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1.
Phytoplankton blooms are strongly impacted by microzooplankton grazing in coastal North Pacific waters 总被引:1,自引:0,他引:1
Phytoplankton growth and microzooplankton grazing were measured in two productive coastal regions of the North Pacific: northern
Puget Sound and the coastal Gulf of Alaska. Rates of phytoplankton growth (range: 0.09–2.69 day−1) and microzooplankton grazing (range: 0.00–2.10 day−1) varied seasonally, with lowest values in late fall and winter, and highest values in spring and summer. Chlorophyll concentrations
also varied widely (0.19–13.65 μg l−1). Large (>8 μm) phytoplankton cells consistently dominated phytoplankton communities under bloom conditions, contributing
on average 65% of total chlorophyll biomass when chlorophyll exceeded 2 μg l−1. Microzooplankton grazing was an important loss process affecting phytoplankton, with grazing rates equivalent to nearly
two-thirds (64%) of growth rates on average. Both small and large phytoplankton cells were consumed, with the ratio of grazing
to growth (g:μ) for the two size classes averaging 0.80 and 0.42, respectively. Perhaps surprisingly, the coupling between microzooplankton
grazing and phytoplankton growth was tighter during phytoplankton blooms than during low biomass periods, with g:μ averaging 0.78 during blooms and 0.49 at other times. This tight coupling may be a result of the high potential growth
and ingestion rates of protist grazers, some of which feed on bloom-forming diatoms and other large phytoplankton. Large ciliates
and Gyrodinium-like dinoflagellates contributed substantially to microzooplankton biomass at diatom bloom stations in the Gulf of Alaska,
and microzooplankton biomass overall was strongly correlated with >8 μm chlorophyll concentrations. Because grazing tended
to be proportionally greater when phytoplankton biomass was high, the absolute amount of chlorophyll consumed by microzooplankton
was often substantial. In nearly two-thirds of the experiments (14/23), more chlorophyll was ingested by microzooplankton
than was available for all other biological and physical loss processes combined. Microzooplankton were important intermediaries
in the transfer of primary production to higher trophic levels in these coastal marine food webs.
Received: 12 November 1999 / Accepted: 4 October 2000 相似文献
2.
Contribution of salps to carbon flux of marginal ice zone of the Lazarev Sea, southern ocean 总被引:3,自引:0,他引:3
In order to estimate the in situ grazing rates of Salpa thompsoni and their implications for the development of phytoplankton blooms and for the sequestration of biogenic carbon in the high
Antarctic, a repeat-grid survey and drogue study were carried out in the Lazarev Sea during austral summer of 1994/1995 (December/January).
Exceptionally high grazing rates were measured for S. thompsoni at the onset of a phytoplankton bloom (0.2 to 0.8 μg chlorophyll a l−1) in December 1994, with up to ≃160 μg of plant pigments consumed by an individual salp of 7 to 10 cm length per day. Dense
salp swarms extended throughout the marginal ice zone, consuming up to 108% of daily phytoplankton production and 21% of the
total chlorophyll a stock. Due to the much faster sinking rates and higher carbon content of salp faecal pellets, the efficiency of downward
carbon flux through salps is much higher than through the other major grazers, krill and copepods. S. thompsoni can thus export large amounts of biogenic carbon from the euphotic zone to the deep ocean. With the observed ingestion rates
during December 1994, this flux could have attained levels of up to 88 mg C m−2 d−1, accounting for the bulk of the vertical transport of carbon in the Lazarev Sea. However, in January 1995, when phytoplankton
concentrations exceeded a threshold level of 1.0 to 1.5 μg chlorophyll a l−1, salps experienced a drastic reduction in their feeding efficiency, possibly as a result of clogging of their filtering apparatus.
This triggered a dramatic reversal in the relationship, during which a dense phytoplankton bloom developed in conjunction
with the collapse of the salp population. Increases in the biomass and geographic range of the tunicate S. thompsoni have occurred in several areas of the southern ocean, often in parallel with a rise in sea-surface temperature during sub-decadal
periods of warming anomalies.
Received: 10 August 1997 / Accepted: 21 October 1997 相似文献
3.
Phytoplankton community structure and primary production in small intertidal estuarine-bay ecosystem (eastern English Channel,France) 总被引:1,自引:0,他引:1
From May 2002 to October 2003, a fortnightly sampling programme was conducted in a restricted macrotidal ecosystem in the
English Channel, the Baie des Veys (France). Three sets of data were obtained: (1) physico-chemical parameters, (2) phytoplankton community structure illustrated
by species composition, biovolume and diversity, and (3) primary production and photosynthetic parameters via P versus E curves. The aim of this study was to investigate the temporal variations of primary production and photosynthetic parameters
in this bay and to highlight the potential links with phytoplankton community structure. The highest level of daily depth-integrated
primary production Pz (0.02–1.43 g C m−2 d−1) and the highest maximum photosynthetic rate P
B
max (0.39–8.48 mg C mg chl a
−1 h−1) and maximum light utilization coefficient αB [0.002–0.119 mg C mg chl a
−1 h−1 (μmol photons m−2 s−1)] were measured from July to September. Species succession was determined based on biomass data obtained from cell density
and biovolume measurements. The bay was dominated by 11 diatoms throughout the year. However, a Phaeocystis globosa bloom (up to 25 mg chl a m−3, 2.5 × 106 cells l−1) was observed each year during the spring diatom bloom, but timing and intensity varied interannually. Annual variation of
primary production was due to nutrient limitation, light climate and water temperature. The seasonal pattern of microalgal
succession, with regular changes in composition, biovolume and diversity, influenced the physico-chemical and biological characteristics
of the environment (especially nutrient stocks in the bay) and thus primary production. Consequently, investigation of phytoplankton
community structure is important for developing the understanding of ecosystem functioning, as it plays a major role in the
dynamics of primary production. 相似文献
4.
Nutrients were added separately and combined to an initial concentration of 10 μM (ammonium) and/or 2 μM (phosphate) in a series of experiments carried out with the giant clam Tridacna maxima at 12 microatolls in One Tree Island lagoon, Great Barrier Reef, Australia (ENCORE Project). These nutrient concentrations
remained for 2 to 3 h before returning to natural levels. The additions were made every low tide (twice per day) over 13 and
12 mo periods for the first and second phase of the experiment, respectively. The nutrients did not change the wet tissue
weight of the clams, host C:N ratio, protein content of the mantle, calcification rates or growth rates. However, ammonium
(N) enrichment alone significantly increased the total population density of the algal symbiont (Symbiodinium sp.: C = 3.6 · 108 cell clam−1, N = 6.6 · 108 cell clam−1, P = 5.7 · 108 cell clam−1, N + P = 5.7 · 108 cell clam−1; and C = 4.1 · 108 cell clam−1, N = 5.1 · 108 cell clam−1, P = 4.7 · 108 cell clam−1, N + P = 4.5 · 108 cell clam−1, at the end of the first and second phases of the experiment, respectively), although no differences in the mitotic index
of these populations were detected. The total chlorophyll a (chl a) content per clam but not chlorophyll a per cell also increased with ammonium addition (C = 7.0 mg chl a clam−1, N = 13.1 mg chl a clam−1, P = 12.9 mg chl a clam−1, N + P = 11.8 mg chl a clam−1; and C = 8.8 mg chl a clam−1, N = 12.8 mg chl a clam−1; P = 11.2 mg chl a clam−1, N + P = 11.3 mg chl a clam−1, at the end of the first and second phases of the experiment, respectively). The response of clams to nutrient enrichment
was quantitatively small, but indicated that small changes in inorganic nutrient levels affect the clam–zooxanthellae association.
Received: 2 June 1997 / Accepted: 9 June 1997 相似文献
5.
Standing crops and vertical distribution of four groups of marine planktonic ciliates in relation to phytoplankton chlorophyll a 总被引:6,自引:0,他引:6
Standing crops and the vertical distribution of four groups of ciliates, autotrophic naked ciliates (ANC), heterotrophic naked ciliates (HNC ), mixotrophic naked ciliates (MNC) and loricated ciliates (LC ), were analysed in relation to phytoplankton chlorophyll a in the western Pacific. Data were gathered from the upper 60 to 200 m of water in the subarctic North Pacific in spring,
in the subtropical North Pacific in spring, in Toyama Bay in summer, off eastern Australia in spring and off Sanriku in spring
and fall. Of the four groups, the standing crop of HNC (cells l−1) showed the highest correlation to phytoplankton chloro- phyll a [CHL, μg l−1; r=0.66, n=365 (HNC=490 ×CHL
0.653)]. Depths of the maximum layers of HNC and MNC were usually shallower than that of chlorophyll a, while those of ANC and LC occurred frequently beneath the chlorophyll maximum layer. This indicates that these four ciliate groups are substantially
different from each other, and that each group holds a different ecological position in the marine microbial food web.
Received: 27 October 1997 / Accepted: 27 June 1998 相似文献
6.
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
7.
C. M. Roden 《Marine Biology》1994,118(2):209-213
Water temperature, chlorophyll a and phaeophytin were recorded every 2 to 4 d, in order to describe short-term variability in phytoplankton blooms. Data were collected from May to September 1984 and March to September 1985 at shore stations on the coast of Connemara, western Ireland. Comparisons with offshore data suggest that the shore data is representative of coastal water. Chlorophyll a was highest at neap tides in spring, and at spring tides in early summer. In late summer, transient chlorophyll blooms occurred at neap tides, possibly due to a localized accumulation of flagellates in stable conditions. 相似文献
8.
The effects of blooms of the cyanobacterium Trichodesmium spp. on penaeid prawn larvae were examined using in situ and laboratory rearing experiments and plankton surveys in Albatross
Bay, Gulf of Carpentaria, Australia. The in situ experiments demonstrated that, during a bloom of Trichodesmium spp., larvae of the prawn Penaeus merguiensis did not develop beyond the first protozoea stage, and survival was low compared with times when diatoms were dominant in
the same study area. Laboratory experiments confirmed the in situ results. None of the prawn larvae fed Trichodesmium sp. in laboratory experiments developed beyond the first protozoeal stage. In contrast, 94% of prawn larvae fed the green
flagellate Tetraselmis suecica successfully developed to the second protozoea stage. Electron microscopy of larvae gut-contents revealed that Trichodesmium spp. were ingested by larvae but were of no nutritional value, resulting in starvation. A 7 yr plankton survey, from 1985
to 1992, showed that minimum abundance of prawn larvae occurs during the annual summer blooms of Trichodesmium spp. and that maximum abundance of prawn larvae generally occurs just after the bloom. There was a negative correlation between
the abundance of larvae and the abundance of Trichodesmium at individual sites, one offshore and one inshore, indicating that the blooms affect the survival of larvae. We conclude that
variations in both timing and magnitude of Trichodesmium blooms are important determinants of prawn larvae abundance in Albatross Bay.
Received: 28 April 1997 / Accepted: 2 April 1998 相似文献
9.
Lena von Harbou Corinna D. Dubischar Evgeny A. Pakhomov Brian P. V. Hunt Wilhelm Hagen Ulrich V. Bathmann 《Marine Biology》2011,158(9):2009-2026
Feeding dynamics of the Antarctic salps Ihlea racovitzai and Salpa thompsoni were studied in the Lazarev Sea in fall 2004, summer 2005–2006 and winter 2006. Pigment concentrations in the guts of both
species were positively correlated with ambient surface chlorophyll a (chl a). No evidence was found for salp clogging even at dense surface concentrations of up to 7 μg chl a L−1. However, gut pigment concentrations had a lower range than ambient pigment concentrations, suggesting that salps increased
retention times of ingested material in low-food environments. For medium-sized I. racovitzai and S. thompsoni, estimated individual daily rations reached 7–10 and >100% of body carbon in winter and summer, respectively. Daily respiratory
needs of I. racovitzai and S. thompsoni accounted for 28 and 22% of daily carbon assimilation based on pigment ingestion rates in winter, and for 2 and 1% in summer,
respectively. The grazing impact of the salp populations on the phytoplankton standing stock was negligible during all seasons
due to generally low salp densities. Fatty acid trophic biomarkers in the salps suggest high year-round contributions of flagellates
and modest contributions of diatoms to the salp’s diet. These markers showed low seasonal variability for I. racovitzai. The more pronounced seasonality of trophic markers in S. thompsoni were likely related to their generally deeper residence depth in winter linked to a seasonal alternation of sexual and asexual
generations. 相似文献
10.
Sexuality and cyst formation of the spring-bloom dinoflagellate Scrippsiella hangoei in the coastal northern Baltic Sea 总被引:3,自引:0,他引:3
The temporal sequence and the magnitude of the sexual reproduction and subsequent cyst deposition of the common spring-bloom
dinoflagellate Scrippsiella hangoei (Schiller) Larsen was studied during spring 1996 on the SW coast of Finland, Baltic Sea. The abundances of the different
size of fractions of S. hangoei (14 to 18 μm, 18 to 22 μm and >22 μm) were monitored in the water column, and the deposition of resting cysts was measured
using moored sediment traps. Cyst sedimentation rates were measured throughout the seasonal cycle in order to estimate cyst
resuspension rates for the quantitative assessment of the fraction of population undergoing encystment. The onset of sexual
reproduction, indicated by a significant increase of the small cells (14 to 18 μm) representing gametes, occurred in a nutrient
replete environment well before the exponential growth phase and peak abundances of vegetative cells. Gamete formation was
followed by high abundances of large cells (>22 μm) representing planozygotes, and subsequent sedimentation of resting cysts.
Approximately 60% of the asexually growing bloom population was estimated to form planozygotes, suggesting that encystment
was an important factor in bloom termination and possibly plays a role in the regulation of the magnitude of the bloom. Finally
encystment accounted for 40% of the entire S. hangoei population, resulting in a considerable loss of the bloom population and an input of the vernal phytoplankton biomass to
the benthos.
Received: 11 December 1998 / Accepted: 8 April 1999 相似文献
11.
Importance of cysts in the population dynamics of the red tide flagellate Heterosigma akashiwo (Raphidophyceae) 总被引:7,自引:0,他引:7
To elucidate roles of cysts in occurrences of Heterosigma akashiwo blooms, cyst dynamics were studied in northern Hiroshima Bay, the Seto Inland Sea of Japan, where H. akashiwo regularly forms red tide in June. Monthly measurements of seasonal changes in the densities of vegetative cells of H. akashiwo and their germinable cysts in surface sediments (top 1-cm layer) were made for 2 years at three stations. Vegetative cells
of H. akashiwo could be detected from April through December throughout the water column, and the existence of vegetative cells was confirmed
in surface waters even in winter after incubation of sampled seawater in culture medium. Germinable cysts, enumerated by the
extinction dilution method, existed in sediments in all seasons, even before and after the seasonal bloom. The effects of
incubation temperature on the germination of natural cysts of H. akashiwo in sediments were examined. Germination was not observed at 5 °C, was low at 10 °C, while it increased at 15 °C, and maintained
a high level to 25 °C. The bottom water temperature reached 15 °C (suitable for the germination of cysts) and the surface
about 18 °C or more (suitable for the growth of vegetative cells) 2 to 3 weeks before the blooms. The dark survival of H. akashiwo cysts was tested, and it was found that the cysts were viable for at least 650 d at 11 °C, and for 165 d at 25 °C, indicating
a significant role of cysts in the survival during winter and summer seasons. The cysts presumably also play an important
role in seeding primary populations into water columns when the bottom water reaches a suitable temperature (around 15 °C);
thereafter the populations develop with great annual regularity to bloom in June. These results suggest that initiation of
H. akashiwo red tides in the Seto Inland Sea could be triggered by bottom water temperature.
Received: 3 July 1998 / Accepted: 12 January 1999 相似文献
12.
Data on phytoplankton primary production, biomass, and species composition were collected during a 5 yr (1985–1989) study of Auke Bay, Alaska. The data were used to examine the interannual differences in the timing, duration, and magnitude of the spring phytoplankton blooms during each year and to relate these differences to interannual variations in weather patterns. Within any given year, a pre-bloom phase was characterized by low available light, low rates of primary production, low biomass, and predominantly small (<10µm) diatoms. During the primary bloom, integrated production rates rose to 4 to 4.5 g C m–2 d–1, and integrated biomass levels reached 415 to 972 mg chlorophyll m–2. Primary blooms were usually dominated by large diatoms (Thalassiosira spp.), and in a single year (1989) byChaetoceros spp. The primary blooms terminated upon nutrient depletion in the euphotic zone. Secondary blooms, triggered by nutrient resupply from below, occurred sporadically after the primary bloom and accounted for 4 to 31% of total spring production. The date of initiation and the duration of the primary bloom varied little from year to year (standard deviation 3 and 5 d, respectively). Seasonal production rates and biomass levels varied interannually by a factor of 2 to 3. In contrast, intra-annual variations of more than an order of magnitude, especially in biomass, occurred over periods as short as 10 d. These large variations over short time periods indicate the importance of synchronous timing between spring blooms and the production of larval fish and shellfish, which depend on an appropriate and adequate food supply for growth and survival. Parameters describing primary production (e.g. peak daily production, mean daily production, and total production during the primary bloom and the entire season) exhibited little interannual variation (coefficient of variation, CV = 10 to 19%), but a large degree of intra-annual variation (CV = 77 to 116%). Similarly, interannual variations in biomass (peak chlorophyll, mean chlorophyll) were also lower (CV = 20 to 33%) than intra-annual variations (CV = 85 to 120%). 相似文献
13.
Martin G. J. Löder Cédric Meunier Karen H. Wiltshire Maarten Boersma Nicole Aberle 《Marine Biology》2011,158(7):1551-1580
Mesocosm experiments coupled with dilution grazing experiments were carried out during the phytoplankton spring bloom 2009.
The interactions between phytoplankton, microzooplankton and copepods were investigated using natural plankton communities
obtained from Helgoland Roads (54°11.3′N; 7°54.0′E), North Sea. In the absence of mesozooplankton grazers, the microzooplankton
rapidly responded to different prey availabilities; this was most pronounced for ciliates such as strombidiids and strobilids.
The occurrence of ciliates was strongly dependent on specific prey and abrupt losses in their relative importance with the
disappearance of their prey were observed. Thecate and athecate dinoflagellates had a broader food spectrum and slower reaction
times compared with ciliates. In general, high microzooplankton potential grazing impacts with an average consumption of 120%
of the phytoplankton production (P
p
) were measured. Thus, the decline in phytoplankton biomass could be mainly attributed to an intense grazing by microzooplankton.
Copepods were less important phytoplankton grazers consuming on average only 47% of P
p
. Microzooplankton in turn contributed a substantial part to the copepods’ diets especially with decreasing quality of phytoplankton
food due to nutrient limitation over the course of the bloom. Copepod grazing rates exceeded microzooplankton growth, suggesting
their strong top-down control potential on microzooplankton in the field. Selective grazing by microzooplankton was an important
factor for stabilising a bloom of less-preferred diatom species in our mesocosms with specific species (Thalassiosira spp., Rhizosolenia spp. and Chaetoceros spp.) dominating the bloom. This study demonstrates the importance of microzooplankton grazers for structuring and controlling
phytoplankton spring blooms in temperate waters and the important role of copepods as top-down regulators of microzooplankton. 相似文献
14.
Short-term variations in the pigment composition of a spring phytoplankton bloom from an enclosed experimental ecosystem 总被引:1,自引:0,他引:1
Phytoplankton samples taken during the spring bloom in the experimental enclosed ecosystem bags at Loch Ewe, Scotland, during 1983 were analysed for carotenoids and chlorophyll compounds using high-performance liquidchromatography (HPLC). Changes in the relative proportions of these pigments were related to day-to-day changes in the composition of the bloom and the physiological state of the algae. There is clear evidence for a change in the chlorophyllide a:chlorophyll a ratio, which reached a maximum as nutrient limitation occurred. No major qualitative changes in the carotenoid components were seen during the bloom; the relative proportion, however, of some carotenoids does provide useful information on the relative abundance of certain algal type in the phytoplankton. 相似文献
15.
The spatial distribution of phytoplankton assemblages, chlorophyll, primary production and physical and chemical parameters were studied in the Pontevedra Ria in Galicia (NW Iberian Peninsula) from October 1997 to October 1998. In addition to the usual oceanographic periods described for the Galician Coast, two other periods were observed: a Prebloom or winter bloom, occurring during calm, sunny days in winter and a Continental period, related to the allochthonous intrusion of low salinity water from the Miño River in late spring. The phytoplankton biomass and production in both periods reached values of up to 145 mgChl-a m?2 and 3.6 gC m?2 day?1, respectively, which were similar to those found in summer upwelling blooms. Throughout the year, the phytoplankton biomass and primary production gradients along the ria’s axis were highly dependent on the balance between upwelling and runoff. When the latter prevailed, increased values were measured toward the inner ria, while the opposite pattern was observed during summer upwelling blooms. According to projections derived from climate models and the analysis of wind patterns, temperature and precipitation trends in the area, a drop in the productivity of the ria would be expected as a result of reduced upwelling intensity in summer and decreasing rainfall in spring. In any case the estuarine part of the ria would be the most seriously affected. 相似文献
16.
Growth and development of Calanus spp. (Copepoda) during spring phytoplankton succession in the North Sea 总被引:1,自引:0,他引:1
Experiments were carried out to determine growth and development rates of the herbivorous copepod Calanus finmarchicus (Gunnerus) under natural conditions during the phytoplankton spring bloom in the northern North Sea. From 28 April to 25 May 1983 copepodite stages I, IV and V were incubated for a 3-d period on board a ship in vessels with naturally occurring phytoplankton or cultured algae as food. Highest rates of growth and development were achieved while the diatom Chaetoceros sp. was the dominant phytoplankton organism. These rates decreased considerably when this chain-forming diatom was succeeded after one week by the small-celled diatom Thalassiosira conferta. Again one week later, during the bloom of the succeeding colonial microflagellate Corymbellus aureus, copepodite stage IV still managed to maintain moderate rates of growth and development, but these rates dropped to almost zero in CV, suggesting the start of a resting stage. Nevertheless, brood collected from this generation and from Calanus helgolandicus (Claus) was raised in the laboratory to the adult stage at high speed. Since temperature and the total phytoplankton concentration in the sea remained almost constant it seems that the retardation and arrestment of growth and development were an immediate response to a qualitative change of the food composition related to the successive blooms of different algal species. 相似文献
17.
C. H. McKenzie D. Deibel R. J. Thompson B. A. MacDonald R. W. Penney 《Marine Biology》1997,129(3):407-416
Water samples from six bays were taken over a 5-year period (1988 to 1992) to determine the distribution and abundance of
loricate choanoflagellates in coastal Newfoundland, and to assess the impact that these organisms might have on this cold
ocean food web. Scanning electron microscopy was used to study the morphology of these flagellates, allowing us to identify
11 species of loricate choanoflagellates. Parvicorbicula socialis (Meunier) Deflandre was the most abundant species (80 × 103 cells l−1), particularly during the spring diatom bloom. Single-cell species, such as Bicosta spini fera (Throndsen) Leadbeater and Calliacantha natans (Grontved) Leadbeater, were found more commonly after the spring diatom bloom in the summer months. Many of the single-cell
choanoflagellates were attached to bacteria-rich microaggregates and debris in the water column and in unpoisoned sediment
traps. The P. socialis cell flux was calculated to be 5.3 × 106 cells m−2 d−1 in late May sediment traps. P. socialis in the upper 100 m of the water column was removing 0.3% of the standing crop of bacteria each day (April/May), and the equivalent
of 7.4% of the daily bacterial production over the water column. Diel studies of P. socialis in Conception Bay suggest that the sharp decline in population numbers observed in midnight samples may be related to the
high number of grazing zooplankton observed during the same period. Pelagic tunicate and zooplankton fecal pellets were found
to contain large numbers of choanoflagellate costae, thus providing a direct link from the microbial loop to the macrozooplankton.
Received: 17 March 1997 / Accepted: 9 May 1997 相似文献
18.
In the eutrophic Veerse Meer lagoon (The Netherlands) large amounts of free-floating thalli from Ulva spp. are present from May to October. In winter however, no algae seem to occur in the lagoon. Sexual reproduction appears
to be negligible, as spore formation and germling growth are observed only sporadically. Results of a field survey showed
that in winter, viable Ulva biomass is present buried in the sediment of the shallow parts of the lagoon. Freezing experiments demonstrated that the
algae are able to survive temperatures of −5 °C for 2 weeks when kept in darkness. In spring, the buried Ulva thalli are liberated out of the sediment to initiate a bloom. A field experiment indicates that bioturbation by the lugworm
Arenicola marina does not stimulate the release of the thalli. Burial and winter survival can explain the rapid increase in Ulva biomass in spring and suggest that the initial spring biomass is one of the major factors determining the maximal biomass
in summer.
Received: 28 October 1997 / Accepted: 20 January 1998 相似文献
19.
S. L. Smith 《Marine Biology》1990,106(1):59-69
Reproductively activeCalanus hyperboreus (Krøyer) andC. glacialis Jaschnov were captured in the upper 100 m of Fram Strait (77° to 79°N) in late winter 1987. There was no evidence of a phytoplankton bloom; chlorophylla concentrations were uniformly low (<0.1 mg m–3), and nitrate concentrations were uniformly high (>11.3 mg-at m–3). Gut-fullness measurements indicated that females were ingesting very little. The maturation state of gonads of bothC. hyperboreus andC. glacialis indicated that 75% of females were in a ripe condition consistent with observed egg laying. The lipid content of females laying eggs was reduced in both species compared to that of females not laying eggs. InC. hyperboreus the reduction was 39% and inC. glacialis it was 44%. All the evidence suggests that bothC. hyperboreus andC. glacialis were laying eggs in late winter by using lipids stored previously; they were not relying on ambient concentrations of phytoplankton. The daily rate of egg laying byC. glacialis using lipids in late winter exceeded the rate reported for summer when ambient food supplies have been shown to be necessary. It is suggested that individuals, spawned well in advance of the spring bloom of phytoplankton, may comprise a major portion of the annual recruitment to the entire population ofC. glacialis in this area, and that their life cycle can be completed within 1 yr. NeitherMetridia longa (Lubbock) norC. finmarchicus (Gunnerus) laid eggs during this study. 相似文献
20.
Valeria A. Guinder Cecilia A. Popovich Juan Carlos Molinero Gerardo M. E. Perillo 《Marine Biology》2010,157(12):2703-2716
The phytoplankton of the Bahía Blanca Estuary, Argentina, has been surveyed since 1978. Chlorophyll a, phytoplankton abundance, species composition and physico-chemical variables have been fortnightly recorded. From 1978 to
2002, a single winter–early spring diatom bloom has dominated the main pattern of phytoplankton interannual variability. Such
pattern showed noticeable changes since 2006: the absence of the typical winter bloom and changes in phenology, together with
the replacement of the dominant blooming species, i.e. Thalassiosira curviseriata, and the appearance of different blooming species, i.e. Cyclotella sp. and Thalassiosira minima. The new pattern showed relatively short-lived diatom blooms that spread throughout the year. In addition, shifts in the
phytoplankton size structure toward small-sized diatoms, including the replacement of relatively large Thalassiosira spp. by small Cyclotella species and Chaetoceros species have been noticed. The changes in the phenology and composition of the phytoplankton are mainly attributed to warmer
winters and the extremely dry weather conditions evidenced in recent years in the Bahía Blanca area. Changing climate has
modified the hydrological features in the inner part of the estuary (i.e. higher temperatures and salinities) and potentially
triggered the reorganization of the phytoplankton community. This long-term study provides evidence on species-specific and
structural changes at the bottom of the pelagic food web likely related to the recent hydroclimatic conditions in a temperature
estuary of the southwestern Atlantic. 相似文献