Multiscale Spatial and Temporal Patterns of Distribution of Marine Fish Larvae—Patchiness and Predator–Prey Overlap

The distribution of fish larvae and other planktonic organisms is highly heterogenous and influenced by a complex interplay of physical, behavioural and ecological processes operating across different scales. Information on patterns and scale of resulting patchiness in plankton distributions is pivotal for understanding the bio-physical linkages, trophodynamics and ecological strategies in the marine pelagic environment. In this study, we examine the distribution and degree of patchiness of four fish larvae species and their copepod prey, placing specific emphasis on the scale of patterns in both horizontal and vertical dimensions. Our sampling effort encompassed a 120 km long transect of stations covering a frontal area in the southern North Sea, employing depth-stratified net sampling at varying station distances. Our results show distinct distributional patterns and migratory behaviours among different taxa of both larvae and their copepod prey, yet some commonalities were apparent. Across all species, we observed increased patchiness at larger spatial scales, significantly influenced by day/night fluctuations and hydrography. The overall findings highlight the dynamic nature of patch distributions and underscore the strong impact of hydrographic interfaces, whether vertically oriented pycnoclines or horizontally structured hydrographic fronts. These insights into bio-physical linkages deepen our understanding of the mechanisms driving larval survival, prey availability and overall ecosystem dynamics.