Primary Production Sources and Bottom-up Limitations in Nearshore Ecosystems

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Kelp forests are among the world’s most productive habitats, but recent evidence suggests that production is highly variable.

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Our ability to forecast the fate of ecosystems and species hinges on an understanding of how biological systems respond to their environment.  In this project, natural indicators of diet (stable isotopes) and production (otolith growth increment width) in two common fishes were used to investigate energy pathways and biophysical relationships in nearshore kelp forests spanning two large marine ecosystems with contrasting oceanography, the upwelling system of the California Current and the downwelling system of the Alaska Coastal Current. This study is an integral component of the USGS Pacific Nearshore Project and the data and results from this project are being used to understand differences in nearshore production from California to Alaska and the resulting population trajectories of sea otters, a keystone predator in kelp forest ecosystems and an important subsistence resource in Alaska.

A map with pie charts depicting the relative carbon contributions of kelp and phytoplankton in black rockfish and kelp greenling

Map of black rockfish (left) and kelp greenling (right) sampling locations in the northeast Pacific Ocean with pie charts representing the relative carbon contributions from kelp (brown) and phytoplankton (green) primary producers estimated using carbon (δ13C) and nitrogen (δ15N) stable isotope values of muscle tissue. Black rockfish feed pelagically in the nearshore water column and kelp greenling feed benthically in nearshore waters. Mixing models were used to estimate carbon contributions based on site-specific phytoplankton and kelp and trophic discrimination factors (mean ± SD) of 1.0 ± 1.0‰ for δ13C per trophic level. Image credits: kelp and phytoplankton Jane Thomas and Tracey Saxby, IAN Image Library (http://ian.umces.edu/imagelibrary) and fish pictures, Washington Department of Fish and Wildlife.  From publication: https://doi.org/10.1016/j.ecss.2016.08.039
(Credit: Vanessa von Biela, USGS. Public domain.)

Biologist removing the ear bones from a fish on a table on a boat in Southeast Alaska

Hans Bruning (left; first mate on the Snow Goose) and Tim Tinker (right) watch as USGS biologist Vanessa von Biela dissects kelp greenling (Hexagrammos decagrammus) for their otoliths—earbones whose growth rings can reveal a fish's age and indicate how fast the fish grew in certain years. Picture taken on board the M/V Snow Goose in southeast Alaska.
​​​​​​​(Public domain.)