We have reached Midway Atoll! We got into midway a day early so we were able to have a extra half-day of diving. Today was a total switch from the conditions that we had at Maro. It was shallow, completely flat, no current or surge, and really clear. This was a nice break after the kind of hectic/intense days that we had at Maro.
At Midway, we are working on two different projects: the “Holey Holes” Project and a bioerosion study. This site, however, has a different set-up for the bioerosion study than the other forereef sites at French Frigate Shoals, Lisianski, and Pearl and Hermes. At Midway we are working on a site within the lagoon.
Lagoon reefs are well-protected from waves and the water is typically low-energy with a high residence time (meaning that there is not much water movement). This allows for a really variable chemical environment which is not seen on forereefs. For example, the pH on a lagoon reef might change from 7.7-8.2 in a given day while the forereef might only change 0.1 or 0.2 pH units in a diurnal cycle. Additionally, different areas of a lagoon reef (high coral cover vs. high algal cover vs. sandy areas) can have diverse, but consistent, chemical environments (see Gagliano et al. 2010 for some examples). I am hoping to capture this variability in the environment and see how different parameters affect bioerosion. Do low pH areas have more bioerosion? Do high nutrient areas have higher erosion? I am answering this question in much more detail on a reef in Kaneohe Bay right now (where I can spend more than 3 days at a site). Midway is really interesting because there is almost no anthropogenic influences whereas in Kaneohe Bay there are a lot. I have set-up the Midway site in a way that I can compare it to our lagoon site in Kaneohe Bay. This way we can see if human impacts have an effect on bioerosion rates.
Gagliano, M., M. I. McCormick, J. A. Moore, and M. Depczynski. 2010. The basics of acidification: baseline variability of pH on Australian coral reefs. Marine Biology 157:1849-1856.