Abstract
Eddies can enhance primary as well as secondary production, creating a diverse meso- and sub-mesoscale 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.
Highlights
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
Combining in-situ underwater imaging with a deep learning approach for the automated identification of plankton images, we investigated the physical-biological processes shaping zoo- and ichthyoplankton distributions in a decaying mesoscale eddy (ME) in the Florida Straits
The sea surface height anomaly (SSHA), together with zonal (Fig. 2) and meridional (Supplementary Fig. S1) velocities derived from a ship-born Acoustic Doppler Current Profiler (ADCP) showed that the progression from Florida Current (FC) water to the inside of the eddy, crossing the eddy edge, was clearly sampled on transects 1 (6/10/15) and 8 (6/14/15; Fig. 2)
Summary
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. Despite the ecological importance of these features, insight into the distribution of plankton both within and at the edge of MEs is limited due to a lack of sufficient fine-scale vertical and horizontal resolution to adequately describe these distributions[7,23]. A better understanding of zoo- and ichthyoplankton distributions around the edges of MEs, including the processes driving these distributions, would further our basic understanding of these ubiquitous features, but increase in the accuracy of biophysical transport models Such biophysical models are used to estimate dispersal and population connectivity[15], and contribute to the spatial management of reef fish stocks[24,25]. Since most zoo- and ichthyoplankton sampling is conducted with nets, there is often a mismatch between these samples and the finer spatial (
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