Exploring New Technologies for Plankton Observations and Monitoring of Ocean Health

oceans where they dominate life in terms of abundance and biomass (Bar-On and Milo, 2019). They are essential players in the functioning of marine ecosystems. Among them, microscopic algae called phytoplankton use sunlight to generate biomass from carbon dioxide and water, forming the basis of planktonic food webs, contributing about half of global primary productivity through photosynthesis, and producing about half of the world’s oxygen (Field et al., 1998). Phytoplankton are grazed by slightly larger, yet often still minuscule, animals called zooplankton that in turn are eaten by large predators such as fish or whales. Fish and many seabed-dwelling organisms such as corals or starfish commonly start their lives as zooplankton larvae. But plankton also include protists (flagellates, broadly defined), bacteria, and viruses, far tinier organisms that may feast on zooplankton leftovers or dead cells, or may live as parasites within the bodies of larger plankton cells. DNA analyses have revealed that less than 10% of the estimated total plankton biodiversity is known and formally described today—and most of the unknown species are smaller than the width of a hair (de Vargas et al., 2015). Plankton diversity is not equally distributed across the ocean. At the global scale, plankton differ from pole to pole according to temperature gradients and the degree of seasonal changes in the environment (Righetti et al., 2019). At local scales, nutrient availability, seasonal environmental variation, and interactions among species or with anthropogenic stressors determine plankton community composition (Beaugrand, 2014). Because plankton have short lifespans (often days or weeks) and their internal dynamics are tightly linked to global and local environmental conditions, they react quickly to environmental changes. These changes have cascading effects through the food web and significantly impact, for example, commercial fish recruitment. With the ocean under increasing stress from human activities, measuring changes in plankton communities is critical for addressing ocean health and food security and for tracking changes in nutrient and carbon cycles (including the effectiveness or disruption of the biological carbon pump; Zhang et al., 2018). Plankton diversity can serve as an indicator for tracking anthropogenic environmental disturbances brought about by the maritime industry (e.g., Figure 1), eutrophication, industrial wastewater, invasive species, overfishing, TOPIC 2. ECOSYSTEMS AND THEIR DIVERSITY