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1.
Tyler L. Lewis Paul L. Flint Dirk V. Derksen Joel A. Schmutz Eric J. Taylor Karen S. Bollinger 《Polar Biology》2011,34(11):1751-1762
From 1976 onward, molting brant geese (Branta bernicla) within the Teshekpuk Lake Special Area, Alaska, shifted from inland, freshwater lakes toward coastal wetlands. Two hypotheses
explained this redistribution: (1) ecological change: redistribution of molting brant reflects improvements in coastal foraging
habitats, which have undergone a succession toward salt-tolerant plants due to increased coastal erosion and saltwater intrusion
as induced by climate change or (2) interspecific competition: greater white-fronted geese (Anser albifrons) populations increased 12-fold at inland lakes, limiting food availability and forcing brant into coastal habitats. Both
hypotheses presume that brant redistributions were driven by food availability; thus, body mass dynamics may provide insight
into the relevance of these hypotheses. We compared body mass dynamics of molting brant across decades (1978, 1987–1992, 2005–2007)
and, during 2005–2007, across habitats (coastal vs. inland). Brant lost body mass during molt in all three decades. At inland
habitats, rates of mass loss progressively decreased by decade despite the increased number of greater white-fronted geese.
These results do not support an interspecific competition hypothesis, instead suggesting that ecological change enhanced foraging
habitats for brant. During 2005–2007, rates of mass loss did not vary by habitat. Thus, while habitats have improved from
earlier decades, our results cannot distinguish between ecological changes at inland versus coastal habitats. However, we
speculate that coastal forage quality has improved beyond that of inland habitats and that the body mass benefits of these
higher quality foods are offset by the disproportionate number of brant now molting coastally. 相似文献
2.
In the geological research of the Holocene coastal deposits of The Netherlands, diatoms are used to reconstruct the sedimentary
facies, palaeo-tide levels and salinity gradients during the deposition of the sediments. In this paper, the results of diatom
research from 4 borings, taken from the early and middle Holocene deposits of central North Holland are presented. The oldest
marine influenced sediments in the area are the deposits of the ‘Velsen layer’, a clay layer rich in organic matter and deposited
about 8000–700014C years before present (BP) at a depth of 20–12 m below present mean sea-level. This clay layer was formed in a shallow, permanently
submerged environment with a limited tidal influence (lagoonal or pond-like conditions). The salinity changed from brackish/freshwater
to marine/brackish. The younger sandy and clayey sediments, formed about 7000–4500 BP at a depth of 16–3 m below present mean
sea-level, are classified as ‘tidal channel’ and ‘interchannel’ deposits. It is argued, on the base of both diatom and non-diatom
criteria, that the lower and middle parts of the interchannel deposits in the central area of the palaeo-tidal basin of North
Holland were formed in a subtidal environment. The upper part of the interchannel deposits and the deposits at the fringe
of the North Holland tidal basin were formed in the intertidal zone or, at the fringe of the basin, even in the supratidal
zone. The salinity in the North Holland tidal basin during the sedimentation of the tidal channel and interchannel deposits
was marine/brackish to marine. This study indicates that diatoms, besides their palaeoecological applications, have chronostratigraphical
significance (on a regional scale). The diatomsCymatosira belgica andActinoptychus splendens appear to be a useful (eco)stratigraphical marker in the Holocene coastal deposits of The Netherlands and Belgium. 相似文献
3.
Edward Castañeda-Moya Robert R. Twilley Victor H. Rivera-Monroy Brian D. Marx Carlos Coronado-Molina Sharon M. L. Ewe 《Ecosystems》2011,14(7):1178-1195
Patterns of mangrove vegetation in two distinct basins of Florida Coastal Everglades (FCE), Shark River estuary and Taylor
River Slough, represent unique opportunities to test hypotheses that root dynamics respond to gradients of resources, regulators,
and hydroperiod. We propose that soil total phosphorus (P) gradients in these two coastal basins of FCE cause specific patterns
in belowground biomass allocation and net primary productivity that facilitate nutrient acquisition, but also minimize stress
from regulators and hydroperiod in flooded soil conditions. Shark River basin has higher P and tidal hydrology with riverine
mangroves, in contrast to scrub mangroves of Taylor basin with more permanent flooding and lower P across the coastal landscape.
Belowground biomass (0–90 cm) of mangrove sites in Shark River and Taylor River basins ranged from 2317 to 4673 g m−2, with the highest contribution (62–85%) of roots in the shallow root zone (0–45 cm) compared to the deeper root zone (45–90 cm).
Total root productivity did not vary significantly among sites and ranged from 407 to 643 g m−2 y−1. Root production in the shallow root zone accounted for 57–78% of total production. Root turnover rates ranged from 0.04
to 0.60 y−1 and consistently decreased as the root size class distribution increased from fine to coarse roots, indicating differences
in root longevity. Fine root biomass was negatively correlated with soil P density and frequency of inundation, whereas fine
root turnover decreased with increasing soil N:P ratios. Lower P availability in Taylor River basin relative to Shark River
basin, along with higher regulator and hydroperiod stress, confirms our hypothesis that interactions of stress from resource
limitation and long duration of hydroperiod account for higher fine root biomass along with lower fine root production and
turnover. Because fine root production and organic matter accumulation are the primary processes controlling soil formation
and accretion in scrub mangrove forests, root dynamics in the P-limited carbonate ecosystem of south Florida have a major
controlling role as to how mangroves respond to future impacts of sea-level rise. 相似文献
4.
José A. Zertuche-González Víctor F. Camacho-Ibar Isaí Pacheco-Ruíz Alejandro Cabello-Pasini Luis A. Galindo-Bect José M. Guzmán-Calderón Víctor Macias-Carranza Julio Espinoza-Avalos 《Journal of applied phycology》2009,21(6):729-736
Bahía San Quintín is a coastal lagoon with large Ulva biomass and upwelling influence. Previous observations suggest that Ulva has increased recently as a result of oyster cultivation. To evaluate the possible role of Ulva as a temporary nutrient sink, biomass and tissue C, N, and P were determined seasonally. Maximum biomass was present during
spring and early summer (1,413–1,160 t (dry)) covering about 400 ha. However, the biomass decreased to 35 t (dry) by winter.
The mean annual percentage of Ulva C, N, and P was 28%, 2%, and 0.14%, respectively. This study shows that Ulva can store up to 28 t of N and 2 t of P in Bahía San Quintín during spring–summer. Ulva may be displacing the seagrass Zostera marina subtidal beds. A partial removal of the seaweed would reduce the risk of eutrophication and the displacement of eelgrass
beds. 相似文献
5.
6.
Eleanor B. Mackay Ian D. Jones Andrew M. Folkard Stephen J. Thackeray 《Hydrobiologia》2011,666(1):85-97
Community structure and diversity patterns of pelagic copepods were investigated for the coastal areas and in the marine lakes
of the Palau islands in the West Pacific. We conducted field surveys during 2004–2007 and collected zooplankton samples from
eight coastal areas and 16 marine lakes. The marine lakes in the islands of Palau are limnologically classified into two types,
meromictic and holomictic lakes. Species diversity indices (Margalef’s species richness d′, Shannon–Wiener index H′, and Simpson’s dominance) were measured at each sampling site. The copepod community structure was analyzed using multivariate
analyses, hierarchical cluster analysis, and non-metric multidimensional scaling (MDS) from the PRIMER package. A total of
36 copepod taxa were identified to the genus or species level from Calanoida, Cyclopoida, Harpacticoida, and Poecilostomatoida.
Multivariate analysis based on the Bray–Curtis similarity index revealed that copepod assemblages could be classified into
three different groups according to their habitat: (I) meromictic lakes, (II) holomictic lakes with an exceptionally shallow
and flat basin (type A holomictic lakes), (III) holomictic lakes with a deep basin (type B holomictic lakes), and all coastal
areas. The meromictic lakes were characterized by markedly decreased species diversity (d′ = 0.15, H′ = 0.41) in which only two brackish-water species, Bestiolina similis and Oithona dissimilis, were dominant. Type A holomictic lakes were characterized by relatively low levels of species diversity (d′ = 1.25, H′ = 1.35). In contrast, type B holomictic lakes were characterized by relatively high levels of species diversity, which was
comparable to that of coastal areas. This result indicated that zooplankton assemblages in the type B holomictic lakes were
closely related to a coastal community. The present study showed that the species diversity of pelagic copepods varies according
to the level of isolation and the local environmental conditions for each marine lake. 相似文献
7.
Cladocora caespitosa is a common zooxanthellate, ahermatypic, constructional scleractinian coral in shallow waters of the present-day Mediterranean.
Extensive coral banks in Upper Pliocene shallow marine deposits of the Almería-Níjar Basin (SE Spain) contain the same species.
These banks occur on debris-flow conglomerates deposited in a fan delta, or on bioclastic accumulations interpreted as storm
deposits. Direct relationships of coral beds with coastal facies indicate that C. caespitosa colonized shallow settings near the paleocoast, probably not deeper than 20–30 m. Low turbulence allowed corals to colonize
substrates, which remained stable for long periods. Activity of organisms in the coral community, storms, and detritic discharges
from the fan delta were the most significant mechanisms disturbing the coral development. The hard substrata provided by coral
banks promoted colonization by cemented and epibyssate organisms. Coral banks marked maximum flooding surfaces at the end
of transgressive systems tracks. They were suddenly buried by sediment input into the basin. Taphonomic signatures measured
on components of the coral bank communities indicate a low turbulence environment, probably a bay. The low hydraulic energy
further inhibited post-burial reworking, thus promoting the in situ preservation of a great part of the organisms inhabiting the bioconstructions.
Accepted: 2 December 1997 相似文献
8.
Dynamics of Mya arenaria beds in two bights of the Chupa Inlet (Kandalaksha Bay, White Sea) were studied on a long-term basis. Observations were carried
out at 1– to 3-year intervals from 1979 up to 1999. The studied soft-shell clam beds were characterised by a substantial instability
of age structure. Since 1988, only one year-class has dominated in the beds while other generations have been scarce and recruitment
was not observed. This pattern of Mya bed dynamics was related neither to interannual environmental changes nor to differential reproduction success or predation
effects in the benthic assemblages. Favourable conditions for spat formation in 1988 (low abundance of other M. arenaria generations), as well as for juvenile survival during the following winter, resulted in high abundance of juveniles in both
investigated locations in 1989. The mortality rate (μ) in this 1988 generation varied throughout the period of investigation and was related to age. The mortality level decreased
for the first 2–4 years of the life cycle, then stabilised for the next 3–4 years, and eventually increased in subsequent
years. Overall μ values ranged from 0 to 1.68 year–1. The oldest specimens observed were 17 years old and had a maximum shell length of 79 mm. Significant differences in average
growth rates were observed between molluscs of different locations.
Communicated by H.-D. Franke 相似文献
9.
Long-term changes in Secchi disk transparency in Lake Nakaumi, Japan, from 1932 to the present, which includes the periods
before and after the loss of eelgrass (Zostera marina L.) beds, were compiled from previous reports. During the first (July 1932–February 1934) and the second (January 1949–November
1950) periods, the mean transparency was greater than 3 m at all observed stations. Data during the third period (July 1954–March
1956) are only available for the station at the center of the lake. The mean transparency during the third period was significantly
lower than that of the second period but higher than the mean during the fourth period. This observation suggests that the
decrease of transparency occurred during the third period. Because the decline of eelgrass beds in Lake Nakaumi occurred in
the mid-1950s, the decrease of transparency most likely resulted from the shift in primary producers from submerged macrophytes
to phytoplankton. Although the maximum transparency sometimes exceeded 3 m, mean transparencies during the fourth period (May
1975–December 2003) were less than 2 m at all stations, significantly lower than those during the first and second periods.
The shift in the chief primary producer, from benthic macrophytes to phytoplankton, caused a subsequent shift in secondary
producers. The opportunistic filter-feeding bivalve Musculista senhousia, regarded as a biofouling species of local fisheries, increased in Lake Nakaumi. The long-term monitoring data of transparency
suggested that restoration of submerged aquatic vegetation may be indispensable for the remediation of the lake environment
in this shallow eutrophic lagoon. 相似文献
10.
Influence of permanent raised bed planting and residue management on physical and chemical soil quality in rain fed maize/wheat systems 总被引:2,自引:1,他引:1
Densely populated, intensively cropped highland areas in the tropics and subtropics are prone to erosion and declining soil
fertility, making agriculture unsustainable. Conservation agriculture in its version of permanent raised bed planting with
crop residue retention has been proposed as an alternative wheat production system for this agro-ecological zone. A five years
field experiment comparing permanent and tilled raised beds with different residue management under rainfed conditions was
started at El Batán (Mexico) (2,240 m asl; 19.31°N, 98.50°W; Cumulic Phaeozem) in 1999. The objective of this study was to
determine the soil quality status after five years of different management practices. The K concentration was 1.65 times and
1.43 times larger in the 0–5 cm and 5–20 cm profiles, respectively, for permanent raised beds compared to conventionally tilled
raised beds. The Na concentration showed the opposite trend. Sodicity was highest for conventionally tilled raised beds and
for permanent raised beds it increased with decreasing amounts of residue retained on the surface. Permanent raised beds with
full residue retention increased soil organic matter content 1.4 times in the 0–5 cm layer compared to conventionally tilled
raised beds with straw incorporated and it increased significantly with increasing amounts of residue retained on the soil
surface for permanent raised beds. Soil from permanent raised beds with full residue retention had significantly higher mean
weight diameter for wet and dry sieving compared to conventionally tilled raised beds. Permanent raised beds with full residue
retention had significantly higher aggregate stability compared to those with residue removal. A lower aggregation resulted
in a reduction of infiltration. Principal component analysis (PCA) was performed using these soil physicochemical variables
that were significantly influenced by tillage or residue management. The PC1 and PC2 separated the conventionally tilled raised
beds from the permanent raised beds and PC3 separated permanent raised beds with at least partial residue retention from permanent
raised beds with no residue retention. These clear separations suggest that tillage and residue management have an effect
on soil processes. The research indicates that permanent raised bed planting increases the soil quality and can be a sustainable
production alternative for the (sub)tropical highlands. Extensive tillage with its associated high costs can be reduced by
the use of permanent raised beds while at least partial surface residue retention is needed to insure production sustainability. 相似文献
11.
Anita Franco Piero Franzoi Stefano Malavasi Federico Riccato Patrizia Torricelli 《Hydrobiologia》2006,555(1):159-174
The small-sized fish assemblages of the Venice Lagoon were investigated and compared among five shallow subtidal habitats
(seagrass beds, sparsely vegetated habitats, unvegetated sand bottoms, mudflats and saltmarsh creeks) in the Northern lagoon
basin. Sampling was carried out seasonally (Spring, Summer and Autumn of 2002) in 4–7 stations for each habitat type, by means
of a fine-mesh, small beach seine. Two-way analysis of variance was applied to assess the differences in species richness,
fish diversity, density and standing stock amongst habitats, whereas fish assemblage composition was investigated by using
multivariate analyses (MDS, ANOSIM, SIMPER). The analyses indicated that seagrass beds and saltmarsh creeks are relevant shallow
habitats in structuring the small-sized fish assemblages of the Venice Lagoon, supporting specialized and recognizable fish
assemblages. Those in seagrass beds, in particular, were characterized by higher species richness and standing stock with
respect to all the others. The structuring role of these habitats was discussed in terms of both habitat complexity and degree
of confinement. In contrast, sandy bottoms, mudflats and sparsely vegetated habitats were identified as “transition” habitats,
with highly variable fish assemblages, influenced by the contribution of the adjacent habitats, and acting probably as both
‘buffer zones’ between the other habitats and migration routes for many fish species in the lagoon. 相似文献
12.
Macrophyte beds have been shown to influence organic matter retention and nutrient processing in streams. Less is known about
the extent to which plant beds contribute to abundance, biomass, and diversity of macroinvertebrate assemblages in low-order
streams. We measured aquatic invertebrate abundance, biomass, and diversity associated with plant beds and sand/gravel patches
in a low-gradient second-order stream in the Central Sand Plains of Wisconsin, USA from March to October. Invertebrate abundance
and biomass were higher on average in plant beds (2,552 m−2 and 1,575 mg m−2) than in sand/gravel patches (893 m−2 and 486 mg m−2). Although sand/gravel habitat was over three times more abundant than plant beds in the study reach, plant beds and sand/gravel
patches contributed similarly to invertebrate abundance and biomass at the whole-reach scale. The abundance and biomass of
invertebrates associated with plant beds decreased from spring to autumn. Non-insect invertebrates in the plant beds increased
in relative abundance as the year progressed. Shannon–Weiner diversity and taxa richness of invertebrates were higher in the
plant beds than in the sand/gravel habitat. Our results suggest that plant beds can represent hot spots for invertebrate abundance
and production in low-gradient streams, and have implications for stream management and restoration in these types of ecosystems.
Handling editor: S. I. Dodson 相似文献
13.
Movements and behavior of satellite-tagged spotted seals (Phoca largha) in the Bering and Chukchi Seas 总被引:1,自引:0,他引:1
Lloyd F. Lowry Kathryn J. Frost Randall Davis Douglas P. DeMaster Robert S. Suydam 《Polar Biology》1998,19(4):221-230
Satellite-linked tags were attached to 12 spotted seals (Phoca largha) captured at a coastal lagoon in the eastern Chukchi Sea during August 1991–1993. Movements of seals were tracked for 32–298
days using the Argos system. Of 9,651 total location records obtained, 7,268 were usable. Individual seals were located on
41–96% of the days that tags were operational. During August–November, tagged seals alternated haul-outs at coastal sites
lasting 1–304 h with trips to sea of 14–901 h. Coastal haul-outs occurred at 14 sites in western Alaska and eastern Russia.
On several trips to sea, seals covered distances of more than 1,000 km. Movement southward from the Chukchi Sea generally
began in October, with most of the seals passing through the Bering Strait during November. Seals first hauled out on sea
ice in October (Chukchi Sea) or November (Bering Sea), and generally moved southward during October–December as sea-ice coverage
increased. Seven seals, whose transmitters were still operating, spent December to June in the Bering Sea region between Kuskokwim
Bay and Anadyr Gulf, which corresponded to the location of the ice front. The seals made active east-west movements within
the ice front. Spotted seals are unlike other ice-breeding seals in that they regularly use coastal haul-outs during summer
and autumn. Compared to the closely related Pacific harbor seal (Phoca vitulina richardsi), spotted seals make much longer trips to sea and spend longer continuous periods at their haul-outs during summer and autumn.
Received: 9 April 1997 / Accepted: 30 September 1997 相似文献
14.
Eutrophication of the Dutch Wadden Sea: External nutrient loadings of the Marsdiep and Vliestroom basin 总被引:1,自引:0,他引:1
Henk W. van der Veer Wim van Raaphorst Magda J. N. Bergman 《Helgoland Marine Research》1989,43(3-4):501-515
The increasing P and N content in the two main tidal basins in the western Dutch Wadden Sea, the Marsdiep and the Vliestroom
basin, has been reconstructed from the 50s onwards. The area is enriched with nutrients by two sources both originating from
the river Rhine, one being the discharge from Lake IJssel and the other the exchange with the coastal zone of the North Sea.
Due to a buffering by Lake IJssel for about 15–20 years, the eutrophication of the western Wadden Sea showed a time lag compared
with the continuously increasing nutrient concentrations in the river Rhine and the coastal zone of the North Sea. At present,
the primary production in part of the area still seems to be nutrient limited in summer, while loadings have already been
decreasing in recent years. So far, no severe, negative effects on the ecosystem have been reported. Some remarks are made
on the eutrophication in other parts of the Dutch' Wadden Sea in relation to the hydrographic characteristics of these areas.
Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List,
FRG, 1–4 November 1988)
Publication No. 18 of the project “Ecological Research of the North Sea and Wadden Sea” (EON) 相似文献
15.
Summary This paper is focused on the facies associations of an Early-Middle Norian stratigraphic succession cropping outin the Northern
Calabria (Buonvicino, Cosenza). These carbonate deposits, pertaining to the Verbicaro Unit, represent a dolomitized platform
characterized by a clear dominance of automicrites over skeletal metazoans.
On the basis of the chronostatigraphic data and sedimentary evolution, two stratigraphic units have been distinguished: the
Lower Unit (object of the present paper) and the Upper Unit. The Lower Unit consists of an Early-Middle Norian high-relief
prograding carbonate platform. The Upper Unit is represented by Middle p.p.-Upper Norian basinal deposits.
Three main facies associations, indicative of different depositional settings, have been identified.
The inner platform facies association is characterized by automicrite (cauliflower-columnar subordinate planar stromatolites)
associated with detrital carbonates (intraclastic breccia, bioclastic grainstone and packstone). Apeculiar facies is represented
by megalodontid-bearing beds. Mud-cracked horizons and low-developed teepees occur quite frequently.
The margin facies association is dominated by automicrite (planar to low relief stromatolites associated with thrombolitic
fenestral boundstone) and detrital carbonates with subaerial exposure features.
The slope facies association includes detrital carbonates (breccia/megabreccia) associated with serpulid/sphinctozoan bioconstructions
and automicrite (planar stromatolites/thrombolitic boundstone).
The whole carbonate body is completely dolomitized; nevertheless the morphology and microarchitecture of carbonate components
(cements, grains and automicrite) is still clearly recognizable. The dolomite Mg content ranges from 40 to 48 mole%, sometimes
reaching the stoichiometric value.
Cements, primary and late, represent a minor component of the rock volume; they occur more frequently on the margin and upper
slope setting. Quantitative tacies analyses lead to the following conclusions:
The sedimentary facies and the low-diversity fossil associations seem to indicate a stressed marine environment; the platform
margin probably flanked an intra-platform basin, not an open marine basin. 相似文献
– | ⊙ the entire platform is largely led by automicrite (50% in the inner platform, 70% in the margin, and 30% in the slope), with planar to columnar stromatolitic or thrombolitic fabrics; |
– | ⊙ primary skeletal framework is usually missing, although small bioconstructions of sphinctozoans and, subordinately, serpulids, occur on the slope; |
– | ⊙ automicrite has been affected by early cementation, as witnessed by non-gravitative microfabric, early fracturing and boring. |
16.
Evan L. Preisser Alexandra G. Lodge David A. Orwig Joseph S. Elkinton 《Biological invasions》2008,10(2):201-213
Although a range of studies have suggested that competition plays a critical role in determining herbivore assemblages, there
has been little work addressing the nature of interactions between competing invasive herbivores. We report the results of
research on the hemlock woolly adelgid Adelges tsugae (‘HWA’) and elongate hemlock scale Fiorinia externa (‘EHS’), invasive herbivores that both feed on eastern hemlock (Tsuga canadensis). HWA has been linked to hemlock mortality throughout the East Coast of the US; the loss of hemlock threatens to permanently
alter surrounding ecosystems. We assessed the spread and impact of both species by resurveying 142 hemlock stands across a
7,500 km2 latitudinal transect, running from coastal CT to northern MA, for HWA and EHS density as well as hemlock mortality. These
stands had been previously surveyed in either 1997–1998 (CT) or 2002–2004 (MA). While the number of HWA-infested stands has
increased, per-stand HWA density has substantially decreased. In contrast, EHS distribution and density has increased dramatically
since 1997–1998. Hemlock mortality was much more strongly related to HWA density than to EHS density, and many stands remain
relatively healthy despite an overall increase in hemlock mortality. There was a positive correlation between HWA and EHS
densities in stands with low mean HWA densities, suggesting the potential for host-plant-mediated facilitation of EHS by HWA.
Our findings underline the importance of research explicitly addressing interactions between competing invasive species, and
of determining the potential consequences of these interactions for the invaded ecosystem. 相似文献
17.
Habitats and the ecosystem services they provide are part of the world’s portfolio of natural capital assets. Like many components
of this portfolio, it is difficult to assess the full economic value of these services, which tends to over-emphasize the
value of extractive activities such as coastal development. Building on recent ecological studies of species–habitat linkages,
we use a bioeconomic model to value multiple types of habitats as natural capital, using mangroves, sea grass, and coral reefs
as our model system. We show how key ecological variables and processes, including obligate and facultative behaviors map
into habitat values and how the valuation of these ecological processes can inform decisions regarding coastal development
(habitat clearing). Our stylized modeling framework also provides a clear and concise road map for researchers interested
in understanding how to make the link between ecosystem function, ecosystem service, and conservation policy decisions. Our
findings also highlight the importance of additional ecological research into how species utilize habitats and that this research
is not just important for ecological science, but it can and will influence ecosystem service values that, in turn, will impact
coastal land-use decisions. While refining valuation methods is not necessarily going to lead to more rational coastal land-use
decisions, it will improve our understanding on the ecological–economic mechanisms that contribute to the value of our natural
capital assets.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
18.
Green algae in Lake Tanganyika: is morphological variation a response to seasonal changes? 总被引:4,自引:4,他引:0
In the framework of a planktological and ecological study in Lake Tanganyika, East Africa (CLIMLAKE, 2001–2005), variations
of cell abundance and size were observed in a green alga, Eremosphaera tanganyikae, at two study sites, one in the north basin of the lake (off Kigoma, Tanzania) and the other in the south basin (off Mpulungu,
Zambia). Whereas most green algae developed better in the rainy season and in the northern part of the lake, Eremosphaera developed better in the southern basin, in the dry season. It also exhibited large variations in cell abundance and cell
size, with maxima in the middle of the dry season, which may be related to increased phosphorus availability. Moreover, increase
in cell size (up to 80 μm in length), without notable change in S/V ratio, may provide the alga with resistance to grazing by copepods, which reach maximal abundance during the dry season. 相似文献
19.
Macrofauna communities in the Amundsen Basin, at the Morris Jesup Rise and at the Yermak Plateau (Eurasian Arctic Ocean) 总被引:3,自引:3,他引:0
I. Kröncke 《Polar Biology》1998,19(6):383-392
Macrofaunal communities of the western Eurasian Arctic Ocean were studied along a transect from the North Pole, across the
Amundsen Basin and Gakkel Ridge towards the Morris Jesup Rise and the Yermak Plateau. Samples were collected during autumn
1991, from depths of 560–4411 m, using a box corer. Macrofaunal species numbers varied from 1 to 11 per 0.02 m2 in the basins approaching the Morris Jesup Rise and from 44 to 81 per 0.25 m2 at the Yermak Plateau. Abundances increased from 1 to 31 per 0.02 m2 in the basin and on the Morris Jesup Rise to 24–60 per 0.02 m2 on the Yermak Plateau. Biomass was low in the basin and at the Morris Jesup Rise (0.5–68.9 mg per 0.02 m2) but increased to 116.64 mg per 0.02 m2 at the Yermak Plateau. A total of 108 taxa were recorded. The results contradict the hypothesis that diversity decreases with
increasing latitude, and the high species richness at low abundance at intermediate depths was comparable with that observed
in Antarctic and tropical regions. 相似文献
20.
In the rhizosphere, exopolymers are also known to be useful to improve the moisture-holding capacity. The ability of the isolates
from coastal sand dunes to produce exopolymers was determined. Among which the isolate, showing very high production of exopolysaccharide
(EPS), Microbacterium arborescens––AGSB, a facultative alkalophile was further studied for exopolymer production. The isolate a gram-positive non-spore forming,
slender rod, catalase positive, oxidase negative, showed growth in 12% sodium chloride. The culture was found to produce exopolymer
which showed good aggregation of sand which has an important role in the stabilization of sand dunes. The exopolymer was further
analysed. The cold isopropanol precipitation of dialysed supernatants grown in polypeptone yeast extract glucose broth produced
partially soluble EPSs with glucose as the sole carbon source. Chemical analysis of the EPS revealed the presence of rhamnose,
fucose, arabinose, mannose, galactose and glucose. On optimization of growth parameters (sucrose as carbon source and glycine
as nitrogen source), the polymer was found to be a heteropolysaccharide containing mannose as the major component. It was
interesting to note that the chemical composition of the exopolymers produced from both unoptimized and optimized culture
conditions of Microbacterium arborescens––AGSB is different from those of other species from the same genera. This study shows that marine coastal environments such
as coastal sand dunes, are a previously unexplored habitat for EPS-producing bacteria, and that these molecules might be involved
in ecological roles protecting the cells against dessication especially in nutrient-limited environments such as the coastal
sand dunes more so in the extreme conditions of pH. Such polysaccharides may help the bacteria to adhere to solid substrates
and survive during the nutrient limitations. 相似文献