Dataset: Histological gonad reproductive scores for purple sea urchins from 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).

Histological and gonad assays

Animals were measured and sacrificed and gonads were carefully excised from the opened test. Using a clean, sterile scalpel we excised an approximately 2 mm cross section from the first gonad, placed in a histological cassette, soaked in Davidson's solution for 24 hours, and placed in 95%EtOH for long term storage. Preserved gonads were then sent to Histology Consultants, Inc. for sectioning, staining with Eosin and Myosin, and mounting on slides. Mounted slides were then analyzed for gametogenic stage. We scored gametogenesis using a standard staging scale of I to IV where IV is fully mature and I is immature (Byrne 1990).

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