Bioluminescence of colonial radiolaria in the western Sargasso Sea

J. Exp. Mar. Biol. Ecol., 1987, Vol. 109, pp. 25-38

25

Elsevier

JEM 00886

Bioluminescence

of colonial radiolaria in the western Sargasso Sea

Michael I. Latz’, Tamara M. Frank’, James F. Case’, Elijah Swift2 and Robert R. Bidigare3 ‘Department of Biological Sciences and Marine Science Institute. University of Ca@omia. Santa Barbara, California. U.S.A. ; ‘Graduate School of Oceanography, University of Rhode Island, Narragansett. Rhode Island, U.S.A.: 3Department of Oceanography, Texas A. & M. University, College Station, Texas, U.S.A.

(Received 2 December 1986; revision received 22 January 1987; accepted 19 February 1987) Abstract: Colonial radiolaria (Protozoa : Spumellarida) were a conspicuous feature in surface waters of the Sargasso Sea during the April 1985 Biowatt cruise. The abundance of colonies at the sea surface at one station was estimated to be 23 colonies. m- 2. Bioluminescence by colonial radiolaria, representing at least six taxa, was readily evoked by mechanical stimuli and measured by fast spectroscopy and photon-counting techniques. Light emission was deep blue in color (peak emissions between 443 and 456 nm) and spectral distributions were broad (average half bandwidth of 80 nm). Single flashes were l-2 s in duration at N 23 a C, with species-dependent kinetics which were not attributed to differences in colony morphology, since colonies similar in appearance could belong to different species (even families) and display different flash kinetics. Although the presence of dinoflagellate symbionts was confirmed by the presence of dinoflagellate marker pigments in the colonies, luminescence in the radiolaria examined most likely did not originate from symbiotic dinoflagellates because of( 1) differences in the emission spectra, (2) unresponsiveness to low pH stimulation, (3) differences in flash kinetics and photon emission of light emission, and (4) lack of light inhibition. The quantal content of single flashes averaged 1 x lo9 photons. flash- I, and colonies were capable of prolonged light emission. The mean value of bioluminescence potential based on measurements of total mechanically stimulated bioluminescence was 1.2 x 10” photons *colony - ‘. It is estimated that colonial radiolaria are capable of producing = 2.8 x lOI photons . m- ’ of sea surface. However, this represented only 0.5% of in situ measured bioluminescence potential. Key words: Bioluminescence; Radiolarian; Emission spectrum; Dinoflagellate; Plant accessory pigment

Colonial radiolaria are found in all oceanic regions (Haeckel, 1887) and may reach extremely high densities in local swarms (Pavshitiks & Pan’Kova, 1966; Khmeleva, 1967). In the Sargasso Sea they are relatively abundant in near-surface waters where they may reach densities of < 540 colonies * m - 3 (Swanberg, 1983). Colonies are composed of hundreds of individual cells surrounded by a gelatinous coat (Anderson, 1983; Swanberg, 1983). Each cell contains a central capsule of Correspondence address: M.I. Latz, Department of Biological Sciences, University of California, Santa Barbara, CA 93106, U.S.A. 0022-0981/87/.$03.50 0 1987 Elsevier Science Publishers B.V. (Biomedical Division)

26

M.I. LATZ

ETAL.

cytoplasm surrounded by the extracapsulum, an outer layer of cytoplasm (Haeckel, 1887; Anderson, 1976). In many radiolaria the extracapsulum contains algal symbionts which exhibit fine structure typical of dinoflagellates (Anderson, 1976, 1978a,b, 1983). Dinoflagellate symbionts, which are enclosed within the extracapsular rhizopodia, are readily differentiated from prey algae which are surrounded with a thickened cytoplasmic sheath (Anderson, 1983). Individual colonies can contain 103-lo6 symbionts, depending on colony size (Anderson, 1978a, 1980). The symbiotic relationship between algal symbionts and radiolaria is well understood and involves translocation of photosynthates to the host cells (Anderson, 1978a, 1980; Anderson et al., 1983, 1985). This symbiosis may account for the abundance of colonial radiolaria in oligotrophic waters (Swanberg, 1983). Brandt (1885) and Haeckel (1887) first observed bioluminescence in solitary and colonial radiolaria. Flashing in response to mechanical (Nicol, 1958) and electrical (Herring, 1979) stimulation has been measured only in solitary forms. Light emission is blue, l-2 s in duration, and originates from the extracapsulum. At present there is no definitive evidence on whether or not dinoflagellate symbionts contribute to radiolarian bioluminescence, except that certain features of radiolaria luminescence suggest a biochemical system different from that of dinoflagellates as well as bacteria (Herring, 1979; Campbell et al., 1981). This study presents additional evidence suggesting that the dinoflagellate symbionts do not contribute to bioluminescence from the colonies. When abundant in surface waters, colonial radiolaria may be important sources of bioluminescence at the sea surface in the Sargasso Sea. MATERIALS AND METHODS Specimens of colonial radiolaria were sampled between 28’ and 35 oN along 70’ W during April 1985 as part of the Office of Naval Research-sponsored Biowatt cruise. Quantitative net tows for abundance estimates were made with double-tripping 0.3-m diameter nets (25-pm mesh) fitted with General Oceanics flowmeters and towed for 5 min. Colonies utilized for laboratory testing were collected during 15-min surface tows using 0.5- and 0.3-m diameter nets (333-pm mesh), placed in filtered sea water, and maintained at 25 “C. All testing was performed within 12 h of collection. Specimens were individually preserved in 4% formalin for later identification. EMISSIONSPECYrRA Bioluminescence emission spectra were measured with a PAR 1215 optical multichannel analyzer (OMA). Bioluminescence was focused on the l-mm entrance slit of a polychromator using quartz optics. The OMA detector, a linear array of 700 intensified photodiodes, instantaneously collects the polychromator output. This system is characterized by high sensitivity, fast response time and high resolution. Details of the OMA operation and calibrations have previously been described (Widder et al., 1983).

BIOLUMINESCENCE

OF COLONIAL

RADIOLARIA

27

Single colonies were suspended in filtered sea water in a quartz cuvette in front of the collection optics of the OMA. Bioluminescence was stimulated by manual agitation of the cuvette contents with a rod. In some cases the effect of low pH conditions was evaluated by adding a few drops of 4-N acetic acid to the cuvette. Careful rinsing of individual colonies with several changes of filtered sea water prior to each measurement was essential to prevent contaminating bioluminescence by adherent organisms such as luminescent dinoflagellates (Alldredge & Jones, 1973). Contaminated samples were readily identified by an altered spectrum characterized by a dramatic shift to longer wavelengths and a significantly narrower bandwidth (Fig. IA). A similar colony rinsed 10 times with filtered sea water yielded a conventional spectrum (Fig. 1A). The characteristics of the altered spectra were similar to those of free-living dinoflagellates (Herring, 1983; Widder et al., 1983). Therefore the source of contamination was probably free-living rather than symbiotic dinoflagellates, since these sources could be removed by rinsing. Examination of specimens by light microscopy confumed that contaminating organisms were not present. FLASH

KINETICS

The temporal characteristics of radiolarian bioluminescence were measured with an integrating sphere apparatus. Single colonies suspended in filtered sea water were mechanically stimulated in a quartz cuvette while enclosed in a 0.25-m diameter integrating sphere (Labsphere). Light emission was detected by an RCA 8850 photomultiplier tube operated at - 1700 V and processed through a discriminator calibrated at - 0.315 V. The resulting frequency signal was counted with an Ortec 776 counter/timer and displayed on a Norland 5400 multichannel analyzer (MCA). Light output was monitored for 8 s. Quantum calibration of the detection system involved determination of the combined spectral responsivity of the integrating sphere and photomultiplier tube with an Optronic Laboratory 310 calibration source. The MCA trace was stored on videotape and later processed by a Megavision 1024XM imageanalysis system to obtain printed records of the flash responses. Flash kinetics were measured from the printed record by a Summagraphics digitizing pad and appropriate software. MEASUREMENTS

OF BIOLUMINESCENCE

POTENTIAL

Measurements of total mechanically stimulable luminescence (TMSL) were made from colonies that had acclimated in the laboratory for 4-8 h following collection. Specimens suspended in filtered sea water were stirred at 1800 rpm to exhaustion of bioluminescence. Light emission was detected by a laboratory photometer (Swift et al., 1985). To eliminate TMSL values which may have originated from damaged organisms or those which may have depleted their luminescence reserves during collection, the dimmer half of the TMSL values were eliminated. Thus the values reported here represent the mean of the brighter half of the bioluminescent responses.

28 PHYTOPLANKTON

M.I. LATZ ETAL. PIGMENT ANALYSIS

The phytoplankton pigment content of the net-collected colonial radiolaria was determined at sea by high-performance liquid chromatography (Smith et al., 1987). Representative specimens were carefully rinsed, homogenized in 2 or 3 ml of 90% acetone and extracted for 24-48 h in the dark at - 10 “C. Following extraction, the samples were centrifuged for 5 min to remove cellular debris. Chlorophyll and carotenoid pigments were separated using a Spectra-Physics SP8 100 liquid chromatograph and Radial-PAK Cl8 column at a flow rate of 10 ml. min- ‘. Samples were prepared for injection according to the method outlined by Mantoura & Llewellyn (1983). A two-step solvent program was used to separate the phytoplankton pigments extracted from the colonies. After injection of a 500-~1 sample, mobile phase A (80 : 15 : 5; methanol : water : ion-pairing agent) was ramped to mobile phase B (methanol) over a 1Zmin period, Mobile phase B was then pumped for 13 min for a total analysis time of 25 min. Individual peaks were detected and quantified with a Waters 440 Fixed Wavelength Detector (436 nm) and a Hewlett-Packard 3392A integrator, respectively. Calibration standards were obtained from Sigma Chemical (chlorophylls a, 6 and P-carotene) or purified by thin-layer chromatography (Jeffrey, 198 1). Concentrations of the pigment standards were determined spectrophotometritally using published extinction coefficients (Jeffrey, 1972; Jeffrey & Humphrey, 1975; Mantoura & Llewellyn, 1983).

RESULTS

Surface net tows investigating the bright surface bioluminescence present during the April 1985 Biowatt cruise revealed the presence of numerous colonial radiolaria at all stations sampled. The vertical abundance of colonies at Station 19 (35’ N : 70 oW) was quantified by a series of double-tripping net tows (Table I). For this net series, sea conditions were calm. Colonial radiolaria were most prevalent within 1 m of the sea surface at a density of 8 colonies * m- 3. Colonies were present only in the upper 5 m. TABLE I

Abundance of colonial radiolaria at Station 19 (35” N 70” W) determined by quantitative net tows at 2100 on 23 April 1985: total volume filtered during each tow was z 23 m3; abundance measurements were made from counts of the entire sample. Depth (m) 0

5 10 20 30 40 50

No,m-3 8.2 0.5 0 0 0 0 0

No. tows 3 1 1 1 1 1 1

BIOLUMINESCENCE

29

OF COLONIAL ~D~OLARIA

Colonial radiolaria were among the most ab~d~t macropl~on collected witbin this depth range. Colonial radiolaria were represented in an assortment of morphological types. Unfortunately, designation of individual colonies by gross morphological criteria (e.g. toroid, spherical, elongate, flattened disk) was inadequate for taxonomic identification. Specimens were identified to the lowest taxonomic level possible although it must be kept in mind that there is some discussion with regard to a single classificatory scheme for radiolarian systematics (see Anderson, 1983, for taxonomic authorities of individual species). Most collosphaerids were juveniles and could not be identified to the species level due to ~~omplete shell formation. The size ranges of colonies tested were as follows: ask-shape ~~~~ozo~~ ucufe~~, 1-2 cm di~eter; sphe~c~ ~~haerozoum species, 0.4-0.5 cm diameter; elongate collosphaerids, 2.5-4 cm length; toroid Collosphaera species, 0.X-1.5 cm diameter; and spherical collosphaerids, 0.3-0.7 cm diameter. The presence of dinoflagellate endosymbionts was confiied by HPLC pigment analysis of acetone extracts prepared from representative colonies (Table 11). The TABLE II

Phytoplankton pigment composition of selected colonial radiolaria: Chl, chlorophyll; Per, peridinin; Died, diadinoxanthin. ChIC

Myxosphaera coerulea Collosphaera huxleyi Rhaphidozoum acuferum Collosphaera sp. Collosphaera sp.

83 10

188

Per Diad cllln (ng pigment. colony - ‘) 179 17 325

123 8 134

Chlc:Chla Per:Chla Diad:Chia (molar pigment ratios)

272 20 215

0.45 0.73 1.28

19

41

18

41

0.59

108

192

19

202

0.78

0.93 1.21 2.15 1.24 1.35

0.69 0.61 0.95 0.59

0.60

dinoflagellate-specific accessory pigments, peridinin, chlorophyll c, and diadinoxanthin (reviewed by P&e@ 1987), were present at mean concentrations of 15 1, 82, and 72 ng * colony - ‘, respectively. The chIorophy~ a content of the individual colonies was within the wide range of values reported for colonial radiol~a (5-1625 ng * colony- ‘) by Swanberg (1983). The v~abi~ty of the pigment data (noosed on a colony basis) can be attributed to size and morphological variations in the colonial radiolaria sampled. The accessory pigment : chlorophyll a ratios (Table II) agree quite well with previous measurements for dinoflagellates (Mandelli, 1972; Chang et al., 1983), except for the relatively high values calculated for Rhuphidozoum ucuferum. Even though radiolaria are omnivorous and may occasionally consume pigmented algae (Anderson, 197Sb), it was assumed that the majority of extracted pigments originated from the symbionts and not prey. Using a value of 1 x lo- 6 nmol peridinin -cell- *, based on pigment determinations with the symbiotic dinoflagellate S~~i~ini~iurn (Chang et al., 1983), each radiol~~ colony was calculated to contain an average of ~2.4 x lo5 s~bionts.

M. I. LATZ ET AL.

30 SPECTRAL

CHARACTERISTICS

The emission maxima of the bioluminescence of colonial radiolaria were clustered within a narrow range in the blue region of the visible spectrum. There were five genera represented, although on the basis of spectral characteristics specimens of the genus b a

0 350

400

450

500

550

600

650

700

WAVELENGTH (nm) Fig. 1. Emission spectra of the bioluminescence of colonial radiolaria: relative intensity of emission as a function of wavelength is shown; (A) careful washing of the colony with filtered sea water is essential for obtaining accurate emission spectra; (a) Collosphaera sp. colony (toroid morphology) contaminated with other luminescent organisms results in an altered spectral distribution (dashed line); max., 473 nm; FWHM, 55 nm; S/N, 53; (b) similar colony rinsed 10 times yields the true emission spectrum (solid line); max., 446 nm; FWHM, 83 nm; S/N, 36; (B) spectral range of bioluminescence of colonial radiolaria; (a) Acrosphaera murrayana colony (solid line); max., 443 nm; FWHM, 80 nm; S/N, 36; (b) Collosphaera huxleyi colony (dashed line); max., 456 nm; FWHM, 79 nm; S/N, 31.

BIOLUMINESCENCE

31

OF COLONIAL RADIOLARIA

Collosphaeru may be represented by three distinct species (Table III). Spectral distributions were unimodal (Fig. lB), with emission spectra falling into two groups on the basis of emission maxima, with one group centered at 445 nm and the other at z 455 nm (the TABLE III

Spectral characteristics of mechanically stimulated bioluminescence of selected colonial radiolaria: the wavelength of maximum emission (Max.), the full bandwidth at half maximum amplitude (FWHM), and the signal to noise ratio (S/N) are presented for each taxon; Collosphaera has been subdivided into three species based on spectral characteristics and colony morphology; a mean -+ SD of the mean, number of specimens measured in parentheses. Taxon

Colony morphology

Max. (nm)

FWHM (nm)

S/N

disk

458 _+4 (2)

87 + 3

28+ 11

elongate spherical green amorphous elongate toroid toroid red spherical

443 450 453 * 2 (2) 456 453 + 4 (2) 445 +_2 (3) 444 + 1 (2)

80 78 84 + 79 76 + 84 + 70 +

36 34 37 t 1 31 27 f 2 42 & 17 45 & 19

Sphaerozoidae Rhaphidozoum acuferum

Collosphaeridae Acrosphaera murrayana Siphonosphaera tenera Myxosphaera coerulea Collosphaera huxleyi Collosphaera sp. Collosphaera sp. Collosphaera sp.

5 3 2 10

mean emission maximum for all spectra was 450 + 6 nm; n = 14). The emissions were broad with an average bandwidth at half maximum amplitude (FWHM) of 80 + 7 nm (range 63-89 nm; n = 14). Emission spectra from dinoflagellates exhibit longerwavelength maxima and narrower bandwidths (e.g. Herring, 1983; Widder et al., 1983). Even though the radiolaria spectral distributions were unimodal, one or more prominent shoulders were usually present (Fig. 1B). Shoulders were most common on the longwavelength portion of the spectrum although occasionally they appeared on the shortwavelength side as well. Emissions extended into the near-ultraviolet; intensities at 400 nm were z 10% of maximum. Since dinoflagellate bioluminescence is known to be chemically stimulated by acetic acid (Sweeney, 1969, 1981; Hamman & Seliger, 1972), colonial radiolaria were tested for their response to acid stimulation. Of six colonies tested, luminescence was undetectable in three colonies. The remaining colonies emitted light that most likely originated from contaminating sources, since the emission maximum (489 nm) and FWHM (33 nm) were not characteristic of radiolarian emissions. The lack of response was not due to protection of the algal symbionts from the chemical stimulus by the host membranes and gelatinous coat, since dissociated colonies were still unresponsive to acetic acid treatment. TEMPORAL CHARACTERISTICS

Bioluminescence was observed to originate from numerous scintillating sources within the colony. Colonies readily responded to mechanical stimulation with flashes

M.I. LATZ ET&.

32

of simple waveform (Fig. 2A). There was a 1: 1 stimulus-response relationship, although at stimulus rates > OS-Hz temporal summation of flashes occurred (Fig. 2B). Response kinetics of the flashes were species specific (Table IV). Rhuphidozoum acuferum exhibited the slowest flashes, averaging > 2 s in duration (range 1.3-3.6 s), due to slow rise and decay times. Flash durations for the other species measured were z 1 s (Table IV). Sphaerozoum verticillatum displayed the slowest as well as the most variable rise times (range 1374300 ms). The related S. punctutum, which had a similar

A

i f

1

Fig. 2. Luminescent responses of colonial radiolaria in response to mechanical stimulation: intensity of output (same arbitrary scale) with time; time bar, 2 s; (A) =0.4-Hz stimulation of Collosphaera sp. colony yielded flashes with the following mean kinetics; rise time, 160 ms; half decay time, 231 ms; flash duration, 1 s; (B) l-Hz stimulation of Rhaphidozoum acuferum colony resulted in temporal summation of flashes. TABLE IV Temporal characteristics of single bioluminescent flashes from colonial radiolaria: total rise time is the interval from flash initiation to maximum intensity; half decay time is the period from maximum flash intensity to one half that value; a mean & SE of the mean; ’ results for colonies with elongate and toroid morphologies have been combined since there are no significant differences between their kinetics (t-test, P > 0.05). Taxon

Sphaerozoidae Rhaphodozoum acuferum Sphaerozoum verticillatum Sphaerozoum punctatum Collosphaeridae Collosphaera huxleyi Collosphaera SP.~

n

Total rise time (ms)

Half decay time (ms)

Total flash duration (s)

9 7 16

375 f 40” 449 k 88 280 k 25

464 k 38 120 * 12 172 + 14

2.4 + 0.2 1.0 * 0.2 0.9 + 0.03

2 65

289 + 6 205 f 8

74 k 6 1X2*6

0.7 * 0.1 1.1 * 0.04

BIOLUMINESCENCE

OF COLONIAL RADIOLARIA

33

spherical colony morphology, exhibited slightly different flash kinetics with a shorter rise time and a longer decay time (Table IV). A source of the different flash kinetics was not attributable to an anatomical constraint based on colony morphology. The two Sphaerozoum species discussed above exhibited different kinetics even though the colonies appeared to be macroscopically identical. As another example, two colonies collected at the same time were morphologically indistinguishable from one another, both being disk-shaped. However, their flash responses had strikingly different kinetics (Fig. 3). The colony exhibiting slower flashes was subsequently identified as Rhaphidozoum acuferum, while the other colony emitting faster flashes was identified as Collosphaera sp., a member of a different family.

Fig. 3. Response kinetics was not due to colony morphology since two colonies with identical disk morphologies exhibited different flash kinetics: time bar, 2 s; (A) slower flashes of Rhaphidozoum act&rum colony; rise time, 465 ms; half decay time, 441 ms; flash duration, 2.4 s; (B) faster flashes of Collosphaeru sp. colony; rise time, 189 ms; half decay time, 149 ms; flash duration, 0.9 s.

Since free-living dinoflagellates are known to be light-inhibited and emit bioluminescence only during the night phase (Sweeney et al., 1959; Esias et al., 1973; Hamman et al., 1981), colonies exposed to fluorescent room lights were tested for photoinhibition. Their luminescence was not suppressed by exposure to light, although the effects of bright illumination comparable to that in surface waters were not determined. QUANTAL

OUTPUT

OF LIGHT

EMISSION

The mean quantal output of single flashes was 1.2 x lo9 photons * flash- ’ (range 1.8 x lo*-5.1 x lo9 photons), and the mean estimate of total mechanically stimulable

M.I. LATZ ETAL.

34

luminescence was 1.2 x 10” (Table V). Therefore the quantum emission of a single flash represented 1y0 of total luminescent capacity.

Quantum emission of bioluminescence of colonial radiolaria: the mean emission of single flashes as well as total light emission for all taxa are combined; total emission represents an estimate of total mechanically stimuiable luminescence (see text). Measurement

n

Mean output (photons)

SE

Single flash Total emission (TMSL)

8 44

1.2 x 10” 1.2 x 10”

5.8 x IOH 1.3 x IO”’ _-_--~._-_..-.

DISCUSSION

The emission spectra presented here are the first for colonial radiolaria. With emission maxima ranging from 443 to 456 nm, they are similar to the peak emission value of 446 nm reported for the solitary radiol~~ Th~~assic~~la(Herring, 1979). As such, radiolaria spectra are confined to a narrow region located at the short-wavelength side of the range of emissions known for marine organisms (Herring, 1983; Widder et al., 1983). In fact, measurable light emission extended down to 360 nm in the nearuftraviolet. The luminescent responses by colonial radiolaria are similar to those reported for solitary radiolaria. Nicol (1958) measured Bashes of 1-2 s duration from Cytocladm major and A~Zosphae~at~odon in response to mechanical stimulation. Single flashes following electrical stimulation of Thalassicolla sp. display similar kinetics, with rise times of 200-300 ms and flash durations of 1 s (Herring, 1979). Repetitive stimuli initially caused glowing followed by a series of post-stimulus rhythmic flashes. This sequence persisted as long as 50 s and contained 625 flashes. Since post-stimulus flashing was not observed during the present study, it is not known whether it is a species-specific phenomenon restricted to Thalassicolla or is due instead to electrical stimuIation. The extent of coordination of flashing among the cells of the colony is also not known. Species differences in flash kinetics observed in the present study did not appear to be related to colony morphology. Radiolaria are potentially important sources of bioluminescence. The bioluminescence potential of colonial radiolaria is greater than that of dinoflagellates (e.g. Biggley et al., 1969; Swift et al., 1985) but less than that of many zooplankton (Swift et al., 1983). Since a single radiolarian is able to produce < 50 flashes, and flash episodes can persist for < 50 set in solitary forms (Herring, 1979), radiolaria possess a capacity for prominent and prolonged lu~nescent displays. Light emission originates from numerous sources within the colony that have yet to be characterized. Even though 6 lo6 symbiotic dinoflagellates - colony - ’ are present in

BIOLUMINESCENCE

35

OF COLONIAL RADIOLARIA

the cell cytoplasm (Anderson, 1983; present study), there is no evidence available to support the possibility that they play a role in light emission. While luminescent dinoflagellates of the genera Pyrocystis and Dissodinium are commensal with the foraminiferan Hastigerina (Alldredge & Jones, 1973), the dmoflagellate symbionts from the solitary Thalussicollu and the colonial radiolaria Collozoum and Sphuerozoum have been characterized (based on their fine structure) as members of the non-luminescent genus Amphidinium (Taylor, 1974; Anderson, 1976, 1978a; Swanberg & Anderson, 1981). The following spectral and excitation characteristics of the bioluminescence of colonial radiolaria also suggest that dinoflagellates are not responsible for light emission (Table VI). (1) Peak spectral emissions of colonial radiolaria are shifted 20-30 nm towards shorter wavelengths compared to those of dinoflagellates. (2) The bandwidth of radiolaria spectra is significantly broader than that of dinoflagellates. (3) The lack of response to acid stimulation for uncontaminated colonies infers that the algal symbionts are non-luminescent, since low pH is quite effective in stimulating dinoflagellate luminescence (Sweeney, 1969, 1981; Hamman & Seliger, 1972). (4) Luminescence in radiolaria is not light-inhibited (Harvey, 1926), while photosynthetic dinoflagellates emit light only during their dark phase (e.g. Sweeney & Hastings, 1957; Biggley et al., 1969; Sweeney, 1969, 1981). (5)The radiolarian flash quantum emission actually contains less energy than a dinoflagellate flash (Latz and Case, unpubl.). (6) Radiolarian TMSL is not > 25 times greater than that of luminescent dinoflagellates. Since a typical colony was calculated to contain z 2 x IO5 algal symbionts, the expected dinoflagellate contribution to radiolarian light output would have resulted in a considerably larger quantum emission. (7) Finally, the biochemical features of the radiolarian luminescent system are different from the dinoflagellate system and utilize a calcium-activated photoprotein as in some coelenterates (Herring, 1979; Campbell et al., 1981).

TABLE VI

Comparison between light emission of colonial radiolaria (present study) and free-living dinoflagellates: mean values are given; a including P. fusifonnis,P. noctiluca, Dissodinium hula; b Seliger et al., 1969; Swift et a!., 1973; Herring, 1983; Widder et al., 1983; c Latz & Case, unpublished (does not include first flash of P.fisiformis; d Biggley et al., 1969; Swift & Meunier, 1976; Swift et al., 1973, 1981, 1983, 1985; e Hamman & Seliger, 1972; Sweeney, 1969, 1981; f Esias et al., 1973; Hamman et al., 1981. Colonial radiolaria Spectral emission maximum (nm) Spectral bandwidth (FWHM) (nm) Flash duration (s) Single flash energy (photons) Total emission (TMSL) (photons) Acid stimulation Light inhibition

443-456 80 l-2 1 x 109 1 x 10” no no

Dinoflagellates (Pyrocysb,

Dissodinium)

470-480b 35b l-5” 7 x 109 - 1 x 1O’OC 4 x 109 - 7 x 1O’Od

yes” yes’

36

M.I. LATZ ETAL.

Colonial radiolaria are present in most open ocean waters (Haeckel, 1887). In the Sargasso Sea colonies are typically present at 0.1-14 * m- 3 (Swanberg, 1983), although they may accumulate at the surface in high densities. Swanberg (1983) measured < 540 colonies. m-3 in the Sargasso Sea while elsewhere they have occurred in swarms ranging from several thousand to 20 000 colonies. m - 3 (Pavshitiks & Pan’Kova, 1966; Khmeleva, 1967). During the 1985 Biowatt cruise, colonial radiolaria were present at all stations and densities of z 8 colonies. m- 3 were measured in surface waters at Station 19, although visual observations indicated periods of higher abundance. Based on linear interpolation of the present data, the abundance of colonial radiolaria was estimated at 23 colonies . m- 2. Based on a TMSL value of 1.2 x 10” photons * colony ‘, colonial radiolaria would produce a maximum of 2.8 x 1012photons 9m - 2. Assuming colonies are evenly mixed in the upper 1 m, they would produce z 1 x 1012photons . m- 3. Since total bioluminescence potential in the upper 1 m of Station 19 was estimated to be 2 x 1014 photons-m-3 (J. Marra et al., unpubl.), colonial radiolarians contributed z 0.5% of the bioluminescence potential during April 1985. However, when present in high densities their contribution may be at least an order of magnitude greater. ACKNOWLEDGEMENTS

For assistance with collection we thank E. Buskey, C. Mann, J. Dugas, and the captain and crew of the R.V. Know. We thank C. Mann, N. Swanberg, S. Bernstein, and E. Widder for technical assistance. This work was supported by grants from the Office of Naval Research (contract number NOOO14-75-C-0242 to J. F. Case, contract number N00014-80-C-0113 to R. R. Bidigare, and contract number N00014-81-C0062 to E. Swift). REFERENCES A.L. & B.M. JONES, 1973. Hastigerina pelagica: Foraminiferal habitat for planktonic dinoflagellates. Mar. Biol., Vol. 22, pp. 131-135. ANDERSON,O.R., 1976. Ultrastructure of a colonial radiolarian Collozoum inerme and a cytochemical determination of the role of its zooxanthellae. Tissue Cell, Vol. 8, pp. 195-208. ANDERSON,0. R., 1978a. Fine structure of symbiont-bearing colonial radiolarian, Coilosphaera globularis, and i4C isotopic evidence for assimilation of organic substances from its zooxanthellae. J. Vltrasfrucfure Res., Vol. 62, pp. 181-189. ANDERSON,O.R., 1978b. Light and electron microscopic observations of feeding behavior, nutrition, and reproduction in laboratory cultures of Thalassicolla nucleata. Tissue Cell, Vol. 10, pp. 401-412. ANDERSON,O.R., 1980. Radiolaria. In, Biochemistry and physiology of protozoa, Vol. 3, edited by M. Levandowsky & S. Hutner, Academic Press, New York, pp. l-42. ANDERSON,O.R., 1983. Radiolaria. Springer-Verlag, New York, 355 pp. ANDERSON,0. R., N. R. SWANBERG& P. BENNETT,1983. Assimilation of symbiont-derived photosynthates in some solitary and colonial radiolaria. Mar. Biol., Vol. 77, pp. 265-269. ANDERSON,O.R., N.R. SWANBERG& P. BENNETT,1985. Laboratory studies ofthe ecological significance of host-algal nutritional associations in solitary and colonial radiolaria. J. Mar. Biol. Ass. U.K., Vol. 65, pp. 263-272. ALLDREDGE,

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OF COLONIAL RADIOLARIA

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