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1.
M. K. S. Lilley S. E. Beggs T. K. Doyle V. J. Hobson K. H. P. Stromberg G. C. Hays 《Marine Biology》2011,158(11):2429-2436
There is concern that overfishing may lead to a proliferation of jellyfish through a process known as fishing down the food
web. However, there has been no global synthesis of patterns of gelatinous zooplankton biomass (GZB), an important first step
in determining any future trends. A meta-analysis of epipelagic-GZB patterns was undertaken, encompassing 58 locations on
a global scale, and spanning the years 1967–2009. Epipelagic-GZB decreased strongly with increasing total water column depth
(r
2 = 0.543, p < 0.001, n = 58): in shallow (<50 m) coastal waters, epipelagic-GZB was typically 742× the levels in deep ocean (>2,000 m) sites. However,
the ratio of GZB to primary productivity showed high values across a range of depths, i.e. this measure of the relative abundance
of gelatinous zooplankton did not co-vary with depth. 相似文献
2.
Positive plant–animal interactions are important in community ecology, but relatively little attention has been paid to their
effect on the production of mangroves, dominant halophytic trees in tropical coastal marshes. Here, the role of fiddler crab
(Uca spp.) burrowing on the growth and production of the white mangrove, Laguncularia racemosa (<2 years old), was examined in a restored marsh in Tampa Bay, Florida (27°41.65 N, 82°30.34 W) with manipulative experiments
from June 2006 to May 2007. Fiddler crab burrowing significantly increased mangrove height by 27%, trunk diameter by 25%,
and leaf production by 15%, compared to mangroves in crab exclusion enclosures. Additionally, the exclusion of fiddler crabs
significantly increased interstitial water salinity from 32.4 to 44.2, and decreased the oxidation–reduction potential of
the low organic sediments, but did not affect soil pH or sulfide concentration. Mangrove height, trunk diameter, and leaf
production along a transect that varied in crab burrow density were positively associated with the number of crab burrows.
Further, the density of sympatric Spartina alterniflora shoots was positively correlated with crab burrow density along the transect. As in temperate marshes, fiddler crabs can
have significant ecological effects on mangrove communities, serving as ecological engineers by modulating the amount of resources
available to marsh plants, and by altering the physical, chemical, and biological state of these soft sediment communities.
In restored coastal systems that typically have very poor sediment quality, techniques such as soil amendment could be used
to facilitate a more natural interaction between crabs and mangroves in ecosystem development. 相似文献
3.
Lilia Araujo Noreiva Villa Nuris Camargo Maikellys Bustos Theobaldo Garc��a Avismelsi de Jesus Prieto 《Environmental Chemistry Letters》2011,9(1):13-18
The occurrence of pharmaceuticals in natural waters is a potential threat to human nutrition and ecosystem quality. The persistence
of the acidic pharmaceuticals gemfibrozil, naproxen and mefenamic acid was studied in surface waters of Maracaibo Lake and
Tule reservoir (Venezuela) under laboratory conditions. A quick and easy analytical method was developed for the determination
of the acidic drugs at microgram per liter levels using aqueous derivatization, liquid–liquid extraction and gas chromatography–mass
spectrometry. Pharmaceuticals degradation followed a pseudo first-order kinetic and their half-lives were calculated for every
experimental condition. Under sunlight, naproxen and mefenamic acid were degraded at moderate rates with half-lives from 9.6 ± 0.5
to 27.0 ± 6.6 days, while gemfibrozil had a higher persistence (t
1/2 = 119.5 ± 15.6 − 288.8 ± 61.3 days). 相似文献
4.
Fu-Lin Evelyn Chu Eric D. Lund Paul R. Littreal Kate E. Ruck Ellen Harvey Jean-René Le Coz Yanic Marty Jeanne Moal Philippe Soudant 《Marine Biology》2009,156(2):155-169
The kinetics and efficiency of sterol production and bioconversion of phytosterols in two heterotrophic protists Oxyrrhis marina and Gyrodinium dominans were examined by feeding them two different algal species (Rhodomonas salina and Dunaliella tertiolecta) differing in sterol profiles. R. salina contains predominantly brassicasterol (≅99%) and <2% cholesterol. The major sterols in D. tertiolecta are ergosterol (45–49%), 7-dehydroporiferasterol (29–31%) and fungisterol (21–26%). O. marina fed R. salina metabolized dietary brassicasterol to produce 22-dehydrocholesterol and cholesterol. O. marina fed D. tertiolecta metabolized dietary sterols to produce cholesterol, 22-dehydrocholesterol, brassicasterol and stigmasterol. G. dominans fed either R. salina or D. tertiolecta metabolized dietary sterols to make cholesterol, brassicasterol and a series of unknown sterols. When protists were fed R. salina, which contains cholesterol, the levels of cholesterol were increased to a magnitude of nearly 5- to 30-fold at the phytoplankton-heterotrophic
protist interface, equivalent to a production of 172.5 ± 16.2 and 987.7 ± 377.7 ng cholesterol per mg R. salina carbon consumed by O. marina and G. dominans, respectively. When protists were fed D. tertiolecta, which contains no cholesterol, a net production of cholesterol by the protists ranged from 123.2 ± 30.6 to 871.8 ± 130.8 ng
per mg algal C consumed. Cholesterol is not only the dominant sterol, but a critical precursor for many physiologically functional
biochemicals in higher animal. As intermediates, these heterotrophic protists increase the amount of cholesterol at the phytoplankton–zooplankton
interface available to higher trophic levels relative to zooplankton feeding on algae directly. 相似文献
5.
The microphytoplankton assemblages were studied from water samples collected at eight discrete depths in the top 120 m at
five central (open ocean) and four western (shelf/slope region) locations in the Bay of Bengal. The Bay is a low-productive
warm pool regime with poor inorganic nutrient inputs to its intensely stratified surface layer despite the very large riverine
influx. In addition, the prolonged cloud cover has an adverse effect on the top 25–40 m, on primary production, chlorophyll
concentration and phytoplankton assemblages. Microphytoplankton were the most abundant in the northern area of the Bay. A
total of 153 phytoplankton species were identified during this study. The most abundant species (at least 1,800 individual
cells belonging to a given species or ≥2% of the total counts of identified specimens) during this study were: Thalassiothrix longissima, Thalassiothrix fauenfeldii, Rhizosolenia styliformis, Nitzschia angularis, Thalassionema nitzschioides, Coscinodiscus radiatus, Chaetoceros eibenii, Skeletonema costatum, Coscinodiscus concinnus and Chaetoceros coarctatus. Similarly, there were 20 moderately abundant (≥0.5 but <2%) species. Thirty-three of the least abundant species (<0.5%)
occurred at one station. Diatom species, T. fauenfeldii and T. longissima were ubiquitous in the study area. The exclusive occurrence of S. costatum in the northernmost stations suggests that it proliferates only in the low-salinity regions with adequate silica from the
land inputs. Abundance of pennate diatoms was higher in the open Bay compared to that of centric diatoms in the more productive
northern locations and the western Bay. There appears to be a basic difference between near shore flora and offshore flora.
This first analysis of phytoplankton assemblages from the offshore Bay suggests that while there is predominance of only a
few species, the Bay harbors very diverse diatom communities that seem to be syntrophic, non-competitive and co-habiting in
the generally low nutrient, stratified surface waters. 相似文献
6.
Michael D. Arendt Albert L. Segars Julia I. Byrd Jessica Boynton Jeffrey A. Schwenter J. David Whitaker Lindsey Parker 《Marine Biology》2012,159(1):113-125
Sixteen satellite-tagged adult male loggerhead sea turtles (Caretta caretta) dispersed widely from an aggregation near Port Canaveral, Florida, USA (28°23′N, −80°32′W) after breeding. Northbound males
migrated further (990 ± 303 km) than southbound males (577 ± 168 km) and transited more rapidly (median initial dive duration = 6
(IQR = 4–16) versus 19 (IQR = 10–31) min, respectively).. Migration occurred along a depth corridor (20–40 m) except where
constricted by a narrow continental shelf width. Males foraged in areas 27 ± 41 km2 day−1 at locations <1–80 km from shore for 100.1 ± 60.6 days, with variability in foraging patterns not explained by turtle size
or geography. Post-breeding dispersal patterns were similar to patterns reported for adult female loggerhead sea turtles in
this region and adult male loggerhead sea turtles elsewhere in the northern hemisphere; however, foraging ground distributions
were most similar to adult female loggerhead sea turtles in this region. 相似文献
7.
Life history and reproductive strategies influence population dynamics at the inter- and intra-specific level. Environmental
conditions suitable for gonad development and spawning, the reproductive range, may be a smaller portion of the broader species
distribution. The only known breeding population of veined rapa whelks (Rapana venosa) in North America is in Chesapeake Bay, USA. There is considerable interest in the potential reproductive range of this non-indigenous
species given the rapa whelk’s negative impacts on commercial shellfish species in both its native and introduced ranges.
Weight-specific reproductive output is described for wild caught Chesapeake Bay rapa whelks maintained in flow-through mesocosms
for 2 years. Measured reproductive output within and between egg capsule deposition seasons (years) in relation to water temperature,
salinity, daylength, and female size is used to describe the rapa whelk’s reproductive range. Egg capsule production is influenced
by seasonal and absolute water temperatures as well as seasonal daylength cycles. Egg capsule deposition by Chesapeake Bay
rapa whelks begins at water temperatures of approximately 18°C and continues for 11–15 weeks. Forty to 70% of female whelks
deposited egg capsules in most weeks during this season, producing 150–200 egg capsules female−1 week−1. Water temperatures >28°C caused reduced egg capsule production relative to temperatures of 20–25°C. Egg capsule production
was positively related to seasonal changes in daylength, and two peaks of egg capsule deposition were observed in the 2001
and 2002 deposition seasons. The combination of declining daylength and higher water temperatures in late summer was associated
with the cessation of egg capsule deposition. A lower average weight specific reproductive output in 130–145 mm SL rapa whelks
(average 12 ± 1%) than in 90–106 mm SL rapa whelks (average 22 ± 1% of body weight) may reflect a life history that balances
the physiological costs of maintaining a large body mass with the production of many planktonic larvae from multiple clutches
of egg capsules per breeding season over a 10–15-year lifespan. Estimates of the cumulative day-degree requirements corresponding
to the annual initiation of egg capsule deposition were 238 and 236 for 2001 and 2002, respectively. Reproductive output and
day-degree requirements for Chesapeake Bay rapa whelks were similar to values calculated from previous studies of native muricids
(Eupleura caudata and Urosalpinx cinerea). A latitudinal range of 30–41° (N and S) is predicted as the realized reproductive range for rapa whelk populations on the
basis of the day-degree requirements for native whelks and reproductively active invasive rapa whelk populations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
The annual population dynamics (nauplii, old copepodites CIV–CV and adults) and seasonal variations in reproductive parameters
of the cyclopoid copepod Oithona similis were investigated on the basis of the data 1999–2006 in Kola Bay, a large subarctic fjord in the Barents Sea. Population
density of O. similis ranged from 110 to 9,630 ind m−3 and averaged 1,020 ± 336 ind m−3. The relative abundance of adults was high during winter (~60%). At the end of winter (mid-March), the population included
a large percentage of later-stage copepodites (stage CIV 23% and stage CV 57%). There were two periods of mass spawning, in
late June and September. Autumn and summer generations strongly differed in abundance, average prosome length (PL), clutch
size (CS), egg diameter (D), egg production rates (EPR and SEPR) and female secondary production. Average PL decreased with increasing water temperature,
while D and CS were strongly correlated with PL but unaffected by temperature. Annual average EPR and SEPR were 0.55 ± 0.18 eggs female−1 day−1 and 0.0011 ± 0.003 day−1, respectively. Female secondary production averaged 0.8 ± 0.3 μg C m−3 day−1 (range 0.001–3.58). There were positive relationships between abundance, EPR, SEPR, production and water temperatures. Reproductive
parameters appeared to be controlled by hydrological factors and food conditions. 相似文献
9.
A. A. Keller C. Taylor C. Oviatt T. Dorrington G. Holcombe L. Reed 《Marine Biology》2001,138(5):1051-1062
The seasonal productivity cycle and factors controlling annual variation in the timing and magnitude of the winter–spring
bloom were examined for several locations (range: 42°20.35′–42°26.63′N; 70°44.19′–70°56.52′W) in Boston Harbor and Massachusetts
Bay, USA, from 1995 to 1999, and compared with earlier published data (1992–1994). Primary productivity (mg C m−2 day−1) in Massachusetts Bay from 1995 to 1999 was generally characterized by a well-developed winter–spring bloom of several weeks
duration, high but variable production during the summer, and a prominent fall bloom. The bulk of production (mg C m−3 day−1) typically occurred in the upper 15 m of the water column. At a nearby Boston Harbor station a gradual pattern of increasing
areal production from winter through summer was more typical, with the bulk of production restricted to the upper 5 m. Annual
productivity in Massachusetts Bay and Boston Harbor ranged from a low of 160 g C m−2 year−1 to a high of 787 g C m−2 year−1 from 1992 to 1999. Mean annual productivity was higher (mean=525 g C m−2 year−1) and more variable near the harbor entrance than in western Massachusetts Bay. At the harbor station productivity varied
more than 3.5-fold (CV=40%) over an 8 year sampling period. Average annual productivity (305–419 g C m−2 year−1) and variability around the means (CV=25–27%) were lower at both the outer nearfield and central nearfield regions of Massachusetts
Bay. Annual productivity in 1998 was unusually low at all three sites (<220 g C m−2 year−1) due to the absence of a winter–spring phytoplankton bloom. Potential factors influencing the occurrence of a spring bloom
were investigated. Incident irradiance during the winter–spring period was not significantly different (P > 0.05) among years (1995–1999). The mean photic depth during the bloom period was significantly deeper (P < 0.05) in 1998, signifying greater light availability with depth. Nutrients were also in abundance during the winter–spring
of 1998 with stratified conditions not observed until May. In general, the magnitude of the winter–spring bloom in Massachusetts
Bay from 1995 to 1999 was significantly correlated with winter water temperature (r
2=0.78) and zooplankton abundance (r
2=0.74) over the bloom period (typically February–April). The absence of the 1998 bloom was associated with higher than average
water temperature and elevated levels of zooplankton abundance just prior to, and during, the peak winter–spring bloom period.
Received: 3 July 2000 / Accepted: 6 December 2000 相似文献
10.
Strong variability in bacterioplankton abundance and production in central and western Bay of Bengal
Veronica Fernandes Nagappa Ramaiah Jane T. Paul Sugandha Sardessai R. Jyoti Babu Mangesh Gauns 《Marine Biology》2008,153(5):975-985
With large influx of freshwater that decreases sea-surface salinities, weak wind forcing of <10 m s−1 and almost always warm (>28°C) sea-surface temperature that stratifies and shallows the mixed layer leading to low or no
nutrient injections into the surface, primary production in Bay of Bengal is reportedly low. As a consequence, the Bay of
Bengal is considered as a region of low biological productivity. Along with many biological parameters, bacterioplankton abundance
and production were measured in the Bay of Bengal during post monsoon (September–October 2002) along an open ocean transect,
in the central Bay (CB, 88°E) and the other transect in the western Bay (WB). The latter representing the coastal influenced
shelf/slope waters. Bacterioplankton abundances (<2 × 109cells l−1) were similar to those reported from the HNLC equatorial Pacific and the highly productive northern Arabian Sea. Yet, the
thymidine uptake rates along CB (average of 1.46 pM h−1) and WB (average of 1.40 pM h−1) were less than those from the northwestern Indian Ocean. These abundances and uptake rates were higher than those in the
oligotrophic northwestern Sargasso Sea (<7 × 108 cells l−1; av 1.0 pM h−1). Concentrations of chlorophyll a (chl a), primary production rates and total organic carbon (TOC) were also measured for a comparison of heterotrophic and autotrophic
production. In the WB, bacterioplankton carbon biomass equaled ∼ 95% of chl a carbon than just 31% in the CB. Average bacterial:primary production (BP:PP) ratios accounted for 29% in the CB and 31% in
the WB. This is mainly due to lower primary productivity (PP) in the WB (281 mg C m−2 d−1) than in the CB (306 mg C m−2 day−1). This study indicates that bacteria–phytoplankton relationship differs in the open (CB) and coastal waters (WB). Higher
abundance and contrastingly low bacterial production (BP) in WB may be because of the riverine bacteria, brought in through
discharges, becoming dormant and unable to reproduce in salinities of 28 or more psu. Heterotrophic bacteria appear to utilize
in situ DOC rather rapidly and their carbon demand is ∼50% of daily primary production. It is also apparent that allochthonous
organic matter, in particular in the western Bay, is important for meeting their carbon demand. 相似文献
11.
Aaron D. Spares Michael J. W. Stokesbury Ron K. O’Dor Terry A. Dick 《Marine Biology》2012,159(8):1633-1646
The influence of salinity, temperature and prey availability on the marine migration of anadromous fishes was determined by describing the movements, habitat use and feeding behaviours of Arctic char (Salvelinus alpinus). The objectives were to determine whether char are restricted to the upper water column of the inter-/subtidal zones due to warmer temperatures. Twenty-seven char were tracked with acoustic temperature/pressure (depth) transmitters from June to September, 2008/2009, in inner Frobisher Bay, Canada. Most detections were in surface waters (0–3 m). Inter-/subtidal movements and consecutive repetitive dives (maximum 52.8 m) resulted in extreme body temperature shifts (−0.2–18.1 °C). Approximately half of intertidal and subtidal detections were between 9–13 °C and 1–3 °C, respectively. Stomach contents and deep diving suggested feeding in both inter-/subtidal zones. We suggest that char tolerate cold water at depth to capture prey in the subtidal zone, then seek warmer water to enhance feeding/digestion physiology. 相似文献
12.
Apurba Kumar Das Dilip Kumar Jha M. Prashanthi Devi Biraja Kumar Sahu N. V. Vinithkumar R. Kirubagaran 《Journal of Coastal Conservation》2014,18(3):249-255
The present study was carried out to determine the mangrove area water quality, mangrove diversity and density at Minnie Bay, Lalaji Bay and Aerial Bay (Andaman Islands, India). The physicochemical parameters such as salinity, nitrate, inorganic phosphate and total phosphorus varied significantly. Mangrove diversity was high at Minnie Bay while density at Aerial Bay. Rhizophora mucronata dominated at all three sites during the study period. Shannon-Wiener diversity index (H′?=?2.261) and Pielou’s evenness (J′?=?0.8348) were high at Minnie Bay. The higher species density cover (5.679 Nos./m2) was recorded at Aerial Bay. Bray-Curtis cluster analysis showed 63.35 % similarity and formed two clusters. Though uplift and subsidence of coastal land due to the Mw 9.3 Sumatra earthquake in 2004 has affected the mangrove vegetation, its rejuvenation was observed in the newly formed inter-tidal areas due to changes in coastal geomorphology. The comparative study on physicochemical parameters, mangrove coverage and conservation are discussed in detail. 相似文献
13.
Strontium (Sr) and calcium (Ca) contents in the otoliths of yellow and silver European eels [Anguilla anguilla (L.)] collected from coastal waters of the Baltic Sea and a freshwater lake in Sweden were examined by wavelength dispersive
X-ray spectrometry with an electron microprobe. The mean Sr/Ca ratios from elver check to otolith edge were significantly
higher for the eels from coastal waters (5.39 ± 1.09‰) than for those from the lake (0.71 ± 0.89‰). The evidence indicates
that European eels in the Baltic Sea do not necessarily migrate into freshwater streams during the growth phase.
Received: 30 September 1999 / Accepted: 6 April 2000 相似文献
14.
Adult Vinciguerria nimbaria are the main prey of tuna during the tuna fishing season (late autumn and winter) in the equatorial Atlantic (0–4°N, and
~15°W). V. nimbaria trophic behavior in the fishing grounds was studied in relation to hydrobiological factors to determine its role in the trophic
food web. Sampling stations spaced by 20 nautical miles were set up along a 15°W north–south transect from 4°N to 0°40S. At
each station, the temperature and vertical fluorescence profiles were recorded. Nitrate and chlorophyll a analyses were performed on water sampled at different levels in the euphotic zone. Vertical plankton hauls were carried out
at depths of 0–100 and 0–200 m using a standard WP2 net fitted with a 200-μm mesh gauze. Vinciguerria nimbaria adults were collected using a young-fish mid-water trawl net (10 × 15 m opening mouth, 10 mm cod end mesh). The weight of
the stomach contents, the stomach fullness index, the number of prey, the frequency of occurrence and the prey preponderance
were recorded for 20 fish from each haul. An oligotrophic typical tropical structure (TTS) was found between 1° and 4°N where
small zooplankton was relatively abundant above or near the thermocline. In the TTS, V. nimbaria behaved as an epipelagic fish, feeding on the dominant small prey during the daytime. In turn, it was a prey for tuna. In
the equatorial zone, where zooplankton was more abundant than in the north equatorial zone, V. nimbaria behaved as a mesopelagic fish and as an opportunistic mesozooplankton feeder. It consumed a wide range of sizes of food,
feeding on the most abundant species of zooplankton as well as the largest zooplankton species, possibly while migrating towards
the surface in the late afternoon or in the deep layer. 相似文献
15.
Octavio Aburto-Oropeza Isaí Dominguez-Guerrero José Cota-Nieto Tomás Plomozo-Lugo 《Marine Biology》2009,156(12):2461-2472
We examined recruitment and ontogenetic habitat shifts of the yellow snapper Lutjanus argentiventris in the Gulf of California, by conducting surveys and collections in multiple mangrove sites and major marine coastal habitats
from 1998 to 2007. Over 1,167 juvenile individuals were collected and 516 otoliths were aged to describe the temporal pattern
of the settlement. L. argentiventris recruits in mangroves, where juveniles remain until they are approximately 100 mm in length or 300-days-old. Back-calculated
settlement dates and underwater surveys indicated a major recruitment peak during September and October, around 8 days before
and after the full moon. The majority of mangrove sites in the Gulf of California had a similar L. argentiventris average size at the beginning of the settlement season for the cohort of 2003; although there were significant differences
in individual sizes at the end of the nursery stage. When sub-adults leave mangroves, they live in shallow rocky reefs and
later become abundant in deeper rocky reefs. The density of migratory individuals (10–20 cm SL) decreased exponentially as
the distance between a reef and a nearby mangrove site increased. This finding has important implications for local fishery
regulations and coastal management plans. 相似文献
16.
While qualitative observations of jellyfish intraguild predation abound in the literature, there are only few rate measurements
of these interactions. We quantified predation rates among two common jellyfish in northern boreal waters, Cyanea capillata and its prey Aurelia aurita, both of which also feed on crustacean zooplankton and fish larvae. A series of incubation experiments using a wide range
of prey concentrations (0.38–3.8 m−3) in large containers (2.6 m3) was carried out. By replenishing the prey continuously as they were captured we maintained a nearly constant prey concentrations.
Ingestion rates increased linearly up to prey concentrations of 1.92 m−3, yielding maximum clearance rates of ∼2.37 ± 0.39 m3 predator−1 h−1 for C. capillata predators 16 ± 2.3 cm in diameter. Mean ingestion rate at saturated prey concentrations (1.92–3.85 m−3) was 4.01 ± 0.78 prey predator−1 h−1. Behavioral observations suggested that predators did not alter their swimming behavior during meals, and thus that feeding
rates were generally handling limited rather than encounter limited. Predators captured more prey than needed, and semi-digested
prey was often discarded when fresh prey was encountered. 相似文献
17.
Holothuroidea represent the dominant benthic megafauna in hadal trenches (~6,000–11,000 m), but little is known about their
behaviour and functional role at such depths. Using a time-lapse camera at 8,074 m in the Peru–Chile Trench (SE Pacific Ocean),
we provide the first in situ observations of locomotory activity for the elasipodid holothurian Elpidia atakama Belyaev in Shirshov Inst Oceanol 92:326–367, (1971). Time-lapse sequences reveal ‘run and mill’ behaviour whereby bouts of feeding activity are interspersed by periods of locomotion.
Over the total observation period (20 h 25 min), we observed a mean (±SD) locomotion speed of 7.0 ± 5.7 BL h−1, but this increased to 10.9 ± 7.2 BL h−1 during active relocation and reduced to 4.8 ± 2.9 BL h−1 during feeding. These observations show E. atakama translocates and processes sediment at rates comparable to shallower species despite extreme hydrostatic pressure and remoteness
from surface-derived food. 相似文献
18.
The food sources of benthic deposit feeders were investigated at three stations in an estuarine mudflat (Idoura Lagoon, Sendai
Bay, Japan) during July and August 2005, using δ13C and δ15N ratios. Sediment at the stations was characterized by low chlorophyll (chl) a content (0–1 cm depth, <4 μg cm−2) and the dominance of riverine–terrestrial materials (RTM) in the sediment organic matter (SOM) pool. Surface-deposit feeders
(Macoma contabulata, Macrophthalmus japonicus, and Cyathura muromiensis) exhibited much higher δ13C values (−18.4 to −12.4‰) than did the SOM pool (<−25‰). A δ13C-based isotopic mixing model estimated that benthic diatoms comprised 45–100% (on average) of their assimilated diet, whereas
RTM comprised a lesser fraction (29% maximum). The major diet of the deep-deposit feeding polychaetes Notomastus sp. and Heteromastus sp. was benthic diatoms and/or marine particulate organic matter (POM), with little RTM assimilated (39% maximum). The consumers
appeared to lack specific digestive enzymes and to use detritus-derived carbon only after its transfer to the microbial biomass.
The isotopic mixing model also showed that the dietary contribution of RTM increased slightly (15% maximum) in the vicinity
of freshwater input, suggesting that spatial changes in RTM supply affect the dietary composition of deposit feeders. These
results clearly demonstrate that deposit feeders selectively ingest and/or assimilate the more nutritious microalgal fractions
in the SOM pool. Such adaptations may allow enhanced energy gain in estuarine mudflats that are rich in vascular plant detritus
with low nutritive value. 相似文献
19.
Phytoplankton and pigment distributions in an anticyclonic slope water oceanic eddy (SWODDY) in the southern Bay of Biscay 总被引:1,自引:0,他引:1
An anticyclonic slope water oceanic eddy (SWODDY), named AE6, was sampled in the southern Bay of Biscay from 12 to 31 August 1998 to assess changes in the abundance and composition of phytoplankton assemblages related to the mesoscale feature. SWODDY AE6 showed characteristic biological signatures. A twofold increase in chlorophyll a concentration was found at the eddy centre relative to surrounding waters. Picoplankton cells accounted for a lower fraction of total chlorophyll a values at the eddy centre (44–50%) than outside the eddy (54–61%). Microscopic cell counts and HPLC pigment analysis showed that diatoms were almost entirely confined to the eddy centre, but both techniques yielded different results when studying other phytoplankton groups. Microscopic cell counts indicated that the spatial distribution of diatoms, dinoflagellates and unidentified flagellates was significantly influenced by SWODDY AE6, showing maximum abundance inside the mesoscale feature. HPLC pigment analysis provided more detailed information about the composition of pico–nanoplanktonic organisms. Pigment data processed by means of the CHEMTAX program showed "chlorophytes", "haptophytes" and "dinoflagellates II" (having haptophyte-like pigments and gyroxanthin-diester) as the more abundant "pigment classes" at the eddy centre, whereas dominance of "chlorophytes" and higher contribution of "cyanobacteria" (type Synechococcus) were estimated in the surrounding waters.Communicated by S.A. Poulet, Roscoff 相似文献
20.
A. Sakka Hlaili B. Grami Hassine Hadj Mabrouk M. Gosselin D. Hamel 《Marine Biology》2007,151(2):767-783
Phytoplankton growth and microzooplankton grazing were investigated in the restricted Bizerte Lagoon in 2002 and 2004. The
2002 study, carried out at one station from January to October, showed significant seasonal variations in phytoplankton dynamics.
High growth rates (0.9–1.04 day−1), chlorophyll a (Chl a) concentrations (6.6–6.8 μg l−1) and carbon biomass (392–398 μg C l−1) were recorded in summer (July), when several chain-forming diatoms had intensively proliferated and dominated the carbon
biomass (74%). In 2004, four stations were studied during July, a period also characterized by the high proliferation of several
diatoms that made up 70% of the algal carbon biomass. In 2004, growth rates (0.34–0.45 day−1) and biomass of algae (2.9–5.4 μg Chl a l−1 and 209–260 μg C l−1) were low, which may be related to the lower nutrient concentrations recorded in 2004. Microzooplankton >5 μm were mainly
composed of heterotrophic dinoflagellates and ciliates. Microzooplankton biomass peaked during summer (2002 320–329, 2004
246–361 μg C l−1), in response to the enhanced phytoplankton biomass and production. The grazer biomass was dominated by ciliates (71–76%)
in July 2002 and by heterotrophic dinoflagellates (52–67%) in July 2004. Throughout the year and at different stations, microzooplankton
grazed actively on phytoplankton, removing 26–58% of the Chl a and 57-84% of the primary production. In 2002, the highest grazing impact was observed on the large algae (>10 μm) during
the period of diatom dominance. These results have a significant implication for carbon export to depth. Indeed, the recycling
of most of the diatom production by the microbial food web in the upper water column would reduce the flux of material to
the seafloor. This should be considered when modeling the carbon cycling in coastal environments and under conditions of diatom
dominance. During both studies, ciliates had higher growth rates (0.5–1.5 day−1) and a higher carbon demand (165–470 μg C l−1 day−1) than dinoflagellates (0.1–0.5 day−1, 33–290 μg C l−1 day−1). Moreover, when grazer biomass was dominated by ciliates (in July 2002), herbivory accounted for 71–80% of the C ingested
by microzooplankton while it accounted only for 14–23% when dinoflagellates dominated the grazer biomass (in July 2004). These
results suggest that, in contrast to findings from open coastal waters, ciliate species of the restricted Bizerte Lagoon were
more vigorous grazers of the large algae (diatoms) than were dinoflagellates. 相似文献