Frequent monitoring of temperature: an essential requirement for site selection in bivalve aquaculture in tropical–temperate transition zones Mar|¤ aTeresa Sicard 1 , Alfonso N Maeda-Mart|¤ nez 1 , Salvador E Lluch-Cota 1 , Cesar Lodeiros 2 , Lucelly M Rolda L n-Carrillo 1 & Roberto Mendoza-Alfaro 3 1 Centro de Investigaciones Biolo¤ gicas del Noroeste (CIBNOR), La Paz, B.C.S., Me¤ xico 2 Instituto Oceanogra Ł ¢co deVenezuela, Universidad de Oriente, Cumana Ł , Sucre,Venezuela 3 Facultad de Ciencias Biolo¤ gicas, Universidad Auto¤ noma de Nuevo Leo¤ n, Monterrey, Nuevo Leo¤ n, Me¤ xico Correspondence: A N Maeda-Mart|¤ nez, Centro de Investigaciones Biolo¤ gicas del Noroeste (CIBNOR), Mar Bermejo195, Col. Playa Palo de Santa Rita, 23090 La Paz, B.C.S., Me¤ xico. E-mail: amaeda04@cibnor.mx Abstract Frequent monitoring of temperature (FMT) for over 1 year at two aquaculture sites in the western Baja California peninsula was analysed in terms of hourly, daily and monthly variability, and with this informa- tion, temperature-change indices were calculated. These data were contrasted against a long-term ser- ies from a global database (Extended Reconstruction of Sea Surface Temperature (ERSST)) to evaluate whether these could substitute for FMT. The com- patibility of species requirements with the thermal conditions was evaluated by comparing the tempera- ture frequency distributions from the two FMTs, with the optimum and lethal temperature information available on ¢ve bivalve species of aquacultural inter- est. We concluded that there was no correlation between ERSST and FMT because the former underestimates the amplitude of real temperature £uctuations and exhibits a di¡erent pattern of varia- tion during the year. Therefore, FMT was needed for a correct selection of an aquaculture site for bivalves. The FMT indicated high temperature variability at both sites studied on di¡erent time scales, with the site located at lower latitude (Rancho Bueno) warmer and with a higher variability than Laguna Manuela. Contrasting these results with optimum and lethal temperature values of bivalve species, it was possible to ¢nd the ideal site, for temperature, for culturing the species, taking into account the variability asso- ciated with large-scale phenomena. Keywords: LD 50 , temperature, oyster, scallop, penshell Introduction Site selection is a key factor in any successful bivalve aquaculture operation. In new ventures, one criter- ion followed by aquaculturists is to verify the pre- sence of the target species in the area, and then the decision may be further based on results of prelimin- ary growout experiments performed at the site for short periods. However, in this site selection process, the importance of climate variability is frequently ne- glected, with catastrophic results (Lechuga-Deve¤ ze, Morquecho-Escamilla, Reyes-Salinas & Herna Ł ndez- Alfonso 2000; Carvalho-Saucedo 2003). In tropical^ temperate transitional zones like those in the wes- tern Baja California peninsula (Lluch-Belda, Lluch- Cota & Lluch-Cota 2003a), Peru, Japan and Bengal (Olson 2001), strong climate £uctuations occur on many time scales, hourly, daily, seasonally (Ponce- D|¤az, Lluch-Cota, Bautista-Romero & Lluch-Belda 2003), interannually (i.e. ENSO; Lluch-Belda, Lluch- Cota & Lluch-Cota 2003b,2003c) and interdecadally (Lluch-Cota, Wooster & Hare 2001), resulting in highly variable biophysical settings including tem- perature and seston quality and concentration, which are the most important factors a¡ecting the physiology of the organisms (Lodeiros, Maeda-Mart|¤- nez, Freites, Uribe, Lluch-Cota & Sicard 2001). In the western Baja California peninsula, seasonal climate variations result from the interaction of the Califor- nia Current during winter (AŁ lvarez-Borrego, Galin- do-Bect & Chee-Barraga Ł n 1975; AŁ lvarez-Borrego & AŁ lvarez-Borrego 1982), and the tropical North Equa- torial Countercurrent during summer (Lluch-Belda et al . 2003a). Aquaculture Research, 2006, 37, 1040^1049 doi: 10.1111/j.1365-2109.2006.01527.x r 2006 The Authors 1040 Journal Compilation r 2006 Blackwell Publishing Ltd