Authors: James P. Barry*, Chris Lovera, Kurt R. Buck, Edward T. Peltzer, Josi R. Taylor, Peter

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1 SUPPORTING INFORMATION Authors: James P. Barry*, Chris Lovera, Kurt R. Buck, Edward T. Peltzer, Josi R. Taylor, Peter Walz, Patrick J. Whaling, Peter G. Brewer, Affiliation: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA Title: Use of a Free Ocean CO2 Enrichment (FOCE) system to evaluate the effects of ocean acidification on the foraging behavior of a deep-sea urchin Number of pages: 6 Number of figures: 3 S1

2 Supporting Information: Title: Use of a Free Ocean CO2 Enrichment (FOCE) system to evaluate the effects of ocean acidification on the foraging behavior of a deep-sea urchin Study Site Carbon dioxide enrichment experiments using the dp-foce system were performed at the Monterey Accelerated Research System (MARS) node at a depth of 887 m on the upper continental slope ca. 35 km west of Monterey Bay, California ( ; Figure 1). The MARS cabled observatory is the location of a connection node for power and Ethernet communications with shore (MBARI). Power for the lights, motors, and all electrical needs, as well as all communications with instruments on the dp-foce system were provide through the MARS cable. Environmental conditions at the MARS deep-sea site are quite stable compared to surface waters, with temperature (ca. 4 o C), salinity (ca psu), oxygen (ca. 10 µmol. kg -1 ), and ph (ca. 7.63) exhibiting minor daily variations and mild seasonal changes. The site is within the core of the oxygen minimum zone (OMZ) off the California coast. Locally, the soft sediment seabed has a shallow undulating slope of ~1-5 degrees with moderate currents mean speeds <0.1 m. s -1. The benthic megafaunal assemblage at the site is typical of OMZ waters at this depth, with a diverse group of echinoderms (mainly urchins, sea stars, sea cucumbers, and brittle stars), cnidarians (sea pens, anemones), gastropods (snails), and fishes. S2

3 The fragile deep-sea urchin Strongylocentrotus fragilis distributed from m depth on the upper contientnal slope is is often observed during ROV dives aggregated around the detrital giant kelp (Macrocystis pyrifera) which has drifted from nearshore habitats to the deep-sea. S. fragilis actively moves toward and consumes giant kelp in laboratory experiments (Figure S2) 1. S. fragilis reaches a size of ~85 mm test diameter after ca. 10 years of growth, though growth rates apparently differ among depths 2 Details of Control Enclosure We used a dp-foce prototype chamber as the Control treatment enclosure (Figure S3) for the experiment. The experimental chamber in the prototype is identical to the FOCE enclosure, but lacks the long wings and the propeller-driven thrusters found on the FOCE enclosure. Thus, flow through the experimental section of the control is more open and less unidirectional than occurs in the FOCE chamber. Observations of urchin behavior in the Control enclosure were made using a a deep-sea time lapse video camera positioned at one end of the enclosure (Figure S3). Although the perspective view limited visibility into the race way, viewing was sufficient to determine the positions of urchins during the experiment. S3

4 FIGURES Figure S1. Map of study site. Red dot indicates the location of the Monterey Accelerated Research Site (MARS) off the central California coast ( ). The dp-foce system was operated while connected to the MARS cable node, at a depth of 885 m. S4

5 Figure S2. Stronglyocentrotus fragilis, the deep-sea fragile sea urchin. S. fragilis feeds preferentially on a clump of giant kelp debris on the continental slope (240 m depth) off central California. S5

6 Figure S3. Control enclosure. A dp-foce prototype chamber was used as the Control enclosure for the urchin behavior experiment. The raceway can be seen inside the enclosure. A time-lapse video camera system is positioned to the right of the enclosure, and was used to record urchin movement. S6

7 Figure S4. Simplified schematic of the Deep FOCE system. The dp-foce system is a flumelike design with wings used to provide a delay for CO2 hydration for CO2-enriched seawater injected at the upstream end of the system prior to entering the experimental section (center). Water flows through the flume from the injection end to the exit at right. Sensors monitor ph at several locations within and around the system. Thruster propellers maintain flow at near-bottom current speeds. A. FOCE system in operation. B. FOCE system folded for deployment by ROV. S7

8 References Cited 1. Taylor, J. R.; Lovera, C.; Whaling, P. J.; Buck, K. R.; Pane, E. F.; Barry, J. P., Physiological effects of environmental acidification in the deep-sea urchin Strongylocentrotus fragilis. Biogeosciences 2014, 11, (5), Sumich, J. L.; McCauley, J. E., Growth of a sea urchin, Allocentrotus fragilis, off the Oregon Coast. Pac Sci 1973, 27, (2), S8

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