Mission & Project Info | NOAA’s Aquarius Undersea Laboratory
Mission Blog

Today we are switching to experiments involving ocean acidification by individual sponges. Sponge are animals and they breath like us, meaning they take up oxygen as they consume food particles and release carbon dioxide (CO2). The carbon dioxide combines with water to make carbonic acid. Sponges now dominate the benthic (seafloor) biomass at Conch Reef as well as many other reefs around the world. Our preliminary data from Conch Reef suggest that their respiration generates enough CO2 to be a significant factor in local acidification in the water column close to the bottom, a zone that oceanographers call the benthic boundary layer or BBL. At Conch Reef we find more than 50 species of sponges, although the giant barrel sponge, Xestospongia muta, dominates. Our data suggest that water passing through a filter feeding X muta sponge drops more than 0.01 pH units, a significant fraction of the 0.1 drop that has already resulted from the acidification of the ocean by the increase in atmospheric carbon dioxide in recent decades. Our work of the past week has revealed a similar; approximately 0.01 pH drop in the BBL relative to the overlying water column, especially at night when there is no removal of carbon dioxide by photosynthesizing phytoplankton.

Hopefully our work out at Aquarius Reef Base will help us to understand how to distinguish local acidification processes, like that from sponge respiration, from the global scale changes now occurring around the world. Only in this decade have scientists fully realized the threat of global acidification to calcifying organisms such as corals. Marine scientists around the world are now attempting to provide the information that we need to both understand and manage this important problem. Aquarius Reef Base has provided us a useful observatory from which to launch some of these efforts.

Aquanaut Chris Martens