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(3). 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 population). 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 4/29/97 / biolum@ucsd.edu