicated that there was no significant change in ambient concentration for all constituents modeled when the effluent discharge was increased from 1,500 m 3 /h to 2,400 m 3 /h, as long as the current quality was maintained. The plume travel distance would also not entrain into foreign waters as long as proposed volumetric discharge rate is no violated. Key words : Visual plumes, coastal, Sabah.

Variations in nutrient concentrations at different time scales in two shallow tidally dominated estuaries

Water-quality observations in estuaries can be highly variable in time and space, making it difficult to quantify nutrient fluxes and to discriminate patterns. We measured nitrate, phosphate and ammonium concentrations in two shallow tidally dominated estuaries in Tauranga Harbour, New Zealand, during four periods (winter, start of spring, end of spring and summer) within 1 year, to determine the source of variability observed in a 19-year monitoring program. These measurements consisted of high-frequency monitoring during one 24-h period (covering a daytime flood-ebb tide and a night-time flood-ebb tide) at each estuary. Concentrations of nitrate and ammonium had distinctive tidal patterns, with rising values during ebb flows. This tidal asymmetry caused a net seaward flux of dissolved inorganic nitrogen (nitrate and ammonium), with higher exports at night. Net fluxes were 34–358 kg N per tidal cycle for nitrate and 22–93 kg N per tidal cycle for ammonium. Fluxes were large relative to previously published model-based predictions for the region, particularly during winter. Our results showed that estuarine sampling strategies need to account for tidal variability and the role of episodic runoff events, and highlighted the importance of correctly validated mass fluxes from field measurements for comparisons with nutrient-loading models.

Kelimpahan Larva Ikan Pada Kondisi Air Pasang Dan Surut Di Muara Sungai Pilang Sari, Desa Pidodo Kulon, Kendal <br><i>[Abundance Of Fish Larvae In Neap And Tide Condition In Estuary Of Pilang Sari River, Pidodo Kulon Village, Kendal ]<i>

Abstract The aim of this research is to know the abundance of fish larvae in neap and tide condition in estuary of Pilang Sari river, Pidodo Kulon village, Kendal. This research is case study where the fish larvae that been caught was deeply observed in the limited time, place and population. Sample was taken in the three place. Data were collected used seine net when the neap and tide of sea level. The number of fish larva that been caught during the research are 12.983. Including from 8 genus are Stolephorus, Ambassis, Periapthalmus, Gerres, Leiognathus, Terapon, Atherinomarus. The composition of fish larvae that been caught when neap and tide was dominated by Stolephorus and Ambassis. When the new moon phase, the number of fish larvae that been caught is 1151, quarter moon is 2379, full moon is 5243 and three–quarters of the moon is 4110 fish larvae. The result of this research shows the relationship between the pattern of tide and amount of the fish larvae that been caught every moon phase. In the sping tide pattern, amount of the fish larvae that been caught was bigger than neap tide pattern. In commonly, fish larvae that been caught when the tide is bigger than abundance of fish larva that caught when the water was neap.

A behavioral mechanism for dispersal in fiddler crab larvae (genus Uca) varies with adult habitat, not phylogeny

The genus Uca (fiddler crabs) includes both estuarine and coastal species, the zoeae of which must travel varying distances to reach the sea. Rapid seaward transport following hatching may be facilitated by tidal currents through an ebb‐phased circatidal rhythm in vertical swimming by larvae. Assuming there is a cost to vertical swimming, we predicted that endogenous swimming rhythms would be stronger in zoeae of species that live far up estuaries (oligohaline and mesohaline areas) and weaker or absent in coastal species and that adult ecology, not phylogeny, would best explain interspecific variation in vertical swimming rhythms. Both predictions were confirmed. Ovigerous females of 15 Uca species in 4 subgenera were collected from 10 locations along the Atlantic and Gulf Coasts of the United States and the Pacific and Caribbean coasts of Panama. Swimming activity of zoeae‐1 larvae was recorded under constant conditions for 72 h. Regardless of subgenus, estuarine species exhibited ebb‐phased circatidal swimming rhythms that persisted for several cycles and matched the tidal patterns at the collection sites, while the swimming of coastal species was arrhythmic. Species‐specific differences in the proximity of adult habitats and hatching areas to the sea accounted for differences in larval behavior that promotes seaward transport. Vertical swimming rhythms of larvae may have evolved together with other traits that permit estuarine living.

Wind Speed Changes of North Atlantic Tropical Cyclones Preceding Landfall

AbstractLandfalling tropical cyclones have been extensively researched, especially their degradation upon coming ashore and the hazardous weather they create along coastlines and farther inland. Many of the factors that weaken storms over land could begin to act when they are still at sea, yet prelandfall intensity change remains poorly documented. This study examined the consistency of prelandfall changes in tropical cyclone intensity throughout the North Atlantic Ocean from 1950 to present. On average, cyclones intensified by 3 m s−1 less in their final 12 h before landfall than in the 12 h preceding those, on both mainland shores and in the Greater Antilles, while smaller islands showed no such change. Contributions of increasing storm age and poleward movement to this reduction were negligible. Two possible contributing factors to declining intensification before landfall were examined. The presence of a spring–neap tidal pattern of ~2 m s−1 in the prelandfall decline is consistent with tidal mixing influencing ocean temperature on the continental shelf. The tendency for the decline to be greater at night suggested the possible influence of solar heating on tropical cyclones near shore.

Effects of Water Temperature Changes on the Oxygen Consumption Rhythm in the Japanese eel, Anguilla japonica

We investigated the effects of temperature changes on the oxygen consumption rhythm in Japanese eels, Anguilla japonica, using an automatic intermittent flow respirometer (AIFR). The endogenous rhythm of the oxygen consumption rate (OCR) in the eels (n = 18; 44-74 cm, 145-690 g), freshly collected by bag net from estuaries, was nearly synchronous with the tidal pattern of the estuarine collection site. The magnitude of mean OCR (mOCR) of eels showed variable range of 82.2 - 116.5 ml <TEX>$O_2\;kg^{-1}ww \;h^{-1}$</TEX> under constant conditions. In case of increasing temperature from 25 to <TEX>$38^{\circ}C$</TEX>, the OCR of eels exhibited a gradually increasing trend with a rhythmic pattern until <TEX>$36^{\circ}C$</TEX>. Above <TEX>$36^{\circ}C$</TEX> the rhythms of the OCR dampened and the OCR decreased rapidly at around <TEX>$36-37^{\circ}C$</TEX>. The OCR of the eels exhibited the maximum value at <TEX>$38^{\circ}C$</TEX>, and then it sharply decreased. The results suggested that the critical thermal maximum (CTM) regarding the endogenous rhythms of the eels was at around <TEX>$36-37^{\circ}C$</TEX> when water temperature increased at <TEX>$0.5^{\circ}C$</TEX>/14 h following the acclimation at <TEX>$25^{\circ}C$</TEX>. In case of decreasing temperature (<TEX>$0.5^{\circ}C$</TEX>/14 h) from 25 to <TEX>$0^{\circ}C$</TEX>, the OCR of the eels displayed a abrupt decrease up to <TEX>$23^{\circ}C$</TEX>, and between at 23 and <TEX>$20^{\circ}C$</TEX>, there was an agitation which showed a slight increase in the OCR with a duration of 1-2 days. Below <TEX>$9^{\circ}C$</TEX>, the OCR rhythm of the eels showed a constant state regardless of temperature decreasing. These results suggest that the Japanese eel has an upper incipient lethal temperature at <TEX>$36^{\circ}C$</TEX>, with a lower thermal limit at <TEX>$9^{\circ}C$</TEX>. The biochemical aspects of the eels influenced by water temperature need to be further studied.

TIDAL DYNAMIC GEOMORPHOLOGY IN NANPU AREA OF BOHAI BAY

With the development of the Jidong oilfield,three large artificial islands have been planned in the coastal water around the Nanpu area in recent years.To well understand the character of dynamic geomorphology of the area is significant for the construction of artificial islands.Using the data of measured tide and related currents offshore,in combination with the data from side-scan sonar and offshore sampling,the authors studied the tidal dynamic geomorphology pattern around the three planned artificial islands,and discussed the possible migration of nearby sand ridges,and its impact on construction of artificial islands.The impact of the construction to the tidal dynamic system is also predicted.

Inter- and intra-annual patterns of Ulva prolifera green tides in the Yellow Sea during 2007–2009, their origin and relationship to the expansion of coastal seaweed aquaculture in China

The large green-tide events that occurred in the Yellow Sea in 2008 (3489km2) and 2009 (4994km2) are shown to be novel events preceded only once by a much smaller event in 2007 (82km2). The blooms originated in the coastal area of Jiangsu province and spread north-east towards the Shandong Peninsula. The blooms grew at different rates and mesoscale variability in surface winds explained the differences in the spatial and temporal patterns of blooms in 2008 and 2009. The 2009 bloom was tracked to its origin immediately offshore of extensive intertidal flats between Yancheng and Nantong where recent rapid expansion of Porphyra aquaculture has occurred. We review published hypotheses which have been advanced to explain the occurrence of blooms and in light of our findings, we conclude that the accumulation and disposal of waste Ulva prolifera from Porphyra aquaculture rafts is the most likely cause of the blooms.

The ocean acidification seascape and its relationship to the performance of calcifying marine invertebrates: Laboratory experiments on the development of urchin larvae framed by environmentally-relevant pCO 2/pH

Variation in ocean pH is a dynamic process occurring naturally in the upwelling zone of the California Current Large Marine Ecosystem. The nearshore carbonate chemistry is under-characterized and the physiology of local organisms may be under constant challenge from cyclical changes in pH and carbonate ion concentration of unexpectedly high magnitude. We looked to environmental pH conditions of coastal upwelling and used those values to examine effects of low pH on 4-arm larvae of purple sea urchin Strongylocentrotus purpuratus. We deployed a pH sensor at a nearshore shallow benthic site for 3 weeks during summer 2010 to assess the changes in pH in the Santa Barbara Channel, a region considered to have relatively less intense upwelling along the US Pacific Coast. Large fluctuations in pH of up to 0.67 pH units were observed over short time scales of several days. Daily pH fluctuations on a tidal pattern followed temperature fluctuations over short time scales, but not over scales greater than a day. The lowest pH values recorded (~ 7.70) are lower than some of those pH values predicted to occur in surface oceans at the end of the century. In the context of this dynamic pH exposure, larvae were raised at elevated pCO 2 levels of 1000 ppm and 1450 ppm CO 2 (pH 7.7 and 7.5 respectively) and measured for total larval length (from the spicule tip of the postoral arm to the spicule tip of the aboral point) along the spicules, to assess effects of low pH upwelling water on morphology. Larvae in all treatments maintained normal development and developmental schedule to day 6, and did not exhibit significant differences in larval asymmetry between treatments. At day 3 and day 6, larvae in the 1450 ppm CO 2 treatment were significantly smaller (p < 0.001) than the control larvae by only 7–13%. The observation of smaller larvae raised under high pCO 2 has an as yet undetermined physiological mechanism, but has implications for locomotion and feeding. These effects of small magnitude in these urchin larvae are indicative of a potential resilience to near-future levels of ocean acidification. Using environmental monitoring of pH to inform experimental parameters provides a means to improve our understanding of acclimatization of organisms in a dynamic ecosystem.

MODELLING TIDAL ENERGY RESOURCE AND EXTRACTION

A number of areas around the UK coast are being investigated as possible locations for tidal energy harnessing. Detailed assessment using regional hydrodynamic modelling supported by field measurements can be used to quantify the energy resource and to determine limitations in the potential development area, including those due to the interactions between waves and tides. Two case studies illustrate the techniques applied and the implications for tidal device deployment: (a) Marine Current Turbines (MCT) are planning to deploy an array of their SeaGen tidal devices off the northwest Anglesey coast, UK; and (b) THETIS Energy Ltd are planning a development off the north Northern Ireland coast in the North Channel.&#x0D; &#x0D; The sites are characterised by moderately severe wave conditions, strong currents, and complex geomorphologic features, yielding highly variable and spatially complex, tidal range dependent current patterns. The regional hydrodynamic models (based on the TELEMAC system, an unstructured finite element solver from Electricité de France, now publicly distributed under an open source license) were calibrated against good quality field data for both sites, and captured the strong variability of the currents to a grid resolution of about 10 m over 30-day tidal cycles. Some areas were found to have strong currents on the flood tide but much weaker currents on the ebb, and vice versa and directions were not necessarily opposite. Areas with appropriate water depths, consistently good flow characteristics and, therefore, commercially attractive energy resource comprised only parts of the pre-selected sites. &#x0D; &#x0D; Off the northwest Anglesey coast, the TELEMAC-2D hydrodynamic model was complemented with a third generation wave transformation model. The local wave conditions are strongly affected by currents, giving rise to potentially dangerous conditions for construction and maintenance operations, as well as complex forces on the energy devices. By simulating the power take-off and physical characteristics of the MCT SeaGen devices, the hydrodynamic model was used to assess the impact of individual devices on the current regime and the actual energy available from the proposed arrays taking account of wake effects (Figure 1). The extent and intensity of the wake areas were calibrated to some degree against field data obtained from the MCT Lynmouth SeaFlow deployment (installed May 2003). Wakes could extend over a significant area, requiring careful placement of the individual devices within each array to avoid reduction in power generation.&#x0D; &#x0D; Off the north Northern Ireland coast, the TELEMAC-3D hydrodynamic model was used to produce maximum and average kinetic power density maps to identify useful site survey locations. The presence of an amphidromic point not far from the site, with virtually no tidal range yet strong currents, was correctly reproduced by the hydrodynamic model. The modelling study followed or exceeded the Assessment of Tidal Energy Resource guidance set by the European Marine Energy Centre for a full feasibility stage. In particular, comparisons with observed bed-mounted current data showed differences in maximum speed at various elevations throughout the water column within 5% or better at two of the three sites (spring tide currents).&#x0D; &#x0D; Numerical modelling has proven to be effective and critical in investigating possible locations for tidal energy harnessing at a number of areas around the UK coast.