The sponge pieces or explants are now healed and ready to be used in the climate change study. To determine the effects of warmer, more acidic waters (= lower pH) on coral reef sponges, we are comparing today’s environmental conditions to what is expected by 2100. But to determine what factor (i.e. temperature or pH) is most important for sponges, we are separating them into 4 treatments: 1) current temperature and pH, 2) current temperature and low pH; 3) high temperature and current pH; and 4) high temperature and low pH. Treatment 1 is called the control, as it is just the normal conditions of today. Treatments 2 and 3 will help us determine the individual effects of warmer water and lower pH. Treatment 4 mimics the predicted future environmental conditions of our oceans.
To maintain constant conditions for each treatment, we are conducting the study in large tanks at the wet-lab at the Discovery Bay Marine Laboratory. Water temperature is controlled by using heaters, the same kind you can get in any aquarium store. To manipulate pH, we are going hi-Tec, and bubbling CO2 into the water. Stored at high pressure in large bottles, CO2 is slowly released at low pressure through regulators, which feed the gas into tubing that snakes into the water. The regulators are turned on (to release gas) or off (to shut gas supply) by pH controllers that use a probe to determine the exact pH of the seawater in the tanks. The pH controller will only turn the regulator on when the pH of the water goes above a certain level (turning on the CO2 will make the water more acidic, lowering the pH). Every tank is “flow through”, meaning seawater constantly enters and drains through a pipe. Each tank also has three tubes bubbling air. The flow through system and additional air bubblers ensures that all waste products from the sponges are removed, and that they have sufficient food and oxygen.
As you can imagine, setting up the experiment involved several days of cutting tubing, feeding extension cords across the room, adjusting the water flows, aeration and pH just right, and countless swatting of mosquitoes that plague the wet-lab. It also involved some on the spot innovation (and frustration) as some of the expensive equipment we had just purchased malfunctioned. Thankfully, we circumvented the problems through some creative reconfigurations. I’m now happy to report that we have several hundred explants of 6 common coral sponge pieces growing in tanks. This experiment will run for 1 month, and at the end we will compare sponge growth, survival and chemistry (what chemicals the sponges are producing) among the 4 treatments to see what effects, if any, temperature and pH change will have on tropical sponges.