Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Project Information
• Funding

This study was conducted from February to March 2018 at the Galapagos Science Center on San Cristobal Island. The rate of Ulva sp. consumption by the two sea urchins, Lytechinus semituberculatus and Eucidaris galapagensis was measured at 10 temperatures: 14°, 16°, 18°, 20°, 22°, 24°, 26°, 28°, 30°, 32°C. L. semituberculatus (green urchin), E. galapaguensis (pencil urchin) and T. depressus (white urchin) are the three most common species in the Galapagos Islands and together make up 91% of the sea urchin biomass.  Ulva sp. was used as the prey item because it is one of the most abundant macroalgal species, together with turf, encrusting coralline algae and Sargassum near the Galapagos  and  coast and because it is highly palatable for herbivores.

For each temperature run (i.e., each experimental level) eight urchins of each species were collected from Cerro Tijieretas cove (0°53’16.78”S, 89°36’29.18”W) at an average depth of 4 m. Urchins were transported in plastic containers filled with sea water to the UNC/USFQ Galapagos Science Center. 

Each individual, whose volume has been calculated using a beaker (ie, via water displacement), was randomly assigned to a numbered mesocosm: green and pencil urchins were placed in 21x11x9 cm and 42x9 cm (circumference x depth), respectively, with 5g (wet weight) of fresh Ulva sp. each taken from the Cerro Tijieretas site. Ulva sp. was weighed after excess water was removed using a salad spinner that was cycled twice for 20 repetitions. The 16 mesocosms were then placed randomly within a large water bath of 130x60x35 dimensions at the temperature to be tested randomly. A chiller and two heaters, paired with an Apex aquarium thermostat, were used to control the water temperature inside the water bath. Each mesocosm closed with a wire mesh top so that the water temperature inside the mesocosm was the same as that in the aquarium and water could be exchanged freely. Before the test, the individuals were left to fast for 24 hours in basins with oxygenators. The water inside the basins was changed approximately every 12 hours with new sea water at an ambient temperature of ~23°C. This procedure was repeated for every temperature tested.

BCO-DMO Processing Notes:
- added conventional header with dataset name, PI name, version date

NSF Award Abstract:
A well-known pattern in coastal marine systems is a positive association between the biomass of primary producers and the occurrence or intensity of upwelling. This is assumed to be caused by the increase in nutrient concentration associated with upwelling, enabling higher primary production and thus greater standing algal biomass. However, upwelling also causes large, rapid declines in water temperature. Because the metabolism of fish and invertebrate herbivores is temperature-dependent, cooler upwelled water could reduce consumer metabolism and grazing intensity. This could in turn lead to increased standing algal biomass. Thus upwelling could influence both bottom-up and top-down control of populations and communities of primary producers. The purpose of this study is to test the hypothesis that grazing intensity and algal biomass are, in part, regulated by temperature via the temperature-dependence of metabolic rates. Broader impacts include the training and retention of minority students through UNC's Course Based Undergraduate Research program, support of undergraduate research, teacher training, and various outreach activities.

The investigators will take advantage of the uniquely strong spatiotemporal variance in water temperature in the Galápagos Islands to compare grazing intensity and primary production across a natural temperature gradient. They will combine field monitoring, statistical modeling, grazing assays, populations-specific metabolic measurements, and in situ herbivore exclusion and nutrient addition to measure the effects of temperature on pattern and process in shallow subtidal communities. The researchers will also test the hypothesis that grazer populations at warmer sites and/or during warmer seasons are less thermally sensitive, potentially due to acclimatization or adaptation. Finally, the investigators will perform a series of mesocosm experiments to measure the effect of near-future temperatures on herbivores, algae, and herbivory. This work could change the way we view upwelling systems, particularly how primary production is regulated and the temperature-dependence of energy transfer across trophic levels.