[Show abstract][Hide abstract] ABSTRACT: Three cultured species of Pyrocystis (Dinoccoccales) reproduced asexually by forming 2 (or 1) aplanospores or zoospores inside the parent cell wall. In all 3 species these small reproductive cells, although they may not resemble the parent cells, swell up rapidly (∼ 10 min) to the approximate size and shape of the parent cell. These swollen cells become new vegetative cells. The above asexual process is the only way by which cells numbers increase in our cultures. Pyrocystis lunula was propagated at the lunula stage of the life cycle. The nonmotile crescent-shaped cells produced reproductive cells that were Gymnodinium-shaped and had, in some cases, a trailing flagellum. With P. fusiformis and P. noctiluca, the reproductive cells were not flagellated. With P. fusiformis, these bodies had a pronounced equatorial constriction like a girdle, while in P. noctiluca the “girdle” was an inconspicuous feature if present. With P. noctiluca and P. fusiformis on a 12:12 ld cycle, reproductive cells were formed early in the dark period and they swelled up at the beginning of the light period. Reproduction of P. lunula was not well phased in our experiments, with reproductive cells developing at the end of the light period and the end of the dark period.
[Show abstract][Hide abstract] ABSTRACT: Living cells of the diatom Ethmodiscus rex (Rat-Iray) Wiseman & Hendey 1953 were found in the plankton of the southern Sargasso Sea. Apparently, this is the first report, of E rex from the plankton of the Atlantic Ocean. Scanning electron microscopy of peroxide-cleaned frustules revealed, some new morphological features for this species. When viewed, from inside the frustule, the puncta appear as rimmed pits. From outside the frustule, they appear to he shallow depressions with a small opening at the bottom. The so-called mucous tubules in the center of the valve were seen from the out side to be elongate slits and from the inside as obliquely directed flattened cylinders which cap the tubes.
[Show abstract][Hide abstract] ABSTRACT: Photoinhibition of mechanically stimulable bioluminescence (MSL) in the heterotrophic dinoflagellate Protoperidinium depressum Bailey was investigated using samples collected from the Massachusetts and southern Texas coasts. The times for both photoinhibition of MSL (ca. 10 min) and dark recovery from photoinhibition of MSL (ca. 45 min) in this species were similar to those reported for autotrophic dinoflagellates. The degree of photoinhibition of MSL was a linear function of the logarithm of photon flux density (PFD). The threshold PFDs for the photoinhibition of MSL were 0.02, 0.6, and 21 μmol photons · m−2· s−1 for broad-band blue, green, and red light, respectively. These PFDs are lower than those required for photoinhibition of MSL by the autotrophic dinoflagellates Pyrocystis lunula and Ceratium fusus. We speculate that photosynthetic pigments in autotrophic dinoflagellates shield the photoreceptor that causes photoinhibition of MSL, thus lowering the sensitivity of these dinoflagellates to light. When field-collected P. depressum were kept in the laboratory without growth for a week, photoinhibition of MSL's sensitivity to light increased progressively along with 1) a decrease in its bioluminescence capacity (BCAP), 2) a decrease in the ratio of MSL to BCAP (MSL/BCAP), and 3) a decrease in the orange pigmentation (probably carotenoid) of the dinoflagellate. The action spectrum for photoinhibition of MSL in P. depressum was characterized primarily with a broad peak in the blue extending into the green. We suggest that carotenoid was not a photoreceptor for the photoinhibition of MSL in P. depressum because the peak of the action spectrum was too broad and extended too far into the green part of the spectrum, and because the orange pigment present decreased as photoinhibition of MSL became more sensitive to light.
[Show abstract][Hide abstract] ABSTRACT: The cell of Pyrocystis spp. is covered by an outer layer of material resistant to strong acids and bases. Internal to this layer much of the cell wall is composed of cellulose fibrils. The presence of cellulose fibrils was established by staining raw and ultra-violet–peroxide-cleaned cell walls and by combining X-ray diffraction spectroscopy with electron microscope observation. Carbon replicas of freeze-etched preparations and thin sections of P. lunula walls show outer layers, inside them ca. 24 layers of crossed parallel cellulose fibrils (4–5 nm thick, ca. 12 nm wide), then a region of smaller (ca. 6–12 nm diameter) fibrils in a disperse texture, and then the plasma membrane. Cellulose fibrils in the parallel texture are constructed of 3–5 elementary fibrils ca. 3 nm in diameter. Walls of P. fusiformis and P. pseudonctiluca also have cellulose fibrils in a crossed parallel texture similar to those of P. lunula.
The Gymnodinium-type swarmer from lunate P. lunula appears to have a cell wall ultrastructure typical of other “naked” dinoflagellates.
[Show abstract][Hide abstract] ABSTRACT: We have examined aspects of the bioluminescence of 5 clones of Dissodinium, 1 clone of Pyrocystis acuta, 4 clones of Pyrocystis fusiformis, and 5 clones of Pyrocystis noctiluca. All clones produced the same color bioluminescence with an intensity peak near 474 nm. The in vivo emission spectra of these clones agreed with those previously determined, for 4 other species of marine dinoflagellates. The amount of light emitted by the dinoflagellates in scotophase when mechanically stimulated to exhaustion was determined for most of the clones. The largest species, P. noctiluca and P. fusiformis, emitted 37–89 × 109 photons cell−1 and 23–62 × 109 photons cell−1, respectively, about a thousand, times as much light as Gonyaulax species. Pyrocystis acuta emitted 3–6 × 109 photons cell−1. Three of the 5 clones of Dissodinium were bioluminescent. The range for 3 clones was 5–13 × 109 photons cell−1. All 5 clones of Dissodinium are morphologically distinct. Both the clones of Dissodinium and Pyrocystis produced much higher numbers of photons per cell nitrogen (ca. 7–50 times) than Gonyaulax polyedra or Pyrodinium bahamense. The data suggested that enzyme turnover occurred in the reactions producing light during mechanical stimulation of Dissodinium and Pyrocystis species.
[Show abstract][Hide abstract] ABSTRACT: The activity of extracted NADH-NO3− reductase was measured in the marine dinoflagellates Amphidinium carteri Hulburt and Cachonina niei Loeblich. Its activity showed a diel periodicity and was ca. twice as great at midday as at midnight. The enzyme activity was unstable, with an in vitro half-life of 2–3 h. Values of enzyme activity were low or undetectable during lag phase but paralleled the instantaneous growth rate value during log phase. Nitrate reductase activity was not found in the stationary phase of growth, but additions of NO3− resulted in enzyme activity after 24h. When A. carteri was exposed to a series of light intensities for several weeks, the division rate and enzyme activity increased with increasing light intensity up to saturating intensities. In 6 h exposures, enzyme activity decreased with decreasing light intensities below light intensities saturating division rate. Additions of NH4+ (0.5–50 μm) to A. carteri cultures decreased the amount of extractable enzyme. The in vitro activity was not inhibited by similar NH+4 concentrations.
[Show abstract][Hide abstract] ABSTRACT: Preadapted cultures were grown in a 12:12 LD cycle at a series of light intensities under cool-white, fluorescent lamps. Pyrocystis fusiformis Murray maintained high division rates at low light intensities at the expense of cell size. In contrast, Dissodinium lunula (Schuett) Taylor had relatively lower division rates at low light intensities with little concomitant decrease in size. The response of P. noctiluca Murray was intermediate between these two species. For all three, cell numbers did not increase above an intensity of 5–10 μEin·m−2·sec−1 and division rate was saturated at ca. 30, 60, and 60μEin·m−2·sec−1 for P. fusiformis, P. noctiluca, and D. lunula, respectively. The capacity for stimulable bioluminescence was saturated at light intensities of 0.15 μEin·m−2·day in short-term (2-day) experiments. In cultures of P. fusiformis and P. noctiluca, maintained for at least one month at lower intensities than needed to saturate division rate, a decrease in the capacity for stimulable bioluminescence was accompanied by a reduction in cell size. Our results suggest that cell size and bioluminescent capacity may prove to be a potentially useful indication of the history of exposure of natural populations of Pyrocystis spp. to ambient intensities.
[Show abstract][Hide abstract] ABSTRACT: The division rate of Cricosphaera elongata was measured as a function of pH in a medium buffered with the CO2-bicarbonate-carbonate system. The optimum pH for cell division of the coccolithophorid was 7.8. A change of the partial pressure of CO2 in the medium from 0.03 to 5% did not affect the division rate. Between pH 6.4 and 7.8 changes in the bicarbonate concentration from 0.1 to 6.0 mm and carbonate concentration from 0.007 to 0.1 mm did not affect the rate of division. At loiv experimental pH, C. elongata was nonmotile and grew in clumps; at higher pH values, it was motile and solitary. Coccoliths were not found covering C. elongata if calcite was soluble in the medium.
[Show abstract][Hide abstract] ABSTRACT: The lunate cysts of Pyrocystis lunula have a bioluminescent emission spectrum with a peak intensity of 477.5 ± 1 mμ. The light originates from the protoplasm in the center of the cysts. Six to eight hr after the cysts were placed in the dark, they produced 300 to 800 times more luminescence than controls maintained under constant, illumination. Plastids contract distally when the cysts are placed in the dark. If kept in the dark, the plastids contract distally and expand with a circadian rhythm persisting several days. At intensities of 2200 μm cm-’or less, the plastids are expanded. The plastids are contracted into the central area of the cysts at light intensities of 4000 μw cm-2 and above. The Gymnodinium stage of the life cycle is not bioluminescent.
[Show abstract][Hide abstract] ABSTRACT: Phosphate uptake by P-replete and P-depleted Pyrocystis noctiluca (Murray) Schütt grown at different ambient N:P ratios was multiphasic between 0.1 and 100 μM PO43-. Within each of the kinetic phases, the saturated uptake rate (Vmax), but not the half saturation constant (Km) was affected by the cellular-P status and light. Uptake rates in the dark were ca. 50% of that in the light and respiratory activity accounted for the observed basal uptake. The combination of multiphasic uptake, and the uncoupling of short term transient uptake from growth resulting in maximum specific uptake rates of 50 h−1 may help explain the abundance of P. noctiluca in oligotrophic regions.
[Show abstract][Hide abstract] ABSTRACT: Ceratium fusus (Ehrenb.) Dujardin was exposed to light of different wavelengths and photon flux densities (PFDs) to examine their effects on mechanically stimulable bioluminescence (MSL). Photoinhibition of MSL was proportional to the logarithm of PFD. Exposure to I μmol photons·m−2s−1 of broadband blue light (ca. 400–500 nm) produced near-complete photoinhibition (≥90% reduction in MSL) with a threshold at ca. 0.01 μmol photons·m−2·s−1. The threshold of photoinhibition was ca. an order of magnitude greater for both broadband green (ca. 500–580 nm) and red light (ca. 660–700 nm). Exposure to narrow spectral bands (ca. 10 nm half bandwidth) from 400 and 700 nm at a PFD of 0.1 μmol photons·m−2·s−1 produced a maximal response of photoinhibition in the blue wavelengths (peak ca. 490 nm). A photoinhibition response (≥ 10%) in the green (ca. 500–540 nm) and red wavelengths (ca. 680 nm) occurred only at higher PFDs (1 and 10 μmol photons·m−2·s−1). The spectral response is similar to that reported for Gonyaulax polyedra Stein and Pyrocystis lunula Schütt and unlike that of Alexandrium tamarense (Lebour) Balech et Tangen. The dinoflagellate's own bioluminescence is two orders of magnitude too low to result in self-photoinhibition. The quantitative relationships developed in the laboratory predict photoinhibition of bioluminescence in populations of C. fusus in the North Atlantic Ocean.
[Show abstract][Hide abstract] ABSTRACT: The effects of small-scale turbulence on two species of dinoflagellates were examined in cultures where the turbulent forces came randomly from all directions and were intermittent both spatially and temporally; much like small-scale turbulence in the ocean. With Lingulodinium polyedrum (Stein) Dodge (syn. Gonyaulax polyedra), division rate increased linearly (from ∼0.35 to 0.5 per day) and the mean cross-sectional area (CSA) decreased linearly (from ∼1100 to 750 μm2) as a function of the logarithmic increase in turbulence energy dissipation rate (ε). These effects were noted when ε values increased between ∼10−8 and 10−4 m2 s−3. However, when ε increased to ∼10−3 m2 s−3, division rate sharply decreased and mean CSA increased. Over the same range of ε, Alexandrium catenella (Wheedon and Kofoid) Balech had its division rate decrease linearly (from ∼0.6 to 0.45 per day) and its CSA increase linearly (from ∼560 to 650 μm2) as a function of the logarithmic increase in ε. Even at the highest ε examined (∼10−3 m2 s−3), which may be unrealistically high for their ambits, both L. polyedra and A. catenella still had fairly high division rates, ∼0.2 and 0.45 per day, respectively. Turbulence strongly affected chain formation in A. catenella. In non-turbulent cultures, the mode was single cells (80–90% of the population), but at ε of ∼10−5 to 10−4 m2 s−3, the mode was 8 cells per chain. At the highest ε (∼10−3 m2 s−3), the mode decreased to 4 cells per chain. The vertical distributions of A. catenella populations in relation to hydrographic flow fields were studied in the summers of 1997 and 1998 in East Sound, Washington, USA (latitude 48°39′N, 122°53′W). In both summers, high concentrations of A. catenella were found as a subsurface bloom in a narrow depth interval (∼2 m), where both current shear and turbulence intensity were at a minimum. Other researchers have shown that A. catenella orients its swimming in shear flows, and that swimming speed increases with chain length. These responses, when combined with our observations, support a hypothesis that A. catenella actively concentrates at depths with low turbulence and shear.
[Show abstract][Hide abstract] ABSTRACT: Field observations and results from previous laboratory studies on the effects of turbulence on dinoflagellates have led to a paradigm in phytoplankton ecology that dinoflagellate growth is negatively affected by turbulence. To test the paradigm, 10 species of autotrophic dinoflagellates were exposed to quantified three-dimensional turbulence generated by vertically oscillating cylindrical rods in 20-L rectangular culture tanks. Turbulence was quantified in the tanks (as the turbulent energy dissipation rate, ε) using an acoustic Doppler velocimeter. Dinoflagellates were exposed to two turbulence treatments: high turbulence (ε∼ 10−4 m2·s−3), low turbulence (ε∼ 10−8 m2·s−3), and an unstirred control. In accord with the paradigm, Ceratium fusus (Ehrenberg) Dujardin had lower net growth rates in high turbulence, whereas Pyrocystis noctiluca Murray ex Haeckel and Ceratium tripos (O. F. Müller) Nitzsch did not increase their numbers in high turbulence. However, Alexandrium tamarense (Lebour) Balech, Pyrocystis fusiformis Wyville-Thomson ex Murray, Alexandrium catenella (Whedon and Kofoid) Balech, and a Gyrodinium sp. Kofoid and Swezy were apparently unaffected by turbulence and had the same net growth rates across all turbulence treatments. Contradicting the paradigm, Lingulodinium polyedrum (Stein) Dodge (= Gonyaulax polyedra), Gymnodinium catenatum Graham, and Alexandrium fundyense Balech had increased net growth rates in high turbulence treatments. Cross-sectional area (CSA) varied little across turbulence treatments for 8 of 10 dinoflagellate species tested, CSA in C. fusus increased when net growth rate decreased in high turbulence, and, conversely, CSA decreased in L. polyedrum when net growth rate increased in high turbulence.
[Show abstract][Hide abstract] ABSTRACT: We investigated mixed-layer bioluminescence from early April to late September (in April 1989, May 1991, July 1983 and 1990, August 1991, September 1988 and 1989) at stations near the Marine-Light-Mixed Layers (MLML) bio-optical moorings site. Volume-specific bioluminescence potential (BPOT, photons per unit volume) from epipelagic organisms was estimated directly with a pump-through bioluminescence photometer (BP) in 1983, 1988, and 1991. For all cruises, BPOT was also estimated by summing for a volume of seawater, the measurements of each species' total stimulable bioluminescence multiplied by each species' numerical abundance in the volume. The abundance data were taken from bottle casts, net tows, and BP effluent nets. After the onset of the spring bloom, from May through September, mixed layer BPOT was fairly constant, ~1-4×1014 photons m-3. On one early April cruise (1989) before the spring bloom, BPOT was two orders of magnitude lower. Heterotrophic dinoflagellates in the genus Protoperidinium generally produced most (90% or more) of the mixed layer BPOT in the spring, summer, and fall. On one cruise in September (1988), the autotrophic dinoflagellate Ceratium fusus produced the bulk of the mixed layer BPOT (more than about 4×1014 photons m-3). Other autotrophic dinoflagellates in the genus Gonyaulax and mesozooplankton produced a minor part of BPOT at most stations. The relative contribution of all autotrophic dinoflagellates to BPOT increase from a few percent during the May-June-July period to ~10% during the August-September period. In situ mechanically stimulable bioluminescence was reduced when underwater scalar irradiance (wavelengths 400-700 nm) was greater than 0.1 mumol photons m-2 s-1.
Journal of Geophysical Research Atmospheres 04/1995; 100(C4):6527-6548. DOI:10.1029/94JC01870 · 3.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cultures of Ceratium fusus were grown at seven light intensities [5 to 400 mumol photons m-1s-1 as photosynthetically active radiation (PAR)] in the laboratory. Measurements of bioluminescence capacity (BCAP), division rate, and cell size were made at each intensity and compared to similar data from natural populations. In cultures, BCAP increased by a factor of 5-10 with increasing light. Division rates ranged from 0 d-1 (5 mumol photons m-2s-1) to about 0.16 d-1 (100 mumol photons m-2s-1). In these cultures, BCAP was highly correlated with both log of light (r2=0.89) and division rate (r2=0.69), suggesting that BCAP may be of use as an in-situ indicator of division rate. In both cultures and natural populations, BCAP was poorly correlated with cell size (r2~0.3 and r2~0.1 respectively). For populations from the Gulf of Maine (~42°N, 69°W) and the Marine light-Mixed Layers (MLML) site (~59°N, 21°W), division rates in the mixed-layer could only be determined with statistical certainty at the Gulf of Maine station (0.04 to 0.17 d-1). At the MLML site, BCAP in C. fusis was greater in the mixed-layer in May and below the mixed-layer in August. The August result is opposite to what cuture photoenhancement studies would predict if light was the factor controlling BCAP.
Journal of Geophysical Research Atmospheres 04/1995; 100(C4):6565-6574. DOI:10.1029/94JC01511 · 3.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Temporal and spatial acoustic backscatter estimates of zooplankton biomass were made using an unmodified hull-mounted 153-kHz acoustic Doppler current profiler (ADCP) during the May 1991 Marine Light-Mixed Layers (MLML) cruises to the North Atlantic. Relative backscatter from the ADCP was converted to zooplankton biomass estimates using individual plankton taxa abundances and weights from zooplankton samples collected during the cruises. There was a small but consistent diel pattern in the 20 to 250-m depth-integrated backscatter, with highest values during darkness. Removal of the diel signal with harmonic analysis revealed slightly higher zooplankton biomass to the southwest and west of the mooring than to the northeast, in common with gradients in surface temperatue and chlorophyll during the mapping cruise. Overall however, depth-integrated zooplankton biomass during the mapping cruise varied by only a factor of 2, comparable to what one observes in replicate plankton tows. The nightly 0 to 250-m obliquely collected zooplankton samples (May 16-24) indicated increasing densities (and biomasses) of probable zooplankton scatterers (especially the copepod Calanus finmarchicus) during middle to late May, soon after the peak in the spring phytoplankton bloom. This increase in May was mirrored by a comparable increase in depth-integrated acoustic backscatter. The distribution of zooplankton changed following two 50+kn (1 kn=1.85 kmh-1) wind storms on May 19 and May 21; zooplankton biomass was higher and extended much deeper in the water column at night following these strong mixing episodes. Before the storm events, the patterns of zooplankton diel vertical redistribution were consistent from day to day. Diel patterns of zooplankton variability measured using shipboard acoustics are qualitatively similar to patterns observed from an ADCP on the MLML mooring, presenting the possibility of calculating a nearly continuous seasonal measure of zooplankton biomass from the mooring ADCP data.
Journal of Geophysical Research Atmospheres 04/1995; 100(C4):6549-6564. DOI:10.1029/94JC00981 · 3.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Day-night changes in the vertical distribution, intensity, and size of bioluminescence flashes were investigated during a series of cruises to the northern Sargasso Sea in 1987 and 1988. Overall, depth integrated bioluminescence potential and flash density estimated from in situ measurements with a pumping bathyphotometer were 2 to 5 x higher at midnight than at midday. Depths from 50 to 100 m exhibited the most substantial day to night increases in bioluminescence potential and flash density. When classified by flash size (photon output per flash event), the increase from day to night was significant for all flash sizes, but was most dramatic for small flashes producing 8 photons flash-1. Bioluminescence potential and flash density increased 2 to 3 x during bathyphotometer measurements made at dusk. Bioluminescent light budgets estimated from day and night net collections in May and August 1987 also predicted 2.5 x higher nighttime than daytime mesoplankton bioluminescence. However, large bioluminescent taxa (mesoplankton) capable of significant vertical migrations only contributed on the order of 15% of the total bioluminescence in surface waters. Our results do not support the idea that most of the nightly increase in bioluminescence potential and flash density are due to vertical migration of bioluminescent organisms; rather they are consistent with an alternate view that photoinhibition of bioluminescent flashing by dinoflagellates may be primarily responsible for the diel patterns.
[Show abstract][Hide abstract] ABSTRACT: The vertical structure of bioluminescence potential (BPOT) and flash density (FD) were measured on five cruises to the northern Sargasso Sea in 1987 and 1988. Depth-integrated (0 to 150 m) BPOT did not vary seasonally, remaining within the range 9 to 15 1015 photons m–2 in all months sampled. Conversely, depth-integrated FD was significantly higher (> 2 105 flashes m–2) during winter (November and March) than during summer (< 9="" ="">4 flashes m–2 in May and August). The vertical patterns of BPOT and FD were well correlated within a single profile, more highly so in summer than in winter. Despite intracruise variability in the vertical pattern of BPOT and FD, there were clear summer-winter differences in the vertical distribution of BPOT and FD. During winter, BPOT and FD were maximal and relatively uniform throughout the surface mixed layer; for example in November they declined sharply within the thermocline at 130 to 150 m. During summer, BPOT and FD were greatest (12 to 25 1013 photons m–3 and 600 to 1 200 flashes m–3, respectively) at subsurface depths. Commonly in summer, the upper depth limit of high BPOT and FD occurred at the base of the surface mixed layer (10 to 40 m) and the lower depth limit was located at the base of the subsurface fluorescence maximum (usually at 100 to 120 m).
[Show abstract][Hide abstract] ABSTRACT: Natural bioluminescence results from the emissions of bioluminescent organisms in the absence of man-made disturbance. Most epipelagic and mesopelagic bioluminescence is caused by plank- tonic organisms. Limited attempts to measure natural bioluminescence in situ with surface deployed and moored instruments have recorded much higher levels of natural bioluminescence than have been observed from submersibles. We present a model predicting the frequency of interactions among planktonic organisms leading to natural bioluminescent emissions. The results suggest that natural bioluminescent flashes caused by interactions between zooplankters may be rare events in the Sargasso Sea, with our model predicting a maximum of nearly 600 flashes h-l m-3 at night in surface waters of the northern Sargasso Sea where there was an unusually high concentration of euphausiids and small bioluminescent dinoflagellates, but < 1 flash h-' m-3 in the southern Sargasso Sea. In both locations most of the natural bioluminescence was predicted to be caused by eu- phausiids and copepods of the genus Pleuromamma and natural bioluminescence generally de- creased with depth. The more intense displays of natural bioluminescence are probably the result of the bioluminescence of numerous smaller dinoflagellates common in coastal waters and may also be the result of disturbances caused by interactions of larger organisms with bioluminescent plankters.
Limnology and Oceanography 01/1990; 35(7):1469-1485. DOI:10.4319/lo.19126.96.36.1999 · 3.79 Impact Factor