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Marine Ecology Progress Series

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MEPS 650:37-61 (2020)  -  DOI:

Fine-scale larval fish distributions and predator-prey dynamics in a coastal river-dominated ecosystem

Kelia E. Axler1,6,*, Su Sponaugle1, Christian Briseño-Avena2,7, Frank Hernandez Jr.3, Sally J. Warner4,8, Brian Dzwonkowski5, Steven L. Dykstra5, Robert K. Cowen2

1Department of Integrative Biology, Hatfield Marine Science Center, Oregon State University, Newport, OR 97365, USA
2Hatfield Marine Science Center, Oregon State University, Newport, OR 97365, USA
3Division of Coastal Sciences, Gulf Coast Research Laboratory, University of Southern Mississippi, Ocean Springs, MS 39564, USA
4College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA
5Department of Marine Sciences, University of South Alabama, Dauphin Island Sea Lab, Dauphin Island, AL 36528, USA
6Present address: Alaska Fisheries Science Center, National Oceanic and Atmospheric Administration, 7600 Sand Point Way, Seattle, WA 98115, USA
7Present address: Department of Environmental and Ocean Sciences, University of San Diego, San Diego, CA 92110, USA
8Present address: Environmental Studies Program, Brandeis University, Waltham, MA 02453, USA
*Corresponding author:
Advance View was available online August 6, 2020

ABSTRACT: River plumes discharging into continental shelf waters have the potential to influence the distributions, predator-prey relationships, and thus survival of nearshore marine fish larvae, but few studies have been able to characterize the plume environment at sufficiently fine scales to resolve the underlying mechanisms. We used a high-resolution plankton imaging system and a sparse convolutional neural network to automate image classification of larval fishes, their planktonic prey (calanoid copepods), and gelatinous planktonic predators (ctenophores, hydromedusae, and siphonophores) over broad spatial scales (km) and multiple pulses of estuarine water exiting Mobile Bay (Alabama, USA) into the northern Gulf of Mexico from 9-11 April 2016. Fine-scale (1 m) plankton distributions were examined to analyze predator-prey relationships across 3 distinct plume regimes that varied by degree of wind-forcing and mixing rates. In calm wind conditions, the water column was highly stratified, and fish larvae and zooplankton were observed aggregating in a region of river plume-derived hydrodynamic convergence. As winds strengthened, the water column was subjected to downwelling and highly turbulent conditions, and there was decreasing spatial overlap between larval fishes and their zooplankton prey and predators. Our results indicate that high-discharge plume regimes characterized by strong wind-forcing and turbulence can rapidly shift the physical and trophic environments from favorable to unfavorable for fish larvae. Multiple pathways for both nearshore retention and advective dispersal of fish larvae were also identified. Documenting this variability is a first step toward understanding how high discharge events and physical forcing can affect fisheries production in river-dominated coastal ecosystems worldwide.

KEY WORDS: Larval fish · River plumes · Fine scale · Predator-prey relationships

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Cite this article as: Axler KE, Sponaugle S, Briseño-Avena C, Hernandez F Jr and others (2020) Fine-scale larval fish distributions and predator-prey dynamics in a coastal river-dominated ecosystem. Mar Ecol Prog Ser 650:37-61.

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