The myriad of particles and organisms that populate the world's oceans are not distributed homogeneously; more often than not, they occur in strongly localized patches. This `patchiness' in distribution can manifest itself in either horizontal or vertical directions and occur over a wide range of spatial and temporal scales. Some examples of patchiness include harmful algal blooms, `thin layers' of phytoplankton and zooplankton, the deep scattering layer, and schools of krill and fish. A diverse set of complex factors contribute to the occurrence of these phenomena. These include, but are not limited to, horizontal and vertical mixing processes at multiple scales and their effects on nutrient and light fields, transport (advection and convection), organismal behavior, life history strategies and interactions.

The resulting heterogeneous distribution of particles and organisms can have significant consequences to several important research areas spanning the ocean sciences, including biological productivity, diversity, predator-prey interactions and export fluxes. For example, patchiness can play a critical role in predator-prey encounters and fish/zooplankton feeding success rates. Recent studies have shown that long aspect ratio phytoplankton chains/particles exhibit preferential orientation, especially within thin layers, potentially increasing the light capture and primary productivity while also significantly modifying optical backscattering.

By virtue of its limited spatial and temporal extent, patchiness can be a challenging problem to study in the field. Furthermore, traditional water sampling methods typically have a depth resolution of a few meters, insufficient to detect `thin layers' of high plankton concentration that can be quite limited in extent vertically (as thin as 10 cm in some instances). An additional observational challenge is posed by the avoidance behavior of zooplankton and other swimming organisms which inhabit the deep scattering layer. Significant technological improvements in the last decade, particularly novel acoustic and optical instrumentation sampling at high frequencies, and computational advances resulting in rapid processing times, have made this a much more tractable problem, leading to increased research efforts in this area.

The goal of this Research Topic is to highlight the diverse research endeavors focused on processes that lead to patchiness of particles and organisms in the marine environment. We encourage manuscript submissions with theoretical, numerical, laboratory and/or field-based experiments addressing specific issues within the general ambit of the description, focusing on spatial scales ranging from a few mm to several km, and temporal scales ranging from a few seconds to several weeks. The topics can include but need not necessarily be limited to:

(a) Plankton/particle interactions with turbulence, including feeding encounters, aggregate formation, and preferential spatio-temporal concentration patterns.

(b) In situ optical and biological characterization of algal bloom and `thin layer' formation, including biophysical interactions as well as spatial and vertical distributions of coexisting species.

(c) Design and deployment of novel instrumentation to enable better characterization of patchiness at various scales.

(d) Individual and/or swarm behavioral and swimming patterns of zooplankton and fish.

(e) Other studies on characterization of biological, chemical and physical processes causing patchiness.

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Frontiers in Marine Science

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