The use of coastal cabled video-observatories to monitor seasonal changes in shallow water fish community

V. Sbragaglia 1, J. Aguzzi 1, G. Santamaria 2, A. Manuel 2, J. Del Rio 2, M. Nogueras 2, F. Sardà 1 1 Marine Science Institute (ICM-CSIC) - Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain 2 Technological center of Vilanova i la Geltrú (SARTI-UPC) - Rambla de l'exposició s/n, 08800, Vilanova i la Geltrú, Spain

Abstract-Seasonality in marine fish communities is usually community temporal fluctuations at scales larger than one year studied by using different sampling techniques (e.g. visual census in are poorly known and dir ect observations in the field are of shallow water or trawling in deeper areas) that are hard to perform over long periods with a high frequency of data recording. extreme importance to obtain valuable information. Furthermore, the coupling with fluctuations in key habitat Seasonality in marine fish communities is usually studied by parameters (e.g. light, temperature, salinity, and turbidity) is not a using different sampling techniques (e.g. visual census in simple task to accomplish. Cabled video-observatories implemented shallow water or trawling in deep water) that are of difficult with multiparametric sensors for habitat monitoring are allowing application over long periods of time at a high frequency. Only for the first time the continuous and long term recording of marine communities' dynamic (e.g. day-night, seasonal, and predator-prey recently cabled video-observatories were applied for this fluctuations). In this scenario, the OBSEA video-cabled observatory purpose [3]. However, the coupling with surrounding has been recently deployed (2009) within a coastal area in the environ mental fluctuations (e.g. light, temperature, salinity, western (Vilanova i la Geltrú - Spain) at a depth and turbidity) is of primary importance in order to obtain of 20 m. It is endowed with a video camera and a CTD. The OBSEA reliable cause-effect explications, but such multiparametric is located in a sandy area in which are placed numerous artificial reefs that pro tect the ground from trawling. The OBSEA is placed in measurement is not a simple task to accomplish. The recent front of one of these reefs. Accordingly, we report here only the development of cabled video-observatories implemented with preliminary results of this study consisting of one month video- multiparametric sensors is allowing for the first time, the monitoring at 30 min frequency of the local fish community in continuous and prolonged recording of marine communities' association with environmental fluctuations. In the future this composition in response to different deterministic cycles (e.g. analysis will cover an entire year. Waveform analysis was carried out in order to detect the occurrence of significant daily periodicity day-night) and stochastic perturbations (e.g. storms). in species abu ndance, while time series of community fluctuations In this scenario, the OBSEA video-cabled seafloor were related to environmental parameters (temperature and observatory (www.obsea.es) has been recently deployed [4] pressure at the sea bottom). In both cases particular attention was within a coastal area in the western Mediterranean Sea directed to interacting species such as predators and preys. (Vilanova i la Geltrú - Spain). Accordingly, the aim of this Preliminary results highlight how cabled observatories could contribute to study community's dynamic. Finally, the analysis of study is to report the preliminary results of one month the entire year observations will allow to study changes of the continuous (night and day) video-monitoring at 30 min artificial reef community among different seasons. Moreover, the frequency of the local fish com munity and couple fish visual long term data from OBSEA could permit to evaluate possible counts with environmental fluctuations (i.e. photoperiod, climate changes effects on the local fish community . temperature, and meteorological perturbations). Daily activity rhythms are also investigated with particular attention to interacting species (predators and preys) in order to elucidate I. INTRODUCTION how community changes could be triggered. movement patterns in time and space are fundamental features to understand ecology and to II. MATERIAL AND METHODS design effective conservation and resource management The OBSEA video-cabled seafloor observatory is located strategies [1]. As regard to time, marine species, such as all within a coastal area in front of Vilanova i la Geltrú (Spanis h living organisms, exhibit biological rhythms that respond to Western Mediterranean) at a depth of 20 m (Fig. 1). OBSEA chang es in photoperiod, food availability, temperature, tides, as lays in a sandy area, in which are placed numerous artificial well as to other organisms [2]. Behavioral rhythms are usually reefs that protect the area from trawling. The OBSEA is placed studied at species level, while the resulting community in front of one of these reefs. The platform is endowed with a dynamic, as the result of all interacting species, is still poorly rotating (360°) video camera (Ocean Presence Technologies characterized. Also, mechanisms trough which species interact OPT-06 Underwater IP Camera, OpticCam) with a resolution (e.g. predator prey fluctuations) determining the overall

978-1-4673-5948-1/13/$31.00 ©2013 IEEE III. PRELIMINARY RESULTS A In this study we preliminary present the result of one month video-imaging survey (1-31 January 2012). We inspected a total of 1488 images, acquired during one month. One of the most important constrains was the water turbidity. In poor visibility condition an image could not be used since individuals were nor distinguishable or countable. In Table I we reported the fish faunal list as detected on the artificial reef over one month. Some frames are presented in Fig. 2 as an example of the field of view considered for fish classification and counting. The most representative species were C. followed by D. annularis , S. maena , and O. melanura , all commonly known as gregarious. Other important species at the artificial B C reef belonged to the genus Diplodus ( D. sargus , D. vulgaris , D. cervinus ). The common ( Dentex dentex ) was also observed representing an important predator among all the recognized species. Other species such as Symphodus sp., S. cabrilla , and C. julis were also observed. In Table I "unknown" refers to all individuals that the trained operator was not able to recognize, principally due to a high turbidity of the water. Figure 1. Different point of view of the OBSEA cabled video-observatory. A: lateral point of view, where the circle indicates the position of the video TABLE I camera and the arrow represents the direction in which images can be acquired SPECIES RECOGNIZED BY THE TRAINED OPERATOR DURING A REPRESENTATIVE in relation to the artificial reef (i.e. partially visible on the right side); B: lateral MONTH . TOTAL NUMBER OF COUNTED SPECIES ARE REPORTED TOGETHER WITH view of the OBSEA platform; C: a top view of the OBSEA, in which are NOT RECOGNIZED INDIVIDUALS . visible the artificial reef and the observatory together (the arrow indicates what stated in A). Scientific name Common name total of 640 x 480 pixels. A CTD (Seabird SBE-37SMP) can be used to record the characteristics of the water mass Damselfish 1586 surrounding the observatory (temperature, salinity, and Annular seabream 924 pressure). Spicara maena Blotched picarel 637 The protocol for image acquisition was completely Oblada melanura Saddled seabrea m 471 automated with a sampling frequency of 30 min. Since the video camera can rotates at 360°, the shooting position was Diplodus sargus White seabream 232 determined as fixed and fully including the reef (Fig. 1). For Two -banded seabream 168 image acquisition during night, OBSEA was equipped with a Scorpaena Black scorpionfish 183 lighting system, which automatically switched on and off 10 s Diplodus cervinus Zebra seabream 66 prior and after the camera shooting. The total power of the Apogon imberbis Cardi nal fish 55 light was 30 W that generated an emission power of 1300 lumens. Trachurus trachurus Horse mackerel 39 Once acquired, all images were visually inspected by a Dentex dentex Common dent ex 17 trained operator in order to classify and count all species Diplodus puntazzo Sharpsnout seabream 7 according to [5]. In case of schooling (many individuals Coris julis Rainbow wrasse 7 together as in the case of Chromis chromis ), we set arbitrarily maxima equal to 100. Waveform analysis was performed using Serranus cabrilla Comber 3 the software el-temps ( www.el-temps.com ) developed by Prof Symphodus melanocercus Wrasse 2 Diez Noguera (University of Barcelona). Only species with a Spondyliosoma cantharus Black seabream 2 number of counts major than 15 was considered, while Symphodus mediterraneus Axillary wrasse 1 unknown species were not analyzed individually, but plotted together with all the community. Sciaena umbra Brown meagre 1 Un known - 860 Total individual counted 5261 Total species recogniz ed 4401 A B 5 A

2,5

0 C D 3 B 2

1

0 2 Figure 2. Some of the species recognized during the one-month video C observation. A: ( Dentex dentex ); B: Zebra seabream (Diplodus cervinus ); C: Cardinal fish ( Apogon imberbis ) during a nocturnal image; D: A schooling of Annular seabream ( Diplodus annularis ) with some 1 individuals of White seabream ( Diplodus sargus ). Average numberindividuals of

Waveform analysis output plots indicated the occurrence of 0 a diel activity rhythm for all classified and counted species. 0,1 Four representative species of the artificial reef ( Cromis D chromis , Spicara maena , Oblada meanura , and Dentex dentex ) were chose as example of diel fluctuations of counted 0,05 individuals (Fig. 3). We can speculate considering the visual counts of individuals as proxy of their swimming activity. Species exhibited different patterns with a major peak occurring during different hours of the day. C. chromis showed 0 a midday centered activity, S. maena a dusk peak, while O. 0 06:00 12:00 18:00 24:00 melanura a weak crepuscular (dusk and dawn) activity. D. dentex exhibited a pronounced peak of activity just before Time of the day sunset, in concomitance with the peak of S. maena . Another weak peak is observed just after sunrise that could be related to Figure 3. Waveform analysis for four selected species. An average the same weak peak of O. melanura. photoperiod (sunrise at 7:15 and sunset at 17:00) was chosen as representative Finally, the fluctuation in visual for the whole community of the average day-night regime during one month. A: Chromis chromis ; B: Spicara maena ; C: Oblada me lanura ; D: Dentex dentex. Top Black and white (individuals of all species considering also the “ unknown ” bars indicate night and day respectively. Also shadowed areas indicate night category) was analyzed focusing on the presence of a predator hours. The horizontal line represents the Midline Estimating Statistic Of such as the common dentex (Fig. 4), together with important Rhythm (MESOR) , which was used as a daily mean to estimate significant abiotic factors such as temperature and pressure. A total increments in visual co unts. number of 17 Dentex were counted during one month. Their presence (identified by the arrows in Fig. 4) coincides with IV. DISCUSSION peaks of abundance in community fluctuations. Moreover, the predator was never observed when the peak of community In this study, we presented the preliminary results of a abundance was occurring in concomitance with an abrupt cabled observatory video-monitoring in a coastal fish water temperature decrease (e.g. days 4, 14, 20). The general community close to an artificial reef. The long-term recording view of the entire month, also considering pressure at 30 min frequency and the associated habitat data measurement, seems to suggest that the presence of Dentex measurement will allow us to answer different questions could be related to meteorological stability. That stability is regarding the community response based on predator-prey detectable by the absence of noise (waves or storms) in the relationships and contingent meteorological changes. However, pressure measurement (i.e. when tidal cycle is clearly one should always bears in mind that any result on the distinguishable such as days 14-19). community dynamic we presented here, is strongly constrained 20,2 ) dBar

( 19,8

19,4 Pressure 100 15

90

80 14,5 Temperature 70

60

50 14 individuals

40 (C ° ) N. of N. 30 13,5 20

10

0 13 1 7 15 22 31 Time ( January )

Figure 4. Fluctuation s in visu al counts form fishes of all species within the local community from 1 to 31 of January ( grey line ). Temperature fluctuations are represented by dotted line while pressure fluctuations are reported by the black line . A rrows indicated the presence of D. dentex (normal arrows : 1 individual; Bold arrow : 2 individuals). by the reduced and fix field of view of the video camera (Fig. information would be needed (e.g. temporized information on 1). Moreover, the swimming activity is of course an indicator the stomach content of the predator). of behavioural rhythms, but it should be taken with precaution Time series presented in Fig. 4 evidenced some possible [6]. In fact, fish counts increases at a single video-location do explanations to describe which are the habitat conditions not directly reveal the activity or resting phase of species. affecting the predator behavior ( D. dentex ). First, within a Finally, the elevated turbidity impairing visibility created biological context, the presence of dentex could be coupled difficulties at the moment to count and recognize individuals at with the presence of its preys. This is also supported by the beginning of the time series. This is reflected in the waveform analysis within a diel scale (see Figure 3). Secondly, apparent lacking of rhythmicity at days 1-5 and 8-9 (Fig. 4). the dentex seemed to be affected by abrupt decreases of water Dentex dentex could be considered as the most important temperature at a diel temporal scale. Also, its presence at the predator of the artificial reef, while the other three species we artificial reef community was related to the meteorological screened for behavioral rhythms by waveform analysis (i.e. stability, which is given by the sea conditions (wave's action). Cromis chromis , Spicara maena , Oblada meanura ; see Figure In the future a complete screening of the artificial reef 3) its common preys [7]. Waveform analysis output plots of throughout one year will permit to clarify the role of these two these four species (Fig. 3) seems to indicated a correlation habitat parameters and also ascertain how biological rhythms between preys and predators diel activity. are modulated by interspecific interactions [2; 10]. Diel activity rhythms at OBSEA during one month have What is presented here evidenced the potential for cabled been recently studied by [6] using the same technological video-observatories in the monitoring of seasonal changes in approach. An important technological remark previously shallow water fish communities. In the next future, our aim is discussed by [6] is that the abrupt decrease of individuals to analyze the complete data set (January-December 2012) in during the night could coincide with a putative resting phase of the following way: ( i) detect differences in fish assemblage fish onto the seabed that has been already documented for (focusing on some key species); ( ii ) compare diel rhythms some species and commonly observed by scuba divers during among different seasons, focusing on the modifications of nocturnal dives [8; 9]. However, as stated at the beginning of interspecific relationship such as predator-prey; ( iii ) determine this section, results taken by a single still camera source does what are the effects of deterministic cycles (i.e. day-night) not directly indicate whether increase their counts for respect to stochastic perturbations (e.g. storms). Finally, the an increase of swimming activity or conversely for resting analysis of video/frames acquired by the OBSEA will permit to quietly more time in front of the camera. Other more direct evaluate the role of artificial reefs on the dynamic of coastal fish communities. In the future, the possibility to have a long term observation throughout many years (historical data) could also permit to evaluate possible effects of the climate change and other human-stressors on the local fish community.

ACKNOWLEDGMENT This research was funded by ESONET (European Seas Observatory NETwork; Framework Program-FP7 Infrastructures-2005-Global-4, ESONET 036851-2), EMSO (European Multidisciplinary Seafloor Observation; Framework Program-FP7 Infraestructures-2007-1, Proposal 211816), RITFIM (CTM2010-16274), and ACI2009-0983 (Operatividad laboratorio Submarino OBSEA). Access to the ADCP and associated sensors used in this work was provided by ICM- CSIC, and they belong to the Coastal Ocean Observatory (http://coo.icm.csic.es). Researchers from the CSIC and UPC are members of the Associated Unit Tecnoterra. VS is a Predoctoral Fellow within the Formation Personal Investigador (FPI) scheme (MICINN). JA is a Ramón y Cajal Program (MICINN) Postdoctoral Fellow.

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