Distribution of the portunid crab Ovalipes punctatus (De Haan) in Algoa Bay and salinity and temperature tolerances of its zoeae

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Abstract
The three-spot swimming crab Ovalipes punctatus is commonly found in surf zones off sandy beaches in Algoa Bay. It is exclusively marine and occurs down to a depth of 38 m. Large crabs were found close inshore while smaller crabs were predominantly found in deeper water, suggesting that settlement mainly occurs offshore in water 25 – 38 m deep. Gravid females were found closer inshore in shallow water. The zoeae could not tolerate high temperatures (>27,5 °C) or low salinities (<15‰). The optimal temperatures and salinities for survival of the zoeae were 15–22 °C and 34–35‰ respectively. Die driekolswemkrap Ovalipes punctatus word algemeen aangetref in die brandersone van sandstrande van Algoabaai. Die krappe is uitsluitlik seelewend en kom gewoonlik voor tot 'n diepte van 38 m. Groot krappe word hoofsaaklik in vlak water aangetref terwyl kleiner krappe in dieper water aangetref word. Dit blyk dus of die larvale stadia hulle vestig in dieper water (25 – 38 m) en dan kuswaarts beweeg soos die krappe groei. Wyfiekrappe met eiers word hoofsaaklik naby die kus aangetref (maksimumdiepte 32 m). Die larwes kan nie lewe in seewater waarvan die temperatuur hoër is as 27,5 °C en die soutgehalte laer is as 15‰ nie. Die optimale temperatuur en soutgehalte van die seewater vir oorlewing van die larwes is onderskeidelik 14–22 °C en 34–35‰.

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