Estuarine Tidal Flats Research Articles

Kingiella chilenica (Bivalvia: Cyamiidae); population dynamics, rates of survival, embryo production and annual recruitment of a semelparous brooding clam

Kingiella chilenica, a brooder mollusc, inhabiting soft bottoms of estuarine tidal flats of southern Chile, is well suited to study larval recruitment. It is a tiny semelparous clam with an annual cycle, and whose recruits must survive an inhospitable winter season prior to growing and reaching reproductive maturity in the following summer season. The population dynamics of this clam was studied through periodic sampling over two successive years to follow fluctuations in its' abundance. Obtained data on embryo production and recruit survival over both periods shows that population abundance varied widely between the two years of study. A high level on recruit survival through the winter of the first year resulted in high numbers of adults in the corresponding summer reproductive season. An inverse situation occurred in the second year, with lower recuit survival and, consequently, fewer reproducing adults. However, the lower abundance of adults in the second year was compensated by their having a higher survival rate over the reproductive season as compared with adults of the previous year. Independently of the abundance of the adults, the number of embryos incubated per female was very similar between both periods. Consequently, we suggest that the net contribution of juveniles produced by females per unit substrate was similar between the annual cycles studied. As predicted for a semelparous species (high reproductive effort), the maximization of the reproductive contribution was clearly reflected by a drop in adult somatic weight, particularly in incubating females. Previous data on abundance for this population suggested inter-annual differences of a high magnitude, with periods (e.g. 1986–1988) with abundances reaching 2–6× that presently reported. Probably, stable environmental conditions (e.g. 1986–1988) promote high abundance and survival of reproducers allowing a large contribution of recruits, which in turn show high degrees of survival through the adult phase. The years reported here (2003–2005), however, represent a period of population decline to lower, perhaps minimum, levels.

Growth and habitat of spotted halibut Verasper variegatus in the shallow coastal nursery area, Shimabara Peninsula in Ariake Bay, Japan

To determine the growth performances and habitat characteristics of spotted halibut Verasper variegatus, successive samplings were conducted in the south-eastern coastal area of Shimabara Peninsula in Ariake Bay. The push-net samplings were performed at Kamaga beach from May 2003 to April 2004 to determine the horizontal distribution of larvae and juveniles, while the gill net samplings were done in the coastal waters of Tatsuishi beach from July 2003 to July 2004 to collect the larger juveniles and adults. A total of 478 individuals from metamorphosing larvae to 2-year-old fish (15.2–447.0 mm total length [TL]) were sampled. In particular, the 2003-year class fish were successively collected from May 2003 to June 2004 (15.2–350.0 mm TL; n=418) and the mean total length in March, June, September, December 2003 and May 2004 was 22.4, 82.5, 172.5, 203.9 and 296.4 mm, respectively. The present study found that metamophosing larvae migrated into the estuarine tidal flats during March 2003; newly settled juveniles inhabited the shallow intertidal areas; and juveniles had a remarkably high growth in shallow coastal areas. It is suggested that young fish around 300 mm TL migrated from the nursery grounds in Ariake Bay to deeper waters around Tachibana Bay during May–June 2004.

Evaluation of Manila clam Ruditapes philippinarum as a sentinel species for metal pollution monitoring in estuarine tidal flats of Korea: Effects of size, sex, and spawning on baseline accumulation

Evaluation of Manila clam Ruditapes philippinarum as a sentinel species for metal pollution monitoring in estuarine tidal flats of Korea: Effects of size, sex, and spawning on baseline accumulation

Importance of drainage channels for waders foraging on tidal flats: relevasnce for the management of estuarine wetlands

Summary Despite covering a relatively small area on a global scale, estuarine tidal flats are vital to many aquatic bird species during much of the yearly cycle. Small‐scale features of tidal flats, such as water drainage channels, can influence the carrying capacity of estuarine wetlands, yet their ecological impact is poorly understood. In this study we evaluated the influence of drainage channels on the quality of feeding habitat for waders in the Tagus estuary, Portugal. We measured the abundance of seven wader species at five distance classes from drainage channels, and analysed the variation in peck rates, step rates, turning rates and success rates. In addition we measured the density of macroinvertebrate prey and the sediment physical–chemical characteristics at different distances from the channels. All wader species occurred at higher densities near the channels. In the study area 44% of the birds fed on just 12% of the available surface, less than 5 m away from drainage channels. Wader foraging behaviour also suggests a greater feeding effort near the channels. While the characteristics of the sediments did not change significantly with distance from channels, prey abundance corresponded closely with wader abundance, suggesting that the small scale distribution of birds on the tidal flats may be related to the presence of their prey. Synthesis and applications. Our study shows that the areas around drainage channels are particularly important feeding sites for waders foraging on tidal flats. Consequently, managers of estuarine wetlands should strive to preserve or improve channel networks. This can be achieved by (i) preserving saltmarshes and saltpans adjacent to tidal flats, (ii) minimizing the reclamation of upshore flats and (iii) avoiding embankments and canalizations of inland water flows that reduce the number of water entry points onto tidal flats.

Variable alluvial sandstone architecture within the Lower Old Red Sandstone, southwest Wales

AbstractSandstone bodies within the Lower Old Red Sandstone (ORS) in southern Pembrokeshire exhibit variability in architecture, sediment grade and composition both spatially and temporally. Four architectural styles are observed, namely decimetre‐ to metre‐thick sheets, metre‐thick multi‐storey amalgamations, inclined‐heterolithic units and ribbon geometries. Sandstone bodies in the Freshwater East Formation are sheet‐like, heterolithic units several metres thick. An association with lingulids and wave ripples alludes to a marine influence, possibly estuarine tidal flats or storm washovers. Within the Moor Cliffs Formation, the most common sandstone bodies are centimetre‐ to metre‐thick sheets with high width‐to‐depth ratios. Fine‐grained sandstones represent sheet‐flood deposition on unconfined, planar surfaces, whereas coarser‐grained sandstones constitute distinctive amalgamations of discrete flood events, reflecting either a change in provenance or tectonic influence. Clear incision of coarse‐grained, multi‐storey units within the Inter‐Tuff Moor Cliffs Formation reflects a change in relative sea‐level, possibly tectonically induced.The base of the Conigar Pit Sandstone Member (CPSM) is marked by a distinctive, exotic‐clast conglomerate defining the base to heterolithic, lateral‐accretion bedsets and sandstone sheets. This association defines a significant influx of coarse‐grained sediment post‐Chapel Point Calcrete formation, an interval of presumed topographic stability across the Anglo‐Welsh Basin. This influx must reflect rejuvenation of source regions, with changes in base‐level reflecting either eustatic or tectonic influences. Commonly observed in the CPSM are fine‐grained, inclined‐heterolithic bedsets recording deposition by highly sinuous rivers with flashy discharge. Up‐sequence within the CPSM are metre‐thick, multi‐storey amalgamations of predominatly trough cross‐stratified medium‐ to coarse‐grained sandstone. It is likely that these units are genetically related to contemporaneous decimetre‐thick sandstone sheets, the latter being ‘splay’ events marginal to the main channel axis. The interbedding of multi‐storey sandstones and fine‐grained laterally accreted units reflects changes in provenance, slope and/or climate.Thickness variations within the Lower ORS detail significant thickening of all units northward into the Benton Fault. It seems likely that this thickening reflects variable accommodation space development associated with active growth along this and other WNW–ESE‐trending faults, and migration of channel belts toward the footwall. Copyright © 2004 John Wiley & Sons, Ltd.

Effects of low-salinity on the growth and development of spotted halibut Verasper variegatus in the larva-juvenile transformation period with reference to pituitary prolactin and gill chloride cells responses

Low-salinity adaptability was investigated in a flatfish spotted halibut Verasper variegatus during the period from late metamorphic larvae to early juveniles by a 20-day rearing experiment under different salinity regimes (1, 4, 8, 16 and 32 ppt). Effects of low-salinity on growth and development were examined and the changes in the prolactin (PRL) production level in the pituitary and the gill chloride cell morphology were examined as physiological backgrounds for low salinity adaptation. PRL cells and chloride cells were identified by immunocytochemistry with a specific antiserum for PRL 188 and Na +,K +-ATPase. Most of the fish exposed to over 4 ppt survived for 20 days, but all the fish exposed to 1 ppt died within 5 days. Fish kept in intermediate salinities (8, 16 ppt) grew significantly better than those in the control group (32 ppt). Fish exposed to 4 ppt attained almost the same body length as the control group at 20 days after transfer, although these fish showed an abnormally dark body color as well as delayed development. These results suggested that spotted halibut has a high-adaptability to low-salinity environments and prefers an intermediate salinity near iso-osmolality (about 12 ppt) from the late metamorphic larval stage, but does not completely adapt to a hypoosmotic of 4 ppt salinity or less than half of the osmolality. The percentage of PRL-cell volume to pituitary volume was significantly higher at 4 ppt than in the control group. The chloride cells in gill filaments were significantly larger at 4 ppt than in the control group. These results suggest that juveniles could adapt to a low-salinity environment due to the activation of PRL production and enlargement of chloride cells. These laboratory findings suggest that late metamorphic larvae and early juveniles of spotted halibut may utilize a low salinity environment such as estuarine tidal flats or very shallow coastal areas as their nursery grounds in the sea.

Terrestrially derived sediment: response of marine macrobenthic communities to thin terrigenous deposits

Coastal marine habitats adjacent to catchments with encroaching human development are likely to experience increased sediment loadings in ensuing decades. Thus, sedimentary distur- bance regimes in which coastal marine benthic communities have evolved may be shifting as depo- sitional events exceeding critical thresholds become more frequent. To understand the threat posed by terrigenous sedimentation in an embayment with increasing urban development, we determined the thickness and frequency at which terrigenous sediment deposits begin to affect the benthos. We performed manipulative experiments involving layers of terrigenous sediment <1 cm thick in a vari- ety of intertidal habitats in the Whitford embayment, North Island, New Zealand. Results of 3 sepa- rate experiments performed at 5 sites were largely consistent. While experimental plots were never completely defaunated, as little as 3 mm of the terrigenous material was sufficient to significantly alter macrobenthic community structure (measured after 10 d, relative to 0 mm controls). The direc- tion of change was predominantly negative; the number of individuals and taxa declined as a result of sediment application, as did the densities of nearly every common species. Large bivalves were less affected than smaller ones, and deeper-dwelling species were less affected than ones at the sed- iment surface. With repeated applications of thin terrigenous layers (3 mm thickness, monthly over a 6 mo period), the sandflat sediments gradually became finer (clay volume % increased), and macro- faunal community composition progressively diverged from controls. To summarise, macrofauna were negatively affected by extremely small amounts of terrigenous sediment, and repeated deposi- tional events did more damage than single ones. With increasing defoliation and excavation of catch- ment hillsides, the frequency of depositional events of a given intensity is likely to quicken, indicat- ing an enhanced likelihood of macrofaunal disturbance and degradation in estuarine tidal flats. Management decisions that protect coastal catchments may partially ameliorate the threat to the benthos in coastal receiving waters.

Latitudinal diversity patterns in estuarine tidal flats: indications of a global cline

Latitudinal diversity gradients are a general feature of the terrestrial realm. Fewer studies have addressed marine habitats and those concerning soft sediments have not reported such consistent trends. This study investigates global patterns of macroinvertebrate α‐diversity in estuarine tidal flats. A literature search was conducted to collect data on species diversity as well as various physical, chemical and biological factors that may prove useful in investigating the cause of trends. Regression analysis revealed a significant association between latitude and diversity expressed as Simpson's index of concentration (r2=0.44), the index being lower (i.e. diversity higher) at low latitudes. There was no significant association between diversity and either available estuary area or annual rainfall. A significant, although weak, relationship between diversity and mean annual temperature was apparent (r2=0.23), together with an increase in species to family ratio in the hottest areas. This could suggest greater evolutionary speed in the tropics (due to temperature increasing mutation rates and generation times) and may provide an explanation for the trend. However, a greater amount of variation is explained by latitude alone and it is suggested that a primary cause of the latitudinal cline in estuarine diversity may be the greater effective evolutionary time available for communities in the tropics, temperate estuaries being regularly disturbed by glaciation during the last 1.8 million years.

Latitudinal diversity patterns in estuarine tidal flats: indications of a global cline

Latitudinal diversity gradients are a general feature of the terrestrial realm. Fewer studies have addressed marine habitats and those concerning soft sediments have not reported such consistent trends. This study investigates global patterns of macroinvertebrate α-diversity in estuarine tidal flats. A literature search was conducted to collect data on species diversity as well as various physical, chemical and biological factors that may prove useful in investigating the cause of trends. Regression analysis revealed a significant association between latitude and diversity expressed as Simpson's index of concentration (r 2 = 0.44), the index being lower (i.e. diversity higher) at low latitudes. There was no significant association between diversity and either available estuary area or annual rainfall. A significant, although weak, relationship between diversity and mean annual temperature was apparent (r 2 = 0.23), together with an increase in species to family ratio in the hottest areas. This could suggest greater evolutionary speed in the tropics (due to temperature increasing mutation rates and generation times) and may provide an explanation for the trend. However, a greater amount of variation is explained by latitude alone and it is suggested that a primary cause of the latitudinal dine in estuarine diversity may be the greater effective evolutionary time available for communities in the tropics, temperate estuaries being regularly disturbed by glaciation during the last 1.8 million years.

Spatial and temporal patterns of microphytobenthic taxa of estuarine tidal flats in the Tagus Estuary (Portugal) using pigment analysis by HPLC

Spatial and temporal patterns of microphytobenthic taxa of estuarine tidal flats in the Tagus Estuary (Portugal) using pigment analysis by HPLC

Continental/marine ratio changes in suspended and settled matter across a macrotidal estuary (the Seine estuary, northwestern France)

Suspended matter movements in the macrotidal Seine estuary (France) are mainly controlled by tidal currents. During high river spates, suspended matter is carried out of the estuary into the English Channel. A large part of the estuarine suspended matter comes from continental inputs. Throughout the year, suspended matter is trapped in the Turbidity Maximum Zone and on the estuarine tidal flats. Marine particles which are concentrated in the Turbidity Maximum Zone can be transported upstream into fresh water conditions. Physical and chemical measurements, as well as grain size analysis associated with scanning electron microscopy techniques, are used to study the characteristics of silty sediments and suspended matter. In the Turbidity Maximum Zone of the Seine estuary, particulate tracers, such as diatoms, indicate a continental/marine ratio more than 90% in the suspended matter. These results are similar with those from radiotracers. Sedimentary analyses on fine deposits from the estuarine tidal flats show close similarities with suspended matter coming from the Turbidity Maximum Zone. The sedimentological processes of the Seine estuary are compared with those in some other estuaries.

Effects of graveling on the primary productivity, respiration and nutrient flux of two estuarine tidal flats

This study was conducted in Puget Sound, USA, and investigated the effect of graveling intertidal mud and sandflats to enhance clam production on the benthic assemblage structure, primary productivity, respiration, and nutrient flux. The study was conducted between spring and autumn (1991), the period of greatest productivity and plant standing stock in Puget Sound. Graveled and control plots were established in the low intertidal zone on a mud flat in a protected embayment (Chapman Cove) and an exposed sandflat (Semiahmoo Bay). Gravel altered benthic assemblage structure, respiration, and nutrient flux rates. Graveled plots contained more surface coverage of sessile animals and seaweeds. Net productivity (NP), which differed relatively little between graveled and control plots, was negative for all but one sampling at the protected embayment plots. In contrast, NP was always positive at the exposed sandflat plots. The respiration rate was 13 to 57% greater in the graveled plot at Chapman Cove than in the adjacent control plot, and 7 to 54% greater in the gravel plot than the control plots at Semiahmoo Bay. Heterotrophy was greater in the graveled plots, as reflected by a lower net productivity to respiration ratio. Effects of graveling on water quality parameters such as dissolved oxygen and inorganic nitrogen concentrations were not detected. Graveling sandy and mud beaches increases secondary productivity, which is associated with increased rates of remineralization and release of dissolved nutrients to the water column.

Sediment exchanges along the coastal margin of the Moray Firth, Eastern Scotland

The Moray Firth is the largest of only three major coastal embayments on the East Coast of Scotland. The relationships between the offshore, coastal margin and fluvial sediments are examined in terms of processes and deposits. These suggest that the large post-glacial accretions of sediment infilling the inner firths are in part attributable to transport of material from the offshore zone. Since the fluvial input to the area appears to be relatively small and much is retained on estuarine tidal flats it is likely that the offshore contribution is the most important constituent of the deposits of the coastal margin. The other major source is glacial and fluvioglacial material now being reworked by marine activity.

Shell fragments as indicators of bed sediment transport in the Tay Estuary

SynopsisThe sediments of the floor of the Tay Estuary are dominated by assemblages of quartzo-feldspathic sands, although pebbles and silts are locally important. The sands are principally of inorganic materials, but they include shell fragments which account for up to 25% of the material, depending upon locality.Detailed analyses of the shell components of the 0.3–1.2 mm size fraction (400 particles from each site) in the area between Balmerino and Monifieth Bay reveal the presence of much molluscan debris (identified as mature and immature bivalves and gastropods), with significant proportions of bryozoan, barnacle or echinoderm skeletal fragments according to locality. Ostracoda and foraminifera are less common. The shelly material occurs mostly within zones inhabited by the same living organisms.The characteristic blue-colouredMytilus edulisshell fragments are also recognised up to 6 km landwards of the westernmost known colonies, along the railway bridge.Shell matter is dissimilar in shape and surface texture to the clastic grains and large shell fragments are frequently associated with sand sized inorganic sediments, which have been shown in flume experiments to respond in a similar manner to hydraulic controls.TheMytilusis therefore suitable for use as a natural tracer. It indicates up-estuary net residual motion of sediments in the middle and upper reaches. This pattern confirms evidence from heavy mineral assemblages that North Sea derived sands enter the estuary and migrate westwards to accumulate on the upper estuarine tidal flats.

Tidal deposits from the Archaean Moodies Group, Barberton Mountain Land, South Africa

Tidal deposits are recognised from the Archaean Moodies Group which is older than 3300 m.y. Lithologies, sedimentary structures and vertical sequences are used to characterize four tidally influenced facies: sandstone—shale, medium- to fine-grained quartzose sandstone, conglomerate—sandstone and medium- to coarse-grained orthoquartzitic sandstone. The sandstone—shale facies with abundant flaser, lenticular and wavy bedding accumulated on mid-tidal flats. Two subfacies are recognized within the medium- to fine-grained sandstones. The first consists predominantly of small-scale bipolar cross-bedding and is considered to have formed on lower intertidal sand flats. The second, which is characterized by large-scale cross-beds associated with plane bedding, probably formed in a complex of flood tidal delta environments. The conglomerate—sandstone facies consists of upward-fining units enclosed within rhythmically interlayered argillaceous sands and clays. These sediments are interpreted as tidal channels which meandered across estuarine tidal flats. Ebb-oriented trough cross-beds passing upwards into plane-bedded sands with clay partings, coupled with the geometry of the sand body, suggest that the medium- to coarse-grained orthoquartzites represent subtidal and intertidal sand shoals. A palaeoenvironmental synthesis of the facies relationships indicates that back-barrier tidal flats occurred lateral to a non-barred estuary.

Transport and Deposition of Suspended Sediments on Estuarine Tidal Flats: ABSTRACT

The suspended sediments in water flushing on and off an estuarine tidal flat have been examined for relative changes in concentration as a function of wind speed, local wave conditions, salinity, temperature, and tidal currents. The shallow water was sampled by plumbing the upper 20 cm of the sediment with buried plastic pipes and pumping water samples from an orthogonally spaced matrix of intake valves positioned across the tidal flat to permit observation of natural sedimentary processes. The sediment interface has been modified over parts of the matrix by introducing roughness elements in the form of small closely spaced stakes and stabilizers, such as eel grass. The data show a decrease in sediment concentration as the water floods over the tidal flat primarily as a function of dilution by more marine waters. As high slack tide is reached, sediment deposition occurs when wave heights are at a minimum. This deposition appears to continue even on the ebbing tide until water depths are extremely shallow, at which time a minor resuspension usually is noted. In contrast, if a slight surface chop develops, the falling water maintains the sediment in suspension and flushes it out on the ebbing tide. End_of_Article - Last_Page 601------------