Dataset: Purple sea urchin morphometrics from Marna Laboratory Experiments at the Quadra Island Ecological Observatory from Sep to Dec 2021

To quantify how different thermal regimes affect investment in gonads and development of gametes in male and female urchins, we first conducted a 10-week experiment in which 300 animals were incubated in replicate 350L mesocosms that simulated El Niño (N = 4 mesocosms, 60 animals per treatment) or La Niña (N = 4 mesocosms, 60 animals) conditions based on historical, empirical benthic temperature time series from Scripps Pier in La Jolla, Californiathat coincide with historical collapses in larval supply in Southern California. 

We paired these treatments with a range of fixed temperature incubations (10, 13, 16, 17, 18, 20 °C, N = 2 mesocosms, 30 animals per treatment), two of which matched the mean temperature of the El Niño (20 °C) and La Niña (16 °C). Experiments were conducted at the Marna Lab at the Hakai Institute’s Quadra Island Ecological Observatory in Heriot Bay, British Columbia due to availability of sophisticated seawater systems for careful, replicated temperature manipulations.

Field Collections and Acclimation

We collected sea urchins by hand on SCUBA in the vicinity of Ucluelet, British Columbia, Canada (48.94°N, 125.56° W) from a depth of 7-8 m relative to mean low tide in September 2021 and transported them to the Marna Lab via truck in seawater filled coolers with bubblers in less than 24 hours. We transferred sea urchins to flow-through sea tables and allowed them to recover for a period of one week before placing animals into the mesocosm system. Animals were haphazardly selected and assigned to the "Wild" group or "Experimental" group (and thereafter treatments) from this pool. 

For the "Experimental" group, we selected healthy individuals within a constrained size range for incubations (n = 300, mean test diameter = 56.09 mm, range test diameter = 42.12 – 69.46 mm). Finally, we assigned animals to mesocosms at random at ambient temperature and exposed each assigned mesocosm to a temperature ramp, where the ramp reached target temperatures after two weeks from the initial incoming, ambient temperature (mean across all tanks of 13.3°C, SD = 0.3°C) to avoid thermal shock. Once initial target temperatures were reached, they were maintained or, for the variable treatments, were manually adjusted daily in the AM (∼8am each day) as needed by 0.5 °C increments in a scheduled manner to match historical mean El Niño and La Niña daily temperature trends.

Mesocosm System

We placed urchins in a custom-built array of twenty replicated 214 L [90(L) x 59.5(W) x 40(H) cm] acrylic mesocosms supplied with flow-through UV sterilized and filtered seawater. Each mesocosm was capable of independent control of temperature and animals were provided a lighting regime for all mesocosms using LED fixtures (Aquamaxx, CA, USA) programmed to provide 10L:14D with two-hour linear light intensity transition periods for dawn and dusk (0-100% from 07:00 to 09:00 “dawn”, and 100-0% from 17:00 to 19:00 “dusk”). Each mesocosm independently maintained temperature treatments using a heat exchanger fitted with a titanium coil regulated by a dual stage digital temperature controller (Resolution = 0.1°C, Dwyer Instruments, LLC.©, Michigan City, IN, USA). The mesocosm system employed central cooling (Aermec Mits Airconditioning Inc., Mississauga, ON, Canada) and heating (boiler array, Viessmann Manufacturing Company Inc., Warwick, RI, USA) to supply independent heat exchangers with on-demand cold and warm glycol loops for down- and up-regulation of water temperature, respectively. We manually checked and re-calibrated sensors, as needed, using digital traceable thermometers twice daily to control potential temperature sensor drift. We randomly assigned mesocosms to the specified treatments.

Animal husbandry

We fed individuals uniform dry pellets combining several macroalgal species formulated for the aquaculture of S. purpuratus (Urchinomics Canada Inc., Halifax, NS, Canada). Animals in mesocosms were fed twice per week and we removed uneaten food and refuse every 72 h. More detail available in the results publication (Okamoto et al. 2023).

Morphometrics

For a focal sea urchin, morphometrics included measurements of test dimensions, wet mass, dry mass, and ash mass as well as visual determinations of the sex and whether gametes were actively extruded immediately following dissection. Test dimensions were measured using digital calipers (Mitutoyo America Corporation®, Aurora IL, USA). Wet weight was measured using a calibrated digital scale (Mettler-Toledo, LLC., Columbus, OH, USA) following a 30 s drying period in a dry dissection tray (United States Plastic Corporation®, Lima, OH, USA). We estimated the amount of metabolically active biomass for an individual by calculating ash-free dry mass (AFDM) for each subject. AFDM quantifies soft tissue biomass while excluding skeletal biomass that does not contribute meaningfully to changes in DO. We calculated AFDM as the difference between dry mass and post-combustion ash mass (i.e., skeletal mass). We measured all mass metrics by weighing samples on a calibrated digital scale (Mettler-Toledo, LLC). To measure dry mass, we first cracked the test of the urchins and discarded the coelomic fluid, then dried the carcasses for 24 hours at 60 ℃ in a drying oven then weighed the dried carcasses. To measure post-combustion ash mass, we combusted these dried carcasses for six hours at 450 ℃ in a muffle furnace, then weighed the resulting ashes of each carcass.

For full methods, see results publication (Okamoto et al. 2023).