共查询到20条相似文献，搜索用时 46 毫秒
1.
Quarterly field sampling was conducted to characterize variations in water column and sediment nutrients in a eutrophic southern
California estuary with a history of frequent macroalgal blooms. Water column and sediment nutrient measures demonstrated
that Upper Newport Bay (UNB) is a highly enriched estuary. High nitrate (NO3
−) loads from the river entered the estuary at all sampling times with a rainy season (winter) maximum estimated at 2,419 mol
h−1. This resulted in water NO3
− concentration in the estuary near the river mouth at least one order of magnitude above all other sampling locations during
every seasons; maximum mean water NO3
− concentration was 800 μM during springer 1997. Phosphorus (P)-loading was high year round (5.7–90.4 mol h−1) with no seasonal pattern. Sediment nitrogen (N)-content showed a seasonal pattern with a spring maximum declining through
fall. sediment and water nutrients, as well as percent cover of three dominant macroalgae, varied between the main channel
and tidal creeks. During all seasons, water column NO3
− concentrations were higher in the main channel than in tidal creeks while tidal creeks had higher levels of sediment total
Kjeldhal nitrogen (TKN) and P. During each of the four sampling periods, percent cover ofEntermorpha intestinalis andCeramium spp. was higher in tidal creeks than in the main channel, while percent cover ofUlva expansa was always higher in the main channel. Decreases in sediment N in both creek and channel habitats were concurrent with increases
in macroalgal cover, possibly reflecting use of stored sediment TKN by macroalgae. Our data suggest a shift in primary nutrient
sources for macroalgae in UNB from riverine input during winter and spring to recycling from sediments duirng summer and fall. 相似文献
2.
Newport Bay is a large estuary in southern California that is subject to anthropogenic nutrient loading, eutrophication, and
hypoxia. Ground-based methods of assessing algal extent for monitoring and management are limited in that they cannot provide
a synoptic view of algal distribution over comparatively large areas. The goal of this study was to explore the application
of color infrared aerial photography as an alternative for analyzing the changes in the abundance of exposed macroalgae. Three
surveys combining remote sensing (color infrared aerial photography) and ground-based sampling to quantify macroalgal mat
coverage were carried out in Upper Newport Bay (UNB) between July and October 2005. Airborne photographs (scale 1:6000) collected
during daytime low tides, clear skies, and appropriate sun angle were digitized to 25-cm resolution, orthorectified, georegistered,
and combined into three mosaic composite digital images: one for each survey. During each aerial photography survey, macroalgal
percent cover was measured on the ground by the pointintercept method in a 6.25-m2 area at ca. 30 locations distributed along the water’s edge throughout the intertidal mudflat area. There were three main
types of cover:Ulva spp. (green algae),Ceranrium spp. (red algae), and bare surface (mud and mussel beds). To analyze similarities between spectral signatures in the images
and cover types, the pixels corresponding to the ground samples from each survey were grouped into clusters based on similarity
of their spectral signatures. To establish relationships between spectral signatures in the images and cover as determined
from ground data, pixels in each composite image corresponding to ground samples from the same day that were characterized
by > 90% of one cover type were attributed to that cover type. Ground samples comprised of a mixture of cover types were used
for accuracy assessment. Before classification, each digital image was transformed by the Minimum Noise Fraction Rotation
method to remove noise and enhance contrast between the classes. For classification of each composite image, the Spectral
Angle Mapper scheme was used: all pixels in each image were attributed to the identified classes and the areal extent of each
class was estimated. According to these assessments, the macroalgal coverage in UNB increased from 37% in July to 57% in September
to 80% in October, and during this timeUlva spp. replacedCeramium spp. as the dominant alga. This analysis showed that color infrared aerial photography is an effective tool for assessing
estuarine, intertidal macroalgal coverage. 相似文献
3.
We examined the spatial and temporal variability in drift macroalgal abundance in two seagrass dominated estuarine systems
on the Texas coast: Redfish Bay (in the Copano-Aransas Estuary) and Lower Laguna Madre. Measurements of benthic macroalgal
variability were made in conjunction with a suite of biotic (seagrass biomass, percent cover, blade width and length, shoot
density, epiphyte biomass, seagrass blade C:N ratios, and drift macroalgal abundance and composition) and abiotic (inorganic
nitrogen and phosphorus concentrations, chlorophylla, total suspended solids, light attenuation, salinity, temperature, total organic carbon and porewater NH4
+) indicators. All parameters were measured at 30 sites within each estuary semiannually from July 2002 to February 2004. Principal
components analysis (PCA) was used to examine relationships between drift macroalgal abundance and biotic and abiotic parameters.
In both Redfish Bay and Lower Laguna Madre, drift macroalgal distribution was widespread, and during three of four sampling
periods, abundance was equal to abovegro und biomass ofThalassia testudinum, the dominant seagrass. Drift macro algal abundance was highly variable within sites, between sites, and between seasons
in both estuaries. No significant differences in drift macroalgal abundance were found between Redfish Bay and Lower Laguna
Madre. In Redfish Bay, drift macroalgae (90.1±10.2 gm−2) tended to accumulate in bare patches within seagrass beds. In Lower Laguna Madre, drift macroalgae (72.7±10.7 gm−2) tended to accumulate in areas of dense seagrass cover rather than in bare areas. We found no relationship between drift
macroalgal abundance and low (<2μM) water column nutrient concentrations, and although several of our measured parameters
were related to drift macroalgal abundance, none alone sufficiently explained the variability in abundance noted between the
two estuarine systems. The contrasting patterns of macroalgal accumulation between Redrish Bay and Lower Laguna Madre likely
reflect differences in water circulation characteristics between the two regions as dictated by local physiography, in cluding
the shape and orientation of the lagoons, with seasonal variations in macroalgal abundance related to changes in freshwater
inflow and nutrient loading. 相似文献
4.
Sophia E. Fox Erica Stieve Ivan Valiela Jennifer Hauxwell James McClelland 《Estuaries and Coasts》2008,31(3):532-541
Anthropogenic inputs of nutrients to coastal waters have rapidly restructured coastal ecosystems. To examine the response
of macrophyte communities to land-derived nitrogen loading, we measured macrophyte biomass monthly for 6 years in three estuaries
subject to different nitrogen loads owing to different land uses on the watersheds. The set of estuaries sampled had nitrogen
loads over the broad range of 12 to 601 kg N ha−1 year−1. Macrophyte biomass increased as nitrogen loads increased, but the response of individual taxa varied. Specifically, biomass
of Cladophora vagabunda and Gracilaria tikvahiae increased significantly as nitrogen loads increased. The biomass of other macroalgal taxa tended to decrease with increasing
load, and the relative proportion of these taxa to total macrophyte biomass also decreased. The seagrass, Zostera marina, disappeared from the higher loaded estuaries but remained abundant in the estuary with the lowest load. Seasonal changes
in macroalgal standing stock were also affected by nitrogen load, with larger fluctuations in biomass across the year and
higher minimum biomass of macroalgae in the higher loaded estuaries. There were no significant changes in macrophyte biomass
over the 6 years of this study, but there was a slight trend of increasing macroalgal biomass in the latter years. Macroalgal
biomass was not related to irradiance or temperature, but Z. marina biomass was highest during the summer months when light and temperatures peak. Irradiance might, however, be a secondary
limiting factor controlling macroalgal biomass in the higher loaded estuaries by restricting the depth of the macroalgal canopy.
The relationship between the bloom-forming macroalgal species, C. vagabunda and G. tikvahiae, and nitrogen loads suggested a strong connection between development on watersheds and macroalgal blooms and loss of seagrasses.
The influence of watershed land uses largely overwhelmed seasonal and inter-annual differences in standing stock of macrophytes
in these temperate estuaries. 相似文献
5.
The relative abundances of the seagrass,Zostera marina L., and associated macroalgae were examined for Yaquina Bay, Oregon, U.S.A., to investigate variability in autotroph abundance along the salinity-temperature gradient and the potential for nuisance algal blooms. Possible explanations for the patterns in autotroph abundances were explored through examination of their correlations with the physicochemical characteristics of the water column. Study sites were established in each of three zones in the estuary defined by temperature and salinity and were sampled monthly June through September 1998 and in July 1999.Z. marina and macroalgal cover andZ. marina shoot density were measured in 0.25-m2 plots at each site. After cover estimates and shoot counts were made, material was harvested for determination ofZ. marina and macroalgal biomass. Water column variables were measured from stations near each study site and composited on a depth-averaged, monthly basis for each zone. BothZ. marina and green macroalgal abundance differed between sites, over the summer in 1998, and between years. Seasonal patterns were most obvious forZ. marina at the site closest to the ocean while the pattern in macroalgal abundance suggested a bloom moving up river as summer progressed. The physicochemical characteristics of the zones differed with the season and could be related to the patterns inZ. marina and macroalgal abundance. In particular, salinity was positively correlated withZ. marina abundance, while abundance of both autotrophs was related to light availability.Z. marina biomass ranged 19–109 g dry weight m?2; green macroalgae biomass ranged 5–234 g dry weight m?2. The biomass of the green macroalgae at several sites and dates equaled or exceed that of theZ. marina suggesting the potential for nuisance algal blooms does exist in Yaquina Bay. 相似文献
6.
We conducted a laboratory experiment to quantify nutrient (nitrogen and phosphorus) limitation of macroalgae collected along
a gradient in water column nutrient availability in Upper Newport Bay estuary, a relatively nutrient-rich system in southern
California, United States. We collectedEnteromorpha intestinalis and water for use in the experiment from five sites ranging from the lower end of the estuary to the head. Initial algal
tissue N and P concentrations and molar N∶P ratios—as well as water column NO3 and total Kjeldahl nitrogen (TKN)—increased along a spatial gradient from the lower end toward the head. Water column soluble
reactive phosphorus (SRP) varied among sites as well but did not follow a pattem of increasing from the seaward end toward
the head. Algae from each site were assigned to one of four experimental treatments: control (C), nitrogen enrichment (+N),
phosphorus enrichment (+P), and nitrogen and phosphorus enrichment (+N+P). Each week for 3 wk we replaced the water in each
unit with the appropriate treatment water to mimic a poorly flushed estuary. After 3 wk, the degree of nutrient limitation
ofE. intestinalis varied spatially with distance from the head of the estuary. Growth ofE. intestinalis collected from several sites increased with N enrichment alone and increased further when P was added in combination with
N This indicated that N was limiting and that when N was sufficient, P became limiting. Sites from whichE. intestinalis exhibited nutrient limitation spanned the range of background water column NO3 (12.9±0.4 to 55.2±2.1 μM) and SRP (0.8±0.0 to 2.9±0.2 μM) concentrations. Algae that were N limited had initial tissue N
levels ranging from 1.18±0.03 to 2.81±0.08% dry weight and molar N∶P ratios ranging from 16.75±0.39 to 26.40±1.98. 相似文献
7.
The purpose of this field study was to determine the relationship between environmental conditions, particularly high nitrate
(NO
3
−
), low salinity events, and both nitrogen (N) storage (NO
3
−
, ammonium [NH
4
+
], free amino acids [FAA], protein, and total N) and nitrate reductase (NR) activity in the macroalgaeEnteromorpha lingulata andGelidium pusillum in the lower Mobile Bay estuary (Alabama, USA). The environmental conditions at the collection site varied over the growing
season with the most notable changes due to late winter and spring runoff entering the estuary (1–30 psu, 0.3–25.8 μM NO
3
−
, 0.9–12.5 μM NH
4
+
, 3–28°C, 61–2,375 μmol PAR m−2 s−1). Principal component analysis reduced the six environmental variables measured to three principal components. Stepwise,
multiple regression analysis was then used to examine the relationship between the principal components and the internal NO
3
−
, NH
4
+
, and FAA pools and NR activity. The results indicate that changes in inorganic N availability and salinity rather than changes
in irradiance determine patterns of N storage and NO
3
−
reduction. BothE. lingulata andG. pusillum are capable of taking up and storing NO
3
−
when it becomes available. Greater NO
3
−
availability produced larger NH
4
+
and FAA pools along with higher rates of NR activity inE. lingulata, but notG. pusillum, suggesting thatE. lingulata is able to metabolize NO
3
−
more rapidly during high NO
3
−
, low salinity events. Differences in the susceptibility ofE. lingulata andG. pusillum to NH
4
+
inhibition and salinity stress combined with their different growth strategies help to explain the seasonal trends in total
N. Total N inE. lingulata ranged from 2.57% to 6.39% dw, while the slower growingG. pusillum showed no significant variation in total N content (3.8–4.1% dw). These results led to the conclusion thatE. lingulata responds more quickly thanG. pusillum to high NO
3
−
, low salinity events and that these events have a larger effect on the overall N content ofE. lingulata. 相似文献
8.
Seasonal variation patterns of aboveground and belowground biomass, net primary production, and nutrient accumulation were
assessed inAtriplex portulacoides L. andLimoniastrum monopetalum (L.) Boiss. in Castro Marim salt marsh, Portugal. Sampling was conducted for five periods during 2001–2002 (autumn, winter,
spring, summer, and autumn). This study indicates that both species have a clear seasonal variation pattern for both aboveground
and belowground biomass. Mean live biomass was 2516 g m−2 yr−1 forL. monopetalum and 598 g m−2 yr−1 forA. portulacoides. Peak living biomass, in spring for both species, was three times greater in the former, 3502 g m−2 yr−1, than in the latter, 1077 g m−2 yr−1. For both the Smalley (Groenendijk 1984) and Weigert and Evans (1964) methods, productivity ofL. monopetalum (2917 and 3635 g m−2 yr−1, respectively) was greater than that ofA. portulacoides (1002 and 1615 g m−2 yr−1, respectively). Belowground biomass ofL. monopetalum was 1.7 times greater than that ofA. portulacoides. In spite of this, the root:shoot ratio forA. monopetalum to aerial components. Leaf area index was similar for both species, but specific leaf area ofA. portulacoides was twice that ofL. monopetalum. The greatest nutrient contents were found in leaves. Leaf nitrogen content was maximum in summer for both species (14.6
mg g−1 forA. portulacoides and 15.5 mg g−1 forL. monopetalum). Leaf phosphorus concentration was minimum in summer (1.1 mg g−1 inA. portulacoides and 1.2 mg g−1 inL. monopetalum). Leaf potassium contents inA. portulacoides were around three times greater than inL. monopetalum. Leaf calcium contents inL. monopetalum were three times greater than inA. portulacoides. There was a pronounced seasonal variation of calcium content in the former, while in the latter no clear variation was registered.
Both species exhibited a decrease in magnesium leaf contents in the summer period. Mangamese content inL. monopetalum leaves was tenfold that inA. portulacoides. Seasonal patterns of nutrient contents inA. portulacoides andL. monopetalum suggest that availability of these elements was not a limiting factor to biomass production. 相似文献
9.
Rapidly growing human populations have caused heavy modifications to the watersheds of many Mediterranean climate estuaries, subjecting them to excessive nutrient enrichment and harmful macroalgal blooms. Despite these impacts, comprehensive studies in these systems are rare and comparisons between systems are lacking. We surveyed five southern California estuaries that ranged in size from 93 to 1,000 ha and incorporated differing land usages and watershed sizes. We sampled environmental variables (sediment redox potential, organic content, total nitrogen and total phosphorus, water column nitrate, ammonium, and salinity) and macroalgal cover and biomass quarterly at three locations within each estuary over 15 months to compare spatial and wet vs. dry season patterns. Maximum mean water column nitrate concentration across all estuaries ranged from 47 to 1,700 μM, showing that all estuaries were highly enriched with nitrogen, at least at some times. Mean macroalgal biomass ranged from 0 to 1,500 g wet wt m?2. However, neither nutrient concentrations nor algal biomass showed consistent seasonal patterns as maximum values occurred in different seasons in different estuaries. Three-dimensional principal components analysis followed by regression analyses confirmed that macroalgal abundance was not directly related to water or sediment N concentrations. Rather each of these southern California estuaries showed individual patterns in all measured variables, which were most likely induced by a suite of physical modifications unique to each system and its watershed. 相似文献
10.
R. Scott Warren Paul E. Fell Jonna L. Grimsby Erika L. Buck G. Chris Rilling Rachel A. Fertik 《Estuaries and Coasts》2001,24(1):90-107
Phragmites expansion rates (linear at 1–3% yr−1) and impacts of this expansion on high marsh macroinvertebrates, aboveground production, and litter decomposition fromPhragmites and other marsh graminoids were studied along a polyhaline to oligohaline gradient. These parameters, and fish use of creeks and high marsh, were also studied inPhragmites control sites (herbicide, mowing, and combined herbicide/mow treatments).Phragmites clones established without obvious site preferences on oligohaline marshes, expanding radially. At higher salinities,Phragmites preferentially colonized creekbank levees and disturbed upland borders, then expanded into the central marsh. Hydroperiods, but not salinities or water table, distinguishedPhragmites-dominated transects. Pooled samples ofPhragmites leaves, stems, and flowers decompose more slowly than other marsh angiosperms;Phragmites leaves alone decompose as or more rapidly than those of cattail. AbovegroundPhragmites production was 1,300 to 2,400 g m−2 (about 23% of this as leaves), versus 600–800 g m−2 for polyhaline to mesohaline meadow and 1,300 g m−2 for oligohaline cattail-sedge marsh. Macroinvertebrates appear largely unaffected byPhragmites expansion or control efforts; distribution and densities are unrelated to elevation or hydroperiod, but densities are positively related to litter cover. Dominant fish captured leaving flooded marsh wereFundulus heteroclitus andAnguilla rostrata; both preyed heavily on marsh macroinvertebrates.A. rostrata andMorone americana tended to be more common inPhragmites, but otherwise there were no major differences in use patterns betweenPhragmites and brackish meadow vegetation. SAV and macroalgal cover were markedly lower within aPhragmites-dominated creek versus one withSpartina-dominated banks. The same fish species assemblage was trapped in both plus a third within the herbicide/mow treatment. Fish biomass was greatest from theSpartina creek and lowest from thePhragmites creek, reflecting abundances ofF. heteroclitus. Mowing depressedPhragmites aboveground production and increased stem density, but was ineffective for control.Phragmites, Spartina patens, andJuncus gerardii frequencies after herbicide-only treatment were 0.53-0.21; total live cover was <8% with a heavy litter and dense standing dead stems. After two growing seasonsAgrostis stolonifera/S. patens/J. gerardii brackish meadow characterized most of the herbicide/mow treatment area;Phragmites frequency here was 0.53, contributing 3% cover. Both values more than doubled after four years; a single treatment is ineffective for long-termPhragmites control. 相似文献
11.
Enteromorpha intestinalis is a bloom-forming species of macroalgae associated with eutrophication. The objective of this study was to investigate how
this alga performs osmoregulation and nutrient uptake in order to proliferate under environmental conditions that covary with
eutrophication. We quantified the response ofE. intestinalis to salinity, light, and nutrients. We performed two short-term (48 h) laboratory experiments (salinity alone and salinity
× nutrients × light) to examine the algal responses of tissue water, potassium (K+), and nutrient (NO
3
−
and total N) content. Tissue water content decreased with increasing salinity, and although K+ concentration decreased from the initial concentration, it decreased less with increased salinity treatment demonstrating
two mechanisms to withstand short-term salinity fluctuation. The salinity × nutrient × light experiment showed that, in the
short term, light had an interaction with tissue K+. Total tissue N content was positively related to N treatment level, and light did not affect total nutrient concentration.
The effect of light was present whether the nutrients were present in the tissue as inorganic or organic forms. With reduced
light, we hypothe size that the assimilation of inorganic to organic N was energy limited. The ability of this alga to take
up available nutrients rapidly for growth and short-term osmoregulation, even under low light and salinity levels, helps to
explain the bloom potential ofE. intestinalis. 相似文献
12.
Jennifer Hauxwell James McClelland Peter J. Behr Ivan Valiela 《Estuaries and Coasts》1998,21(2):347-360
Macroalgal biomass and competitive interactions among primary producers in coastal ecosystems may be controlled by bottom-up processes such as nutrient supply and top-down processes such as grazing, as well as other environmental factors. To determine the relative importance of bottom-up and top-down processes under different nutrient loading conditions, we estimated potential amphipod and isopod grazer impact on a dominant macroalgal species in three estuaries in Waquoit Bay, Cape Cod, Massachusetts, that are subject to different nitrogen loading rates. We calculated growth increases and grazing losses in each estuary based on monthly benthic survey data of macrophyte biomass and herbivore abundance, field grazing rates of amphipods (Microdeutopus gryllotalpa andCymadusa compta) and an isopod (Idotea baltica) on the preferred and most abundant macroalga (Cladophora vagabunda) and laboratory grazing rates for the remaining species, and in situ macroalgal growth rates. As nitrogen loading rates increased, macroalgal biomass increased (3×), eelgrass (Zostera marina) was lost, and herbivore abundance decreased (1/4×). Grazing rates increased with relative size of grazer (I. baltica > C. compta > M. gryllotalpa) and, for two of the three species investigated, were faster on algae from the high-nitrogen estuary in comparison to the low-nitrogen estuary, paralleting the increased macroalgal tissue percent nitrogen with nitrogen load. Macroalgal growth rates increased (2×) with increasing nitrogen loading rate. The comparison between estimated growth increases versus losses ofC. vagabunda biomass to grazing suggested first, that grazers could lower macroalgal biomass in midsummer, but only in estuaries subject to lower nitrogen loads. Second, the impact of grazing decreased as nitrogen loading rate increased as a result of the increased macroalgal growth rates and biomass, plus the diminished abundance of grazers. This study suggests the relative impact of top-down and bottom-up controls on primary producers varies depending on rate of nitrogen loading, and specifically, that the impact of herbivory on macroalgal biomass decreases with increasing nitrogen load to estuaries. 相似文献
13.
Ronald M. Thom 《Estuaries and Coasts》1984,7(1):51-60
Twenty-nine taxa of macroalgae were collected from the Grays Harbor Estuary, Washington, from 17 April 1980 to 4 June 1981. Outer (oceanic) sites contained higher numbers of species than sites located in the inner portion of the estuary. Macroalgae were found in several habitats including attached to boulders, logs, tree roots, other algae, and angiosperms, as mats in sand, and drift.Fucus distichus ssp.edentatus andEnteromorpha intestinalis occurred at the greatest number of sites and were found throughout the year. The standing stock of the perennialFucus remained relatively consant, while that of anE. intestinalis andBlidingia minima var.subsalsa complex showed a significant peak between late spring and early summer as well as a winter minimum. The occurrence of most other taxa was highly seasonal. Net productivity rates for the most abundant macroalgal taxa were moderate to high relative to rates published for algae in other North American estuaries. It is concluded that, although inconspicuous, macroalgae may represent an important contributor of organic carbon to the Grays Harbor estuarine system. 相似文献
14.
Shahidul Islam Md. Manabu Hibino Taro Ohta Kouji Nakayama Masaru Tanaka 《Estuaries and Coasts》2006,29(3):519-529
Larval and juvenile Japanese temperate bass (Lateolabrax japonicus) samples were collected from a wide range of spatial gradients (covering a distance of approximately 30 km) in Chikugo estuary,
Ariake Bay, Japan over a period of 8 yr (1997–2004) in order to observe changes in diet. Gut contents were studied by separating,
identifying, counting, and estimating the dry weight of prey organisms. Copepod samples were collected during each cruise
to observe the numerical composition, abundance, and biomass in the estuary. Considerable spatial and temporal variations
were observed in copepod distributions in ambient water and the diets of the fish. Two distinctly different copepod assemblages
were identified in the estuary: One in the upper estuarine turbidity maximum (ETM), dominated by a single speciesSinocalanus sinensis and the other in the lower estuary consisting of a multispecies assemblage, dominated byOithona davisae, Acartia omorii, Paracalanus parvus, andCalanus sinicus. The gut content composition of the fish in the upper estuary was dominated byS. sinensis, while in the lower estuary, it consisted ofP. parvus, O. davisae, andA. omorii. Within the size group analyzed (13.0–27.0 mm SL), the smaller individuals were found to feed on a mixed diet composed of
smaller prey. The diets gradually shifted to bigger prey composed predominantly ofS. sinensis for larger size groups. Greater proportions of empty guts were recorded in the smaller individuals and dropped with increasing
fish size. Higher dry biomass of copepods in the environment, as well as higher dry weights of gut contents, were recorded
in the upper estuary, indicating that the upper estuarine ETM areas are important nursery grounds for the early life stages
of the Japanese temperate bass. The early life stages of the Japanese temperate bass are adapted to use the upstream nursery
grounds and ascending to the nursery areas to useS. sinensis is one of the key survival strategies of the Japanese temperate bass in the Chikugo estuary. 相似文献
15.
Margot L. Hessing-Lewis Sally D. Hacker Bruce A. Menge Steve S. Rumrill 《Estuaries and Coasts》2011,34(6):1169-1181
Land-based eutrophication is often associated with blooms of green macroalgae, resulting in negative impacts on seagrasses.
The generality of this interaction has not been studied in upwelling-influenced estuaries where oceanic nutrients dominate
seasonally. We conducted an observational and experimental study with Zostera marina L. and ulvoid macroalgae across an estuarine gradient in Coos Bay, Oregon. We found a gradient in mean summer macroalgal
biomass from 56.1 g dw 0.25 m−2 at the marine site to 0.3 g dw 0.25 m−2 at the riverine site. Despite large macroalgal blooms at the marine site, eelgrass biomass exhibited no seasonal or interannual
declines. Through experimental manipulations, we found that pulsed additions of macroalgae biomass (+4,000 mL) did not affect
eelgrass in marine areas, but it had negative effects in riverine areas. In upwelling-influenced estuaries, the negative effects
of macroalgal blooms are context dependent, affecting the management of seagrass habitats subject to nutrient inputs from
both land and sea. 相似文献
16.
Patterns of mangrove forest structure and soil nutrient dynamics along the Shark River estuary, Florida 总被引：1，自引：0，他引：1
The basal area and productivity of managrove wetlands are described in relation to selected soil properties to understand the general pattern of optimum forest stature at the mouth of estuaries in the Everglades, such as the Shark River Slough, Florida (U.S.). The basal area of mangroves decreases from 40.4 m2 ha−1 and 39.7 m2 ha−1 at two stations 1.8 km and 4.1 km from the estuary mouth to 20.7 m2 ha−1 and 19.6 m2 ha−1 at two sites 9.9 km and 18.2 km from the mouth, respectively. The gradient in basal area at these four sites is mostly the result of approximately 34 yr of growth since Hurricane Donna. Wood productivity is higher in the lower estuary (10.7 Mg ha−1 yr−1 and 12.0 Mg ha−1 yr−1) than in the upper estuary (3.2 Mg ha−1 yr−1 and 4.2 Mg ha−1 yr−1). Porewater salinity among these four mangrove sites during seasonal sampling in 1994 and 1995 ranged from 1.6 g kg−1 to 33.5 g kg−1, while sulfide was generally<0.15 mM at all sites. These soil values indicate that abiotic stress cannot explain the decrease in forest structure along this estuarine gradient. Concentrations of nitrogen (N) and phosphorus (P) are more closely related to patterns of forest development, with higher soil fertility at the mouth of the estuary as indicated by higher concentrations of extractable ammonium, total soil P, and available P, along with higher ammonium production rates. The more fertile sites of the lower estuary are dominated by Laguncularia racemosa, whereas the less fertile sites in the intermediate and upper estuary are dominated by Rhizophora mangle. Relative N mineralization per unit of total N is higher in the lower estuary and is related positively to concentrations of available P, indicating the importance of turnover rates and nutrient interactions to soil fertility. Concentrations of Ca-bound P per volume soil in the lower estuary is 40-fold higher than in the upper estuary, and along with an increase in residual P in the upper estuary, indicate a shift from mineral to organic P along the estuarine gradient. Mineral inputs to the mouth of Shark River estuary from the Gulf of Mexico (rather than upland inputs) apparently control the patterns of mangrove structure and productivity. 相似文献
17.
The present study focused on detecting variations in trophic relationships among blue crab (Callinectes sapidus) consumers according to water quality along two estuaries in North Carolina. Stable isotope (δ15N and δ13C) analyses of particulate organic matter and bivalve(Rangia cuneata andCorbicula fluminea) food sources were examined in combination with an Isosource mixing model. Results suggest that blue crab δ13C values increased significantly with increasing salinity from upper to lower sites along the Neuse River estuary (NRE; R2
= 0.87, p < 0.01) and Alligator River estuary (R2 = 0.92, p < 0.01). There was a positive relationship between blue crab δ15N values and nitrate concentrations for the NRE (R2 = 0.48, p = 0.12). This study found that blue crab δ13C values increased with salinity from upper to lower regions along both estuaries. Results suggest that blue crab production
may have used alternative food sources that were isotopically (δ13C) depleted, especially in the upper NRE, and enriched sources in the mid to lower regions of both estuaries. Consumers sampled
from the upper NRE may be influenced by higher nitrogen input from urban land use and municipal wastewater. 相似文献
18.
C. A. Currin S. C. Wainright K. W. Able M. P. Weinstein C. M. Fuller 《Estuaries and Coasts》2003,26(2):495-510
The invasion ofPhragmites australis into tidal marshes formerly dominated bySpartina alterniflora has resulted in considerable interest in the consequences of this invasion for the ecological functions of marsh habitat. We examined the provision of trophic support for a resident marsh fish,Fundulus heteroclitus, in marshes dominated byP. australis, byS. alterniflora, and in restored marshes, using multiple stable isotope analysis. We first evaluated our ability to distinguish among potential primary producers using the multiple stable isotope approach. Within a tidal creek system we found significant marsh and elevation effects on microalgal isotope values, and sufficient variability and overlap in primary producer isotope values to create some difficulty in identifying unique end members. The food webs supportingF. heteroclitus production were examined using dual isotope plots. At both sites, the δ13C values ofF. heteroclitus were clustered over values for benthic microalgae (BMI) and approximately midway between δ13C values ofSpartina andPhragmites. Based on comparisons of fish and primary producer δ13C, δ15N, and δ34S values, and consideration ofF. heteroclitus feeding habits, we conclude that BMI were a significant component of the food web supportingF. heteroclitus in these brackish marshes, especially recently-hatched fish occupying pools on the marsh surface. A 2‰ difference in δ13C betweenFundulus occupying nearly adjacentSpartina andPhragmites marshes may be indicative of relatively less reliance on BMI and greater reliance onPhragmites production inPhragmites-dominated marshes, a conclusion consistent with the reduced BMI biomass found inPhragmites marshes. The mean δ13C value ofF. heteroclitus from restored marshes was intermediate between values of fish from naturally occurringSpartina marshes and areas invaded byPhragmites. We also examined the isotopic evidence for ontogenetic changes in the trophic position of larval and juvenileF. heteroclitus. We found significant positive relationships betweenF. heteroclitus δ15N values and total length, reflective of an increase in trophic position as fish grow.F. heteroclitus δ15N values indicate that these fish are feeding approximately two trophic levels above primary producers. 相似文献
19.
The response of deltaic emergent marsh vegetation to increases in precipitation was examined over a 14-mo period at three
sites in the lower Nueces Estuary in south Texas. At all three sites, significant changes in plant biomass, percent cover,
and allocation of aboveground and belowground tissues were associated with more than double the rainfall in late winter and
early spring 1992 compared to the previous year and the 50-yr average for this region. Water column salinities, which ranged
from 10‰ to 35‰ at all three sites in 1991, remained below 10‰ through August 1992. Significant changes in marsh vegetative
structure included decreases in bare space, increases in the percent cover and aboveground biomass of a relatively less salt
tolerant halophytes (Borrichia frutescens), and significant increases in root:shoot ratios inB. frutescens, Batis maritima andSuaeda linearis (inSalicornia virginica root:shoot ratios decreased significantly). Higher precipitation generally led to an overall increase in the biomass of most
marsh perennials, but these increases were not statistically significant. For one species,Lycium carolinianum, additional rainfall extended its growing season through August 1992, 2 mo longer than in the previous year. The expansion
(+58%) ofB. frutescens at one site was also coincident with the significant loss ofB. maritima, whose cover decreased nearly 20%. In an ecological context, these responses suggest that precipitation events in arid environments
may be considered a major physical disturbance that can result in large changes in the composition and relative abundance
of emergent vascular plants over a relatively short period. The long-term significance of these changes is unknown and demonstrates
the value of ecological studies that are conducted over several years for a more complete understanding of the dynamic processes
that regulate marsh productivity. 相似文献
20.
We compared nekton densities over a range of measured flooding conditions and locations withinPhragmites australis andSpartina alterniflora (salt marsh cordgrass) at the Charles Wheeler Salt Marsh, located on the lower Housatonic River estuary in southwestern Connecticut.
Nekton were sampled on nine spring high tide events from May to October 2000 using bottomless lift nets positioned between
0–5 and 10–20 m from the creek edge. Flooding depth, duration, and frequency were measured from each vegetation type during
each sampling month. Benthic macroinvertebrate density was also measured within each vegetation type in May, July, and September.
Frequency of flooding was 52% lower and flooding depth and duration were also significantly reduced inP. australis relative toS. alterniflora. A total of 4,197 individuals representing 7 species, mostlyPalaemonetes pugio (dagger-blade grass shrimp) andFundulus heteroclitus (common mummichog), were captured.P. pugio densities were significantly greater inS. alterniflora as were benthic macroinvertebrate density and taxa richness during May, but not during June or October. Total fish density
was not significantly different betweenP. australis andS. alterniflora and was independent of location on the marsh. Significantly more juvenileF. heteroclitus were collected withinS. alterniflora relative toP. australis in June and July, suggesting that recruitment of this species may be lower inP. australis habitat. Fish density generally did not vary predictably across the range of flooding depth and duration; there was a positive
relationship between flooding depth and fish density inS. alterniflora. The measured reduction in flooding frequency (52%) withinP. australis at the Housatonic site would result in an average total monthly fish use, expressed as density, of 447 ind m−2 forP. australis and 947 ind m−2 forS. alterniflora. WhenP. australis expansion results in reduction of flooding frequency and duration, nekton community composition can change, access to the
marsh surface is reduced twofold, and nursery habitat function may be impaired. 相似文献