Automated system for laboratory simulation of a thermal gradient for studies with marine organisms

Abstract

The design and operation tests of a thermal gradient simulation system for studying temperature preferences in marine benthic organisms are reported. The system consists of a glass fiber tank divided into an experimental channel flanked by distal sections where extreme gradient temperatures are controlled by cooling or heating with the support of heat pumps. The system is automated in terms of temperature control and recording and features an image acquisition module with a high-resolution camera and a relay controller that allows the air pump to be turned off and light lamps to be lit just before taking the photographs. The system was challenged to evaluate its efficiency. The results indicated that 1) high aeration along the entire experimental channel allows not only the maintenance of oxygen saturation conditions in the tank, but also a better response of the thermal gradient, 2) that the efficiency of the gradient is greater at smaller depths of the system and acceptable at 15 cm, 3) that from homogeneous conditions the system takes approximately 30 h to stabilize the gradient, 4) that on average the system reaches within the experimental canal a 60% of the programmed gradient in the heat pumps, and 5) that once established the system is successful maintaining the gradient for long periods (weeks) still under experimental conditions with manipulation and water replacement. Opportunities for improving the system are discussed, including increasing the experimental units, incorporation of sensors for the autonomous registration of other water quality indicators, as well as in the image acquisition system, and the monitoring and observation of organisms and their responses.