Data to support "delta13C and delta15N values from a mesocosm experiment showing sea urchins mediate the availability of kelp detritus to benthic consumers"

The purple sea urchin Strongylocentrotus purpuratus is an important
herbivore and detritivore in southern California giant kelp
(Macrocystis pyrifera) forests that grow on shallow rocky reefs
(~3-20m depth) off southern California, including Santa Barbara
where this study was done. To investigate the shredder activity of
purple urchins, we assembled communities of common detritivores and
suspension feeders from local reefs in mesocosms. Three species of
brittle stars (Ophiopteris papillosa, Ophioplocus esmarki, and
Ophiothrix spiculata), one vermetid gastropod (Thylacodes
squamigerus), two barnacles (Chthamalus sp. and Megabalanus
californicus), one polychaete worm (Chaetopterus sp.), and three sea
cucumbers (Cucumaria piperata, Pachythyone rubra, and Cucumaria
salma) were collected from the seafloor of local kelp forests at
5-15m depth in the Santa Barbara Channel. Ten of each species were
placed in each of six 50 L (51x38x27 cm) flow-through unfiltered
seawater tanks, each containing two concrete bricks for hard
substrate on top of 3 cm of sand. Because sea urchins are highly
mobile, capable of bulldozing other occupants, we isolated them
above the experimental communities on plastic mesh (1cm). Mesh
dividers were secured horizontally across each mesocosm 16 cm above
the bottom. Ten individuals of each consumer species, along with 2-3 blades,
totaling 47.3 g (±1.2 SE), of isotopically labeled kelp (see below)
were placed on the floor of each tank, below the divider. On top of
the mesh divider, we placed an additional 229.8 g (±6.1 SE) of
enriched kelp blades, and in half of the tanks, 10 adult urchins
(total mass 343.3 g ±1.3 SE) per tank. The kelp below the mesh
ensured that the detritivores had direct access to degrading kelp
detritus regardless of the urchin treatment, similar to the
situation in the kelp forest, allowing us to more clearly ascertain
the degree to which the detritivores were dependent on urchins for
kelp detritus assimilation. The experiment was run for 28 days (Jul
26 - Aug 24, 2016); above-mesh kelp was removed and replenished once
after 13 days. The duplicated data table has been published in Dryad: Yorke,
Christie E.; Page, Henry M.; Miller, Robert J. (2019), Data from:
Sea urchins mediate the availability of kelp detritus to benthic
consumers, Dryad, Dataset, https://doi.org/10.5061/dryad.38m3dc6