Pergamon J. therm. Bid. Vol. 21, No. 516, 319-322, 1996 pp. Copyright 0 1996 Elsevier Science Ltd PII: so306-4565(%)ooo13-7 Printed in Great Britain. AU rights reserved 0306-4565/96 $15.00 + 0.00 BEHAVIORAL THERMOREGULATION OF BULLA GOULDIANA (GASTROPODA: OPISTHOBRANCHIA: CEPHALASPIDEA) FERNANDO DiAZ HERRERA,* FERNANDO BUCKLE RAMIREZ, BENJAMIN BARON SEVILLA and CLAUDIA FARFAN Departamento de Acuicultura, Centro de Investigation Cientifica y de Education Superior de Ensenada (C.I.C.E.S.E.), Ave. Espinoza #843, Ensenada 22830, Baja California, Mexico zyxwvutsrqponmlkjihgfe (Received 18 December 1995; revised 27 April 1996; accepted 27 April 1996) zyxwvutsrqponmlkjihgfedcbaZY Abstract-l. The preferred temperature of Bulla gouldiana is 26.7- 28.7” C. 2. In constant scotophase, photophase, and light and dark photoperiod the organisms do not have a die1 cycle of thermoregulation. 3. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA It ta ke s the animal 616 h to reach the preferred temperature. 4. The lowest and highest temperatures visited were 11 and 33°C. 5. Spawning of the species occurred in the thermal gradient between 27 and 28.X. Copyright 0 1996 Elsevier Science Ltd. Key W ord Ina’ex: Thermoregulation; Mollusca; Gastropoda; Bulla gouldiana INTRODUCTION It is established that temperature is a fundamental factor in the life of the aquatic organisms. Marine gastropods exploit the heterogeneous thermal en- vironment with a behaviour established in a specific thermal framework to avoid the extreme tempera- tures, preferring those that favor growth and reproduction (Brett, 1971; Richards et al., 1977; Reynolds and Casterlin, 1979; Giattina and Garton, 1982). Few observations have been made on thermoregu- lation in marine and freshwater gastropods as in Nassarius trivittatus (Casterlin and Reynolds, 1980) and Helisoma trivolis (Kavaliers, 1980) respectively. The shelled opistobranch Bulla gouldiana is dis- tributed from Morro Bay in California (U.S.A.) to the south of Ecuador (Brusca, 1980). This gastropod lives in mud and sand at the low tide level of bays and estuaries (Brandon and Rokop, 1985), amongst seaweed or clusters of conspecific individuals in tidepools where they reproduce (Ricket et al., 1985; Farfan and Buckle, 1988). We present here the thermal interval of preferred temperature of B. gouldiana investigated by the gravitational method. *To whom correspondence should he addressed at C.I.C.E.S.E., Department of Aquaculture, P.O. Box 434844, San Diego, CA 92143-4844, U.S.A. MATERIALS AND METHODS Adults of B. gouldiana (3.040 cm long) were collected during the low tide in the intertidal mudflats of the Ester0 de Punta Banda in Baja California, Mexico (31”44’ lat. N; 116”38’ long. W). The organisms were maintained in the laboratory in aquaria of 40 1, 35% salinity and 19 rl: 1°C as at the moment of capture. The photoperiod was maintained in 12-12 h light-dark with a period of transition of 30 min between them controlled with an electronic programmable device. The organisms were fed with macroalgae and marine phanerogams. In order that the position of individuals (N = 90) could be determined in the trough, they were tagged with a marker 72 h before beginning each experiment. They were not fed 24 h prior to being put in the thermal gradient of 100 1. The gastropods were introduced to the thermal gradient with an interval of -0°C as described by Hernandez et al. (1995), in the chamber where the temperature was equal to that of acclimatization and a salinity of 34%0,pH 7.65-7.84; Or 4.1-9.3 mg/l and a rate of 80-85 ml/mm of water refill. The positions of the animals and temperature were recorded with 15 equidistant digital thermometer for 34 h during a photophase (day phase) with a luminous intensity of 0.160 x 1 016 quanta seg - ’ cm - 2 and during a scotophase (night phase) of 0.06 x 10” quanta seg-’ cme2. Two experiments were also 319