Seafloor Ecology Expedition 2018
MBARI Expedition #453
Expedition goal: Our cruise off the central California coast has several objectives related to three research themes in deep-sea ecology: 1) study the sponge and coral communities at Sur Ridge, 2) revisit a corn stover to sample the colonizing communities, and 3) begin a wood-fall experiment to see how species colonize these ephemeral sources in the deep-sea.
Expedition dates: November 30 – December 5, 2018
Ship: R/V Western Flyer
Expedition chief scientist: Jim Barry
Our primary goals focus on studies of deep-sea coral and sponge communities at Sur Ridge, a seamount about 60 kilometers (40 miles) off the coast at 800-1,400 meters (2,600-4,600 feet) depth. This rocky ridge is rich with beautiful coral and sponge gardens containing centuries-old corals towering two-to-three meters tall like small oak trees, sponges one-to-two meters wide that may be even older, as well as a suite of fishes, sea stars, and other species that call these gardens home. The corals and sponges filter plankton and organic particles from currents sweeping over the ridge and must avoid being consumed by predators such as sea slugs and sea stars.
Some of the questions we have about the Sur Ridge sponge and coral communities include: Why are corals and sponges thriving on some parts of the ridge but sparse in others? Is this difference attributed to food and feeding success, predators, and/or competition with their neighbors? How vulnerable are sponges and corals to human activities like climate change, which is now penetrating the depths of the ocean? To begin answering these questions, we have a variety of methods, from deploying and recovering current meters and other sensors to measuring respiration rates of sponges using novel sensors, and rates of predation by sea stars consuming corals.
Our second goal is to revisit a large bale of corn stover (essentially a hay bale) we sunk to a depth of 3,200 meters (10,500 feet) nine years ago. We wanted to test the deep-sea carbon sequestration notion proposed to mitigate climate warming: storing carbon in the deep-sea rather than allowing it to be emitted to the atmosphere. One idea for deep-sea carbon sequestration is to gather up crop residue (stalks, husks, and other plant material), package it, and sink it in the deep ocean where it will remain for many centuries, rather than allowing it to degrade in the soil and ultimately release CO2 into the atmosphere. This peculiar idea was suggested years ago and, in preparing for a cruise in 2009, we decided to sink one corn bale to test this notion. We’ll revisit the bale on this cruise to probe it with sensors to measure its rate of decay, giving us some idea of how long its carbon will remain in the deep sea before eventually making its way back to the atmosphere.
Our third goal for the cruise is to initiate an experiment measuring the diversity of animals that colonize wood falls in the deep sea. Logs and other woody debris are carried to the sea by rivers and eventually sink, some to great ocean depths. These wood falls can be a bonanza for some organisms living in the food-poor abyss. Wood-fall organisms—perhaps most notably wood-boring clams, are notorious for their damage to wooden ships, but several related species live in the deep ocean. Some are wood-fall specialists and are found nowhere else. Our experiment will place small wood falls (4 x 4 x 18 inch wood blocks) on the seafloor across an area the size of 10 football fields to see if the assemblage of organisms (clams, snails, crustaceans, worms, etc.) that colonize each block are related to the distance between blocks. This will help us understand if larvae drifting over the seafloor may sense a wood fall or if the colonization process is more random. From this and similar experiments, we are building an understanding of how food limitation and the challenging conditions in the deep sea have shaped the evolution of species and their abilities to exploit ephemeral “food falls” (wood, whales, or anything in between).
Updates from researchers on the R/V Western Flyer:
Monday, December 3, 2018
Monterey Bay National Marine Sanctuary Research Coordinator Andrew DeVogelaere
Two of the many nice things about being at sea are being rocked to sleep in your bunk by waves and the short, 30-step commute from your stateroom to the lab. This morning, launch prep began at 6:00, with a remotely operated vehicle dive starting promptly at 6:30. Because poor weather conditions were predicted by the end of the day, we canceled the plan to go farther offshore and continued research at Sur Ridge. Flexibility, plan B, plan C, and plan D are needed when working in the ocean. Today, the plan was to retrieve instruments that have been measuring deep-sea currents for the last five months, check on more of our transplanted corals, measure oxygen consumption rates in sponges, collect water samples for environmental DNA and particulate organic matter, survey the Sur Ridge communities on the southern end of the ridge, and then end the day by retrieving the benthic respirometer.
In the morning, we successfully retrieved and replaced ocean current meters. This information, along with assessing particles in water samples, will help us understand why Sur Ridge is such a spectacular place in the deep sea. Knute Brekke, an ROV pilot for 30 years who has seen deep-sea habitats around the globe said, “you’re seeing one of the most beautiful places in the world.” We want to know why this is so. This information will also help us model and predict what other areas of the deep we should protect, because we can’t visit everywhere in the world ocean with an ROV.
Just as crime scene investigators look for DNA in blood and hair samples to match with criminals and victims, environmental DNA can also be collected in ocean water samples. As sea creatures shed skin, mucus, and fecal matter DNA “leaks” from the cells floating in the water. We are learning how to detect what animals have been in an area of the ocean (over the last few days) by filtering and replicating DNA, and comparing it to known DNA sequences. On Sur Ridge, we have successfully detected DNA from humpback whales, squid, corals, sponges, and a variety of other taxa. Eventually, sending out an autonomous vehicle equipped with this technology could be the standard way to monitor and assess the health of the ocean.
In the early afternoon we focused on describing community patterns in the unexplored south-west area of Sur Ridge. We saw many more corals than expected for this relatively flat area, but none were particularly large. One of the more interesting species we saw was Asbestopluma monticola, a predatory sponge. Covered with spikes, it spears small crustaceans and slowly digests them through its outer skin. After collecting pieces of specimens for positive identification and microbial analyses, we left the bottom to successfully retrieve the benthic respirometer system.
Sur Ridge is a Sanctuary Ecologically Significant Area (SESAs), within the Monterey Bay National Marine Sanctuary (MBNMS). As the MBNMS research coordinator, I work with scientists to encourage research in these SESAs, and MBARI makes significant contributions to science and society by focusing research on Sur Ridge. In resource management decisions (for example, where bottom fishing should or should not occur), SESAs receive extra attention, and these are also sentinel areas for learning about long-term changes to deep-sea ecosystems. The chief scientist on this cruise, Jim Barry, has made Sur Ridge a “coral observatory” to understand ecosystem function and long-term changes to this spectacular habitat. Despite some limitations due to weather, this has been a spectacular cruise.
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.