Light and vision in the deep-sea benthos: I. Bioluminescence at 500-1000 m depth in the Bahamian islands.

Bioluminescence is common and well studied in mesopelagic species. However, the extent of bioluminescence in benthic sites of similar depths is far less studied, although the relatively large eyes of benthic fish, crustaceans and cephalopods at bathyal depths suggest the presence of significant biogenic light. Using the Johnson-Sea-Link submersible, we collected numerous species of cnidarians, echinoderms, crustaceans, cephalopods and sponges, as well as one annelid from three sites in the northern Bahamas (500-1000 m depth). Using mechanical and chemical stimulation, we tested the collected species for light emission, and photographed and measured the spectra of the emitted light. In addition, in situ intensified video and still photos were taken of different benthic habitats. Surprisingly, bioluminescence in benthic animals at these sites was far less common than in mesopelagic animals from similar depths, with less than 20% of the collected species emitting light. Bioluminescent taxa comprised two species of anemone (Actinaria), a new genus and species of flabellate Parazoanthidae (formerly Gerardia sp.) (Zoanthidea), three sea pens (Pennatulacea), three bamboo corals (Alcyonacea), the chrysogorgiid coral Chrysogorgia desbonni (Alcyonacea), the caridean shrimp Parapandalus sp. and Heterocarpus ensifer (Decapoda), two holothuroids (Elasipodida and Aspidochirota) and the ophiuroid Ophiochiton ternispinus (Ophiurida). Except for the ophiuroid and the two shrimp, which emitted blue light (peak wavelengths 470 and 455 nm), all the species produced greener light than that measured in most mesopelagic taxa, with the emissions of the pennatulaceans being strongly shifted towards longer wavelengths. In situ observations suggested that bioluminescence associated with these sites was due primarily to light emitted by bioluminescent planktonic species as they struck filter feeders that extended into the water column.

Bioluminescence and toxicity as driving factors in harmful algal blooms: Ecological functions and genetic variability.

Dinoflagellates are an ecologically important group of marine microbial eukaryotes with a remarkable array of adaptive strategies. It is ironic that two of the traits for which dinoflagellates are best known, toxin production and bioluminescence, are rarely linked when considering the ecological significance of either. Although dinoflagellate species that form some of the most widespread and frequent harmful algal blooms (HABs) are bioluminescent, the molecular and eco-evolutionary associations between these two traits has received little attention. Here, the major themes of biochemistry and genetics, ecological functions, signaling mechanisms, and evolution are addressed, with parallels and connections drawn between the two. Of the 17 major classes of dinoflagellate toxins, only two are produced by bioluminescent species: saxitoxin (STX) and yessotoxin. Of these, STX has been extensively studied, including the identification of the STX biosynthetic genes. While numerous theories have been put forward as to the eco-evolutionary roles of both bioluminescence and toxicity, a general consensus is that both function as grazing deterrents. Thus, both bioluminescence and toxicity may aid in HAB initiation as they alleviate grazing pressure on the HAB species. A large gap in our understanding is the genetic variability among natural bloom populations, as both toxic and non-toxic strains have been isolated from the same geographic location. The same applies to bioluminescence, as there exist both bioluminescent and non-bioluminescent strains of the same species. Recent evidence demonstrating that blooms are not monoclonal events necessitates a greater level of understanding as to the genetic variability of these traits among sub-populations as well as the mechanisms by which cells acquire or lose the trait, as sequence analysis of STX+ and STX- species indicate the key gene required for toxicity is lost rather than gained. While the extent of genetic variability for both bioluminescence and toxicity among natural HAB sub-populations remains unknown, it is an area that needs to be explored in order to gain greater insights into the molecular mechanisms and environmental parameters driving HAB evolution.

Field-Validated Detection of Aureoumbra lagunensis Brown Tide Blooms in the Indian River Lagoon, Florida, Using Sentinel-3A OLCI and Ground-Based Hyperspectral Spectroradiometers.

Frequent Aureoumbra lagunensis blooms in the Indian River Lagoon (IRL), Florida, have devastated populations of seagrass and marine life and threaten public health. To substantiate a more reliable remote sensing early-warning system for harmful algal blooms, we apply varimax-rotated principal component analysis (VPCA) to 12 images spanning ~1.5 years. The method partitions visible-NIR spectra into independent components related to algae, cyanobacteria, suspended minerals, and pigment degradation products. The components extracted by VPCA are diagnostic for identifiable optical constituents, providing greater specificity in the resulting data products. We show that VPCA components retrieved from Sentinel-3A Ocean and Land Colour Instrument (OLCI) and a field-based spectroradiometer are consistent despite vast differences in spatial resolution (~50 cm vs. 300 m). Furthermore, the VPCA components associated with A. lagunensis in both spectral datasets indicate high correlations to Ochrophyta cell counts (R2 ≥ 0.92, p < 0.001). Recombining components exhibiting a red-edge response produces a Chl a algorithm that outperforms empirical band ratio algorithms and preforms as well or better than a variety of semianalytical algorithms. The results from the VPCA spectral decomposition method are more efficient than traditional Empirical Orthogonal Function or PCA, requiring fewer components to explain as much or more variance. Overall, our observations provide excellent validation for Sentinel-3A OLCI-based VPCA spectral identification and indicate A. lagunensis was highly concentrated within the Banana River region of the IRL during the study. These results enable improved brown tide monitoring to identify blooms at an early stage, allowing more time for stakeholder response to this public health problem.

Bioluminescence in Dinoflagellates: Evidence that the Adaptive Value of Bioluminescence in Dinoflagellates is Concentration Dependent.

Three major hypotheses have been proposed to explain why dinoflagellate bioluminescence deters copepod grazing: startle response, aposematic warning, and burglar alarm. These hypotheses propose dinoflagellate bioluminescence (A) startles predatory copepods, (B) warns potential predators of toxicity, and (C) draws the attention of higher order visual predators to the copepod's location. While the burglar alarm is the most commonly accepted hypothesis, it requires a high concentration of bioluminescent dinoflagellates to be effective, meaning the bioluminescence selective advantage at lower, more commonly observed, dinoflagellate concentrations may result from another function (e.g. startle response or aposematic warning). Therefore, a series of experiments was conducted to evaluate copepod grazing (Acartia tonsa) on bioluminescent dinoflagellates (during bioluminescent and nonbioluminescent phases, corresponding to night and day, respectively) at different concentrations (10, 1000, and 3000 cells mL-1 ), on toxic (Pyrodinium bahamense var. bahamense) and nontoxic (Lingulodinium polyedrum) bioluminescent dinoflagellates, and in the presence of nonluminescent diatoms (Thalassiosira eccentrica). Changes in copepod ingestion rates, clearance rates, and feeding preferences as a result of these experimental factors, particularly during the mixed trails with nonluminescent diatoms, indicate there is a concentration threshold at which the burglar alarm becomes effective and below which dinoflagellate bioluminescence functions as an aposematic warning.

Propagation and perception of bioluminescence: factors affecting counterillumination as a cryptic strategy.

Many deep-sea species, particularly crustaceans, cephalopods, and fish, use photophores to illuminate their ventral surfaces and thus disguise their silhouettes from predators viewing them from below. This strategy has several potential limitations, two of which are examined here. First, a predator with acute vision may be able to detect the individual photophores on the ventral surface. Second, a predator may be able to detect any mismatch between the spectrum of the bioluminescence and that of the background light. The first limitation was examined by modeling the perceived images of the counterillumination of the squid Abralia veranyi and the myctophid fish Ceratoscopelus maderensis as a function of the distance and visual acuity of the viewer. The second limitation was addressed by measuring downwelling irradiance under moonlight and starlight and then modeling underwater spectra. Four water types were examined: coastal water at a depth of 5 m and oceanic water at 5, 210, and 800 m. The appearance of the counterillumination was more affected by the visual acuity of the viewer than by the clarity of the water, even at relatively large distances. Species with high visual acuity (0.11 degrees resolution) were able to distinguish the individual photophores of some counterilluminating signals at distances of several meters, thus breaking the camouflage. Depth and the presence or absence of moonlight strongly affected the spectrum of the background light, particularly near the surface. The increased variability near the surface was partially offset by the higher contrast attenuation at shallow depths, which reduced the sighting distance of mismatches. This research has implications for the study of spatial resolution, contrast sensitivity, and color discrimination in deep-sea visual systems.

Polarization sensitivity as a contrast enhancer in pelagic predators: lessons from in situ polarization imaging of transparent zooplankton.

Because light in the pelagic environment is partially polarized, it has been suggested that the polarization sensitivity found in certain pelagic species may serve to enhance the contrast of their transparent zooplankton prey. We examined its potential during cruises in the Gulf of Mexico and Atlantic Ocean and at a field station on the Great Barrier Reef. First, we collected various species of transparent zooplankton and micronekton and photographed them between crossed polarizers. Many groups, particularly the cephalopods, pelagic snails, salps and ctenophores, were found to have ciliary, muscular or connective tissues with striking birefringence. In situ polarization imagery of the same species showed that, while the degree of underwater polarization was fairly high (approx. 30% in horizontal lines of sight), tissue birefringence played little to no role in increasing visibility. This is most likely due to the low radiance of the horizontal background light when compared with the downwelling irradiance. In fact, the dominant radiance and polarization contrasts are due to unpolarized downwelling light that has been scattered from the animal viewed against the darker and polarized horizontal background light. We show that relatively simple algorithms can use this negative polarization contrast to increase visibility substantially.

Giant deep-sea protist produces bilaterian-like traces.

One of the strongest paleontological arguments in favor of the origin of bilaterally symmetrical animals (Bilateria) prior to their obvious and explosive appearance in the fossil record in the early Cambrian, 542 million years ago, is the occurrence of trace fossils shaped like elongated sinuous grooves or furrows in the Precambrian. Being restricted to the seafloor surface, these traces are relatively rare and of limited diversity, and they do not show any evidence of the use of hard appendages. They are commonly attributed to the activity of the early nonskeletonized bilaterians or, alternatively, large cnidarians such as sea anemones or sea pens. Here we describe macroscopic groove-like traces produced by a living giant protist and show that these traces bear a remarkable resemblance to the Precambrian trace fossils, including those as old as 1.8 billion years. This is the first evidence that organisms other than multicellular animals can produce such traces, and it prompts re-evaluation of the significance of Precambrian trace fossils as evidence of the early diversification of Bilateria. Our observations also render indirect support to the highly controversial interpretation of the enigmatic Ediacaran biota of the late Precambrian as giant protists.

Crepuscular and nocturnal illumination and its effects on color perception by the nocturnal hawkmoth Deilephila elpenor.

Recent studies have shown that certain nocturnal insect and vertebrate species have true color vision under nocturnal illumination. Thus, their vision is potentially affected by changes in the spectral quality of twilight and nocturnal illumination, due to the presence or absence of the moon, artificial light pollution and other factors. We investigated this in the following manner. First we measured the spectral irradiance (from 300 to 700 nm) during the day, sunset, twilight, full moon, new moon, and in the presence of high levels of light pollution. The spectra were then converted to both human-based chromaticities and to relative quantum catches for the nocturnal hawkmoth Deilephila elpenor, which has color vision. The reflectance spectra of various flowers and leaves and the red hindwings of D. elpenor were also converted to chromaticities and relative quantum catches. Finally, the achromatic and chromatic contrasts (with and without von Kries color constancy) of the flowers and hindwings against a leaf background were determined under the various lighting environments. The twilight and nocturnal illuminants were substantially different from each other, resulting in significantly different contrasts. The addition of von Kries color constancy significantly reduced the effect of changing illuminants on chromatic contrast, suggesting that, even in this light-limited environment, the ability of color vision to provide reliable signals under changing illuminants may offset the concurrent threefold decrease in sensitivity and spatial resolution. Given this, color vision may be more common in crepuscular and nocturnal species than previously considered.

MARINE BIOLUMINESCENCE SPECTRA MEASURED WITH AN OPTICAL MULTICHANNEL DETECTION SYSTEM.

The emission spectra of 70 bioluminescent marine species were measured with a computer controlled optical multichannel analyzer (OMA). A 350 nm spectral window is simultaneously measured using a linear array of 700 silicon photodiodes, coupled by fiber optics to a microchannel plate image intensifier on which a polychromator generated spectrum is focused. Collection optics include a quartz fiber optic bundle which allows spectra to be measured from single photophores. Since corrections are not required for temporal variations in emissions, it was possible to acquire spectra of transient luminescent events that would be difficult or impossible to record with conventional techniques. Use of this system at sea on freshly trawled material and in the laboratory has permitted acquisition of a large collection of bioluminescence spectra of precision rarely obtained previously with such material. Among unusual spectral features revealed were organisms capable of emitting more than one color, including: Umbellula magniflora and Stachyptilum superbum (Pennatulacea), Parazoanthus lucificum (Zoantharia), and Cleidopus gloria-maris (Pisces). Evidence is presented that the narrow bandwidth of the emission spectrum for Argyropelecus affinis (Pisces) is due to filters in the photophores.

VARIABILITY IN FLASH CHARACTERISTICS OF A BIOLUMINESCENT COPEPOD.

Bioluminescence of the copepod, Pleuromamma xiphias, was investigated with an optical multichannel analyzer(OMA) to measure emission spectra, an integrating sphere-photon counting detector system to determine flash kinetics and quantum emission, and an ISIT video system to image spatial patterns of emission. Light emission was in the blue spectral region, with maximum emission at approximately 492 nm. Spectral waveforms were unimodal, or bimodal with the secondary peak at 472 nm. Flashes in response to a single stimulus consisted of two components: a fast component attaining maximum intensity in under 100 ms, and a slow element which peaked after 600 ms. The fast component originated from thoracic and abdominal light organs while the slow component represented a large expulsion of luminescent material from the abdominal organ only. Both components exhibited first order exponential decay although the decay rate of the fast component was approximately one order of magnitude greater. The typical flash response to a single stimulus exhibited a response latency of 30 ms, initial rise time of 87 ms, duration of 2.4 s, and quantum emission of 1.4 x 1010 photons flash-1. Quantum emission increased with increasing stimulus strength. Both response waveform and total quantum emission were affected by the frequency of electrical stimuli. Stimulation at 1 Hz generated the greatest luminescence, averaging 1.1 x 1011 photons response-1 for 11 s emissions. Higher rates of stimulation decreased total quantum emission and response episode duration, and resulted in greater temporal summation of the emission waveform. Variability in flash characteristics due to electrical stimulation suggests a versatility of luminescent displays in situ.

GFP-like proteins as ubiquitous metazoan superfamily: evolution of functional features and structural complexity.

Homologs of the green fluorescent protein (GFP), including the recently described GFP-like domains of certain extracellular matrix proteins in Bilaterian organisms, are remarkably similar at the protein structure level, yet they often perform totally unrelated functions, thereby warranting recognition as a superfamily. Here we describe diverse GFP-like proteins from previously undersampled and completely new sources, including hydromedusae and planktonic Copepoda. In hydromedusae, yellow and nonfluorescent purple proteins were found in addition to greens. Notably, the new yellow protein seems to follow exactly the same structural solution to achieving the yellow color of fluorescence as YFP, an engineered yellow-emitting mutant variant of GFP. The addition of these new sequences made it possible to resolve deep-level phylogenetic relationships within the superfamily. Fluorescence (most likely green) must have already existed in the common ancestor of Cnidaria and Bilateria, and therefore GFP-like proteins may be responsible for fluorescence and/or coloration in virtually any animal. At least 15 color diversification events can be inferred following the maximum parsimony principle in Cnidaria. Origination of red fluorescence and nonfluorescent purple-blue colors on several independent occasions provides a remarkable example of convergent evolution of complex features at the molecular level.