St. Petersburg Coastal and Marine Science Center
As the burning of fossil fuels continues, the partial pressure of carbon dioxide (pCO2) increases in the atmosphere, and a large portion of this anthropogenic CO2 is absorbed by the oceans. As a consequence, the chemistry of the ocean is changing, a phenomenon now commonly referred to as "ocean acidification." This is a problem for marine organisms that precipitate calcium carbonate to form their skeletons, tests, and shells.
Unappreciated until very recently, experimental work has demonstrated decreases in calcification rates of corals and other calcifying organisms under conditions simulating ocean acidification. If the experimental data are directly applicable to the field, we should already be seeing measurable declines in calcification rates of important reef-building organisms compared to during pre-industrial times, and some recent studies are suggesting that this may be so. However, ocean acidification is occurring against a background of increases in sea surface temperature (SST) and changes in water quality stemming from land-use change. It is critical to start measuring calcification rates in a systematic way now, particularly at subtropical latitudes where conditions fluctuate seasonally, so that we can understand how changing ocean chemistry and temperatures are affecting calcifying organisms today and predict possible changes in the future.
Our published work (Kuffner et al. 2013) has provided important baseline information on the spatial and seasonal variability in calcification rates of reef-building corals. We found that one species, the massive starlet coral, calcified about 50 percent faster in summer compared to winter, and about 50 percent greater in the remote Dry Tortugas than at three other sites on the Florida Keys outer reef tract (Fig. 1). We have recently begun to monitor calcification of three more species of coral. To accomplish this research, first we obtain scientific research permits (see below) from the National Park Service and the NOAA National Marine Sanctuaries where we are working. Then we transplant coral colonies onto plastic discs, which are then bolted to concrete blocks we previously fixed to the reef (Fig. 2) so that they can be periodically weighed using a method wherein the corals are kept submerged in seawater. Several of the calcification monitoring stations are co-located with NOAA CMAN stations that record meteorological variables including wind speed and direction, barometric pressure, water temperature, and solar irradiance. We continuously collect underwater temperature data at each site using temperature loggers attached to the calcification blocks.
In addition to the corals, we are monitoring the growth of other important calcifiers known as crustose coralline algae (CCA). This community of encrusting algae coats most hard surfaces within the photic zone of the oceans (Fig. 3). We monitor the growth of CCA by placing "cow tags" at our stations every six months and weighing the tiles before and after deployment (Fig. 4). CCA communities perform many ecosystem services like acting as cement that binds reefs together, acting as a settlement cue for all kinds of invertebrate larvae, and production of sand for beaches. Our work so far has not identified clear seasonal patterns in CCA calcification, but some sites seem to have better growth than others overall. Previous USGS research has demonstrated that CCA are extremely vulnerable to ocean acidification (Kuffner et al. 2008 [408 KB PDF]).The Florida Keys represent a northerly position in latitudinal range for many tropical species. Because of the natural latitudinal gradient and seasonality in SST and carbonate saturation state (an index of a body of water's conduciveness to calcification), Florida's northern coral reefs and associated carbonate systems will likely be among the first to be impacted by changes in ocean pH and SST. Both corals and crustose coralline algal communities are important contributors to reef accretion. This study is contributing empirical data to make educated predictions about future reef accretion that will be essential to guiding national, state, and local resource managers and policy makers toward sound decisions regarding the management of carbonate ecosystems.
Scientific permitting information:
The coral transplantation work was conducted under permits from Biscayne National Park: BISC-2009-SCI-0019; BISC-2010-SCI-0035; BISC-2011-SCI-0025; BISC-2013-SCI-0011; BISC-2014-SCI-0020; BISC-2015-SCI-0003; BISC-2016-0003; accession number BISC-228, Florida Keys National Marine Sanctuary: FKNMS-2008-062-A1; FKNMS-2010-068; FKNMS-2010-122; FKNMS-2013-024-A2, and Dry Tortugas National Park: DRTO-2009-SCI-0009; DRT0-2011-SCI-0004; DRTO-2013-SCI-0008; DRTO-2015-SCI-0010;DRTO-2016-SCI-0010; accession number DRTO-274.
Kuffner, I.B., K.E. Roberts, J.A. Flannery, J.M. Morrison, and J.N. Richey, 2017, Fidelity of the Sr/Ca proxy in recording ocean temperature in the western Atlantic coral Siderastrea siderea: Geochemistry Geophysics Geosystems 18, doi:10.1002/2016GC006640.