In this paper we review the technologies available to make globally quantitative observations of particles in general-and plankton in particular-in the world oceans, and for sizes varying from sub-microns to centimeters. Some of these technologies have been available for years while others have only recently emerged. Use of these technologies is critical to improve understanding of the processes that control abundances, distributions and composition of plankton, provide data necessary to constrain and improve ecosystem and biogeochemical models, and forecast changes in marine ecosystems in light of climate change. In this paper we begin by providing the motivation for plankton observations, quantification and diversity qualification on a global scale. We then expand on the state-of-the-art, detailing a variety of relevant and (mostly) mature technologies and measurements, including bulk measurements of plankton, pigment composition, uses of genomic, optical and acoustical methods as well

The large data sets provided by in situ optical microscopes are allowing us to answer longstanding questions about the dynamics of planktonic ecosystems. To deal with the influx of information, while facilitating ecological insights, the design of these instruments increasingly must consider the data: storage standards, human annotation, and automated classification. In that context, we detail the design of the Scripps Plankton Camera (SPC) system, an in situ microscopic imaging system. Broadly speaking, the SPC consists of three units: (1) an underwater, free-space, dark-field imaging microscope; (2) a server-based management system for data storage and analysis; and (3) a web-based user interface for real-time data browsing and annotation. Combined, these components facilitate observations and insights into the diverse planktonic ecosystem. Here, we detail the basic design of the SPC and briefly present several preliminary, machine-learning-enabled studies illustrating its utility and efficacy.

Eddies can enhance primary as well as secondary production, creating a diverse meso-and submesoscale seascape at the eddy front which can affect the aggregation of plankton and particles. Due to the coarse resolution provided by sampling with plankton nets, our knowledge of plankton distributions at these edges is limited. We used a towed, undulating underwater imaging system to investigate the physical and biological drivers of zoo-and ichthyoplankton aggregations at the edge of a decaying mesoscale eddy (ME) in the Straits of Florida. Using a sparse Convolutional Neural Network we identified 132 million images of plankton. Larval fish and Oithona spp. copepod concentrations were significantly higher in the eddy water mass, compared to the Florida Current water mass, only four days before the ME's dissipation. Larval fish and Oithona distributions were tightly coupled, indicating potential predator-prey interactions. Larval fishes are known predators of Oithona, however, Random forests models showed that Oithona spp. and larval fish concentrations were primarily driven by variables signifying the physical footprint of the ME, such as current speed and direction. These results suggest that eddy-related advection leads to largely passive overlap between predator and prey, a positive, energy-efficient outcome for predators at the expense of prey. Eddies are ubiquitous features of the ocean, turning mechanical energy into trophic energy 1. The footprint of a mesoscale eddy can extend 100-300 km in diameter and can last for several weeks to months 2. Through their upwelling effect, cyclonic mesoscale eddies (MEs) have been shown to enhance primary 3,4 and secondary production 5-7. This enhanced productivity may increase growth 8 and survival 9 of larval fishes, which normally experience up to 99% mortality due to starvation and predation 10. Eddies may also physically retain larval fishes 11 , leading to higher larval fish concentrations inside eddies, relative to outside ambient waters, and are considered effective vectors for the transport of zoo-, and ichthyoplankton 12-14. As such, mesoscale eddies play an important role in the connectivity of holo-and meroplankton populations 15. Eddy divergence and convergence patterns in the ocean lead to a cascading flow of energy from large to small scales 16 , with turbulent frictional coupling inducing smaller anti-cyclonic eddies at the periphery of larger cyclonic eddies thereby creating a feature-and energy-rich seascape 17. Upwelling occurs in the centre of cyclonic MEs during their spin-up phase (termed a 'forced' eddy), but during the decay/spin-down phase (termed a 'free' eddy), this switches to downwelling at the core with upwelling occurring at the eddy edge 1,18. In both instances, due to its frontal character, the eddy edge is an important feature for predator-prey interactions 1. Less motile prey are often passively aggregated at the eddy edge and can be exploited by higher trophic levels and top predators

Although plankton thin layers have been described and modeled in a variety of environments, the physical structure surrounding the layer, associated biological rates, and distributions of multiple trophic levels are rarely examined simultaneously. Similar combinations of measurements, such as growth, mortality, and spatial relationships among plankton, are key to understanding how physical processes generating thin layers can influence abundances, composition, and predator‐prey interactions. An in situ imaging system was deployed along a southward‐oriented transect to describe the full ~ 2.3‐km extent of a thin layer arching from 8 to 4 m deep, with Chlorophyll a enhanced by an order of magnitude inside the layer (23.9 mg m−3 peak concentration). Physical oceanographic measurements, distributions of different plankton groups, and output from a high‐resolution model indicated that surface convergence and vertical shear drove the formation of the layer, which was dominated by Odontella sp. diatoms that were relatively scarce in the broader study region. Phytoplankton apparent growth (0.64 d−1) balanced microzooplankton grazing rates (0.52 d−1) within the layer, whereas grazing mortality (2.23 d−1) greatly exceeded phytoplankton growth (−0.39 d−1) outside the thin layer. Mesozooplankton had starkly differing distributions; copepods aggregated south of the layer near the surface, and doliolids followed the thin layer trajectory. A physical oceanographic model run over a 1‐month time period, including the time of sampling, indicated that similar surface convergences occurred frequently. Thin layers driven by convergence and shear may be common, with behavioral and buoyancy differences among plankton likely contributing to community structure and modification of trophic transfer.