Conducting a census of mesophotic communities is not exactly part of my dissertation focus. As a graduate student at the Hawaii Institute of Marine Biology, University of Hawaii, Manoa, my dissertation focus is looking at evolutionary patterns in shallow reef species. However, I have been trained as a rebreather diver for the sole purpose to assist in expeditions like what we are currently conducting in Pohnpei as part of a collaborative effort with the Bishop Museum (Honolulu, Hi). As Richard Pyle and others have mentioned previously in this blog, we are conducting deep, mesophotic dives to areas that few have explored. For example yesterday, my lab mate, Joshua Copus, and the Dive Safety Officer for the University of Hawaii went deeper than 400 feet (~122 meters). As a team, we have already collected several new species as well as expanding the range for species that already exist.
After one dive to 305 feet (93 meters) to test our equipment, I have since been confined to the shallow depths (depths below 130 feet, 40 meters). This is to allow more time to become comfortable conducting transects in an timely and efficient manner. You see, my presence here, in addition to collecting specimens for myself, other members of the team, and multiple institutions as part of collaborations with the Toonen-Bowen (ToBo) Lab, is to conduct fish surveys with the help of my lab mate Garrett Johnson. We already have an idea of the fish species that occur here, however we don’t know at what depth range that the community shifts between shallow water and mesophotic communities, an important question for science. By conducting surveys at specific intervals we intend to show a fine scale transition between these two communities.
As with any method of diving, we are limited in the amount of time that we can stay at certain depths. Based on decompression theory and the depths we are diving, a five-minute pause at deep depths can lead to 45 minutes waiting around in the shallows. So it is vital to be able to become in sync with my diving partner and work out any kinks that could disrupt the workflow prior to attempting to conduct the surveys as deep depths.
By utilizing rebreathers, I have also noticed a difference in how fish respond to me. Typically on open circuit diving most fish are scared off by the bubbles and scatter when I approach. However, with rebreathers what we exhale is recycled and the CO2 removed, but importantly for the fish surveys, no bubbles are expelled. So the fish that would generally be scared off stick around and we get a more accurate representation of what is there. I have already had a cleaner wrasse attempt to clean me and have sat and watched a blenny feed out in the open for about five minutes – something I would never be able to accomplish using open circuit.
Tomorrow will be the first fish survey to be conducted at mesophotic depths and I feel very prepared. As we become more comfortable we will move further and further down the slope and into deeper depths. In the next few days I hope to be able to share an update of any general patterns that we are seeing.