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Creation of Temperate-Climate Intertidal Mudflats: Factors Affecting Colonization and Use by Benthic Invertebrates and their Bird Predators
Abstract
Colonization of a recreated area of intertidal land by marine invertebrates and their bird predators was studied from April 1993 to August 1997. The most important food of large shorebirds, the ragworm Nereis diversicolor, did not reappear until late summer 1995 and did not become abundant until the following autumn. Annual attempts at colonization by the crustacean Corophium volutator, the main food of several small shorebird species, failed until summer 1996 when animals survived through the subsequent winter for the first time. Colonization by the mud-snail Hydrobia ulvae took place a year after flooding of the site, but densities in 1997 were still well below those found elsewhere on the adjacent estuary.The delay in successful colonization by Nereis and Corophium may be attributable in part to the compaction of the intertidal muds caused by the earthmoving equipment used to contour the site. The slow increase in Hydrobia density may be a consequence of low organic content of the mud. Bird use is concentrated chiefly during the hours when the adjacent estuarine mudflats (with unrestricted tidal flow) are covered by the tide, since the new site then provides a supplementary feeding area. Peak daytime usage occurs during the migratory passage periods when birds need to feed for longer periods than usual, in order to refuel for their migrations; high usage is also anticipated in cold winters.On this evidence, creation of intertidal areas in mitigation for any lost nearby to industrial or other development should take place at least three years before the losses, in order to make the new areas profitable for feeding waterfowl.
... Geist and Hawkins (2016) emphasised the need to define a clear target state in an aquatic restoration scheme. However, when creating intertidal habitats, outcomes can be unpredictable and may not match the desired goals, for example, as waterbird communities evolve over time in response to physical and biological processes (Evans et al., 1998;Brusati et al., 2001;Armitage et al., 2007). ...
... In the United Kingdom, monitoring studies at MR sites have been short-term but have focussed on both physical and biological developments (Garbutt et al., 2006;Mazik et al., 2007;Garbutt and Boorman, 2009) with some examples of studies on waterbird colonisation (Evans et al., 1998;Atkinson et al., 2004;Mander et al., 2007). The re-created intertidal habitats monitored for wintering waterbirds in the UK have been small in size, but the studies at these sites have shown that natural waterbird communities may be successfully reproduced in just a few years Mander et al., 2007). ...
... Intertidal areas with higher elevations have shorter exposure times to water during tidal immersions, with lower food supplies, higher temperatures, and desiccation stresses for benthic invertebrate prey species. We included elevation in the models given the known relationships between the food resources of benthivorous species and cumulative accretion at MR sites (Evans et al., 1998;Atkinson et al., 2004;Garbutt et al., 2006), including the Paull Holme Strays site (Mazik et al., 2010). The models demonstrated that elevation was a major source of variability in the abundance of benthivorous FIGURE 4 | Temporal guild composition (% abundance) of the foraging assemblage at the MR site. ...
Estuaries have historically been subject to considerable habitat loss, and continue to be subjected to such in areas where the natural landward migration of intertidal habitats is constrained by hard coastal defences. Thus, in estuaries where direct (e.g., port development) or indirect (e.g., sea level rise) processes are predicted to threaten intertidal habitats and associated waterbird species, there is a regulatory requirement to produce compensatory intertidal habitats. Managed realignment (MR) is a shoreline management practise that is undertaken to build sustainable coastal defences and create intertidal habitats in estuaries. This nature-based solution brings multiple benefits in the form of carbon storage, increased resilience to flooding, and, potentially, the formation of new habitats, which is the topic of this study. A 75-ha site at the Paull Holme Strays (Humber Estuary, United Kingdom) was monitored over a 10-year period following MR to examine the change in the abundance of waterbirds in the chosen site in response to the physical processes occurring there. Using digital terrain models (DTMs) collected via light detection and ranging (LiDAR), we examined how four compensatory target species responded to changes in elevation after the creation of the site. It was shown that the very rapid accretion of estuarine sediment occurred in the first decade of the new re-created intertidal, which, over time, led to changes in the numbers of benthic foraging birds supported. Furthermore, elevation change was also driven by this sediment accretion, the rate of which depended on the initial bed elevation of the sectors within the site. Ten years after the recreation of the habitat, the spatial heterogeneity in the bed elevation remained high; however, the sectors with the lowest elevations accreted the most over the 10-year period. The foraging number of the four waterbird species that colonised the MR site significantly declined above a certain elevation, with this effect being most pronounced for the Eurasian curlew ( Numenius arquata ). The number of common shelducks ( Tadorna tadorna ), dunlins ( Calidris alpina ), and common redshanks ( Tringa totanus ) declined significantly after initial peaks 5–7 years after the creation of the site, reflecting the ongoing elevation changes. Thus, this study highlighted the need for long-term studies to understand how species respond to large-scale habitat construction. It can also aid in predicting the suitability of an MR site for waterbirds in the medium and long term.
... Benthic macrofauna such as polychaetes and bivalves are the foundation for food webs and ecological functioning in coastal marine ecosystems [6][7][8]. Various organisms, including fish, crustaceans and birds, depend on benthic macrofauna as a food source [9,10]. The rate of development of benthic macrofaunal communities in newly flooded areas can, therefore, be expected to exert a critical control on total biodiversity [4,9,10]. ...
... Various organisms, including fish, crustaceans and birds, depend on benthic macrofauna as a food source [9,10]. The rate of development of benthic macrofaunal communities in newly flooded areas can, therefore, be expected to exert a critical control on total biodiversity [4,9,10]. Furthermore, marine benthic macrofauna have been shown to modulate sediment composition and biogeochemical processes through bioturbation activities [11]. ...
... Successful establishment of M. viridis and C. capitata is thus critical for a benthic community with a structure and functioning comparable to ambient marine communities. The dominance of N. diversicolor inside the lagoon corroborates with other findings of N. diversicolor as one of the first species of benthic infauna to colonize newly formed salt marshes and tidal flats [9,22]. Although C. capitata and other capitellid species such as H. filiformis were present in low abundances inside the lagoon, they should have the potential to develop into higher abundances, as normally found for these rapid colonizers during early succession of disturbed areas [69]. ...
How will coastal soils in areas newly flooded with seawater function as habitat for benthic marine organisms? This research question is highly relevant as global sea level rise and coastal realignment will cause flooding of soils and form new marine habitats. In this study, we tested experimentally the capacity of common marine polychaetes, Marenzelleria viridis, Nereis (Hediste) diversicolor and Scoloplos armiger to colonize and modify the biogeochemistry of the newly established Gyldensteen Coastal Lagoon, Denmark. All tested polychaetes survived relatively well (28–89%) and stimulated carbon dioxide release (TCO2) by 97–105% when transferred to newly flooded soils, suggesting that soil characteristics are modified rapidly by colonizing fauna. A field survey showed that the pioneering benthic community inside the lagoon was structurally different from the marine area outside the lagoon, and M. viridis and S. armiger were not among the early colonizers. These were instead N. diversicolor and Polydora cornuta with an abundance of 1603 and 540 ind m⁻², respectively. Considering the species-specific effects of N. diversicolor on TCO2 release and its average abundance in the lagoon, we estimate that organic carbon degradation was increased by 219% in the first year of flooding. We therefore conclude that early colonizing polychaetes modify the soils and may play an important role in the ecological and successional developments, e.g. C cycling and biodiversity, in newly flooded coastal ecosystems. Newly flooded soils have thus a strong potential to develop into well-functioning marine ecosystems.
... According to our results, the feeding areas located within dredge islands might play an important role for waders at a lagoon scale, especially in winter. This confirms the importance of man-made coastal wetlands for the foraging of waders, as already observed at salt ponds (Múrias et al. 2002;Dias et al. 2014), abandoned basins for underground salt deposits (Davidson and Evans 1986), rice fields (Fasola and Ruiz 1996) and newly created intertidal habitats (Evans et al. 1998;Mander et al. 2007). ...
... Since our study sites comprised about 6 % of the total dredge island area available in 2009-2010 in the lagoon, it is likely that large fractions of these shorebird populations exploit the dredge island habitats for foraging during a single winter. These results agrees with findings of Evans et al. (1998) and Dias et al. (2014) on the use of aquatic man made habitats as alternative feeding sites. ...
... This is probably due to different grain size composition, which in turn affects the distribution of many benthic wader preys (Spruzen et al. 2008;Jing et al. 2007). Evans et al. (1998) observed that after 4 years, sediments of man-made intertidal habitats were still poorer in prey biomass than tidal flats. Our study sites had a mean age of 13 years, which indicate that reaching comparable biomass densities may take even more years; comparative data between tidal flats and dredge islands prey biomass at our study area are lacking at the moment to support this hypothesis. ...
Man-made habitats provide suitable nesting, resting and feeding habitats for many birds at coastal sites. Despite intensive study outside Europe, very few data are available to date on the bird communities that exploit artificial intertidal sites along the European coasts. Between July 2009 and December 2010, 32 ornithological surveys were performed at six artificial intertidal sites in the lagoon of Venice (Italy). Overall, 101 species (with 23,399 birds) were observed, about a third of those occurring in the lagoon of Venice; 58 of these species were of conservation concern. Ten species comprised about 80 % of the total; bird abundance was the highest during the post-breeding migration and wintering period. Multivariate analysis identified similarity among sites, seasons and observed behaviours. Dredge islands were mostly used by waders as foraging sites, when surrounding tidal flats were still flooded. In winter the six dredged islands supported about 2 % of the dunlins Calidris alpina occurring in the whole lagoon of Venice and about 10 % of the grey plovers Pluvialis squatarola. Since the study sites comprised just the 6 % of the total dredge island area available in 2009–2010, the results indicate as large fractions of these shorebird populations might exploit the dredge island habitats for foraging. Among the newly created habitats, intertidal ponds and inner tidal flats were the most heavily used by birds, followed by dykes and mounds with ruderal vegetation. Maintenance of the habitat mosaic is a need for a conservation- based management of the dredge islands.
... Nereis is a significant trophic link for many important resident and migrating bird species in SE England (i.e. Grey Plover, Curlew, Dunlin, Redshank) that use the intertidal areas as feeding, roosting and breeding grounds (Evans et al., 1998;Atkinson, 2004). The importance of the region is recognised by it having the greatest proportion by area of protected sites in the UK,, including 28% and 20 % respectively of coastal RAMSAR and Special Protected Areas (SPAs) (Plaze & Keddie, 1996). ...
... Water Neap Tide Level (MHWNTL), when in the absence of Nereis and other burrowing invertebrates (Hughes, 1999)., Hughes et al., (2000) Nereis may also affect the recruitment of other species which are important prey items for fish and birds using managed realignment sites (Evans et al., 1998). Nereis exhibits territorial behaviour (Reise, 1979), with its own conspecifics and other invertebrates being less abundant in areas where Nereis deposit feeds, because of predation, disturbance or exploitation competition for food resources (Jensen & André, 1993;Hiddink et al., 2002;Fidalgo e Costa et al., 2006). ...
... Studies of saltmarsh restoration and creation often focus on the vascular plant and fish assemblages rather than the invertebrate infauna (Moseman et al., 2004). Nereis is an important ecosystem engineer through its feeding and bioturbatory activities, and is a key trophic link for many fish and birds that utilize realignments for nursery and feeding grounds (Evans et al., 1998). ...
... Seal Sands comprises a section of the Teesmouth National Nature Reserve (NNR) in the Cleveland Coast, and is the most extensive area of intertidal mudflat on the East Coast of England in a ~230 km stretch of coastline between Humberside and Lindisfarne (Natural England, 2001). Large scale land reclamation at Seal Sands prior to 1975 greatly reduced the area of land subject to tidal influence (Doody, 2004), from ~2500 ha in 1820 to ~400 ha by 1970 (Evans et al., 1999). The remaining area of intertidal flats was partitioned by the deposition of a slag wall, leading to the annexing of the southern intertidal sector, and the subsequent formation of brackish or freshwater marshland in the absence of regular tidal inundation. ...
... Seal Sands area has been severely impacted by the effects of agricultural expansion, industrial N 10km development, and channel dredging (Davidson et al., 1991;Evans et al., 1999), and is subject to a number of international, European and national protocols regarding further anthropogenic encroachment. Teesmouth and Cleveland Coast is listed as a Wetland of International Importance under the Ramsar Convention (Ramsar Convention, 2007), and the Seal Sands area is recognised as a site of international significance under the European Community Directive on the Conservation of Wild Birds due to the presence of a number of rare wading bird and migratory wildfowl species (Davidson et al., 1991;Evans et al., 1999;Natural England, 2001;Ratcliffe, 1977). ...
... Seal Sands area has been severely impacted by the effects of agricultural expansion, industrial N 10km development, and channel dredging (Davidson et al., 1991;Evans et al., 1999), and is subject to a number of international, European and national protocols regarding further anthropogenic encroachment. Teesmouth and Cleveland Coast is listed as a Wetland of International Importance under the Ramsar Convention (Ramsar Convention, 2007), and the Seal Sands area is recognised as a site of international significance under the European Community Directive on the Conservation of Wild Birds due to the presence of a number of rare wading bird and migratory wildfowl species (Davidson et al., 1991;Evans et al., 1999;Natural England, 2001;Ratcliffe, 1977). The area is also a Site of Special Scientific Interest (SSSI) under the Wildlife and Countryside Act (1981), with particular notice given to the internationally significant counts of knot and redshank wading bird species. ...
... As a consequence of the demographic increase, the biodiversity of these habitats has declined, mainly due to anthropogenic pollution and land reclamation (Costanza et al., 1997). Habitat loss has occurred over the past 300 years in many estuaries and coastal areas in developed countries through land claim for agriculture, port development, harbours, housing and infrastructure (Evans et al., 1998;Atkinson, 2003;McLusky and Elliott, 2004). Although in recent years they have been the sites of habitat gain, albeit to date on a smaller scale than the previous loss, 50-80% of wetlands have been lost from many estuaries along NW European and North American coastlines (Elliot and Cutts, 2004). ...
... Colclough et al., 2005) and birds (Atkinson et al., 2004;Mander et al., 2007). Research on managed realignment sites of colonization by macrobenthic infauna and community development has been studied by Evans et al., 1998;Atkinson et al., 2004;French, 2006;Mazik et al., 2007. Other studies also briefly refer to invertebrate communities (e.g. ...
... Colonization of a newly created site appears to be related to the availability of suitable sediments (Garbutt et al., 2006). Compaction of sediment caused by the earth-moving equipment may mean that the colonization of a created area by invertebrates is slower than expected (Evans et al., 1998). The presence of large individuals of H. diversicolor in the bottom layer of the sample suggests that from the beginning sediment characteristics were suitable for macrofauna to bury sufficiently deep in the sediment to avoid mortality by hard frosts or desiccation (Evans et al., 1998). ...
The colonization process by macrobenthic infauna after the completion of managed realignment on the fertile plain of Jaitzubia, along the Bidasoa estuary, is assessed here. The benthic invertebrate fauna was sampled annually for three years in the newly recovered intertidal areas. The results show a rapid colonization process. Six months after the completion of the restoration works, all the stations exhibited a large number of small opportunistic benthic species, as well as some large individuals of Hediste diversicolor, that dominated the biomass of the community. One year later, a new stage of development or succession towards the settlement of the Scrobicularia plana–Cerastoderma edule community was observed, showing a reduction of both abundance and species richness, and an increase in biomass, mainly due to the presence of individuals of S. plana (which were absent previously). The following year, a further reduction in the abundance and number of species was observed, as well as an increase in biomass, but on this occasion S. plana was the main contributor to community biomass. Evidence of the importance of passive or active dispersion in the adult stage of the species H. diversicolor and S. plana in the recovery process was also observed.
... Intertidal flat and marsh construction projects have been predominantly studied in the USA (e.g. Zedler, 1984Zedler, , 1988Levin et al., 1996;Ray, 2000), UK (Evans et al., 1998) and Japan (Lee et al., 1998). In the USA, salt marsh creation has been used increasingly to mitigate loss of wetlands (Zedler, 1984;Moy and Levin, 1991). ...
... In the USA, salt marsh creation has been used increasingly to mitigate loss of wetlands (Zedler, 1984;Moy and Levin, 1991). Losses of tidal flat in the UK and USA have led to creation of intertidal flats on dredge spoil to provide supplementary feeding habitat for migratory birds (Evans et al., 1998;Ray, 2000). While the intended outcome of constructed wetlands is the creation of habitats that have similar ecological function to those lost (Warren et al., 2002), assessing their success is fraught with difficulties, is time consuming and often limited to quantitative measures of ecological components such as invertebrate assemblages (Zedler and Callaway, 1999). ...
... Colonisation of soft-bottom invertebrate communities in constructed habitats may be affected by factors such as proximity to larval supply (Zajac and Whitlach, 1982a,b;Diaz-Castaneda et al., 1993), seasonal timing of disturbance (Zajac and Whitlach, 1982a,b), compaction of substrate (Evans et al., 1998), slope of tidal flat (Lee et al., 1998) and the presence of other infauna (Thrush et al., 1992). Studies suggest that even after 4 years of establishment, constructed systems may be significantly different from natural areas of marsh and tidal flat with respect to abundance, species richness and distribution of infaunal invertebrates (Zedler, 1984(Zedler, , 1988Moy and Levin, 1991;Levin et al., 1996) and some may take decades to restore populations . ...
Abstract The diversity and abundance of arboreal and flying arthropods, in three mangrove patches along the south coast of New South Wales, Australia, was investigated to determine the degree of spatial variability in the assemblages among patches. Intercept traps and restricted canopy fogging were used to sample the communities at Minnamurra, Bonnievale and Kurnell. Twelve orders of arthropods were detected, incorporating 252 morphospecies. Abundance, species richness and species composition were very similar across all patches, the variation being much smaller than expected. These findings suggest that the composition of the arboreal and flying fauna associated with mangrove patches are very similar among patches, but preliminary results also showed that species composition could be highly variable within a patch.
Variation between the trapping methods was large, as expected. Intercept trapping and restricted canopy fogging techniques were found to sample different suites of species and therefore complement each other well in sampling programs. Cumulative species curves differed between time periods but generally were flatter for intercept traps than for restricted canopy fogging. Results suggested, for a given level of effort, intercept traps caught a more representative sample of the species composition available to them.
... This in turn leads to soil compaction and it is a common phenomenon in many saltmarshes when the soil is submerged by tidal waters (Crooks, 1998;Crooks et al., 2002). These compacted soil surfaces inhibit the infiltration of new sediments, lead to the underlying soil becoming hypoxic (Crooks et al., 2002), and affect some ecological processes above the ground (Evans et al., 1998). Once saltmarshes are inundated by tidal waters, the largescale treatment of compacted soil to make it suitable for saltmarsh plant colonization is very challenging (Brooks et al., 2015). ...
... This suggests that even the seeds that were present in these bare patches did not have suitable conditions for emergence. They could not obtain moisture and nutrients from the soil to sustain their emergence (Evans et al., 1998). However, on the surface of natural saltmarshes, topographic heterogeneity and plant structures provide sufficient opportunities for seeds to stay. ...
Human activities have profoundly affected coastal wetlands. Apart from direct occupation, indirect influences are usually caused by modifications to environmental conditions, which are various and complex. Saltmarsh bare patches might be related to these artificial modifications. They have little or no vegetation cover and lose some important functions. Hence, the mechanisms underlying saltmarsh bare patches and the effects of artificial modifications should be studied. We took the Yellow River Delta as our research object and explored the characteristics of saltmarsh bare patches in the Yellow River Estuary Natural Reserve. Our results show that artificial modifications limit some key plant life stages and thus hinder the natural regeneration process. Once suffering from fatal events, such as long-term inundation or artificial damage, this limitation will lead to the formation of persistent bare patches in saltmarshes. First, a shortage of local seed sources will be induced by the death of local plants when they are affected by a fatal event. Second, the replenishment of external seeds is often constrained by dikes and dams. Third, construction activities and the prolonged high-water inundation events can lead to soil compaction and the lack of microtopographic heterogeneity, which will hinder the retention and anchorage of seeds. Overall, it is essential to realize the underlying mechanisms of persistent bare patches and their potential to be included in cost-effective restoration or management plans.
... Few studies are reporting the relationships of avifauna with their food sources on the basis of landscape and/or physical properties of foraging grounds (VanDusen et al. 2012). Intertidally distributed macrobenthos polychaetes and bivalves, for instance, are the main preys of shorebirds while fish are the main preys of egrets (Nybakken 1993, Evans et al. 1999, Jiang 1999, Caldow et al. 2004 and insects contribute a significant diet to foliage gleaners (Fitzpatrick 1985). Local physical driving forces largely control polychaete and bivalve distributions, including hydrology, geomorphology and sedimentology (Sanders 1958;Rhoads and Young 1970;Jumars and Nowell 1984;Snelgrove and Butman 1994;Howe et al. 2017), while insect distributions are tightly associated with vegetation composition (Holmes and Robinson 1981). ...
... At Wazihwei Nature Reserve, the shorebird abundance depends on increasing open surface areas of intertidal flats, agreeing with our expectation that the shorebird prefers foraging on tidal flats with large open surface area in mangrovevegetated wetland. Our findings are also consistent with the records that open tidal area, a land-cover type in estuarine wetlands, functions importantly as foraging grounds for most migratory shorebirds (Burger et al. 1997;Evans et al. 1999;Straw and Saintilan 2006). Wintering migratory egrets, gray heron (Ardea cinerea), great egret (Ardea alba) and Chinese egret (Egretta eulophotes) and a common resident egret, little egret (Egretta garzetta) are another bird group relying on open intertidal flats for foraging in the Wazihwei Reserve (Table S10). ...
Mangrove overexpansion monopolizes estuarine landscapes by diminishing land-cover type diversity and hence biodiversity. Preferences of land-cover types by polychaete and bird assemblages as they relate to associated physical driving forces warrant investigation. In a mangrove-vegetated nature reserve, six land-cover types were found and aligned along elevation, inundation and sedimentary gradients. However, only three land-cover types were preferred by polychaetes, mainly tidal flats with intermediate and high inundation, and mangroves. Each land-cover type was differentiated by a distinctive species. The density of the nereid, the prey of shorebirds, was well explained by increasing flow velocity of the tidal flats. Five land-cover types were preferred by birds. Shorebirds recognized tidal flats for foraging where large, open surface areas shaped the places. Wintering egret also preferred feeding on open tidal flats and the residential egret favors nesting on tall and thick trunk mangroves. These egret-differentiated land-covers were regulated by lengthening inundation. Foliage and ground gleaners preferred dense, tall and thick trunk mangroves. The shorebird abundance could be enhanced 2.25 times if the open tidal surface area increased 1.5 times more than the current level. Our results identify useful, applicable physical driving parameters and suggest effective management strategies for conserving mangrove-vegetated wetlands.
... By the 1980s, however, about 40% had unfortunately disappeared (Kimura, 1994). In recent years, useful functions of tidal flats such as biological production, water quality clarification and recreation have been recognized more and more (Miyoshi et al., 1991;Kimura et al., 1992;Imamura, 1997;Evans et al., 1998;Ishii et al., 2001;Morrison et al., 2002;Tiner et al., 2003;Sakamaki et al., 2006;Magni and Montani, 2006). For example, Kimura et al., (1992) compared water quality at the seashore where an artificial tidal flat existed, and its offing region. ...
... Benthic microalgae are primary producers in tidal flats (McConnaugley & McRoy, 1979;Herman et al., 1999;Posey et al., 2006). Macrobenthos are near the bottom of the food web, providing food for large crustaceans, fish and birds (Day et al., 1989;Evans et al., 1998), and also play a role in water purification by the tidal flats (Herman et al., 1999;Magni and Montani, 2006). Certain bivalves, such as clams, form fisheries (Ishii et al., 2001). ...
This research was carried out to investigate the feasibility of using dredged sediment (DS) as the additive of silt and clay for artificial tidal flats. A series of experiments conducted in the real seashore and in a tidal flat simulator demonstrated that DS could be used for artificial tidal flats. Furthermore, the tidal flat simulator experiment showed that the macrobenthos population increased with the DS addition. However, use of conditioners made of paper sludge and poly-aluminum chloride for DS granulation treatment was associated with a time lag in the growth of the macrobenthos: these agents may be released during the course of the experimental period. Possible reasons for the increased polychaete and gastropod abundances in the artificial tidal flats might be an increase in supplied organic matter and stimulated benthic microalgae growth due to the DS addition. Finally, a growth test was carried out for the short neck clam Ruditapes philippinarum, which showed that it can grow in artificial tidal flats to which DS has been added. Too much DS, however, may suppress its growth.
... In the most studies on the benthic communities established on artificially constructed mud flats, the main interest was focused on estimating how many years are required until the benthic communities on the tidal flats reach to the mature levels similar to those on the natural tidal flats. In the case of artificially constructed tidal flats at Sheep Island in Maine, USA, from 1988 to 1989, it took within two years from the construction that the richness of infaunal taxa, total numerical abundance, species composition, and diversity of the benthic communities developed to the similar levels with those of a surrounding reference area [3], and it took three or four years on the restored mudflat in Tees Estuary, UK [4]. However, it took more than 10 years in the benthic communities on the mud flats in the Bay of Fundy [5]. ...
... According to Evans et al., the benthic communities of a restored mudflat in Tees Estuary, UK did not sustain sufficient abundances of important taxonomic groups (e.g. Nereis diversicolor (Muller) and Corophium volutator (Pallas)) to shorebirds compared to the undisturbed flats after three years [4]. Wilcox also noted that shorebird usage of newly restored mudflats in Upper Newport Bay, California, USA was less than natural mudflats, and this was presumably due to lower densities of their benthic invertebrate prey [29]. ...
... Intertidal areas can be created by moving the flood defence inland, allowing estuaries to flood the previous terrestrial land (French, 2006). Long term ecological monitoring at several managed realignment sites has compared the colonisation by the benthic invertebrate communities of restored or created estuarine mudflats with the adjacent, established mudflats (Evans et al., 1998;Garbutt et al., 2006;Mazik et al., 2007Mazik et al., , 2010; Marquiegui and Aguirrezabalaga, 2009). Similarly, several studies have assessed the success of new intertidal habitats for waterbirds (Simenstadt and Thom, 1996;Evans et al., 1998Evans et al., , 2001Atkinson et al., 2001Atkinson et al., , 2004Armitage et al., 2007;Mander et al., 2007), focussing on species richness and abundance. ...
... Long term ecological monitoring at several managed realignment sites has compared the colonisation by the benthic invertebrate communities of restored or created estuarine mudflats with the adjacent, established mudflats (Evans et al., 1998;Garbutt et al., 2006;Mazik et al., 2007Mazik et al., , 2010; Marquiegui and Aguirrezabalaga, 2009). Similarly, several studies have assessed the success of new intertidal habitats for waterbirds (Simenstadt and Thom, 1996;Evans et al., 1998Evans et al., , 2001Atkinson et al., 2001Atkinson et al., , 2004Armitage et al., 2007;Mander et al., 2007), focussing on species richness and abundance. However, these parameters provide only limited structural ecological information when assessing the responses of birds to habitat restoration and creation in the intertidal zone; here we consider that functioning information is more valuable as a measure of successful restoration . ...
The loss of intertidal habitat in estuaries has resulted in the need to
create new habitats in order to protect waterbird populations. In order
to examine the waterbird colonisation of restored intertidal areas
created in 2003 through the realignment of the flood defence in the
Humber Estuary (UK), the feeding behaviour of Redshank (Tringa totanus)
was observed in April 2008. Numbers of pecks, probes and paces (numbers
of steps) and the prey intake events were compared between Redshank
foraging on the restored mudflat and on the adjacent established
mudflat. Redshank prey intake and success rate (prey intake divided by
the total numbers of pecks and probes) were significantly lower on the
restored mudflat compared to the adjacent established mudflat.
Conversely, the number of steps taken while foraging and the number of
paces per successful feeding event were significantly greater on the
restored mudflat. This shows that focal behaviour in restored intertidal
areas can be directly compared with that in natural established mudflat
in order to examine differences in foraging behaviour. The findings
emphasise that a study of foraging behaviour should be incorporated into
the assessment of restoration success of intertidal areas as an
indication of habitat quality.
... Although many wetland organisms are tolerant of a wide range of physical conditions (Kneib 1984), both biotic and abiotic characteristics often influence invertebrate distribution and ability to colonize new habitats (Levin & Talley 2000). Sediment organic content, for example, is often closely related to grain size and influences food availability for detritivores and other benthic consumers (Moy & Levin 1991;Sacco et al. 1994;Levin et al. 1996;Scatolini & Zedler 1996;Minello & Webb 1997;Evans et al. 1998;Talley & Levin 1999;Zajac & Whitlatch 2001). Many created wetlands are constructed from sandy dredge spoil (Cammen 1976;Broome et al. 1988;Zedler & Lindig-Cisneros 2000), which can take 1530 years to develop organic matter levels comparable to those in natural areas (Craft et al. 1988), potentially limiting macrofaunal food availability in those sites. ...
... In North Carolina, Nassarius obsoletus (eastern mud snail) achieved only 50% of natural densities in a 27-month-old restoration site (Levin et al. 1996). In England, Hydrobia ulvae (mud snail) rapidly colonized a mudflat following restoration of tidal flooding, but after 4 years, snail densities remained one-third of those in natural areas (Evans et al. 1998). Reduced snail densities in our study site and other created wetlands were likely caused by some combination of limited dispersal ability and unsuitable habitat characteristics. ...
We investigated the assumption that populations of epibenthic macroinvertebrates readily establish in created coastal wetlands by quantifying the spatial and temporal patterns of Cerithidea californica (California horn snail) density in a newly created wetland and an adjacent natural area in Mugu Lagoon, southern California, United States, for 3.5 years. The natural and created sites differed in vascular plant cover and sediment grain size, organic content, salinity, and moisture content. Densities of C. californica in the created site changed little during the study period, and were often lower than those in the natural site. The influences of habitat suitability and dispersal limitation on C. californica colonization of the created site varied among snail age classes. Sediment moisture and organic content explained some of the variability in subadult (47%) and adult (55%) density and relative abundance, but none of the variability in juvenile abundance. Adult snail density was also strongly influenced by distance from the natural/created site transition zone. Juvenile and subadult snail densities were not related to distance from the natural site, possibly due to greater dispersal ability. Between-site differences in C. californica densities and size structure suggested that adult snails were affected by both habitat characteristics and dispersal ability, subadults were influenced to a lesser degree by habitat characteristics, and juveniles were not related to either factor. Accordingly, the influence of habitat characteristics and dispersal ability on created site colonization may change with snail age. Successful restoration of benthic invertebrate communities requires consideration of both habitat characteristics and dispersal ability of the target species, even in created sites in close proximity to natural areas.
... In addition feeding and foraging behaviour by animals at the upper end of the food chain such as fish (during inundation) and birds (during exposure) have been found to influence tidal flat stablility (e.g. Dabom et al., 1993;Evans et al., 1999). As one of the foci of this thesis, the processes of erosion and stability of intertidal mudflats and the biological processes involved are reviewed below in more detail. ...
p>Interdisciplinary research, incorporating macrobenthic ecology and sediment dynamics, was undertaken in order to investigate the effects of recharge on the lower shore of an intertidal mudflat at Hythe, Hampshire, UK. A field programme was carried out to examine the impact of a trial recharge experiment (planned and carried out by ABP) on the macrofauna community and associated sediments, and to collect baseline information on the site. The fieldwork included biological sampling, in situ physico-chemical measurements of key environmental parameters, measurements to identify changes in bed elevation indicative of accretion or erosion at the site, and the collection of sediment cores for analysis of sediment properties and structure.
Both the field (and the CT) studies indicated that no significant deposition of material occurred at the site as a result of recharge and the benthic community was unaffected. This is in agreement with the results of surveys carried out by ABP which concluded that the deposited material was transported away from the site by the tidal currents (ABP, 2001). Results obtained from the smothering experiments indicated that effects were species specific, and were dependent upon animal functional morphology. Tolerance thresholds for species ranged from less than 2 cm of burial (e.g. H. ulvae ) to >50 cm ( N. diversicolor ). No clear relationship was identified between τ<sub>c</sub> and macrofauna density from the erosion experiments. Results suggest that erosion rate and gradient as a relative measure of internal friction coefficient («problem!») may be better parameters for future investigation, as causative relationships were implied. Experimental effects arising from instrument differences, laboratory effects and treatment effects were identified and are addressed. CT proved to be a highly suitable technique for the investigation of sediment structure and fine-scale bulk density distribution. Several distinct layers of sediment including a collapse zone ( sensu Droppo and Amos, 2001) and self-weight consolidation were identified from the bulk density data. Faunal modification of sediment structure by bioturbation, and individual burrows were also identified. No long-term, or seasonal trends of erosion or deposition were revealed by the CT images and data, and earlier observations were supported in that no clear signs of recharge were evident.</p
... This is of concern given the increased pressures associated with protected areas, such as habitat loss due to sea-level rise and proposed developments on the margins of some sites (Alves and Dias, 2020;Galbraith et al., 2002). Whilst amelioration of the negative impacts associated with these changes may be possible through interventions such as habitat restoration or creation (Mander et al., 2007), it may be some time before these interventions are effective (Evans et al., 1999). Given many migratory species are highly philopatric (Burton and Evans, 1997;Burton, 2000;Frederiksen et al., 2002), such interventions may be insufficient to compensate for reduced survival, negating any positive gains made through increased productivity. ...
Migratory species face geographically dispersed pressures over the course of their annual cycles. Designing effective conservation strategies for these species requires a detailed understanding of how these different pressures affect demographic rates throughout the annual cycle. As a long-lived species, population trends in the rapidly declining Eurasian curlew Numenius arquata are likely to be highly sensitive to impacts on adult survival. We combine data from multiple sources to analyse survival rates of overlapping populations that breed and/or winter in the United Kingdom. Our analyses demonstrate that curlew survival rates are reduced by cold weather and at high density; however, overall survival rates are high and have increased in recent years. Current population declines are, therefore, likely to be driven by low productivity. As such, efforts to stabilise and reverse declines should focus on increasing breeding success from current estimated levels of 0.25 chicks nest⁻¹ to 0.43 chicks nest⁻¹. In addition to increasing productivity, effective conservation strategies will need to maintain high levels of survival, which requires an improved understanding of population connectivity and demographic variation throughout the annual cycle.
... Since ocean disposal of industrial waste and sewage sludge has been phased out in the United Kingdom and many European countries, there is now greater focus on behalf of the public and legislative bodies on the disposal of sedimentary material such as dredged material or inert mine tailings (Vogt and Walls, 1991;Kvassnes and Iversen, 2013;Ramirez-Llodra et al., 2015). Dredging has been shown to cause negative effects on the benthos (e.g., Sanchez-Moyano et al., 2004;Robinson et al., 2005) so there is now a greater emphasis on relocating dredged material in such a way as to derive environmental or other benefits (Bolam et al., 2006;Bolam, 2014) such as creating or enhancing mudflats (Ray et al., 1994;Evans et al., 1998) and saltmarshes (Laselle et al., 1991;Posey et al., 1997). For mine tailings, the millions of tons of waste produced annually limits potential transport options so tailings tend to be disposed of in slurry form directly to the coastal environment through de-aerated pipelines (Kvassnes and Iversen, 2013;Ramirez-Llodra et al., 2015). ...
Fine-grain, waste rock (or tailings) produced during mining processes are the main waste product following the extraction of valuable minerals and metals from ores. The proximity of mineral resources to coastal regions in some countries has meant that the organically inert mine tailings are often deposited into the marine environment as a submarine tailings placement or STP. This creates a real environmental challenge since the deposition of tailings at the seafloor can completely smother the benthic environment and reduce benthic biodiversity and alter ecosystem function. A limited number of studies have attempted to quantify the speed of seafloor recovery following tailings disposal and have suggested that one of the main factors limiting seafloor colonization is the lack of organic matter of the tailings deposited. In this experimental study, we used hydrodynamically unbiased settlement trays within a complete randomized block design to test whether macrofaunal colonization of mine tailings, and resemblance toward ambient assemblages, is enhanced when tailings become more enriched in organic C (Corg). Our experiment showed that tailings with Corg contents ≥ 1% exhibited lower faunal abundance and biomass and different macrofaunal community composition after 1 year compared to background sediments. Macrofaunal species richness (defined as the total number of different taxa) in the 0 and 0.5% Corg tailings treatments, however, was statistically indistinguishable from ambient intertidal sediments after 1 year. Furthermore, macrofaunal community structure was more similar to that of the background intertidal sediments after 1 year, which collectively suggest partial recovery of seafloor biodiversity in tailings with zero to low Corg levels. Nevertheless, macrofaunal abundance and biomass in these treatments remained significantly less than the background community after 1 year suggesting factors other than the Corg content of tailings may be structuring macrofaunal colonization and impeding seafloor recovery of tailings deposits. We propose that the non-marine physical structure of the tailings particles, which show great angularity is predominantly responsible for the observed delayed recovery.
... This in turn results in over-compaction when flooded by sea water, a process that has led to the widespread development of overconsolidated sediments in the Holocene estuarine deposits of southeast England (Crooks 1998;Crooks et al. 2002). These consolidated layers can impede drainage in freshly deposited sediment and contribute to the development of anoxic conditions at low lying sites (Crooks et al. 2002), and overcompaction of sediments also seems to have hindered the ecological development of the Seal Sands managed realignment (Evans et al. 1998). Once a marsh has been flooded, large scale sediment treatment to break up over-consolidated sediment is extremely challenging. ...
1.Halophyte distributions on saltmarshes are strongly related to elevation in the tidal frame. However, collinearity between elevation, the consequent inundation regime, and sediment waterlogging/redox potential obscures the proximate causes of distribution patterns. We sought to distinguish the effects of elevation per se from those of waterlogging by manipulating microtopography. 2.We experimentally manipulated elevation by ±15 cm at locations that spanned the elevation ranges of three saltmarshes recently reactivated by managed coastal realignment. Experimental plots were initially cleared of any vegetation. Elevation and sediment redox potential were determined for each plot. We planted five perennial species (Armeria maritima, Atriplex portulacoides, Limonium vulgare, Plantago maritima and Triglochin maritima) in half of the plots, recording survival over four years, and monitored natural colonisation of the other plots. 3.Overall, redox potential increased with elevation. Sediments were more oxidising in raised plots and more reducing in lowered plots. Redox reductions in lowered plots were in line with those that would be predicted from the overall redox/elevation relationship, but increases in raised plots were greater than predicted from elevation alone. 4.Plant colonisation and survival was poorer in lowered plots and, for most species, improved in raised plots. This poorer colonisation and survival can, in part, be attributed to the concomitant alterations in redox potential and elevation in the tidal frame, but microtopographic manipulation also had substantial independent effects on plant performance, including on the survival of all planted species and the colonisation of Puccinellia maritima, Salicornia europaea agg. and Tripolium pannonicum. 5.Synthesis: Microtopography can have effects on sediment chemistry and plant performance similar in magnitude to those of overall tidal elevation. Understanding how its effects modulate the relationship between tidal elevation, redox and other environmental conditions helps clarify the abiotic factors that fundamentally determine halophyte colonisation and survival. These results support the use of topographic manipulation to enhance the diversity of created saltmarshes. This article is protected by copyright. All rights reserved.
... For example, between 1980 and 2015, 472 km 2 of coastal wetlands have been reclaimed in the Yellow River Delta region of China (Yu et al., 2017). While coastal land reclamation provides a lever for economic development (Murray et al., 2014), it also leads to the loss and degradation of habitat for biodiversity (Bulleri and Chapman, 2010;Chapman and Blockley, 2009), such as the macrozoobenthos (Dugan et al., 2008;Yan et al., 2015) which, in turn, are important for other biota such as migratory birds (Arocena, 2007;Evans et al., 1999;Goss-Custard et al., 2006). Biodiversity offsetting is emerging as a key policy employed to manage the impacts of development on natural habitats, having been adopted in approximately 40 countries (Maron, 2015;Gibbons et al., 2018). ...
... The intertidal coastal areas are of capital importance for the survival of many species of waders. The capacity of these sites to host large numbers of waders depends on the importance of their mudflats rich in benthic invertebrates, the main food resources for these birds (Goss-Custard 1996;Evans et al. 1998; Van de Kam et al. 2004;Rolet 2015;Ponsero et al. 2016). These preys constitute, in fact, key organisms that condition and influence all the benthos-waders trophic interactions. ...
The distribution of shorebirds is strongly linked to the availability of their prey consisting mainly of benthic invertebrates, especially during wintering and migratory stopovers. To better understand the functioning of this trophic link benthos-shorebirds at intertidal mudflats, it is necessary to evaluate the vertical distribution and importance of the fraction of benthic macrofauna accessible to shorebirds at these habitats. Nineteen stations were sampled in the main mudflats frequented by birds. Samples were cut into three slices of 0–5 cm, 5–15 cm and >15 cm. The results showed a vertical stratification of the benthic macrofauna negatively correlated with the depth of the Merja Zerga lagoon intertidal sediments. The specific richness, density and biomass were concentrated at the surface layer of the sediments and shrink as we go more in depth. The polychaetes showed the most diverse distribution pattern along the three sedimentary layers. While the Bivalves dominated in term of biomass, the Gastropods dominated with regard to density. We observed also that the upper layer is mainly colonized by small species and / or individuals with high density and low biomass; this phenomenon is gradually reversed as we go more in depth. The sedimentary parameters (organic matter content and granulometry of the substrate) were not responsible for the variations observed in the distribution of the macrofauna along the sedimentary profile, as the vertical distribution of these factors was homogeneous to a depth of 20 cm.
... The diversity of plants and animals also decreases due to the stress of the polluted estuary environment [1,6,14]. However, it is unclear whether microbial diversity is affected. ...
Pyrosequencing and metagenomic profiling were used to assess the phylogenetic and functional characteristics of microbial communities residing in sediments collected from the estuaries of Rivers Oujiang (OS) and Jiaojiang (JS) in the western region of the East China Sea. Another sediment sample was obtained from near the shore far from estuaries, used for contrast (CS). Characterization of estuary sediment bacterial communities showed that toxic chemicals potentially reduced the natural variability in microbial communities, while they increased the microbial metabolic enzymes and pathways. Polycyclic aromatic hydrocarbons (PAHs) and nitrobenzene were negatively correlated with the bacterial community variation. The dominant class in the sediments was Gammaproteobacteria. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) enzyme profiles, dominant enzymes were found in estuarine sediments, which increased greatly, such as 2-oxoglutarate synthase, acetolactate synthase, inorganic diphosphatase, and aconitate hydratase. In KEGG pathway profiles, most of the pathways were also dominated by specific metabolism in these sediments and showed a marked increase, for instance alanine, aspartate, and glutamate metabolism, carbon fixation pathways in prokaryotes, and aminoacyl-tRNA biosynthesis. The estuarine sediment bacterial diversity varied with the polluted river water inputs. In the estuary receiving river water from the more seriously polluted River Oujiang, the sediment bacterial community function was more severely affected.
... he size of Nereis and Hydrobia was significantly different (Reading et al . 1999). At Orplands, Essex, large bivalves had not colonized after 4 years despite substantial populations being present on the adjacent estuary. Biologically active mudflats were created at Seal Sands, Teeside, but it was recommended that a 5-year lead-in time was required (Evans et al . 1998(Evans et al . , 2001. ...
With current losses of saltmarsh running at > 100 ha per year in the UK, creation of new intertidal habitats through managed realignment is likely to be increasingly used. Potentially, this has biodiversity as well as engineering benefits. However, assessing the conservation value of many of the current UK schemes is difficult as the biological monitoring has been generally poor, with a few notable exceptions. At the Tollesbury and Orplands realignment sites, Essex, bird communities were dominated by terrestrial species during the first year of inundation and waterbird communities rapidly developed during the second and third years. Five years after the initial breach in the sea wall, communities were similar to surrounding mudflats but with some notable exceptions. Dunlin Calidris alpina and Common Redshank Tringa totanus that prey on the early colonizing Nereis and Hydrobia used the sites in the first 2 years. Eurasian Oystercatcher Haematopus ostralegus did not occur on the realignment site as there were no large bivalves, whereas Red Knot Calidris canutus used the site after 4–5 years coincidentally with the appearance of Macoma balthica. The differences in the bird communities occurred because UK sites are often small, enclosed and poorly drained. If at a suitable height in the tidal frame, UK managed realignment sites are successful in that they have developed saltmarsh and biologically active mudflats but they may lack the full range of biodiversity found in surrounding natural intertidal habitats, even decades after inundation.
... However, other studies have shown that beach filling often decimates infaunal invertebrate communities, resulting in cascading effects to higher trophic levels such as shorebirds (Peterson et al., 2006;Convertino et al., 2011). The duration of these effects can vary (Colosio et al., 2007;Evans et al., 1998;Peterson et al., 2006), and despite the frequency of beach nourishment projects in Louisiana, little research has been conducted on subsequent impacts to these imperiled ecosystems. Though habitat should ultimately be expanded by nourishment, it stands to reason that endangered species may be disproportionately affected as their prey base diminishes due to their own low abundance. ...
... This in turn results in over-compaction when flooded by sea water, a process that has led to the widespread development of overconsolidated sediments in the Holocene estuarine deposits of southeast England (Crooks 1998;Crooks et al. 2002). These consolidated layers can impede drainage in freshly deposited sediment and contribute to the development of anoxic conditions at low lying sites (Crooks et al. 2002), and overcompaction of sediments also seems to have hindered the ecological development of the Seal Sands managed realignment (Evans et al. 1998). Once a marsh has been flooded, large scale sediment treatment to break up over-consolidated sediment is extremely challenging. ...
Restored salt marshes frequently lack the full range of plant communities present on reference marshes, with upper marsh species underrepresented. This often results from sites being too low in the tidal frame and/or poorly drained with anoxic sediments. A managed coastal realignment scheme at Abbotts Hall, Essex, UK, has oxic sediments at elevations at which upper marsh communities would be expected. But 7 years after flooding, it continued to be dominated by pioneer communities, with substantial proportions of bare ground, so other factors must hinder vegetation development at these elevations. The poorly vegetated areas had high sediment shear strength, low water and organic carbon content and very flat topography. These characteristics occur frequently on the upper parts of created marshes. Experimental work is required to establish causal links with the ecological differences, but other studies have also reported that reduced plant β-diversity and lower usage by fish are associated with topographic uniformity. Uniformity also leads to very different visual appearance from natural marshes. On the upper intertidal, sediment deposition rate are slow, water velocities are low and erosive forces are weak. So, topographic heterogeneity cannot develop naturally, even if creeks have been excavated. Without active management, these conditions will persist indefinitely.
... Estas áreas de transição entre os am bientes terrestre, dulceaquícola e marinho têm um valor extemamente elevado, na medida em que asseguram serviços essenciais dos ecossistemas, nos quais se incluem: protecção das zonas costeiras, melhoria da qualidade da água, área de viveiro para muitos organismos marinhos, habitat e alimento para animais migratórios e residentes que compreendem al gumas das mais valiosas espécies comerciais (e.g. Van der Veer et al., 1990;Henderson & Seaby, 1994;Evans et al., 1998;Levin et al., 2001;Beck et al., 2001). Estes sistemas são caracterizados por flutuações locais extremas de factores abióticos tais como salinidade, temperatura, nível de água e oxigénio dissolvido, restringindo o número de espécies que aí podem ocorrer. ...
The Venta Moinhos salt marsh area (Castro Marim, Algarve) was reclaimed and used during decades as an extensive agricultural and grazing production field system. Its return to a salt marsh ecosystem was recently done by the administration of the nature reserve (Reserva Natural do Sapal de Castro Marim e Vila Real de St.º António). A lagoon like system adjacent to the Guadiana river estuary has been formed. The colonization of this new habitat by benthic macroinvertebrates communities have been followed from two weeks after the hydraulic regeneration of that area. A two year sampling period was established from September 1999 to September 2001. 31 taxa of macroinvertebrates were recorded. Diversity was low during the two year study period, mainly due to the very low salinity values subsequent to atypical rainy periods during the colonization process. Polychaetes and gastropods were the more relevant taxonomical groups concerning presence and abundance of organisms. The gathered data emphasize a disturbed benthic community.
... Hence, CRT offers extended feeding time for species that also forage on the adjacent tidal flats, especially when large areas are created. This may explain the tide effect on Forbs and Mudflat communities when the adjacent river flats were submerged at high tide and thus unavailable for birds, as already shown in wetlands adjacent to an estuary (Davidson and Evans, 1986;Evans et al., 1998). This hypothesis was rejected since abundances were not determined by the availability of the adjacent flats (Table A.5, Fig. A.2). ...
... Several studies have examined the recolonization of invertebrate macrofauna following the placement of dredged material on intertidal mudflats (Ray 2000, Bolam & Whomersley 2003, Bolam et al. 2004, or the creation of mudflats with earthmoving equipment (Evans et al. 1998). These studies have shown that recovery, in terms of taxa richness, abundance and species composition, may take from 6 to 24 mo depending on the size of the area, the timing of the scheme and the properties of the sediment. ...
Fine sediments derived from maintenance dredging in estuarine and coastal zones may provide a potential resource for enhancing or creating intertidal habitats (i.e. 'beneficial use' schemes). This study investigates the temporal changes in biota and sediment erodability following the placement of fine dredge material (ca. 0.6 m depth) on the upper shore at 2 trial 'beneficial use schemes' in estuaries situated in Essex, UK. There was a rapid process of sediment consolidation and dewatering within 7 d, reaching bulk densities and water contents typical of intertidal sediments within 6 wk. This was accompanied by an increase in critical erosion velocity (U-crit) from 0.13 to 0.25 m s(-1) (equivalent to a bed shear stress of 0.04 and 0.12 Pa) and a reduction in sediment erosion by 2 orders of magnitude. There was evidence of marked spatial (inter-site) and temporal variation in sediment stability which correlated with changes in the abundance of key species. The temporal changes in sediment erodability reflected the nature of benthic assemblages established during the recovery period (up to 19 mo). There were statistically significant correlations between microphytobenthos chl a, extracellular polymeric substances (EPS) and U-crit, and between total abundance of tube building/dwelling polychaetes and oligochaetes (minus Hediste diversicolor) and mass of sediment eroded at 0.3 m s(-1). The annual salt marsh plant Salicornia europaea was also found to reduce sediment erodability by reducing near-bed flows by up to 90%, as well as increasing Ucrit. These biota represented ecosystem engineers with a functional role as bio-stabilisers. There were also significant correlations between U-crit and the abundance of H. diversicolor and Corophium volutator, and between sediment mass eroded at 0.3 rn s-1 and H. diversicolor and Hydrobia ulvae. These biota represented ecosystem engineers with a functional role as bio-destabilisers. Most of the recorded correlations were consistent with previous species-specific flume studies establishing density-dependent effects on sediment erodability, thus indicating cause-effect relationships.
... Teesmouth (54°37′N 1°12′W) is a heavily industrialized estuary in the northeast of England and has been subject to considerable change over the last 30 years (Evans et al. 1998), including the building of a tidal barrier in the mid-1990s. The area supports some 25 000 wintering waterbirds, with nationally important populations of Knot Calidris canutus and Sanderling Calidris alba. ...
Capsule: Serious violations of the model assumptions were seen. Aims: To illustrate the manner in which violations of the mark-recapture model assumptions may occur. Methods: Attempts were made to model annual and seasonal survival of several shorebird species at Teesmouth, northeast England. The database contained 25 years of colour-ring resightings and several suites of models were tested. Results: There was significant heterogeneity in survival and recapture probabilities for all five species of shorebird that had been colour-marked. Various attempts and blocking, stratifying and constraining our survival models, while in many cases providing more parsimonious solutions, had no effect on these heterogeneities. Conclusions: Our problems stem from both the methodology used and lack of information about the status of individuals (e.g. territoriality and variability in the level of site fidelity). We suggest ways in which data more appropriate to survival analyses might be collected in future.
... The distance from a source of colonists is also predicted to have a substantial influence on the rate of colonization . Sites that are particularly isolated from colonists may be subject to extremely long periods (years) before returning to initial community composition; this prediction has also been supported by field studies (Evans et al. 1999). ...
Evidence of limited larval exchange and high levels of self-recruitment in marine populations continues to accumulate, implying that marine systems are not as open as we once believed. In estuaries, some organisms with long larval periods, such as crab and bivalve species, are capable of long-distance transport, while others, including many polychaete and gastropod species with crawling or brooded larvae, lack long-distance larval dispersal mech- anisms and may disperse as juveniles and adults. To predict transport rates and colonization potentials of macrofaunal life stages transported in the water column, we use a combined hydrodynamic and particle tracking model. We vary particle release location to investigate how different habitats (i.e., main channel, lower sandflat, high sandflat, tidal creek) will contribute to the supply of colonists in different parts of the estuary. Most particles traveled short distances and settled within their release habitat. Slightly negatively buoyant particles (corresponding to small larvae) traveled much farther than more negatively buoyant particles (corresponding to larger, heavier larvae and juveniles). Particles released from high intertidal locations had lower rates of transport and transfer among habitats compared to lower intertidal sites. Other influences on organism transport include timing of release (with respect to tide), release location within the water column, tidal range, and magnitude of freshwater flood events. In general, estuarine communities dominated by organisms with limited dispersal periods are likely to be recruitment limited and limited in their ability to reach mature community states when subject to increasing frequencies or spatial extent of distur- bance.
... Intertidal salt marshes and sandflats are important feeding grounds for shorebirds, which are attracted to refuge and prey such as infaunal polychaetes and amphipods (Evans et al. 1998). In turn, birdwatchers are attracted by the birds, and recreational pressures become more intense in those wetlands with rich natural resources. ...
We examined the effects of recreational trampling on wetland sediments, saltmarshes, and macroinfauna in November 2006 and April and July 2007. We used penetration resistance to measure sediment compaction at the Kaomei wetland, a protected intertidal coastal wetland harbor- ing the largest tuberous bulrush marsh grass bed in Taiwan. We also examined the relationship of sediment compaction to visitor intensity and distribution of macroinfauna. Four compaction levels (low, medium-low, medium-high, and high) were identified using hierarchical cluster analysis. The spatial contour of sediment compaction was consistent with the level of visitor intensity, suggesting that human trampling is the main cause of sediment compaction in this wetland. Macroinfaunal abundance in low and medium-low compacted sediments was 4968 and 3376 ind. m-2, while no macroinfauna was recorded in highly consolidated sediments. Compared to those at medium-low compaction, taxon richness and community density at medium-high compaction were significantly reduced by 80.5 and 52.6%, respectively. Polychaetes were more sensitive to sediment compaction than amphipods and bivalves, and could thus serve as a bioindicator of human trampling impact. A decrease in polychaete abundance may be attributed to their life history, which is controlled by sub- stratum compaction. Our results showed that 25.7% of the study area was significantly compressed and that muddy vegetated areas were more vulnerable than sandy areas. We conclude that losses of macroinfauna and microhabitats are serious, and we propose management strategies to prevent further deterioration of this wetland.
... The lack of shorebird feeding (personal observation) may be due to the short time scale and the limited size of the restored area. Evans et al. (1999) noted that the establishment of new habitats in temperate intertidal areas to compensate for lost ones required at least 3 years for the benthos to fully re-colonize and to subsequently provide enough food for foraging birds. Smart and Gill (2003) reported that relatively small-scale restoration was unable to provide enough resources, including food, to attract foraging shorebirds. ...
Expansion of the monospecific mangrove, Kandelia obovata, has converted intertidal mudflats and other habitats into mangrove forests, thus reducing estuarine biodiversity in the Danshuei River estuary, northern Taiwan. Dense mangrove vegetation was removed to create a small patchwork of mudflats and a tidal creek in February 2007. Subsequent changes in sediment properties and biodiversity of the macrobenthos and avian communities were examined. The results showed that the creation of different habitats led to changes in sediment properties and biodiversity. The water content and sorting degree of the sediments differed significantly among the restored mudflat, the tidal creek, and the mangrove control site. Silt/clay, organic carbon content, and chlorophyll a concentrations varied seasonally, but not among sites. The abundance of polychaetes in the creek was greater than that in the mudflat or the mangrove (12.5 vs. 5.3 and 2.2 individuals/m2, respectively), suggesting preferential colonization of infaunal polychaetes in habitats with prolonged submersion. Crabs showed seasonal changes in density, with higher densities in summer than in autumn and winter. The species richness of wintering shorebirds on the created mudflat increased dramatically from 2002 to 2007. The transformation of a vegetated area into an open mudflat appeared to benefit shorebirds by providing roosting habitat. Our study demonstrated that controlling the spread of estuarine mangrove forests could increase biodiversity, and could particularly benefit the migratory shorebird community.
... The topdown control by grazers is conditioned by grazer density, type or species Smith et al., 1996;Anderson, 1999;Pillay et al., 2009). The gastropod density is directly depended on growth rate and indirectly affected by several other factors, such as salinity, temperature, sediment grain size, and organic content (Evans et al., 1999). ...
Mud snails Hydrobia ulvae occupy different habitats in complex estuarine ecosystems. In order to determine if fatty acid profiles displayed by mud snails can be used to identify the habitat that they occupy within the same estuary, fatty acids of H. ulvae from one mudflat and one seagrass meadow in the Ria de Aveiro (Portugal) were analyzed and compared to those displayed by microphytobenthos (MPB), the green leaves (epiphyte-free) of Zostera noltii, as well as those exhibited by the epiphytic community colonizing this seagrass. MPB and epiphytic diatom-dominated samples displayed characteristic fatty acids, such as 16:1n-7 and 20:5n-3, while 18:2n-6 and 18:3n-3 were the dominant fatty acids in the green leaves of Z. noltii. Significant differences between the fatty acid profiles of H. ulvae specimens sampled in the mudflat and the seagrass meadow could be identified, with those from the mudflat displaying higher levels of fatty acids known to be characteristic of MPB. This result points towards the well known existence of grazing activity on MPB by mud snails. The fatty acid profiles displayed by H. ulvae inhabiting the seagrass meadows show no evidence of direct bioaccumulation of the two most abundant polyunsaturated fatty acids of Z. noltii (18:2n-6 and 18:3n-3) in the mud snails, which probably indicates that either these compounds can be metabolized to produce energy, used as precursors for the synthesis of essential fatty acids, or that the snails do not consume seagrass leaves at all. Moreover, the fatty acid profiles of mud snails inhabiting the seagrass meadows revealed the existence of substantial inputs from microalgae, suggesting that the epiphytic community colonizing the leaves of Z. noltii displays an important role on the diet of these organisms. This assumption is supported by the high levels of 20:5n-3 and 22:6n-3 recorded in mud snails sampled from seagrass meadows. In conclusion, fatty acid analyses of H. ulvae can be successfully used to identify the habitat occupied by these organisms within the same estuary (e.g. mudflats and seagrass meadows) and reveal the existence of contrasting dietary regimes.Highlights► Fatty acid profiles of Hydrobia ulvae were compared to those of food sources. ► Differences were found between mud snails from the mudflat and the seagrass meadow. ► Those differences were related with different food sources. ► Significant inputs of microalgae were found. ► Fatty acid profiles can be used to identify the habitat occupied by Hydrobia ulvae.
... The advantages of reduced levels of predation, higher food availability, and utilization of resources that are temporarily unavailable to potential competitors during closed phases may, however, be oVset by the disadvantages of low levels of gene Xow among populations. These include increased vulnerability to localised extinctions (Valentine and Jablonski 1986; Wares and Cunningham 2001 ) and slow recolonisation of habitats from which a species has been eliminated, e.g. as a result of freshwater Xoods or habitat degradation (Moy and Levin 1991; Evans et al. 1998; Lockyear et al. 2006). To determine how the reduction or absence of larval stages has inXuenced genetic connectivity among southern African coastal invertebrate populations, we conducted phylogeographic analyses of Wve species with three major types of development: long-lived planktonic, abbreviated planktonic, and direct. ...
The amount of genetic structure in marine invertebrates is often thought to be negatively correlated with larval duration.
However, larval retention may increase genetic structure in species with long-lived planktonic larvae, and rafting provides
a means of dispersal for species that lack a larval dispersal phase. We compared genetic structure, demographic histories
and levels of gene flow of regional lineages (in most cases defined by biogeographic region) of five southern African coastal
invertebrates with three main types of larval development: (1) dispersal by long-lived planktonic larvae (mudprawn Upogebia africana and brown mussel Perna perna), (2) abbreviated larval development (crown crab Hymenosoma orbiculare) and (3) direct development (estuarine isopod Exosphaeroma hylecoetes and estuarine cumacean Iphinoe truncata). We hypothesized that H. orbiculare, having abbreviated larval development, would employ a strategy of larval retention, resulting in genetic structure comparable
to that of the direct developers rather than the planktonic dispersers. However, regional population structure was significantly
lower in all species with planktonic larvae, including H. orbiculare, than in the direct developers. Moreover, nested clade analysis identified demographic histories resulting from low levels
of gene flow (isolation by distance and allopatric fragmentation) in the direct developers only, and migration rates were
significantly higher in all three species having planktonic larvae than in the direct developers. We conclude that the amount
of genetic structure within marine biogeographic regions strongly depends on the presence or absence of free-swimming larvae.
Whether such larvae are primarily exported or retained, whether they have long or short larval duration, and whether or not
they are capable of active dispersal seems to have little effect on connectivity among populations.
... Soft mud at Foundry Cove was probably removed by dredging, leaving sediment that had been compressed over many years. Compression of sediments can negatively affect benthic organisms (Kelaher et al. 1998; Evans et al. 1998) and, in this TABLE 6. Correlation coefficients (n 40) for comparisons between macrobenthic community and combinations of environmental variables from BIO-ENV analyses. Values indicate the strength of relationships relative to the other comparisons. ...
We studied changes in macrobenthic communities following the environmental clean-up of metal-polluted (cadmium, nickel, and
cobalt) sediments in Foundry Cove, a small inlet within the Hudson River estuary of New York. We used a BACI-style experiment
to test the hypotheses that high levels of cadmium in sediments change macrobenthic assemblages relative to unpolluted areas,
and removal of metals (especially cadmium) by dredging will restore the benthos, such that benthic fauna in Foundry Cove are
not different from unpolluted areas. In 1984, prior to the restoration work, there were no significant differneces between
macrobenthic assemblages in polluted and unpolluted locations, indicating that cadmium had little effect on community structure.
The lack of an observed toxicity effect may have been caused by the compensatory evolution of resistance to cadmium in dominant
organisms. Six years after the restoration work and despite a substantial reduction in metal pollution, there were lower abundances
of oligochaetes, nematodes, and chironomids and a higher abundance of polychaetes at Foundry Cove relative to reference locations.
Correlative analyses identified greater sediment compaction caused by dredging at Foundry, Cove as a possible cause of faunal
differences. The results demonstrate that it is difficult to accurately predict, the effects of anthropogenic disturbances
and restorations in complex natural systems and that unforeseen side effects are inevitable. Documenting these unpredicted
effects and experimentally understanding their causes in past restorations will greatly improve the success and cost-effectiveness
of future projects of a similar type.
The burrowing activity of fiddler crabs inhabiting intertidal flats creates visually distinct patches within these habitats. However, differences in the composition and abundance of shorebirds and their macroinvertebrate prey between areas inhabited or not by crabs are yet to be studied. Here, we compare the macroinvertebrate and shorebird assemblages in low and high crab density areas in the intertidal flats of the Bijagos archipelago, Guinea-Bissau. High crab density areas are associated with lower richness and densities of macroinvertebrates. Shorebird assemblages were also less rich at high crab density areas and the differences in species composition occurred according to prey type preferences. Fiddler crab density was the most important variable explaining macroinvertebrate abundance, after accounting for the effects of fine fraction of sediment and distance to coast. Nonetheless, a controlled experimental setup would be required to attribute differences found to the engineering activity of fiddler crabs rather than other unaccounted habitat features. Our findings suggest that crab patches should be taken into account when assessing the distribution and abundance of macroinvertebrates and shorebirds in intertidal areas. Since low and high crab density areas differ markedly in terms of shorebird carrying capacity, monitoring variations in their extent will be important to interpret past and present population trends.
Mangrove expansion monopolizes estuarine landscapes by diminishing habitat diversity and hence biodiversity. Physical landcover types, including mangrove vegetation, influence polychaete and avifauna habitat uses. The connections between the physical to biota-associated landscapes warrant investigation. We determine how to best describe the landscape in a mangrove-vegetated wetland according to the physical, polychaete and bird domains and identify what physical attributes would affect the biota-associated landscapes. Differences among the physical and biota-associated landscapes were evaluated using multivariate ordination analyses. Six physical landcover types were aligned along elevation, inundation and sedimentary gradients. The polychaete-associated landscape was structured by three landcover types, mainly mangroves and tidal flats with intermediate and high inundation. Deposit-feeding spionid and nereid, carnivorous goniadid and suspension-feeding sabellid polychaetes depended on the different landcover types. Shorebirds occurred distinctively in tidal flats with large, open surface areas. Egrets characterized tidal flats and mangroves, and foliage and ground gleaners characterized mangroves. Open tidal flats are crucial to polychaetes, which are the main prey of shorebirds and are also important to egret foraging. Our results suggest that effective management strategies for conserving these migratory birds require the maintenance of open tidal flats in the landscape.
Estuaries are among the most productive environments in the coastal zone that may act as sink of pollutants. In this study we evaluated how levels of heavy metal contamination can be reflected in the macroinvertebrate communities of six Tagus Estuary mudflats, inferring their consequences to upper trophic levels. We used Shannon-Wiener's diversity, Pielou's evenness and Simpson's dominance indices, and macroinvertebrate densities to characterize benthic communities at the sites that presented different metal contamination loads. Those stations with high levels of contamination presented a lower diversity but also the highest prey density. This study indicated that unhealthy areas can still perform their ecosystem function with costs that remain to be evaluated. The biodiversity can be impoverished compared with other less contaminated sites, but with regard to their utilization as feeding areas by birds and fishes this is not a limiting factor. For this particular function of the mudflats, prey availability is the main characteristic determining the choice of one particular site as a bird and fish feeding area that may not be affected by heavy metal contamination.
The disposal of maintenance dredged material constitutes one of the most important problems in coastal zone management. To minimise ecological impacts, a number of ‘beneficial use’ options have developed whereby the material is regarded as a potential resource and used to recharge or recreate intertidal habitats. This paper presents the results of a sampling programme to investigate the macrofaunal recovery rates, and the underlying mechanisms responsible for them, following a beneficial use scheme involving the placement of fine-grained dredged material on a salt marsh in southeast England.
Three stations in the recharge area and three reference stations, located within the same salt marsh system, were selected. These stations were sampled prior to recharge (recharge stations only) then 1 week, 3, 6, 12 and 18 months after the recharge. Sediment redox potentials (1, 2 and 4 cm sediment depths) were also measured on each sampling occasion. The results indicated a rapid recolonization of the fauna typical of the surrounding salt marsh channels. All univariate parameters had recovered after 3 months after the recharge. Active post-juvenile immigration is likely to have been the predominant recovery process. Multivariate data analysis revealed that the community structure of the recharge stations, however, did not progress towards those of the reference sites. Natural spatial variability in community structure at the scale of the recharge-reference station distance, and differences in eventual tidal elevations are factors responsible for these differences. The need to carefully assess reference site suitability in monitoring beneficial use schemes is discussed.
A study for bird habitats was conducted in inter-tidal flat area of Chongxi Wetland, Yangtze Estuary, during the periods from 2006 to 2007. A 7-hm 2 area was established for wetland restoration with 50% of the area for restoration and 50% of the area for control, respectively. Results showed that there were significantly developments in vegetation communities, macrobenthic, fish and bird habitats on the landscape of the restoration site. During restoration period, Reed (Phragmites australis) marsh in restoration site developed to a diverse area with open-water (40%), mud flat (30%), and multi-vegetation communities (30%). A diversity of vegetation succession with patch reeds, forest belt and other species was established during the study period; even the number of macrobenthic species was declined at the beginning of study period. However, it was found that there are more macrobenthic species (> 65%) in the restoration site than that of the control site in 2007. After restoration, 16 fish species were found in autumn and winter. The most significant development of this restoration site was bird communities. 56 bird species were found, including Charadriiformes and Ciconiiformes which we expected to obtain through ecological restoration, which was 56% more than the controlled area. This ecological restoration study shows that the idea and technique developed by ecological engineering is reasonable and feasible. It is suggested that this study can apply to ecological restoration of the estuarine wetlands in China.
Natural coastal habitats play an important role in protecting coastal areas from sea water flooding caused by storm surge events. Many of these habitats, however, have been lost completely or degraded, reducing their ability to function as a natural flood defense. Once degraded, natural habitats can potently be destroyed by storm events, further threatening these systems. Much of the loss of coastal habitats is caused by increased human activity in coastal areas and through land claimed for urban, industrial, or agricultural use. As a result, some coastal habitats have become rare and threatened across much of Europe and the world. An associated problem is that of sea level rise, which has the combined impact of both increasing the risk of flooding in coastal ecosystems and increasing the severity of storm surge events. This chapter addresses two key topics: (1) the use of natural habitats as a form of coastal defense focusing on the required management and how to restore and/or create them and (2) ecological considerations in the design of hard coastal defense structures. The habitats that play a role in coastal deface and considered here are: (1) saltmarshes, (2) sand dunes, (3) seagrass meadows, and (4) biogenic reefs, including Sabellaria reefs, oyster beds, and mussel beds. As part of coastal habitat restoration and management, the process of saltmarsh creation, either through seaward extension or managed realignment is discussed focusing on potential benefits. Finally, key cumulative stressors that can hinder ecological approaches to coastal risk mitigation are reviewed.
The distribution, composition, density, and biomass of benthic macrofauna within estuarine environments typically exhibit significant variations attributable to heterogeneity in and interactions between physical, biological, and chemical processes. The spatial and temporal dynamics of benthic macroinfauna assemblages and physicochemical sediment parameters within the intertidal mudflats of a subtropical estuarine lake (Coombabah Lake, Southern Moreton Bay) were studied at four sites from August 2006 to April 2007. No significant seasonal changes were observed at any site for all physical sediment parameters. The northern sample sites were characterised by fine- to medium-grained to moderately to poorly sorted sediments and the southern sample sites by fine-grained to moderately well to well-sorted. A total of 1029 individuals representing species from three orders, including deposit feeding and filter feeding macroinfaunal groups, were collected. The highest combined species densities occurred in the fine-grained southern sites, with the greatest combined species density occurring at Site 4 during winter. Amphipods (Victoriopisa australiensis) and polychaete worms (Simplisetia aequisetis) dominated the lake-wide faunal community with V. australiensis, representing 49% of the total retrieved macroinfauna. Significant correlations between mean macroinfauna densities, biomassDW, sediment parameters, and seasonal maximum monthly temperatures were identified during the study. Seasonal trends in combined site densities were observed at each of the lake sites, with the highest combined density occurring during winter. Spatial and temporal variations might also be partially explained by the predation pressures of fish and migratory wading birds within the lake, with the seasonal presence of migratory wading birds coinciding with the minimum observed macroinfauna densities at each sample site.
There is a growing need to understand the functional implications of anthropogenic pressures, such as those following coastal disposal of dredged material. Current assessments, based on taxonomic structure of benthic organisms, only provide a limited capacity to determine functional impacts or recovery. This study assesses recovery of two intertidal dredged material recharge schemes, comparing results obtained based on taxonomic structure (univariate and multivariate approaches) and function (biological trait composition, functional diversity, secondary production) of the benthic assemblages.
The assemblages recolonising both schemes were consistently less speciose, less densely-populated and exhibited multivariate community structures that differed from those of the reference areas. However, for both schemes metrics of functionality converged to those of reference areas, although some differences in trait composition persisted for up to 3 years.
These data support the proposition that impacts of, and recovery from, anthropogenic disturbance should be assessed using a combination of both functional and taxonomic structural approaches.
Carrying out wildlife conservation in a changing climate requires planning on long timescales at both a site and network level, while also having the flexibility to adapt actions at sites over short timescales in response to changing conditions and new information. The Royal Society for the Protection of Birds (RSPB), a land-owning wildlife conservation charity in the UK, achieves this on its nature reserves through its system of management planning. This involves setting network-wide objectives which inform the 25-year vision and 5-year conservation objectives for each site. Progress toward achieving each site's conservation objectives is reviewed annually, to identify any adjustments which might be needed to the site's management. The conservation objectives and 25-year vision of each site are reviewed every 5 years. Significant long-term impacts of climate change most frequently identified at RSPB reserves are: loss of intertidal habitat through coastal squeeze, loss of low-lying islands due to higher sea levels and coastal erosion, loss of coastal freshwater and brackish wetlands due to increased coastal flooding, and changes in the hydrology of wetlands. The main types of adaptation measures in place on RSPB reserves to address climate change-related impacts are: re-creation of intertidal habitat, re-creation and restoration of freshwater wetlands away from vulnerable coastal areas, blocking artificial drainage on peatlands, and addressing pressures on freshwater supply for lowland wet grasslands in eastern and southeastern England. Developing partnerships between organizations has been crucial in delivering large-scale adaptation projects.
Proceedings of the First Asian Wetland Convention and Workshop 23‐ 26 October Tai pei , Tai wan, ROC
Estuaries are among the most productive environments in the coastal zone that may act as sink of pollutants. In this study we evaluated how levels of heavy metal contamination can be reflected in the macroinvertebrate communities of six Tagus Estuary mudflats, inferring their consequences to upper trophic levels. We used Shannon-Wiener is diversity, Pielou is evenness and Simpson is dominance indices, and macroinvertebrate densities to characterize benthic communities at the sites that presented different metal contamination loads. Those stations with high levels of contamination presented a lower diversity but also the highest prey density. This study indicated that unhealthy areas can still perform their ecosystem function with costs that remain to be evaluated. The biodiversity can be impoverished compared with other less contaminated sites, but with regard to their utilization as feeding areas by birds and fishes this is not a limiting factor. For this particular function of the mudflats, prey availability is the main characteristic determining the choice of one particular site as a bird and fish feeding area that may not be affected by heavy metal contamination.
In this work we evaluated the vertical distribution pattern of benthic infauna during the tidal cycle at one of the most important mudflats of the Tagus estuary. Samples were collected hourly during 24 h periods at four complete tidal cycles, using a corer specifically designed for the study purpose that allowed easy and effective separation of 15 different sediment layers. A particular case of general linear models, the hurdle model, was used to analyse data sets. We found that different species have different distribution and abundance according to sediment layers. Results showed that individuals tend to go deeper into sediment with a lower water column height and that these migrations are more visible during spring tides.
1Saltmarshes in south-east England have been eroding rapidly since 1960. Recently, Hughes & Paramor (2004) and Morris et al. (2004) have presented contrasting views on the extent to which physical and biological processes might contribute to the erosion. There are three contentious issues: (i) saltmarsh erosion is the result of coastal squeeze, where sea walls prevent a landward migration of a saltmarsh in response to sea level rise; (ii) saltmarsh erosion is linked to bioturbation and herbivory of seedlings by the ragworm Nereis diversicolor; (iii) new saltmarshes will not develop on managed realignment sites where existing sea walls have been removed because of the effects of ragworms.2In this paper, we provide a literature review of physical and biological processes relevant to the above three issues, and discuss the relative importance of these processes at different spatial and temporal scales.3Our synthesis shows that, at a regional scale, the combination of strong winds, high tides and increased wave height appears to be responsible for the increased rate of marsh erosion and creek dissection recorded in the 1970s. There is also some laboratory evidence that bioturbation and herbivory from populations of Nereis can lead to sediment instability and loss of pioneer plant species, such as Salicornia spp. However, the field evidence is more equivocal and has been conducted at small spatial scales.4At a large number of different managed realignment sites there is strong evidence that even if bioturbation and herbivory by Nereis have occurred, overall the effects have been insufficient to restrict plant succession of exposed sediment.5Synthesis and applications. There is an urgent need for long-term field studies that integrate and quantify physical and biological processes and the related feedbacks at different spatial and temporal scales. Until this is completed, terms such as coastal squeeze will remain contentious and management decisions will invite criticism.
With current losses of saltmarsh running at > 100 ha per year in the UK, creation of new intertidal habitats through managed realignment is likely to be increasingly used. Potentially, this has biodiversity as well as engineering benefits. However, assessing the conservation value of many of the current UK schemes is difficult as the biological monitoring has been generally poor, with a few notable exceptions. At the Tollesbury and Orplands realignment sites, Essex, bird communities were dominated by terrestrial species during the first year of inundation and waterbird communities rapidly developed during the second and third years. Five years after the initial breach in the sea wall, communities were similar to surrounding mudflats but with some notable exceptions. Dunlin Calidris alpina and Common Redshank Tringa totanus that prey on the early colonizing Nereis and Hydrobia used the sites in the first 2 years. Eurasian Oystercatcher Haematopus ostralegus did not occur on the realignment site as there were no large bivalves, whereas Red Knot Calidris canutus used the site after 4–5 years coincidentally with the appearance of Macoma balthica. The differences in the bird communities occurred because UK sites are often small, enclosed and poorly drained. If at a suitable height in the tidal frame, UK managed realignment sites are successful in that they have developed saltmarsh and biologically active mudflats but they may lack the full range of biodiversity found in surrounding natural intertidal habitats, even decades after inundation.
The Schelde estuary is an important wintering area and stop-over place for waders and waterfowl using the East Atlantic fly-way. The port of Antwerp is situated in the Lower Zeeschelde, the transition area between the brackish- and freshwater tidal part. Three intertidal areas in this zone (Groot Buitenschoor, Galgenschoor and Schor Ouden Doel) are protected under several international and national legislations. In this study long-term datasets (1982–1998) on water birds in these intertidal areas were analysed and attempts were made to assess the impact of two container terminals, constructed during the covered period. Overall abundance of water birds in the study area did not show any significant trends. Looking at individual areas, maxima and winter means on the Galgenschoor and Groot Buitenschoor were very variable but the peak seasons levelled out with time. On the Schor Ouden Doel, where hunting was banned, maximal numbers increased by a factor of four between 1985 and 1990, mainly due to an increase in Greylag Goose numbers. The trophic composition of the bird populations showed major shifts. Initially, species compositions in winter differed considerably between the three areas, but they became more similar during the study period. The results suggest that the area became more important as wintering and resting place for herbivores such as Greylag Goose and Wigeon while its function as feeding ground and stop-over site for migrating benthivorous birds became relatively less important, especially on the right bank. The water bird populations in the study area varied greatly with the geographic and regional trends for the different species and were influenced by winter severity but no direct proof of impacts from the container terminals could be established. Nearly every season the international 1 level was exceeded by one or more species, but the species of international importance changed with time. National and international protection measures are valuable but insufficient tools for the conservation of these estuarine habitats. A more comprehensive conservation strategy is proposed.
The disposal of maintenance dredged material constitutes one of the most important problems in coastal zone management. To minimise ecological impacts, a number of ‘beneficial use’ options have developed whereby the material is regarded as a potential resource and used to recharge or recreate intertidal habitats. This paper presents the results of a sampling programme to investigate the macrofaunal recovery rates, and the underlying mechanisms responsible for them, following a beneficial use scheme involving the placement of fine-grained dredged material on a salt marsh in southeast England.
Three stations in the recharge area and three reference stations, located within the same salt marsh system, were selected. These stations were sampled prior to recharge (recharge stations only) then 1 week, 3, 6, 12 and 18 months after the recharge. Sediment redox potentials (1, 2 and 4 cm sediment depths) were also measured on each sampling occasion. The results indicated a rapid recolonization of the fauna typical of the surrounding salt marsh channels. All univariate parameters had recovered after 3 months after the recharge. Active post-juvenile immigration is likely to have been the predominant recovery process. Multivariate data analysis revealed that the community structure of the recharge stations, however, did not progress towards those of the reference sites. Natural spatial variability in community structure at the scale of the recharge-reference station distance, and differences in eventual tidal elevations are factors responsible for these differences. The need to carefully assess reference site suitability in monitoring beneficial use schemes is discussed.
Reclamation of 90% of intertidal land at Teesmouth, northeast England, has left the remaining mudflats, Seal Sands, exposed for only 7.5-8.5 h out of each 12.5 h tidal cycle but surrounded by a suite of man-made and man-modified peripheral wetlands. Shorebirds made extensive use of these wetlands for feeding, especially during severe weather. The extent of use and site choice varied seasonally and interspecifically. Shorebirds used peripheral wetlands both to extend feeding time beyond the period when Seal Sands was uncovered and during the low water period, probably mostly for shelter from strong winds. Peripheral wetlands also provided many of the safe roosting sites at Teesmouth. Conservation effort on estuaries concentrates on the low tidal mudflats used for feeding by shorebirds, often at the expense of peripheral wetlands, especially when these are man-made. Our findings emphasize the importance of peripheral wetlands to the winter survival of shorebirds. Creation of such wetlands is a vital goal in ameliorating reclamation losses to estuaries.
A comprehensive survey of the size, wildlife importance and human uses in the 1980s of all 155 estuaries in Great Britain. This is part 1 of the report, which is available in four .pdf sections. For the complete document visit: http://jncc.defra.gov.uk/page-2563
Body condition (fat and protein reserves) was analysed for redshanks in Tringa totanus and oystercatchers Haematopus ostralegus that died during severe weather on the Ythan estuary (Grampian) in January and February 1979 and the Montrose Basin (Tayside) in January 1982. All birds died after using almost all their fat and protein reserves, and in very similar condition. Even in the exceptionally low temperatures in January 1982, waders mobilised fat enough to supply their energy requirements. In January 1982 death occurred after fat reserves were exhausted, through an inability to mobilise protein reserves rapidly. Small individuals died with larger pectoral muscles and relatively higher lean mass than large conspecifics, probably because of differences in metabolic rate. High first-year mortality may be partly a consequence of small first-year body size, in addition to poorer feeding efficiency.-Authors
Focuses on problems in estimating the energy intake and expenditure by shorebirds, and in considering over what time period the balance needs to be assessed. Emphasises quantitative techniques for assessing food intake of waders under field conditions.-from Author
This paper describes methods and reports the accuracy of predictions made within a very limited time span of the effects on shorebirds of large scale partial reclamation of the Tees Estuary. It then summarizes subsequent, more detailed studies on processes determining the numbers of shorebirds found at coastal sites and notes how these can be used to help predictive studies elsewhere, provided that the personnel required to make the predictions are sufficiently experienced in work on coastal birds. Refs.
Study of Haematopus ostralegus on the Dutch Wadden Sea suggests that competition occurs on migration and on the wintering grounds. Oystercatchers feeding in poor areas suffered higher mortality than those roosting near good feeding areas. All roosts were near to each other so competition probably occurred. The low status of some individuals may be related to severe abnormalities.-after Authors
The diets, feeding rates, foraging times during daylight, the extent of nocturnal feeding and food intakes of Grey and Ringed plovers Pluvialis squatarola and Charadrius hiaticula are described or estimated from field observations, checked by ciné-film, in Northumberland, England, from autumn to spring of the years 1973–76. (Gut analysis was unreliable as a quantitative guide to diet.) Main prey at Lindisfarne for both plovers were the polychaete worms Notomastus, Arenicola and probably Scoloplos and Phyllodoce and, for Ringed plovers, also various small Crustacea, particularly Bathyporeia and Eurydice. Comparisons with diets of the same species elsewhere showed that they are not specialized but vary their diet in accordance with the prey species common in a particular area. In autumn and spring, but not in winter, food requirements could be met during daylight. An increase in the percentage of the daylight hours spent feeding in winter was inadequate to compensate for the decreases in both hours of daylight and feeding rate which occur at this season. Both plovers were able to feed at night, but, on dark nights at least, at a slower rate than by day. High winds apparently depressed the extent of nocturnal feeding. In mid-winter, the birds maintain high fat levels, probably to buffer the effects of days when they have difficulty in obtaining their energy requirements, such as during cold and windy weather. Because plovers' feeding rates are reduced more by low temperatures than those of waders foraging by touch, their rates of energy intake fall more in such conditions. An attempt is made to predict the minimum densities of prey required for energy balance in various conditions and to compare the foraging strategies of visually foraging plovers and tactilely-foraging sandpipers.
Observation on the shore show that the density of the population of the prosobranch Hydrobia ulvae and of the bivalve Macoma balthica at Whitstable varies considerably With the grade of deposit, dense populations being found in fine deposits and sparse populations in coarse deposits. From laboratory experiments it seems probable that these animals feed by abstracting proteins, which can be assessed as nitrogen, from the bodies of microorganisms in the deposits and that the micro-organisms are more abundant in fine deposits than in coarse ones.As a result of these conclusions it is suggested that the rapid increase in population density of Hydrobia ulvae and Macoma balthica, and by inference of other deposit-feeders, towards regions of fine-grained deposits is attributable to the increase in density of the micro-organism population. this, in turn, is related to the surface area of the deposits rather than to the abundance of organic debris.Finally, the nature of detritus is discussed and it is recommended that this term is replaced by “organic debris”.
The annual mean biomass of the macrobenthos along almost one hundred 1 km-transects scattered over the 1300 km2 of tidal flats of the Dutch Wadden Sea was found to amount to 27 g.m.−2 ashfree dry weight, with 95% confidence limits of about 19 and 34 g.m−2.In total 41 species were observed at a total sampled area of 44 m2. Individual transects (0.45 m2) yielded 3 to 20 species, with an average of 11.3 species (confidence limits 10.6 and 12.0).The estimates found were evaluated spatially by calculation of weighted means (as to sediment composition and zonation), and temporally by sampling a limited number of stations during 6 years.Only 6 species, viz. Mytilus edulis, Arenicola marina, Mya arenaria, Cerastoderma edule, and Macoma balthica, made up 90% of the total macrozoobenthic biomass. Suspension feeders dominated with 55% and were found to live mostly strongly aggregated (e.g. musselbanks). Deposit feeders made up 40% of the total biomass and were distributed more evenly.Biomass was found to increase steeply with species density over most of the range of species densities observed. Transects located at extreme levels in the intertidal zone or at extreme silt contents of the sediment yielded low estimates of both biomass and species richness. It is concluded that adverse abiotic conditions, rather than primary production or food density, limit the occurrence of species and in that way biomass in most of the Wadden Sea.
The invertebrate macrofauna of Seal Sands, Teesmouth, is very limited in species composition. Nereis diversicolor has a two-year life cycle; the larger size-class provides the main prey of the birds Pluvialis squatarola, Numenius arquata and Limosa lapponica. Hydrobia ulvae is an important food of P. squatarola and Calidris canutus. Small Carcinus maenas occur in late autumn and are taken by the larger shorebirds. Small Macoma balthica are also taken, but are scarce and not an important bird food. Tadorna tadorna and Calidris alpina subsist chiefly on species of small oligochaetes and polychaetes which occur at very high densities (Gray 1976). Feeding areas of the shorebird species show some segregation, particularly in groups of species taking the same prey. It is calculated that birds removed about 90% of the standing crops of large Hydrobia and Nereis during a single winter. This followed the reclamation of more than half the intertidal land used as feeding grounds by the birds.
An overview of the results of the Monitoring Programmes related to Nature Conser-vation concerns arising from the River Tees Barrage and Crossing Act 1990
- P R Evans
- R M Ward
- T Mercer
Evans, P. R., Ward, R. M. and Mercer, T. (1996) An overview of the results of the Monitoring Programmes related to Nature Conser-vation concerns arising from the River Tees Barrage and Crossing Act 1990. Teesside Development Corporation, Stockton-on-Tees.
Balancing the budget: measuring the energy intake and requirements of shorebirds in the ®eld Dierences in quality of roosting ¯ocks of Oystercatchers
- M W Pienkowski
- P N Ferns
- N C Davidson
- D H Worrall
Pienkowski, M. W., Ferns, P. N., Davidson, N. C., Worrall, D. H., (1984) Balancing the budget: measuring the energy intake and requirements of shorebirds in the ®eld. In: Evans, P. R., Goss-Custard, J. D., Hale, W. G. (Eds.), Coastal Waders and Wildfowl in Winter Cambridge University Press, Cambridge, pp. 29±56. Swennen, C., (1984) Dierences in quality of roosting ¯ocks of Oystercatchers. In Coastal Waders and Wildfowl in Winter, Evans, P. R., Goss-Custard, J. D. Hale, W. G. eds., Cambridge University Press, Cambridge, pp. 177±189.
Aspects of the ecology of Hydrobia ulvae. Unpublished M.Sc. dissertation
- J B Wood
Wood, J. B. (1972) Aspects of the ecology of Hydrobia ulvae. Unpublished M.Sc. dissertation, University of Durham.
Effects of habitat loss at migration staging posts on shorebird populations
- P R Evans
- N C Davidson
- T Piersma
- M W Pienkowski
Evans, P. R., Davidson, N. C., Piersma, T., Pienkowski, M. W. (1990) Eects of habitat loss at migration staging posts on shorebird populations. Proc. XX International Ornithological Congress, pp. 2228±2235.
National Standard Methodology for Benthic Sampling. I. Intertidal Soft Sediments. National Rivers Authority, Anglian Region
- B E Barnett
Diet and energy intake of Grey and Ringed Plovers in the non-breeding season
- Pienkowski
An overview of the results of the Monitoring Programmes related to Nature Conservation concerns arising from the River Tees Barrage and Crossing Act 1990. Teesside Development Corporation
- P R Evans
- R M Ward
- T Mercer
Improving the accuracy of predicting the local effects of habitat loss on shorebirds: lessons from the Tees and Orwell estuary studies
- P R Evans