A Benthic Underwater Microscope with Pulse Amplitude Modulated Imaging Capability (BUMP)

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

The health and long-term dynamics of coastal ecosystems such as kelp forests, mangroves, sea grass beds, and especially coral reefs, are significantly driven by processes that occur on scales of a millimeter or less. Many inhabitants of these ecosystems are primary producers, allowing transformation of sunlight energy into molecular energy, which is what flows through food chains and drives ecosystems climax. The energy transformation takes place in particulate units (from chloroplasts to unicellular algae, depending on the context) and the performance of each of these units is dictated by their direct surrounding physical-chemical conditions. Hence, assessing the performance of each of these units is critical to better understand adaptation and productivity in the ecosystem, while also being a good proxy for the organisms overall health and ability to photosynthesize. These fundamental microscopic processes are of interest to scientists across diverse disciplines such as physiology, photobiology, ecology, and organisms' interactions. Despite the importance of small-scale processes, the availability of tools to study them at the appropriate scales has been severely lacking. As one way of assessing physiological processes, Pulse Amplitude Modulated (PAM) technology is an important method that has been implemented in both the lab and the underwater environment. The resultant data allows inference of photosynthetic rates, providing a measure of photosynthetic activity. Such systems have been implemented for bulk measurements underwater but never at the resolution needed to monitor individual microscopic organisms. In this project, the underwater BUMP microscope (Benthic Underwater Microscope with Pulse amplitude modulated imaging) will be created that will measure these processes at the microscopic level in their natural environment. The system will enhance the capacity to better understand benthic marine processes by enabling in situ measurement of microscopic photosynthetic organisms as well as their physiological status without disturbing or removing them from their natural environment. The results provided by this imaging system will thereby promote new discoveries to better understand factors that structure marine communities globally. To achieve this goal, the BUMP will incorporate a number of features of an existing system for subsea microscopic imaging while, at the same time, adding the capability to observe dynamic fluorescent changes that have been induced with incident modulated light. The system will use a long working distance (45 mm in water) lens with a resolving power of 1.5 micro-meters over a 1.5 mm x 1.5 mm field of view. An inclined ring illuminator consisting of 12 high power broadband LEDs with focusing optics will provide photosystem saturation pulses, actinic light, as well as illumination for reflectance images. The system will provide sufficient illumination for short exposures of 100 microseconds or less. The design includes multiple optical paths allowing for dual-mode imaging with 2 cameras and two illumination sources. Taken together with an IPAD in an underwater housing for controlling the system, a fully functional Pulse Amplitude Modulated imaging system at the microscopic level will be built and tested in both the lab and then moved to the field for diver operation in various environments such as kelp forests and coral reefs.