Reproductive and population aspects of Mactra stultorum (Linnaeus, 1758) in the littoral of Huelva (SW Spain)
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1
Oceanographic Center of Cádiz, Spanish Institute of Oceanography, Spain
The surf clam Mactra stultorum (Linnaeus, 1758) is widely distributed in sandy bottoms at depths ranging between 1 and 30 m along the Black Sea, Mediterranean Sea and Atlantic Ocean, from France to Senegal. This species is part of the accompanying fauna of commercial species such as Chamelea gallina and Donax trunculus. M. stultorum is presented with two different and well-defined morphotypes, easily distinguishable by the colour of the shell: the white variant and the brownish radiating bands variant (Guarniero et al., 2010). Despite its abundance and commercially importance in many countries, no studies regarding its reproductive cycle have been carried out to date in the Atlantic coasts. The aim of this study is to provide information on aspects of the gametogenic cycle and the population structure of M. stultorum in its two morphological variants by means of histological analysis, physiological indices and length-frequency distribution.
To achieve this objective, populations of M. stultorum in its two variants were monitored during one year. Samples were collected monthly from the lower part of the intertidal area of Doñana beach (36°48′20.6 N/6°23′8.29 W) using two hand-dredges, one with an experimental mesh size (3 x 3 mm) to allow the collection of the smallest individuals and juveniles and the other with a commercial mesh size (7x7 mm). Shell length (antero-posterior axis) of retained individuals was recorded using a digital vernier caliper to the nearest 0.01 mm to produce length-frequency distributions. Additionally, twenty five individuals for each morphotype were sampled monthly for histological analysis. A piece of visceral mass was taken for each individual and fixed in buffered formaldehyde (4%), dehydrated through ethanol series and subsequently embedded in hydroxyethylmethacrylate (Technovit 7100). Sections (5 μm thick) were cut and stained with Harris Hematoxylin and eosin (H-E). Histological preparations were observed under a light microscope (Nikon Eclipse 90i) and the stages of gonad development were scored according to the scale proposed by Delgado et al. (2013) for C. gallina. To determine the condition index twenty five individuals for each morphotype were sampled per month. Body soft parts and valves were separated and dried at 100º C during 24 h (until constant weight). Soft tissues and valves were then weighted with a precision balance to the nearest 0.0001 g. The index used was:
CI = Soft tissue dry weight/Valves dry weight
Data on surface sea water temperature was collected in situ and samples of water were taken for chlorophyll a determination.
The reproductive cycle of marine bivalves is influenced by a number of environmental factors including temperature and food availability. Water temperature showed high fluctuations along the study year, with maximum values in August (26ºC) and minimum in December (10ºC). The histological results suggest that spawning occurs during spring and summer when sea water temperature was higher. The condition index showed a similar pattern, with a high peak in spring and a decrease during the summer that can be related to a spawning event. The sexes in M. stultorum were clearly separate and sexual dimorphism was not observed. No significant differences between both morphotypes were found. These results are in concordance with a previous study carried on M. stultorum from Tunisia (Chetoui et al., 2018). Several cohorts were identified in the monthly length-frequency distributions throughout the study period.
Acknowledgements
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) and the project “FEMP_AND_04” (Programa plurianual en el ámbito de la recopilación de datos de la comunidad autónoma de Andalucía: Análisis de la pesquería de coquina en el caladero del Golfo de Cádiz)
References
Chetoui, I., Telahigue, K., Bejaoui, S., Rabeh, I., Ghribi, F., Denis, F., ElCafsi, M. (2018). Annual reproductive cycle and condition index of Mactra corallina (Mollusca: Bivalvia) from the north coast of Tunisia. Invertebrate Reproduction and Development, DOI: 10.1080/07924259.2018.1529636.
Delgado, M., Silva, L., Juarez, A. Aspects of reproduction of striped venus Chamelea gallina in the Gulf of Cadiz (SW Spain): Implications for fishery management. Fisheries Research. 146: 86-95.
Guarniero, I., Plazzi, F., Bonfitto, A., Rinaldi, A., Trentini, M., Passamonti, M. (2010). The bivalve mollusc Mactra corallina: genetic evidence of existing sibling species. Journal of the Marine Biological Association of the United Kingdom. 90(3): 633-644.
Keywords:
Mactra stultorum,
length-frequency distribution,
Gametogenic cycle,
Huelva (Spain),
condition index
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:
Rodriguez-Rua
A,
Silva
L,
Cojan
M,
Blanco
R,
Roman
S,
García
E and
Delgado
M
(2019). Reproductive and population aspects of Mactra stultorum (Linnaeus, 1758) in the littoral of Huelva (SW Spain).
Front. Mar. Sci.
Conference Abstract:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) .
doi: 10.3389/conf.fmars.2019.08.00066
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Received:
02 May 2019;
Published Online:
27 Sep 2019.
*
Correspondence:
Mx. Ana Rodriguez-Rua, Oceanographic Center of Cádiz, Spanish Institute of Oceanography, Cádiz, Spain, ana.rodriguez@ieo.es