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1.
Beam trawls are a practical method for sampling vagile fauna from deep seagrass beds. The catches of fish and macroinvertebrates associated with Posidonia australis from two beam trawl designs were compared with the catch from a new design of beam trawl. Greater numbers of species and individuals of fish and macroinvertebrates were caught by the new trawl. Its catch also included almost the full range of species taken by the other two trawls. The new trawl was then trialed in the day and at night to compare differences in the catch of species between these times. Trawling at night yielded significantly more species and individuals of macroinvertebrates. In general, more fish were caught at night than during the day, but this was not the case at all sites, nor for all species. We emphasize the need for testing of sampling methods, and consideration of diel behavior patterns, when estimating abundance and species richness of macrofaunal seagrass communities. 相似文献
2.
We used a mesocosm approach to examine howratch characteristics influenced predation and habitat selection in a tritrophic food web. Our experiments included juvenile
red drum (Sciaenops ocellatus; RD), juvenile pinfish (Lagodon rhomboides; PF), and grass shrimp (Palaemonetes sp.; GS), members of a food web common in seagrass meadows of the northern Gulf of Mexico. We added an additional level of
complexity to the experiment by including a predator that could feed at two different trophic levels. RD were top predators,
PF were both prey items for RD and predators of GS, and GS were prey for RD and PF. We used 4 different artificial seagrass
habitats that varied by size (0.049 and 0.203 m2) and shape (circular and stellate) to control for covariation between patch size and seagrass density. Predation on GS was
measured in each habitat when PF, RD, and PF+RD were present, and predation on PF was measured when RD and RD+GS were present.
Habitat selection by each of these 3 species was measured individually and in the presence of every other combination of the
3 species. Neither predation nor habitat selection were consistently influenced by patch characteristics (size, shape, or
perimeter: area ratios) or the number of trophic levels. For GS, there was a significant negative relationship between patch
size and predation rates in the GS+PF+RD treatment. Habitat selection by GS without the threat of predation suggested a preference
for smaller habitats, but when in the presences of RD or RD+PF, GS preferred larger habitats. In predation experiments, PF
predation by RD showed no significant relationships with patch characteristics or trophic structure. For our habitat selection
experiments, PF preference was for larger habitats in the PF only and GS+PF+RD treatments. There were no significant relationships
between patch size, shape, or trophic structure and RD habitat selection. 相似文献
3.
Spatial and temporal patterns of distribution and abundance were examined for postsettlement sciaenids collected from seagrass meadows in the Aransas Estuary, Texas. Overall, 5443 sciaenid larvae and early juveniles were identified from biweekly epibenthic sled collections taken from August 1994 to August 1995. Eight species were present in seagrass meadows, with five accounting for over 99.9% of sciaenids collected: silver perch (Bairdiella chrysoura), spotted seatrout (Cynoscion nebulosus), spot (Leiostomus xanthurus), Atlantic croaker (Micropogonias undulatus), and red drum (Sciaenops ocellatus). Settlement to seagrass meadows was partitioned temporally with little overlap among the five species. Postsettlers from inshore spawners (B. chrysoura, C. nebulosus, S. ocellatus) inhabited seagrass meadows during the spring and summer, while individuals from offshore spawners (L. xanthurus, M. undulatus) were present in the late fall and winter. Densities ofB. chrysoura, C. nebulosus, S. ocellatus were highest for small individuals (4–8 mm SL) and these taxa remained in seagrass sites through the early juvenile stage. Conversely,L. xanthurus andM. undulatus maintained longer pelagic periods and generally entered seagrass meadows at larger sizes (10–14 mm SL). Moreover, these taxa were only temporary residents of selected seagrass meadows, apparently migrating to alternative habitats shortly after arrival. During peak settlement, mean and maximum densities among species ranged from 0.1 m?2 to 0.8 m?2 and 0.7 m?2 to 23.8 m?2, respectively. Density and mean size of possettlement sciaenids differed significantly between seagrass species (Halodule wrightii, Thalassia testudinum) and among sites within the estuary. 相似文献
4.
Seven species of mojarras (Gerreidae) were collected from three stations in the Indian River lagoon near the Sebastian Inlet, Florida over an eighteen month period to study spatial and temporal variations in occurrence and feeding habits. Two major habitats common to this area were represented in the study; a sandy beach and a seagrass flat. Of the 2,899 gerreids collected,Eucinostomus gula represented 67% and was found primarily in theHalodule seagrass site. The next most abundant species,E. argenteus (11%),E. jonesi andE. lefroyi (each 10%), were found most frequently at the inlet site.Diapterus auratus, E. melanopterus, andGerres cinereus were captured infrequently and were considered incidental. Prey items found included amphipods, bivalves, copepods, fish eggs, foraminifera, isopods, nematodes, ostracods, polychaetes and crustacean parts. Significant amounts of sand and unidentifiable amorphous debris were also included in the gut content analysis. Little interspecific variation in diet was found among the four major species examined. The general shift seen from a diet composed primarily of copepods and other crustaceans to one of polychaetes suggests an intraspecific ontogenetic progression. Spatial variations in diet composition were also indicated between the two major habitats. Feeding analyses showed gerreids to be diurnal feeders with the greatest consumption (total gut content weight) occurring at dusk. 相似文献
5.
The pelagic fish assemblage within a temperate estuary was examined to determine if there were diel differences in species richness, total abundance, biomass, and species composition. These comparisons were made over both seasonal (January–December 1996) and annual (August–November 1995; August–December 1996) scales with pop net collections in a shallow (<2 m MLW) embayment within Great Bay in southern New Jersey, USA. In the complete year of sampling in 1996, more than 335,000 pelagic fish, representing 13 families (23 species), were collected during diel sampling with 12 species constituting over 99.9% of the total catch including Clupea harengus (84%), Menidia menidia (10%), and Anchoa mitchilli (4%). A detailed examination determined that nighttime species richness, total abundance and biomass may have been enhanced during some seasons by using artificial light. Diel variation in species composition was similar regardless of the use of the artificial light in all seasons but fall. Annual comparisons between 1995 and 1996 during late summer and fall found these results to be consistent. In general, these findings point out the importance of sampling during both day and night to understand the movement and abundance patterns of estuarine pelagic fishes and their ecological significance in temperate estuaries. 相似文献
6.
Fish-habitat relationships on the shallow inner continental shelf were quantified with video sled and metered beam trawl on
Fenwick and Weaver shoals offshore of Maryland and Delaware, U.S. These areas provide megascale physical relief and habitat
complexity, but for juvenile fishes, mesoscale and microscale habitat is very important particularly as refuge from predation.
At these smaller scales, much of the relief on the inner continental shelf is contributed by bedforms or sand waves and biogenic
structures such as tubes, shell beds, or pits. A quantitative association for juvenile fishes between and within benthic habitats
was found and related primarily to bedform size and amount of biogenic structure. The incidence of fishes was about four-times
higher for large bedforms (> 30 cm wavelength and about 10 cm crest height) relative to smaller bedforms (<30 cm wavelength
and about 5 cm crest height). For biogenic structure, going from high patch-mat tube densities to lower densities or no biogenic
structure increased fish incidence by 5.4 and 3.3 times, respectively. The significant relationships of fishes with bedform
size and density of biogenic structure indicated that seemingly small differences in physical structure of a habitat can make
the difference between unacceptable and essential habitat for juvenile fishes. Proximity of complex and simple habitats was
important in the diel use of habitat and in balancing pressure of refuge from predation provided by complex habitats with
foraging for increased resources available in simpler habitats. During the day, spatially complex habitats comprised ofDiopatra andAsabellides tube mats had about twice as many fishes relative to bare sandy habitats (8.3–9.9 versus 4.0–4.1 fishes 100 m−2, respectively). At night, the pattern was reversed with more fishes present in the bare sandy habitats (12.4–13.5 versus
5.6–8.7 fishes 100 m−2). Some fish, such asAmmodytes spp., were very habitat specific and occurred only on dynamic coarser sands near the top of the shoals. Others, such asUrophycis regia, showed less habitat preference and occurred in all habitats during both day and night. Combining the effects of physical
relief and biogenics, the habitat with the highest incidence of fishes had large bedforms with some biogenic structure. More
emphasis needs to be placed on quantifying the relationship between fishes and their habitats for the fisheries management
concept of essential fish habitat to develop into an effective tool on the inner continental shelf. The juvenile life history
stages need to be emphasized because fish-habitat interactions are the strongest for these stages and may be the most ecologically
important. 相似文献
7.
Christopher P. Buzzelli 《Estuaries and Coasts》1998,21(4):659-672
The fringing environments of lower Chesapeake Bay include sandy shoals, seagrass meadows, intertidal mud flats, and marshes. A characterization of a fringing ecosystem was conducted to provide initialization and calibration data for the development of a simulation model. The model simulates primary production and material exchange in the littoral zone of lower Chesapeake Bay. Carbon (C) and nitrogen (N) properties of water and sediments from sand, seagrass, intertidal silt-mud, and intertidal marsh habitats of the Goodwin Islands (located within the Chesapeake Bay National Estuarine Research Reserve in Virginia, CBNERR-VA) were determined seasonally. Spatial and temporal differences in sediment microalgal biomass among the habitats were assessed along with annual variations in the distribution and abundance ofZostera marina L. andSpartina alterniflora Loisel. Phytoplankton biomass displayed some seasonality related to riverine discharge, but sediment microalgal biomass did not vary spatially or seasonally. Macrophytes in both subtidal and intertidal habitats exhibited seasonal biomass patterns that were consistent with other Atlantic estuarine ecosystems. Marsh sediment organic carbon and inorganic nitrogen differed significantly from that of the sand, seagrass, and silt habitats. The only biogeochemical variable that exhibited seasonality was low marsh NH4 +. The subtidal sediments were consistent temporally in their carbon and nitrogen content despite seasonal changes in seagrass abundance. Eelgrass has a comparatively low C:N ratio and is a potential N sink for the ecosystem. Changes in the composition or size of the vegetated habitats could have a dramatic influence over resource partitioning within the ecosystem. A spatial database (or geographic information system, GIS) of the Goodwin Islands site has been initiated to track long-term spatial habitat features and integrate model output and field data. This ecosystem characterization was conducted as part of efforts to link field data, geographic information, and the dynamic simulation of multiple habitats. The goal of these efforts is to examine ecological structure, function, and change in fringing environments of lower Chesapeake Bay. 相似文献
8.
Fish and invertebrate assemblages in seagrass, mangrove, saltmarsh, and nonvegetated habitats 总被引：1，自引：0，他引：1
Many studies compare utilization of different marine habitats by fish and decapod crustaceans; few compare multiple vegetated
habitats, especially using the same sampling equipment. Fish and invertebrates in seagrass, mangrove, saltmarsh, and nonvegetated
habitats were sampled during May–August (Austral winter) and December–January (Austral summer) in the Barker Inlet-Port River
estuary, South Australia. Sampling was undertaken using pop nets in all habitats and seine nets in seagrass and nonvegetated
areas. A total of 7,895 fish and invertebrates spanning 3 classes, 9 orders, and at least 23 families were collected. Only
one fish species,Atherinosoma microstoma, was collected in all 4 habitats, 11 species were found in 3 habitats (mangroves, seagrass, and nonvegetated), and 13 species
were only caught in seagrass and nonvegetated habitats. Seagrass generally supported the highest numbers of fish and invertebrates
and had the greatest species richness. Saltmarsh was at the other extreme with 29 individuals caught from two species. Mangroves
and nonvegetated habitats generally had more fish, invertebrates, and species than saltmarsh, but less than seagrass. Analyses
of abundances of individual species generally showed an interaction between habitat and month indicating that the same patterns
were not found through time in all habitats. All habitats supported distinct assemlages although seagrass and nonvegetated
assemblages were similar in some months. The generality of these patterns requires further investigation at other estuaries.
Loss of vegetated habitats, particularly seagrass, could result in loss of species richness and abundance, especially for
organisms that were not found in other habitats. Although low abundances were found in saltmarsh and mangroves, species may
use these habitats for varying reasons, such as spawning, and such use should not be ignored. 相似文献
9.
Ana L. Hernández Cordero Rochelle D. Seitz Romuald N. Lipcius Caitlin M. Bovery David M. Schulte 《Estuaries and Coasts》2012,35(5):1340-1345
Bay scallop (Argopecten irradians) populations existed in Chesapeake Bay until 1933, when they declined dramatically due to a loss of seagrass habitat. Since then, there have been no documented populations within the Bay. However, some anecdotal observations of live bay scallops within the lower Bay suggest that restoration of the bay scallop is feasible. We therefore tested whether translocated adults of the southern bay scallop, Argopecten irradians concentricus, could survive during the reproductive season in vegetated and unvegetated habitats of the Lynnhaven River sub-estuary of lower Chesapeake Bay in the absence of predation. Manipulative field experiments evaluated survival of translocated, caged adult scallops in eelgrass Zostera marina, macroalgae Gracilaria spp., oyster shell, and rubble plots at three locations. After a 3-week experimental period, scallop survival was high in vegetated habitats, ranging from 98% in their preferred habitat, Z. marina, to 90% in Gracilaria spp. Survival in Z. marina was significantly higher than that in rubble (76%) and oyster shell (78%). These findings indicate that reproductive individuals can survive in vegetated habitats of lower Chesapeake Bay when protected from predators and that establishment of bay scallop populations within Chesapeake Bay may be viable. 相似文献
10.
Seasonal ichthyoplankton surveys were made in the lower Laguna Madre, Texas, to compare the relative utilization of various nursery habitats (shoal grass,Halodule wrightii; manatee grass,Syringodium filiforme; and unvegetated sand bottom) for both estuarine and offshore-spawned larvae. The species composition and abundance of fish larvae were determined for each habitat type at six locations in the bay. Pushnet ichthyoplankton sampling resulted in 296 total collections, yielding 107,463 fishes representing 55 species in 24 families. A broad spectrum of both the biotic and physical habitat parameters were examined to link the dispersion and distribution of both pre-settlement and postsettlement larvae to the utilization of shallow seagrass habitats. Sample sites were grouped by cluster analysis (Ward’s minimum variance method) according to the similarity of their fish assemblages and subsequently examined with a multiple discriminant function analysis to identify important environmental variables. Abiotic environmental factors were most influential in defining groups for samples dominated by early larvae, whereas measures of seagrass complexity defined groups dominated by older larvae and juveniles. Juvenile-stage individuals showed clear habitat preference, with the more shallowHalodule wrightii being the habitat of choice, whereas early larvae of most species were widely distributed over all habitats. As a result of the recent shift of dominance fromHalodule wrightii toSyringodium filiforme, overall reductions in the quality of nursery habitat for fishes in the lower Laguna Madre are projected. 相似文献
11.
Little is known about the importance of salmarshes to juvenile and adult fishes in temperate Australia. We assessed diel and
feeding patterns of fish inhabiting saltmarsh in a sheltered embayment along the coast of Victoria, Australia, between October
2002 and May 2003. The saltmarsh flat was generally only inundated during low-pressure weather systems (barometric pressure
<1,013 hP). Fish were sampled over the saltmarsh flats using fyke and seine nets. A total of 2,047 individuals (10 species,
including juveniles and adults) were caught.Atherinasoma microstoma was most abundant (fyke [F], μ=1.6 fish h−1; seine [S], μ=28.2 fish shot−1), followed byFavonigobius, lateralis (F: 0.5; S: 0.6),Galaxias maculatus (F: 0.1),Heteroclinus adelaide (F:<0.1),Kestratherina esox (F: <0.1; S: 1.6),Leptatherina presbyteroides (F: <0.1; S: 7.1) andTetractenos glaber (F: 1). Commercial species, includingAldrichetta forsteri (F: <0.1; S: 3.2),Sillaginodes punctata (F: <0.1; S: 0.9), andRhombosolea tapirina (F: 0.4), were commonly sampled. Variability in species richness or fish abundance was not explained by water temperature,
salinity, depth, or barometric pressure. Significantly more species were sampled with the seine during nocturnal periods (p=0.002);
fish abundance did not vary between diel periods, nor did fish abundance and species richness in fyke net samples. Diets of
the most abundant species (A. microstoma, A. forsteri, andF. lateralis) were primarily composed of gammaridean amphipods and hemipteran insects. There was no correlation between fish diets and
the composition of benthic invertebrates as sampled at 3 different regions of the saltmarsh flat. The saltmarsh flats in our
study region are inhabited by several species normally associated with alternative habitat types such as seagrass, and the
patterns of habitat use observed appear to be partially attributed to foraging behavior. 相似文献
12.
The utilization of an intertidal salt marsh creek in South Carolina during January 1977 was determined by sampling every third ebb tide for 13 days. All fishes leaving the creek during that period were captured in a channel net. This procedure produced a time-series of samples which permitted analysis of the fish community occupying the intertidal creek at all times of day and night. A total of 14,730 larval, juvenile, and adult fishes comprising at least 22 species in 16 families were collected. The most common larval and juvenile fishes wereLeiostomus xanthurus, Mugil spp.,Myrophis punctatus leptocephali,Lagodon rhomboides, Paralichthys spp., andMicropogon undulatus. Catch sizes for all species varied widely between samples. No diurnal-nocturnal pattern in catches was evident forL. xanthurus, Mugil spp.,L. rhomboides andM. undulatus. M. punctatus was taken in large numbers only when the flood tide occurred during the day, while moreParalichthys spp. larvae were taken in late afternoon-evening flood tide samples. The most common invertebrate,Palaemonetes pugio, was taken in large quantities only in late afternoon-night flood tide samples. Three diversity indices were computed for each sample. Values for all indices varied widely between successive samples. The results emphasize a high degree of utilization of the intertidal creek habitat by larval and juvenile fishes. The diurnal-nocturnal activity patterns of some species, and the wide variation in catch size of the other species can permit use of the intertidal salt marsh habitat with reduced competition for available space and energy. 相似文献
13.
Estuaries contain mosaic habitats which support fish across different life stages. Artificial reefs represent a form of habitat enhancement which can provide additional structure for fishes and improve fishing opportunities, but the role of artificial reefs within the broader estuarine seascape has not been extensively studied. We used a VEMCO Positioning System (VPS) to monitor the fine-scale movements of yellowfin bream (Acanthopagrus australis, referred to as Bream), an estuarine predator and important recreational species. Fish were implanted with acoustic tags with accelerometer sensors (to measure relative fish activity), and their movements monitored on an artificial reef and adjacent habitats. Elevated activity patterns during crepuscular periods indicated that foraging was likely occurring over a large seagrass bed adjacent to the artificial reef system. Alternatively, lower activity was observed when fish were on the artificial reef, which may reflect the role of this habitat as a refuge, or that alternative foraging strategies were being employed. All fish exhibited a high degree of fidelity to the artificial reef on which they were tagged, and there was minimal movement among other reef groups within the array. There was extensive overlap in space use contours for smaller fish on the seagrass edge, but no overlap for larger fish that also tended to forage further afield. These findings have implications for the way in which artificial reefs support fish production, especially the importance of connectivity with other key habitats within the estuarine seascape. 相似文献
14.
Predation is often the largest source of mortality for juvenile fish and the risk of predation can influence growth rates
by either forcing young fish into suboptimal foraging habitats or reducing the amount of time spent foraging. We used field
experiments to test effects of predation risk by gulf flounder (Paralichthys albigutta) on juvenile pinfish (Lagodon rhomboides) growth rates by measuring changes in length and weight in three habitats (sand, low density, and high density shoalgrass,Halodule wrightii) in Perdido Key, Florida. Benthic cores, seagrass samples, and stomach contents were also analyzed to examine differences
in pinfish prey densities, grass densities and epiphyte coverage, and diet, respectively, among habitat and predator treatments.
Both length and weight growth rates were determined and showed similar results. We found that pinfish inhabiting seagrass
habitats, particularly low densityHalodule displayed the fastest growth rates in the beginning of the growing season (June) and those in sand had the fastest growth
rates later in the season (October). These differences in growth rates did not appear to be influenced by densities of pinfish
prey items since the treatment having the highest density of prey was not that in which growth rates were the greatest. This
seasonal shift may be attributed to increasing pinfish size. Larger pinfish in October may have been inhibited by high density
grass, reducing foraging efficiency. These results demonstrate how occupying a suboptimal foraging habitat can affect juvenile
pinfish growth rates. Predation risk significantly reduced length and weight growth rates of pinfish in June, but not October.
This suggests that smaller pinfish early in the season traded time spent foraging for predator avoidance, while larger pinfish
were likely to have reached a size refuge from predation. This study demonstrates that nonlethal effects from predation are
also important influences on juvenile pinfish. 相似文献
15.
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
16.
Historical Comparison of Fish Community Structure in Lower Chesapeake Bay Seagrass Habitats 总被引：1，自引：0，他引：1
Kathryn L. Sobocinski Robert J. Orth Mary C. Fabrizio Robert J. Latour 《Estuaries and Coasts》2013,36(4):775-794
Seagrass beds provide important habitat for fishes and invertebrates in many regions around the world. Accordingly, changes in seagrass coverage may affect fish communities and/or populations, given that many species utilize these habitats during vulnerable early life history stages. In lower Chesapeake Bay, seagrass distribution has contracted appreciably over recent decades due to decreased water clarity and increased water temperature; however, effects of changing vegetated habitat on fish community structure have not been well documented. We compared fish community composition data collected at similar seagrass sites from 1976–1977 and 2009–2011 to investigate potential changes in species richness, community composition, and relative abundance within these habitats. While seagrass coverage at the specific study sites did not vary considerably between time periods, contemporary species richness was lower and multivariate analysis showed that assemblages differed between the two datasets. The majority of sampled species were common to both datasets but several species were exclusive to only one dataset. For some species, relative abundances were similar between the two datasets, while for others, there were notable differences without directional uniformity. Spot (Leiostomus xanthurus) and northern pipefish (Syngnathus fuscus) were considerably less abundant in the contemporary dataset, while dusky pipefish (Syngnathus floridae) was more abundant. Observed changes in community structure may be more attributable to higher overall bay water temperature in recent years and other anthropogenic influences than to changes in seagrass coverage at our study sites. 相似文献
17.
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
18.
We used clear, acrylic chambers to measure in situ community oxygen and nutrient fluxes under day and night conditions in seagrass beds at five sites across Florida Bay five times between September 1997 and March 1999. Underlying sediments are biogenic carbonate with porosities of 0.7–0.9 and with low organic content (<1.6%). The seagrass communities always removed oxygen from the water column during the night and produced oxygen during daylight, and sampling date and site significantly affected both night and daytime oxygen fluxes. Net daily average fluxes of oxygen (?4.9 to 49 mmol m?2 day?1) ranged from net autotrophy to heterotrophy across the bay and during the 18-month sampling period. However, the Rabbit Key Basin site, located in the west-central bay and covered with a dense Thalassia testudinum bed, was always autotrophic with net average oxygen production ranging from 4.8 to 49 mmol m?2 day?1. In November 1998, three of the five sites were strongly heterotrophic and oxygen production was least at Rabbit, suggesting the possibility of hypoxic conditions in fall. Average ammonium (NH4) concentrations in the water column varied widely across the bay, ranging from a mean of 6.9 μmol l?1 at Calusa in the eastern bay to a mean of 0.6 μmol l?1 at Rabbit Key for the period of study. However, average NH4 fluxes by site and date (?240 to 110 μmol m?2 h?1) were not correlated with water column concentrations and did not vary in a consistent diel, seasonal, or spatial pattern. Concentrations of dissolved organic nitrogen (DON) in the water column, averaged by site (15–25 μmol l?1), were greater than mean NH4 concentrations, and the range of day and night DON fluxes (?920 to 1,300 μmol m?2 h?1), averaged by site and date, was greater than the range of mean NH4 fluxes. Average DON fluxes did not vary consistently from day to night, seasonally or spatially. Mean silicate fluxes ranged from ?590 to 860 μmol m?2 h?1 across all sites and dates, but mean net daily fluxes were less variable and most of the time contributed small amounts of silicate to the water column. Mean concentrations of filterable reactive phosphorus (FRP) in the water column across the bay were very low (0.021–0.075 μmol l?1); but site average concentrations of dissolved organic phosphorus (DOP) were higher (0.04–0.15 μmol l?1) and showed a gradient of increasing concentration from east to west in the bay. A pronounced gradient in average surficial sediment total phosphorus (1.1–12 μmol g DW?1) along an east-to-west gradient was not reflected in fluxes of phosphorus. FRP fluxes, averaged by site and date, were low (?5.2 to 52 μmol m?2 h?1), highly variable, and did not vary consistently from day to night or across season or location. Mean DOP fluxes varied over a smaller range (?8.7 to 7.4 μmol m?2 h?1), but also showed no consistent spatial or temporal patterns. These small DOP fluxes were in sharp contrast to the predominately organic phosphorus pool in surficial sediments (site means?=?0.66–7.4 μmol g DW?1). Significant correlations of nutrient fluxes with parameters related to seagrass abundance suggest that the seagrass community may play a major role in nutrient recycling. Integrated means of net daily fluxes over the area of Florida Bay, though highly variable, suggest that seagrass communities might be a source of DOP and NH4 to Florida Bay and might remove small amounts of FRP and potentially large amounts of DON from the waters of the bay. 相似文献
19.
A broad-scale survey of seagrass species composition and distribution along Florida's central Gulf Coast (known as the Big
Bend region) was conducted in the summer of 2000 to address growing concerns over the potential effects of increased nutrient
loading from adjacent coastal rivers. Iverson and Bittaker (1986) originally surveyed seagrass distribution in this region
between 1974–1980. We revisited 188 stations from the original survey, recording the presence or absence of all seagrass species.
Although factors such as accuracy of station relocation, differences in sampling effort among studies, and length of time
between surveys preclude statistical comparisons, several interesting patterns emerged. While the total number of stations
occupied by the three most common seagrass species,Thalassia testudinum, Syringodium filiforme, andHalodule wrightii, was similar between the two time periods, we observed a change in the number of records of each species as well as changes
in distribution with depth.T. testudinum andHalophila engelmanni occurrence declined in the deepest areas of the region, while the number of stations occupied byS. filiforme andH. wrightii increased in nearby areas. We observed several localized areas of seagrass loss, frequently associated with the mouths of
coastal rivers. These results suggest that increased nutrient loading to coastal rivers that discharge into the Big Bend area
may be affecting seagrasses by increasing phytoplankton abundance in the water column, thus changing water clarity characteristics
of the region. 相似文献
20.
Two different habitats in the Chesapeake Bay were tested for the occurrence of diel vertical migration (DVM) by members of the zooplankton community. During July of 1997 diel samples were collected from Jones Creek, a small, protected, 3-m deep tidal gut, and a station in Hampton Roads, a 20-m deep, expansive section of the bay. Temperature, salinity, light penetration, water clarity, dissolved oxygen, total particulate nitrogen and carbon, chlorophyll concentration, and algal density were also determined for depth increments at these stations, ca. midday and midnight. Significant differences in zooplankton depth distribution occurred over the day at both stations. The calanoid copepod,Acartia tonsa, dominated the zooplankton community and the larger stages were strong migrators. Mysid shrimp, the largest sized crustaceans, displayed significant DVM at both stations. Although diel differences were also detected in chlorophylla concentrations, with 25% reduction at night in Jones Creek and 18% in Hampton Roads, counts of algal cells revealed no differences between night and day numbers. The nightly losses of chlorophyll were not driven by mesozooplankton grazers. Using grazing rates from the literature, we estimated that mesozooplankton harvested less than 5% of the standing crop of phytoplankton each day in both locations. Food quantity and quality (as determined by chlorophyll concentrations, cell counts, and C:N ratio) were uniform in the Jones Creek water column, but higher near the surface in Hampton Roads. While it was clearly advantageous for zooplankton to migrate to surface waters at night for feeding in Hampton Roads, it is paradoxical for DVM to persist in Jones Creek when ample food was found in deeper water. 相似文献