The fishes associated with three intertidal salt marsh creeks in a temperate southern African estuary

This study compares the fish assemblages in a range of intertidal salt marsh creeks in the Kariega Estuary, South Africa, as well as highlighting any differences between the ichthyofaunal structure of the creeks and adjacent Zostera bed habitats. The superimposition of environmental variables on the creek biotic groupings (60% similarity level) indicated consistent relationships between both the creek water depth and mouth area with the major creek fish clusters. Water temperature, salinity and turbidity did not display any pattern which could explain the disparity between the ichthyofaunal groupings. The results also indicated that intertidal creeks form a unique littoral habitat within the Kariega Estuary, with ichthyofaunal compositions very different to those found in nearby eelgrass beds. Furthermore, intertidal creeks in the Kariega system appear to be similar to creeks found elsewhere in the world in that their fish assemblages are dominated by 0+ juveniles, have a conspicuous marine transient and estuarine resident component, and very few piscivorous representatives. These results also give weight to the hypothesis that southern African salt marsh creek habitats serve as temporary refuges to juvenile fishes, a role that has also been proposed in other parts of the world.     

Intertidal habitat utilization patterns of birds in a Northeast Pacific estuary

A habitat-based framework is a practical method for developing models (or, ecological production functions, EPFs) to describe the spatial distribution of ecosystem services. To generate EPFs for Yaquina estuary, Oregon, USA, we compared bird use patterns among intertidal habitats. Visual censuses were used to quantify abundance of bird groups and general species richness in: Zostera marina (eelgrass), Upogebia (mud shrimp)/mudflat, Neotrypaea (ghost shrimp)/sandflat, Zostera japonica (Japanese eelgrass), and low marsh estuarine habitats. Also assessed were (1) spatial variation within a habitat along the estuary gradient and, (2) temporal variation based on bi-monthly samples over a year at five tidal ranges. Z. marina was an important estuarine habitat based on nearly all metrics of bird use, except for shorebird densities. This suggests that reductions in native eelgrass habitat may reduce the abundance and diversity of birds in Yaquina estuary. Our results suggest that a habitat based assessment approach is generally feasible for developing relative EPFs related to the presence of birds within estuarine systems.     

Linkages between seagrass,mangrove and saltmarsh as fish habitat in the Botany Bay estuary,New South Wales

Shallow-water vegetated estuarine habitats, notably seagrass, mangrove and saltmarsh, are known to be important habitats for many species of small or juvenile fish in temperate Australia. However, the movement of fish between these habitats is poorly understood, and yet critical to the management of the estuarine fisheries resource. We installed a series of buoyant pop nets in adjacent stands of seagrass, mangrove and saltmarsh in order to determine how relative abundance of fishes varied through lunar cycles. Nets were released in all habitats at the peak of the monthly spring tide for 12 months, and in the seagrass habitat at the peak of the neap tide also. The assemblage of fish in each habitat differed during the spring tides. The seagrass assemblage differed between spring and neap tide, with the neap tide assemblage showing greater abundances of fish, particularly those species which visited the adjacent habitats when inundated during spring tides. The result supports the hypothesis that fish move from the seagrass to the adjacent mangrove and saltmarsh during spring tides, taking advantage of high abundances of zooplankton, and use seagrass as a refuge during lower tides. The restoration and preservation of mangrove and saltmarsh utility as fish habitat may in some situations be linked to the proximity of available seagrass.     

The fish assemblage of the intertidal salt marsh creeks in North Bull Island, Dublin Bay: seasonal and tidal changes in composition, distribution and abundance

An intertidal salt marsh fish assemblage inhabiting two creeks on North Bull Island, Dublin Bay was sampled monthly from June 2000 until May 2002. Water temperature and salinity were recorded in situ and samples were also taken for Suspended Particulate Matter (SPM) and Chlorophyll a. All fish caught were weighed and measured and classified into functional guilds. A total of 6,549 individuals comprising 10 fish species from 10 families were recorded within the two creeks. The community was dominated by a few species, a feature common to other estuarine fish populations. Of the 10 species found, the common goby, Pomatoschistus microps, the 3-spined stickleback, Gasterosteus aculeatus, the thick-lipped grey mullet, Chelon labrosus and the flounder, Platichthys flesus contributed 98.4% of all fish sampled. The fish population of the channels at Bull Island, Dublin, was dominated by the resident gobies (true estuarine resident species), but also hosted juveniles of species such as the bass, Dicentrarchus labrax (marine juvenile migrant species). In turn, the nekton populations were dominated by the brown shrimp, Crangon crangon and the fairy shrimp, Palaemonetes varians especially in winter when fewer fish (numbers of species and abundance) were found. Multivariate analysis of fish diversity and abundance revealed a strong seasonal pattern but there was little evidence of difference between creeks, nor of tidal (spring/neap) effects. The estuarine fish using the intertidal marsh creeks have been little studied in Europe yet they play a major role with the decapods in these habitats. This role needs to be quantified for a proper understanding of the system’s function.     

Habitat use by fishes after tidal reconnection of an impounded estuarine wetland in the Indian River Lagoon,Florida (USA)

Most of the wetlands located along the Indian River Lagoon (IRL) ineast-central Florida (USA) have been impounded since the 1950's and1960's to reduce mosquito reproduction. Impounded marsh (i.e.,impoundment) dikes physically separate the wetlands from the estuary toallow artificial flooding of the impoundments during the mosquito breedingperiod (May to October). Presently, Rotational ImpoundmentManagement (RIM) is the preferred impoundment management techniquein the IRL. Impoundments maintained under RIM have culverts installedthrough the dikes which are kept closed during the mosquito breedingseason (to control mosquitos) and are allowed to remain open for theremainder of the year (to allow tidal flow). A 24.3 ha impoundment8 km north of Sebastian Inlet that had been isolated from the IRL for over39 years was studied for 12 months to determine habitat use by fishes aftertidal reconnection and the implementation of RIM. Fish sampling wasconducted with a seine in the perimeter ditch and with clover and minnowtraps in the upper marsh and tidal creek areas of the impoundment. Waterlevel, impoundment bottom topography, and the seasonal nursery functionof the impoundment were factors that contributed to observed patterns offish habitat use during the study. Within the first 15 weeks of perimeterditch sampling, an increase from 9 to 40 species was observed. Transientspecies used the perimeter ditch almost exclusively and entered theimpoundment primarily during the spring open period. Juvenile Pogonias cromis (Linnaeus), Elops saurus Linnaeus, Centropomusundecimalis (Bloch), and Megalops atlanticus Valenciennes were themost abundant recreationally important species, respectively. Habitat useby the most abundant resident species (Gambusia holbrooki Girard,Poecilia latipinna (Lesueur), Cyprinodon variegatus Lacepède, andFundulus confluentus Goode & Bean) was influenced primarily bywater level fluctuations. Resident species used the upper marsh and tidalcreek habitats during summer flooded periods and the cyprinodontids leftthe interior surface of the impoundment last as water levels decreased. Thisstudy is the first to document the recovery of fish populations in areconnected impoundment north of Sebastian Inlet using both active andpassive sampling techniques.     

Effects of exotic <Emphasis Type="Italic">Spartina alterniflora</Emphasis> on the habitat patch associations of breeding saltmarsh birds at Chongming Dongtan in the Yangtze River estuary,China

Smooth cordgrass (Spartina alterniflora) is one of the most invasive exotic plants of saltmarshes worldwide. To understand the effects of smooth cordgrass invasion on the habitat use and selection by breeding saltmarsh birds, we compared species number and abundance of breeding birds in native reed (Phragmites australis) and smooth cordgrass-invaded habitats (reed-cordgrass mixed habitats and cordgrass monocultures) at Chongming Dongtan in the Yangtze River estuary, China. We further examined the similarity of bird communities in different habitats and habitat selection by dominant bird species. For saltmarsh generalists, species number and abundance did not differ among the habitats. For saltmarsh specialists, species number and abundance did not differ in reed monocultures and reed-cordgrass mixed habitats but were significantly lower in cordgrass monocultures than in reed monocultures and reed-cordgrass mixed habitats. ANOSIM indicated that the difference in bird communities was larger between cordgrass monocultures and the habitats with reed than between the habitats with reed. The saltmarsh specialists preferred reed monocultures, while saltmarsh generalists avoided reed monocultures. Most species indicated no selection (neither preferred nor avoided) on reed-cordgrass mixed habitats, and no species preferred the cordgrass monocultures. The use of cordgrass monocultures by the common saltmarsh birds was negatively related to their body size. This study suggests that the spread of exotic smooth cordgrass has greatly affected the species composition and structure of local bird communities and has been especially disadvantageous to the saltmarsh specialists.     

Evidence for effects of Spartina anglica invasion on benthic macrofauna in Little Swanport estuary,Tasmania

Spartina anglica is an exotic perennial grass that can rapidly colonise the intertidal zone of temperate estuaries and lagoons. Consequently, there is considerable concern about its impact on estuarine flora and fauna. This study provides the first investigation of ecological impacts by S. anglica in Australia. The objective was to investigate the impacts of S. anglica on benthic macroinvertebrate communities inhabiting mudflat and native saltmarsh habitats at Little Swanport estuary, Tasmania. The null hypothesis that species richness and species abundance of benthic macroinvertebrates in exotic S. anglica marsh does not differ from adjacent native saltmarsh and mudflat habitats was tested. Eighteen species and 3716 macroinvertebrates were collected from 60 intertidal core samples in three habitats. Species richness, total abundance of invertebrates, crustacean abundance and mollusc abundance of mudflat communities were significantly (P < 0.05) lower when compared to those inhabiting adjacent S. anglica marsh and native saltmarsh. However, species richness and total abundance of invertebrates of native saltmarsh and S. anglica marsh did not differ significantly. Ordination of macroinvertebrate data clearly separated mudflat sites from vegetated sites but showed remarkable similarity between exotic and native vegetated sites.     

Recovery of fish and crustacean communities during remediation of tidal wetlands affected by leachate from acid sulfate soils in north-eastern Australia

In the 1970s, acid sulfate soils (ASS) distributed within about 720 ha of predominantly mangrove and salt pan wetlands at East Trinity in north Queensland were developed after the area was isolated from tidal flooding by a surrounding seawall and the installation of tidal gates on major drainage creeks. Following drainage and oxidation of these estuarine acidic sediments, resultant acid leachate caused considerable, ongoing environmental problems including regular fish kills. A rehabilitation program covering much of these former tidal wetlands commenced in 2000 using a lime-assisted tidal exchange management regime. Changes in the established populations of estuarine fish and crustaceans were monitored in the two creeks (Firewood and Hills Creeks) where tidal flows were reinstated. In Firewood Creek between 2001 and 2005, there was a progressive increase in fish species richness, diversity and abundance. The penaeid prawn Fenneropenaeus merguiensis was a major component of the cast net catches in the lower sections of both Firewood and Hills Creeks but its relative abundance decreased upstream of the tidal gates on the seawall. Well established stocks of predominantly juvenile, male Scylla serrata resident upstream of the tidal gates indicated suitable habitats with acceptable water and sediment quality and adequate availability of food. The regular fish kills that occurred prior to the management regime abated and, overall, the implementation of the rehabilitation program is yielding positive benefits for the local fisheries.     

Saltmarsh as habitat for fish and nektonic crustaceans: Challenges in sampling designs and methods

This is a review of research into the ecological role of saltmarsh as habitat used directly by fish and nektonic crustaceans such as shrimp (prawns) and portunid crabs. The quality of information about direct use of saltmarshes by nekton is poor, with even the most influential works suffering from obvious limitations. Attempts to generalize about nekton use of saltmarshes are hampered by sampling difficulties, poor sampling design, and inconsistent reporting of flooding regime and landscape structure. The difficulty in sampling nekton from shallow, vegetated marsh flats while inundated contributes to the fragmentary results of nekton work. A range of sampling methods have been described that vary in portability, size, amount of above-ground structure, escape rates of nekton, and expense; none has yet become standard. Poor experimental design in studies of saltmarsh nekton includes lack of replication, limited spatial scale, and lack of baseline data before management changes are made. Attempts to determine effects on commercial fisheries of losses in area or quality of saltmarsh by correlations between catch data and marsh loss should use active adaptive management. A second type of study, aimed at understanding how the saltmarsh is important to fisheries, can be tackled usefully at a smaller scale. To assist in the comparison of results from different studies, flooding regime should be reported as a proportion of time the marsh is submerged, and landscape structure as proportions of the marsh that are covered by intertidal flats, pools and drainage creeks. Flooding regime and landscape structure at the sites and at the time of sampling should then be put in the context of the typical pattern for the marsh under study.     

The role of salt marshes in the Mira estuary (Portugal)

The Mira estuary is a narrow entrenched pristine estuary of the Ria type, about 30 km long. It comprises an area of 285 ha of salt marsh, of which250 ha have been proposed for reclamation for aquaculture. Dredging, village and recreation development menace the yet undisturbed estuarine ecosystem. To assess the biological importance of this wetland, a multidisciplinary study was conducted in apart of the salt marsh, considered as being representative of the whole area. Halophytic vegetation covering 75% of the total salt marsh site is dominated by Spartina maritima (28% of total vegetation area). Total primary production attains63,766 kg/yr (dw). A net export of 1541 kg/yr of COM to the relatively oligotrophic adjacent waters was also found. Insects and birds are described for the first time in the saltmarsh. Macrobenthic communities are dominated by Hediste diversicolor, Nepthys caeca and Scrobicularia plana. The fiddler crabUca tangeri attains here its north distribution limit. The mud flats and creeks associated with the salt marsh act as a nursery for 40.8% of the fish species present. The food web is dominated by detritivorous species like the grey mullets. The results obtained in this study support the need for an effective conservation of this area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rehabilitation of impounded estuarine wetlands by hydrologic reconnection to the Indian River Lagoon,Florida (USA)

Salt marshes of the Indian River Lagoon, Florida (USA) were once prolific producers of mosquitoes. Mosquitoes lay their eggs on the infrequently-flooded high marsh surface when the soil surface is exposed. The eggs hatch when the high marsh is flooded by the infrequent high tides or summer rains. To control mosquito production, most of the salt marshes (over 16.200 ha) were impounded by the early 1970s. Flooding, usually by pumping water from the Lagoon, effectively controlled mosquitoes. However, impounding had a profoundly negative impact on the wetland plant, fish, and invertebrate communities. Isolation from the Lagoon cut off aquatic access by transient estuarine species that used the wetlands for feeding or as nursery area. In one study, the number of fish species dropped from 16 to 5 after impounding. Wetland vegetation within some impoundments was totally eliminated; other impoundments developed into freshwater systems. When tidal exchange is restored through hydrologic connection, usually by culverts installed through the perimeter dike, recovery to more natural conditions is often rapid. In one impoundment where wetland vegetation was totally eliminated, recovery of salt-tolerant plants began almost immediately. In another, cover of salt-tolerant plants increased 1,056% in less than 3 years. Fisheries species that benefitted the most were snook, ladyfish, and striped mullet. Over 1,500 juvenile snook were captured in a single 3-hr flood-tide culvert trap as they attempted to migrate into an impoundment. The zooplankton community rapidly returned to the more typical marsh-Lagoon community. Water quality and sediment sulfides returned to typical marsh values. Overall, reconnection enhances natural productivity and diversity, although water quality in the perimeter ditch, an artifact of dike construction, remains problematic. Earlier experiments demonstrated that flooding only during the summer mosquito breeding season provided as effective mosquito control as year-round flooding. In standard management, the impoundment is flooded in summer, then left open to the Lagoon through culverts the rest of the year. Culverts are typically opened when the fall sea level rise first floods the high marsh. Impoundment reconnection is being implemented by a multi-agency partnership. The total reconnected area is expected to reach 9,454 ha by the end of 1998, representing 60% of the impounded wetlands in the entire IRL system. One stumbling block is private ownership of many of the remaining isolated impoundments.     

Estuarine and habitat-related differences in growth rates of young-of-the-year winter flounder (Pseudopleuronectes americanus) and tautog (Tautoga onitis) in three northeastern US estuaries

Instantaneous growth rates of young-of-the-year winter flounder Pseudopleuronectes americanus (Walbaum) (12.0-60.4 mm standard length, SL) and tautog Tautoga onitis (Linnaeus) (21.4-73.8 mm total length, TL) from three estuarine systems in New Jersey (Great Bay-Little Egg Harbor and Navesink River) and Connecticut (Hammonasset River) were used in an attempt to assess the relative quality of selected nominal habitats. A series of short-term field caging experiments were conducted during 1994 and 1995 in: macroalgae (primarily, Ulva lactuca), eelgrass (Zostera marina), unvegetated areas adjacent to macroalgae and eelgrass and tidal creeks in Spartina dominated marsh. Growth rates varied with habitat, estuary and year. Comparisons across nominal habitats within and among estuaries did not show any one habitat with consistently higher growth, and growth was relatively independent of whether a habitat was vegetated or adjacent to vegetation. The growth rates of winter flounder and tautog from the Hammonasset River were not different among habitats in either year of the study. In the Great Bay-Little Egg Harbor, both winter flounder and tautog had higher growth rates in macroalgae with growth in eelgrass varying significantly between years. Conversely, in the Navesink River both species had higher growth rates in eelgrass. Environmental changes associated with temperature and dissolved oxygen appeared to influence growth rates. Winter flounder growth rate and survival was depressed in tidal marsh creeks in the three estuaries and in vegetated macroalgae habitats in the Navesink River where dissolved oxygen levels were often very low (<2 mgl(-1)) for extended periods. In summary, the growth rates of the young-of-the-year of these two species varied temporally and were dependent on the interaction of both the specific estuary and habitat in which the experiments took place. Further, habitat quality, as defined by relative growth rate, was difficult to evaluate because it can be variable and nominal habitat designations are often not sufficient to define the boundaries of a species habitat requirements.     

Factors affecting the establishment success of the invasive piscivorous chub in small irrigation ditches in northern Kyushu,Japan

Habitat matching is an important factor for the establishment of alien fishes in recipient environments. The piscivorous chub, Opsariichthys uncirostris uncirostris, originally exclusively inhabited large water areas; however, the species has been introduced and established in small irrigation ditches on Kyushu Island. The evaluation of the habitat use of the piscivorous chub suggested that this alien fish uses the lentic-type irrigation ditches as a nursery ground and the lotic-type ditches as a spawning ground. This finding implies that the establishment of the piscivorous chub may require connectivity between lentic and lotic habitats.     

Fish Assemblages in Different Shallow Water Habitats of the Venice Lagoon

The small-sized fish assemblages of the Venice Lagoon were investigated and compared among five shallow subtidal habitats (seagrass beds, sparsely vegetated habitats, unvegetated sand bottoms, mudflats and saltmarsh creeks) in the Northern lagoon basin. Sampling was carried out seasonally (Spring, Summer and Autumn of 2002) in 4–7 stations for each habitat type, by means of a fine-mesh, small beach seine. Two-way analysis of variance was applied to assess the differences in species richness, fish diversity, density and standing stock amongst habitats, whereas fish assemblage composition was investigated by using multivariate analyses (MDS, ANOSIM, SIMPER). The analyses indicated that seagrass beds and saltmarsh creeks are relevant shallow habitats in structuring the small-sized fish assemblages of the Venice Lagoon, supporting specialized and recognizable fish assemblages. Those in seagrass beds, in particular, were characterized by higher species richness and standing stock with respect to all the others. The structuring role of these habitats was discussed in terms of both habitat complexity and degree of confinement. In contrast, sandy bottoms, mudflats and sparsely vegetated habitats were identified as “transition” habitats, with highly variable fish assemblages, influenced by the contribution of the adjacent habitats, and acting probably as both ‘buffer zones’ between the other habitats and migration routes for many fish species in the lagoon.     

Rehabilitation of impounded estuarine wetlands by hydrologic reconnection to the Indian River Lagoon, Florida (USA)

Salt marshes of the Indian River Lagoon, Florida (USA) were once prolific producers of mosquitoes. Mosquitoes lay their eggs on the infrequently-flooded high marsh surface when the soil surface is exposed. The eggs hatch when the high marsh is flooded by the infrequent high tides or summer rains. To control mosquito production, most of the salt marshes (over 16.200 ha) were impounded by the early 1970s. Flooding, usually by pumping water from the Lagoon, effectively controlled mosquitoes.However, impounding had a profoundly negative impact on the wetland plant, fish, and invertebrate communities. Isolation from the Lagoon cut off aquatic access by transient estuarine species that used the wetlands for feeding or as nursery area. In one study, the number of fish species dropped from 16 to 5 after impounding. Wetland vegetation within some impoundments was totally eliminated; other impoundments developed into freshwater systems.When tidal exchange is restored through hydrologic connection, usually by culverts installed through the perimeter dike, recovery to more natural conditions is often rapid. In one impoundment where wetland vegetation was totally eliminated, recovery of salt-tolerant plants began almost immediately. In another, cover of salt-tolerant plants increased 1,056% in less than 3 years. Fisheries species that benefitted the most were snook, ladyfish, and striped mullet. Over 1,500 juvenile snook were captured in a single 3-hr flood-tide culvert trap as they attempted to migrate into an impoundment. The zooplankton community rapidly returned to the more typical marsh-Lagoon community. Water quality and sediment sulfides returned to typical marsh values. Overall, reconnection enhances natural productivity and diversity, although water quality in the perimeter ditch, an artifact of dike construction, remains problematic.Earlier experiments demonstrated that flooding only during the summer mosquito breeding season provided as effective mosquito control as year-round flooding. In standard management, the impoundment is flooded in summer, then left open to the Lagoon through culverts the rest of the year. Culverts are typically opened when the fall sea level rise first floods the high marsh.Impoundment reconnection is being implemented by a multi-agency partnership. The total reconnected area is expected to reach 9,454 ha by the end of 1998, representing 60% of the impounded wetlands in the entire IRL system. One stumbling block is private ownership of many of the remaining isolated impoundments.University of Florida, IFAS, Journal Series No. R-05201.Harbor Branch Contribution Number 1152.Corresponding editor: R.E. Turner     

Fish community responses to ecosystem stressors in coastal estuarine wetlands: a functional basis for wetlands management and restoration

Functional responses of estuarine fish species to environmental perturbations such as wetland impoundment, changes in water quality, and sediment accretion are investigated. The study focuses on the feeding, growth and habitat use by California killifish (Fundulus parvipinnis), topsmelt (Antherinops affinis), and juvenile California halibut (Paralichthys californicus) in impacted coastal wetlands to provide an ecological basis for guidance on the management and restoration of these ecosystems. The ecology of California killifish, Fundulus parvipinnis, is closely tied with the marsh surface, which they access at high tide to feed and grow. Field estimates of food consumption show that killifish can increase their food intake by two-fold to five-fold by adding marsh surface foods to their diet. Bioenergetics modeling predicts that killifish can grow over an order of magnitude faster if they add intertidal marsh surfaces to their subtidal feeding areas. Tidal inlet closures and increased marsh surface elevations due to sediment accretion can restrict killifish access to the marsh surface, affecting its growth and fitness. An open tidal inlet and tidal creek networks that allow killifish to access the marsh at high tide must be incorporated into the restoration design. Topsmelt and California halibut are also adversely affected by tidal inlet closures. Food consumption rates of topsmelt are 50% lower when the tidal inlet is closed, compared to when the estuary is tidally-flushed. Tidal inlet closures inadvertently induce variations in water temperature and salinity and negatively affect growth of juvenile California halibut. Tidal creek networks which consist of channels and creeks of various orders are also important to halibut. Large halibut (>200 mm TL) inhabit deeper, high order channels for thermal refuge, while small halibut (<120 mm TL) are abundant in lower order channels where they can feed on small-sized prey which are typically less abundant in high order channels. Maintaining an open tidal inlet, implementing sediment management programs and designing coastal wetlands with tidal creek networks adjacent to intertidal salt marsh habitat (for fish access) are key elements that need to be considered during the planning and implementation of coastal wetland restoration projects.     

Composition and abundance of resident marsh-surface nekton: comparison between tidal freshwater and salt marshes in Virginia,USA

Previous research on intertidal nekton communities has identifiedimportant determinants of community structure and distribution; however, fewstudies have compared nekton utilization of disparate marsh habitats. Inthis study, abundance and distribution patterns of resident nekton werecompared between tidal freshwater marsh and salt marsh surfaces varying inflooding depth and duration. Nekton were collected in pit traps installedalong elevational transects at four marshes in coastal Virginia (twofreshwater, two saline) from April through November 1992–1993. Thedominant fish collected at all sites was the mummichog Fundulusheteroclitus. The daggerblade grass shrimp Palaemonetes pugio was thedominant nekton species collected at salt marsh sites, and was seasonallyabundant on tidal freshwater marshes. A positive correlation betweenflooding depth and nekton abundance was observed on salt marshes; anopposite pattern was observed on tidal freshwater marshes. Tidal floodingregime influences the abundance of resident nekton, however, the effect maybe confounded by other environmental variables, including variation insurface topography and seasonal presence or absence of submerged aquaticvegetation (SAV) in adjacent subtidal areas. In mid-Atlantic tidalfreshwater wetlands, SAV provides a predation refuge and forage site forearly life stages of marsh-dependent nekton, and several species utilizethis environment extensively. Salt marshes in this region generally lackdense SAV in adjacent subtidal creeks. Consequently, between-sitedifferences in species and size-specific marsh surface utilization byresident nekton were observed. Larvae and juveniles represented 79%and 59% of total fish collected at tidal freshwater and salt marshsites, respectively. The resident nekton communities of tidal freshwater andsalt marsh surfaces are characterized by a few ubiquitous species with broadenvironmental tolerances. This revised version was published online in July 2006 with corrections to the Cover Date.     

The role of connectivity and physicochemical conditions in effective habitat of two exploited penaeid species

The value of estuarine habitats is often measured by their contribution to the adult component of the population, but a broader suite of attributes can also contribute to nursery function. Identifying and quantifying these elements allows habitat repair to be effectively targeted toward improving ecosystem function for desirable species. We present a study that incorporates stable isotopes and quantitative sampling to investigate the relative importance of different estuarine areas for juveniles of exploited prawn species within the context of habitat rehabilitation, and the potential drivers of these relationships. Eastern King Prawn (Penaeus [Melicertus] plebejus) and School Prawn (Metapenaeus macleayi) were studied for two years in the lower Hunter River estuary, on the temperate east coast of Australia. The higher salinity areas near the lower end of the estuary were most important for Eastern King Prawn, and marsh systems in the lower estuary were only important for the species where there was good connectivity with oceanic water. Areas along the estuary were important for juvenile School Prawn, especially marsh habitats, and relative abundance tended to increase with increasing distance along the estuary. Designation of effective juvenile habitat for School Prawn may have been affected by high fishing mortality in fished areas, but this requires further investigation. Salinity, depth, turbidity and distance along the estuary were all important indicators of prawn distribution. The implications of these patterns for current and future habitat rehabilitation in temperate Australia are discussed.     

The Effects of Road Culverts on Nekton in New England Salt Marshes: Implications for Tidal Restoration

In recent years, salt marsh restoration projects have focused upon restoring hydrology through culvert enlargement to return functional values lost due to reduced tidal flow. To evaluate culvert effects on upstream nekton assemblages, fyke nets were set upstream of tidally restricted creeks, creeks recently restored with larger culverts, and paired reference creeks in New Hampshire and Maine, U.S.A. Subtidal habitats created or enlarged by scour were found immediately upstream of undersized culverts. All marshes supported similar assemblages and densities of fish, suggesting that marshes upstream of moderately restrictive culverts provide suitable habitat to support fish communities. However, densities of Crangon septemspinosa (sand shrimp) were significantly reduced upstream of culverts. A mark–recapture study was conducted in tidally restricted, restored, and reference marsh creeks to evaluate culvert effects on the movement of Fundulus heteroclitus (mummichog), the numerically dominant fish species in New England salt marshes. Recapture data indicated that small culvert size and consequently increased water velocity significantly decreased fish passage rates. We infer that upstream subtidal habitats and greater water velocities due to undersized culverts decreased nekton movements between upstream and downstream areas, resulting in segregated nekton populations. Restoration of salt marsh hydrology by the installation of adequately sized culverts will support increased fish access to marsh habitats and nekton‐mediated export of marsh‐derived production to coastal waters.     

Fine-scale movement and assimilation of carbon in saltmarsh and mangrove habitat by resident animals

Despite theories of large-scale movement and assimilation of carbon in estuaries, recent evidence suggests that in some estuaries much more limited exchange occurs. We measured the fine-scale movement and assimilation of carbon by resident macroinvertebrates between adjacent saltmarsh and mangrove habitats in an Australian estuary using δ¹³C analysis of animals at different distances into adjacent patches of habitat. δ¹³C values of crabs (Parasesarma erythrodactyla –15.7 ± 0.1‰, Australoplax tridentata –14.7 ± 0.1‰) and slugs (Onchidina australis –16.2 ± 0.3‰) in saltmarsh closely matched that of the salt couch grass Sporobolus virginicus (–15.5 ± 0.1‰). In mangroves, δ¹³C values of crabs (P. erythrodactyla –22.0 ± 0.2‰, A. tridentata –19.2 ± 0.3‰) and slugs (–19.7 ± 0.3‰) were enriched relative to those of mangroves (–27.9 ± 0.2‰) but were more similar to those of microphytobenthos (–23.7 ± 0.3‰). The δ¹³C values of animals across the saltmarsh-mangrove interface fitted a sigmoidal curve, with a transition zone of rapidly changing values at the saltmarsh-mangrove boundary. The width of this transition indicated that the movement and assimilation of carbon is limited to between 5 and 7 m. The δ¹³C values of crabs and slugs, especially those in saltmarsh habitat, clearly indicate that the movement and assimilation of carbon between adjacent saltmarsh and mangrove habitat is restricted to just a few metres, although some contribution from unmeasured sources elsewhere in the estuary is possible. Such evidence demonstrating the extent of carbon movement and assimilation by animals in estuarine habitats is useful in determining the spatial arrangement of habitats needed in marine protected areas to capture food web processes.