Abstracts of Selected Publications

Latz, M.I., J.C. Nauen, and J. Rohr. 2004. 
Bioluminescence response of four species of dinoflagellates to fully 
developed pipe flow. Journal of Plankton Research 26: 1529-1546.
Dinoflagellate bioluminescence provides a nearly instantaneous index of flow sensitivity. 
This study compared flow sensitivity in four species of morphologically diverse luminescent 
dinoflagellates (Ceratium fusus, Ceratocorys horrida, Lingulodinium polyedrum and 
Pyrocystis fusiformis) using fully developed laminar and turbulent pipe flow. 
Bioluminescence response thresholds always occurred in laminar flows with wall shear 
stress levels that, depending on species, ranged from 0.02 to 0.3 N m^-2. With few 
exceptions, such as breaking waves and wave-forced bottom shears in shallow nearshore 
areas, these threshold shear stress levels are several orders of magnitude larger than typical 
oceanic ambient flows. For laminar flows above threshold, species also differed in the 
proportion of organisms responding and the minimum shear stress level where individual 
flashes reached their highest intensity. Following transition to turbulent flow, there was never 
a dramatic increase in bioluminescence, even when energetic turbulent length scales were 
similar to the cell size. On the basis of their bioluminescence response in laminar flow, these 
species were ranked in order of decreasing sensitivity as C. horrida > P. fusiformis > C. 
fusus > L. polyedrum. This ranking, though not conclusive, is consistent with increased flow 
sensitivity due to increasing size and the presence of spines. With the exception of a small 
fraction of the C. horrida population that is sensitive enough to flash within the feeding 
current of a predator, the present study suggests that flashes only occur with predator 
contact. Nevertheless, flow sensitivity may serve as an index of the response to mechanical 
agitation during predator contact/handling. Flow sensitivity may be constrained to maximize 
the response to predator contact/handling while minimizing stimulation by background 
oceanic flows to avoid depleting luminescent reserves.

Latz, M.I., A.R. Juhl, A.M. Ahmed, S.E. Elghobashi, and J. Rohr. 2004. 
Hydrodynamic stimulation of dinoflagellate bioluminescence: a 
computational and experimental study. Journal of Experimental Biology 207: 1941-1951. 
Dinoflagellate bioluminescence provides a near-instantaneous reporter of cell 
response to flow. Although both fluid shear stress and acceleration are thought to 
be stimulatory, previous studies have used flow fields dominated by shear. In the 
present study, computational and experimental approaches were used to assess the 
relative contributions to bioluminescence stimulation of shear stress and 
acceleration in a laminar converging nozzle. This flow field is characterized by 
separate regions of pronounced acceleration away from the walls, and shear along 
the wall. Bioluminescence of the dinoflagellates Lingulodinium polyedrum and 
Ceratocorys horrida, chosen because of their previously characterized different 
flow sensitivities, was imaged with a low-light video system. Numerical simulations 
were used to calculate the position of stimulated cells and the levels of 
acceleration and shear stress at these positions. Cells were stimulated at the 
nozzle throat within the wall boundary layer where, for that downstream position, 
shear stress was relatively high and acceleration relatively low. Cells of C. 
horrida were always stimulated significantly higher in the flow field than cells of 
L. polyedrum and at lower flow rates, consistent with their greater flow 
sensitivity. For both species, shear stress levels at the position of stimulated 
cells were similar to but slightly greater than previously determined response 
thresholds using independent flow fields. L. polyedrum did not respond in 
conditions where acceleration was as high as 20 g. These results indicate that 
shear stress, rather than acceleration, was the stimulatory component of flow. 
Thus, even in conditions of high acceleration, dinoflagellate bioluminescence is an 
effective marker of shear stress.

Stokes, M.D., G.B. Deane, M.I. Latz, and J. Rohr. 2004. 
Bioluminescence imaging of wave-induced turbulence. 
Journal of Geophysical Research 109: C01004 (8 pages).
The ability to measure turbulent processes on small spatial and temporal scales 
is a long standing problem in physical oceanography. Here we explore a novel 
means of measuring fluid shear stress using the cell flashing behavior of 
bioluminescent dinoflagellates. To illustrate this technique, we present 
estimates of the heterogeneous, time-varying shear stress inside a breaking wave 
crest. These results have implications for a better understanding of upper ocean 
wave physics, air-sea gas transfer, and the biology of planktonic near-surface 
organisms as well as providing a new quantitative fluid visualization tool.

Chen, A.K., Latz, M.I. and J.A. Frangos. 2003.
The use of dinoflagellate bioluminescence to characterize cell stimulation 
in bioreactors. Biotechnology & Bioengineering 83: 93-103.
Bioluminescent dinoflagellates are flow-sensitive marine organisms that 
produce light emission almost instantaneously upon stimulation by fluid 
shear in a shear stress dose-dependent manner. In the present study we 
tested the hypothesis that monitoring bioluminescence by suspended 
dinoflagellates can be used as a tool to characterize cellular response to 
hydrodynamic forces in agitated bioreactors. Specific studies were performed to 
determine: (1) impeller configurations with minimum cell activation, 
(2) correlations of cellular response and an integrated shear factor, and 
(3) the effect of rapid acceleration in agitation. Results indicated that 
(1) at a volumetric mass transfer coefficient of 3X10^-4 s^-1, marine impeller 
configurations were less stimulatory than Rushton configurations, 
(2) bioluminescence response and a modified volumetric integrated shear 
factor had an excellent correlation, and (3) rapid acceleration in agitation 
was highly stimulatory, suggesting a profound effect of temporal gradients in 
shear in increasing cell stimulation. By using bioluminescence stimulation as an 
indicator of agitation-induced cell stimulation and/or damage in microcarrier 
cultures, the present study allows for the verification of hypotheses and 
development of novel mechanisms of cell damage in bioreactors.

von Dassow, P. and M.I. Latz. 2002.
The role of calcium ions in stimulated bioluminescence of the dinoflagellate 
Lingulodinium polyedrum. Journal of Experimental Biology 205: 
Many marine dinoflagellates emit bright discrete flashes of light nearly 
instantaneously in response to either laminar or turbulent flows as well as direct 
mechanical stimulation.  The flash involves a unique pH-dependent luciferase and a 
proton-mediated action potential across the vacuole membrane.  The 
mechanotranduction process initiating this action potential is unknown. The present 
study investigated the role of Ca2+ in the mechanotransduction process regulating 
bioluminescence in the dinoflagellate Lingulodinium polyedrum. Calcium 
ionophores and digitonin stimulated bioluminescence in a Ca2+-dependent manner in 
the absence of mechanical stimulation. Mechanically stimulated bioluminescence was 
strongly inhibited by the intracellular Ca2+ chelator BAPTA-AM; there was only a 
partial and irreversible dependence on extracellular Ca2+.  Ruthenium Red, a blocker 
of intracellular Ca2+ release channels, inhibited mechanically stimulated 
bioluminescence.  Bioluminescence was also stimulated by increasing K+ even in the 
absence of extracellular Ca2; K+ stimulation was inhibited both by BAPTA-AM and 
Ruthenium Red.  These results support the hypothesis that Ca2+ mediates stimulated 
bioluminescence and also indicate the involvement of intracellular Ca2+ stores.  
Rapid coupling between mechanical stimulation and mobilization of intracellular Ca2+ 
stores may occur through a mechanism similar to excitation-contraction coupling in 
skeletal muscle.

Juhl, A.R. and M.I. Latz. 2002.
Mechanisms of fluid shear-induced inhibition of population growth of a 
red-tide dinoflagellate. Journal of Phycology 38: 683-694.
Net population growth of some dinoflagellates is inhibited by fluid shear at shear 
stresses comparable to those generated during oceanic turbulence.  Decreased net 
growth may be due to a reduction in cell division, increased mortality, or both.  
Experiments to determine the dominant mechanism under various flow conditions used 
the red-tide dinoflagellate Lingulodinium polyedrum (Stein) Dodge (= 
Gonyaulax polyedra).  Daily cell division and mortality were determined by 
direct observation of isolated cells in 0.5-mL cultures in the wells of multiwell 
plates.  Shaking the plates generated unquantified fluid shear in each well.  Larger 
volume cultures were exposed to quantified laminar shear generated in Couette-flow 
chambers (shear stresses of 0.004 - 0.019 N.m^-2) and to unquantified flow in shaken 
flasks. Daily cell division frequency was calculated from flow-cytometric 
measurements of DNA.cell^-1.  In multiwell-plate experiments and in Couette-flow 
experiments with low shear stress, growth inhibition was attributed to lowered cell 
division without mortality.  In Couette-flow experiments at higher shear stresses 
and in shaken-flask experiments, cell division did not decrease and mortality was 
inferred to be responsible for the decline in net population growth.  
Elevated mortality from high shear stress, and the lack thereof in lower 
shear-stress exposures, was confirmed using a suite of behavioral, morphological and 
physiological assays. Shear-induced mortality was characterized by increased 
disrupted or dead cells, and by increases in cells with damaged outer membranes and 
elevated intracellular H2O2 concentration.  The lowest shear stress did not cause 
mortality in early exponential-phase cultures, although it caused high mortality in 
late exponential-phase cultures. High shear stress did cause mortality in early 
exponential-phase cultures.  The results predict that growth of rapidly growing, 
healthy populations of L. polyedrum may be inhibited by oceanic turbulence through 
decreased cell division but mortality would not be expected unless turbulent shear 
levels were unusually high.  Shear-induced mortality may occur when in situ growth 
conditions resemble those in late exponential/stationary phase cultures, as may 
occur during later phases of in situ blooms.

S.K. Mallipattu, M.A. Haidekker, P. von Dassow, M.I. Latz, and J.A. Frangos. 2002.
Evidence for shear-induced increase in membrane fluidity in the dinoflagellate 
Lingulodinium polyedrum. Journal of Comparative Physiology A 188: 409-416.
Fluid shear stress has been demonstrated to affect the structure and
function of various cell types. In mammalian cells, it was hypothesized that
shear-induced membrane fluidization leads to activation of heterotrimetric 
G-proteins. The purpose of this study was to determine if a similar mechanism exists 
in the dinoflagellate Lingulodinium polyedrum, a single-celled eukaryotic 
aquatic organism that bioluminesces under shear stress. Membrane fluidity changes in 
L. polyedrum were monitored using the molecular rotor 
9-(dicyanovinyl)-julolidine, whose fluorescence intensity changes inversely with 
membrane fluidity. Dual-staining with 9-(dicyanovinyl)-julolidine and the membrane 
dye 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulfonate 
indicates membrane localization. Subjecting L. polyedrum cells to increasing 
shear stress reversibly decreased 9-(dicyanovinyl)-julolidine fluorescence, while 
autofluorescence of the cytoplasmic chlorophyll did not change. The relationship 
between shear stress (0.63 Pa, 1.25 Pa, 1.88 Pa, and 2.5 Pa) and membrane fluidity 
changes was linear and dose-dependent with a 12% increase in fluidity at 2.5 Pa. To 
further explore this mechanism a membrane fluidizing agent, dimethyl sulfoxide was 
added. Dimethyl sulfoxide decreased 9-(dicyanovinyl)-julolidine emission by 41▒15% 
and elicited a dose-dependent bioluminescent response at concentrations of 0.2%, 
0.5%, 1.0%, and 1.25%. This study demonstrates a link between fluid shear stress and 
membrane fluidity, and suggests that the membrane is an important flow mechanosensor 
of dinoflagellates.

Juhl, A.R., V.L. Trainer, and M.I. Latz. 2001.
Effect of fluid shear and illumination on population growth and cellular 
toxin content of the dinoflagellate Alexandrium fundyense. Limnology and 
Oceanography 46: 758-764.
The potential for in situ turbulence to inhibit dinoflagellate population growth 
has been demonstrated by experimentally exposing dinoflagellate cultures to 
quantified shear flow. However, despite interest in understanding environmental 
factors that affect the growth of toxic dinoflagellates, little is known of the 
effect of shear on the growth of toxin-producing dinoflagellate species. Cultures 
of the dinoflagellate, Alexandrium fundyense, a producer of toxins 
responsible for paraltyic shellfish poisoning, were exposed to quantified laminar 
shear generated in Couette flow for 1-24 h d^-1 over 6-8 d. Shear stress in all 
experiments was 0.003 N m^-2, similar to levels expected in near-surface waters 
on a windy day. Net population growth decreased with shear exposures 1 h d^-1 and 
became negative with exposures 12 h d^-1. Cellular toxin content at the end of 
each experiment was measured by a receptor-binding assay that used [3H]saxitoxin. 
Toxin cell^-1 of cultures sheared for 1 h d^-1 increased up to three times that 
of control cultures. Cellular toxin content increased significiantly as growth 
rate of sheared cultures decreased. However, varying culture growth rate using 
irradiance had no significant effect on toxin cell^-1. Because shear stress levels 
used in this study were plausible for near-surface turbulent flows, oceanic 
turbulence may inhibit population growth and increase cellular toxin content of 
A. fundyense. However, in natural populations it would be difficult to 
distinguish the effect of turbulence on toxin content from other influences on 
toxin variability, particularly if volume- or mass-specific, rather than 
cell-specific, measures of toxin are used.

Juhl, A.R., V. Velasquez, and M.I. Latz. 2000.
Effect of growth conditions on flow-induced inhibition of population growth 
of a red-tide dinoflagellate. Limnology and Oceanography 45: 905-915.
The population growth of some dinoflagellates is known to be reduced by exposure to 
fluid flow. The red-tide dinoflagellate Lingulodinium polyedrum, was used to 
examine the effect of growth conditions on flow-induced inhibition of population 
growth. Three factors were tested: time of exposure relative to the light:dark 
cycle, illumination level, and culture growth phase (early vs. late exponential 
phase). Cultures maintained on a 12:12 h light:dark cycle were exposed to one of two 
flow conditions: quantified laminar shear produced by Couette flow or unquantified 
flow generated in shaken flasks. The duration of exposure to flow was 1 h d^-1 for 5
-8 d in all experiments; the shear stress in Couette shear experiments was 0.004 N 
m^-2. There were many qualitative similarities in the pattern of response to flow in 
the two hydrodynamic conditions. In both cases, exposure to flow in the last hour of 
the dark phase resulted in greater reduction of net growth than exposure during the 
light phase. Cultures grown under lower illumination had proportionally greater 
reductions in net growth than cultures under higher light. Finally, late exponential 
phase cultures exhibited much greater reductions in net growth following a given 
flow exposure than early exponential phase cultures. The higher sensitivity of late 
exponential phase cultures did not appear to be linked to nutrient limitation or 
changes in pH of the medium; it may be partially attributed to exudates from late 
exponential phase cells. These results suggest that the response of red-tide 
dinoflagellate population growth to in situ turbulence may depend on both 
environmental conditions and the physiological state of the cells.

Zirbel, M.J., F. Veron, and M.I. Latz. 2000.
The reversible effect of flow on the morphology of  
Ceratocorys horrida (Peridiniales, Dinophyta). Journal of Phycology 36: 46-58.
Most cells experience an active and variable fluid environment, in which 
hydrodynamic forces can affect aspects of cell physiology including gene regulation, 
growth, nutrient uptake, and viability. The present study describes a rapid yet 
reversible change in cell morphology of the marine dinoflagellate, Ceratocorys 
horrida Stein, due to fluid motion. Cells cultured under still conditions 
possess six large spines, each almost one cell diameter in length. When gently 
agitated on an orbital shaker under conditions simulating fluid motion at the sea 
surface due to light wind or surface chop, as determined from digital particle 
imaging velocimetry, population growth was inhibited and a short-spined cell type 
appeared which possessed a 49% mean decrease in spine length and a 53% mean decrease
in cell volume. The reduction in cell size appeared to result primarily from a 39% 
mean decrease in vacuole size. Short-spined cells were first observed after 1 h of 
agitation at 20˚C; after 8 to 12 d of continuous agitation, long-spined cells were 
no longer present. The morphological change was completely reversible; in previously 
agitated populations devoid of long-spined cells, cells began to revert to the 
long-spined morphology within 1 d after the return to still conditions. During 
morphological reversal, spines on isolated cells grew up to 10 Ám·d-1. In 30 d the 
population morphology had returned to original proportions, even though the overall 
population growth was zero during this time. The reversal did not occur as a result 
of cell division, because single-cell studies confirmed that the change occurred in 
the absence of cell division, and much faster than the 16 d doubling time. The 
threshold level of agitation causing morphology change in C. horrida was too 
low to inhibit population growth in the shear-sensitive dinoflagellate, 
Lingulodinium polyedrum. At the highest level of agitation tested, there was 
negative population growth in C. horrida cultures, indicating that fluid 
motion caused cell mortality. Small, spineless cells constituted a small percentage 
of the population under all conditions. Although their abundance did not change, 
single-cell studies and morphological characteristics suggest that the spineless 
cells can rapidly transform to and from other cell types. The sinking rate of 
individual long-spined cells in still conditions was significantly less than that of 
short-spined cells, even though the former are larger and have a higher cell 
density. These measurements demonstrate that the long spines of C. horrida 
reduce cell sinking. Shorter spines and reduced swimming would allow cells to more 
rapidly sink away from turbulent surface conditions. The ecological importance of 
the morphological change may be to avoid conditions which inhibit population growth 
and potentially cause cell damage.

Lindsay, S.M., Frank, T.M., Kent, J., Partridge, J.C., and M.I. Latz. 1999. 
Spectral sensitivity of vision and bioluminescence in the midwater 
shrimp, Sergestes similis. Biological Bulletin 197: 348-360.
In the oceanic midwater environment, many fish, squid, and shrimp use luminescent 
countershading to remain cryptic to silhouette-scanning predators. The midwater 
penaeid shrimp, Sergestes similis Hansen, responds to downward-directed light 
with a dim bioluminescence that dynamically matches the spectral radiance of oceanic 
downwelling light at depth. Although the sensory basis of luminescent countershading 
behavior is visual, the relationship between visual and behavioral sensitivity is 
poorly understood. In this study, visual spectral sensitivity, based on 
microspectrophotometry and electrophysiological measurements of photoreceptor 
response, is directly compared to the behavioral spectral efficiency of luminescent 
countershading. Microspectrophotometric measurements on single photoreceptors 
revealed only a single visual pigment with peak absorbance at 495 nm in the 
blue-green region of the spectrum. The peak electrophysiological spectral 
sensitivity of dark-adapted eyes was centered at about 500 nm. The spectral 
efficiency of luminescent countershading showed a broad peak from 480 to 520 nm. 
Both electrophysiological and behavioral data closely matched the normalized 
spectral absorptance curve of a rhodopsin with lmax = 495 nm, when rhabdom length 
and photopigment specific absorbance were considered. The close coupling between 
visual spectral sensitivity and the spectral efficiency of luminescent 
countershading attests to the importance of bioluminescence as a camouflage strategy
in this species.

Latz, M.I. and J. Rohr. 1999.
Luminescent response of the red tide dinoflagellate Lingulodinium polyedrum 
to laminar and turbulent flow. Limnology and Oceanography 44: 1423-1435.
While it is universally accepted that plankton continually experience a dynamic
fluid environment, their sensitivity to the features of the surrounding flow 
field at the relevant length and time scales of the organism is poorly
characterized. The present study uses bioluminescence as a tool to understand 
how the red tide dinoflagellate Lingulodinium polyedrum (=Gonyaulax 
polyedra) responds to well characterized hydrodynamic forces present in 
fully developed laminar and turbulent pipe flow. The response of L. polyedrum 
to hydrodynamic stimulation was best characterized by wall shear stress; at 
similar values of wall shear stress the response was similar for laminar and 
turbulent flows.

The response threshold occurred in laminar flow at a wall shear stress of 
approximately 0.3 N m^-2. At these low flow rates, video analysis of the 
velocity of flash trajectories revealed that responding cells were positioned 
only near the pipe wall, where local shear stress levels were equal or greater 
than threshold. For cell concentrations ranging over four orders of magnitude, 
threshold values of wall shear stress were restricted to a narrow range, 
consistent with an antipredation function for dinoflagellate bioluminescence. 
For laminar flows with above-threshold wall shear stress values <1 N m^-2, 
mean bioluminescence increased with wall shear stress according to a power 
(log-log) relationship, with the slope of the power function dependent on cell 
concentration. The increase in bioluminescence within this range was due primarily 
to an increasing population response rate, and to a lesser extent an increase in 
maximum flash intensity per cell and the increased flux of organisms with higher 
flow rates. For wall shear stress levels greater than 1 N m^-2, the maximum 
intensity per cell remained approximately constant with increasing wall shear 
stress, even as the flow transitioned from laminar to turbulent, and the smallest 
turbulent length scales became less than the average cell size.

Rohr, J., M.I. Latz, S. Fallon, J.C. Nauen, and E. Hendricks. 1998. 
Experimental approaches towards interpreting dolphin-stimulated bioluminescence. 
Journal of Experimental Biology 201: 1447-1460. 
Flow-induced bioluminescence provides a unique opportunity for visualizing the flow 
field around a swimming dolphin. Unfortunately, previous descriptions of 
dolphin-stimulated bioluminescence have been largely anecdotal and often 
conflicting. Most references in the scientific literature report an absence of 
bioluminescence on the dolphin body, which has been invariably assumed to be 
indicative of laminar flow. However, hydrodynamicists have yet to find compelling 
evidence that the flow remains laminar over most of the body. The present study 
integrates laboratory, computational and field approaches to begin to assess the 
utility of using bioluminescence as a method for flow visualization by relating 
fundamental characteristics of the flow to the stimulation of naturally occurring 
luminescent plankton.

Laboratory experiments using fully-developed pipe flow revealed that the 
bioluminescent organisms identified in the field studies can be stimulated in both 
laminar and turbulent flow when shear stress values exceeded approximately 0.1 
N/m^2. Computational studies of an idealized hydrodynamic representation of a 
dolphin (modeled as a 6:1 ellipsoid), gliding at a speed of 2 m/s, predicted 
suprathreshold surface shear stress values everywhere on the model, regardless of 
whether the boundary layer flow was laminar or turbulent. Laboratory flow 
visualization of a sphere demonstrated that the intensity of bioluminescence 
decreased with increasing flow due to the thinning of the boundary layer, while flow
 separation caused a dramatic increase due to the significantly greater volume of 
stimulating flow in the wake. Intensified video recordings of dolphins gliding at 
speeds of approximately 2 m/s confirmed that brilliant displays of bioluminescence 
occurred on the body of the dolphin. The distribution and intensity of 
bioluminescence suggest that the flow remained attached over most of the body. A 
conspicuous lack of bioluminescence was often observed on the dolphin rostrum, melon 
and the leading edge of the dorsal and pectoral fins, where the boundary layer is 
thought to be the thinnest. To differentiate between effects related to the 
thickness of the stimulatory boundary layer and those due to the latency of the 
bioluminescence response and the upstream depletion of bioluminescence, laboratory 
and dolphin studies of forced separation and laminar to turbulent transition were 
conducted. The observed pattern of stimulated bioluminescence is consistent with the 
hypothesis that bioluminescent intensity is directly related to the thickness of the 
boundary layer. 

Rohr, J., J. Allen, J. Losee, and M.I. Latz. 1997. 
The use of bioluminescence as a flow diagnostic. 
Physics Letters A 228: 408-416. 
The flash response of luminescent plankton is studied in 
laminar and turbulent pipe flow. Maximum intensity levels 
of individual plankton are nearly constant for wall shear 
stress values exceeding approximately 10 dyn/cm2 -- regardless 
of the nature of the flow. This result necessitates a reevaluation 
of previous inferences made about the stimulating flow field. 

Omori, M., M.I. Latz, H. Fukami, and M. Wada. 1996. New 
observations on the bioluminescence of the pelagic shrimp Sergia 
lucens (Hansen, 1922). pp. 175-184. In: Zooplankton: Sensory Ecology 
and Physiology. P.H. Lenz, D.K. Hartline, J.E. Purcell, and D.L. Macmillan, eds. 
Gordon and Breach Publishers, Amsterdam.
Bioluminescence of the sergestid shrimp, Sergia lucens, was confirmed 
experimentally. To the unaided eye, light emission was oriented downward 
as a dim glow which originated from the ventral and lateral body surfaces. 
Image intensification revealed that this steady glow actually consisted of 
scintillating sources. Photophores first appear at 4.3 mm in carapace 
length (CL), and increase in number with growth. The arrangement is completed 
when the shrimp is sexually mature at 9.3 mm CL. The number of photophores 
of adults ranges between 158 and 169. Physiological mechanisms controlling 
the light emission are unknown. Gentle prodding of the body and electrical 
stimulation were ineffective, and there was very little response to serotonin 
treatment. The most effective stimuli were a strobe light flash and eyestalk 
crushing. Although the average emission measured from ovigerous females was 
approximately twice that from males, the differences in bioluminescence according 
to gender or reproductive conditions were not statistically significant.

Latz, M.I., and H.J. Jeong. 1996. Effect of red tide 
dinoflagellate diet on the bioluminescence of the heterotrophic dinoflagellate, 
Protoperidinium spp. Marine Ecology Progress Series 132: 275-285.
The effects of diet and cannibalism were assessed from changes in the 
bioluminescence potential of two species of the heterotrophic 
dinoflagellate Protoperidinium fed on 4 species of red tide dinoflagellate 
prey, and with no added prey. The use of bioluminescence as a sensitive 
indicator of nutritional status and feeding was explored. The 
bioluminescence of Protoperidinium cf. divergens and P. crassipes 
was significantly affected by dinoflagellate diet. Total 
mechanically stimulable luminescence (TMSL) of P. cf. divergens 
fed different dinoflagellate diets was significantly correlated 
with feeding frequency (the percent of feeding P. cf. divergens 
cells) rather than with population growth rate. P. cf. divergens 
displayed high levels of TMSL and feeding frequency on a diet of 
Scrippsiella trochoidea which did not support population growth. 
Diet did not affect the total number of flashes produced per cell; 
therefore changes in TMSL with dinoflagellate diet were related to 
the amount of chemical substrate available for luminescence, 
rather than changes in the excitation/transduction process. 
Individually isolated cells remained viable for only 3 - 5 days 
without food, and exhibited reduced bioluminescence. However, 
cells maintained in groups survived at least 16 days ithout added 
prey and maintained levels of bioluminescence similar to those 
during favorable prey conditions. Cannibalism observed during this 
time may have enabled cells of Protoperidinium cf. divergens to 
feed and therefore produce high levels of bioluminescence in the 
absence of added prey. Changes in swimming speed were less than 
changes in bioluminescence. The results of the present study 
suggest that energy utilization may be prioritized in the 
following order: swimming (for grazing)  bioluminescence (for 
reducing predation)  reproduction (for increasing the 

Latz, M.I. 1995. Physiological mechanisms in the control of 
bioluminescent countershading in a midwater shrimp. Journal of Marine and 
Freshwater Physiology and Behavior 26: 207-218.
In the oceanic midwater environment, most animals have evolved an extraordinary 
anti-predation behavior using bioluminescent countershading 
(counterillumination) to help them remain cryptic to visual 
predators. For the midwater penaeid shrimp, Sergestes similis, the 
interaction of both hormonal and neural systems may be involved in 
the control of counterillumination. S. similis responds to 
downward-directed illumination, detected by the eyes, with light 
emission from five hepatic light organs. Dark-adapted specimens 
undergo a slow induction process prior to production of the 
conventional counterillumination response. The induction of 
bioluminescence may involve a hormonal pathway mediated by the 
light-adapting retinal distal pigment dispersing hormone. Once 
induced, the rapid control of counterillumination may involve a 
neural pathway. Because counterilluminating animals directly 
respond to their optical environment, an understanding of the 
control of bioluminescence provides an insight into the poorly 
understood visual processing capabilities of deep-sea animals. 

Latz, M.I. and A.O. Lee. 1995. Spontaneous and stimulated 
bioluminescence of the dinoflagellate, Ceratocorys horrida 
(Peridiniales). Journal of Phycology 31: 120-132.
This is the first report of spontaneous bioluminescence in the autotrophic 
dinoflagellate, Ceratocorys horrida von Stein. Bioluminescence was 
measured, using an automated data acquisition system, in a strain 
of cultured cells isolated from the Sargasso Sea. Ceratocorys 
horrida is only the second dinoflagellate species to exhibit 
rhythmicity in the rate of spontaneous flashing, flash quantum 
flux (intensity), and level of spontaneous glowing. The rate of 
spontaneous flashing was maximal during hours 2 - 4 of the dark 
phase [i.e. circadian time (CT)16-18 for a 14:10 h light:dark 
cycle (LD10:14)], with approximately 2% of the population 
flashing.min-1, a rate approximately one order of magnitude 
greater than that of the dinoflagellate, Gonyaulax polyedra. Flash 
quantum flux was also maximal during this period. Spontaneous 
flashes were 134 ms in duration with a maximum flux (intensity) of 
3.1 x 109 quanta.s-1. Light emission presumably originated from 
blue fluorescent microsources distributed in the cell periphery 
and not from the spines. Values of both spontaneous flash rate and 
maximum flux were independent of cell concentration. Isolated 
cells also produced spontaneous flashes. Spontaneous glowing was 
dim except for a peak of 6.4 x 104 quanta.s-1.cell-1 which 
occurred at CT22.9 for LD14:10 and at CT22.8 for LD12:12. The 
total integrated emission of spontaneous flashing and 
glowing during the dark phase was 4 x 109 quanta.cell-1, 
equivalent to the total stimulable luminescence (TSL). The rhythms 
for C. horrida flash and glow behavior were similar to those of 
Gonyaulax polyedra, although flash rate and quantum flux were 
greater. Spontaneous bioluminescence in C. horrida may be a 
circadian rhythm because it persisted for at least three cycles in 
constant dark conditions. This is also the first detailed study of 
the stimulated bioluminescence of C. horrida, which also displayed 
a diurnal rhythm. Cultures exhibited  200 times more mechanically 
stimulated bioluminescence during the dark phase than during the 
light phase. Mechanical stimulation during the dark phase resulted 
in 6.7 flashes.cell-1; flashes were brighter and longer in 
duration than spontaneous flashes. Cruise-collected cells 
exhibited variability in quantum flux with few differences in 
flash kinetics. The role of dinoflagellate spontaneous 
bioluminescence in the dynamics of near-surface oceanic 
communities is unknown, but it may be an important source of 
natural in situ bioluminescence.

Latz, M.I., J.F. Case, and R.L. Gran. 1994. Excitation of 
bioluminescence by laminar fluid shear associated with simple 
Couette flow. Limnology and Oceanography 39: 1424-1439.
The effect of fluid motion on the excitation of bioluminescence 
was examined for cultured dinoflagellates and plankton samples 
subjected to steady-state laminar shear associated with simple 
Couette flow established in the gap between concentric cylinders, 
with only the outer cylinder rotating. The excitation threshold 
for the thecate dinoflagellate, Gonyaulax polyedra, occurred 
at a shear stress of 1 dyn cm^-2. At higher shear stresses light output 
per cell was proportional to pproximately the second power of shear 
stress. At each maintained shear stress, bioluminescence decreased 
exponentially at a rate proportional to the magnitude of shear 
stress. The nonthecate dinoflagellates, Pyrocystis fusiformis and 
P. noctiluca, were more sensitive to stimulation and exhibited an 
order of magnitude higher rate of depletion than for G. polyedra. 
Plankton samples from the Sargasso Sea and eastern Pacific had 
similar excitation thresholds but differed in the slope of the 
intensity vs. shear response most likely due to different 
luminescent populations. The excitation threshold obtained from 
this study is several orders of magnitude greater than oceanic 
shear stress values in the mixed layer, suggesting that ambient 
fluid motion, with the exception of surface breaking waves, does 
not stimulate bioluminescence. 
Abstracts / Updated 7/16/03 / biolum@ucsd.edu