Sunday, December 2, 2018
Postdoctoral Fellow Amanda Kahn
Yesterday we left Moss Landing Harbor on the morning’s high tide and made the five-hour trip to Sur Ridge. The winds and waves were extreme so we could not do any research operations. Instead, we stayed near the coastline and waited for conditions to improve, which happened this morning.
Our first objective was to release the benthic respirometer system (BRS) off the back of the ship. The BRS is a “free vehicle” meaning it is not connected to the ship by any kind of tether or cable. Instead, we release it over the back of the ship and it sinks slowly to the seafloor. Eventually, when it is time to recover the BRS, the ship sends out a sound that the BRS is tuned to listen for. When that sound is detected by the BRS’s acoustic modem, the instrument will begin to float up toward the surface. Once it reaches the surface, it announces its arrival on a specific radio frequency. Then all hands go on deck to look in all directions, trying to spot the orange waving flags of the BRS sticking out of the water’s surface.
The BRS is used to measure the metabolic rate of deep-sea animals. On this trip, we focused on corals of the genus Isidella. We load animals into the chambers of BRS using ROV Doc Ricketts, so after the BRS went over the side it was time to send the vehicle down.
Upon reaching the seafloor we made our way over to where the BRS had landed. The currents were so strong that the flags on the BRS were waving in the water flow. The ROV pilots carefully took small fragments of Isidella corals and loaded them into the chambers of the BRS. The coral pieces will sit in enclosed chambers where oxygen levels and associated respiration rates will be measured repeatedly over several days, until the BRS is recovered.
After the BRS was filled, we made our way to an area where an array of instruments has been taking measurements since July, or even longer. Two acoustic Doppler current profilers have been measuring the speed and direction of water flow in the area. A mooring with optical backscatter sensors sat measuring the amount of sediments suspended in the water (called turbidity). Water flow and turbidity can both have big effects on suspension feeders like corals and sponges, so by understanding the water conditions and flow regime, we can learn something about the needs of the corals and sponges that live at Sur Ridge.
On the way to the instruments, we also collected dead coral skeletons for Natasha Vokhshoori and Eve Pugsley, graduate students at the University of California, Santa Cruz. Both are working with Professor Tom Guilderson to use stable isotopes and radioisotopes locked in the skeletons to determine the age and growth rates of these long-lived corals, and to use the skeletons, which grow concentrically like tree rings, as a record of plankton community shifts back through time. We also revisited several coral transplants, part of work that researchers Jim Barry and Charlie Boch (not on this cruise) are working on in partnership with Andrew DeVogelaere of the Monterey Bay National Marine Sanctuary. Over the past two years they have tested the survival of deep-sea corals that were fragmented and transplanted to different areas in Sur Ridge. Though they are slow-growing, some coral species look healthy even two years after being transplanted. Finally, the precise navigation abilities of Doc Ricketts allowed us to revisit individual marked corals to look at changes over time, some growing by themselves and others with predators on them.
All in all, it was a full day of diving and we accomplished many objectives for this first dive. The forecast looks good for tomorrow so we are looking forward to another day of diving at Sur Ridge—check back in to find out how it goes!
Senior Scientist Jim Barry
Although we had planned to depart from Moss Landing yesterday morning, a gale was blowing and waves were breaking all the way across the harbor mouth throughout the day, making it a no-brainer to postpone the cruise. The Western Flyer finally departed Moss Landing at 7:00 this morning, churning through a rough, but reasonable sea. It is now just after noon and we are on station at Sur Ridge, assessing the sea and wind conditions, which are marginal for ROV launch and recovery. A squall is drifting through with sustained winds near 30 knots (35 miles per hour) and gusts of 35 knots (40 miles per hour). We’ll wait for a while to see if conditions calm down. If we’re lucky, we’ll have our first dive today, but the waiting game is on for now. In the meantime, we are settling in, storing our gear, and finalizing any preparations for our abbreviated cruise—and a few of us may have found time for a nap during the bumpy four-hour ride to the site.
Once the winds ease we will begin operations at Sur Ridge in earnest. First we will launch a benthic elevator holding our benthic respirometer system (BRS). The elevator is a simple platform designed to carry gear (in this case the respiration system) to the bottom or up to the surface. It is launched over the side of the ship with the crane, then sinks to the bottom. The respiration system attached to it has eight chambers into which we will place a branch from a live coral colony (collected using ROV Doc Ricketts’ robotic arm), then close the chamber.
From the rate of decrease in oxygen, we can estimate metabolic rates for corals in each chamber. Why? These corals live in an oxygen-poor layer of the ocean called the oxygen minimum zone (OMZ), where oxygen levels are low enough that they may be stressful or even lethal for some animals living in the region. We will compare the metabolic rates of the corals under oxygen levels found in the OMZ with measurements at both higher and lower ambient oxygen levels, which we can produce in the respiration chambers. This will help us predict how these corals may respond to future climate change.