Eyes and extraocular photoreceptors in midwater cephalopods and fishes: Their roles in detecting downwelling light for counterillumination

The means of detecting downwelling light for counterillumination in several midwater animals has been examined. Eyes and extraocular photoreceptors (drosal photosensitive vesicles in the enoploteuthid squid Abraliopsis sp. B and pineal organs in the myctophid fish Myctophum spinosum) were alternately exposed to overhead light or covered by a small opaque shield above the animal and the bioluminescent response of the animal was monitored. Covering either the eyes or the extraocular photoreceptors resulted in a reduction in the intensity of counterillumination. Preliminary experiments examining the bioluminescent feedback mechanism for monitoring intensity of bioluminescence during counterillumination in the midwater squid Abralia trigonura indicated that the ventral photosensitive vesicles are responsible for bioluminescent feedback.     

Development of symbiotic bacterial bioluminescence in a nearshore cephalopod,Euprymna scolopes

The small neritic cephalopod Euprymna scolopes possesses a large glandular light organ that contains the symbiotic luminous bacterium Vibrio fischeri. Adult and immature E. scolopes were caught in the evening with dip nets in shallow water along the shore of Kanohe Bay, Oahu, Hawaii, during late February 1984. The initiation of the symbiosis was investigated by rearing the cephalopods either in seawater taken from aquaria containing adult E. scolopes or in seawater with reduced bacterial concentrations due to filtration or due to absence of adults. Light production was measured during early development. Bioluminescence was not detected in E. scolopes immediately after hatching. Most individulas of E. scolopes that hatched into seawater containing, or previously exposed to, adults produced light within 24 h. Individuals that hatched into filtered seawater did not produce light. The data suggest that each generation aquires an infection from free-living bacteria rather than from the egg, and that light production is dependent on the nutritional state of the host. Access to an initial inoculum of free-living, luminous bacteria seems to be critical for establishing a successful symbiosis.     

Disruptive counterillumination and its anti-predatory value in the plainfish midshipman Porichthys notatus

The plainfin midshipman Porichthys notatus Girard occurs in nearshore waters off the western coast of North America. We found that the ventrally directed photophores of juvenile laboratory-grown P. notatus function in counterillumination. Their bioluminescence matched downwelling light to obscure the silhouette as viewed from below. P. notatus did not obligatorily counterilluminate at all times in appropriate light. A hydrodynamic stimulus, in addition to appropriate downwelling light, was required to induce counterillumination. This is perhaps an adaptation to conserve its Vargula-type luciferin, which is obtained from its diet. The angular distribution of light produced by P. notatus approximated that typical of downwelling light in the ocean. There was a direct relationship between downwelling irradiance and the maximum intensity of P. notatus luminescence. Insufficient light was produced to replace the light blocked by the fish under lighting conditions typical of the natural environment. The luminescence was, however, effective in eliminating the silhouette of P. notatus as observed with an image-intensifying camera and by dark-adapted human observers. Consequently, the effectiveness of counterillumination probably originates in part from the disruptive pattern of the luminous photophores. P. notatus from the Puget Sound population, which lacks a luciferin source and is non-luminous, displayed counterillumination behavior when its luminescent system was activated by force-feeding the fish with dried Vargula hilgendorfi. Experiments using adult P. notatus as predators on a mixed population of non-luminous (Puget Sound) and luminous (Santa Barbara Channel) juvenile P. notatus revealed that under conditions of dim overhead illumination non-luminous P. notatus were preyed upon at twice the rate of luminous individuals. This is the first experimental evidence suggesting that counterillumination is effective as an anti-predatory strategy. Received: 25 August 1998 / Accepted: 25 March 1999     

Inception of formation and early morphogenesis of the bacterial light organ of the sea urchin cardinalfish, <Emphasis Type="Italic">Siphamia versicolor</Emphasis>

The cardinalfish Siphamia versicolor (Perciformes: Apogonidae) forms a bioluminescent symbiosis with the marine luminous bacterium Photobacterium mandapamensis, harboring the bacteria in a ventral, disc-shaped light organ and using the bacterial light apparently for counterillumination and attracting prey. Little definitive information has been available on the developmental and microbiological events surrounding the initiation of symbiosis, a critical stage in the life history of the fish, in S. versicolor or any of the many other species of bacterially luminous fish. To identify the stage at which light organ formation begins, to determine the origin of cells forming the light organ, and to characterize its bacterial colonization status during development, early developmental stages of S. versicolor obtained and reared from wild-caught mouth-brooding males were examined with histological and microbiological methods. A light organ primordium was not evident in embryos, post-embryos, or pre-release larvae, whereas the light organ began to form within 1 day of release of full-term pre-flexion larvae from the mouths of male fish. Analysis of post-release larvae revealed that the light organ arises from a proliferation and differentiation of intestinal epithelial cells, and that it quickly develops structural complexity, including the formation of chambers and gaps contiguous with the intestinal epithelium. However, the nascent light organ remained uncolonized by the symbiotic bacteria through several days of post-release development, even in the presence of high numbers of the symbiotic bacteria. These results demonstrate that the inception of light organ formation in S. versicolor occurs independently of its symbiotic bacteria and that receptivity to bacterial colonization apparently requires substantial post-release development of the light organ. Larvae therefore most likely acquire their symbiotic bacteria from seawater, during or shortly after the transition from the pre-flexion to the flexion developmental stage.     

Three new modes of luminescence in the leiognathid fish Gazza minuta: Discrete projected luminescence,ventral body flash,and buccal luminescence

Three new modes of luminescence are described for Gazza minuta (Bloch) (Perciformes: Leiognathidae) as observed in specimens collected in the Philippines in April and May, 1982: discrete projected luminescence (DPL), ventral body flash, and buccal luminescence. DPL sharply contrasts with previously reported modes of diffuse luminescence in leiognathids (counterillumination and opercular flash) in being a pair of bright collimated beams of light emanating from the fish in an anteroventral direction. The brightness, coherence, directionality, and control of DPL suggest striking similarities to luminescence in anomalopid (flashlight) and monocentrid (pinecone) fishes and perhaps in certain apogonids (cardinalfishes). The structural correlate for DPL is a small clear patch of skin lying at the posterior margin of each opercular cavity. Luminescence from the internally located light organ traverses transparent bone and translucent muscle before passing through the clear skin of the patch area. Behavioral and anatomical observations of ventral body flash and buccal luminescence are also presented. These new modes of luminescence indicate a much greater than expected diversity of luminescent behaviors in leiognathids, perhaps greater than that of any other organism yet studied. The internal location of the light organ is recognised as providing the potential for this diversity.     

Planktonic bioluminescence in the pack ice and the marginal ice zone of the Beaufort Sea

An icebreaker cruise into the Beaufort Sea in the fall of 1986 provided a unique opportunity for studying planktonic bioluminescence in ice fields and in the marginal ice zone. Bathyphotometer casts (bioluminescence intensity, seawater temperature, beam attenuation coefficient, and salinity) and biological collections were made to a depth of 100 m. A light budget, which describes the planktonic species responsible for the measured bioluminescence, and a dinoflagellate species budget were constructed from the mean light output from luminescent plankton and plankton counts. The vertical distribution of bioluminescence among the ice stations was similar. The maximum intensities were 2 to 8×10⁶ photons s^-1 cm^-3 in the upper 50 m of the sea-ice interface. The marginal ice zone station (MIZ) exhibited a maximum intensity of 2 to 3×10⁸ photons s^-1 cm^-3 between 5 and 30 m depth. At Ice Station 2, Metridia longa and their nauplii contributed approximately 80% of stimulable bioluminescence in the upper 10 m but, overall, Protoperidinium spp. dinoflagellates contributed most of the light to a depth of 100 m. In the MIZ, Protoperidinium spp. dinoflagellates contributed 90% of the light within the upper 10 m, decreasing to 43% of the contributed light at a depth of 40 m. Below 40 m, dinoflagellate bioluminescence decreased to a few percent of the total to a depth of 90 m. Metridia spp. copepods contributed more than 50% of the light at depths from 40 to 90 m. Ostracods, larvaceans, and euphausiid furcilia contributed <1% of all bioluminescence at all depths sampled. Correlation analyses between measured bioluminescence (photons s^-1 cm^-3), the number of bioluminescent dinoflagellates and the light budget for the MIZ indicated highly significant associations: r=0.919, p=0.001, and r=0.912, p<0.001, respectively (Student's two-tailed t-tests). Bioluminescence was negatively correlated with seawater salinity at all stations (p=0.001). Maximum bioluminescence was measured in the less saline surface waters at all stations.     

Effect of arsenic compounds on Vibrio fischeri light emission and butyrylcholinesterase activity

The effect of organic arsenic compounds and inorganic As(V) and As(III) on Vibrio fischeri luminescence and butyrylcholinesterase activity were evaluated using Microtox and microcalorimetric analysis. Organic arsenic compounds were arsenocholine (AsC), arsenobetaine (AsB), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and the antibiotic 4-hydroxy-3-nitrobenzene arsonic acid (HNAA, Roxarsone^(R)). HNAA, As(III) and As(V) were found to inhibit Vibrio fischeri light emission whereas MMA, DMA, AsC and AsB produced only a slight effect. By contrast, only AsC, AsB and As(III) were found to inhibit butyrylcholinesterase activity. Selected article from the 6th European Meeting on Environmental Chemistry, University of Belgrade, Serbia and Montenegro organized by Prof. Dr. Branimir Jovancicevic (www.research.plymouth.ac.uk/ace).     

Evaluation of tests to assess the quality of mine-contaminated soils

An acid metal-contaminated soil from the Aljustrel mining area (a pyrite mine located in SW Portugal in the Iberian Pyrite Belt) was subjected to chemical characterisation and total metal quantification (Cd, Cr, Cu, Ni, Pb and Zn). Water-soluble metals were determined and a sequential extraction procedure was used to investigate metal speciation. Two bioavailable metal fractions were determined: a mobile fraction and a mobilisable fraction. Soil ecotoxicity was studied using a battery of bioassays: plant growth test and seed germination with cress (Lepidium sativum L.), earthworm (Eisenia fetida) mortality, E. fetida avoidance behaviour, luminescent inhibition of Vibrio fischeri and Daphnia magna immobilisation. Although the total content of Cu, Zn and Pb in the soil was large (362, 245 and 1,250 mg/kg dry matter, respectively), these metals were mostly structurally bound (87% for Cu, 81% for Zn and 89% for Pb) and, therefore, scarcely bioavailable. Nonetheless, the D. magna immobilization test using soil leachate showed an EC₅₀ (48 h) of 36.3% (v/v), and the luminescent inhibition of V. fischeri presented an EC₂₀ (15 min) of 45.2% and an EC₂₀ (30 min) of 10.7% (v/v), suggesting a considerable toxic effect. In the direct exposure bioassays, E. fetida avoided the mine soil at the highest concentrations (50%, 75% and 100% v/v). At the same soil concentrations, cress showed negligible growth. The results suggest the need to use a battery of toxicity tests, in conjunction with chemical methods, in order to assess the quality of mine-contaminated soils correctly.     

Luminescence from non-bioluminescent tissues in oceanic cephalopods

Several tissues (e.g. kidney, blood, digestive gland) in oceanic cephalopods which do not exhibit in vivo bioluminescence, luminesce when homogenized in the presence of air or when simply exposed to air in a vial (blood). The source of the luminescence appears to be a luciferin: treatment of kidney homogenates and blood with a photophore extract presumably containing luciferase resulted in a 20-fold increase in light production. Luminescence was also found in the renal fluid, which may be the source of luminescent clouds produced by squids. The variability in luminescence found in some tissues of cephalopods appeared to be related to feeding. Luminescence was also detected in the digestive glands of midwater octopods.     

Luminescent flashing in the midwater squids Pterygioteuthis microlampas and P. giardi

The luminescent flashing capabilities and swimming behavior were examined for two species of small midwater squids (Pterygioteuthis microlampas and P. giardi). Recently captured squid were placed in a small aquarium, where their movements and luminescent flashes could be recorded with an image intensifier, a photomultiplier tube and associated equipment. Flashing behavior was initiated by disturbing the squid with an eletrical shock. The following 4 behaviors were observed: (1) a short flash and a rapid departure from the electrode; (2) a short flash and a delayed, slow departure from the electrode; (3) a longer flash persisting after a rapid departure from the electrode; (4) a longer flash when departure was prevented by continuing the shock. Luminescent flashes probably have a general defensive function, discouraging or disrupting an attack by potential predators, and within this context there may exist numerous strategies involving flashes.     

Sites of bioluminescence in the appendicularians Oikopleura dioica and O. labradoriensis (Urochordata: Larvacea)

Although bioluminescence is known in larvacean tunicates, its origin has not been reported. Two species, Oikopleura dioica and O. labradoriensis, from the northeastern Pacific Ocean, were examined during 1979–1982 to determine the sites of luminescence. An appendicularian lives within a secreted, mucous house, and its body is tightly invested by a house rudiment. Mechanical stimulation elicited multiple, summated blue-green flashes from free individuals invested by house rudiments and from empty houses that were virtually free of contamination by exogenous luminescent bacteria or dinoflagellates. Direct microscopic observations showed that the light is produced by clusters of 1 to 2 m fluorescent granules that form intricate, species-specific patterns of inclusions in the house rudiment. These granular inclusions are probably present in the expanded house, where they account for the multiple, point-sources of light observed in flashing houses. Neither fluorescence nor luminescence were observed in any other parts of the house rudiments, expanded houses, or free appendicularians (including the oral glands, which were previously suspected of producing bioluminescent secretions).     

Bioluminescence of deep-sea coronate medusae (Cnidaria: Scyphozoa)

Bioluminescence is the production of visible light by a living organism. The light commonly appears as flashes from point sources (involving one or more cells, usually described as photocytes) or as a glandular secretion. A visible flash usually involves synchronous light emission from a group of cells or, if from a single-celled organism such as a dinoflagellate, from a group of organelles. The number of cells (or organelles) responding synchronously is the main determinant of the flash intensity. Bioluminescence is a common phenomenon in many deep-sea animals and is widespread among the Cnidaria. In this paper, we compare and contrast in situ and laboratory recordings of the bioluminescent responses of specimens of the deep-sea scyphozoans Atolla wyvillei, Atolla vanhoffeni, Atolla parva, Nausithoe rubra, Paraphyllina intermedia, Periphyllopsis braueri and Periphylla periphylla. Displays in all seven species consist of localised flashes and propagated waves of light in the surface epithelium. The first few single waves propagate at rates of up to 60 cm s^-1 but subsequent ones in any sequence of stimuli gradually decrease in speed. After several single wave responses, a subsequent stimulus may elicit multiple waves that persist for several seconds. Following such a frenzy, the specimen becomes temporarily refractory to further stimuli, but if rested will recover its normal responses and may produce further frenzies. The dome area, situated above the coronal groove, of the genera Paraphyllina, Periphylla, and Nausithoe is covered with luminescent point sources. Such point sources are generally absent from the dome of species of Atolla. Captured specimens of A. parva also produce secretory bioluminescence, corroborating prior in situ observations of this ability. Secretory bioluminescence in P. periphylla takes the form of scintillating particles released from the lappet margins. We did not observe secretory displays in specimens of any other species in the laboratory, but one instance of apparent secretory luminescence was recorded in situ in a specimen of A. wyvillei.Communicated by J. P. Thorpe, Port Erin     

南方某铀矿山废水对生物的急性毒性研究

为探明铀矿山对周围环境的联合毒性机制,本研究以常用生物毒性测试菌种——发光细菌青海弧菌Q67和费氏弧菌以及禾花鲤为受试生物代表,实地采集的铀矿山废水为目标废水,研究铀矿山废水对发光细菌和禾花鲤的急性毒性。实验结果表明,矿山废水对3种生物的急性毒性存在显著的剂量-效应关系,毒性效应浓度EC_(50)(LC50)的大小顺序为禾花鲤幼鱼费氏弧菌青海弧菌Q67,Pb~(2+)/U~(6+)浓度分别为6.052/3.026 mg·L~(-1)、2.284/1.142 mg·L~(-1)、1.339/0.669 mg·L~(-1),均可有效指示矿山废水的毒性水平,其中发光细菌更为灵敏、快速;且青海弧菌Q67的EC_(50)值最小,灵敏度最高,可作为表征矿山废水毒性风险的首选指示物。研究结果能够为放射性矿区废水生态风险预警、安全处理处置、水质基准制定及流域水环境管理提供依据。     

Superoxide production by marine microalgae

This study investigated the possible roles of superoxide produced by raphidophyte and prymnesiophyte microalgae as an ichthyotoxic agent to damselfish and an allelopathic agent to bacteria. We found that the rate of superoxide production varied with algal cell density, with cell densities of the raphidophyte Chattonella marina >10,000 cells ml^–1 producing less environmental levels of superoxide per cell (94±14 chemiluminescence units) than cell densities <10,000 cells=">^–1 (390±54 units per cell). Microalgal cells have the capacity to change their superoxide production rate over a period of 1 h, dependent on cell density and metabolic activity. We also examined the effect of superoxide on suppression of bioluminescence of the marine bacterium Vibrio fischeri as a model for bacterial alleopathy and found that both superoxide and free fatty acids such as eicosapentaenoic acid (EPA; 20:53) present in raphidophyte microalgal cells cause suppression of bacterial bioluminescence. The combination of superoxide in the presence of EPA further enhanced bioluminescence suppression. Superoxide was also found to enhance the toxicity of free fatty acid EPA to damselfish (Acanthochromis polycanthus) at concentrations as low as 0.2 mg l^–1. In conclusion, consideration should be given to density dependent and/or metabolic variations of toxicity when publishing minimum alert levels for superoxide producing ichthyotoxic microalgal species. A secondary role of superoxide production may be to enhance the toxicity of algal exudates or serve as an allelopathic agent against bacterial fouling.     

Observations of planktonic bioluminescence in the euphotic zone of the California Current

The distributions of bioluminescence, temperature, salinity, oxygen. pH, and chlorophyll a were measured at 10 m intervals, to a depth of 100 m at a station (33°46N; 119°36W) in the California Current from 17 to 20 July 1982. The distribution of bioluminescence showed a marked day-night change which was consistent over the sampling period. The nighttime maximum was at the surface, and the daytime maximum was between 30 and 40 m. The shapes of the day and night distributions were independent of the absolute intensity of bioluminescence and were also insensitive to advection, as inferred from changing temperature-salinity relationships. The nighttime depth distribution broadened during a period of high wind Day to night differences in the color spectrum at the depth of maximum bioluminescence suggest that the luminescent organisms differed from day to night.     

Diel patterns of planktonic bioluminescence in the northern Sargasso Sea

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 <7 x 10⁸ 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.     

Synchronized development of gonad and bioluminescent light organ in a highly sexually dimorphic leiognathid fish, Photoplagios rivulatus

In order to investigate the possible coupling between sexual maturation and the light organ system (LOS) development in leiognathid fish, we determined the seasonal changes in the gonad maturation and the light organ enlargement in Photoplagios rivulatus, one of the leiognathid species possessing highly sexually dimorphic LOS. The fish specimens collected from March 2001 to August 2002 were assessed for standard length (SL), body weight (BW), sex, gonad weight (GW) and the light organ weight (LW). Gonadosomatic index (GSI = 10²GW/BW) and percent weight of the light organ to body weight (PLW = 10² LW/BW) were used to demonstrate the extent of development of gonad and the LOS, respectively. Mean GSIs in both male and female increased in June through August. The mean PLW in males showed a similar trend to that of the GSI, while PLW in females showed no clear seasonal trends. A significant positive correlation was found between the GSI and the PLW in males but not in females. The onset of sexual maturity in males (55 mm SL) coincided with that of the light organ enlargement. These results strongly support the functional coupling between reproduction and bioluminescence in this species of leiognathid. From an evolutionary perspective, sexual dimorphism in the LOS is likely to have evolved through sexual selection for reproductive success in leiognathid fishes.     

The trophic link between squid and the emperor penguin <Emphasis Type="Italic">Aptenodytes forsteri</Emphasis> at Pointe Géologie,Antarctica

Cephalopod beaks retrieved from stomachs of dead emperor penguin chicks at Pointe Géologie, Terre Adélie, provide information on taxonomic and size composition of the penguin’s squid diet, on the trophic range of the squid species preyed upon and on the fractional trophic impact of the penguin on the whole food web. Emperor penguins prey upon four squid species (Psychroteuthis glacialis, Kondakovia longimana, Gonatus antarcticus, Alluroteuthis antarcticus) and do not take squid larger than 480 mm mantle length. Larger squid live either below the penguin’s diving range or are beyond its handling capacity. Nitrogen stable isotope ratios indicate that squids cover a range of about two trophic levels (2.5–8‰ δ¹⁵N). The impact of the emperor penguin, however, concentrates on the upper part of this range, about 68% of its squid prey being >6‰ δ¹⁵N. The principal components of the emperor’s diet, fish, krill and squid, differ distinctly in average trophic level. Consequently the trophic position of the emperor penguin changes accordingly with diet composition and may differ by almost one trophic level between different emperor penguin colonies.     

Epipelagic planktonic bioluminescence in the marginal ice zone of the Greenland Sea

Epipelagic planktonic bioluminescence in the marginal ice zone of the Fram Strait was investigated during April and May 1989. Vertical profiles of bioluminescence potential were measured using a HIDEX (High Input Defined EXcitation) design bathyphotometer. Mesozooplankton samples were collected with oblique tows using a 153 m mesh net. The amount of bioluminescence produced by mechanical stimulation of individual organisms was measured using an integrating sphere and photon-counting system. These measures of bioluminescence potential along with estimated abundances of bioluminescent organisms allow an independent estimated of integrated epipelagic bioluminescence potential. The zooplankton community structure was relatively simple in this region and the number of bioluminescent species correspondingly small. The majority of epipelagic bioluminescence was produced by copepods (Metridia spp.), larvaceans (Oikopleura spp.), euphausiids (Thysanoeassa spp.) and ostracods (Conchoecia spp.), although the relative contribution of these organisms to the overall bioluminescence potential varied considerably with time and location over the 2 mo period. Bioluminescent dinoflagellates were rare and did not contribute significantly to epipelagic bioluminescence. Integrated bioluminescence potential in the water column was significantly correlated with zooplankton biomass, but not with any other measured environmental parameter. No enhancement of chlorophyll, zooplankton biomass or bioluminescence was observed in the marginal ice zone compared to the adjacent open waters of the Fram Strait during this spring cruise.     

Rapid response to changing light environments of the calanoid copepod<Emphasis Type="Italic"> Calanus sinicus</Emphasis>

Calanus sinicus is a large calanoid copepod and a dominant species in the coastal waters of Japan. During a research cruise in Sagami Bay on 18 June 1996, we found C. sinicus performing an unusual diel vertical migration (DVM), a behavior that has not been reported in previous studies on this species. This study examined the DVM of C. sinicus under different light environments and revealed the copepods characteristic response to light. Field and laboratory results show that the DVM of C. sinicus is flexible and also confirmed its sensitivity and its rapid response to changing light environments. It is suggested that C. sinicus reacts to changes in absolute light intensity. This feature may be common in oceanic copepod species. The copepods quick reaction to light variation provides decreased predation risks and increased feeding opportunities, which make them a dominant survivor in coastal water habitats.Communicated by T. Ikeda, Hakodate