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1.
Beginning in late 1987 Florida Bay experienced a large and unprecedented die-off ofThalassia testudinum. The die-off occurred only in stands of denseT. testudinum. We initiated an experimental monitoring effort in 1989 to attempt to ascertain the cause of this die-off phenomenon. From 1989 to 1995 the abundance and productivity ofT. testudinum was measured at five stations associated with the seagrass die-off and three stations where no die-off had occurred (including one on the seaside of Key Largo, outside of Florida Bay). Early in the study the salinity was very high, exceeding 46 psu, but it has decreased to 29–38 psu in recent years. Seagrass standing crop and either short-shoot density or mass per short shoot declined at nearly all stations, including the stations without die-off (unaffected stations). Over the course of the study, areal productivity declined at three die-off stations; but mass-specific productivity increased at all die-off stations and one unaffected station. Seasonality was pronounced; detrended standardized residuals showed responses for all of the seagrass parameters to be greater than the yearly mean in spring and summer and less than the mean in fall and winter. Detrended residuals also showed decreased productivity to be correlated with increased salinities in the summer despite a long-term record of declining salinities. We propose a conceptual model of the seagrass die-off phenomenon. We document that salinity does contribute to stress onT. testudinum in Florida Bay, but salinity is believed to be only one contributing factor to the loss of seagrasses. The documented increase in the mass-specific productivity ofT. testudinum over the period 1989–1995 suggests seagrasses are growing rapidly in Florida Bay by 1995; we predict that the loss ofT. testudinum may be slowing down and that recovery is possible. 相似文献
2.
Margaret O. Hall Michael J. Durako James W. Fourqurean Joseph C. Zieman 《Estuaries and Coasts》1999,22(2):445-459
The Florida Bay ecosystem has changed substantially in the past decade, and alterations in the seagrass communities have been particularly conspicuous. In 1987 large areas ofThalassia testudinum (turtlegrass) began dying rapidly in western Florida Bay. Although the rate has slowed considerably, die-off continues in many parts of the bay. Since 1991, seagrasses in Florida Bay have been subjected to decreased light availability due to widespread, persistent microalgal blooms and resuspended sediments. In light of these recent impacts, we determined the current status of Florida Bay seagrass communities. During the summer of 1994, seagrass species composition, shoot density, shoot morphometrics, and standing crop were measured at 107 stations. Seagrasses had been quantified at these same stations 10 yr earlier by Zieman et al. (1989).T. testudinum was the most widespread and abundant seagrass species in Florida Bay in both 1984 and 1994, and turtlegrass distribution changed little over the decade. On a baywide basis,T. testudinum density and biomass declined significantly between surveys; mean short-shoot density ofT. testudinum dropped by 22% and standing crop by 28% over the decade.T. testudinum decline was not homogeneous throughout Florida Bay; largest reductions in shoot density and biomass were located principally in the central and western bay. Percent loss ofT. testudinum standing crop in western Florida Bay in 1994 was considerably greater at the stations with the highest levels of standing crop in 1984 (126–215 g dry wt m−2) than at the stations with lower levels of biomass. While turtlegrass distribution remained consistent over time, both the distribution and abundance of two other seagrasses,Halodule wrightii andSyringodium filiforme, declined substantially between 1984 and 1994. Baywide,H. wrightii shoot density and standing crop declined by 92%, andS. filiforme density and standing crop declined by 93% and 88%, respectively, between surveys. Patterns of seagrass loss in Florida Bay between 1984 and 1994 suggest die-off and chronic light reductions were the most likely causes for decline. If die-off and persistent water-column turbidity continue in Florida Bay, the long-term future of seagrasses in the bay is uncertain. 相似文献
3.
Darrell Anthony Herbert William B. Perry Bernard J. Cosby James W. Fourqurean 《Estuaries and Coasts》2011,34(5):973-992
Historic changes in water-use management in the Florida Everglades have caused the quantity of freshwater inflow to Florida
Bay to decline by approximately 60% while altering its timing and spatial distribution. Two consequences have been (1) increased
salinity throughout the bay, including occurrences of hypersalinity, coupled with a decrease in salinity variability, and
(2) change in benthic habitat structure. Restoration goals have been proposed to return the salinity climates (salinity and
its variability) of Florida Bay to more estuarine conditions through changes in upstream water management, thereby returning
seagrass species cover to a more historic state. To assess the potential for meeting those goals, we used two modeling approaches
and long-term monitoring data. First, we applied the hydrological mass balance model FATHOM to predict salinity climate changes
in sub-basins throughout the bay in response to a broad range of freshwater inflow from the Everglades. Second, because seagrass
species exhibit different sensitivities to salinity climates, we used the FATHOM-modeled salinity climates as input to a statistical
discriminant function model that associates eight seagrass community types with water quality variables including salinity,
salinity variability, total organic carbon, total phosphorus, nitrate, and ammonium, as well as sediment depth and light reaching
the benthos. Salinity climates in the western sub-basins bordering the Gulf of Mexico were insensitive to even the largest
(5-fold) modeled increases in freshwater inflow. However, the north, northeastern, and eastern sub-basins were highly sensitive
to freshwater inflow and responded to comparatively small increases with decreased salinity and increased salinity variability.
The discriminant function model predicted increased occurrences of Halodule wrightii communities and decreased occurrences of Thalassia testudinum communities in response to the more estuarine salinity climates. The shift in community composition represents a return to
the historically observed state and suggests that restoration goals for Florida Bay can be achieved through restoration of
freshwater inflow from the Everglades. 相似文献
4.
Anna R. Armitage Thomas A. Frankovich Kenneth L. Heck James W. Fourqurean 《Estuaries and Coasts》2005,28(3):422-434
We examined the spatial extent of nitrogen (N) and phosphorus (P) limitation of each of the major benthic primary producer groups in Florida Bay (seagrass, epiphytes, macroalgae, and benthic microalgae) and characterized the shifts in primary producer community composition following nutrient enrichment. We established 24 permanent 0.25-m2 study plots at each of six sites across. Florida Bay and added N and P to the sediments in a factorial design for 18 mo. Tissue nutrient content of the turtlegrassThalassia testudinum revealed a spatial pattern in P limitation, from severe limitation in the eastern bay (N:P>96:1), moderate limitation in two intermediate sites (approximately 63:1), and balanced with N availability in the western bay (approximately 31:1). P addition increasedT. testudinum cover by 50–75% and short-shoot productivity by up to 100%, but only at the severely P-limited sites. At sites with an ambient N:P ratio suggesting moderate P limitation, few seagrass responses to nutrients occurred. Where ambientT. testudinum tissue N:P ratios indicated N and P availability was balanced, seagrass was not affected by nutrient addition but was strongly influenced by disturbance (currents, erosion). Macroalgal and epiphytic and benthic microalgal biomass were variable between sites and treatments. In general, there was no algal overgrowth of the seagrass in enriched conditions, possibly due to the strength of seasonal influences on algal biomass or regulation by grazers., N addition had little effect on any benthic primary producers throughout the bay. The Florida Bay benthic primary producer community was P limited, but P-induced alterations of community structure were not uniform among primary producers or across Florida Bay and did not always agree with expected patterns of nutrient limitation based on stoichiometric predictions from field assays ofT. testudinum tissue, N:P ratios. 相似文献
5.
We evaluate if the distribution and abundance ofThalassia testudinum, Syringodium filiforme, andHalodule wrightii within Biscayne Bay, Florida, are influenced by salinity regimes using, a combination of field surveys, salinity exposure
experiments, and a seagrass simulation model. Surveys conducted in June 2001 revealed that whileT. testudinum is found throughout Biscayne Bay (84% of sites surveyed),S. filiforme andH wrightii have distributions limited mainly to the Key Biscayne area.H. wrightii can also be found in areas influenced by canal discharge. The exposure of seagrasses to short-term salinity pulses (14 d,
5–45‰) within microcosms showed species-specific susceptibility to the salinity treatments. Maximum growth rates forT testudinum were observed near oceanic salinity values (30–40‰) and lowest growth rates at extreme values (5‰ and 45‰).S. filiforme was the most susceptible seagrass species; maximum growth rates for this species were observed at 25‰ and dropped dramatically
at higher and lower salinity.H. wrightii was the most tolerant, growing well at all salinity levels. Establishing the relationship between seagrass abundance and
distribution and salinity is especially relevant in South Florida where freshwater deliveries into coastal bays are influenced
by water management practices. The seagrass model developed by Fong and Harwell (1994) and modified here to include a shortterm
salinity response function suggests that freshwater inputs and associated decreases in salinity in nearshore areas influence
the distribution and growth of single species as well as modify competitive interactions so that species replacements may
occur. Our simulations indicate that although growth rates ofT. testudinum decrease when salinity is lowered, this species can still be a dominant component of nearshore communities as confirmed by
our surveys. Only when mean salinity values are drastically lowered in a hypothetical restoration scenario isH. wrightii able to outcompeteT. testudinum. 相似文献
6.
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
7.
Estuaries located in the northern Gulf of Mexico are expected to experience reduced river discharge due to increasing demand for freshwater and predicted periods of declining precipitation. Changes in freshwater and nutrient input might impact estuarine higher trophic level productivity through changes in phytoplankton quantity and quality. Phytoplankton biomass and composition were examined in Apalachicola Bay, Florida during two summers of contrasting river discharge. The <20 μm autotrophs were the main component (92?±?3 %; n?=?14) of phytoplankton biomass in lower (<25 psu) salinity waters. In these lower salinity waters containing higher dissolved inorganic nutrients, phycocyanin containing cyanobacteria made the greatest contribution to phytoplankton biomass (69?±?3 %; n?=?14) followed by <20 μm eukaryotes (19?±?1 %; n?=?14), and phycoerythrin containing cyanobacteria (4?±?1 %; n?=?14). In waters with salinity from 25 to 35 psu that were located within or in close proximity to the estuary, >20 μm diatoms were an increasingly (20 to 70 %) larger component of phytoplankton biomass. Lower summer river discharges that lead to an areal contraction of lower (5–25 psu) salinity waters composed of higher phytoplankton biomass dominated by small (<20 μm) autotrophs will lead to a concomitant areal expansion of higher (>25 psu) salinity waters composed of relatively lower phytoplankton biomass and a higher percent contribution by >20 μm diatoms. A reduction in summer river discharge that leads to such a change in quantity and quality of estuarine phytoplankton available will result in a reduction in estuarine zooplankton productivity and possibly the productivity of higher trophic levels. 相似文献
8.
The responses of Spartina alterniflora above- and belowground biomass to various combinations of N, P, and Fe were documented in a 1-year field experiment in a
Louisiana salt marsh. Five levels of N additions to 0.25 m2 plots resulted in 18% to 138% more live aboveground biomass compared to the control plots and higher stem densities, but
had no effect on the amount of live belowground biomass (roots and rhizomes; R&R). There was no change in the aboveground
biomass when P or Fe was added as part of a factorial experiment of +P, +N, and +Fe additions, but there was a 40% to 60%
decrease in the live belowground biomass, which reduced the average R&R:S ratio by 50%. The addition of various combinations
of nutrients had a significant affect on the belowground biomass indicating that the addition of P, not N, eased the need
for root foraging activity. The end-of-the-growing-season N:P molar ratios in the live above- and belowground tissues of the
control plot was 16.4 and 32.7, respectively. The relative size of the belowground standing stocks of N and P was higher than
in the aboveground live tissues, but shifted downwards to about half that in fertilized plots. We conclude that the aboveground
biomass was directly related to N availability, but not P, and that the accumulation of belowground biomass was not limited
by N. We suggest that the reduction in belowground biomass with increased P availability, and the lower absolute and relative
belowground standing stocks of P as plant tissue N:P ratios increased, is related to competition with soil microbes for P.
One implication for wetland management and restoration is that eutrophication may be detrimental to long-term salt marsh maintenance
and development, especially in organic-rich wetland soils. 相似文献
9.
Kelly M. Darnell Tim J. B. Carruthers Patrick Biber Ioannis Y. Georgiou Thomas C. Michot Ronald G. Boustany 《Estuaries and Coasts》2017,40(5):1288-1300
Seagrasses are submerged marine plants that are anchored to the substrate and are therefore limited to assimilating nutrients from the surrounding water column or sediment, or by translocating nutrients from adjacent shoots through the belowground rhizome. As a result, seagrasses have been used as reliable ecosystem indicators of surrounding nutrient conditions. The Chandeleur Islands are a chain of barrier islands in the northern Gulf of Mexico that support the only marine seagrass beds in Louisiana, USA, and are the sole location of the seagrass Thalassia testudinum across nearly 1000 km of the coastline from west Florida to central Texas. Over the past 150 years, the land area of the Chandeleur Islands has decreased by over half, resulting in a decline of seagrass cover. The goals of this study were to characterize the status of a climax seagrass species at the Chandeleur Islands, T. testudinum, in terms of leaf nutrient (nitrogen [N] and phosphorus [P]) changes over time, from 1998 to 2015, and to assess potential drivers of leaf nutrient content. Thalassia testudinum leaf nutrients displayed considerable interannual variability in N and P content and molar ratios, which broadly mimicked patterns in annual average dissolved nutrient concentrations in the lower Mississippi River. Hydrological modeling demonstrated the potential for multiple scenarios that would deliver Mississippi River water, and thus nutrients, to T. testudinum at the Chandeleur Islands. Although coastal eutrophication is generally accepted as the proximate cause for seagrass loss globally, there is little evidence that nutrient input from the Mississippi River has driven the dramatic declines observed in seagrasses at the Chandeleur Islands. Rather, seagrass cover along the Chandeleur Islands appears to be strongly influenced by island geomorphological processes. Although variable over time, the often elevated nutrient levels of the climax seagrass species, T. testudinum, which are potentially driven by river-derived nutrient inputs, raises an important consideration of the potential loss of the ecosystem functions and services associated with these declining seagrass meadows. 相似文献
10.
An investigation of seagrass-epiphyte controlling factors was conducted within aThalassia testudinum meadow in Florida Bay from March 2000 to April 2001. Univariate and multivariate analyses were performed using water column
nutrient concentrations, temperature, salinity, and turbidity, and gastropod grazer abundances, seagrass leaf area index,
and leaf turnover rate data to explain the variation in total epiphyte standing stock, epiphyte chlorophylla, and epiphyte autotrophic index. Turbidity was positively correlated with total epiphyte standing stock and accounted for
the most variation. Observations of adhered sediment onT. testudinum leaves and the combination, of increased total epiphyte standing stocks and low autotrophic indices observed in February
and April 2001 suggest that the settling of resuspended sediments following turbidity events is one of the temporal mechanisms
for increased epiphyte accumulation. Total epiphyte standing stock was also negatively correlated with the abundance of a
robust gastropod grazer community dominated byTurbo castanea, Tegula fasciata, andModulus modulus. Distinct temporal size cohorts ofT. castanea andT. fasciata throughout the study period suggest recruitment in spring and an annual lifespan. Nutrient concentrations can also account
for some of the temporal variation in total epiphyte standing stock, epiphyte chlorophylla, and autotrophic index. The low variation ofT. testudinum leaf turnover rates was unable to account for any of the variation in the epiphyte parameters. 相似文献
11.
Salinities occupied by different life stages of bay anchovy (Anchoa mitchilli) were compared over annual cycles at 128 stations in 12 Florida estuaries. The comparison included eight stations in an oligotrophic,
groundwater-based estuary in which all life stages were rare or absent. At other stations, adults, eggs, and early larvae
occurred in intermediate to high salinities (10-30 psu) with no apparent central salinity tendency. The larva-juvenile transition
was marked by an upstream shift to lower salinities (0-15 psu), also with no central salinity tendency. Mean salinities of
the juvenile catch were strongly dependent on the salinities of the sampling effort. This dependence was strongest in estuaries
that had weak horizontal salinity gradients. Weak salinity gradients were either natural or resulted from estuarine dams.
After using nonlinear regression to account for the interaction between effort salinity and catch salinity, catch salinities
were found to be similar from year to year within estuaries, but widely different among estuaries, with interestuarine differences
ranging as high as 10–13 psu. Lower salinities were occupied by juveniles in estuaries that had long freshwater turnover times.
Inherent geomorphic and inflow-related effects on the distribution of prey resources, coupled with an ontogenetic diet shift,
are proposed as the explanation for both the habitat shift and the strong interestuarine variability in salinity at capture. 相似文献
12.
Eight meadows of the seagrassThalassia testudinum Banks ex König representing a gradient of freshwater influence in Charlotte Harbor, Florida (United States), were sampled on a bimonthly basis from April 1995 to August 1996. Spatial and temporal variation in the density, biomass, productivity, and epiphyte loads of short shoots were determined. Physical factors such as water temperature, salinity, and light extinction coefficients were also measured. Areal blade production (g dw m?2 d?1) ofT. testudinum was not strongly associated with water temperature, salinity, or the amount of subsurface irradiance reaching the bottom at each station. Variation in production could be described by a linear combination of the independent variables water temperature and salinity. Water clarity (expressed as the percent of subsurface irradiance reaching the bottom) was positively related to salinity. The lack of a clear relationship between water clarity and areal production was probably due to water clarity being highest during times of the year when water temperatures were too cold to support growth ofT. testudinum. Our results suggest that seagrass light requirements determined by averaging irradiance levels measured during the growing season might be more relevant than those established by averaging light measurements collected throughout the year. The use of field studies for estimating lower salinity tolerances of seagrasses might be inappropriate for those systems where water clarity is positively associated with salinity. 相似文献
13.
Thomas K. Frazer Sky K. Notestein Charles A. Jacoby Chanda Jones Littles Stephanie R. Keller Robert A. Swett 《Estuaries and Coasts》2006,29(6):943-953
Hurricanes and other major storms cause acute changes in salinity within Florida's streams and rivers. Winddriven tidal surges
that increase salinities may have long-lasting effects on submersed aquatic vegetation (SAV) and the associated fauna. We
investigated potential effects of salinity pulses on SAV in Kings Bay, Florida, by subjecting the three most common macrophytes,Vallisneria americana, Myriophyllum spicatum., andHydrilla verticillata, to simulated salinity pulses. In Kings Bay, we documented changes in salinity during three storms in September 2004 and
measured biomass and percent cover before and after these storms. During experiments, macrophytes were exposed to salinities
of 5‰, 15‰, or 25‰ for 1, 2, or 7 d, with a 28-d recovery period in freshwater. Relative to controls, plants subjected to
salinities of 5‰ exhibited few significant decreases in growth and no increase in mortality. All three species exhibited decreased
growth in salinities of 15‰ or 25‰.H. verticillata, exhibited 100% mortality at 15‰ and 25‰, irrespective of the duration of exposure.M. spicatum andV. american exhibited increased mortality after 7-d exposures to 15‰ or any exposure to 25‰ Maximum daily salinities in Kings Bay approached
or exceeded 15‰ after each of the three storms, with pulses generally lasting less than 2 d. Total aboveground biomass and
percent cover of vascular plants, were reduced following the storms.M. spicatum exhibited an 83% decrease in aboveground biomass and an 80% decrease in percent cover.H. verticillata exhibited a 47% and 15% decline in biomass and percent cover, respectively.V. americana, exhibited an 18% increase in aboveground biomass and a 37% increase in percent cover, which suggests greater tolerance of
salinity pulses and release from competition with the invasiveH. verticillata andM. spicatum. Our results indicate that rapid, storm-induced pulses of high salinity can have important consequences for submersed aquatic
vegetation, restoration efforts, and management of invasive species. 相似文献
14.
The effects of light and salinity onVallisneria americana (wild celery) were studied in outdoor mesocosms for an entire growing season. Morphology, production, photosynthesis, and
reproductive output were monitored from sprouting of winter buds to plant senescence and subsequent winter bud formation under
four salinity (0, 5, 10, and 15 psu) and three light (2%, 8%, and 28% of surface irradiance) regines. Chlorophylla fluorescence was used to examine photochemical efficiency and relative electron transport rate. High salinity and low light
each stunted plant growth and reproduction. Production (biomass, rosette production, and leaf area index) was affected more
by salinity than by light, apparently because of morphological plasticity (increased leaf length and width), increased photosynthetic
efficiency, and increased chlorophyll concentrations under low light. Relative maximum electron transport rate (ETRmax) was highest in the 28% light treatment, indicating increased photosynthetic capacity. ETRmax was not related to salinity, suggesting that the detrimental effects of salinity on production were through decreased photochemical
efficiency and not decreased photosynthetic capacity. Light and salinity effects were interactive for measures of production,
with negative salinity effects most apparent under high light conditions, and light effects found primarily at low salinity
levels. For most production and morphology parameters, high light ameliorated salinity stress to a limited degree, but only
between the 0 and 5 psu regimes. Growth was generally minimal in all of the 10 and 15 psu treatments, regardless of light
level. Growth was also greatly reduced at 2% and 8% light. Flowering and winter bud production were impaired at 10 and 15
psu and at 2% and 8% light. Light requirements at 5 psu may be approximately 50% higher than at 0 psu. Because of the interaction
between salinity and light requirements for growth, effective management of SAV requires that growth requirements incorporate
the effects of combined stressors. 相似文献
15.
We report the first data on belowground tissue mass and nitrogen (N) concentration forSpartina foliosa in southern California, assessing one natural and two constructed marshes on San Diego Bay. Biomass at the natural marsh was low compared to that of otherSpartina spp., but higher than values reported forS. foliosa in northern California. In sandy constructed marshes planted 5 and 10 years before this study,S. foliosa had lower belowground tissue N, lower N crop (%N×biomass), and shallower roots than in the adjacent natural marsh. We took advantage of a 2-yr, large-scale fertilization project being performed in the older constructed marsh and examined biomass and N storage after N additions. Although there was a trend toward N accumulation with fertilization, N crop remained at approximately 50% of natural marsh levels, unlike the large aboveground responses to N addition in our previous studies. Lower belowground reserves help to explain poor aerial growth in the created marshes and suggest the need for finer sediments (with greater potential for holding and supplying nutrients) to sustain (S. foliosa. While fine sediments are beginning to accumulate on the surface of the created marshes, vertical accretion is more likely to shift the plant community toward other species than to enhanceS. foliosa growth. We suggest salvaging and importing fine, organic marsh sediments or providing organic amendments to establish proper substrate conditions. Overexcavating and allowing fine sediments to accumulate remains an option, although the time scale is unpredictable due to the stochasticity of accretion events. 相似文献
16.
Jerome J. Lorenz 《Estuaries and Coasts》1999,22(2):500-517
Historically, large volumes of fresh water from the Everglades reached Florida Bay in the form of overland sheet flow. South Florida's extensive canal system has diverted fresh water from its historic course, resulting in shorter hydroperiods and higher salinities than would have occurred in an unaltered system. The mixing zone between the freshwater Everglades and euryhaline Florida Bay is primarily characterized as a dwarf red mangrove forest. The small, demersal fishes found in this habitat are an important food source for a variety of predators and are excellent bioindicators for both short-term and long-term perturbations in the system. I examine the effect of fluctuating water level, salinity, and temperature on this fish community in order to better understand the impact water diversion has had on the ecotone. Fish were collected at four sites within the ecotone over a t-yr period using a 9-m2 drop trap. Principal components analysis was used to generate 10 composite variables (PCs) from a temporal array of 59 physicochemical variables. These composite variables were used in regression analyses to evaluate spatial and temporal changes in the fish community. Regression analysis indicated fish density was significantly related to short-term and long-term changes in water level and with long-term temperature variation (r2=0.50). An ANOVA of density between sites supports the regression results, indicating that sites with longer hydroperiod had higher density than sites with shorter hydroperiod. The impact of changes in density on biomass was reflected by regression analysis, which indicated that increased water level and decreased variability in depth were correlated with higher biomass (r2=0.61). Biomass was also influenced by changes in the salinity regime, presumably through increases in individual fish body size or through a shift in the community toward heavier-bodied fish species. An ANOVA of biomass between sites indicates sites with longer freshwater periods had higher biomass than sites with shorer freshwater periods. The first two axes of a detrended correspondence analysis on community biomass explained 59.2% of the variance in the community and supported the hypothesis that salinity was a primary determinant of community structure. These results indicate historic changes in water deliver could have altered the mangrove fish community, thereby lowering prey availability for higher trophic levels. 相似文献
17.
Thomas Anthony Frankovich Douglas Morrison James Warren Fourqurean 《Estuaries and Coasts》2011,34(1):20-31
Annual mean salinity, light availability, and sediment depth to bedrock structured the submerged aquatic vegetation (SAV)
communities in subtropical mangrove-lined estuaries. Three distinct SAV communities (i.e., Chara group, Halodule group, and Low SAV coverage group) were identified along the Everglades–Florida Bay ecotone and related to water quality
using a discriminant function model that predicted the type of plant community at a given site from salinity, light availability,
and sediment depth to bedrock. Mean salinity alone was able to correctly classify 78% of the sites and reliably separated
the Chara group from the Halodule group. The addition of light availability and sediment depth to bedrock increased model accuracy to 90% and further distinguished
the Chara group from the Halodule group. Light availability was uniquely valuable in separating the Chara group from the Low SAV coverage group. Regression analyses identified significant relationships between phosphorus concentration,
phytoplankton abundance, and light availability and suggest that a decline in water transparency, associated with increasing
salinity, may have also contributed to the historical decline of Chara communities in the region. This investigation applies relationships between environmental variables and SAV distribution
and provides a case study into the application of these general principals to ecosystem management. 相似文献
18.
Net primary production was measured in three characteristic salt marshes of the Ebre delta: anArthrocnemum macrostachyum salt marsh,A. macrostachyum-Sarcocornia fruticosa mixed salt marsh andS. fruticosa salt marsh. Above-ground and belowground biomass were harvested every 3 mo for 1 yr. Surface litter was also collected from each plot. Aboveground biomass was estimated from an indirect non-destructive method, based on the relationship between standing biomass and height of the vegetation. Decomposition of aboveground and belowground components was studied by the disappearance of plant material from litter bags in theS. fruticosa plot. Net primary production (aboveground and belowground) was calculated using the Smalley method. Standing biomass, litter, and primary production increased as soil salinity decreased. The annual average total aboveground plus belowground biomass was 872 g m−2 in theA. macrostachyum marsh, 1,198 g m−2 in theA. macrostachyum-S. fruticosa mixed marsh, and 3,766 g m−2 in theS. fruticosa biomass (aboveground plus belowground) was 226, 445, and 1,094 g m−2, respectively. Total aboveground plus below-ground net primary production was 240, 1,172, and 1,531 g m−2 yr−1. There was an exponential loss of weight during decomposition. Woody stems and roots, the most recalcitrant material, had 70% and 83% of the original material remaining after one year. Only 20–22% of leafy stem weight remained after one year. When results from the Mediterranean are compared to other salt marshes dominated by shrubbyChenopodiaceae in Mediterranean-type climates, a number of similarities emerge. There are similar zonation patterns, with elevation and maximum aboveground biomass and primary production occurring in the middle marsh. This is probably because of stress produced by waterlogging in the low marsh and by hypersalinity in the upper marsh. 相似文献
19.
The seasonal pattern of phytoplankton biomass (chlorophyll and particulate organic carbon) and the salinity-related pattern
of phytoplankton biomass and size composition were determined in Apalachicola Bay, Florida, throughout 2004. Phytoplankton
biomass was highest during summer and lowest during winter. During summer, phytoplankton biomass was highest in waters with
salinity between about 5 and 23. In waters between 5 and 23, phytoplankton biomass was primarily (> 50%) composed of < 5 μm
cells. The results from this study support the idea that a microbial food web characterizes mass and energy flow through the
planktonic food web in Apalachicola Bay and other estuaries. During winter, the carbonxhlorophylla ratio averaged 56 ± 60 (standard deviation). During summer, the ratio ranged from 23 to 345, with highest values occurring
in waters with salinity between about 8 and 22. The carbonxhlorophylla ratio was positively related to the percent of chlorophyll < 5 μm in size during summer. 相似文献
20.
John D. Lopez Mark S. Peterson Jake Walker Gretchen L. Grammer Mark S. Woodrey 《Estuaries and Coasts》2011,34(1):148-158
The saltmarsh topminnow (Fundulus jenkinsi) is federally listed as a Species of Concern due to a its rarity, impacts from human activities, and lack of information
on its biology and ecology. From 2007 through 2008, we used Breder traps to fish the marsh edge on a falling tide in four
regions from Louisiana through the Florida panhandle during winter, spring, and summer periods. Out of 2,108 Breder traps
deployed, 661 F. jenkinsi were collected as far east as Escambia Bay, Florida, with Weeks Bay, National Estuarine Research Reserve (NERR), Alabama,
yielding the highest F. jenkinsi abundance. Principal component analysis (PCA) was used to ordinate physical–chemical data into two meaningful components:
a geomorphic axis (water depth, bank slope, and plant stem density) and a seasonal/spatial axis of species occurrence (water
temperature, salinity, and turbidity). PCA showed a higher mean catch-per-unit-effort (CPUE) in environments comprised of
low to moderate stem density (<25 stems/0.25 m−2), depth (<25 cm), bank slope (<15°), turbidity (<30 NTU), and salinity (<16) coupled with spring and early summer water temperatures
(>15°C). F. jenkinsi CPUE was significantly higher in Spartina cynosuroides marsh edge compared with five other habitat types, even though it was one of the least sampled habitats. This species appears
to be collected more frequently and in higher CPUE in small dendritic creeks off of main channels than suggested by our previous
work in main channel edge habitat. This suggests that small creeks are important vectors for marsh access and supports the
value of the dendritic nature of salt marshes to marsh residents. 相似文献