Nekton Habitat Research Articles

Assessing habitat enhancement by living shoreline restoration: exploring potential caveats of nekton community metrics

Living shorelines (LS) are a nature‐based restoration technique that aims to stabilize shorelines while enhancing multiple ecosystem services. In particular, LS are frequently promoted as beneficial for enhancing essential coastal habitats for fish and mobile crustaceans (nekton). In this study, we aimed to assess the effects of LS on nekton habitat across eight LS restoration sites in coastal Alabama, U.S.A., by applying widely‐used community metrics. Nekton abundance, species richness, evenness, and diversity tended to be higher in LS and adjacent unrestored control sites than along nearby hardened shorelines. Community metrics showed no clear effect of LS compared to their adjacent controls, with substantial among‐site variation masking any restoration effect. While this may suggest an ecological equivalence between restored and control sites, there are other possible interpretations; that a lack of difference reflects sampling the same populations at nearby control and restored sites, that differences do exist but sampling effort was insufficient to detect them, or that community metrics may be too insensitive for comparing the effects of various restoration approaches on nekton habitat quality. Further exploration of individual‐based metrics such as growth and condition of key species is warranted, as these may be more sensitive for assessing restoration outcomes and guiding future project designs.

Drift macroalgal distribution in northern Gulf of Mexico seagrass meadows.

Drift macroalgae, often found in clumps or mats adjacent to or within seagrass beds, can increase the value of seagrass beds as habitat for nekton via added food resources and structural complexity. But, as algal biomass increases, it can also decrease light availability, inhibit faunal movements, smother benthic communities, and contribute to hypoxia, all of which can reduce nekton abundance. We quantified the abundance and distribution of drift macroalgae within seagrass meadows dominated by turtle grass Thalassia testudinum across the northern Gulf of Mexico and compared seagrass characteristics to macroalgal biomass and distribution. Drift macroalgae were most abundant in areas with higher seagrass shoot densities and intermediate canopy heights. We did not find significant relationships between algal biomass and point measures of salinity, temperature, or depth. The macroalgal genera Laurencia and Gracilaria were present across the study region, Agardhiella and Digenia were collected in the western Gulf of Mexico, and Acanthophora was collected in the eastern Gulf of Mexico. Our survey revealed drift algae to be abundant and widespread throughout seagrass meadows in the northern Gulf of Mexico, which likely influences the habitat value of seagrass ecosystems.

Ecological equivalency of living shorelines and natural marshes for fish and crustacean communities

Salt marshes provide valued services to coastal communities including nutrient cycling, erosion control, habitat provision for crustaceans and fish (including juvenile and forage fish), and energy transfer from the detrital based food web to the greater estuarine system. Living shorelines are erosion control structures that recreate natural shorelines, such as fringing marshes, while providing other beneficial ecosystem services. Living shorelines are expected to provide fish and crustacean (nekton) habitat, but few comprehensive studies have evaluated nekton habitat use across a range of living shoreline settings and ages. We sampled the intertidal marsh and subtidal shallow water nekton community at 13 paired living shoreline and reference marsh sites, with living shorelines ranging in age from 2 to 16 years from construction. We compared nekton diversity, nekton community abundance, nekton community biomass, forage abundance, and juvenile abundance at reference marshes and living shorelines. Our results indicate that living shorelines are providing suitable marsh habitat for nekton communities, including juveniles and forage base species. The difference in living shoreline construction (rock sill, soil composition) did not appear to diminish habitat quality in the marsh or in nearshore waters, and rock sills may provide enhanced structural shoreline habitat. Living shorelines have the potential to combat marsh habitat loss and provide resilient nekton nursery habitat.

Another piece of the puzzle: Abiotic habitat properties of salt-marsh creeks benefit small fishes and crustaceans

Inundated salt marshes are valued as nekton habitat due to their low predator and high prey abundance. But habitat quality depends also on abiotic properties. We measured hydrological (temperature, oxygen concentration) and hydrodynamic (flow velocity, turbidity, sediment grain size) parameters in four German salt-marsh creeks and compared these with the adjacent tidal flat and subtidal area. Water temperatures in the salt-marsh creeks varied with season, daytime and over the tides. In contrast to deeper subtidal areas, the small water body in the marsh creeks adapted rapidly to air temperatures, resulting in relatively cool water temperatures in winter and relatively warm temperatures in summer. Despite high summer temperatures, the oxygen concentration in the creeks remained year round within the tolerance range of most fishes and crustaceans (above 5 mg/L), probably due to tidal mixing and primary production. Furthermore, the water body in the salt-marsh creeks was sheltered by the vegetated marsh surface from wind and waves and thus characterized by low flow velocities (0.15 ms−1), as well as lower turbidity and finer sediments than in the subtidal. As the specific set of habitat characteristics in the marsh creeks could explain utilization of this habitat by nekton, we performed a constrained redundancy analysis including temperature and turbidity as explanatory variables. Turbidity explained almost 21% of the variation in nekton species occurrence, while temperature accounted for only 2% of the variation. Compared to larger animals, small-sized nekton, which dominated the salt-marsh nekton community, is more capable to deal with extreme temperatures and will profit more from reduced currents than larger animals. Despite the limited accessibility for aquatic organism, intertidal salt-marsh creeks appear to provide favourable habitat for small nekton due to increased growth potential during seasonally higher temperatures, reduced swimming effort, and increased prey visibility and availability in the muddy sediments.

Effects of Nonnative Eurasian Watermilfoil, Myriophyllum spicatum, on Nekton Habitat Quality in a Louisiana Oligohaline Estuary

Submerged aquatic vegetation (SAV) provides critical habitat for estuarine nekton in the Gulf of Mexico, but habitat quality of SAV beds may change when nonnative species, such as Eurasian watermilfoil (Myriophyllum spicatum), become established. We compared the habitat value of Myriophyllum with another common native SAV (Ruppia maritima) by using field collections to document shifts in nekton community structure and a field experiment to compare growth rates of commercially important juvenile white shrimp (Litopenaeus setiferus). Similar communities were collected from both SAV species, though nekton abundance scaled with SAV biomass. The habitat quality provided by Myriophyllum for white shrimp appeared to meet or exceed that of Ruppia, with densities and growth rates of shrimp in Myriophyllum (2.2 ± 0.47 m−2, 1.0 ± 0.07 mm TL day−1, 25.7 ± 2.98 mg day−1) higher than in Ruppia (1.0 ± 0.36 m−2, 0.6 ± 0.09 mm TL day−1, 11.6 ± 2.04 mg day−1). Though differences were detected between SAV species, other factors, such as hypoxia and interspecific competition, likely contributed to the differences we documented between these habitat types in shrimp densities and growth. Our study provides an example of a nonnative habitat-forming species providing a viable alternative to native habitat. This result contradicts the paradigm of negative effects associated with nonnative species following their introduction into an ecosystem.

Introduction: Coastal Seagrass and Submerged Aquatic Vegetation Habitats in the Gulf of Mexico

IntroductionCoastal Seagrass and Submerged Aquatic Vegetation Habitats in the Gulf of Mexico Patrick Biber* and Hyun Jung Cho* This special issue compiles original research and reviews of previous research on an important geographic constitution at the water-land interface: the seagrass/Submerged Aquatic Vegetation (SAV) beds in the Gulf of Mexico (GoM) coastal zone. SAV are a group of vascular plants that grow underwater; and seagrass is a specialized subgroup of SAV that have adapted to live in the high salinity coastal and marine waters. Presence of, types of, and seasonality of SAV beds have substantial influences on geography, ecology, landscape, culture, and economy in the coastal zone. Healthy SAV beds help shape, maintain, and modify coastal landscapes by buffering wave energy, modifying water currents, protecting shorelines from erosion, aiding sediment deposition, consolidating substrate, and changing littoral profiles and water depth. Coastal seagrass resources are among the most productive ecosystems on Earth. Seagrass beds perform numerous vital ecological functions and provide food and shelter for commercially and ecologically important organisms, including blue crabs, shrimp, turtles, manatees, and waterfowl. Therefore, assessment of SAV distribution, composition, and abundance has been of particular interest to coastal environmental managers, scientists, developers, and recreationists as this information serves as an excellent indicator of estuarine environmental quality. Coastal areas containing seagrass and SAV beds carry geographical and historical importance in the Southeast, especially throughout the GoM. The GoM and its resources have immense ecological, economical, and historic values to the U.S. but have been going through several major environmental disturbances and disasters including, but not limited to, major hurricanes (e.g., 2005 Hurricane Katrina), the 2010 Deepwater Horizon Oil Spill, red tides, rapid subsidence, marsh erosion, threats from sea level rise, and river water diversions. Man-made levees [End Page 208] along major rivers (e.g., Mississippi River) prevent natural flooding from the rivers that historically used to deliver the necessary nutrients and sediments for coastal wetland growth and delta formation. This has resulted in coastal wetland retreat and subsidence. In addition, environmental quality has been significantly degraded, which in turn, results in the loss of ecological/economical services in the region. Loss of coastal land and environmental degradation are projected to be amplified with changing global climate, which is a growing threat to coastal SAV beds (Scavia et al. 2002, Doyle et al. 2010, Unsworth et al. 2014). The low-lying coastal areas of the GoM are particularly vulnerable to natural/anthropogenic disturbances due to the effects of sea-level rise, increases in population density, extensive landscape alternation, modification, and armoring of natural shorelines, as well as natural/man-made disasters. Documentation of habitat conditions, change over time, and interactions with the human environment are critical needs to better assess current status and predict future trends for SAV/seagrass habitats, a critical component of coastal geography. However, many regionally focused relevant studies on these habitats have not been addressed in the increasingly international scope of many pertinent scientific journals. We, the Guest Editors, agreed that compiling regional studies on a unifying topic would help enhance understanding of long-term and larger scale trends in SAV/seagrass beds of the GoM. In response, requests for manuscripts on sea-grass and other SAV occurring in tidally-influenced GoM coastal habitats were sent out to several regional seagrass/SAV scientists. In order to comply with the scope of Southeastern Geographer, the papers in this issue present studies on SAV/seagrass with a regional geography focus, particularly relating to issues of temporal variation and changes related to land use change, human alteration, and climate change. The five papers published in this special issue synergistically help to summarize change occurring across the GoM. Geographically, this special issue covers coastal habitats from Texas (the Coastal Bend and Laguna Madre), Louisiana (Terrebonne Bay, the Pontchartrain basin), areas around the borders of Mississippi and Alabama (Grand Bay National Estuarine Research Reserve), and west Florida (Tampa Bay). The topics of the papers extend from (1) evaluation of SAV for nekton habitat value in comparison to marshes during one season (Jerabek et al.), (2) test of a model to assess carbon stocks in seagrass meadows in a single year (Congdon & Dunton), (3) temporal...

A hybrid shoreline stabilization technique: Impact of modified intertidal reefs on marsh expansion and nekton habitat in the northern Gulf of Mexico

To mitigate shoreline erosion numerous armoring techniques have been employed extensively along the degrading shores of the Gulf of Mexico (GoM). Shoreline armoring strategies incorporating built vertical structures have resulted in numerous undesired ecological consequences. Bioengineering hybrid techniques consisting of “living shorelines” are emerging as an alternative option to mitigating shoreline loss and overcoming ecological shortcomings of hardened structures. Hitherto, only a few studies have assessed efficacy of hybrid techniques on shoreline stabilization and adjacent habitat enhancement. In this study, we integrated permeable intertidal reef-breakwaters (also known as wave attenuation units or WAUs) and predominantly restored native Spartina alterniflora marsh vegetation to mitigate erosion along severely degrading shores of a narrow peninsula in the northern GoM. Particularly, we evaluated impacts of a large-scale WAU reef deployment on a range of physical and biological parameters including erosion mitigation (shoreline stabilization), facilitation of created marsh expansion and habitat provision to marsh-utilizing nekton. We compared WAU reefs to adjacent gap areas without WAUs to evaluate the effects of tidal openings on the metrics measured. Our results of over 3 years suggest that, intertidal WAU reefs facilitate in created marsh expansion and the tidal openings between the reef complexes allow free movement of marsh-utilizing nekton fauna. Based on our results, we conclude that hybrid restoration technique is highly efficacious on erosion mitigation, adjacent marsh expansion and habitat creation. However, more works in other coastal systems are required to confirm the impacts of hybrid techniques on erosion mitigation and consequently on marshes and marsh-utilizing nekton.

Living shorelines can enhance the nursery role of threatened estuarine habitats.

Coastal ecosystems provide numerous services, such as nutrient cycling, climate change amelioration, and habitat provision for commercially valuable organisms. Ecosystem functions and processes are modified by human activities locally and globally, with degradation of coastal ecosystems by development and climate change occurring at unprecedented rates. The demand for coastal defense strategies against storms and sea-level rise has increased with human population growth and development along coastlines world-wide, even while that population growth has reduced natural buffering of shorelines. Shoreline hardening, a common coastal defense strategy that includes the use of seawalls and bulkheads (vertical walls constructed of concrete, wood, vinyl, or steel), is resulting in a "coastal squeeze" on estuarine habitats. In contrast to hardening, living shorelines, which range from vegetation plantings to a combination of hard structures and plantings, can be deployed to restore or enhance multiple ecosystem services normally delivered by naturally vegetated shores. Although hundreds of living shoreline projects have been implemented in the United States alone, few studies have evaluated their effectiveness in sustaining or enhancing ecosystem services relative to naturally vegetated shorelines and hardened shorelines. We quantified the effectiveness of (1) sills with landward marsh (a type of living shoreline that combines marsh plantings with an offshore low-profile breakwater), (2) natural salt marsh shorelines (control marshes), and (3) unvegetated bulkheaded shores in providing habitat for fish and crustaceans (nekton). Sills supported higher abundances and species diversity of fishes than unvegetated habitat adjacent to bulkheads, and even control marshes. Sills also supported higher cover of filter-feeding bivalves (a food resource and refuge habitat for nekton) than bulkheads or control marshes. These ecosystem-service enhancements were detected on shores with sills three or more years after construction, but not before. Sills provide added structure and may provide better refuges from predation and greater opportunity to use available food resources for nekton than unvegetated bulkheaded shores or control marshes. Our study shows that unlike shoreline hardening, living shorelines can enhance some ecosystem services provided by marshes, such as provision of nursery habitat.

Comparison of Bottomless Lift Nets and Breder Traps for Sampling Salt‐Marsh Nekton

AbstractVegetated salt‐marsh surfaces provide refuge, forage, and spawning habitat for estuarine nekton, yet are threatened by accelerating rates of sea‐level rise in southern New England and elsewhere. Nekton responses to ongoing marsh surface changes need to be evaluated with effective and quantitative nekton sampling gear. The goal of this study was to evaluate the effectiveness of different gear for monitoring nekton in emergent salt‐marsh vegetation by comparing nekton parameters between Breder traps and bottomless lift nets and between Breder traps made from different materials. Breder traps collected a significantly different nekton community, fewer species, and larger‐sized Mummichogs Fundulus heteroclitus than did lift nets. Nekton community composition, richness, and the size of green crabs Carcinus maenas also differed significantly between Breder traps constructed from acrylic and wire mesh. These results show that it is not appropriate to directly compare nekton data between Breder traps and lift nets, nor between Breder traps made from different materials. Our lift‐net data correspond well to other data collected with enclosure traps in southern New England. We recommend lift nets or similar enclosure traps for sampling nekton in emergent marsh vegetation and caution against using Breder traps in monitoring and assessment programs.

Oyster reef restoration: effect of alternative substrates on oyster recruitment and nekton habitat use

Eastern oysters (Crassostrea virginica) in Gulf of Mexico estuaries create complex reefs and provide important habitat for fish and crustaceans. Oyster reefs have suffered historic losses due to overharvest, disease, and degraded water quality, and recent efforts have focused on restoring reefs to benefit nekton populations. Oyster shell is the preferred substrate for oyster reef restoration, but as a consequence of its limited supply, a variety of alternative substrates are being used. We used field experiments to quantify the effects of substrate type (concrete, porcelain, limestone, river rock, and oyster shell) on oyster recruitment, growth, and nekton habitat use in St. Charles Bay, TX. After 4 months, oyster spat recruitment density, nekton density and community structure were similar across substrate types—and analogous to those on natural reefs—but differed from samples collected on bare sediment. To determine refuge value of the alternative substrates, we tested mud crab (Panopeidae) prey mortality with and pinfish (Lagodon rhomboides) or blue crab (Callinectes sapidus) predators. Prey mortality was similar across substrate types for both predators, and was significantly lower than no substrate and bare sand controls. Alternative substrates can provide important structural materials to support the development of oyster populations and nekton assemblages, and may be used to promote sustainable management of oyster reef resources via restoration.

Spatial Diversity in Composition and Structure of Nekton in Ngenep Spring and its Channels, Karangploso - Malang

Water springs and its channel degradation due to anthropogenic pollution may alter the community structure of aquatic organisms. Water spring degradation tehrefore affect the quality of water as tourism resources. This study aims to investigate the changes in community structure of nekton and determine the relationships between water quality characteristics to the diversity of nekton. The field survey was set up in Ngenep spring and its channels. Results showed that nekton species found in Ngenep spring and its channels consists of 4 classes, 4 orders, 6 families, and 7 species with total 627 nekton samples. It is comprises of fishes, shrimp, frogs and waterstriders. Nekton diversity index (H’) in the spring and irrigation channel were in moderate level (1<H'<3) while in settlement channel was low (0,67). Evenness values of nekton ranged 0,24 – 0,53, whereas dominancy index of nekton ranged 0,41 – 0,74. Evenness value in settlement channel was very low (0, 24) with high dominancy index (0, 74); it indicates that nekton species were spread not evenly in the channel, it dominated by fish Rasbora sp. (highest IVI, 184,95). There were spatial variations of physico-chemical water qualitiy parameters in Ngenep springs and its channels (temperature, stream velocity, turbidity, conductivity, pH, DO, BOD and TOM) which affected to nekton diversity and community structure. Clustering analyses and PCA result shows correlation pattern between nekton distribution with physico-chemical water quality parameters. However, physico-chemical water quality parameters in Ngenep springs and its channel were still optimum as nekton habitat (PP No. 82/ 2001). Keywords: Community structure , Nekton, Spatial diversity, Spring, Water channel

Assessing the Link Between Coastal Urbanization and the Quality of Nekton Habitat in Mangrove Tidal Tributaries

To assess the potential influence of coastal development on habitat quality for estuarine nekton, we characterized body condition and reproduction for common nekton from tidal tributaries classified as undeveloped, industrial, urban or man-made (i.e., mosquito-control ditches). We then evaluated these metrics of nekton performance, along with several abundance-based metrics and community structure from a companion paper (Krebs et al. 2013) to determine which metrics best reflected variation in land-use and in-stream habitat among tributaries. Body condition was not significantly different among undeveloped, industrial, and man-made tidal tributaries for six of nine taxa; however, three of those taxa were in significantly better condition in urban compared to undeveloped tributaries. Palaemonetes shrimp were the only taxon in significantly poorer condition in urban tributaries. For Poecilia latipinna, there was no difference in body condition (length–weight) between undeveloped and urban tributaries, but energetic condition was significantly better in urban tributaries. Reproductive output was reduced for both P. latipinna (i.e., fecundity) and grass shrimp (i.e., very low densities, few ovigerous females) in urban tributaries; however a tradeoff between fecundity and offspring size confounded meaningful interpretation of reproduction among land-use classes for P. latipinna. Reproductive allotment by P. latipinna did not differ significantly among land-use classes. Canonical correspondence analysis differentiated urban and non-urban tributaries based on greater impervious surface, less natural mangrove shoreline, higher frequency of hypoxia and lower, more variable salinities in urban tributaries. These characteristics explained 36 % of the variation in nekton performance, including high densities of poeciliid fishes, greater energetic condition of sailfin mollies, and low densities of several common nekton and economically important taxa from urban tributaries. While variation among tributaries in our study can be largely explained by impervious surface beyond the shorelines of the tributary, variation in nekton metrics among non-urban tributaries was better explained by habitat factors within the tributary and along the shorelines. Our results support the paradigm that urban development in coastal areas has the potential to alter habitat quality in small tidal tributaries as reflected by variation in nekton performance among tributaries from representative land-use classes.

Nekton Community Structure Varies in Response to Coastal Urbanization Near Mangrove Tidal Tributaries

To assess the potential influence of coastal development on estuarine-habitat quality, we characterized land use and the intensity of land development surrounding small tidal tributaries in Tampa Bay. Based on this characterization, we classified tributaries as undeveloped, industrial, urban, or man-made (i.e., mosquito-control ditches). Over one third (37 %) of the tributaries have been heavily developed based on landscape development intensity (LDI) index values >5.0, while fewer than one third (28 %) remain relatively undeveloped (LDI < 3.0). We then examined the nekton community from 11 tributaries in watersheds representing the four defined land-use classes. Whereas mean nekton density was independent of land use, species richness and nekton-community structure were significantly different between urban and non-urban (i.e., undeveloped, industrial, man-made) tributaries. In urban creeks, the community was species-poor and dominated by high densities of poeciliid fishes, Poecilia latipinna and Gambusia holbrooki, while typically dominant estuarine taxa including Menidia spp., Fundulus grandis, and Adinia xenica were in low abundance and palaemonid grass shrimp were nearly absent. Densities of economically important taxa in urban creeks were only half that observed in five of the six undeveloped or industrial creeks, but were similar to those observed in mosquito ditches suggesting that habitat quality in urban and mosquito-ditch tributaries is suboptimal compared to undeveloped tidal creeks. Furthermore, five of nine common taxa were rarely collected in urban creeks. Our results suggest that urban development in coastal areas has the potential to alter the quality of habitat for nekton in small tidal tributaries as reflected by variation in the nekton community.

Linking Hydrogeomorphology and Food Webs in Intertidal Creeks

Intertidal creeks are shallow, photic ecosystems that potentially serve as sources of prey for many predators within estuaries. In a previous study, the link between nekton community structure and hydrogeomorphological variables for eight intertidal creeks was assessed for North Inlet estu- ary, South Carolina. Herein, we advance their findings through ecological network analysis of foodweb structure within two creeks and infer nekton trophic relationships to geomorphology and potential influences of hydrological condition and change. A summer network of a shallow, wide creek demonstrated greater carbon recycling, trophic effi- ciency and flow through consumers than that of a deep, narrow creek representing the same period. We infer greater export of nekton carbon from the former creek. These results were supported by analyses of nekton effective trophic levels and guilds across the eight creeks. Shallow, wide intertidal creeks appear to provide both physical and foodweb attri- butes that promote good nekton habitat relative to deeper and narrower creeks. Human alterations to flow regimes and sea- level rise have the ability to affect geomorphology of indi- vidual creeks and the landscape as a whole. These changes in turn have the potential to alter food webs of intertidal creeks and their ability to serve as sources of food for the larger estuary.

Seasonal nekton assemblages in a flooded coastal freshwater marsh, Southwest Louisiana, USA

Marsh flooding and drying may be key factors affecting seasonal nekton distribution and density because habitat connectivity and water depth can impact nekton accessibility to the marsh surface. Recent studies have characterized freshwater nekton assemblages in marsh ponds; however, a paucity of information exists on the nekton assemblages in freshwater emergent marshes. The principal objectives of this study are to characterize the seasonal nekton assemblage in a freshwater emergent marsh and compare nekton species composition, density, and biomass to that of freshwater marsh ponds. We hypothesize that 1) freshwater emergent marsh has lower taxa richness than freshwater marsh ponds; and 2) freshwater emergent marsh has a lower seasonal density and biomass than freshwater marsh ponds. Mosquitofish Gambusia affinis and least killifish Heterandria formosa were abundant species in both habitats while some abundant species (e.g., banded pygmy sunfish Elassoma zonatum) in freshwater ponds were absent in freshwater emergent marsh. Our data did not support our first and second hypotheses because taxa richness, seasonal density and biomass between freshwater emergent marsh and ponds did not statistically differ. However, freshwater emergent marsh was dry during the summer months and thus supports no fish species during this period. Additional long-term research on the effects of flow regime in the freshwater marsh on nekton assemblages would potentially improve our understanding of nekton habitat requirements.

Nekton density patterns and hurricane recovery in submerged aquatic vegetation, and along non-vegetated natural and created edge habitats

We compared nekton habitat value of submerged aquatic vegetation, flooded non-vegetated natural and man-made edge habitats in mesohaline interior marsh areas in southwest Louisiana using a 1-m2 throw trap and 3-mm bag seine. When present, SAV habitats supported close to 4 times greater densities and higher species richness of nekton as compared to either natural or man-made edge habitats, which supported similar densities to one another. Three species of concern (bayou killifish, diamond killifish, chain pipefish) were targeted in the analysis, and two of the three were collected almost entirely in SAV habitat. During the course of the study, Hurricanes Ike and Gustav passed directly over the study sites in September 2008. Subsequent analyses indicated significant reductions in resident nekton density 1-mo post hurricanes, and only limited recovery 13-mo post-hurricane. Possible alteration of environmental characteristics such as scouring of SAV habitat, deposition of sediment over SAV, edge erosion and marsh loss, and extended high salinities may explain these lasting impacts.

Comparison of salt marsh creeks and ditches as habitat for nekton

Salt marshes are dynamic systems supporting a diverse assemblage of resident and transient nekton (free-swimming fish and decapod crustaceans). Within a marsh, many sub-habitats are used by nekton, including ditches and natural creeks. While the use of natural creeks is well doc- umented, the role of ditches as habitat for nekton remains less well known. The present study describes the nekton-support function of this prolific marsh sub-habitat, and compares it to tidal creeks. Sampling was conducted in the summer of 2008 in a microtidal, polyhaline salt marsh on Fire Island, NY, USA. Ditches and creeks were found to have different nekton communities. Creeks had significantly higher species richness and represented nearly all ditch species. Prolonged anoxia (up to 18 h) in ditches is suggested as a significant factor contributing to differences in the creek and ditch nekton community. Upper portions of ditches and creeks differed for resident nekton species, with higher species richness and density of the mummichog Fundulus heteroclitus in the upper portion of creeks than in the upper portion of ditches. Additional differences were seen in the nekton commu- nity composition of open and naturally plugged ditches, where the densities of individual species (such as F. heteroclitus, which was more abundant in open ditches) also differed. Ditches are a major habitat type in salt marshes of the northeastern USA, such as at the Fire Island marsh site studied here, and as efforts are considered to remove ditches from marshes as a habitat restoration technique, their nekton support function should be considered.

Determination of Trophic Transfer at a Created Intertidal Oyster (Crassostrea ariakensis) Reef in the Yangtze River Estuary Using Stable Isotope Analyses

Oysters can create reefs that provide habitat for associated species resulting in elevated resident abundances, lower mortality rates, and increased growth and survivorship compared to other estuarine habitats. However, there is a need to quantify trophic relationships and transfer at created oyster reefs to provide a better understanding of their potential in creating suitable nekton habitat. Stable isotope analyses (δ13C and δ15N) were conducted to examine the organic matter sources and potential energy flow pathways at a created intertidal oyster (Crassostrea ariakensis; hereinafter, oyster) reef and adjacent salt marsh in the Yangtze River estuary, China. The δ13C values of most reef-associated species (22 of 37) were intermediate between those of suspended particle organic matter (POM) and benthic microalgae (BMI), indicating that both POM and BMI are the major organic matter sources at the created oyster reef. The sessile and motile macrofauna colonizing the reef make up the main prey of transient nekton (e.g., spotted sea bass, Asian paddle crab, and green mud crab), thus suggesting that the associated community was most important in supporting higher trophic levels as opposed to the direct dietary subsidy of oysters. The created oyster reef consistently supported higher trophic levels than the adjacent salt marsh habitat due to the dominance of secondary consumers. These results indicate that through the provision of habitat for associated species, created oyster reefs provide suitable habitat and support a higher average trophic level than adjacent salt marsh in the Yangtze River estuary.

Trophic importance of a temperate intertidal wetland to resident and itinerant taxa: evidence from multiple stable isotope analyses

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

Ecological periodic tables for nekton usage of four US Pacific Northwest estuarine habitats

We compared the species composition and abundance of the total nekton community, using the Bray–Curtis similarity coefficient, and mean total nekton, fish and crab species richness, abundance and biomass, and shrimp abundance across four intertidal habitats in a US Pacific Northwest estuary: (i) eelgrass ( Zostera marina ); (ii) burrowing mud shrimp ( Upogebia pugettensis ); (iii) burrowing ghost shrimp ( Neotrypaea californiensis ); and (iv) unvegetated sand. Field sampling was conducted during daytime high tides, and was quantitative, stratified-by-habitat, randomized, and estuary-wide. More than 10 000 nekton specimens belonging to 64 taxa were collected in 454 samples during 10 sampling periods, each approximately one-month-long (from June to November), over 3 years (1998–2000). Non-metric multidimensional scaling analyses revealed annually recurring across-habitat patterns in total nekton Bray–Curtis similarity. Two-way (habitat, year) analyses of variance revealed annually recurring across-habitat patterns on 10 indicators of nekton-habitat quality and preference. Total nekton species richness, abundance, and biomass were, respectively, on average, 8 ×, 25 ×, and 25× greater in eelgrass, 4 ×, 6 ×, and 5× greater in mud shrimp, and 2 ×, 3 ×, and 2× greater in ghost shrimp, than in sand habitat. Our findings validate the ecological relevance of our habitats to nekton, and suggest they can serve as elements in ecological periodic tables of nekton habitat usage.