Amanda Kahn

Today was a mixed day of deploying and recovering moorings along with an ROV dive. In the morning, the sediment trap mooring we recovered yesterday was redeployed at the top of Sur Ridge. The sediment traps will remain there until December, collecting marine snow that rains down from the ocean’s surface. Corals and sponges are thought to grow well on bumps and ridges like Sur Ridge because deep currents around these structures continually sweep in new water filled with marine snow created by plankton blooms above, delivering abundant food. The sediment traps show us how much marine snow falls at different times of the year, and how much of that marine snow makes it to the depths of Sur Ridge.

Still, there is a lot we don’t know about what sponges and corals need to thrive. In many parts of the ocean, we see habitat that visually appears like it should be excellent coral/sponge habitat. It’s cold, dark, has rocky hard surfaces to attach to, and has similar currents to what we see at Sur Ridge. But there are not corals and sponges growing into the remarkable communities we see at Sur Ridge. To understand what makes Sur Ridge a particularly good place for a coral or sponge to live and grow, another mooring was deployed today: the McClane Profiler.

The profiler measures temperature, depth, and salinity (conductivity). There are also sensors to measure oxygen, water clarity (turbidity), current speed and direction, and to detect elements of sinking plankton in the water using fluorescence and CDOM (colored dissolved organic matter), which can tell us something about the food quality and quantity arriving to Sur Ridge. The profiler takes these measurements while traveling up and down a mooring line, so it gives us a view of water column properties across 500 meters (1,600 feet) of depth! It was deployed at the top of Sur Ridge, and surveyed from 950 meters to 450 meters (3,100 – 1,500 feet).

We recovered the profiler in the afternoon, after the ROV dive had concluded for the day. The ROV dive shared the goal of observing the conditions that make life at Sur Ridge so abundant. Acoustic Doppler current profilers (ADCPs) that had been deployed since December were recovered and new ones redeployed to measure water currents among and above the corals. We also collected water samples from sponges, which will help us understand how much food they eat and how much food they have in the water around them. The samples were collected using a small pump with a nozzle that could be inserted near where we wanted to sample, then pumping water slowly into IV bags. In addition, we collected samples for future stable isotope analyses on corals, sponges, crabs, snails, sea stars, squat lobsters, and other seafloor animals to determine who eats whom in the complex Sur Ridge food web.

Finally, we collected water samples at different depths and different locations around Sur Ridge that will be analyzed for environmental DNA (eDNA). The eDNA profiles are assessed over time to study changes in coral and sponge communities at Sur Ridge, and to test the limits and capabilities of this method of remote detection.

It was a full, busy day and the team worked together until late into the evening to process samples and record all of the great science from the day.