Changing with the tides: fine-scale larval fish prey availability and predation pressure near a tidally modulated river plume

Abstract

Tidally controlled river plumes form distinct frontal boundaries that can alter the spatial distributions of larval fishes and their planktonic prey and predators. Variable in nature, they may expose larval fishes to different trophic environments over small spatio-temporal scales, with unknown consequences for survival and recruitment. In the northern California Current, the Columbia River Plume is strongly influenced by twice-daily freshwater injections that create a highly dynamic coastal environment. Using the In situ Ichthyoplankton Imaging System, we examined changes in the fine-scale horizontal and vertical distributions of larval fishes, their prey, and their predators over space and time (ebb/flood tide). In total, 6095 fish larvae and ~1.5 million prey/predator zooplankton were imaged and measured. Plume regions provided substantially higher concentrations of prey and enhanced spatial overlap between larval fishes and their prey relative to oceanic waters. The functionality of river plumes as a refuge from predators was less clear. Predator concentrations were also higher in plume regions, but overlap with larval fishes was taxon-specific and varied with the tide. Notably, regions of high zooplankton concentrations did not necessarily confer high spatial overlap on small scales (meters vertical, kms horizontal) relevant to trophic interactions. Surface salinity and chlorophyll a were the most important factors influencing the spatial overlap of zooplankton with larval fishes. In the vicinity of river plumes, larval fishes experience a diversity of unique prey and predator fields over short spatio-temporal scales, which likely contribute to variable growth and mortality patterns at much finer scales than previously thought.

Big or small, patchy all: Resolution of marine plankton patch structure at micro- to submesoscales for 36 taxa

“…Initial research using this system demonstrated habitat partitioning across the shelf-slope front by gelatinous plankton ( 40 ) and pelagic tunicates and larval fishes ( 41 ). Subsequent studies revealed the importance of phytoplankton thin layers, internal waves, hypoxia, and lateral salinity gradients on submesoscale (≈3 to 70 km) patchiness of larval fishes, copepods, chaetognaths, shrimps, and gelatinous plankton ( 42 , 12 , 43 ). Through the resolution of submesoscale spatial patterns across a suite of trophically linked, taxonomic groups (including rare and delicate ones), this collective work has set the stage to answer questions of patchiness in a broad range of plankton in contrasting marine environments.…”

In situ imaging across ecosystems to resolve the fine-scale oceanographic drivers of a globally significant planktonic grazer

“…A convolutional neural network (CNN) classified the images using different training sets for each ecosystem. This method has produced accurate distributions for many types of zooplankton, including gelatinous organisms and larval fishes (Faillettaz et al 2016; Schmid et al 2020; Axler et al 2020; Swieca et al 2020). The doliolids were classified into three life stages (nurse, phorozooid, and gonozooid) in all ecosystems except the Straits of Florida, which classified all doliolids as one category.…”

“…The copyright holder for this preprint this version posted September 2, 2022. ; https://doi.org/10.1101/2022.08.31.506093 doi: bioRxiv preprint 8 2020; Swieca et al 2020). The doliolids were classified into three life stages (nurse, phorozooid, and gonozooid) in all ecosystems except the Straits of Florida, which classified all doliolids as one category.…”

Larval Fish Assemblage Structure at Coastal Fronts and the Influence of Environmental Variability

“…As an example, in a river plume system which forms a distinct frontal boundary, complex patterns of larval fish occurred, compared to offshore locations, with further investigation of species-specific fine-scale interactions suggested by the authors (Swieca et al, 2020).…”