Academic literature on the topic 'Intertidal wetland habitats'

Many natural wetlands have been converted to human-influenced wetlands. In some instances, human-influenced wetlands could provide complementary habitats for waterbirds, compensating for the loss of natural wetlands. Inner Deep Bay in Hong Kong is composed of both natural and human-influenced wetlands and is under immense development pressure. From an ecology perspective, we need to understand if different wetland types play the same ecological role. To achieve this, we tracked nine little egrets (Egretta garzetta) using GPS loggers for 14 months to study their spatial ecology, home range, movement and habitat use. We found that over 88% of the home range of all individuals comprised of wetlands (commercial fishponds, mangrove, gei wai, channel, and intertidal mudflat). Among these wetland types, nearly all (seven of nine) individuals preferred commercial fishponds over other habitats in all seasons. Little egrets exhibited seasonal movement and habitat use among seasons, with largest home range, greatest movement, and most frequent visits to commercial fishponds in winter compared to spring and autumn. Our results highlight the significant role of commercial fishponds, providing a feeding ground for little egrets. However, other wetland types cannot be ignored, as they were also used considerably. These findings underscore the importance of maintaining a diversity of wetland types as alternative foraging and breeding habitats.

Juveniles of commercially important fish species congregate in shallow vegetated estuarine habitats during high tides. Considerable debate has centred on whether the significance of these habitats lies in their provision of greater feeding opportunities, or shelter from predation afforded by greater structural complexity. We tested the hypothesis that an inundated mangrove and saltmarsh wetland provided feeding opportunities for itinerant species, and that the contribution of wetland primary producers and grazing herbivores could be identified in their diet, using stable isotopes of carbon and nitrogen. Potential sources of dietary carbon included mangrove, saltmarsh, seagrass, seagrass epiphytic material and benthic organic material. Saltmarsh plants (mostly Sporobolus virginicus and Juncus kraussii) and fine benthic organic material appeared to be the primary sources of dietary carbon for the resident grazing herbivores in the wetlands, based on IsoSource mixing models. During high tide, species of itinerant fish enter the mangrove and, when inundated, the saltmarsh, and feed primarily on crab larvae and copepods. Fine benthic organic matter, seagrass epiphyte, and C3 and C4 plant materials also supplement the diet of some fish. The crab larvae therefore provide a significant source of nutrition and an important link between the intertidal wetlands and the adjacent estuarine ecosystem. The carnivorous fish Acanthopagrus australis, at the highest trophic level, hunted within or adjacent to the mangrove–saltmarsh wetland and fed on several lower-order consumers within the wetland. The present study highlights the significance of mangrove and saltmarsh wetlands as a feeding habitat for resident grazers and itinerant nekton.

Context Successful eradications of invasive rats from islands are paying tremendous conservation dividends, but failed eradications are economically and environmentally costly. For an eradication using rodenticides, every rat in every habitat must have sufficient exposure to toxic bait to receive a lethal dose. A post-operational review of a failed rat eradication on Wake Atoll, central Pacific Ocean, suggested that inadequate treatment of an intertidal habitat within the lagoon might have caused or contributed to the failure to kill all Polynesian rats (Rattus exulans), which have since recovered in number. This habitat could not be treated by aerial broadcast due to concerns about loss of bait to tidal action and perceived contamination of the marine environment. Aims In preparation for a second attempt, we developed two alternative bait application strategies to distribute enough bait for a long enough period of time to successfully target rats, while minimising bait entering the ocean. Methods We used camera traps and experimental bait provisioning methods to document rat foraging in the target habitat and uptake of bait. We developed two baiting strategy alternatives, and employed one of these strategies in a placebo bait application to demonstrate bait uptake by rats foraging within this tidally inundated habitat. Key results Our results show active foraging by rats in the target habitat. Provisioning of placebo bait by various means preventing bait spillage into the marine environment was followed by heavy feeding by rats and minimal bait interference by crabs. Conclusions We consider it likely that such a bait application strategy will be considered as an alternative during a future eradication attempt on Wake Atoll. Implications The techniques we explore here will be useful for rodent suppression in other wetland areas requiring rodent control while protecting sensitive aquatic resources.

The delta of the Colorado River in Mexico historically contained 780,000 ha of riparian, marsh, and gallery forest habitat. Similar to other desert river deltas, such as the Nile and Indus, the lower delta of the Colorado River has been severely affected by the upstream diversion of water for human use. However, several large marsh areas of conservation interest still occur below the agricultural fields in Mexico. They are supported by flood water, agricultural drainage water, and municipal sewage effluent, as well as by seawater in the intertidal zone. The main anthropogenic marshes are the Rio Hardy wetland, maintained by geothermal discharge and Mexicali irrigation return flows in the western delta, and Cienega de Santa Clara, maintained by local irrigation return flows and by discharge of Wellton-Mohowk Valley drainage from the United States, imported via a 80-km canal to Mexico. These wetlands provide valuable habitat to resident and migratory waterfowl, shorebirds, mammals, and endangered species, including the Yuma Clapper Rail and the Desert Pupfish. Both wetlands are currently threatened by water management actions that do not take the wetland value of agricultural drainage into consideration. If agricultural drainage water and other available waste streams were explicitly managed to support wetlands, the Colorado River detla could potentially contain 50,000 ha or more of permanent, high-quality brackish wetlands below the agricultural fields.

SummaryEvaluating the ability of anthropogenic habitats to serve as surrogates for natural habitats is an increasingly relevant issue in conservation biology. This issue is especially urgent in tropical coastal wetlands that support large concentrations of migratory shorebird populations and are under pressure from development. Here we evaluated the species composition, abundance, and habitat use of Nearctic migratory shorebirds using recently harvested aquaculture ponds during two non-breeding seasons at shrimp farms surrounding Bahía Santa María (BSM), northwestern Mexico. We also estimated shorebird densities at intertidal units in BSM during and after the harvesting season to explore the connectivity with shrimp farms. Over 25,000 individuals of 25 shorebird species used the surveyed farms (∼13% of shrimp-farm development in BSM; 2014–2015: 10 farms, 994 ha; 2015–2016: 8 farms, 924 ha) during the harvest season. The most abundant species were: Western Sandpiper Calidris mauri, Willet Tringa semipalmata, Marbled Godwit Limosa fedoa, dowitchers Limnodromus spp., Black-necked Stilt Himantopus mexicanus and American Avocet Recurvirostra americana. Numbers of birds decreased as the harvest cycle progressed. Most birds (> 70%) were foraging on the ponds, regardless of tidal stage, while numbers increased during high tide for the most abundant species. At surveyed intertidal areas, shorebird densities were overall similar within and between non-breeding seasons. These results indicate that shrimp farms offer ephemeral but consistent foraging habitats used by non-breeding shorebirds, even in vast coastal wetlands offering a high availability of natural intertidal mudflats. Assuming a similar shorebird use in other shrimp ponds not surveyed within BSM, a significant proportion (> 1% of the biogeographic population) of Willet, Marbled Godwit, and Western Sandpiper, as well as imperilled Red Knot Calidris canutus, might use shrimp farms throughout the harvesting season. Before including current semi-intensive shrimp farms within management plans of BSM, further research is mandatory to assess their utility as alternative foraging habitats for shorebird conservation at tropical areas.

SummaryThe widespread decline of migratory shorebirds in the East Asian-Australasian Flyway (EAAF) is one of the greatest crises for migrating birds. Among the migratory species with known population trends, 88% (22 of 25 species) show population declines, and seven have been listed as threatened or Near Threatened in the IUCN Red List. The decline of migratory shorebirds is related to the deterioration of stopping sites (including staging and stopping sites) in the Yellow Sea, including loss of intertidal wetlands, spread of invasive smooth cordgrass Spartina alterniflora on intertidal flats, an increase in pollution, and an increase in human disturbance. We review research concerning shorebird migration through the Yellow Sea and highlight key research activities required for the conservation of shorebirds in the region. These activities include: confirming the population consequences of loss of stopping sites, estimating migration timing and numbers of shorebirds at stopping sites, determining the differing abilities of species to use alternative habitats, understanding intra- and interspecific differences in the use of stopping sites, maintaining and expanding surveys on shorebirds and habitat condition, and identifying threats to shorebirds beyond habitat loss by reclamation. The information generated by these research activities is required for the design and selection of effective conservation actions to reverse the decline in shorebird populations.

Abstract Studies of foraminiferal assemblages in intertidal marshes and subtidal creeks usually rely upon sediment samples collected along transects, such that associations with other organisms often go unnoticed. We show that ecologically useful data can be obtained by sampling that is stratified by substrate and microenvironment. The tidal wetland at Lower LaHave, Nova Scotia, Atlantic Canada (44º16′37.39″N, 64º19′46.45″W, area ∼1 km2) comprises mostly sandy sediment occupied largely by the low marsh grass Spartina alterniflora. The wetland is situated next to LaHave Estuary, which is polluted with domestic waste. Microenvironments within the marsh were sampled for total (living + dead) foraminiferal assemblages. The mass of dried sediment examined at each site was used to calculate the foraminiferal number (FN, number of foraminiferal tests per gram of sediment). Sediment samples from the intertidal grass beds reflect a typical low- to high-marsh zonal distribution of benthic foraminifera [FN = 24.7 ± 16.6 g−1 (mean ± standard deviation); n = 716 tests]. Samples from a tidal channel yielded few tests (FN = ∼0.3 ± 0.7 g−1; n = 22). Clutches of the mussel Mytilus edulis occurred in areas of strong current action within the channel and on lower energy slip-off slopes. Mussel clutches from the channel base yielded few tests (FN = ∼0.7 ± 0.7 g−1; n = 25), mostly Miliammina fusca. Clutches from slip-off slopes yielded a significantly richer assemblage (FN = 8.7 ± 4.6 g−1; n = 229) dominated by Elphidium umbilicatulum. We concluded that mussel clutches in low energy areas can be suitable habitat for E. umbilicatulum, either associated with structural complexity of the clutches or with waste products excreted by mussels that may stimulate growth of bacteria or microalgae upon which the foraminifera feed. The results from this study provide a baseline for examining the biotic impact of remediation of the LaHave River on the Lower LaHave wetland.

ABSTRACT Some oil spills cause losses of ecological services in coastal wetlands, other shoreline environments, intertidal ecosystems, and upland environments. In the United States, habitat equivalency analysis (HEA) is being used frequently in natural resource damage assessments for such oil spills to determine the scale of compensatory-restoration projects needed to offset the ecological service losses. The cost of the scaled compensatory-restoration project(s) that offset the ecological service losses is the measure of natural resource damages for the lost ecological services. Our paper describes the HEA process and provides an example of its application. Then we examine several challenges that arise in some HEA applications, including the role of leasing versus purchasing compensatory habitat, increasing values of compensatory habitat over time due to decreasing availability, accounting for service gains from compensatory habitat in the distant future when the present value of those services is essentially zero, and addressing uncertainties in estimating HEA inputs (such as the magnitude of annual service losses and gains). The final section of our paper provides our conclusions with respect to these challenges.

Intertidal wetland habitats in southeastern Australia have changed significantly during the past sixty years. Mangrove habitats have expanded both seawards and landwards, the latter being at the expense of saltmarsh habitats. This relatively common phenomenon is generally suggested to be an outcome of sea-level rise. Several factors potentially responsible for this change are examined, including changes in mean sealevel during the past 50 to 100 years, changes in climate, population growth, catchment landuse, and estuary type. A protocol for mapping estuarine habitats was developed and implemented, incorporating the application of geographic information systems. Spatial and temporal coastal wetland habitat changes at nine sites along the New South Wales coast are illustrated. These habitat dynamics were shown to not correlate between sites. The results demonstrate that sea-level rise in this region cannot solely account for the extent of change during the past sixty years. With the exception of one site (Careel Bay), there have been no correlations between contemporary mean sea-level rise and mangrove incursion of the saltmarsh habitats at the study sites, or with rainfall patterns, at the scale of observation in this study, which was largely decadal. The only correlations determined during this study have been between population growth and coastal wetland habitat dynamics in some sites. In spite of saltmarsh habitat loss being a regional phenomenon, local factors appear to have a profound bearing on the rates of change. Neither contemporary mean sea-level rise, rainfall patterns, estuary type, catchment landuse, catchment natural cover nor population pressure can account solely for the patterns in the spatial and temporal dynamics of the coastal wetlands of New South Wales. It seems apparent that regional factors create preconditions favourable for mangrove incursion, but that localised conditions have been responsible for the extent of these incursions from site to site. That is, despite higher sea-level and greater rainfall, the extent of change has been determined by the unique characteristics of each site. The results have important implications for current estuary management practices in the state of New South Wales. The lack of spatial and temporal trends in coastal wetland habitat dynamics point to the need for management to be conducted on a localised, rather than regional scale. Additionally, anthropogenic influences must be carefully managed, since the extent of mangrove habitat expansion into saltmarsh areas is unlikely to be a natural occurrence.

Runnelling is a popular method of physical habitat modification employed on saltmarshes to control pest mosquito populations. The runnelling method involves linking the tidal source to isolated mosquito breeding pools via shallow channels that enable slow water movement of low amplitude tides. Increased tidal flushing inhibits mosquito development. The range of organisms which inhabit saltmarsh are likely to be influenced by altered tidal conditions as they exhibit specific physicochemical requirements for feeding, burrowing or growth. The dynamic nature of saltmarsh may mean that changes to the tidal frequency of a particular region of the saltmarsh promotes extension of marine-like conditions. Because runnels increase the frequency of flooding tidal events in specific regions of the saltmarsh this study predicted that resulting changes would be evident in the physical conditions of saltmarsh substrate, in the transport of buoyant vegetative propagules, in the population characteristics of surface grazing snails and in the density and aperture of crab burrows after flooding and non-flooding tidal events. The physical impacts of runnelling were determined at three marshes which appeared similar in terms of topography, substrate and tidal conditions. Soil water content and consolidation were measured using two sampling protocols: a) comparisons between modified and unmodified shores; and, b) comparisons with increasing lateral distance across the shore from the runnel edge. At one marsh, moisture levels were significantly higher at runnelled than at unrunnelled sites when tides filled the runnels, but this pattern was not found at the other marshes. Soil consolidation was greater at higher shore heights, but was not different between runnelled and unrunnelled shores. Measurements at different lateral distances from runnels demonstrated higher moisture levels and lower consolidation up to 5 m from the edge but not further away. Groups of marked Avicennia marina propagules were released at the three runnelled saltmarshes during flooding and non-flooding tidal events. Groups of propagules released within 10 m of a runnel were always transported significantly further from the starting position and further up the saltmarsh shore after both flooding and non-flooding tides than any other groups. In addition, the pattern of stranding on saltmarsh for significantly different groups was closely associated with the path of runnel construction so that propagules were located either in the runnel or in depressions linked to the runnel that had been isolated mosquito-breeding pools prior to runnelling. It is likely that altered physical soil conditions significantly affected the distribution and size structures of Salinator solida and Ophicardelus spp. snails recorded at the three saltmarshes. The interaction of tidal period and the presence of a runnel contributed to patterns with significant differences between runnelled and unrunnelled regions of the marsh. Generally, the runnel population of snails exhibited flood-like features even during non-flood periods. The distribution and size classes of snails did not differ with lateral distance from runnels. The burrow characteristics of the crab Helograpsus haswellianus were compared to increase the accuracy of estimating abundance from burrow counts. Including only those burrows which were obviously maintained by resident crabs significantly increased the confidence limits of estimating crab abundance using only burrow density counts. This method was applied to runnelled and unrunnelled sites to assess any changes in the density of burrows associated with the presence of runnels. Again, it is likely that physical soil conditions resulting from increased tidal frequency at the runnel did influence crab burrowing with fewer small burrows being found at the runnelled site, low on the shore. In addition, mid- and large-sized burrows tended to dominate close to the runnel edge. Site-specific soil characteristics may help to explain the lack of continuity in patterns associated with runnel effects on non-target saltmarsh resources. While the runnel may increase the soil water content of clayey substrates at some sites it could also result in de-watering of porous sandy soils at other shores. This was evident in the structure of the snail population and distribution of crab burrows which appeared to reflect altered soil physical characteristics associated with the runnel. Runnelling does affect non-target organisms in saltmarsh. However, the scale of impact was usually locally restricted (< 10 m from the runnel edge). The fact that patterns were not recorded at all sites suggests that the influence of runnels is variable and limited by substrate and some biological conditions. Given the efficiency and popularity of runnelling as a physical control method for reducing pest vector mosquito habitat, this study found no evidence to suggest that its use should be discontinued on any ecological basis measured.

I estimated patterns of shorebird abundance and species diversity in the Colorado River Delta and Upper Gulf of California wetlands in order to determine the relative contribution of intertidal wetlands and non-tidal anthropogenic wetlands to support shorebird habitat use. Species richness varied from 15 to 26 species among sites and 29 species were detected across sites. Density during the peak migration month was higher at the anthropogenic wetland Cienega de Santa Clara (mean = 168 ind/ha, 95% C.I. 29-367), and the intertidal Golfo de Santa Clara (mean = 153 ind/ha, 95% C.I. 17-323). Anthropogenic wetlands (playa and lagoons) supported high abundance of shorebirds along with intertidal wetlands in the Colorado River Delta (mudflats). In contrast, intertidal wetlands farther south on the Sonoran Coast presented lower abundance but higher diversity of shorebird, likely as a result of the higher diversity of habitats (rocky shore, sandy beach, estuary). I modeled water management scenarios for the Cienega in order to determine the response of the dominant vegetation (southern cattail, Typha domingensis Pers.) and the area of the outflow pool below the marsh to different scenarios of water management. The model indicates that if the inflow rate is reduced below the current 4-5 m³s⁻¹ the vegetated area of the Cienega that supports habitat for marsh birds would decrease in proportion, as would the area of the outflow pool in the Santa Clara Slough identified previously as shorebird habitat. Increases in salinity will also reduce the vegetated area due to the low salt tolerance of T. domingensis. In winter about 90% of inflow water exits the Cienega into the Santa Clara Slough due to low evapotranspiration contributing to inundate areas that are used by wintering and migrating shorebirds. Lastly, I explored the feasibility of using Vegetation Indices (NDVI and EVI) to model Yuma Clapper Rail detections in the Cienega de Santa Clara as well as the effects of adding other habitat variables and the presence of fire events in the performance of linear models based on NDVI. Both NDVI and EVI were positively related to the Yuma Clapper Rail detections. The relationship was weak to moderate, but significant (P<0.001), which suggests other factors besides the vegetation condition play an important role in the bird distribution pattern. A model including all the variability among years was a better predictor of the rails detected per transect, than models for fire and non-fire years. We did not find a significant effect from adding habitat features (water % or vegetation %), and we recommend to include variables at both microhabitat level and landscape level, relevant before and during the breeding season in order to increase the explanatory power of models.

<em>Abstract.</em>—The abundance, quality, and ecological fate of wood in estuarine and coastal ecosystems result from watershed and, ultimately, landscape-scale processes. Estuaries and coasts receive the wood exported from watersheds, in which fluvial import, retention, processing, and export mostly determine how much wood is available. The dynamics of wood in estuaries and coasts reflect somewhat different processes and rates than in rivers, however. Bidirectional and fluctuating fluvial-tidal flows, multiple sources, and retentive mechanisms generate complex patterns of wood movement through tidal ecosystems. Too often, wood is assumed to perform the same functions in estuaries as in rivers. With a few exceptions— such as wood acting as a disturbance in the rocky intertidal zone—these assumed similarities have not been demonstrated empirically. The dynamics and role of wood need to be examined across the continuum of watershed, estuarine, and marine ecosystems, with the coastal ocean serving as both sinks and sources of wood. Wood’s function in juvenile salmonid habitat is a prime example of extrapolating the role of wood in river ecosystems, often without substantiation, to estuaries and oceans. Large wood is often designed into estuarine wetland restoration projects at significant cost without any real evidence of its importance to fish in tidal environments. The use of wood by juvenile salmonids may be scale-dependent, and it may vary with factors that affect availability of refugia and predation rates, such as tidal elevations, river flow, and diel changes in light intensity. Tides and wind can produce heterogeneous distributions of wood, which may help support the tidal and seasonal movements of juvenile salmon. Management and restoration plans should protect upstream wood sources and delivery processes to maintain and retain the supply of wood to estuaries and coasts. Research on large wood is still needed to evaluate its habitat functions in coastal and estuarine ecosystems to develop criteria for assessing and restoring habitat and to understand variation in the role of large wood across estuary-ocean landscapes.

A brief overview of the coastal biodiversity of Vietnam based on surveys conducted by the A.V. Zhirmunsky Institute of Marine Biology, Far Eastern Branch of the Russian Academy of Sciences for last 35 years. Main problems related to threats to biodiversity are discussed on the example of the intertidal communities, coral reefs, and molluscan diversity. Threats to marine biodiversity in Vietnam are summarized as follows: habitat degradation, fragmentation and loss (especially important are mangrove forest destruction, loss of coral reefs, change in landscape mosaic of wetland, estuary, sand and mud flats); global climate change including sea level rise, storm events, rainfall pattern change, warming of the coastal ocean; effects of fishing and other forms of overexploitation; pollution and marine litter; species introduction/invasions; physical alterations of coasts; tourism. Consolidated data of Vietnamese and Russian researchers on biodiversity and coastal zone management can be used in interpretations of ecosystem changes and for development of recommendations for local/national decision-makers.

A brief overview of the coastal biodiversity of Vietnam based on surveys conducted by the A.V. Zhirmunsky Institute of Marine Biology, Far Eastern Branch of the Russian Academy of Sciences for last 35 years. Main problems related to threats to biodiversity are discussed on the example of the intertidal communities, coral reefs, and molluscan diversity. Threats to marine biodiversity in Vietnam are summarized as follows: habitat degradation, fragmentation and loss (especially important are mangrove forest destruction, loss of coral reefs, change in landscape mosaic of wetland, estuary, sand and mud flats); global climate change including sea level rise, storm events, rainfall pattern change, warming of the coastal ocean; effects of fishing and other forms of overexploitation; pollution and marine litter; species introduction/invasions; physical alterations of coasts; tourism. Consolidated data of Vietnamese and Russian researchers on biodiversity and coastal zone management can be used in interpretations of ecosystem changes and for development of recommendations for local/national decision-makers.