Live imaging of Aiptasia larvae, a model system for studying coral bleaching, using a simple microfluidic device

Abstract

Coral reefs, and their associated diverse ecosystems, are of enormous ecological importance. In recent years, coral health has been severely impacted by environmental stressors brought on by human activity and climate change, threatening the extinction of several major reef ecosystems. Reef damage is mediated by a process called coral bleaching where corals, sea anemones, and other cnidarians lose their photosynthetic algal symbionts (genus Symbiodinium) upon stress induction, resulting in drastically decreased host energy harvest and, ultimately, coral death. The mechanism by which this critical cnidarian-algal symbiosis is lost remains poorly understood. Here, we report Traptasia, a simple microfluidic device with multiple traps designed to isolate and image individual live larvae of Aiptasia, a sea anemone model organism, and their algal symbionts over extended time courses. Aiptasia larvae are ~100 m in length, deformable, and highly motile, posing particular challenges for long-term imaging. Using a trap design optimized via fluid flow simulations and polymer bead loading tests, we trapped Aiptasia larvae containing algal symbionts and demonstrated stable imaging for >10 hours. We visualized algal migration within Aiptasia larvae and observed algal expulsion under an environmental stressor. To our knowledge, this device is the first to enable live imaging of cnidarian larvae and their algal symbionts and, in further implementation, could provide important insights into the cellular mechanisms of coral bleaching under different environmental stressors. The device is simple to use, requires minimal external equipment and no specialized training to operate, and can easily be adapted to study a variety of large, motile organisms.