首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 0 毫秒
1.
In September 2004, the Loxahatchee River Estuary was affected by Hurricanes Frances and Jeanne, which resulted in a monthly rainfall record of 610 mm and abnormally high freshwater discharges to the system. The occurrence, density, and biomass ofSyringodium filiforme in the Loxahatchee River Estuary declined significantly following the September 2004 storms based on 15 mo of pre-hurricane monitoring and 12 mo of post-hurricane monitoring. Throughout posthurricane monitoring,S. filiforme showed no sign of recovery, thoughHalophila johnsonii increased considerably during the post-hurricane period. Freshwater discharges resulting from the September 2004 hurricanes lowered minimum daily salinity values to near zero and increased standard deviation of daily salinity values to 11‰. Extremely low minimum daily salinity values and high daily salinity fluctuations likely resulted in the observed decline ofS. filiforme. We advise the use of minimum daily salinity values when assessing seagrass habitat suitability or when modeling the effects of alternative water management scenarios.  相似文献   

2.
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.
Decreased salinity and submarine light associated with hurricanes of 2004?C2005 impacted seagrass habitats in the Florida coastal zone. A combination of salinities ??20 and light attenuation ??1.5?m?1 resulting from the freshwater discharge in 2005 were among the drivers for a widespread decrease in the coverage and biomass of Syringodium filiforme (manatee grass) in 2006. These observations provided an opportunity to develop and apply a modeling framework to simulate responses of S. filiforme to variable water quality. The framework connects water column variables to field monitoring of seagrass abundance and salinity growth response experiments. The base model was calibrated with macrophyte abundance observed in southern Indian River Lagoon (IRL) from 2002 to 2007 and tested against shoot data from a different time (1997?C2002) and nearby location in the IRL. Model shoot biomass (gC?m?2) was similar to field observations (r 2?=?0.70) while responding to monthly seasonal fluctuations in salinity and light throughout the 6-year simulations. Field and model results indicated that S. filiforme growth and survival were sensitive to, and increased with, rising salinity throughout 2007. This modeling study emphasizes that discharge, salinity, and submarine light are inter-dependent variables affecting South Florida seagrass habitats on seasonal to inter-annual time scales.  相似文献   

4.
Environmental characteristics were measured and recorded in the Skagit Marsh, a brackish intertidal marsh on Puget Sound, Washington. Four transects were placed perpendicular to a known gradient of increasing salinity which began with fresh water at the bank of one of the outlets of the Skagit River and reached a surface water salinity of 22‰ at a point alongshore 5 km north of the outlet. The environmental characteristics which were measured varied along gradients (soil texture, organic carbon in fines, soil column temperature, free soil water salinity) or had a patchy distribution (soil redox potential, soil macro-organic matter). Growth and production vary across the marsh. The maximum aboveground standing crop (1,742 g m?2 dry weight) was measured at a site with 0–4‰ free soil water salinity, dominated by the sedgeCarex lyngbyei. In more saline areas (8–12‰), the bulrushScirpus americanus was dominant and standing crop values dropped to a third of the maximum. Species performance varied in a complex manner as did the environment.C. lyngbyei had diminished growth and decreased standing crop in areas where salinity was higher.S. americanus was equally productive in low elevation, high salinity sites and in high elevation, low salinity sites. An increase in shoot density for dominant species occurred in saline areas as individual shoot weights and leaf areas decreased. Because species responded differently, environmental variation was magnified in the population and community responses of the marsh vegetation.  相似文献   

5.
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   

6.
Effects of soil factors on physiological indicators ofSpartina patens and live standing crop of the macrophyte community were investigated in a brackish marsh. Three distinct physiognomic zones were studied along a transect perpendicular to a tidal creek: the marsh edge, which was directly adjacent to the creek; the levee berm, 6 to 8 m from the creek; and the inland zone, which extended through the marsh interior. Soil physicochemical factors (soil moisture, redox potential, interstitial pH, salinity, and ammonium and sulfide concentrations) were compared to physiological indicators ofSpartina patens (leaf adenine nucleotides, root alcohol dehydrogenase (ADH) activity, and levels of ethanol, lactate, alanine and malate in the roots). In correlation matrices of soil and plant factors, increases in soil moisture and decreases in redox potential were associated with depressed leaf adenylate energy charge ratios (AEC, an integrative measure of plant stress) and elevated ADH activities and metabolite levels in the roots. ADH activity was greatest in roots from the inland zone where soil waterlogging was greatest and exhibited seasonal increases that followed seasonal declines in soil redox potential. Leaf AEC was greatest in the berm and generally lowest in the inland plants. End of season live standing crop was also greatest on the berm, but did not closely follow any edaphic trends across the three zones. This suggests that several factors, (i.e., soil aeration, and sulfide and nitrogen levels) may be of greater importance to standing crop than any single factor, as is thought for salt marshes dominated byS. alterniflora.  相似文献   

7.
Tagging studies ofSpartina alterniflora Loisel showed no significant differences in stem longevity of short, medium, and tall height forms. Mean stem longevity was 7.9 months, and the experimental turnover rate was 1.5 crops per yr. Five methods to measure productivity (peak standing crop, Milner and Hughes, Smalley, Wiegert and Evans, and Lomnicki, et al.) yielded annual net aerial primary production (NAPP) estimates ranging from 214 to 1,038 g dry wt per m2 per yr in a stand of shortSpartina. Turnover rates were computed for each of the methods by dividing the respective production value by the peak standing crop (242 g dry wt per m2 per yr). Each computed turnover rate was compared with the experimental value of 1.5 crops per yr to ultimately determine that the methods of peak standing crop, Milner and Hughes, and Smalley were underestimates and that the Wiegert and Evans method was an overestimate of NAPP in tidal marsh systems. Based on its calculated turnover rate of 1.9 crops per yr, a modified Lomnicki, et al. method provided the best NAPP estimate (454 g dry wt per m2 per yr).  相似文献   

8.
Seagrasses are sensitive to local environmental conditions such as salinity, the underwater light environment, and nutrient availability. To characterize seagrass coverage and condition, as well as to relate changes in community structure to local environmental and hydrologic conditions, we monitored seagrass communities in the Upper Laguna Madre (ULM), Texas annually from 2011 to 2015. In 2011 and 2012, the lagoon was dominated primarily by Halodule wrightii, with mixed meadows of H. wrightii and Syringodium filiforme located in the northwest of our study area. By 2013, the expansive S. filiforme meadows had disappeared and the species was restricted to the northernmost reaches of the lagoon. The S. filiforme mortality occurred following an extended period of extremely high salinity (salinities 50–70) during a regional drought. Continuous measurements of underwater photosynthetically active radiation and stable carbon isotopic signatures of seagrass blade tissues did not suggest light limitation, and H. wrightii N/P molar ratios near 30:1 were not indicative of nutrient limitation. Based on the absence of strong evidence for light or nutrient limitation, along with the known tolerance of H. wrightii for higher salinities, we conclude that hypersalinity driven by regional drought was likely the major driver behind the observed S. filiforme mortality. With a substantial portion of the global seagrass distribution threatened by drought in the next 50 years, the increased frequency of hypersaline conditions is likely to exacerbate stress in seagrass systems already vulnerable to the effects of rising water temperatures, eutrophication, and sea level rise.  相似文献   

9.
Fifteen species of elasmobranchs, eight sharks and seven rays, have been recorded with reasonable certainty from the Indian River lagoon system on the central east coast of Florida. We collected four shark and six ray species during a three and one-half year study of the northern portion of the lagoon system. Five of these appear to be year-round residents, and the remainder utilize the area only at restricted times of the year or as a nursery ground. The most abundant resident species areDasyatis sayi, D. sabina, andCarcharhinus leucas. Pristis pectinata, once a common resident species, has been extirpated from the lagoons. The distribution of ocean inlets and salinity appear to be major factors affecting diversity and numbers of elasmobranchs in the Indian River system.  相似文献   

10.
Species richness and abundance of epibenthic fishes and decapod crustaceans were quantified with day-time beam trawl tows and throw traps to provide information on nekton assemblages inZostera marina and unvegetated sandy habitats in northern latitudes. Sampling at randomly selected stations with a 1.0-m beam trawl occurred in eelgrass (Zostera marina) and unvegetated sandy substrates of two mid-coastal Maine estuaries: Casco Bay and Weskeag River. Random 1.0-m throw trap samples were collected inZostera and adjacent unvegetated sandy substrates in Casco Bay and Weskeag River as well. Species richness and faunal abundances were positively associated with the occurrence ofZostera within Weskeag River and Casco Bay estuaries using both gear types. A total of 17 species of fishes and 6 species of decapods were collected in the two estuaries using both gears. Populations of most species were dominated by young-of-the-year and juvenile life history stages. Number and densities of fishes were higher inZostera, due primarily to the abundances of eelgrass residents such as threespine,Gasterosteus aculeatus, and fourspine sticklebacks,Apeltes quadracus, grubby,Myoxocephalus aenaeus, and cunner,Tautogolabrus adspersus. Crangon septemspinosa dominated decapod catch per unit effort and density in both estuaries and habitats.  相似文献   

11.
A comparative study of the standing crop of marsh vegetation was made of the Patuxent River and Parker Creek, two tributaries of Chesapeake Bay. The biomass of marsh vegetation in the tidal freshwater and brackish regions of the Patuxent was relatively uniform with regard to salinity, seasonally high concentrations of dissolved nitrogen, and phosphorus and nutrient gradient. Maximum values of biomass occurred in the tidal freshwater and slightly brackish water region of Parker Creek, a system whose nutrient concentrations approximated 20% of those of Patuxent River. Biomass values for the Patuxent River and Parker Creek averaged about 1417 and 895 g m?2 dry weight, respectively. Estimates of total annual marsh production based on the maximum standing crop was 27×103 and 519 metric tons, respectively, for the Patuxent River and Parker Creek.  相似文献   

12.
A 70% reduction in freshwater discharge through the Cooper River Basin, South Carolina, has provided a unique opportunity to study changes in estuarine plant communities in response to a system-wide increase in salinity. A one-dimensional tidal prism mixing model was used to simulate the changes in the longitudinal salinity distribution which have occurred in the Cooper River since a diversion in 1985 reduced the mean flow from 442 to 130 m3 s?1. Model simulations indicate that a salinity increase of 10–14‰ has occurred in the region of the river where the marsh plant community shifts from a virtual monoculture ofSpartina alterniflora to a more diverse brackish community. The flow reduction and associated salinity increase are expected to result in an increased dominance of the halophyte,S. alterniflora, and a progressive exclusion of the less halotolerant species which currently inhabit this region.  相似文献   

13.
In situ ecosystem gas exchange measurements were taken monthly for a 15-month period during low tide forJuncus roemerianus Scheele and short, medium, and tall height forms ofSpartina alterniflora Loisel. in three salt marshes near Southport, North Carolina. Multiple regression analysis was used to obtain empirical relationships betwen gas exchange values and the physical and biotic variables measured. Preliminary models for net ecosystem photosynthesis, ecosystem respiration, and respiration of aboveground standing crop were developed. Validation of models was carried out in the following manner: (1) net primary productivity of aboveground standing crop was calculated from model data and compared with harvest estimates of net primary productivity for the same year; and (2) carbon exchange and energy efficiency values were compared with literature values. In general, theSpartina models, because of their larger data base, were more useful than theJuncus models. Annual primary productivity of aboveground standing crop calculated from gas exchange values was 1.8 to 3.6 times greater forSpartian than values calculated from harvest data by Smalley's method.Juncus values were approximately equal. Since values calculated from carbon data and harvest data are not entirely equivalent, required adjustments to the carbon values are discussed. Both species have two growth periods—one in ths pring and one in the fall—with the spring growth in excess of that in the fall. Net ecosystem productivity was highest in the spring and lowest in the summer. Ecosystem respiration amounted to 71% of gross annual photosynthesis. The aboveground standing crop contributed approximately 35% to this ecosystem respiration and the soil, the remaining 36%. Efficiency for gross photosynthesis per unit of solar radiation ranged from 0.22 to 1.11%. Efficiencies for net primary production of aboveground standing crop ranged from 0 to 0.82% and those of net ecosystem production from 0 to 0.56%.  相似文献   

14.
Spatial distribution patterns ofScirpus validus were studied in tidal marshes of the lower Savannah River. The hypothesis that changes in spatial pattern forS. validus would accompany differences in environmental parameters was tested by sampling densities and biomass along environmental gradients of salinity and elevation. Coefficients of dispersion were calculated forS. validus and used to compare spatial patterns among freshwater, midly oligohaline, strongly oligohaline, and mesohaline tidal marshes. Results indicated significantly greater clumping ofS. validus in mesohaline marsh than in freshwater marsh. Only the mildly oligohaline site supported a random population ofS. validus, while the strongly oligohaline marsh supported a uniform spatial distribution. Spatial pattern and relative importance ofS. validus, as well as composition of co-occurring species, changed significantly with changing salinity. The relations between changes in relative importance ofS. validus and differences in soil organic matter and elevation were also significant.  相似文献   

15.
Nitrogen and phosphorus content ofSpartina alterniflora Loisel and soil nitrogen were measured along a transect perpendicular to a stream in a Louisiana salt marsh in order to provide information on differences between the so-called streamside and inland regions. Total plant nitrogen and phosphorus levels in June and September tended to be greater at streamside than inland sites. Total soil nitrogen on a dry soil weight basis increased with distance inland from a natural stream toward an interdistributary basin in the marsh. Soil extractable ammonium-nitrogen levels measured in June were very low in vegetated streamside and inland areas, but they were much higher in inland areas devoid of plants. Nitrogen and phosphorus utilization byS. alterniflora was also investigated at an inland location in the salt marsh. Labelled ammonium-nitrogen and phosphate-phosphorus were added in May at a rate of 200 kg/ha to the soil of replicated plots. Added nitrogen significantly increased total above-ground plant biomass and plant height by 28 and 25%, respectively, 4 months after application. The ratio of belowground macro-organic matter to total aboveground biomass was decreased from 5.7 to 4.7 by the additional nitrogen. Added phosphorus did not significantly affect plant height and biomass. The use of15N-depleted nitrogen tracers showed that about half of the nitrogen in the aboveground portion ofS. alterniflora from 1 to 4 months after the nitrogen addition was derived from the added ammonium-nitrogen. After 4 months, 28 and 29% of the added labelled nitrogen was recovered in the aboverground and belowground biomass ofS. alterniflora, respectively. Recovery of added nitrogen was overestimated with a non-tracer method based on the difference in total nitrogen uptake between nitrogen-amended plots and untreated plots. Soil organic nitrogen comprised the majority of the nitrogen in the salt marsh. Nitrogen in the standing crop biomass ofS. alterniflora represented only about 2% of the total nitrogen in the plantsoil system of an inland marsh to a 20 cm soil depth.  相似文献   

16.
The correspondence between maximum depth of growth (Zmax) for two seagrases,Halodule wrightii andSyringodium filiforme, and the attenuation of diffuse photosynthetically active radiation (KdPAR) were evaluated over a 3.5-yr period in the southern Indian River Lagoon, Florida. The lower limit of seagrass depth distribution was controlled by light availability. Both species grew to the same maximum depth, indicating they have similar minimum light requirements. Based on average annual values of KdPAR, estimates of seagrass minimum light requirements ranged from 24% to 37% of the light just beneath the water surface (Io), much hgiehr than a photic zone for many phytoplankton and macroalgae (1–5% incident light). In less transparent waters of Hobe Sound, where turbidity (NTU) and color (Pt-Co) had their highest concentrations, minimum light requirements for growth were greatest. These results suggest that more sophisticated optical models are needed to identify specific water quality constituents affecting the light environment of seagrasses. Water quality criteria and standards needed to protect seagrasses from decreasing water transparency must be based on parameters that can be routinely measured and reasonably managed.  相似文献   

17.
A year-long analysis of the characteristics of the seagrassSyringodium filiforme and the associated dynamics of the nutrient pool in the sediment pore water was done to assess co-variation. Changes in seagrass growth rate and standing stock throughout the year were accompanied by seasonal changes in the nutrient pools. The link between plant production and morphometrics and the sediment nutrient pool was found to be predominantly physiological, with the plant balancing the ability to photosynthesize with the nutrients needed for maintaining production. Measurements of whole plant growth for this seagrass, rather than the more typical leaf growth measurements, show that the production of new shoots and rhizome elongation for these plants represents as substantial amount of growth that usually goes unmeasured. Further, these whole plant growth measures demonstrate the rapid lateral rhizome spread of this species, exceeding one meter per plant per year. The primary cause of seasonal variation in the yearly seagrass cycle was investigated. Correlation analysis supported the hypothesis that the major factor controlling seasonal variation in this seagrass was light. During the peak growing season, however, growth was not regulated by light but by nitrogen. Depletion of the sediment ammonium pool and reduction in pore water ammonium relative to adsorbed ammonium, as well as changes in N content of seagrass leaves, support our hypothesis of peak growing season nitrogen limitation. Our results forSyringodium filiforme in terrigenous sediments are in contrast to our recent findings of phosphorus limitation in this same species occurring in carbonate sediments.  相似文献   

18.
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   

19.
Net annual primary production of a sedge Carex lyngbyei dominated tidal marsh in the Fraser River estuary, British Columbia, Canada was 634 g ash-free dry weight (AFDW) per m2 per yr (687 g dry weight per m2 per yr). Mean maximum shoot elongation during the short (May to August) growing season was 1.88 cm per day from overwintering shoots. The maximum aboveground standing crop of 690 g AFDW per m2 represented only 25% of the total below-ground biomass, which appears to be controlling most of the critical life history processes of the sedge marsh. An estimate of 14 percent of the aboveground standing crop was lost through leaching of dissolved organic carbon from the growting plant. Aboveground tissue losses, which were negligible during the growing season, occurred primarily via translocation in autumn and tidal export during the winter. In situ measurements showed that of the original maximum standing crop, approximately 38%, 37%, and 25% were lost by downward translocation, tidal export, and sediment burial, respectively. Based on changes in above and belowground nutrient pools, rapid spring (May to late June) uptake rates of 109 mg N per m2 per day and 23.0 mg P per m2 per day by shoots were followed by downward translocation rates of 44.8 mg N per m2 per day and 12.2 mg P per m2 per day during late June to the end of August. Aboveground leaching rates were estimated as 23.9 mg N per m2 per day and 7.8 mg P m2 per day and belowground uptake rates as 100 mg N per m2 per day and 26 mg P per m2 per day; root uptake occurred primarily after late June. Nutrient levels in decomposing litter more than doubled over the winter period showing a pattern of nutrient enrichment characteristic of marsh ecosystems. *** DIRECT SUPPORT *** A01BY023 00004  相似文献   

20.
An attempt has been made to understand the Pleistocene bottom water history in response to the paleoclimatic changes in the northern Indian Ocean employing quantitative analyses of deep sea benthic foraminifera at the DSDP sites 219 and 238. Among the 150 benthic foraminifera recorded a few species show dominance with changing percent frequencies during most of the sequence. The dominant benthic foraminiferal assemblages suggest that most of the Pleistocene bottom waters at site 219 and Early Pleistocene bottom waters at site 238 are of North Indian Deep Water (NIDW) origin. However, Late Pleistocene assemblage at site 238 appears to be closely associated with a water mass intermediate between North Indian Deep Water (NIDW) and Antarctic Bottom Water (AABW). Uvigerina proboscidea is the most dominant benthic foraminiferal species present during the Pleistocene at both the sites. A marked increase in the relative abundance ofU. proboscidea along with less diverse and equitable fauna during Early Pleistocene suggests a relative cooling, an intensified oceanic circulation and upwelling of nutrient rich bottom waters resulting in high surface productivity. At the same time, low sediment accumulation rate during Early Pleistocene reveals increased winnowing of the sediments possibly due to more corrosive and cold bottom waters. The Late Pleistocene in general, is marked by relatively warm and stable bottom waters as reflected by low abundance ofU. proboscidea and more diverse and equitable benthic fauna. The lower depth range for the occurrence ofBulimina aculeate in the Indian Ocean is around 2300 m, similar to that of many other areas.B. aculeata also shows marked increase in its abundance near the Pliocene/Pleistocene boundary while a sudden decrease in the relative abundance ofStilostomella lepidula occurs close to the Early/Late Pleistocene boundary.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号