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Reproductive cycle of the Argentinean surf clam Donax hanleyanus (Philippi, 1845) (Bivalvia: Donacidae)

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Metzner, J. , Herrmann, M. , Laudien, J. , Penchaszadeh, P. E. and Arntz, W. (2006): Reproductive cycle of the Argentinean surf clam Donax hanleyanus (Philippi, 1845) (Bivalvia: Donacidae) , VI Jornadas Nacionales de Ciencias del Mar, Puerto Madryn, Argentina 4 al 8 de diciembre de 2006. .
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Abstract:

Donax hanleyanus (Philippi, 1845) is a free-spawning marine bivalve inhabiting exposed Atlantic intertidal sandy beaches from Rio de Janeiro, Brazil (22°51S) to Mar del Plata, Argentina (38°20S). The reproductive cycle of Argentinean D. hanleyanus was investigated monthly at Santa Teresita, Mar de las Pampas and Faro Querandí from November 2004 to September 2005. Gonadal development was monitored using histological sections (N = 978), condition indices, and numbers and sizes of oocytes. The latter are ripe when they achieve a diameter exceeding 36 µm (up to 83,5 µm). D. hanleyanus attains first maturity at 11 mm anterior-posterior length. The sex ratio was 1:1; hermaphroditism was not recorded. The gametogenic cycle can be divided into an active period from November to March and an inactive period from April to September. However, absolute gonadal inactivity was not ob-served. Rising sea surface temperature is a stimulant for gamete proliferation and spawning, however it remains unexplained why females showed an extended period of gonadal activity at Mar de las Pampas. The condition indices support the histo-logical result showing a positive correlation between the temperature and the inten-sity of reproductive activity. However a histological validation is always needed as unfavourable environmental conditions such as the lack of suitable food and thus starvation impacts the condition of the clams in the same way. The poster discusses further if recruitment is coupled to the spawning period and can thus be predicted from gonadal monitoring.

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