Data/hora: 08/06/2024 09:43:21

Provedor de dados: 	20	
País: 	Belgium	
Título: 	Biologie, abondance et cartographie de deux espèces de bivalves : l’huitre perlière &lt;Pinctada radiata&gt; et la coque glauque &lt;Cerastoderma glaucum&gt; dans le golfe de Gabes

Biology, abundance and cartography of two bivalve species: the pearl oyster &lt;Pinctada radiata&gt; and the cockle &lt;Cerastoderma glaucum&gt; in the Gulf of Gabes (South of Tunisia)	
Autores: 	Derbali, Abdelkarim.	
Data: 	2014-05-06	
Ano: 	2011	
Palavras-chave: 	Abundance; Biology; Shellfish.	
Resumo: 	The pearl oyster Pinctada radiata and the cockle Cerastoderma glaucum are among the most abundant bivalve molluscs in southern Tunisian waters. These species are not currently subject to any investigation despite their important economic value in the world. For this reason, their biological parameters, their spatial distribution and their stock assessment were undertaken in the Gulf of Gabes. The reproductive cycle was studied in relation to variations of the environment parameters. The specimens were collected monthly during one year (2007) in sites of El Kraten and El Jorf (Kerkennah Islands) for the first species and sites of Sidi Mansour and El Hicha (North of Sfax and Gabes) for the second. An intraspecific polymorphism biometric trait for P. radiata and C. glaucum was performed using statistical comparison methods and multivariate analysis methods. Results of analyzes showed heterogeneity between populations. For Pinctada radiata, the sex ratio unbalanced, although males dominated among smaller individuals and females were predominant in larger size-classes. Evidence of protrandric hermaphroditism was observed with males maturing earlier than females. Seasonal changes in macroand microscopic properties of the gonads of both sexes showed that this species displayed a clearly defined annual reproductive cycle with a major peak in summer and a minor peak in autumn. The onset of reproduction appears to be triggered by the rising seawater temperature during spring and summer. P. radiata exhibited a short resting phase that occurred simultaneously in both sexes from the end of December until early February. For Cerastoderma glaucum, the overall samples presented a balanced sex ratio, with males dominating among smaller individuals and females predominating in larger size classes. The seasonal changes assessed through macro- and microscopic properties in the gonads of both sexes indicated a clearly defined annual reproductive cycle. Reproductive activity of C. glaucum was greatest from spring to late autumn, with two reproductive peaks (May and November). Gametogenic activity in both sexes was apparently triggered by the rising seawater temperature during spring and summer. These results support previous findings of latitudinal changes in the reproductive behaviour of C. glaucum. Due to the extensive period of gonadal activity, C. glaucum exhibited a short resting phase that occurred simultaneously in both sexes throughout January and February.  In terms of stock assessment and spatial distribution of P. radiata, results showed a scattered distribution pattern of the species according to location and depth ranging between 0 and 145 ind.m-². P. radiata was encountered from the intertidal zone to 40 m depth, with a highest population densities recorded at depth range of 2-20 m. The total stock was estimated to be 27584.9 ± 11504.5 million individuals. Oyster distribution seems influenced by the substrate type. This high population of pearl oysters was associated with large cover of seagrass Posidonia oceanica which provides an excellent substratum for attachment. The littoral zone seems not to be the preferred habitat for the proliferation of this immigrant species. Oysters’ size increased steadily with depth, ranging from a mean of 37.98 ± 0.40 mm SH at 0-1 m to 60.98 ± 0.68 mm SH at 20-100 m depth range. Size structure analysis showed that deep water population was dominated by large individuals reaching 96 mm SH.  In terms of geographical occupation and stock assessment of C. glaucum, results showed a scattered distribution pattern of the species according to location. The consequence was a remarkable biomass which represented 4736 tons of total fresh weight and high abundance levels reaching over 1982 million individuals estimated in the area of 20122 hectares.   In conclusion, this study is the first report of an extraordinary abundance of Pinctada radiata and Cerastoderma glaucum in southern Tunisian waters. It gives more information about their stocks in the colonization area. The data may help to determine future quantitative changes indicating trends in the study area that are exposed to various factors of environmental conditions and human activities.	
Tipo: 	Theses and Dissertations	
Idioma: 	Francês	
Identificador: 	http://hdl.handle.net/1834/5404	
Formato: 	170	
Fonte: 	http://creativecommons.org/licenses/by-nc/3.0/