Data from: Sea urchins mediate the availability of kelp detritus to benthic consumers

Detritus can fundamentally shape and sustain food webs, and shredders can
facilitate its availability. Most of the biomass of the highly productive
giant kelp, Macrocystis pyrifera, becomes detritus that is exported or
falls to the seafloor as litter. We hypothesized that sea urchins process
kelp litter through shredding, sloppy feeding, and egestion, making kelp
litter more available to benthic consumers. To test this we conducted a
mesocosm experiment in which an array of kelp forest benthic consumers
were exposed to 13C- and 15N-labeled Macrocystis with or without sea
urchins, Strongylocentrotus purpuratus, present. Our results showed that
several detritivore species consumed significant amounts of kelp, but only
when urchins were present. Although they are typically portrayed as
antagonistic grazers in kelp forests, sea urchins can have a positive
trophic role, capturing kelp litter before it is exported and making it
available to a suite of benthic detritivores.