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Spatiotemporal distribution and growth pattern of Venus nux (Gmelin, 1791) in the Gulf of Cádiz (Southern Spain)

Marina Delgado1*, Ana Rodríguez-Rua1, Luis Silva1, Esperanza Garcia1, Miguel Cojan1, Sara Roman1 and Raimundo Blanco1
  • 1 Oceanographic Center of Cádiz, Spanish Institute of Oceanography, Spain

The venerid clam Venus nux (Gmelin, 1791) is a species distributed along the Atlantic from southern Portugal to Senegal, and is also present in the Mediterranean (Poppe & Goto 1993). Dense populations seem to be restricted to the Alboran Sea and the Ibero-Moroccan Gulf (southern Spain), usually inhabiting muddy sand bottoms from;30 to 350m in depth (Salas 1996). The decline of catches of commercial bivalves in southern Spain has pointed out an overexploitation of these resources. For this reason, a new research line of shellfish resources have been opened in the last years among them this venerid V. nux (Tirado et al., 2011). In this sense, Tirado et al. (2011) have studied the reproductive cycle of Atlantic and Mediterranean populations of V. nux from southern Spain. The main objectives of the present work are intended to complete this previous study, an particularly were (i) to analyse the spatiotemporal distribution and (ii) to provide an updated age-length key for V. nux from the Gulf of Cádiz (Atlantic waters). First the spatiotemporal distribution of this species was investigated using time series data from trawl surveys conducted in the Gulf of Cádiz. The geographic and bathymetric variability in the population distribution was analyzed. Secondly, an in-depth analysis of the shell and updated estimation of growth parameters of the V. nux population were performed using thin-layer cross section methodolgy. Data on species abundance are derived from 1993-2015 monitoring bottom-trawl surveys (ARSA surveys) conducted to evaluate demersal habitats of the continental shelf and slope of the Gulf of Cádiz. We calculated spatial indices of location in longitude, latitude and depth (i.e. center of gravity, CG) to explore and analyze trends in the 21 yr time series of scientific surveys for each year as decribed by Woillez et al. (2009) and using the RGeostat package in R software (Renard et al., 2014; R Core Team 2015). CG is the mean location of a population and also the mean location of an individual clam taken at random in the field (each data location was weighted by clam density) The inertia is the variance of the location of individuals in the population, that is, the mean square distance between an individual clam and the centre of gravity of the population (Bez, 1997). Additionally, a total of 480 V. nux individuals (size range: 20-43 mm) were collected from 2017. Shell length, height and width from each individual were measured to nearest 0.1 mm with a digital vernier caliper to produce length frequency distributions and to estimate relative growth. To determine the species microgrowth pattern by means of the thin-layer technique, a modified protocol of Schenk et al. (1984) for calcified tissues was applied. The left valve of each clam was embedded in poly methyl metachrylate, and thin sections from the umbo to the ventral edge of 100 µm thickness were obtained using low-speed diamond (ISOMET 4000) and grounding and polishing with sequential grinders (sandpaper from 120 to 1 µm) (Delgado et al., 2017). After the identification of annual growth bands, the distance between the umbo and the annual ring was measured using the image analysis software NIS-Elements AR 3.2. Because these measurements are relative to shell height, they were transformed into shell length using the morphometric relationship. Figure 1 shows the spatial distribution of V. nux densities as well as the center of gravity (CG) and inertia (latitude and longitude) in 2015. Geographical range distribution varied between 36º53’40” and 36º25’31” in CG latitude, and -6º35’3” and -7º5’43” in CG longitude. Figure 2 displays the time series of changes in the center of gravity in depth. CG depth varied between 66 and 103 m and a trend towards deeper waters can be observed. The morphometric relationships between shell height (SH), shell width (SW) and shell length (SL) were: SH = 1.096 SL 0.936 (r2: 0.94) and SW=0.837 SL0.937 (r2:0.85). The embedding in poly methyl metachrylate and the subsequent procedures of sectioning, grounding and polishing until obtain thin sections allowed for highly detailed direct observations and analysis of the inner structure of valves. V. nux shell growth pattern is printed in the external prismatic layer. Growth bands were clearly visible in sections of analyzed shells (Fig. 3). Wide translucent zones alternate with opaques zones, probably showing the alternation of fast and slow growth periods (Fig. 3). Translucent growth lines were also present either on the umbo or close to the edge.

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Figure 2
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Figure 3
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Acknowledgements

We thank the scientific and technical staff of ARSA surveys and its funding support (project PESCADIZ-IEO). The present study was funded within the framework of the project “VENUS” (Estudio integral de los bancos naturales de moluscos bivalvos en el Golfo de Cádiz para su gestión sostenible y la conservación de sus hábitats asociados) (0139_VENUS_5_E; INTERREG-POCTEP).

References

Bez, N. (1997). Statistiques individuelles et géostatistique transitive en écologie halieutique. [PhD Thesis]. [Paris]: Ecole Nationale Supérieure des Mines. Delgado, M., Silva, L., Gómez, S., Masferrer, E., Cojan, M., and Gaspar, M.B. (2017). Population and production parameters of the wedge clam Donax trunculus (Linnaeus, 1758) in intertidal areas on the south west Spanish cost: Considerations in relation to protected areas. Fish. Res. 193, 232-241. Poppe, G. T., and Goto, Y. (1993). “Scaphopoda, Bivalvia, Cephalopoda” in: European sea shells vol.2, ed. C. Hemmen (Wiesbaden, Christa Hemmen), pp. 1–121. Renard, D., Bez, N., Desassis, N., Beucher, H., Ors, F, and Freulon, X. (2014). RGeostats: the geostatistical package [10.0.8]. Mines Paris Tech/ARMINES, Fontainebleau. R Core Team. 2015. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna. www.r-project.org. Salas, C. (1996). Marine bivalves from off the southern Iberian Peninsula collected by the Balgim and Fauna 1 expeditions. Haliotis 25, 33–100. Tirado, C., Rueda, J.L., and Salas, C. (2011). Reproductive Cycles in Atlantic and Mediterranean Populations of Venus nux Gmelin, 1791 (Bivalvia: Veneridae), from Southern Spain. J. Shell. Res. 30(3), 813-820. Schenk, R.K., Olah, A.J., and Hermann, W. (1984). “Preparation of calcified tissues for light microscopy” in: Methods of calcified tissue preparation, ed. G.R.Dickson(Elsevier Science Publishers, Amsterdam), pp. 1-56. Woillez, M., Rivoirard, J., and Petitgas, P. (2009). Notes on survey-based spatial indicators for monitoring fish populations. Aquat. Living Resour. 22, 155-164.

Keywords: Venus nux, spatiotemporal distribution, Gulf of Cádiz, Growth pattern, geostatistics

Conference: XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019.

Presentation Type: Poster Presentation

Topic: Fisheries, Aquaculture and Biotechnology

Citation: Delgado M, Rodríguez-Rua A, Silva L, Garcia E, Cojan M, Roman S and Blanco R (2019). Spatiotemporal distribution and growth pattern of Venus nux (Gmelin, 1791) in the Gulf of Cádiz (Southern Spain). Front. Mar. Sci. Conference Abstract: XX Iberian Symposium on Marine Biology Studies (SIEBM XX) . doi: 10.3389/conf.fmars.2019.08.00065

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Received: 29 Apr 2019; Published Online: 27 Sep 2019.

* Correspondence: Mx. Marina Delgado, Oceanographic Center of Cádiz, Spanish Institute of Oceanography, Cádiz, Spain, marina.delgado@ieo.es