A Novel Real-Time Monitoring System for Coral Larvae Detection Using In Situ Imaging

Alessandra Gomes, Leandro Ticlia de la Cruz and Rubens Mendes Lopes, University of Sao Paulo, Department of Biological Oceanography, Sao Paulo, Brazil
The coral genus Tubastraea, popularly known as sun coral, is endemic from the Pacific Ocean and has spread in several areas of the Atlantic. Despite the taxonomic uncertainties, species of Tubastraea are considered invasive in Brazil, being targets of a National Plan for Prevention, Control and Monitoring. Scarce information is available on the larval liberation cycle and subsequent dispersion patterns, which represents fundamental knowledge to establish management strategies. In the context of a multidisciplinary project “Research and implementation of technologies for sun coral detection/monitoring and biofouling prevention”, a cooperation agreement between USP and CENPES/PETROBRAS, we developed and implemented a new technology to detect coral spawning events in situ, and in real-time. Integrated with a circulation model and considering larval behavior data, we aim to predict major larval advection patterns and potential settlement areas. The implemented observatory includes an underwater component, containing an imaging device, environmental probes and an electronic control unit integrated with a data transmission device and energy housing. The imaging system is based on the shadowgraphic technique and acquires focused coral larvae images in a configuration set to scan approximately 70 L min-1. A single board computer and internal storage, coupled to the optical system, provides real-time particle identification thanks to a dedicated computer vision software suite (LAPS Plankton Detector, LPD) running a convolutional neural network. When particles resembling Tubastraea larvae are detected, the monitoring system sends warning text messages and example images through a web-based interface. The long-term power autonomy and customized mechanical structure allow the observatory to be installed in a variety of consolidated substrates, bringing to the light a new possibility for in situ real-time environmental monitoring of coral larvae and other planktonic organisms.