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Multiple annual ovipositions of Cancer setosus along a latitudinal cline: aquaria experiments and analysis of field data

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Fischer, S. and Thatje, S. (2007): Multiple annual ovipositions of Cancer setosus along a latitudinal cline: aquaria experiments and analysis of field data , The Crustacean Society mid-year symposium. 14-17.10.2007, Coquimbo, Chile. .
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Abstract:

Ovigerous females of Cancer setosus are present year-round throughout most of this species extended distributional range along the Chilean/Peruvian Pacific coast (46°S 2°S). However, their annual number of egg-masses remains speculative and as such hasnt been considered in latitudinal comparisons of this species reproduction. To reveal the effect of temperature on egg-mass production and egg-development female C. setosus were held in through-flow aquaria under natural seasonal temperature conditions (16 23 °C) in Antofagasta (23°S), Northern Chile (06/2005 - 03/2006), and at three fixed temperatures (09/2006 - 02/2007) in Puerto Montt (41°S), Central-Southern Chile. Female crabs uniformly produced up to 3 viable egg-masses within 4 1/2 months in Antofagasta and in Puerto Montt (at 19.3 °C). The second oviposition followed the first, and the third the second, after 62.5 d (± 7.6, N = 7) and 73.5 d (± 12.5, N = 11) in Antofagasta and 64.4 d (± 9.8, N = 5) and 67.0 d (± 2.8, N = 2) in Puerto Montt. At the two lower temperatures in Puerto Montt of 15.9 °C and 12.1 °C the production of a second egg-mass was observed after 82.8 d (± 28.9; N = 4) and 137 d (N = 1) respectively. The duration of egg- development from oviposition until larval hatching decreased from 65 d at 12.5 °C to 22.7 d at the observed upper temperature threshold of 22.0 °C. Based on the derived relationship between temperature and the duration of egg-development (y = 239.3175e-0.107x; N = 21, r2 = 0.83) and reports on monthly percentages of ovigerous females from field studies the annual number of egg-masses of C. setosus was calculated. This analysis revealed an annual output of about one egg-mass close to the species northern and southern distributional limits in Casma (9°S) and Ancud (43°S), respectively, while around Coquimbo (29°S) about two and in Concepción (36°S) more than 3 egg-masses are produced per year.

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