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An in situ video camera for plankton studies: Design and preliminary observations
Abstract
A design for an in situ video camera for plankton observations is presented. A light weight aluminium rig supports a video camera with an opposing stroboscope which produces dark field images of plankton >0.3 mm. In the present configuration the camera can be used down to 100 m and provides video images of 10 to 40x magnification when viewed on a 14' (ca 35 cm) monitor. Video recordings from the field show moderate aggregations of small copepods to the subsurface fluorescence maximum and at times indications of horizontal patchiness. The large copepod Calanus finmarchicus was found to aggregate 5 m below the fluorescence maximum at night. In comparisons with a traditional WP-2 plankton net, the video camera provided similar length frequency distributions while abundance estimates from video recordings were 10 to 20% higher than net estimates. It is concluded that the presented video camera offers excellent observations of the pelagic environment at an affordable cost.
... Foremost is the problem of jellyfish patchiness. Though patchiness is a universal concern among marine zooplankton populations (Omori & Hamner 1982, Hamner 1988, Laval et al. 1989, Davis et al. 1992, Tiselius 1998), jellyfish patchiness in the form of aggregations and swarms is especially pronounced at horizontal scales of 10s to 1000s of m and at vertical scales of 1 to 10s of m (Graham et al. 2001). Problematically, jellyfish patchiness at these critical spatial scales corresponds to typical zooplankton tow lengths, and in turn contributes to the large variance between replicate tows. ...
... Since the WHOI instrument was developed for open-ocean investigation, the cost of replication of the instrument will likely prohibit its widespread use among the oceanographic community. However, at least 1 lowcost alternative to the WHOI VPR design has emerged (Tiselius 1998). Should a cost-efficient industry standard emerge, the VPR will likely gain in popularity since it is relatively portable and can be deployed and recovered with standard oceanographic deck equipment . ...
... The second consideration is the light source, since many zooplankters , including jellyfish, are sensitive to 'white' light (Forward 1988). Other video systems targeting smaller zooplankton (< 2 cm) have overcome light effects by using strobes (Davis et al. 1992, Tiselius 1998) or red light (Gallagher et al. 1996). While many large jellyfish are sensitive to light (Hamner 1995, Schuyler & Sullivan 1997), reaction times to stimuli are much longer than the brief (<1 s) exposure of jellyfish to the collimated light beam. ...
Ecological studies involving large jellyfish have been limited by the inability of oceanographers to measure the abundance and distribution patterns of these highly aggregated ani- mals at local scales. Conventional plankton nets are undesirable in these applications because they cannot sample volumes large enough to accurately determine jellyfish concentration, nor do they have adequate spatial resolution to account for the ubiquitous patchiness of most large jellies. Nets are also notorious for damaging the watery bodies of jellyfish. To overcome these problems, we have developed a video system for use in the in situ study of large jellyfish. The design of our JellyCam is easily replicated since it incorporates commercially available components within a frame designed to hold hydrographic instrumentation available at most marine laboratories. We present data sets from 2 occasions as a demonstration of the utility of the JellyCam. On one occasion, a vertical profile of medusae of Pelagia noctiluca revealed intense layering of these jellyfish at the pronounced halo- cline/pycnocline. Most jellyfish in this layer were swimming toward the surface, and it was hypothe- sized that retarded forward-swimming velocity at the halocline, due to salt retention in jellyfish, caused this accumulation. A separate 800 m long horizontal transect of Phyllorhiza punctata medusae revealed distinct concentrated bands of jellyfish associated with increased chlorophyll concentration. Concomitant hydrographic data from the JellyCam showed that accumulation of both jellyfish and chlorophyll was associated with a hydrographic front. These data sets demonstrate that this system is capable of the desired 2 m 3 resolution, which is adequate for the observation and quantification of jellyfish distributions around small-scale physical discontinuities (e.g. fronts and pycnoclines). A series of side-by-side comparisons with a conventional plankton trawl resulted in comparable mea- surements of large jellyfish (Aurelia aurita) concentrations. Though in situ videography by itself is a powerful tool for investigating jellyfish, its use in conjunction with conventional nets or other technologies, such as acoustics and self-propelled vehicles (e.g. remotely operated vehicles and submersibles), will provide the most comprehensive view of jellyfish distribution in 3 dimensions.
... Indeed, the swarms and schools formed by macrozooplankton typically show more intense and finer spatial aggregates that the smaller (and less mobile) micro-and mesozooplankton (Mackas et al., 1985). The behavioral mechanisms (Bollens and Frost, 1991;Rios-Jara and Gonzalez, 2000) and physical processes (Petersen et al., 1998;Tiselius, 1998;Yen et al., 1998) affecting the patchiness of zooplankton are likely to be species-and size-specific. Thus, considering the spatial scale is a requirement when examining zooplankton patchiness in order to understand the controlling mechanisms. ...
... Assuming that small zooplankton is less mobile than large zooplankton, wind-induced currents might be implicated in the generation of the broad-scale patterns of small zooplankton in the GCSM lagoon. Indeed, small copepods in marine coastal waters aggregate in a food layer during calm conditions, but when winds are strong both copepods and algae are dispersed through the surface layer (Tiselius, 1998). The patterns of phytoplankton and salinity also support our assumption given that phytoplankton and salinity are passive tracers of hydrodynamic features (Geyer, 1997). ...
... The differences have been attributed to water masses (Webber et al., 1996;Alvarez-Cadena et al., 1998) and habitat characteristics (Alvarez-Cadena et al., 1998;Rios-Jara, 1998;Suárez-Morales and Gasca, 2000). Fine-scale patchiness of zooplankton is regulated not only by physical, but also by biological processes (Tiselius, 1998;Folt and Burns, 1999) including feeding, predation, migration, and reproduction (associated with individual behavior). These mechanisms, which affect zooplankton patchiness, are likely to be species-specific (Bollens and Frost, 1991;Rios-Jara and Gonzalez, 2000). ...
... During the last two decades, three advanced sampling techniques have been developed, which solve some problems linked to spatial scales (e.g., limitation of the size of sampling grain and/or the sampling extent). These techniques are: i) particle sizing/counting instruments, including the optical plankton counter (OPC; Herman 1992) and the dual light sheet sensor (DLS; see in Sutton et al. 2001); ii) optical sensors, including the video plankton recorder (VPR; Davis et al. 1992a), the in situ video camera (Tiselius 1998), and the shadow image particle profile evaluation recorder (SIPPER; see in Sutton et al. 2001); and iii) multiple-frequency acoustic sensors (Sameoto et al. 1993;Greene et al. 1998;Swartzman et al. 1999;Coyle 2000). Although each of these techniques has limitations (see in Williamson et al. 1992;Pinel-Alloul 1995;Folt and Burns 1999), they permit to acquire continuous in situ data, and/or rapidly cover large areas without compromising high-resolution data at small spatial scales. ...
... New studies about fine-scale biological processes (Tiselius 1998) have altered our perception of the behavioural capacity and flexibility of zooplankton. They also grappled with the quantitative assessment of the relative contributions of biology and physics to patchiness (Lewis and Boers 1991;Pinel-Alloul 1995;Alvarez-Cadena et al 1998), and the extent to which biological processes counteract physical driving forces (Folt and Burns 1999). ...
Previous studies on the abundance/biomass and species distribution of coastal tropical zooplankton have been done at a few stations, making them unsuitable to study spatial patterns. Whereas several physical and biological processes have been found to generate and maintain the spatial patterns of coastal tropical zooplankton, the scales of spatial dependency of these processes and their effects on zooplankton spatial variability have not been investigated. In this paper, we review current research on zooplankton spatial structure and the invoked generating processes in coastal marine environments. Our aim is to highlight the importance of scale, and of a multiscale approach for the study of zooplankton spatial variability, and promote arguments supporting this type of study to understand community,dynamics,and the interaction of zooplankton with other planktonic and nektonic compartments — and, as a result, the implications for the structure and function of coastal tropical ecosystems. 3
... Different types of cameras are used to image organisms along the tow path of an instrument [25]. Quantitative instruments in this category are camera-net systems and include towed systems such as the ichthyoplankton recorder, video plankton recorder (VPR) [2,25], in situ video recorder [107], and the shadowed image particle platform and evaluation recorder [98] (Table 1). Additionally, there are profiling systems, such as the underwater video profilers (UVP) [41] and holographic instruments [69]. ...
... They all provide sufficient resolution for class/order categorisation and for the estimation of organism size, which may be used to estimate biomass (see [121] for a review of optical systems). These include ( Table 2): stand-alone imaging systems such as the Video Plankton Recorder (VPR, [26]), mixed optical-net systems such as the camera-net system [78,79] and the ichthyoplankton recorder [67,119]; and Zooscan [41], in situ video profiler [107], Shadowed Image Particle Profiling Evaluation Recorder (SIPPER, [89]), zooplankton visualization and imaging system (ZOOVIS, [9]), and the Flow-Cam [95]. The use of higher resolution, digital formats has permitted an increase in image volume although most systems still record the contents of volumes of several ml to a few liters per image. ...
The ever expanding fields of UW (underwater) optics cover principal measurements of the optical properties of the sea, development of new methods of monitoring optical properties, techniques for measurements of organisms or structures in the sea and the development and application of optical instru-mentation. In this respect, ocean optics is a mul-tidisciplinary (and multinational) endeavour of science and engineering. Ocean optics has applications in the study of upwelling irradiance and chlorophyll concentrations in the ocean, in the penetration of solar radiation in shallow shelf seas and how this influences temperature profiles and ulti-mately its effect on sound propagation. Recent development in optical holography allow underwater visual inspection and precision measurements, estimation of the biological diversity of ocean plankton and benthos. One requirement is the de-velopment of high-resolution tools for the imaging of speci-mens in the field. We review here current developments of ocean optics as an integrative tool of biological oceanography that holds for surveys in the field as for laboratory studies.
... Third, novel studies of smallscale biological processes [11][12][13] are altering our perception of the behavioural capacity and flexibility of zooplankton. There have also been breakthroughs in field monitoring of both large-and small-scale processes and spatial patterns (Table 1), which have improved our resolution of zooplankton patchiness and spatial dynamics under natural conditions. ...
... In a like manner, it is now appreciated that the effect of food abundance on zooplankton aggregation and dissipation can be modified by factors such as turbulence and predators: # Small copepods in marine coastal waters aggregate in a food layer during calm conditions, but, when winds are strong, both copepods and algae are dispersed throughout the surface layer 13 . # Downward swimming by a clone of Daphnia in response to changing light intensity is enhanced by the presence of food, which counteracts hunger, and by fish kairomones without, surprisingly, any interactive effect of food and predators 30 . ...
Until recently, biological drivers of plankton aggregation were under-appreciated, because most studies concentrated on physical processes. New technological advances, novel experiments and theory have shifted focus to the pivotal role of behaviour in plankton patch dynamics. Our review highlights four biological drivers of zooplankton spatial patchiness and brings together recent research on well studied marine and freshwater taxa, primarily copepods and cladocerans. Diverse and powerful behavioural responses by zooplankton to physical and chemical signals are shown to contribute to the formation and breakdown of zooplankton patches over several different spatial scales.
... In situ particle sizing by laser diffraction is a relatively recent development which has been accurately implemented by several research teams (Agrawal & Pottsmith, 1989;Gentien et al., 1995, Bale & Morris, 1996. Over the last years, the importance of video systems has also increased (Eisma et al., 1990;Gorsky et al., 1992Gorsky et al., , 2000Fennessy et al., 1994;Van Leussen & Corneliss, 1996;Davis et al., 1996;Knowles & Wells, 1998;Tiselius, 1998;Dyer & Manning, 1999;Katz et al., 1999;Widder et al., 1999;Franks & Jaffe, 2001). The optical and mechanical designs of these developed systems varied depending on the objectives and the quantity and quality of the particles under study. ...
... Taking into account a possible bias due to phototropism in the box, the concentration was estimated between 60 and 600 animals l -1 . Such thin layers, with abundance of copepods found above the density discontinuities in the water column, were also described by research teams using video techniques (Tiselius, 1998;Widder et al., 1999). More over, Cercopagis pengoi, an invasive Baltic cladoceran species was also detected from in situ video observations. ...
A design for a new underwater video-system to detect and observe suspended particles is presented. Particles are collected and isolated in a rectangular box where they are highly illuminated by a white light plane. The total field of view is determined. The camera, equipped with a remote controlled zoom, can resolve particles sizes ranging from 25 mum to several millimetres. Real-time image analyses are therefore performed. Particle counts and size spectra are calculated and displayed. Total light intensity scattered by the illuminated particles is closely related to the back-scattering values determined by an optical back-scatter sensor. A particle size analyser using diffraction analysis is associated to this video-system on a custom profiler. Hydrological parameters are measured by a standard CTD probe associated to a chlorophyll sensor. Results are acquired and graphically presented in real time. This custom profiler presents numerous advantages in oceanographic research. Two examples of its use in different coastal areas are presented. In an estuary, temporal evolution of particle characteristics was described in relation to the tide cycle. While the video-system allows direct visualization and characterization of the largest particles, the particle-size analyser performs precise quantification of the finest ones. it was shown that the two methods were in accordance for quantification of large aggregates, which were observed around slack tide when salinity decreased. Video analyses cannot be performed above 25 mg l(-1) dry weight equivalent. The system reliability, resolution and limits were also demonstrated during a cruise in the Gulf of Finland. A typical profile is presented here showing different layers, one characterized by the association of heterotrophic flagellates and detritals, and another dominated by zooplankton, the surface layer being characterized by cyanobacterial colonies. Video associated to diffraction analyses allows the study of flocculation processes in estuaries and a detailed description of thin layers.
... Quanto maiores os organismos zooplanctônicos de interesse de estudo, maiores são os volumes a serem amostrados para que se obtenha uma melhor estimativa de suas populações. Esses problemas associados à relação tamanho/densidade pode, ainda, ser agravado pela ocorrência em manchas do zooplâncton, característica bastante destacada para o grupo, devido a processos físicos (passivos) e comportamentais (ativos) (Omori & Hamner, 1982, Laval et al., 1989, Davis et al., 1992, Tiselius, 1998. ...
Imagens subaquáticas obtidas com o uso de câmeras digitais tem se tornado uma das principais ferramentas para estudos, no próprio ambiente, do comportamento e da ecologia de organismos marinhos. Com esse objetivo testou-se a obtenção de imagens por arrasto e por perfil vertical de uma câmera comercial montada em uma estrutura de aço denominada de Sino. Foram obtidas 54 vídeos de arrastos horizontais (estratificadas) de maior duração (10 minutos) e 27 vídeos de perfilagem vertical de curta duração (3 minutos) e avaliado a qualidade das imagens associadas a identificação dos organismos. Foi determinado a melhor forma de trabalho com o Sino, necessidade de acessórios e adaptações e protocolo de uso, assim como a relação entre a transparência da água (disco de Secchi) e a possibilidade de identificação e quantificação de formas planctônicas nas imagens. Os resultados apontam para o uso do Sino em baixa velocidade, ou seja, em perfilagem vertical e com iluminação apresentando os melhores resultados e maior eficiência na identificação das ocorrências de organismos. A relação entre a transparência da água e a obtenção de imagens de boa qualidade foram observadas, de forma mais segura, em condições de Secchi superior a 2,5 m. Em função das condições de transparência da água e da variabilidade de ocorrência dos organismos a probabilidade de registro de organismos foi de 37,5% do total de saídas a campo. Por fim, as análises dos vídeos indicaram um possível comportamento de migração vertical de Olindias sambaquiensis (Hydrozoa) e chamaram a atenção pela abundância de Pseudo-TEPs (Transparent Exopolymer Particles), que acredita-se são de grande importância na ecologia pelágica de águas costeiras.
... These include: hybrid optical-net systems such as the camera-net system (Ortner et al. 1981, Olney & Houde 1993 and the ichthyoplankton recorder (Welsch et al. 1991, Lenz et al. 1995; and stand-alone imaging systems such as the Video Plankton Recorder (VPR, Davis et al. 1992; Fig. 1), Zooscan (Gorsky et al. 1992(Gorsky et al. , 2000Fig. 2), in situ video profiler (Tiselius 1998), Shadowed Image Particle Profiling Evaluation Recorder (SIPPER, Samson et al. 2001, zooplankton visualization and imaging system (ZOOVIS, Benfield et al. 2003; LISA, C. P. Gallienne, pers. comm.; Fig. 3), and the Flow-Cam (Sieracki et al. 1998, Fig. 4) In addition, several in situ holographic systems have been developed for 3D imaging of plankton , Hobson et al. 2000. ...
ABSTRACT: In the future, if marine science is to achieve any progress in addressing biological diversity of ocean plankton, then it needs to sponsor development of new technology. One requirement is the development of high-resolution sensors for imaging field-collected and in situ specimens in a non-invasive manner. The rapid automatic categorisation of species must be accompanied by the creation of very large distributed databases in the form of high-resolution 3D rotatable images of
species, which could become the standard reference source for automatic identification. These 3D images will serve as classification standards for field applications, and (in adjusted optical quality) as training templates for image analysis systems based on statistical and other pattern-matching processes. This paper sets out the basic argument for such developments and proposes a long-term
solution to achieve these aims.
... High-frequency digital camera images and vegetation indices allow better tracking of plants' phenological responses to environmental changes, aiding the development of improved predictive phenological models [36]. Digital camera images facilitate individual organism observation, long-term canopy monitoring, automated phenological monitoring from regional to continental scales, and tracking responses to experimental treatments [36][37][38][39]. ...
... Underpinning this, a Nature article 48 outlined several optical techniques for subsea research in the recent oil spill in the Gulf of Mexico. However this is not new, the need for new investigative methods for the marine environment has been discussed for decades 49,50 . The importance for ecological or pollutional investigations and the socio-economic relevance has already been documented in section 1.3-strategic applications. ...
Our objective is to develop a modular multi-sensor optical imaging system based on innovative, state-of-the-art optical imaging technologies to be operated and deployed alongside, and in parallel with, acoustic imaging and oceanographic devices on an integrated framework of data extraction, migration and analysis tools. The characteristics of non-destructive and non-intrusive, highresolution
imaging are key factors that allow optics to offer innovation and fresh insights. However, subsea optical imaging has not been exploited to its full potential and performance capabilities: field deployment of subsea optical instrumentation is still somewhat underdeveloped and underused. The specific objectives are:
1. To design, develop and build an advanced, enhanced, suite of fully-featured, modular, multi-sensor optical imaging systems incorporating and integrating micro- and macro-scale holographic imaging, Lightframe On-sight Keyspecies Investigation, and ultralow light level bioluminescence camera.
2. To develop and incorporate rapid data capture, extraction, image identification and analysis tools for monitoring of fine-scale interactions in phytoplankton and zooplankton congregations and other marine organisms and particulates which are applicable to a wide range of sensing systems
3. To integrate with and operate alongside traditional acoustic and oceanographic systems and to facilitate data migration between the different datasets
4. To operate alongside current acoustic and oceanographic systems, across a range of locations, and on observation platforms such as research vessels, on tows or free-fall landers
5. To apply the integrated systems to a series of key challenges and strategic applications in marine science and the marine ecosystems management and monitoring policy
6. To deploy the integrated system and apply it to a series of key challenges and strategic applications
7. To take system development to the point of commercial exploitation by SME partners
... Other authors agreed with this (Riley 1963;Mullin 1965), noting how natural aggregations could be broken up during sampling or rendered unidentifiable and biased when using standard preservation techniques (Murphy and Haugen 1985;Ortner et al. 1981;Zarauz and Irigoien 2008), "which probably accounts for the fact that this phenomenon passed largely unnoticed until the advent of direct undersea observation" (Riley 1963). Hence, in situ water photography presented an excellent sampling approach compared to traditional net-sampling techniques, demonstrating the advantage of sampling the fragile taxa that would be damaged in other circumstances (Olney and Houde 1993;Tiselius 1998). ...
Plankton are an important component of life on Earth. Since the 19th century, scientists have attempted to quantify species distributions using many techniques, such as direct counting, sizing, and classification with microscopes. Since then, extraordinary work has been performed regarding the development of plankton imaging systems, producing a massive backlog of images that await classification. Automatic image processing and classification approaches are opening new avenues for avoiding time-consuming manual procedures. While some algorithms have been adapted from many other applications for use with plankton, other exciting techniques have been developed exclusively for this issue. Achieving higher accuracy than that of human taxonomists is not yet possible, but an expeditious analysis is essential for discovering the world beyond plankton. Recent studies have shown the imminent development of real-time, in situ plankton image classification systems, which have only been slowed down by the complex implementations of algorithms on low-power processing hardware. This article compiles the techniques that have been proposed for classifying marine plankton, focusing on automatic methods that utilize image processing, from the beginnings of this field to the present day.
... Mobile zooplankton (e.g., crustacean larvae, fish larvae, and large holoplankton) may also possess swimming abilities and senses that allow them to overcome microscale turbulence to actively form and maintain groups. It has been shown that planktonic larvae are sensitive to turbulence, using it as a cue to orient in tidal currents and nearshore environments ( Fujimura et al., 2014;Fuchs et al., 2018;Shanks, 1986 ). Turbulence has also been identified as a factor in controlling the spatiotemporal scale of plankton patches, with plankton swarming in calm surface waters due to lower-energy turbulent diffusion ( Tiselius, 1998 ). Therefore, planktonic organisms have the capacity to detect microscale turbulence, and could actively maintain group cohesion if the organisms exhibited group behavior. ...
... At different food concentrations, copepods often change swimming speeds, turning angles, or hopping rates, as well as intersperse bouts of jumping with periods o f resting or sinking. Thus they can actively locate and remain longer with food patches over small scales (Tiselius, 1998). Larvae (crustacean, mollusks and echinoderms), often concentrate near the surface in response to both light and tidal cues (Manuel et al., 1997). ...
Small islands play a strategic role in the fisheries, tourism and military activities of the Southern California Bight (SCB). They are also ideal systems to study coastal processes such as the formation of eddies, fronts, wakes and upwelling systems. A literature review on the subject reveals that research on this topic is abundant but still uneven and single disciplined. Biologists first described increases in productivity near islands but they explained this as an ill defined “island mass effect,” whereas when physicists investigated eddies, upwelling regions and fronts around islands they called these “island wakes.” Only a few recent investigations integrate both physics and biology to fully describe the biological consequences of physical forcing phenomena due to the presence of an island. In my work, I focused on Santa Catalina Island as the first case study of the island mass effect for the Southern California Bight. I combined the use of in situ surveys (using simultaneous CTD-Conductivity Temperature Depth, and net sampling), satellite remote sensing data (AVHRR-Advance Very High Resolution Radiometer and SAR-Synthetic Aperture Radar) and numerical model simulations from ROMS (Regional Ocean Model System) to study the effect of the island’s bathymetry to the incoming ocean currents and its consequent effect on the local productivity. Results have shown the distinct formation o f wind versus current wakes on opposite sides of the island. Wind sheltering effects in the wind wake of Santa Catalina Island served as a basis to interpret the decrease in surface mixing due to weaker inshore winds and an increase in SST, frequently observed during spring and summer months inshore for the whole SCB. Island wind wakes tend to function as important retention zones whereas current wakes serve to bring nutrients to the euphotic zone, maximizing productivity. Also apparent was a statistically significant difference between mesozooplankton communities that live within the island’s shelf and those offshore from it. Catalina Island sustains a unique pelagic, shelf ecosystem.
... The Underwater Video Profiler (Gorsky et al. 1992(Gorsky et al. , 2000 and other high-resolution video systems (Welsch et al. 1991, Waite et al. 1997, Tang et al. 1998, Tiselius 1998) have been developed to examine phytoplankton aggregations and feeding behaviour in zooplankton and obtain visual records of planktonic organisms. These techniques also have been utilised in the study of sediment flocs and aggregations in estuaries (Van Leussen & Cornelisse 1993, Thomsen et al. 1996). ...
Over the last 40 years, underwater stereo-image measurement systems have employed stereo-cameras and paired single cameras in a variety of configurations. Both still and movie cameras have been used, based on film, video tube and digital sensors. Whilst measurement configurations of all varieties have been used, the transect has been, and still is, the predominant sampling technique. These basic approaches to photogrammetric geometry and sampling techniques are still in use today; however, the image quality has advanced considerably and the use of fully digital video systems and digital still cameras is now commonplace. The wider use of precalibrated, self-contained stereo-image systems, plus the substantial improvements in image resolution and image fidelity, is enabling new possibilities for accurate and reliable measurement of 3-dimensional lengths, surfaces and volumes. These advances are leading to significant improvements in the effectiveness of the management of marine ecosystems for conservation and the estimation of biomass for aquaculture. This work reviews the status of underwater stereo-image measurement and illustrates applications of stereo-image measurement in marine biology and ecology.
... Since the VPR, there has been substantial progress in devel- oping stand-alone, digital zooplankton imaging systems with similar or different capabilities. Some systems have attempted to duplicate the capabilities of the VPR at lower cost (Tiselius, 1998). Some have evolved to image larger volumes in order to quantify less abundant or larger taxa. ...
... The current options for semi-automated planktonic community analysis include hybrid optical-net systems such as the camera-net system (Olney and Houde, 1993;Ortner, Hill, and Edgerton, 1981). More recently, stand-alone imaging systems have been developed, such as the video plankton recorder (VPR, Davis et al., 1992), ZooScan (Gorsky et al., 1992(Gorsky et al., , 2010, in situ video profiler (Tiselius, 1998), shadowed image particle profiling evaluation recorder (SIPPER, Samson et al., 2001;Remsen, Hopkins, and Samson, 2004), zooplankton visualization and imaging system (ZOOVIS, Benfield et al., 2003; LISA, C. P. Gallienne), and the FlowCAM (Sieracki, Sieracki, and Yentsch, 1998). ...
planktonic community analysis;semi-automated;classification;plankton imaging
... Since the mid-1980's, approximately eight different in situ 2-D imaging systems have been developed (see Wiebe & Benfield, 2003 for a review of imaging-optical systems). These include hybrid opticalnet systems such as the camera-net system (Ortner et al 1981, Olney & Hood 1993 and ichthyoplankton recorder (Welsch et al 1991, Lenz et al 1995, as well as stand-alone imaging systems such as the Video Plankton Recorder (VPR, Davis et al 1992), Zooscan (Gorsky et al 1992; Fig. 3, in situ video profiler (Tiselius, 1998) (Sieracki et al 1998) In addition, several in situ holographic systems have been developed for 3-D imaging of plankton , Hobson et al 2000. ...
... Six years later, McGehee & Jaffe [32] used a threedimensional acoustic imaging system with the aim of non-invasively examining zooplankton swimming behavior. Soon after Tiselius [110] was using an in situ video camera to record zooplankton aggregation, with a system able to reach 100 m depth. ...
Animal behavior is an important aspect for the knowledge of the ecological role of a species: it permits to understand the interactions between individuals, and on a larger scale on population dynamics. Copepod behavior occurs at very different scales, ranging from millimeters to tens of meters and over time spans ranging from milliseconds to hours. In the first case, events such as food encounter, creation of feeding currents and escape responses develop over very short times (milliseconds to seconds) and occur over a few millimeters or less. On the opposite extreme large scale processes like vertical migrations take place. At intermediate scales (minutes and centimeters), it is possible to obtain information on how an individual copepod moves during longer periods while feeding or how its behavior is modified in relation to unfavorable environmental conditions or to chemical or mechanical stimuli. In this contribution, we review the most critical aspects of copepod behavior, with a peculiar emphasis on the swimming, feeding and mating behavioral adaptations of these organisms, which, despite the small dimensions, display a great repertoire of modalities of interaction with the surrounding environment.
... Richardson and Jackson (2007) demonstrated that floc formation scavenges picoplankton from surface waters, resulting in an additional important organic carbon source for zooplankton in the deep ocean. Tiselius et al. (1998) and Peperzak et al. (2003) indicated that although single diatoms settle slowly their aggregates rapidly settle and are enriched in carbon content. Variable flocculation may explain the wide range in organic carbon settling rates reported in field studies. ...
... phone 0532-66782913; fax 0532-66782913. began with a photographic camera mounted in a net and include towed systems such as the camera net system [6], the ichthyoplankton recorder [7], Video Plankton Recorder (VPR) [8], in situ video recorder [9], and the Shadowed Image Particle Platform and Evaluation Recorder (SIPPER) [10]. In addition, there are profiling systems, such as the Underwater Video Profiler (UVP) [11] and holographic instruments [12,13]. ...
Marine plankton play an important role in ocean web structure and global environment change. As an alternative to traditional sampling methods, real time imaging systems are particularly useful in studying the abundance and behavior of plankton in the appropriate spatial and temporal scales at high sampling rate. In this paper, the design of a noninvasive, high resolution, low power consumption optical imaging device is presented. The device is designed in a compact size and this makes it suitable to be deployed on underwater vehicle platforms for plankton monitoring. The reported imaging system is a balanced compromise of object distance, focal length of the lens, and the coverage of the sampling area. The results of laboratory evaluation of the combination of different parameters of the optical lens for plankton monitoring are presented. Light illumination based on light emitting diode (LED) is investigated. It is showed that the system is capable of obtaining relatively good resolution images at high sampling rate that allow quantification of the plankton in the appropriate spatial and temporal scales.
... Several in situ video systems have been developed over the last 15 years, allowing a direct description of the vertical variability of particle populations. Mechanical designs and size resolution of the imaging systems have been adapted to observe large organisms like zooplankton and marine snow (Davis et al. 1996;Tiselius 1998;Katz et al. 1999;Widder et al. 1999;Gorsky et al. 2000;Lunven et al. 2003;Schulz et al. 2010;Picheral et al. 2010). The direct imaging of small-living organisms, such as phytoplankton in their natural environment is not common because the resolution of such microscopic particles requires a very high magnification camera and the proportion of non-living organisms is high in this size range (Stemmann and Boss 2012). ...
Recent advances in laser and video technologies have enabled single particles to be visualized in aqueous solution. Here, we describe a new instrument enabling the analysis of the fluorescence signatures of marine particles directly in seawater: the Video Fluorescence Analyser (VFA). A field of view is produced inside a measurement chamber by a laser beam at 473 nm that illuminates a shallow region, 3500 μm deep. Individual cells or particles in this field appear as individual spots of light, which are clearly resolved by video against a dark background. The method can resolve particles ranging from 6 μm to several millimeters. The camera is equipped with mobile optical filters: band-pass filter, 520-580 nm, for phycoerythrin visualisation and high-pass filter, > 600 nm, for Chlorophyll a pigment. These filters are remotely controlled and displaced in front of the CCD camera, allowing imaging and discrimination between fluorescent particles. We report here experimental procedures and calibrations performed in the laboratory with phytoplankton cells (Dunaliella tertiolecta, Karenia mikimotoi, Pseudonitzschia australis) and calibrated fluorescent beads. Image analysis processing enabled particle counts, measurements, and size classification. The auto-fluorescence of individual particles was also tested in situ during a field cruise. In relation to other sensors, the VFA allowed particle enumeration and discrimination and detecting spatial variability of the phytoplankton size spectra in relation to hydrology. The results indicate that fluorescence/video analysis techniques can be easily used in the laboratory or at sea for direct in situ visualization and analyses of phytoplankton populations.
... Image-forming optics use various types of cameras to image organisms along the tow path 9 of the instrument. Quantitative instruments in this category began with a photographic camera mounted in a net and currently include towed systems 10 such as the camera net system [5], the ichthyoplankton recorder [6], Video Plankton Recorder (VPR) [7], in situ video recorder [8], and the Shadowed Image Particle Platform and Evaluation Recorder (SIPPER) [9]. In addition, there are profiling systems, such as the Underwater Video Profiler (UVP) [10] and holographic instruments [11,12]. ...
... It is difficult to measure planktonic distribution at submeter scales in the natural environment, but several recent developments in sampling methodology have greatly enhanced knowledge of the prevalence and characteristics of microscale plankton patchiness [see Folt and Burns (1999) for a more complete discussion]. Some examples video plankton recorder (e.g., Davis et al., 1992) and dark-field in situ video (Tiselius, 1998) observations of zooplankton abundance and orientation in patches with length scale <1 m; acoustic measurements of high concentrations of multiple species in depth strata <0.5 m thick (Holliday et al., 1998); and centimeter-scale chlorophyll variability revealed by an in situ optical imaging system (Jaffe et al., 1998) and by high-resolution profiling instruments Hanson and Donaghay, 1998). Laboratory experiments (Tiselius, 1992;Saiz et al., 1993) have demonstrated that zooplankton respond to phytoplankton patches a few centimeters in size. ...
... Unfortunately, the state-of-the-art technology of the VPR makes it prohibitively expensive, and its wide use is unlikely at present. Recently, Tiselius (1998) presented a similar but cheaper optical sampler based on a single CCD video camera. The volume sampled with this device was 0.42 mL, and Tiselius used it to identify calanoid copepodites to species. ...
For marine benthic invertebrates with meroplanktonic larvae, the relative importance of hydrodynamics and swimming behaviour in determining larval dispersal in the water column, particularly at small spatial scales, has not been determined. In the field, larval aggregations recorded at physical and biological discontinuities in the water column were attributed to hydrodynamics. Similar aggregations obtained in the absence of flow in the laboratory indicate a potentially significant role of behaviour. At large spatial scales, larval distribution in the plankton is mainly regulated by horizontal advection. However, the ability of larvae to behaviourally regulate their position at scales of micrometres to metres when exposed to turbulent fluid motion in the water column, as evidenced in the benthic boundary layer, is unknown. Evaluation of swimming in turbulent flows in the water column is an intriguing area of research, which involves several constraints. In the field, quantification of behaviour is limited by low success in tracking larvae and lack of appropriate observational tools. In the laboratory, the generation and quantification of flow regimes that are representative of those in the field remains a challenge. An approach that integrates biological and physical measurements within realistic ranges is necessary to advance our understanding of larval dispersal.
... These include: hybrid optical-net systems such as the camera-net system (Ortner et al. 1981, Olney & Houde 1993 and the ichthyoplankton recorder (Welsch et al. 1991, Lenz et al. 1995; and stand-alone imaging systems such as the Video Plankton Recorder (VPR, Davis et al. 1992; Fig. 1), Zooscan (Gorsky et al. 1992(Gorsky et al. , 2000Fig. 2), in situ video profiler (Tiselius 1998), Shadowed Image Particle Profiling Evaluation Recorder (SIPPER, Samson et al. 2001, zooplankton visualization and imaging system (ZOOVIS, Benfield et al. 2003; LISA, C. P. Gallienne, pers. comm.; Fig. 3), and the Flow-Cam (Sieracki et al. 1998, Fig. 4) In addition, several in situ holographic systems have been developed for 3D imaging of plankton , Hobson et al. 2000. ...
In the future, if marine science is to achieve any progress in addressing biological diversity of ocean plankton, then it needs to sponsor development of new technology. One requirement is the development of high-resolution sensors for imaging field-collected and in situ specimens in a non-invasive manner. The rapid automatic categorisation of species must be accompanied by the creation of very large distributed databases in the form of high-resolution 3D rotatable images of species, which could become the standard reference source for automatic identification. These 3D images will serve as classification standards for field applications, and (in adjusted optical quality) as training templates for image analysis systems based on statistical and other pattern-matching processes. This paper sets out the basic argument for such developments and proposes a long-term solution to achieve these aims.
... The Underwater Video Profiler (Gorsky et al. 1992(Gorsky et al. , 2000 and other high-resolution video systems (Welsch et al. 1991, Waite et al. 1997, Tang et al. 1998, Tiselius 1998) have been developed to examine phytoplankton aggregations and feeding behaviour in zooplankton and obtain visual records of planktonic organisms. These techniques also have been utilised in the study of sediment flocs and aggregations in estuaries (Van Leussen & Cornelisse 1993, Thomsen et al. 1996). ...
Over the last 40 years, underwater stereo-image measurement systems have employed stereo-cameras and paired single cameras in a variety of configurations. Both still and movie cameras have been used, based on film, video tube and digital sensors. Whilst measurement configurations of all varieties have been used, the transect has been, and still is, the predominant sampling technique. These basic approaches to photogrammetric geometry and sampling techniques are still in use today; however, the image quality has advanced considerably and the use of fully digital video systems and digital still cameras is now commonplace. The wider use of precalibrated, self-contained stereo-image systems, plus the substantial improvements in image resolution and image fidelity, is enabling new possibilities for accurate and reliable measurement of 3-dimensional lengths, surfaces and volumes. These advances are leading to significant improvements in the effectiveness of the management of marine ecosystems for conservation and the estimation of biomass for aquaculture. This work reviews the status of underwater stereo-image measurement and illustrates applications of stereo-image measurement in marine biology and ecology.
... The advantage of holography over digital or video imaging, which has had considerable success (e.g. Gallager 1996, Tiselius 1998), is its ability to resolve small particles over a considerably larger sample volume. A planar imaging system which can resolve 20 µm can do so over a depth of field, D, equal to d 2 /λ, where d is the resolution and λ is the wavelength of the light. ...
A submersible holography system for in situ recordings of the spatial distribution of plankton has been developed and deployed. The system utilizes a ruby laser with an in-line recording configuration and has a sample volume of 732 ml. The reconstructed images have a resolution ranging from 10-20 µm for spherical particles and 3 µm for linear particles that lie within 100 mm from the film. Reconstructed volumes from holograms recorded during two recent deployments in the Strait of Georgia are scanned to obtain focused images of the particles, their position, size and orientation. The particles are also classified to several groups based on their morphological characteristics. The holograms include a set recorded during a 15 min vertical transect of the top 30 m of the water column. Along with the holograms, the data include records of depth, temperature, salinity, dissolved oxygen and optical transmissivity. The results show substantial variations in population makeup between layers spaced a short distance apart, particle concentration maxima at and near a pycnocline and evidence of zooplankton migration. A predominant horizontal diatom orientation is indicated in the region of peak diatom concentration. Individual holograms show clustering within different classes of plankton.
... A number of different types of imaging systems are currently in use to assess the abundance, distribution, and behavior of zooplankton (e.g., Davis et al., 1996; Jaffe et al., 1998; Tiselius, 1998; Sieracki and Sieracki, 1999 ). Here, we describe a highspeed digital line scan camera that was developed for the collection of continuous pictures of marine particles ranging in size from 200 µm to many centimeters, including fragile particles, such as marine snow and entire siphonophore colonies, that normally are destroyed in nets (Samson et al, 2001; http://www.marine.usf.edu/sipper/). ...
The composition and structure of marine food webs and it's variation in space and time influence the quality and quantity of carbon exported from surface water, the concentration of inorganic nutrients, and the elemental ratios of particulate and dissolved pools in the ocean. Marine phytoplankton, microzooplankton and larger zooplankton important to the biological pump, range over several orders of magnitude in size, occur over widely varying vertical and horizontal scales, exhibit different behaviors (e.g., vertical migration), and may occur seasonally or episodically. Consequently, assessing the efficiency and variability of the biological pump remains a major challenge. Two different sensor systems used to assess the abundance and distribution of marine biota will be described. The first approach uses a split-beam digital echo sounder system and the second approach uses a high-speed digital line scan imaging system. The merits, limitations, and recent developments of these systems will be presented. Although hardware and software used to assess marine biota have improved significantly during the last few decades, researchers still face serious technical issues in relating the detected image or signal to a biologically useful measure. Recommendations from a recent workshop on sensor technology are discussed.
... In this context, it is important to remember that density estimates obtained from plankton net hauls do not represent the actual density of plankton organisms in small-scale aggregations. Physical (accumulation in estuarine convergence zones, estuarine and coastal fronts, turbulence, internal waves, etc.) and biological (predator avoidance, swarming behaviour, etc.) processes lead to plankton and particle densities that may be several orders of magnitude higher than those calculated from net hauls (Conover et al., 1988; Currie et al., 1998; Eggleston et al., 1998; Tiselius, 1998; Wiebe & Benfield, 2003, and references therein). Considering that 'bottle effects', handling stress, changes in turbulence, changes in phytoplankton microscale patchiness and food web effects are unavoidable in any zooplankton food selection experiment (Roman & Rublee, 1981; Ba˚mstedtBa˚mstedt et al., 2000; Nejstgaard, et al., 2001; Mouritsen & Richardson, 2003), more studies may be necessary before these results can be used directly for trophic models. ...
Ingestion rates of zoeae of Aratus pisonii Milne Edwards (Brachyura: Grapsidae) were determined offering natural plankton-detritus mixtures in laboratory food selection
experiments. The food mixtures were sampled in the Itamaracá estuary, north-eastern Brazil, and standardised to a size range
of 50–200μm. Zoeae ingested significant amounts of large centric diatoms (Coscinodiscus spp.), mangrove detritus, tintinnids (Favella ehrenbergi) and adult copepods during feeding experiments. Diatoms were positively selected by A. pisonii zoeae in all three experiments, with ingestion rates of 3.3–21.3cellszoea−1day−1. Detritus particles were always more abundant than phytoplankton and zooplankton in the particle size spectrum offered. Detritus
was ingested in two of three experiments, with ingestion rates of up to 34.1particleszoea−1day−1, being the most important food item during one experiment. Adult copepods (up to 1.8ind.zoea−1day−1) and tintinnids (up to 0.4ind.zoea−1day−1) were ingested by A. pisonii zoeae during one experiment each. In spite of a wide range of zoeal density, food particle composition, and density, zoeae
of A. pisonii displayed a consistent pattern of food selectivity. This hints at a consistent sensory and behavioural mechanism related
to capture and handling of food particles, that most likely also affects larval feeding under natural conditions. Although
detritus showed to be quantitatively ingested under estuarine conditions, zoeae of A. pisonii preferred large diatoms and ingested zooplankton only occasionally.
... Since then, instruments designed to run underway and measure changes in plankton abundance and composition have become common and are continuously improved, e.g. fluorometers (Wesson et al., 1999; Franks and Jaffe, 2001; Leboulanger et al., 2002), video plankton recorders (Lenz et al., 1995; Tiselius, 1998 ), highfrequency acoustics (Coyle et al., 1998; Warren et al., 2002; Wiebe et al., 2002), continuous plankton recorders (Batten et al., 2003; Johns et al., 2003), small-scale sampling systems (Waters and Mitchell, 2002; Waters et al., 2003). Uneven plankton distributions have subsequently been widely described (e.g., Mackas and Boyd, 1979; Denman and Powell, 1984; Bennett and Denman, 1985; Mackas et al., 1985; Davis et al., 1991; Daly and Smith, 1993; Currie et al., 1998), but intermittency, as defined in the present work, has seldom been quantified. ...
Intermittency, a fundamental property of high Reynolds number turbulence, has seldom been described in ocean sciences. As a consequence, and despite several recent studies describing the intermittent distributions of temperature, salinity, nutrient concentrations, phytoplankton biomass and zooplankton abundance, the implications of intermittency on (i) the distribution of purely passive and biologically active scalars (e.g., phytoplankton cells) and (ii) biophysical couplings in the ocean are still poorly understood. We thus present both terminological and phenomenological clarification of the intermittency concept in turbulence studies. Next, univariate multifractal procedures investigating the properties of intermittent stochastic processes are presented. They characterize the statistics of intermittent variables using a set of three basic parameters in the multifractal framework, whatever the scales and the intensity. The multifractal formalism is then extended to more than one variable to investigate the degree of dependence among random fields by investigating the nature of their joint distribution. The main advantages of these unusual formalisms are that they make no assumptions about the spectrum or the distribution of data sets, fully take into account the intrinsic multiscaling properties of the data, and more generally explore qualitatively and quantitatively the correlations of large and small fluctuations of processes.
... The family of image-forming systems has grown continuously since 1990. The Ichthyoplankton Recorder (IR) [50,99], Video Plankton Recorder (VPR) [31], Underwater Video Profiler (UVP) [55], Optical-Acoustic Submersible Imaging System (OASIS) [75], In situ Video Camera [152], FlowCam [144], Holocamera [88], Shadowed Image Particle Profiling and Evaluation Recorder (SIPPER) [138], Zooplankton Visualization and Imaging System (ZOOVIS) [10], HOLOCAM [166], In situ CritterCam [147], and Optical Serial Section Tomography (OSST) [48] all belong to this category. In this thesis, images from the VPR were used. ...
Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2006. Includes bibliographical references (leaves 155-173). A fundamental problem in limnology and oceanography is the inability to quickly identify and map distributions of plankton. This thesis addresses the problem by applying statistical machine learning to video images collected by an optical sampler, the Video Plankton Recorder (VPR). The research is focused on development of a real-time automatic plankton recognition system to estimate plankton abundance. The system includes four major components: pattern representation/feature measurement, feature extraction/selection, classification, and abundance estimation. After an extensive study on a traditional learning vector quantization (LVQ) neural network (NN) classifier built on shape-based features and different pattern representation methods, I developed a classification system combined multi-scale cooccurrence matrices feature with support vector machine classifier. This new method outperforms the traditional shape-based-NN classifier method by 12% in classification accuracy. Subsequent plankton abundance estimates are improved in the regions of low relative abundance by more than 50%. Both the NN and SVM classifiers have no rejection metrics. In this thesis, two rejection metrics were developed. (cont.) One was based on the Euclidean distance in the feature space for NN classifier. The other used dual classifier (NN and SVM) voting as output. Using the dual-classification method alone yields almost as good abundance estimation as human labeling on a test-bed of real world data. However, the distance rejection metric for NN classifier might be more useful when the training samples are not "good" ie, representative of the field data. In summary, this thesis advances the current state-of-the-art plankton recognition system by demonstrating multi-scale texture-based features are more suitable for classifying field-collected images. The system was verified on a very large real-world dataset in systematic way for the first time. The accomplishments include developing a multi-scale occurrence matrices and support vector machine system, a dual-classification system, automatic correction in abundance estimation, and ability to get accurate abundance estimation from real-time automatic classification. The methods developed are generic and are likely to work on range of other image classification applications. by Qiao Hu. Ph.D.
... This, of course, is limited to plankton organisms that are visible with the naked eye, but has revealed important insight into such diverse phenomena as larvacean feeding biology and sinking rates of marine snow aggregates. A second approach has been to deploy underwater cameras to obtain still pictures or video recordings in situ (Davis et al., 1992: Tiselius, 1998, Malkiel et al., 2006). Due to the high magnification required to observe small plankton, and the high water velocity past the camera, also when mounted on a free floating device, even video recording provides only still pictures, albeit many of them. ...
A simple water sampler that brings undisturbed water samples to the deck-laboratory and that allows video recording of plankton
and small-scale plankton phenomena directly in the sampler is described. Using the sampler, it is possible to follow individual
plankton organisms and marine snow aggregates for longer periods of time in an environment where the original three-dimensional
organization of particles and chemical gradients have been retained. The sampler has been used to film sinking marine snow,
the microbial life on a snow flake, and the behaviour of delicate zooplankters that are otherwise difficult to collect live.
Video clips demonstrating the utility of the sampler are available online.
... Advances in acoustic and bathyphotometric profilers (Holliday et al., 1998;Widder et al., 1999) have greatly enhanced our ability to locate concentrations of the larger zooplankton, while optical absorption profiling (Twardowski et al., 1999) and two-dimensional fluorometry (Franks and Jaffe, 2001) have aided in identifying chlorophyll maxima, indicating potential food concentrations for herbivores. Underwater video observations Tiselius, 1998) have been used to make zooplankton and plankton counts, occasionally to species level, when supplemented with ocean truthing based on net tows (Benfield et al., 1996). These methods can provide detailed spatial correlations of in situ species concentration, which can be used to infer trophic dynamics. ...
A film-based holography system was used in conjunction with instrumentation that detected bioluminescent thin layers to record the spatial distribution of zooplankton and their prey in the Gulf of Maine, USA. The holocamera and instruments were mounted on the Johnson Sea Link (JSL) in a setup that minimized the disturbance to the sample volume. More than 143 holograms were automatically scanned to provide focused images of 5000–10 000 particles and their three-dimensional coordinates in each 894 cm3 sample. The reconstructed volumes provided clear images of intermingling copepods species, nauplii, Pseudonitzschia diatoms and particles in the 10 μm–5 mm size range. Spatial analysis of the nearest neighbor distance (NND) of the smallest particles showed a random distribution, but detritus particles showed small-scale clustering in regions below the pycnocline. A detritus maximum, found several meters below the pycnocline, at 20–30 m, was determined to be caused by fecal pellets in various stages of degradation. This region also contained elevated concentrations of calanoids, cyclopoids and harpacticoids. In one third of the cases, the harpacticoids, Aegisthus sp, were attached to detritus.
... Furthermore, net hauls do not represent the actual density of plankton organisms in small-scale aggregations. Physical (accumulation in convergence zones, turbulence, internal waves, etc.) and biological (predator avoidance, swarming behaviour, etc.) processes lead to densities that may be several orders of magnitude higher than those calculated from net hauls [ (Conover et al, 1988;Currie et al., 1998;Tiselius, 1998) and references therein]. The alternative would have been to use lower mesozooplankton densities and to dilute the nano-and microplankton samples, but the reduced food densities would have affected the feeding behaviour of the mesozooplankton community, producing serious artefacts. ...
The objective of the present study was to quantify mesozooplankton grazing in the eutrophic waters of Guanabara Bay. Mesozooplankton (>200 μm) was dominated by the copepods Acartia lilljeborgi , Acartia tonsa , Parvocalanus crassirostris and Paracalanus furcatus . Dinoflagellates, specifically the species Prorocentrum triestinum , were an important group for mesozooplankton nutrition, being ingested in significant amounts during all experiments. On average, 12.3 ± 2.9 P. triestinum cells were ingested copepod−1 min−1 (other dinoflagellates: 11 ± 8 cells copepod−1 min−1). Filamentous cyanophyceae and nanoplankton were ingested in one experiment each, but the mesozooplankton community generally preferred dinoflagellates to these groups, which were always abundant in the water column. Euglenophyceae were not ingested, although they dominated in one experiment. Mesozooplankton ingested, on average, only 0.2% of the nano- and microplankton biomass per day. The results suggest that grazing was not a controlling process for the nano- and microplankton community in the study area. Addition of zoeae larvae of Chasmagnatus granulata (Decapoda: Brachyura: Grapsidae) in one experiment had a significant effect on the mortality of adult copepods, probably due to a predator–prey relationship.
... These areas cover both pelagic and coastal environments, and suggest that thin layers are an important features in plankton communities worldwide, and thus may play vital roles in a variety of ecological and biogeochemical cycles. Most studies of thin layers have occurred in the northeast Pacific off the coast of Oregon [USA] Cowles, 2004 and the San Juan Islands near Washington [USA] (Dekshenieks et al., 2001;Cowles et al., 1998), and some studies have occurred in the Baltic Sea (Tiselius, 1998). Other observations of thin layers have also been documented in the Gulf of Mexico near Destin, FL, in the Ogeechee River Estuary, GA, in Monterrey Bay, CA, and on Georges Bank, Gulf of Maine (McManus, pers. ...
In the current study, behavioral responses of several species of calanoid copepods to mimics of oceanographic structure were observed and evaluated in the context of foraging and aggregation. Zooplankton distributions in oceanic habitats are often attributed to physical forcing; however, physical factors only act to drive ecological patterns at large scales (m to km). At fine to intermediate scales (cm to m) zooplankton behavior is believed to govern observed distributions, but the mechanisms and ecological significance of these behaviors are not well understood. In a water column, biological activity is often concentrated into one or a few regions, called thin layers, on the order of a meter thick, and zooplankton, such as copepods, must be able to reliably locate and exploit these patches for survival. Thin layers commonly are associated with oceanic structure such as flow gradients, fluid density jumps, or chemical composition gradients. Utilization of mechanosensory or chemosensory cues associated with thin layers may increase foraging success, thus translating into a significant ecological advantage. A laboratory apparatus was developed to create isolated and combined thin layer properties. Copepods then were exposed to laboratory mimics of thin layers. All of the tested species of copepods exhibited behavioral responses associated with area-restricted search behavior to one of the physical gradients (flow velocity or fluid density), but not both. Similar responses were observed for chemical exudate layer experiments and included increased proportional residence times, swimming speeds, and turn frequency. Food layers induced feeding responses from all tested species (increased proportional residence time, decreased swimming speed). Responses to various combinations of gradients were not fully synergistic, but suggested that some copepods employ a cue hierarchy to locate food-rich areas. Velocity or density gradients acted as initial cues for narrowing search regions, while chemical exudates induced responses that strengthened or removed the initial reactions. A simple foraging model was used to illustrate how such behavioral changes can lead to observed aggregations at larger temporal and spatial scales. Consequently, these results suggest that individual responses to oceanographic structure may have far reaching influence on population dynamics, succession, and biodiversity in coastal and pelagic ecosystems. Ph.D. Committee Chair: Webster, Donald R.; Committee Member: Roberts, Phillip; Committee Member: Sturm, Terry; Committee Member: Weissburg, Marc; Committee Member: Yen, Jeannette
... Fragile particles such as jellyfish, some marine snow, etc., are typically destroyed in net collection; these particles require the use of in situ optical recording techniques for accurate representation. Previous in situ recording methods have included underwater photography [2] and camera-based video systems [3]- [6]. Both systems require an intermediate step of remotely digitizing the collected images before computer processing may be performed. ...
We discuss an in situ marine imaging system based on high-speed
digital line scan cameras for collection of a continuous picture of
microscopic marine particles ranging in size from 200 μm to several
centimeters. The system is built to operate on a 53-cm-diameter
autonomous underwater vehicle or a tethered platform. The digital
imaging system provides a continuous record of all particles passing
through a symmetric 96×96 mm sampling tube and provides views from
two orthogonal directions. Data are compressed using a lossless encoding
technique and stored onto a disk drive. Over 50 h of continuous imaging
is possible using the system. Data are suitable for studies requiring
sizing, identification, quantification, and spatial recording of
semi-transparent and opaque particles. This paper summarizes the
mechanical, optical, and data processing design of this instrument and
discusses recent improvements. We also present images and quantitative
results from recent deployments in the Gulf of Mexico
Thèse de doctorat réalisée en cotutelle entre l'Univeristé Paris VI, l'Université de Montréal, Canada (directeur de thèse: Pr Pierre LEGENDRE) et l'Université des Antilles et de la Guyane, Guadeloupe (codirecteur de thèse: Pr Max LOUIS). Mention Très Honorable décernée par le jury composé de: M. G. BOUCHER, Directeur de Recherche, CNRS, Examinateur M. J. CLAVIER, Professeur, Université de Brest, Rapporteur M. F. IBANEZ, Maître de conférences, Université Paris 6, Rapporteur M. P. LEGENDRE, Professeur, Université de Montréal (Canada), Directeur de thèse M. M. LOUIS, Professeur, Université Antilles-Guyane (France), Directeur de thèse M. P. NIVAL, Professeur, Université Paris 6, Président du jury et Examinateur
A fundamental problem in limnology and oceanography is the inability to quickly identify and map distributions of plankton. This thesis addresses the problem by applying statistical machine learning to video images collected by an optical sampler, the Video Plankton Recorder (VPR). The research is focused on development of a real-time automatic plankton recognition system to estimate plankton abundance. The system includes four major components: pattern representation/feature measurement, feature extraction/selection, classification, and abundance estimation. After an extensive study on a traditional learning vector quantization (LVQ) neural network (NN) classifier built on shape-based features and different pattern representation methods, I developed a classification system combined multi-scale cooccurrence matrices feature with support vector machine classifier. This new method outperforms the traditional shape-based-NN classifier method by 12% in classification accuracy. Subsequent plankton abundance estimates are improved in the regions of low relative abundance by more than 50%. Both the NN and SVM classifiers have no rejection metrics. In this thesis, two rejection metrics were developed.
A long-standing problem in plankton ecology is sparseness of taxa-specific data. New optical imaging systems are becoming available which can acquire high-resolution data on the abundance and biomass of plankton taxa. The Video Plankton Recorder (VPR) has been designed and used for automatic sampling and visualization of major planktonic taxa at sea in real time, providing high-resolution data over a broad range of scales. Although these optical systems produce digital images of plankton that can be automatically identified by computer, the limited accuracy of automatic classification methods can reduce confidence in subsequent abundance estimates, especially in areas where a taxon is in low relative abundance. This paper describes an improved classification system for automatic identification of plankton taxa from digital images. Classifiers are trained from a set of images that were classified by human experts. The data set used to verify the classification system contains over 20 000 planktonic images manually sorted into 7 different categories. The new method uses co-occurrence matrices (COM) as the feature, and a Support Vector Machine (SVM) as the classifier. This new method is compared against a previous plankton recognition system, which used moment invariants, Fourier descriptors and granulometry as features and a learning vector quantization neural network as a classifier. The new method reduced the classification error rate from 39 to 28 %. Subsequent plankton abundance estimates are improved by more than 50 % in regions of low relative abundance. In general, the reduction in classification error was due to a combination of the use of COM and SVM.
The development of quantitative zooplankton collecting systems began with Hensen (1887 Berichte der Kommssion wissenschaftlichen Untersuchung der deutschen Meere in Kiel5, 1–107; 1895 Ergebnisse der Plankton-Expedition der Humbolt-Stiftung. Kiel and Leipzig: Lipsius and Tischer). Non-opening closing nets, opening closing nets (mostly messenger based), high-speed samplers, and planktobenthos net systems all had their start in his era — the late 1800s and early 1900s. This was also an era in which many of the fundamental questions about the structure and dynamics of the plankton in the worlds oceans were first posed. Fewer new systems were introduced between 1912 and 1950 apparently due in part to the two World Wars. The continuous plankton recorder stands out as a truly innovative device developed during this period (Hardy 1926b Nature, London118, 630). Resurgence in development of mechanically-based instruments occurred during the 1950s and 1960s. A new lineage of high-speed samplers, the Gulf series, began in the 1950s and a number of variants were developed in the 1960s and 1970s. Net systems specifically designed to collect neuston first appeared in the late 1950s. During the 1960s, many focused field and experimental tank experiments were carried out to investigate the hydrodynamics of nets, and much of our knowledge concerning net design and construction criteria was developed. The advent of reliable electrical conducting cables and electrically-based control systems during this same period gave rise first to a variety of cod-end samplers and then to the precursors of the acoustically and electronically-controlled multi-net systems and environmental sensors, which appeared in the 1970s. The decade of the 1970s saw a succession of multi-net systems based both on the Bé multiple plankton sampler and on the Tucker trawl. The advent of the micro-computer stimulated and enabled the development of sophisticated control and data logging electronics for these systems in the 1980s. In the 1990s, acoustic and optical technologies gave rise to sensor systems that either complement multiple net systems or are deployed without nets. Multi-sensor systems with high data telemetry rates through electro-optical cable are now being deployed in towed bodies and on remotely operated vehicles. In the offing are new molecular technologies to identify species in situ, and realtime data analysis, image processing, and 3D/4D display. In the near future, it is likely that the use of multi-sensor systems deployed on autonomous vehicles will yield world wide coverage of the distribution and abundance of zooplankton.
Patchiness of planktonic microorganisms may have important implications in microbial communities not only at small scale within
habitats but also at large scales within lake basins and districts in landscapes, and within oceanic regions and biogeographical
provinces. However, studies are generally limited to one specific planktonic entity (bacterio-, phyto-, or zooplankton) or
one spatial scale and extent (across oceans or freshwater systems, or within systems), and there is still no functional perspective
on multiscale patchiness patterns of microbial communities and their generative processes. This review presents some of the
key aspects of plankton spatial heterogeneity including concepts, patterns, and processes in the context of a multiscale perspective.
The ecological significance of spatial heterogeneity for planktonic microorganisms is presented with a functional perspective
relating distribution patterns to environmental processes. The importance of abiotic and biotic forces and that of the biophysical
coupling in structuring microbial community in aquatic systems at scales relevant to ecological states or processes of organisms,
populations, and ecosystems is discussed. The importance of the application of new and advanced technology, as well as statistical
approches is presented and their spatial relevance discussed. Keywords: Spatial heterogeneity, microorganisms, plankton communities,
marine and freshwater ecosystems
Fisheries research surveys are designed and conducted for a variety of purposes. Some examples are those of defining geographical limits of distribution, describing diurnal movements or seasonal migrations, and determining abundance. The main purpose considered here is that of determining abundance.
We developed Autonomous Buoy, which is composed of embedded system, OPC (Optical Particle Counter) and CTD (Conductivity, Temperature, Depth) sensors, to observe underwater environment. The vehicle is an autonomous profiling float that uses a buoyancy engine to cycle horizontally while moving up and down. The autonomous buoy is controlled by embedded system composed of field-programmable gate array (FPGA) and high performance CPU, which is designated to perform image signal processing, data compression, power management and satellite communication. Embedded system acquires high-resolution particle image using linear-CCD for counting particle and CTD value and analyzes particle images in underwater environment. It reduces amount of particle image data using on-board processing that provides good performance when autonomous vehicle communicates with a satellite.
A self-contained, analog Video Plankton Recorder (VPR) mounted on a 1-m2 MOCNESS sampling system was used to obtain data on micro-scale (<10 m) distributions of zooplankton as prey for larval cod
and haddock during May 1997 and May 1999 on Georges Bank. The negative binomial frequency distribution was selected to best
describe the more abundant plankton categories in 10-second bins for 10-m depth intervals. Most of the strata had asymmetrical
frequency distributions with low means and low k values indicating a clumped distribution. Water-column stratification was
especially important in structuring micro-scale high-density layers of phytoplankton and copepods. The most symmetrical Poisson-like
distributions with high means and high k values occurred in the upper 30 m above the base of the thermocline.
The Baltic Sea is the largest semi-enclosed brackish sea in the world and consists of several consecutive deep basins. Due to fresh water input, physical processes and topographic structures pronounced hydrographic stratifications persist. These are created from water masses of incompatible densities due to different temperatures and salinities.A total of 832 multinet samples from different sites and depths were analysed for composition of the dominant zooplankton species and the relation to ambient environmental parameters by means of multivariate methods, weighted depth centroids and individual analyses of the vertical distribution. Species and developmental stages were bound to distinct layers and partially migrate between them during the season. The layers put different demands on the physiology of the individual species and can be conceived as habitats, determining the vertical distribution.When assessing the vertical distribution of plankton using nets the depth integration is a limiting factor intrinsic to the method, making a precise assessment of zooplankton species in different horizons more difficult. To solve these problem new concepts for optical in-situ detection of plankton species is introduced.
The concentration of phytoplankton in the sea is affected by biological processes, such as growth/mortality rates, predatory zooplankton concentrations and nutrient levels. Phytoplankton concentrations are also influenced by physical processes, in particular the mixing properties of the local fluid environment. On planktonic scales (approximately 10-1000 microm) one can assume the local turbulent flow is isotropic, with no distinction between horizontal and vertical mixing. However, agglomerations of phytoplankton into patches are observed on larger scales of up to hundreds of metres, whose formation will be influenced by the anisotropic advection/mixing properties and large-eddy structures prevalent in the surface mixed layer. This paper presents the results of the coupling of a large-eddy simulation (LES) model of the mixed layer with an advection-diffusion system of coupled equations for nitrate-phytoplankton-zooplankton (NPZ) concentration, incorporating sub-grid parameterizations of the biological processes. Typically these include phytoplankton growth due to light levels and ambient nitrate concentration, offset by grazing losses due to the presence of zooplankton. The primary goal of this work is to investigate how the characteristics of the mixed layer turbulence influence the observed distribution of phytoplankton. One novel feature is the incorporation of a 'vortex-force' term in the LES code in order to generate Langmuir circulations. It has been speculated that the enhanced mixing rates associated with 'Langmuir turbulence' play a significant role in regulating planktonic activity. Results derived from the coupled LES-NPZ model, run with and without the presence of Langmuir circulations, are presented in order to investigate these ideas.
This paper introduces a free-drifting submersible digital holography system (holo-sub), shown in fig. 1, and issues associated with processing the massive amount of data involved. Studying behavior of marine micro-organisms in-situ requires the ability to follow them in time and observe their interactions with the local biological, chemical, and physical environment. Holographic imaging allows reconstruction of in-focus images of all planes within a sample volume that has a substantial depth. To facilitate observations of organisms over many frames, thus allowing for analysis of in-situ behavior, the holo-sub is designed to drift with the ambient flow. Two cameras record holograms simultaneously, each at 15 frame/sec. Two optional optical configurations have been implemented to-date. In one configuration, the sample volumes are perpendicular, allowing for 3D resolution of 7.4 mum in all directions. In the second, the first camera maintains a sample volume with a cross-section of 15times15 mm, while the other records holograms of part of the same volume at a higher magnification, enabling us to resolve smaller particles. This system was deployed in the Ria de Pontevedra, Spain in 2005, and in the Bay of Biscay, France in 2006, in collaboration with several European research groups. Over 3 TB of holographic data have been acquired during these deployments. Extracting relevant information from the large holographic dataset requires two important steps: 1 - locating and reconstructing the desired organism, and 2 - processing the reconstructed images to obtain quantitative data on behavior. A series of software tools have been developed to facilitate efficient manual search for organism location, followed by recording of their in-focus images, and tracking them in time. Analysis of reconstructed images to obtain quantitative data begins with classification of behavior, followed by development of image processing routines to perform specific measurements. For example, app-
endicularians, zooplankton that create gelatinous "houses" with which they filter small particles for feeding are one of the most numerous large organisms that have been observed in our data set. Software has been developed to provide swimming velocity, house shape and size, particle distributions within the house, organism size, and tail flapping frequency.
Submersible film-based holographic systems have demonstrated the unique ability of holography to provide high resolution, three-dimensional, in-situ images of marine organisms. Inherently, use of film limits the frame rate and total number of holograms. This paper describes a submersible, free-drifting, digital holographic cinematography system that has a real-time fiber optic communication link. This system collects dual-view digital holograms at a rate of 15 frames per second, enabling the user to observe the behavior of marine plankton and distinguish motile organisms from abiotic particles. In order to follow the particles in time, the sample should have as little motion relative to the cameras as possible. To achieve this goal, the submersible is neutrally buoyant, and has high drag generating elements at the height of the sample volume. In addition, the components surrounding the sample are streamlined and designed to minimize the local flow disturbance. The data from the two digital cameras and other sensors are transmitted at 120 MB/s through a 1 km long, 250 μm diameter, fiber optic cable to an acquisition system located on a research vessel. The optical fiber is spooled out from the submersible by a powered mechanism, as the submersible drifts away from the vessel Releasing the fiber out at a rate greater than that of the drifting speed minimizes the transmission of forces through the cable, effectively decoupling the submersible from the cable and vessel dynamics. A variable buoyancy system provides vertical position control while still allowing the system to drift vertically with the surrounding fluid, i.e., follow internal waves. The dual-view holo-camera records two in-line holograms from orthogonal directions, each with a volume of 40.5 cm3. Without lenses, the resolution in the 3.4 cm3 volume where the beams cross each other, is about 7.4 μm in all three directions. Outside of the overlapping region, the resolution in the beam axial direction is lower, but the lateral resolution remains 7.4 3. An optional 2× lens doubles the resolution, but reduces the sample volume. The first field deployment for this system took place in June 2005, in the Ria de Pontevedra, Spain. It was used for examining thin layer- s of harmful algal blooms.
Turbulence may enhance contact rates between planktonic predators and their prey. We formulate simple and general models of prey encounter rates, taking into account the behaviours and motility patterns of both prey and predator as well as turbulent fluid motion. Using these models we determine the levels of turbulence (as dissipation rate) at which ambient fluid motion is important in enhancing prey encounter rates for various types of predators (e.g, ambush and cruise predators, suspension feeders). Generally, turbulence has the largest effect on prey encounters for predators with low motility and long reaction distances. Also, turbulence is most important for meso-sized (mm to cm) predators and insignificant for smaller and larger predators. The effect of turbulence on copepods is specifically examined. For copepods that establish feeding currents, turbulence is of minor importance; for ambush feeding copepods, such as Acartidae and many cyclopoids, turbulence has a dominant influence on prey encounter rates. The effect on cruising predators is intermediate. Application of the models to situations examined experimentally demonstrates a high predictive performance. Finally we explore and model the potentially negative effects of turbulence on copepod feeding currents, prey perception and capture success. At typical and even high turbulent intensities, none of these is significantly affected.
Except at high numerical densities (>10(6) m(-3)), nearest-neighbor distances in monospecific aggregations of copepods are much greater than known perception distances (usually <2-4 body lengths). Most copepod aggregations are several orders of magnitude less dense, with nearest-neighbor distances much greater than three body lengths. Biological mechanisms for the formation and maintenance of aggregation require recognition of, and appropriate behavioral response to, conspecifics. While it appears obvious that such mechanisms are responsible, invoking them to explain most aggregations has little support from either laboratory/field evidence or theory. More research is needed on zooplankton behavior, sensory modalities and]earning to reconcile the difference in scales between known perception distances and spacing in aggregations.
Clearance rates on different sizes of spherically shaped algae were determined in uni-algal experiments for all developmental stages (NII through adult) of the copepodAcartia tonsa, and used to construct food size spectra. Growth and developmental rates were determined at 7 food levels (0 to 1 500 μg C l-1 ofRhodomonas baltica). The lower size limit for particle capture was between 2 and 4 μm for all developmental stages. Optimum particle size and upper size limit increased during development from ∼7 μm and 10 to 14 μm for NII to NIII to 14 to 70 μm and ∼250 μm for adults, respectively. When food size spectra were normalized (percent of maximum clearance in a particular stage versus particle diameter/prosome length) they resembled log-normal distributions with near constant width (variance). Optimum, relative particle sizes corresponded to 2 to 5% of prosome length independent of developmental stage. Since the biomass of particulate matter is approximately constant in equal logarithmic size classes in the sea, food availability may be similar for all developmental stages in the average marine environment. Juvenile specific growth rate was exponential and increased hyperbolically with food concentration. It equaled specific female egg-production rate at all food concentrations. The efficiency by which ingested carbon in excess of maintenance requirements was converted into body carbon was 0.44, very similar to the corresponding efficiency of egg-production in females. On the assumptions that food availability is similar for all developmental stages, and that juvenile and female specific growth/egg-production rates are equal, female egg-production rates are representative of turnover rates (production/biomass) of the entireA. tonsa population and probably in other copepod species as well. Therefore, in situ estimates of female fecundity may be used for a rapid time- and site-specific field estimate of copepod production. This approach is shown to be fairly robust to even large deviations from the assumptions.
Swarms of 8 copepod species were visually observed in temperate and subtropical waters along the coast of Japan from 1975to 1981. Irregular ball-shaped swarms, with diameters less than 1 m, were common for Acartia plumosa, A. erythraea, A. steueri, A. japonica, A. hamata and Oithona oculata. They generally occurred on or a little above the bottom near the shore during the day and maintained their position against slight water currents. A. clausi in Shijiki Bay and O. oculata in Tanabe Bay formed continuous flat swarms and carpeted the bottom with copepods. A. steueri in Shijiki Bay, 1978, swarmed within sea grass beds. Labidocera pavo formed small swarms, in which the copepods swirled with each other. Copepod swarms were almost monospecific aggregations except for A. erythraea, which was observed to swarm jointly with A. plumosa. Within swarms, adult copepods generally dominated and females outnumbered males. For some of Acartia spp., swarms consisted almost entirely of adults, especially females, indicating that the swarming of these species is age- and sex-specific. Adaptive functionis of copepod swarms are discussed. Swarming of copepods appears to be a common phenomenon in temperate shallow waters and of significant importance as food resource for some demersal fishes.
© 1997 Inter-Research Many species of copepods form dense aggregations, known as swarms. In the laboratory, we experimentally induced 5 different species of copepod to swarm in response to a point source of light. To map out the (x, y, z, t) positions of swarm members, 2 right-angle views of the 3-dimensional swarm were videotaped. Since images of individual copepods appear indistinguishable on the paired 2-dimensional projections, an algorithm was developed which matched the temporal changes of the vertical (z) positions of all images from the 2-dimensional projections of the 3-dimensional copepod movement to produce (x, y, z, t) positions of each individual. With the temporal/spatial positional data of swarm members, we tested the hypothesis that the fluid disturbance surrounding individual moving copepods, rather than the exoskeleton, maintains minimum separation distance. As the density of the swarm increased, the average nearest-neighbor distance NND decreased, as did the mean minimum NND (MNND). For 3 of the 5 species, the MNND was significantly greater than that predicted from a random distribution, and was greater than twice the antennule or prosome length. While occasional physical contact may occur, resulting in escapes or attempted mating, it appears that most swarm members remain outside the field of self-generated fluid motion in the boundary layers surrounding their neighbors.
The behavior of the swarm-forming copepod Dioithona oculata was studied both in situ and in the laboratory using a video-computer system for motion analysis. In nature, swarms form in light shafts between the prop roots of red mangroves. Swarms maintain their position within these light shafts despite currents of up to 2 cm s-1. In the laboratory, swimming speeds and turning rates of swarming copepods in still water were lower than those observed in the field. Copepods studied in a flowthrough chamber in the laboratory had swimming behaviors similar to those observed in nature; the stimulation from water movement caused increases in both swimming speed and rate of change of direction. Increased current speeds also caused the swarms to become more tightly packed within the center of a vertical light shaft. Nonswarming copepods were unable to maintain their position in a current in darkness. In laboratory experiments, the presence of actively feeding planktivorous fish caused swarms to temporarily disperse due to escape responses of the copepods. However, planktivorous fish were rarely observed feeding on swarms in nature, perhaps due to the presence of predatory fish hiding among the prop roots.
The surfaces of most pelagic diatoms are sticky at times and may therefore form rapidly settling aggregates by physical coagulation. Stickiness and aggregate formation may be particularly adaptive in upwelling systems by allowing the retention of diatom populations in the vicinity of the upwelling center. We therefore hypothesized that upwelling diatom blooms are terminated by aggregate formation and rapid sedimentation. We monitored the de- velopment of a maturing diatom (mainly Chaetoceros spp.) bloom in the Benguela upwelling current during 7 d in February. Chlorophyll concentrations remained consistently high during the observation period (-500 mg Chl m ?) and phytoplankton grew at an average specific rate of 0.25 d-l. The diatoms were extraordinarily sticky, with stickiness coefficients of up to 0.40, which is the highest ever recorded for field populations. Combined with estimates of turbulent shear in the ocean such stickiness coefficients predict very high specific coagulation rates (0.3 d-l). In situ video observation demonstrated the occurrence of abundant diatom aggregates with surface water concentrations between 1,000 and 3,000 ppm. Despite the very high concentration of aggregates, vertical fluxes of phytoplankton were very low, with fractional losses CO.005 d-l, and the aggregates thus seemed to be near neutrally buoyant. Losses due to copepod grazing were also low (-0.025 d-l). Most of the aggregates were colonized by the heterotrophic dinoflagellate Noctiluca scintilluns that feed upon diatoms in the aggregates. The system appeared to be in near steady state; specific diatom growth rate, coagulation rate, and loss rate due to N. scintillans feeding were all of the same magnitude (0.25-0.3 d-l) and the latter two varied in concert. Our observations provide only partial support for the population retention hypothesis because aggregate buoyancy and N. scintillans grazing effi- ciently reduced the vertical flux of aggregates in this system.
Aggregate size and abundance were monitored in situ at a fixed station in the southern North Sea during a 6 wk investigation which covered the phytoplankton spring bloom and the pre- and post-bloom periods. Particle aggregates were abundant during the entire period of study. Biologically derived material, such as algal cells, played a central role in aggregate formation. Maximum total aggregate volume coincided with the peak of the bloom. Maximum aggregate size did not correlate with either phytoplankton biomass or total suspended matter. Despite a distinct increase in the amount of aggregated material during the development of the bloom, maximum aggregate size remained at about 1 mm diameter during most of the investigation. The formation of large, marine-snow-sized aggregates up to 5 cm in longest dimension, which was restricted to a short period following the decline of the phytoplankton bloom, coincided with comparatively low shear rates. Results are consistent with physical coagulation models. Aggregate formation can be described by a 2-state system in which the amount of aggregated matter is low during the development and following the decline of a bloom, and high during the peak of a bloom.
The paper presents the results from a study in which two commonly used plankton nets, the Nansen net and the WP 2 net, were compared. The study was performed at six stations in the Baltic Sea and the samples were collected during seasons of both high and low particle abundance. The comparison included both qualitative and quantitative filtration capacity of the nets under different environmental conditions. Different mesh sizes were also tested. The results show that the Nansen net has an efficiency of 50-70% compared to the WP 2 net under favourable conditions. When conditions are unfavourable, i.e. during periods of high particle abundance or during long hauls, the efficiency may be as low as 25-30%. The mesh size of the nets proved to be of decisive importance for the qualitative composition of the samples. Most of the smaller size fractions such as rotifers, copepod nauplii and young copepodites passed through the 160 and 200 μm meshes. The 90 μm nets sampled these fractions well but with the drawback of retaining vast amounts of phytoplankton at certain times of the year.
An apparatus for the subsampling of plankton is described. It is shown that the samples obtained conform to the characteristics of a Poisson distribution. Limits to the efficiency of the apparatus are encountered when certain organisms with a tendency to clump together are present in high concentrations, but these limits are well within the accuracy required and achieved with the present methods of collecting plankton; otherwise the accuracy of the apparatus apparently does not vary with different types of organism.
For a 6 wk period covering the time before, during, and after the phytoplankton spring bloom, macroscopic aggregates (2 0.5 mm diameter) were repeatedly collected and water column properties simultaneously measured at a fixed station in the Southern North Sea. Distinct changes in aggregate structure and composition were observed during the study. Predominantly detrital aggregates d u r ~ n g the early phase of the study were followed by diatom-dominated algal flocs around the peak of the bloom. Mucus-rich aggregates containing both algal and detrital components and with large numbers of attached bacteria dominated the post-bloom interval. The phytoplankton succession within the aggregates closely reflected the succession in the water column with a time delay of a few days. Algal flocculation did not occur as a simultaneous aggregation of the entire phytoplankton community, but as a successional aggregat~on of selected diatom species. Although the concentrations of ~norganic nutrients diminished considerably during the development of the phytoplankton bloom, the termination of the bloom appeared to be mostly controlled by physical coagulation processes. The importance of biologically-controlled factors for physical coagulation is discussed.
Recent numerical studies of turbulent flow show the presence of “organized structures” within the flow. I will speculate on the behavior of planktonic organisms in conjunction with such structures. Breaking waves cause an enormous number of bubbles at the ocean surface, and the Langmuir circulation transports them into deeper sections of water. Rising bubbles can induce a flotation process and complicate the environment of plankton. Hence, I also provide conjecture on the possible role of bubbles for productivity in the upper ocean. To properly take these small-scale non-linear processes into account, we must use Lagrangian models. I will introduce two Lagrangian models which mimic an aggregation of planktonic organisms.
Many experiments have been made in the laboratory by different workers to study the swimming behaviour of plankton animals in relation to light and other factors. At the present time the special apparatus described by Hardy & Bainbridge (1951) is being used for a study of vertical migration, and other experimental work on the inter-relationships of zooplankton and phyto-plankton (Bainbridge, 1949) is also in progress. Both this type of work and current theories (see Cushing, 1951) on the migrations of zooplankton make it of some consequence to learn the actual nature of the movements of these animals in the sea itself; and it is of special importance to compare their swimming behaviour in the different types of apparatus with their behaviour in the sea.
An in-situ silhouette camera system that permits assessment of vertical and horizontal zooplankton distributions on meter scales, yet retains considerable taxonomic information, is described. Representative data are presented from initial deployments in the Gulf Stream off Miami, Florida. Advantages and disadvantages of this approach are discussed.
The swimming behavior of the marine cyclopoid copepodOithona davisae Ferrari and Orsi, collected in Tokyo Bay, Japan, between 1980 and 1983, was studied after acclimation to various food concentrations. Males and females exhibited forward and circular swimming movements. Males search mainly for mates, not for food. Their circular swimming behavior may serve for the mate search. The spiraling movement during mate-pursuit is peculiar to males. Circular swimming in females may function as a spontaneous search behavior for rich food areas and less crowded conditions. Females acclimated to a low food concentration, with net production about zero, responded sensitively to the increased food concentration by decreasing their swimming distance per unit time. Females acclimated to higher levels also responded similarly, but less sensitively. On the other hand, females kept without food exhibited no changes in swimming behavior and exhibited a stereotyped behavior at every food level. Females, when exposed to a low food level, may prefer to search for richer areas rather than capture food. The combined effect of the degree of internal activity (DIA) and the intensity of external stimulus (IES) determines the behavior pattern ofO. davisae. The behavioral response to IES depends on DIA.
The potential for identifying and separating copepod species and stages with an in situ electronic zooplankton counter, which was developed and tested as a biological tool, has been examined. The instrument was mounted on the Batfish, a depth-controllable towed body equipped to measure chlorophyll a, temperature, salinity, and depth. Zooplankton length and diameter distributions measured by the zooplankton counter were compared with measurements made using a microscope. Detailed analysis of the data shows that the electronic counter has sufficient resolution to separate and identify dominant species of copepods consisting of Clausocalanus arcuicornis, Metridia lucens, Calanus finmarchicus, and Euchirella rostrata sampled from the Scotian Shelf, and Centropages brachiatus, Calanus chiliensis, and Eucalanus inermis sampled from the Peruvian Shelf. The examples of Batfish data included show the separation of dominant species and copepod abundance estimates from the Peruvian Shelf. The relative merits of the electronic measurements and microscope analysis are discussed.
A new optical plankton counter capable of counting and sizing zooplankton and simultaneously measuring light attenuance is described. The submersible model can be towed or lowered on station while a laboratory version is used to process samples from a pump outflow or animals preserved in formalin. The submersible model has been mounted on the Batfish vehicle and towed for extended periods of 15–20 h allowing it to be used as a survey tool. Data showing copepod layers in deep shelf basins are presented and comparisons made between light attenuance measured with the plankton counter and chlorophyll fluorescence measured with an in situ fluorometer also mounted on the Batfish. The submersible counter was also towed while mounted on the BIONESS (a multiple opening and closing net system) and comparisons are made between the measured profiles and size distributions of copepods.
During the spring of 1994, we determined the factors responsible for the decline of the seasonal diatom bloom in the Gullmar fjord, on the west coast of Sweden. Four species constituted >75% of the biomass— Detonula confervacea, Chaetoceros diadema, Skeletonema costatum and Thalassiosira nordenskioeldii —reaching concentrations of 4900, 350, 8200 and 270 cells ml−1, respectively. Growth of phytoplankton was exponential (growth rate = 0.12 day−1) from 3 to 21 March, after which a gale with winds >15 m s−1 caused massive aggregation. A maximum of 130 p.p.m. (v/v) of marine snow aggregates was observed by in situ video at the peak of the bloom. Critical concentrations (Jackson, Deep-Sea Res ., 37, 1197–1211, 1990) were similar to observed showing that coagulation theory could explain the sudden decline of the bloom. The heterotrophic dinoflagellate Gyrodinium cf. spirale increased exponentially after the peak of the bloom with maximum (temperature-adjusted) growth rates. After the rapid aggregation and sedimentation of the bloom, they were able to control any further growth of diatoms. Nitrate and silicate were never depleted, but phosphate may have been limiting by the end of the study period. We conclude that mass aggregation during a gale marked the end of the bloom, and that intense grazing by heterotrophic dinoflagellates prevented any subsequent increase of diatoms.
Oceanic plankton have been hypothesized to occur in micropatches (<10 meters) that can have a large impact on marine ecosystem dynamics. Towed video microscopy was used to unobtrusively determine distributions of oceanic plankton over a continuum of scales from microns to hundreds of meters. Distinct, taxa-specific aggregations measuring less than 20 centimeters were found for copepods but not for nonmotile (cyanobacterial colonies) or asexual (doliolid phorozooids) forms, which suggests that these small patches are related to mating. Significant patchiness was also found on larger scales and was correlated among taxa, indicating physical control. These video observations provide new insights into basic plankton ecology by allowing quantitative assessment of individual plankton in their natural, undisturbed state.
Colonization of dlatom aggregates by the dinoflagellate Noctjluca santlllans
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