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1.
Three factors affecting the structure of nekton communities 9fishes and decapod crustaceans) in eelgrass beds were identified and evaluated: contiguous shoreline type, distance from shore, and macrophyte biomass. Throw traps (1 m2) were used to sample eelgrass nekton at seven locations in Great South Bay (New York, U.S.) along Fire Island National Seashore from May through October 1995. Abundances ofGobiosoma ginsburgi, Apeltes quadracus, andOpsanus tau were significantly higher in eelgrass beds adjacent to salt marshes.Menidia menidia, Syngnathus fuscus, Pseudopleuronectes americanus, andPalaemonetes pugio were significantly more abundant in eelgrass adjacent to beaches. Regression analyses indicated thatSyngnathus fuscus, Pseudopleuronectes americanus, andAnguilla rostrata abundances were positively related to eelgrass biomass, andApeltes quadracus andGobiosoma ginsburgi abundances were highest at moderate levels of macroalgae biomass. The distance of an eelgrass bed from shore was also important. Species generally associated with salt marshes (Fundulus heteroclitus, Cyprinodon variegatus, Lucania parva, andPalaemonetes pugio) were more abundant in eelgrass near the marsh shore. Abundances ofApeltes quadracus, Syngnathus fuscus, Menidia menidia, Hippolyte pleuracanthus, andCrangon septemspinosa increased with distance from the shoreline. Shoreline type, distance from shore, and macrophyte biomass appear to affect the abundance and distribution of some nekton species. The effect of shoreline type may be related to the distribution of macrophyte biomass; the biomasses of eelgrass and macroalgae were significantly higher along beach and marsh shorelines, respectively. Explaining within-habitat variability and identifying microhabitat preferences for nekton will aid in the proper design of future studies and habitat restoration efforts. 相似文献
2.
Subsidence and erosion of intertidal salt marsh at Galveston Island State Park, Texas, created new areas of subtidal habitat
that were colonized by seagrasses begining in 1999. We quantified and compared habitat characteristics and nekton densities
in monospecific beds of stargrassHalophila engelmanni and shoalgrassHalodule wrightii as well as adjacent nonvegetated substrates. We collected 10 replicates per habitat type during April, July, October, and
December 2001. Most habitat characteristics varied with season. Water temperature, salinity, and dissolved oxygen were similar
among habitat types. Turbidity and depth were greatest inH. engelmanni beds and least inH. wrightii beds.H. engelmanni exhibited shorter leaves and higher shoot density and biomass core−1 thanH. wrightii. Densities of almost all dominant species of nekton (fishes and decapods) were seasonally variable, all were higher in seagrass
habitats than in nonvegetated habitats, and most were higher in one seagrass species than the other. Naked gobyGobiosoma bosc, code gobyGobiosoma robustum, bigclaw snapping shrimpAlpheus heterochaelis, and blue crabCallinectes sapidus, were most abundant inH. engelmanni. Brown shrimpFarfantepenaeus aztecus, brackish grass shrimpPalaemonetes intermedius, and daggerblade grass shrimpPalaemonetes pugio were most abundant inH. wrightii. PinfishLagodon rhomboides and pink shrimFarfantepenaeus duorarum were equally abundant in either seagrass. Most dominant nekton varied in size by month, but only two (L. rhomboides andC. sapidus) exhibited habitat-related differences in size. Nekton densities in these new seagrass habitats equaled or exceeded densities
associated with historical and current intertidal smooth cordgrassSpartina alterniflora marsh. Continued seagrass expansion and persistence should ensure ecosystem productivity in spite of habitat change. 相似文献
3.
Decapod crustaceans occupying seagrass, salt marsh edge, and oyster habitats within the St. Martins Aquatic Preserve along
the central Gulf coast of Florida were quantitatively sampled using a 1-m2 throw trap during July–August 1999 and March–April 2000. Relative abundance and biomass were used as the primary measures
to compare patterns of occupancy among the three habitat types. Representative assemblages of abundant and common species
from each habitat were compared using Schoener's Percent Similarity Index (PSI). In all, 17,985 decapods were sampled, representing
14 families and 28 species. In the summer sampling period, mean decapod density did not differ between oyster and seagrass
habitats, which both held greater densities of decapods than marsh-edge. In the spring sampling period oyster reef habitat
supported greater mean decapod density than both seagrass and marsh-edge, which had similar densities of decapods. Habitat-specific
comparisons of decapod density between the two sampling periods indicated no clear seasonal effect. In summer 1999, when seagrasses
were well established, decapod biomass among the three habitats was not significantly different. During spring 2000, decapod
biomass in oyster (41.40 gm−2) was greater than in marshedge (4.20 gm−2), but did not differ from that of seagrass (9.73 g m−2). There was no significant difference in decapod biomas between seagrass and marsh-edge habitats during the spring 2000 sampling
period. The assemblage analysis using Schoener's PSI indicated that decapod assemblages associated with oyster were distinct
from seagrass and marshedge habitats (which were similar). The results of this study suggest that in comparison to seagrass
and marsh-edge habitats, oyster reef habitats and the distinct assemblage of decapod crustaceans that they support represent
an ecologically important component of this estuarine system. 相似文献
4.
The US Army Corps of Engineers recently dredged and permanently reopened Packery Channel, historically a natural tidal inlet,
to allow water exchange between the Gulf of Mexico and the Laguna Madre, TX, USA. The main objective of this study was to
characterize estuarine-dependent recruitment and community structure in seagrass habitats adjacent to Packery Channel pre-
and post-channel opening. We sampled fish and crustacean abundance using an epibenthic sled in Halodule wrightii seagrass meadows in both control and impact locations over 2 years, 1 year before the opening of Packery Channel (October
2004–May 2005) and 1 year after (July 2005–April 2006). Using the before–after control–impact design, we found significantly
fewer nekton post-channel opening. However, we found significantly higher mean densities of newly settled estuarine-dependent
species (Sciaenops ocellatus, Micropogonias undulatus, Lagodon rhomboides, Callinectes sapidus, and penaeid shrimp) post-opening. Multivariate analyses showed significant community assemblage changes post-opening with
increased contribution of estuarine-dependent species post-opening. Our results show that estuarine-dependent nekton are using
Packery Channel as a means of ingress into areas of the upper Laguna Madre’s seagrass meadows that were previously inaccessible,
which may lead to higher fisheries productivity for some of these economically and ecologically important fishery species. 相似文献
5.
We examined the distribution of nekton across the marsh landscape using a 1-m2 drop sampler to compare nekton densities across three different salinity zones (intermediate, brackish, saline), three pond
sizes (diameter <40 m = small, ∼250–300 m = medium, >750 m = large), and two habitat types (pond, adjacent marsh) in the Barataria
Bay Estuary, Louisiana. Nekton assemblages of ponds and the adjacent marsh appeared to be structured by the responses of individual
species to the estuarine salinity gradient at the landscape scale and to pond habitat attributes locally. Our results indicate
that ponds in the brackish and saline zones are more important nursery areas for most fishery species than ponds in the intermediate
zone. Medium and large ponds supported higher densities of most species than small ponds. Most species of nekton were associated
with vegetation structure, and individuals of these species were either concentrated among plant stems at the marsh edge or
within submerged aquatic vegetation in ponds. 相似文献
6.
Núria Marbà Carlos M. Duarte Jorge Terrados Zayda Halun Esperança Gacia Miguel D. Fortes 《Estuaries and Coasts》2010,33(1):107-117
We examined the rhizosphere structure of 14 seagrass meadows (seven mixed, three Enhalus acoroides, two Zostera japonica, one Thalassia hemprichii, and one Halophila ovalis) in the Philippines and Vietnam and tested their effect on sediment redox potential by comparing the redox potential in vegetated
vs unvegetated sediments. The effect of seagrass photosynthesis on sediment redox potential was tested in an E. acoroides meadow during a short-term (2-day) clipping experiment. In all the meadows, the centroidal depth (i.e., depth comprising
50%) of seagrass belowground biomass was within the top 15 cm sediment layer. Redox potentials in vegetated sediments tended
to be higher than those in adjacent unvegetated ones; sediment redox potential anomaly ranged from −61 to 133 mV across the
meadows. The centroidal depths of positive redox potential anomaly and seagrass root biomass were significantly correlated
across the meadows investigated (type II regression analysis, slope = 0.90, lower confidence limit [CL] = 0.42 upper CL = 1.82,
R
2 = 0.59, p < 0.01). Experimental removal of E. acoroides leaves resulted in a decrease in rhizosphere redox potential by 20 mV, further confirming the positive effect of seagrass
roots and rhizomes on sediment redox potential and, thus, the general conditions for microbial processes in the coastal zone. 相似文献
7.
We investigated the effects of differing spatial scales of seagrass habitat architecture on the composition and abundance of settling bivalves in a sub-tropical seagrass community. The density of newly settled bivalves was generally greater atThalassia testudinum grass bed edge (<1 m) compared to interior portions of the bed (>10 m). Deviation from this generalized pattern occurred when high densities of newly settled tulip mussels (Modiolus americanus) were recorded from the interior of the meadow, associated with aggregations of adult mussels. Bivalve settling densities appear to reflect settlement shadows of passively delivered larvae, bedload transport of newly settled individuals from unvegetated regions, as well as gregarious settlement among adult conspecifics. We also investigated the impact of seagrass patch shape and size on settlement by using artificial seagrass units (ASU) in separate short-term and long-term experiments. We found a positive relationship between ASU perimeter and bivalve abundance, suggesting that larval encounter rates with seagrass habitat may determine initial settlement patterns. Using ASUs we also investigated the relative role seagrass epiphytes play in determining the density of settling bivalves. Results showed greater settling densities where epiphytic secondary structure was elevated compared to controls, and bivalve density was significantly greater when ASUs were fouled with a natural community of epiphytes, suggesting that both microstructure and biofilms positively influenced bivalve settlement. We conclude that structural components of seagrass habitats increase bivalve settlement at multiple spatial scales, including epiphytic micro-structure, small-scale patch shape and size, and large-scale within habitat differences. 相似文献
8.
To test whether invasive Spartina alterniflora marshes were functionally equivalent to native Scirpus mariqueter marshes, the present study used bottomless lift nets (20 m2) during 12 high-tide events from August to October 2008 to compare nekton densities and biomass between the two marsh types
in the Dongtan wetland. A total of eight species of fish, two species of shrimp, and three species of crab were collected.
So-iny mullet Chelon haematocheilus, keeled mullet Liza carinata, Asian freshwater goby Acanthogobius ommaturus, and ridge-tail prawn Exopalaemon carinicauda dominated samples from the two marsh types and accounted for over 90% of the total catch. There were significantly greater
densities and biomass (p < 0.05) of total nekton (all species combined) and two mullets (C. haematocheilus and L. carinata) in S. alterniflora marshes than in S. mariqueter marshes in August 2008, while no significant differences (p > 0.05) between the two marsh types were observed for densities and biomass of any species or total nekton in September and
October 2008. Non-metric multidimensional scaling ordination did not show clear separation of samples between the two marsh
types (r = 0.071, p = 0.159). Furthermore, there were no habitat-specific differences (p > 0.05) in the size distributions of the three numerically dominant species (C. haematocheilus, L. carinata, and A. ommaturus). We concluded that S. alterniflora marshes were utilized by nekton in a fashion similar to their utilization of native S. mariqueter marshes under similar physical conditions. 相似文献
9.
To assess the potential for habitat isolation effects on estuarine nekton, we used two species with different dispersal abilities
and life history strategies, mummichog (Fundulus heteroclitus) and pinfish (Lagodon rhomboides) to examine: (1) distribution trends among estuarine shallow-water flat and various intertidal salt marsh habitats and (2)
the influence of salt marsh habitat size and isolation. Collections were conducted using baited minnow traps set within nonisolated
interior marshes (interior), nonisolated fringing marshes (nonisolated), isolated island marshes (isolated), and shallow-water
flat habitats (flat) that were adjacent to isolated and nonisolated marshes. Size range of individuals collected included
juvenile and adult F. heteroclitus (20–82-mm standard length) and L. rhomboides (22–151-mm standard length). During high tide, F. heteroclitus exclusively used marsh habitats, particularly high marsh, whereas L. rhomboides used marshes and flats. F. heteroclitus abundance followed an interior > nonisolated > isolated pattern. L. rhomboides abundance patterns were less consistent but followed a nonisolated > isolated > interior pattern. A size-dependent water
depth relationship was observed for both species and suggests size class partitioning of marsh and flat habitats during high
tide. Minimum water depth (~31 cm) restricted L. rhomboides populations in marshes, while maximum water depth (~69 cm) restricted F. heteroclitus population use of marshes and movement between marsh habitats. Disparities in F. heteroclitus young of year contribution between isolated compared to nonisolated and interior marsh types suggests isolated marshes acted
as population sinks and were dependent on adult emigrants. Resident and transient salt marsh nekton species utilize estuarine
habitats in different ways and these fundamental differences can translate into how estuarine landscape might affect nekton. 相似文献
10.
In recent decades, marshes naturally dominated bySpartina spp. have been replaced byPhragmites australis throughout the northeastern United States. We suggest that early in this invasion there was little effect on the fish fauna. As the invasion proceeds, the marsh surface habitat became more altered (i.e., elevated, flattened, reduced water-filled depressions, and reduced standing water), which resulted in a reduction of feeding, reproduction, and nursery function for fishes, especiallyFundulus spp. These potential changes in marsh habitat and function have resulted in numerous attempts to removePhragmites and restoreSpartina spp. To evaluate the response of marsh surface fishes toPhragmites treatment, we examined fish use in the brackish water reaches of Alloway Creek in the Delaware Bay estuary. ReferencePhragmites habitats were compared with referenceSpartina alterniflora-dominated habitats and sites treated (1996–1998) to removePhragmites to restore former vegetation (i.e., restored, now comprised of 100%Spartina). Fish were sampled with an array (n=9 at each site) of shallow pit traps (rectangular glass dishes, 27.5×17.5×3.7 cm). Small individuals (mean=17.5, 5–45 mm TL) dominated all pit trap collections. Fish abundance was highest at the restored (catch per unit effort [CPUE]=2.16) andSpartina (CPUE=0.81) sites with significantly lower values atPhragmites (CPUE=0.05) habitats. Samples were dominated by young-of-the-year mummichog,Fundulus heteroclitus (98% of total fish, n=631). The only other fish species collected was spotfin killifish,Fundulus luciae (2% of total catch, n=14), which was only present in restored andSpartina habitats. These observations suggest that the restored marsh is providing habitat (water-filled depressions on the marsh surface) for young-of-the-yearFundulus spp. These marshes are responding favorably to the restoration based on the much greater abundance of fish in restored versusPhragmites habitats and the overall similarity between restored andSpartina habitats. 相似文献
11.
Geoffrey R. Hosack Brett R. Dumbauld Jennifer L. Ruesink David A. Armstrong 《Estuaries and Coasts》2006,29(6):1150-1160
The complexity of habitat structure created by aquatic vegetation is an important factor determining the diversity and composition
of soft-sediment coastal communities. The introduction of estuarine organisms, such as oysters or other forms of aquaculture,
that compete with existing forms of habitat structure, such as seagrass, may affect the availability of important habitat
refugia and foraging resources for mobile estuarine fish and decapods. Fish and invertebrate communities were compared between
adjacent patches of native seagrass (Zostera marina), nonnative cultured oyster (Crassostrea gigas), and unvegetated mudflat within a northeastern Pacific estuary. The composition of epibenthic meiofauna and small macrofaunal
organisms, including known prey of fish and decapods, was significantly related to habitat type. Densities of these epifauna
were significantly higher in structured habitat compared to unstructured mudflat. Benthic invertebrate densities were highest
in seagrass. Since oyster aquaculture may provide a structural substitute for seagrass being associated with increased density
and altered composition of fish and decapod prey resources relative to mudflat, it was hypothesized that this habitat might
also alter habitat preferences of foraging fish and decapods. The species composition of fish and decapods was more strongly
related to location within the estuary than to habitat, and fish and decapod species composition responded on a larger landscape
scale than invertebrate assemblages. Fish and decapod species richness and the size of ecologically and commercially important
species, such as Dungeness crab (Cancer magister), English sole (Parophrys vetulus), or lingcod (Ophiodon elongatus), were not significantly related to habitat type. 相似文献
12.
Sediment microphytobenthos, such as diatoms and photosynthetic bacteria, are functionally important components of food webs
and are key mediators of nutrient dynamics in marine wetlands. The medium to long-term recovery of benthic microproducers
in restored habitats designed to improve degraded coastal wetland sites is largely unknown. Using taxon-specific photopigments,
we describe the composition of microphytobenthic communities in a large restoration site in southern California and differences
in the temporal recovery of biomass (chlorophylla), composition, and taxonomic diversity between vegetatedSpartina foliosa salt marsh and unvegetated mudflat. Visually distinct, spatially discreet, microphytobenthic patches appeared after no more
than 7 mo within the restoration site and were distinguished by significant differences in biomass, taxonomic diversity, and
the relative abundance of cyanobacteria versus diatoms. Sediment chlorophylla concentrations within the restored site were similar to concentrations in nearby natural habitat 0.2–2.2 yr following marsh
creation, suggesting rapid colonization by microproducers. RestoredSpartina marsh very rapidly (between 0.2 and 1.2 yr) acquired microphytobenthic communities of similar composition and diversity to
those in naturalSpartina habitat, but restored mudflats took at least 1.6 to 2.2 yr to resemble natural mudflats. These results suggest relatively
rapid recovery of microphytobenthic communities at the level of major taxonomic groups. Sediment features, such as pore water
salinity andSpartina density, explained little variation in microphytobenthic taxonomic composition. The data imply that provision of structural
heterogeneity in wetland construction (such as pools and vascular plants) might speed development of microproducer communities,
but no direct seeding of sediment microfloras may be necessary. 相似文献
13.
We examined the effect of nutrients and grazers on Thalassia testudinum in Jobos Bay, Puerto Rico by fertilizing sediment and manipulating grazer abundances. Bottom-up effects were variable: Added
nutrients did not increase seagrass aboveground biomass, but decreased belowground biomass—perhaps as a result of less biomass
being allocated to belowground structures in response to greater nutrient supply in porewater. Experimental fencing of 1.5 × 1.5 m
plots provided shelter that attracted large aggregations of fish, including seagrass herbivores. Seagrass biomass and shoot
density decreased with increasing abundance of herbivorous fish, indicating a significant top-down effect. There were interactions
between nutrient supply, provision of shelter, and grazing pressure. Fertilization enhanced seagrass %N; however, %N also
increased in unfertilized plots that were fenced, most likely due to uptake of N excreted from the large numbers of fish associated
with the fences. Only plots where shelter was provided and fertilizer was applied to sediments exhibited evidence of heavy
grazing, reducing both seagrass cover and aboveground biomass. In the unfertilized fenced plots, signs of grazing were fewer
despite large abundances of fish and enhanced nutritional quality of seagrass leaves. This suggests the possibility that high
nutrient availability in sediments lowered concentrations of chemical defense compounds in the seagrass and that cues other
than %N may have been involved in stimulating grazing. This study highlights the complexity of bottom-up and top-down interactions
in seagrass systems and the important role of refuge availability in shaping the relative strengths of these controls. 相似文献
14.
Karen L. Bushaw-Newton Danielle A. Kreeger Sarah Doaty David J. Velinsky 《Estuaries and Coasts》2008,31(4):694-703
Phragmites australis has been invading Spartina-alterniflora-dominated salt marshes throughout the mid-Atlantic. Although, Phragmites has high rates of primary production, it is not known whether this species supports lower trophic levels of a marsh food
web in the same manner as Spartina. Using several related photochemical and biological assays, we compared patterns of organic matter flow of plant primary
production through a key salt marsh metazoan, the ribbed mussel (Geukensia demissa), using a bacterial intermediate. Dissolved organic matter (DOM) was derived from plants collected from a Delaware Bay salt
marsh and grown in the laboratory with 14C-CO2. Bacterial utilization of plant-derived DOM measured as carbon mineralization revealed that both species provided bioavailable
DOM to native salt marsh bacteria. Total carbon mineralization after 19 days was higher for Spartina treatments (36% 14CO2 ± 3 SE) compared with Phragmites treatments (29% ±2 SE; Wilcoxon–Kruskal–Wallis rank sums test, P < 0.01). Pre-exposing DOM to natural sunlight only enhanced or decreased bioavailability of the DOM to the bacterioplankton
during initial measurements (e.g., 7 days or less) but these differences were not significant over the course of the incubations.
Mixtures of 14C-labeled bacterioplankton (and possibly organic flocs) from 14C-DOM treatments were cleared by G. demissa at similar rates between Spartina and Phragmites treatments. Moreover, 14C assimilation efficiencies for material ingested by mussels were high for both plant sources ranging from 74% to 90% and
not significantly different between plant sources. Sunlight exposure did not affect the nutritional value of the bacterioplankton
DOM assemblage for mussels. There are many possible trophic and habitat differences between Spartina- and Phragmites-dominated marshes that could affect G. demissa but the fate of vascular plant dissolved organic carbon in the DOM to bacterioplankton to mussel trophic pathway appears
comparable between these marsh types. 相似文献
15.
D. M. Chate 《Natural Hazards》2011,56(1):81-91
A very high number concentration of aerosols in urban locations has a wide impact on health and ecosystem. The evolutions
of urban aerosol distributions at elapse-time 30 and 60 min are simulated at rainfall rates, 0.5 and 0.9 mm h−1 applying scavenging coefficients to initial aerosols number concentrations (before rain). We show how thunderstorm rain scavenges
number concentrations of urban aerosols in the ultrafine and fine modes. Elapsed-time evolutions of urban aerosols presented
in this work show washout of about 50–60 and 70–80% number concentrations of particles in the diameter range 0.02 μm ≤ D
p
≤ 0.1 μm after 30 and 60 min of thunderstorm rain when compared to initial number concentrations (before rain). Assuming
37 and 24% Sulfate and Organic Carbon particles in aerosol distributions in the urban environment and by applying scavenging
coefficients to these initial number concentrations, elapse-time evolutions after 30 and 60 min of thunderstorm rain are presented
in this work. The health impact is addressed in terms of depositions of particles within respiratory system by deposition
fractions as a function of particle size. For D
p
≤ 0.1 μm, 33 and 41% of initial number concentrations of Sulfate and Organic Carbon particles deposits within respiratory
system. Whereas elapsed-time evolutions show 60 and 80% cleansing of initial number concentrations of Sulfate and Organic
Carbon particles after 30 and 60 min of thunderstorm rain. 相似文献
16.
Isolated patches ofSpartina anglica (cordgrass) at two sites on a wave-exposed mid-intertidal flat of the 340 km2 Manukau Harbor (Auckland, New Zealand) have developed very differently since being planted in the mid-1970s. Although the
two sites are only 0.5 km apart and at the same intertidal elevation,Spartina patches at the easternmost site (site 1) have as much as an order of magnitude higher biomass and accumulated sediment volume
thanSpartina patches at site 2. A field experiment was conducted to characterize waves and associated sediment dynamics at each site,
which might explain whySpartina patches at the two sites have developed so differently over the past 25 yr or so. Suspended sediments were measured and wave
characteristics were inferred from subsurface pressure data measured for 5 wk at bothSpartina sites and at an intermediate location. Bed-orbital speeds and frictional wave-energy dissipation were consistently lower
at the easternmost site with the largerSpartina patches. The west-to-east reduction in wave energy is due to the spatial arrangement of theSpartina sites relative to the predominant wind fetches. The wave-energy gradient is maintained by tidal-cycle variations in fetch
and bed friction and results in a west-to-east reduction in sand suspension. Silt, which is largely resuspended under southwest
winds, is redeposited in the low wave-energy conditions in and around the larger site 1Spartina patches. Shell accumulation bySpartina patches at site 1 occurs infrequently, during southwest winds >10 m s−1 and water depths >0.7 m, when waves are least attenuated by bed friction. Large between-site differences in the growth of
and sediment accumulation by theSpartina patch are consistent with the observed wave-energy gradient. The resulting spatial patterns of silt, sand, and shell resuspension
and deposition directly influence the rate of sediment accumulation bySpartina patches and the composition of accumulated sediment on this wave-exposed intertidal flat. 相似文献
17.
Seagrass meadows are often cited as important nursery areas for newly settled red drum even though many estuaries, such as Galveston Bay, Texas, support large numbers of red drum and have limited seagrass cover, suggesting the use of alternate nursery areas. We examined patterns of habitat use for newly settled red drum at six sampling areas in Galveston Bay; two areas had seagrass beds and four areas had no seagrass. We measured densities in different habitat types using epibenthic sleds and enclosure samplers. Peak recruitment of young red drum to the estuary occurred during September through December. Highest densities of new settlers were found in seagrass meadows (primarilyHalodule wrightii), but when seagrass was absent, the highest densities of red drum occurred along theSpartina alterniflora marsh edge interface. Densities were relatively low on nonvegetated bottom away from the marsh edge. We also examined density patterns in other habitat types at selected sampling areas and found no red drum within marsh vegetation away from the marsh edge interface (5 and 10 m into the marsh interior). Oyster reefCrassostrea virginica was sampled using lift nets, and we found no red drum using this habitat, although adjacent seagrass and marsh interface habitats were used. Even though red drum densities in marsh edge were low relative to seagrass, the large areal extent of marshes in the bay complex probably makes marsh edge the most important nursery habitat for red drum in Galveston Bay. 相似文献
18.
George R. Priest Chris Goldfinger Kelin Wang Robert C. Witter Yinglong Zhang António M. Baptista 《Natural Hazards》2010,54(1):27-73
To explore the local tsunami hazard from the Cascadia subduction zone we (1) evaluate geologically reasonable variability
of the earthquake rupture process, (2) specify 25 deterministic earthquake sources, and (3) use resulting vertical coseismic
deformations for simulation of tsunami inundation at Cannon Beach, Oregon. Maximum runup was 9–30 m (NAVD88) from earthquakes
with slip of ~8–38 m and M
w ~8.3–9.4. Minimum subduction zone slip consistent with three tsunami deposits was 14–15 m. By assigning variable weights
to the source scenarios using a logic tree, we derived percentile inundation lines that express the confidence level (percentage)
that a Cascadia tsunami will not exceed the line. Ninety-nine percent of Cascadia tsunami variation is covered by runup ≤30 m and 90% ≤16 m with a “preferred”
(highest weight) value of ~10 m. A hypothetical maximum-considered distant tsunami had runup of ~11 m, while the historical
maximum was ~6.5 m. 相似文献
19.
Seagrass both disappeared and recovered within 4 yr in one region of northern Indian River Lagoon (IRL). For the specific
area referred to as Turnbull Bay, a relatively pristine area of the IRL, over 100 ha of seagrass completely disappeared from
1996 to 1997 and then recovered by 2000. Based on lagoon-wide mapping from aerial photographs taken every 2–3 years since
1986, coverage of seagrass in Turnbull Bay declined from 124 ha in 1989 to 34 ha by 1999 and increased to 58 ha in 2003. Bi-annual
monitoring of fixed seagrass transects tells a more detailed story. Species composition along the Turnbull transect shifted
fromHalodule wrightii toRuppia maritima beginning in 1995, and macroalgal abundance increased. By the summer of 1997, seagrass completely disappeared along the transect,
as well as in most of the surrounding areas in Turnbull Bay; macroalgae covered much of the sediment surface. No significant
water quality changes were detected. Light attenuation and suspended solid values did increase after the seagrass disappeared.
Porewater sulfide concentrations, taken after all the grass was gone in 1997, were high (2,000 μM), but did improve by 1998
(1,200 μM). Seagrass recovery was rapid and occurred in the reverse sequence of species loss. Seedlings ofR. maritima were the first colonizers, then patches ofH. wrightii appeared. In 2000,Halophila engelmannii returned in the deeper water (>0.6m). By the summer of 2000, the beds had completely recovered. We conclude that this demise
was a natural event caused by a long-term buildup of seagrass biomass and a thick (10–15 cm) layer of organic detritus and
ooze. We surmise that such a crash and subsequent recovery may be a natural cycle of decline and recovery within this semirestricted,
poorly-flushed area. The frequency of this cycle remains uncertain. 相似文献
20.
We evaluated nekton habitat quality at 5 shallow-water sites in 2 Rhode Island systems by comparing nekton densities and biomass,
number of species, prey availability and feeding, and abundance of winter flounderPseudopleuronectes americanus. Nekton density and biomass were compared with a 1.75-m2 drop ring at 3 sites (marsh, intertidal, and subtidal) in Coggeshall Cove in Narragansett Bay and two subtidal sites (eelgrass
and macroalgae) in Ninigret Pond, a coastal lagoon. We collected benthic core samples and examined nekton stomach contents
in Coggeshall Cove. We identified 16 species of fish, 16 species of crabs, and 3 species of shrimp in our drop ring samples.
A multivariate analysis of variance indicated differences in total nekton, invertebrates, fish, and winter flounder across
the five sites. Relative abundance of benthic invertebrate taxa did not match relative abundance of prey taxa identified in
the stomachs. Nonmetric multidimensional scaling plots showed groupings in nekton and benthic invertebrate prey assemblages
among subtidal, intertidal, and marsh sites in Coggeshall Cove. Stepwise multiple regression indicated that biomass of macroalgae
was the most important variable predicting abundance of nekton in Coggeshall Cove, followed by elevation and depth. In Rhode
Island systems that do not experience chronic hypoxia, macroalgae adds structure to unvegetated areas and provides refuge
for small nekton. All sites sampled were characterized by high abundance and diversity of nekton pointing to the importance
of shallow inshore areas for production of fishes and decapods. Measurements of habitat quality should include assessment
of the functional significance of a habitat (this can be done by comparing nekton numbers and biomass), some measure of habitat
diversity, and a consideration of how habitat quality varies in time and space. 相似文献