Low Tide Level Research Articles

Marine notches in the Maltese islands (central Mediterranean Sea)

We present the first detailed survey of tidal notches in the central Mediterranean area, in particular along the coastline of Gozo and Comino (Malta). The Maltese Islands represent one of the few sites in the Sicily Channel which exhibits coastal carbonate rocks. Marine notches on the islands of Gozo and Comino were surveyed by means of a seven day continuous snorkeling survey around the entire perimeter of the two islands. We surveyed the occurrence, lack and typology of marine notches and we correlated them with late Holocene sea level changes. Sea temperature (T) and electrical conductivity (EC) were collected along the route in order to locate the submarine springs and to relate them to the surveyed notches.A well-carved continuous roof notch was discovered along most of the plunging cliffs. It is well-carved out, in particular along the northern and western coast of Gozo. It develops from about 0.2 m above the mean sea level down and it can be up to 1.5–2 m deep. On the contrary, tidal notches are localised only in 8 sites. In 2 sites, Vermetid trottoirs develop at low tide level. In addition, at about −7 m to −10 m m.s.l., a 2–5 m wide marine terrace develops along extensive tracts of plunging cliffs, always in correspondence with the roof notches. This submerged terrace seem to be the result of the late Holocene slowdown of the sea level rise, which started to smooth the terrace and to carve out the submerged part of the roof notch, thanks to the exposed location of the islands and the favourable lithology.Through the collection of hydrological data, the presence of 21 submarine springs were detected. They occur mainly in the south-western coast of Gozo and on eastern coast of Comino. Anyway, marine notches seem not to be related to the freshwater outflow, such as those in the Adriatic Sea, because the studied islands are very exposed. As a consequence, along the Maltese islands bioerosion seems to be the most effective process in notch development.

Impact of rainfall on spatio-temporal distribution of sediment organic matter along the Chittagong Coast, Bangladesh

Sediment organic matter regulates the coastal biogeochemical cycle which is influenced by rainfall pattern and has potential relationship with organic carbon as well as mud characteristics. The objective of present research was to identify the impact of precipitation on the spatiotemporal variation inorganic features of intertidal mudflats. Three locations were selected in freshwater zone; two were in brackish water region and last three locations situated in marine waters from Halda to Salimpur coast. Two sites from each location were designated as the highest high tide level (onshore) and lowest low tide level (offshore) of the intertidal zone during winter (December to February) and monsoon (June to August) spanning between 2013 and 2014. Sediment organic matter and carbon were measured by combustion and Walkey-Black wet oxidation in turn. Average organic matter content in monsoon were found 4.5±0.03, 2.3±0.01 and 2.4 in freshwater, brackish and marine locations whereas 5.2±0.6, 3.9±0.14 and 5.4±0.04% investigated during winter. Precipitation pattern varies from different seasons and locations that have impact on land runoff, freshwater inflow, mixing and circulation. Mud dominated coastal intertidal zones represented high organic matter content than sand dominated coast. Furthermore, depositional pattern, transport, erosion-accretion processes, tidal action, wave characteristics and seasonal inconstancy control the organic matter characteristics in the coastal sediment. This research suggests the necessity of periodic observation of rainfall pattern and organic matter distribution to assess the intertidal deposits which support the stabilization of local geomorphology and biogeochemistry in Chittagong coastal region.Res. Agric., Livest. Fish.3(1): 175-186, April 2016

Assessment of beach and dune erosion and accretion using LiDAR: Impact of the stormy 2013–14 winter and longer term trends on the Sefton Coast, UK

An important question for coastal management concerns the importance of individual storms and clusters of storms on longer term beach sediment budgets, beach and dune erosion, and coastal flood risk. Between October 2013 and March 2014 a series of deep Atlantic low pressure systems crossed the Northeast Atlantic, and strong winds, high waves and high water levels affected many coastal areas in the UK and other parts of western Europe. Net dune recession of up to 12.1m occurred around Formby Point. On 5 December 2013 the highest water level ever recorded at Liverpool (6.22m ODN) coincided with waves of Hs of 4.55m and Tp of 9.3s in Liverpool Bay. Wave trimming of the dune toe occurred along the entire length of the Sefton coast, but significant dune erosion occurred only where the upper beach (between the mean high water spring tide level and the dune toe) was <25m wide. Sediment budget calculations based on LiDAR surveys in October 2013 and May 2014 indicated a net loss of 127×103m3 of sediment from the beach (above 0m ODN) and a loss of 268×103m3 from the frontal dune system, mostly at Formby Point. However, some parts of the beach to the south of Formby Point gained sediment, indicating net north to south transport over the winter. When considered in a longer term context, the 2013–14 winter represents only a small perturbation on the longer-term coast trend of erosion at Formby Point and progradation to the north and south. Analysis of LiDAR data over a longer time period 1999–2014 indicated upper beach and dune sediment loss of 780×103m3 from the north-central part of Formby Point, with net gains of 806×103m3 and 2116×103m3 in areas to the north and south, respectively. This indicates a net onshore transport of 2142×103m3 from Liverpool Bay towards the coast between Birkdale and Altcar, with a further net total of 210×103m3 transported towards the shore between Altcar and Crosby. In view of the demonstrated value of airborne LiDAR surveys for the quantification of storm impacts and longer term coastal changes, it is recommended that such surveys should be undertaken before and after each winter storm period, covering the area between mean low water spring tide level and a line 200m landward of the dune toe, of as a part of the regional coastal monitoring programme.

ÜBER EIN HOLOZÄNES KORALLEN- UND MANGROVENVORKOMMEN NAHE SANTA MARTA, KOLUMBIEN

In November 1969 high swell from a hurricane in the northwestern Caribbean Sea caused temporary beach erosion at the "Punta La Loma", a sandy spit situated in front of the airport of Santa Marta. The erosion revealed the substrate of the spit which is formed of granodiorite incrusted by reef corals and covered with cemented sand, in which numerous remains of lithiied roots have been found. All the corals belong to species presently known from the Recent fauna of the Caribbean coast of Colombia. Based on their internal structure the lithiied roots have been attributed to mangroves. The fossil deposits are situated up to 1 m above low tide level. Their age has been estimated as Holocene. This is supported by the obvious lack of recrystallization of the corals. The considerable uplift of the Sierra Nevada that occurred during Pleistocene time, too suggests a very young i. e. Holocene age of the fossils

Hormosira banksii (Phaeophyceae): a tough survivor in the harsh conditions of high intertidal pools in southeast Australia

Hormosira banksii, the most successful intertidal fucoid in the southern hemisphere, usually inhabits only the lower shore. On Kainga Reef, at 36°S on the New South Wales coast, it is one of only two macroalgae in most of the pools on a platform above xthe lowest high water; 29 pools in the middle of the platform were monitored photographically for 12 years. Recruitment was not seasonal. It took about 5–8 months for germlings to become visible, when they consisted of about 3 vesicles. The growth rate of germlings was between linear and exponential. Individuals could become fertile when they were 11–14 months old. Adult frond growth rate in the mid-platform pools, measured in situ, was highest in autumn but similar in the other seasons. In summer, however, in pools at the edge of the reef, often flushed by waves, the growth rate was as fast in summer as in autumn, either because of better provision of scarce nutrients or because of less inhibition by high temperature. Mortality, both of individuals and of fronds, was highest in the summer when pool isolation for one or more tidal cycles, caused by the coincidence of low high tide levels and a calm sea, was more common. Hormosira could tolerate full summer sunlight, water temperatures of up to 40°C, 140 psu (four times the strength of seawater) but not dehydration. Dehydration caused inter-annual variation in cover and in the total number of plants present, but with no overall trend over 12 years. Sand cover and rotting cast weed could also cause mortality. Survivorship was Slobodkin’s Type IV, with few plants reaching 4 years but high longevity after that, due to the establishment of a holdfast which could regenerate new fronds. Compared with other fucoids, growth was slow. The lifestyle resembles that of Ascophyllum nodosum.

Geophysical imaging of the post-earthquake structural integrity of flood-control stopbanks, Christchurch, New Zealand

On 4 September 2010, a MW 7.1 earthquake struck the Canterbury region of the South Island of New Zealand. Widespread liquefaction caused major damage to many structures, including the flood-control stopbanks along the lower reaches of the Waimakariri and Kaiapoi Rivers. Additional damage occurred during the subsequent MW 6.2–6.3 earthquakes of 22 February and 13 June 2011. Repeated LiDAR surveys indicated that up to 1 m of subsidence occurred in places. Visual inspections identified areas of significant damage, which have been repaired. However, internal damage to the stopbanks cannot be recognized by visual inspection. Thus electromagnetic (EM) and ground penetrating radar (GPR) surveys were undertaken.A pilot study was completed upstream of the confluence of the two rivers, along the northeast segment of the Waimakariri stopbanks and the southwest section of the Kaiapoi stopbanks. A complementary horizontal loop EM (HLEM) survey was carried out in advance of the GPR surveys. The HLEM measurements were done with the instrument oriented both parallel and perpendicular (transverse) to the stopbanks. Anomalous HLEM responses were noted at one location; subsequent GPR surveys indicated a change in the style of stopbank construction and repair, and possibly some internal cracking. HLEM readings were also taken at high and low tide levels along the tidally-influenced lower Kaiapoi River, and significant differences were observed. Finally, during the surveys, a surface crack was observed at one location, and a GPR line across that site suggested that the crack extended to depth.The results were complemented by velocity analyses using subsurface diffractions, and velocity variations were noted along the lengths of the stopbanks. The velocity changes appear to be broadly correlated with changes in the HLEM conductivity, which is not unexpected given the effects of water content and clay content on both the electrical conductivity and the GPR velocity.

Bio-Monitoring of Mangal Sediments and Tissues for Heavy Metal Accumulation in the Mangrove Forest of Cross River Estuary

Background: Mangroves are among the most productive intertidal ecosystems on earth. They serve as nursery and breeding grounds for several commercially important species of marine fauna. Despite their economic and ecological importance, they are under threat from over-exploitation and organic and inorganic pollution sources. This has led to their use as bio-indicators for pollution monitoring programmes. Therefore, the need to periodically monitor the Cross River Estuary mangroves for heavy metals pollution should not be overemphasized given the high premium placed on this ecosystem. Objectives: The present study was aimed at evaluating mangrove sediments and tissues for heavy metals accumulation in the different tidal levels of Cross River Estuary which will be an indicator for pollution. Method: Ten random samples of composite surface sediments (0-5 cm) were collected from low, mid and high tidal levels using a modified Van Veen (0.1 m 2 ) grab sampler. Also samples of senescent leaves, barks and roots of randomly selected ten individual plants of Nypa fruticans (low tide), Rhizophora racemosa (mid tide) and Avicennia africana (high tide) were also collected for heavy metal analyses during the year 2011. Result: The results showed that there were significant variations (p bark >leaves, the mangrove notwithstanding. It was also observed that cadmium deposition in sediments was comparatively higher than RSV indicating possible cadmium pollution. Generally, accumulation of heavy metals in the mangrove forest of Cross River estuary was within permissible limits. Conclusion: Although the concentrations obtained for the heavy metals studied are generally below documented toxic levels, however, the increasing level of urbanization and industrialization in Calabar municipality and its environs calls for continuous vigilance, surveillance and monitoring of this sensitive and all important ecosystem to protect and ensure that heavy metal pollution is minimal.

Hydrodynamic constraints and storm wave characteristics on a sub‐horizontal shore platform

ABSTRACTFew studies of wave processes on shore platforms have addressed the hydrodynamic thresholds that control wave transformation and energy dissipation, especially under storm conditions. We present results of a field experiment conducted during a storm on a sub‐horizontal shore platform on the east coast of Auckland, New Zealand. Small (&lt;0.5 m) locally generated waves typically occur at the field site, whereas during the experiment the offshore wave height reached 2.3 m. Our results illustrate the important control that platform morphology has on wave characteristics. At the seaward edge of the platform a scarp abruptly descends beneath low tide level. Wave height immediately seaward of the platform was controlled by the incident conditions, but near the cliff toe wave height on the platform was independent of incident conditions. Results show that a depth threshold at the seaward platform edge &gt; 2.5 times the gravity wave height (0.05–0.33 Hz) is necessary for waves to propagate onto the platform without breaking. On the platform surface the wave height is a direct function of water depth, with limiting maximum wave height to water depth ratios of 0.55 and 0.78 at the centre of the platform and cliff toe, respectively. A relative ‘platform edge submergence’ (water depth/water height ratio) threshold of 1.1 is identified, below which infragravity (&lt;0.05 Hz) wave energy dominates the platform energy spectra, and above which gravity waves are dominant. Infragravity wave height transformation across the platform is governed by the relative platform edge submergence. Finally, the paper describes the first observations of wave setup on a shore platform. During the peak of the storm, wave setup on the platform at low tide (0.21 m) is consistent with measurements from planar sandy beaches, but at higher tidal stages the ratio between incident wave height and maximum setup was lower than expected. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Phenotypic variation in shell form in the intertidal acorn barnacle Chthamalus montagui: distribution, response to predators and life history trade-offs

The acorn barnacle Chthamalus montagui can present strong variation in shell morphology, ranging from flat conic to a highly bent form, caused by a substantial overgrowth of the rostrum plate. Shell shape distribution was investigated between January and May 2004 from geographical to microhabitat spatial scales along the western coast of Britain. Populations studied in the north (Scotland and Isle of Man) showed a higher degree of shell variation compared to those in the south (Wales and south-west England). In the north, C. montagui living at lower tidal levels and in proximity to the predatory dogwhelk, Nucella lapillus, were more bent in profile. Laboratory experiments were conducted to examine behavioural responses, and vulnerability of bent and conic barnacles to predation by N. lapillus. Dogwhelks did not attack one morphotype more than the other, but only 15 % of attacks on bent forms were successful compared to 75 % in conic forms. Dogwhelk effluent reduced the time spent feeding by C. montagui (11 %), but there was no significant difference between conic and bent forms. Examination of barnacle morphology indicated a trade-off in investment in shell structure and feeding appendages associated with being bent, but none with egg or somatic tissue mass. These results are consistent with C. montagui showing an induced defence comparable to that found in its congeners Chthamalus anisopoma and Chthamalus fissus on the Pacific coast of North America, but further work to demonstrate inducibility is required.

Chapter 14 The rock coast of Australia

Abstract The rocky coast of Australia has been the focus of scientific enquiry since Charles Darwin visited Sydney during the voyage of the Beagle (1831–1836). As the philosophy of geomorphological enquiry has evolved from Davisian landscape theory to modern questions of landscape response to climate change, so has the understanding of Australian shore platforms. Early work was focused on penultimate levels of coastal planation; however, the majority of research has focused on the balance between marine and subaerial erosion in forming shore platforms. As field instrumentation has advanced there has been a greater variety of data available to researchers which has led to studies of microerosion and the distribution of wave energy across platform surfaces. Platforms formed in Quaternary carbonates and volcanics as well as Mesozoic sediments have been the focus of research. Those found in softer carbonates form closer to low-tide level while those in resistant basalt form at high-tide elevation. Rock hardness and structure are the primary drivers of platform morphology; however at an individual field site the surface morphology, such as the presence of a ramp, will be determined by the balance between wave and subaerial processes as well as local variations in lithology.

Population dynamics of Megapitaria squalida (Bivalvia: Veneridae) at Magdalena Bay, Baja California Sur, Mexico

The population dynamics of an intertidal population of Megapitaria squalida was studied from September 2002 to February 2003 in Bahia Magdalena, Mexico. To obtain information about the artisanal and recreational fishery of M. squalida, local fishermen at different parts of the bay were interviewed. Clam densities were determined at one unexploited and two exploited sites along perpendicular transects from the shore line. Average clam density was 2.01+/-1.41 ind/m2, densities did not differ significantly between the three sampling sites. The length-total mass relation was Mtot = 0.0001*SL3.1644 (r2 = 0.9804, n = 92) and the length-tissue mass relation was Mtis = 0.0002*SL2.7144 (r2 = 0.945, n = 92). Von Bertalanffy-growth parameters were determined using marked individuals. Strong interindividual and also seasonal differences in growth were observed. Average annual values were: K = 0.655, Linfinity = 83 mm. Since M. squalida can reach a shell length of more than 135 mm in deeper waters, it is necessary to consider intertidal and subtidal populations separately. Average total mortality (Z) was 1.61 y(-1). No fishing mortality was calculated because total mortality Z at the unexploited control site was higher than Z at the exploited sites. It appears that M. squalida migrates into deeper water with increasing shell length, as average shell length increased at lower tidal levels and marked specimens showed a clear migration towards deeper waters. As yet no overexploitation could be found in the study area.

Impacts of Climate-Change-Driven Sea Level Rise on Intertidal Rocky Reef Habitats Will Be Variable and Site Specific

Intertidal rocky reefs are complex and rich ecosystems that are vulnerable to even the smallest fluctuations in sea level. We modelled habitat loss associated with sea level rise for intertidal rocky reefs using GIS, high-resolution digital imagery, and LIDAR technology at fine-scale resolution (0.1 m per pixel). We used projected sea levels of +0.3 m, +0.5 m and +1.0 m above current Mean Low Tide Level (0.4 m). Habitat loss and changes were analysed for each scenario for five headlands in the Solitary Islands Marine Park (SIMP), Australia. The results indicate that changes to habitat extent will be variable across different shores and will not necessarily result in net loss of area for some habitats. In addition, habitat modification will not follow a regular pattern over the projected sea levels. Two of the headlands included in the study currently have the maximum level of protection within the SIMP. However, these headlands are likely to lose much of the habitat known to support biodiverse assemblages and may not continue to be suitable sanctuaries into the future. The fine-scale approach taken in this study thus provides a protocol not only for modelling habitat modification but also for future proofing conservation measures under a scenario of changing sea levels.

Monitoring and Assessment of Leaf Litter Dynamics in a Mixed Mangal Forest of the Cross River Estuary, Nigeria

The leaf litter decomposition of Nypa fruticans, Rhizophora racemosa and Avicennia africana were studied across a tidal gradient in a mixed mangrove forest of the Cross River estuary Nigeria. Leaf litter decomposition was measured along the tidal gradients (low, mid, high) using litter bags. A single exponential model was used to study the decomposition rates of the leaves. Leaf decomposition varied significantly (P < 0.001) among species and spatially across tidal gradients over the study period. Decomposition was fastest in A. africana and slowest in N. fruticans and spatially, it was fastest at the low tide level and slowest at the high tide level. Tidal effects were much larger than species differences in the decomposition rates. The time (days) required for the loss of half the initial dry mass (T50) of the decomposing leaves at the low, mid and high tide levels were A. africana, 46, 57 and 77, R. racemosa 69, 86 and 115, and N. fruticans 86, 99 and 115 respectively. Estimates of leaf litter turnover rates showed that the actual litter turnover based on the relative measure of leaf litterfall and biomass on the forest floor (Kt) were much shorter than the projected litter turnover based on the leaf decomposition rates (Kd). The estimated actual residence times were less than one day while the projected residence times ranged from 83 to 142 days across tidal gradients, suggesting involvement of other ecological processes in litter loss and their possible transport into the Cross River estuary. The nitrogen contents and nutritional value of the decomposing leaves increased with time during the study. The increase varied significantly (P <0.001) among species, as well as temporally (P < 0.001) and spatially (P ≤ 0.05). The average C:N ratio decreased from 27.7 to 22.1 in A. africana, 26.4 to 23.9 in R. racemosa and 32.8 to 23.6 in N. fruticans. The overall changes in nutrients during decomposition indicated net mineralization. Mangrove leaf litter dynamics, trophic value and organic matter exchange of the system have implications on the productivity of the Cross River estuary and ultimately the Gulf of Guinea. Knowledge of these processes is critical for the maintenance and long term sustainability of the mangrove and surrounding ecosystems.

Correlation between perkinsosis and growth in clams Ruditapes spp.

Perkinsosis is one of the most widespread diseases affecting commercially important species of molluscs globally. We examined the impact of Perkinsus spp. on shell growth at the individual scale in 2 clam species: Ruditapes decussatus from Mundaka Estuary (Spain) and R. philippinarum from Arcachon Bay (France). At Arcachon, 2 contrasting sites in terms of environment and Perkinsus olseni presence were chosen: Arguin (disease-free) and Ile aux Oiseaux (infected site). We monitored the dynamics of perkinsosis over the course of the experiment at Mundaka and Ile aux Oiseaux. Prevalences were high (>70%), and intensities were around 105 cells g-1 wet gills at Ile aux Oiseaux, and 106 cells g-1 at Mundaka. No significant differences in prevalence or intensity were observed over time. A 2 yr field growth experiment of tagged-recaptured clams was performed to determine individual clam growth rate, condition index (CI), and Perkinsus spp. infection intensity. Clams were collected at Ile aux Oiseaux and transplanted to Arguin. The growth rate was always significantly and negatively correlated with Perkinsus spp. infection, and positively correlated with CI. CI and Perkinsus spp. infection explained 19% and 7% of the variability of the growth rate at Mundaka and Ile aux Oiseaux, respectively. In experimental clams at Arguin, P. olseni infection explained 26% of the variability of the growth rate at the lower tidal level. Our results suggest that at a concentration of between 105 and 106 cells g-1, perkinsosis affects the physiological functions of the clams, highlighted by its impact on the growth rate.

Accelerated low water corrosion of steel piling in harbours

Accelerated low water corrosion of steel piling in sea water harbours in the UK, Europe and elsewhere has been shown recently to be the result primarily of water pollution. Elevated levels of dissolved inorganic nitrogen in sea and brackish waters are responsible for microbiologically influenced corrosion of steel piling below the low water tide level. This is demonstrated in field data from 13 Australian experimental sites, nine US naval sites and some severe sites in Australia, Norway, Japan and the UK. Localised perforation of sheet piling, often associated only with the webs of U and Z profile piles, is shown to be the result of centreline segregation, porosity and composition differences in steel profiles. These stem from the steelmaking process and are likely to be less severe for modern steels. The results explain most of the observations for actual steel piling in various harbours, both vertically and horizontally (i.e. for U and Z and other pile profile types).

Scale of temperature variability in the maritime Antarctic intertidal zone

The Antarctic Peninsula is currently considered as one of the fastest changing regions on Earth yet temperature variability in some of its environments and habitats is not well-documented. Given the increased glacier retreat, summer melts, sea level rise and ozone losses the intertidal zone is likely to be one of the most rapidly altering of environments but also one of the least investigated in polar waters. This study aims to quantify summer temperature variability in some habitats of the intertidal zone at King George Island. Three transects were selected across tidal flat. Four temperature loggers were deployed at each of them from extreme low water spring tide level to extreme high water spring tide level between 07.12.2010 and 18.03.2011. All the loggers were deployed at the rocky substratum. The temperature range across the study tidal flat was between −2.26°C and +21.18°C. The average (summer) temperature obtained from 12 loggers varied from +1.89 to +3.26°C. In all the three transects average temperature increased with tidal height. Much higher temperature variability was recorded at higher than at lower tide locations. Differences in temperature between the three study transects existed. Results obtained from the studied tidal flat show that several factors combined altogether, including: water movement by tidal forces, wave action, air temperature, sun light intensity, shore lithology and the presence of ice and snow in the area, seem to influence its temperature.

Numerical Simulation of Tidal Waves Variation in the North Branch of the Changjiang Estuary

A 2D numerical model about the Changjiang Estuary was set up with MIKE 21 in this study, which was well calibrated and verified with the observed tidal levels, flow velocities and flow directions, the computed results agree well with the measured data. Then the model has been applied to calculate the tidal level in the North Branch during spring and neap tide in flood season. The results show that, from the middle reach to the upper reach of the North Branch, the high tidal level is lower and lower and the low tidal level is upper and upper, so the tidal range is decreased, and tidal range during spring is greater than the one during neap. The tidal peak appearing time in the upper reach of the North Branch lags behind that of the middle reach, which is obviously during neap tide. The tidal level curve of the middle reach of the North Branch is smooth and close to the simple harmonic curve, while that of the upper reach of the North Branch deformities, the tidal level curve of ebb tide change fluctuant, much more obviously at spring tide.

Numerical Analysis of the Influence of Sea Level Rise on Flood and Tidal Stage in the Yangtze River Estuary

A two-dimensional numerical model was set up to simulate the tidal current of the Yangtze River Estuary with MIKE21 FM. This model has been calibrated and validated with the observed tidal level. We simulated the change of flood and tidal stage in the Yangtze River Estuary after the sea level rising by 20~60cm. The simulate results indicate that: (1)With sea level rising, the extent of rise of the high tide is greater than that of rise of low tide. Under the same sea level rise, the closer to the lower reaches of the Yangtze River Estuary, the more obvious the increase in the low tide level is, the rise of the high tide does not change significantly. (2)For the changes of the tidal range increase, under the same sea level rise, the closer to the upper reaches of the Yangtze Estuary, the greater the tidal range increase is.

Effect of Tide Level and Time of Day on Detection Rate and Abundance of Clapper Rails (Rallus longirostris) in a Mid-Atlantic Tidal Marsh System

Obligate marsh bird detection rates during surveys are affected by the time of day and the tide level, but previous research on both factors has produced conflicting results and no research has been conducted in east coast tidal marshes. Relative abundance and detection rate of Clapper Rails (Rallus longirostris) were compared between morning and evening surveys at high, medium, and low tide levels in Worcester County, Maryland, during 2006. The detection rate of Clapper Rails was greatest in the morning at the medium tide level ( = 0.69, SE = 0.14, F5,40 = 5.87, P = 0.001). Morning surveys ( = 1.2, SE = 0.14) resulted in a greater relative abundance of Clapper Rail detections compared to evening surveys ( = 0.8, SE = 0.12, F1,195 = 5.31, P = 0.022), and surveys done at medium tide level ( = 1.3, SE = 0.17) resulted in greater relative abundance than those conducted at low ( = 0.8, SE = 0.15) or high levels ( = 0.7, SE = 0.15, F2,195 = 6.56, P = 0.002). The results suggest that surveys should be conducted in the morning at medium tide to maximize detection rate of Clapper Rails. The detection rate of obligate marsh birds during surveys is affected by time and tide level so additional research is necessary to determine how these variables affect the detection rate of marsh birds other than Clapper Rails.

Diversity and Habitat Distribution of Birds in Coastal Marshes and Comparisons with Surrounding Upland Habitats in Southeastern South America

We studied variation in bird assemblages with plant associations for three different coastal marshes from Southeastern South America (SESA) and assessed how marsh bird assemblages related to nearby upland bird assemblages. We surveyed bird species and plant structure along the tidal gradient of each locality from the low tide level to the upper habitats bordering coastal marshes. Twenty species frequently used coastal marshes, including relatively few migratory species. We found that birds occurring in SESA coastal marshes do not have distributions constrained to coastal marshes. Nonetheless, four bird assemblages were recognized in association with vegetation types and/or sites. Among the recorded coastal marsh species, the bay-capped wren-spinetail (Spartonoica maluroides) is both the most frequent and the most habitat constrained. Bird richness increases steadily along the tidal gradient associated with the increase in vegetation structure, suggesting that bird richness is directly explained by vegetation and indirectly by the physical conditions influencing vegetation structure. Results highlight the importance of SESA middle marshes as habitat for conservation of some threatened SESA grassland birds.