Francesc Sardà

The new seafloor observatory (OBSEA) for remote and long-term coastal ecosystem monitoring

A suitable sampling technology to identify species and to estimate population dynamics based on individual counts at different temporal levels in relation to habitat variations is increasingly important for fishery management and biodiversity studies. In the past two decades, as interest in exploring the oceans for valuable resources and in protecting these resources from overexploitation have grown, the number of cabled (permanent) submarine multiparametric platforms with video stations has increased. Prior to the development of seafloor observatories, the majority of autonomous stations were battery powered and stored data locally. The recently installed low-cost, multiparametric, expandable, cabled coastal Seafloor Observatory (OBSEA), located 4 km off of Vilanova i la Gertrú, Barcelona, at a depth of 20 m, is directly connected to a ground station by a telecommunication cable; thus, it is not affected by the limitations associated with previous observation technologies. OBSEA is part of the European Multidisciplinary Seafloor Observatory (EMSO) infrastructure, and its activities are included among the Network of Excellence of the European Seas Observatory NETwork (ESONET). OBSEA enables remote, long-term, and continuous surveys of the local ecosystem by acquiring synchronous multiparametric habitat data and bio-data with the following sensors: Conductivity-Temperature-Depth (CTD) sensors for salinity, temperature, and pressure; Acoustic Doppler Current Profilers (ADCP) for current speed and direction, including a turbidity meter and a fluorometer (for the determination of chlorophyll concentration); a hydrophone; a seismometer; and finally, a video camera for automated image analysis in relation to species classification and tracking. Images can be monitored in real time, and all data can be stored for future studies. In this article, the various components of OBSEA are described, including its hardware (the sensors and the network of marine and land nodes), software (data acquisition, transmission, processing, and storage), and multiparametric measurement (habitat and bio-data time series) capabilities. A one-month multiparametric survey of habitat parameters was conducted during 2009 and 2010 to demonstrate these functions. An automated video image analysis protocol was also developed for fish counting in the water column, a method that can be used with cabled coastal observatories working with still images. Finally, bio-data time series were coupled with data from other oceanographic sensors to demonstrate the utility of OBSEA in studies of ecosystem dynamics.

Responses of deep-water shrimp populations to intermediate nepheloid layer detachments on the Northwestern Mediterranean continental margin

A clear link between the distribution of intermediate nepheloid layer detachments on the Northwestern Mediterranean continental margin and the population structure of five congeneric megafaunal species of deep-water benthic shrimps inhabiting different depth ranges between 100 and 1100 m was found. The results of the multidisciplinary approach presented in this study provide evidence for the ecological conditions that affect the spatial distribution of juveniles and females of a deep-water fishery resource. The significantly higher occurrence of juveniles and females in regions where intermediate nepheloid layers detach from the seabed allows us to define these areas as potential deep-water nursery habitats. The spatial recognition of these habitats could contribute to the management of the stocks concerned and afford a basis for protecting these vulnerable habitats from fishing pressure. Overall, our findings furnish support for the hypothesis that deep-water benthic biological processes are linked to pelagic processes, suggesting that the detachments of intermediate nepheloid layers serve as one of the physical links between these two environments.

Light intensity determines temporal niche switching of behavioral activity in deep-water Nephrops norvegicus (Crustacea: Decapoda).

The temporal distribution of behavioral programs throughout the 24-h day, known as temporal niche of a species, is determined by ecological factors that directly affect the adaptive value of the timing of specific behaviors. Temporal niche switching has been described in several species and is likely adaptive in habitats where the daily timing of those factors changes. Benthic species whose habitats span a wide range of water depths are exposed to considerable depth-dependent environmental changes. Temporally scheduled trawl surveys of the Norway lobster, Nephrops norvegicus, reveal that animals emerge from burrows at night on the shallow shelf (10-50 m deep), at crepuscular hours on the lower shelf (50-200 m), and at daytime on the slope (200-400 m). The mechanisms underlying nocturnality/diurnality switches are chiefly unknown, and Nephrops offers a unique model for their study. The depth-dependent decrease in luminance is a likely candidate determining the temporal distribution of behavior. The authors explored this possibility in the laboratory by exposing Nephrops to light:dark (LD) cycles of 470-nm monochromatic lighting that mimic conditions at the 100-m-deep shelf (10 lux) or the 300-m slope (0.1 lux). Two groups of animals were respectively exposed to each light intensity according to the following protocol: an initial 12:12 LD stage followed by constant darkness (DD), followed in turn by a second 12:12 LD stage. Activity at the burrow opening (door-keeping = DK), as well as full emergence (E), was continuously monitored. Under 10-lux LD cycles, most animals showed nocturnal DK activity—with some being crepuscular or diurnal—and all animals showed nocturnal E activity. In contrast, both behaviors were clearly diurnal in animals under 0.1-lux LD cycles. The phase of the nocturnal and diurnal DK rhythms detected respectively at 10 and 0.1 lux upon release into DD revealed that these rhythms are entrained circadian rhythms. The present data indicate that nocturnality/diurnality switches in Nephrops in its natural habitat, evidenced by captures at different depths, are likely determined by light intensity. This temporal niche switching involves different patterns of photic entrainment, leading to bona fide circadian diurnal or nocturnal phenotypes, as well as exogenous masking of behavioral outputs.

Nephrops norvegicus population and morphometrical characteristics in relation to substrate heterogeneity

Abstract Norway lobster ( Nephrops norvegicus ) populations were sampled by trawling over the Catalan Sea (NW Mediterranean) continental shelf and slope, covering the whole depth range for the species in the area studied (about 100–700 m). Sediment samples were collected and analysed to characterise the substrate of this burrowing decapod crustacean. Univariate and multivariate statistical methods were employed to study some biological parameters of the Nephrops populations and their relationship to environmental parameters. Cluster analysis of sediments indicated two main substrate environments in the study area: shelf and slope. Statistical analysis of Nephrops morphometrical and population data showed that Norway lobsters dwelling on the shelf differed significantly from slope-dwelling individuals in morphometrical measurements, relative growth and female sexual maturity. Canonical correlation analysis allowed us to establish a correspondence between these biological differences and some variables of the sediment, grain size and redox potential. It is argued that grain size and, to a lesser extent, redox potential determine relative growth and morphometrical differences in NW Mediterranean Nephrops populations. Temperature differences play a minor role, explaining only the advancement of sexual maturation in female individuals of the slope.

A New Laboratory Radio Frequency Identification (RFID) System for Behavioural Tracking of Marine Organisms

Radio frequency identification (RFID) devices are currently used to quantify several traits of animal behaviour with potential applications for the study of marine organisms. To date, behavioural studies with marine organisms are rare because of the technical difficulty of propagating radio waves within the saltwater medium. We present a novel RFID tracking system to study the burrowing behaviour of a valuable fishery resource, the Norway lobster (Nephrops norvegicus L.). The system consists of a network of six controllers, each handling a group of seven antennas. That network was placed below a microcosm tank that recreated important features typical of Nephrops’ grounds, such as the presence of multiple burrows. The animals carried a passive transponder attached to their telson, operating at 13.56 MHz. The tracking system was implemented to concurrently report the behaviour of up to three individuals, in terms of their travelled distances in a specified unit of time and their preferential positioning within the antenna network. To do so, the controllers worked in parallel to send the antenna data to a computer via a USB connection. The tracking accuracy of the system was evaluated by concurrently recording the animals’ behaviour with automated video imaging. During the two experiments, each lasting approximately one week, two different groups of three animals each showed a variable burrow occupancy and a nocturnal displacement under a standard photoperiod regime (12 h light:12 h dark), measured using the RFID method. Similar results were obtained with the video imaging. Our implemented RFID system was therefore capable of efficiently tracking the tested organisms and has a good potential for use on a wide variety of other marine organisms of commercial, aquaculture, and ecological interest.

A new morphometric implemented video-image analysis protocol for the study of social modulation in activity rhythms of marine organisms

Video-image analysis can be an efficient tool for microcosm experiments portraying the modulation of individual behaviour based on sociality. The Norway lobster, Nephrops norvegicus is a burrowing decapod the commercial capture of which occurs by trawling only when animals are engaged in seabed excursions. Emergence behaviour is modulated by the day-night cycle but a further modulation occurs upon social interaction in a still unknown fashion. Here, we present a novel automated protocol for the tracking of the movement of different animals at once based on a multivariate morphometric approach. Four black and white tags were customized according to a precise geometric design. Shape Matching and Complex Fourier Descriptors analyses were used to track tag displacement through consecutive frames in a 7-day experiment under monochromatic blue light (480 nm)-darkness conditions. Shape Matching errors were evaluated in relation to tag geometry. Time series of centroid coordinates in pixels were transformed in centimetres. The FD analysis was slightly less efficient than the Shape Matching, although more rapid (i.e. up to 20 times faster). Nocturnal rhythms were reported for all animals. Waveform analysis indicated marked differences in the amplitude of activity phases as proof of interindividual interaction. Total diel activity presented a decrease in the rate of out of burrow locomotion as the testing progressed. N. norvegicus is a nocturnal species and present observations sustain the efficiency and fidelity of our automated tracking system.

Studying the behaviour of Norway lobster using RFID and infrared tracking technologies

Different solutions are presented to study species in laboratory. The proposed designs used infrared and RFID technology to locate and track the species in the zone of analysis, the data is processed to extract information about their activity and behaviour.