After a few days in New York enjoying Thanksgiving with my family, I’m now back in Jamaica. While I was away, Amber Stubler, a graduate student from Stony Brook University, was monitoring the experiment and making sure that water temperature, water flow rates, pH/CO2 levels and dozens of other factors were okay. The experiment is at the halfway point and I’m happy to report that it is going extremely well. Most of 360 sponge pieces or explants have survived. Two of the 6 coral reef sponge species I’m studying are comparatively less hardy, with a few explants dying, but differences in survival (and growth) between species are common. Although only halfway through the experiment, it does not appear that there are any major differences in survival between the 4 climate change treatments (see the blog “Climate Change Sponges, Jamaica: Experiment” below for descriptions). That is neither high temperature nor low pH seems to killing sponges, which is a very promising result for the future of coral reef sponges.
Many of the explants are growing, being noticeably larger than when the experiment started. However, because I cannot weigh them until the end of the experiment, I do not know by how much, and whether growth differs between the 4 climate change treatments.
In addition to survival and growth, I’m also recording how quickly the explants attach to the bottom of the tank. Many coral reef sponges reproduce through fragmentation, generated through predation or storm damage. These little fragments or pieces then get washed around the bottom by water currents until they attach to solid substrate like coral rubble. In doing so, sponges help bind the reef together, making it stronger. It is therefore important to know whether climate change will affect sponge fragments attaching to the coral reef. Attachment rates in this study vary greatly between the 6 coral reef sponge species. Some species like Aplysina fistularis (yellow tube sponge) and Aplysina cauliformis (lavender rope sponge) attach quickly (most explants attached within 1 week), while other species like Ectyoplasia ferox (octopus sponge) take a lot longer (only 1 of 60 explants has attached after 2 weeks). How they attach can also vary. Some, like Aplysina fistularis and Aiolochroia crassa, spread out over the bottom from all sides. Others, like Aplysina cauliformis, appear to attach by their ends. Similar to sponge survival, attachment rates do not seem to differ between the 4 climate change treatments. Again, this is a very promising sign for the future of sponges on coral reefs.