Innovation and Sunshine

guest post by Sara Rivera

Sara got crafty with duct tape to protect her water samples from sunlight-induced photo-oxidation. Photo courtesy of Sara Rivera.

Sara Rivera is a graduate student in the Aluwihare Lab at Scripps Institution of Oceanography. Here, she recounts some of her challenges in sampling at sea.

Being at sea for research requires innovative solutions for problems not typically experienced on land.  One of the main issues faced when sampling for microorganisms and organic chemistry is the impact of light on samples.  On land, it is easy to grab a piece of foil to cover a rack of vials.  At sea, it is not so easy because it is fast, windy, and there are limited supplies.  At first, I used foil to cover my tube rack, like I would on land, to block the sunshine.  I found that with the fast pace at sea that I needed to get my samples done, I constantly ripped the foil and needed to get a new piece.  I would also end up chasing pieces of foil as they were blown across the deck.  As my supply of foil dwindled, I contemplated what else would efficiently block the sunshine while allowing easy and efficient access to the sample tubes.

Lo and behold, the answer sat in front of me in an essential piece of cruise equipment: a roll of duct tape.  I created a barn-like structure out of duct tape that would slide over the tube rack and completely block out any sunlight.  It is waterproof and reusable.  It is also removable, allowing me to continue to use the tube rack for other experiments as needed.

Why do I care this much about keeping the samples out of the sunlight?  Sunlight impacts both chemical and biological processes.  The untraviolet (UV) region of sunlight leads to photo-oxidation of organic molecules, changing the chemistry of the sample before I have time to process it.   Recent work by Neal Arakawa (Science Advances, September 2017) demonstrated that a single type of molecule, β-carotene, can photooxidize to generate a slew of carotenoid degradation products that is linked to 4% of the total dissolved organic matter in the ocean.  If one molecule can degrade to such a large number of other molecules, from simply sitting in the sunshine, I do not want that happening in my samples! I want the samples to reflect the chemistry of the sea water from the depth from which I collected it.

Sara’s work involves taking lots of water samples from the ocean. She relies on the CTD and bottle rosette (pictured here) to sample certain depths of the water column. The CTD goes out several times per day and requires careful manhandling to bring back onboard. Photo courtesy of Sara Rivera.

UV also damages biological cells. The biological damage can impact both the biology and chemistry as distressed cells will take up and release different molecules than in their normal state.  Since I measure both the biology and chemistry, this one is doubly bad.

The visible light regions of sunlight are absorbed by the green pigment chlorophyll, found in the organelles called chloroplasts, which is essential to photosynthesis in the majority of marine phytoplankton.  These chloroplasts also give the phytoplankton their green color.  Light is attenuated as you go deeper in the ocean.  We sample at a variety of depths from the surface down to 515 meters (1690 ft).  The organisms below the surface are not acclimated or adapted to the light on the deck of the ship- it is much too bright for them.  It can also lead to fast growth and production from increased photosynthesis.  Because I want to capture the biology at the different depths we sample, I don’t want them to suddenly start growing faster because of the additional light.

Ocean aggregations

by Laura Lilly

The CTD rosette is a popular aggregating/sampling stop for many of the ship’s scientists during all-night transects.

It’s a well-known fact that, in the ocean’s endless expanses of blue, creatures flock to any semblance of structure. Fishermen will tell you that some of the best places to drop a line are around buoys, kelp patties, and bottom rubble. Divers love oil rigs because they create platforms for mussels, barnacles, and sponges, which in turn attract fish and larger predators. Even seamounts concentrate upwelled nutrients and particles underwater, fueling productive hotspots for migratory fishes and sharks (side note: we just finished sampling in a region near the Davidson Seamount off Central California, which comes up to 1300 m below the ocean’s surface. Our work wasn’t related to the seamount, but perhaps we caught some seamount-related creatures in the MOCNESS). If you’ve been reading the news lately, you may have heard about the giant raft of aggregated pumice pieces that emerged from an underwater volcano near Tonga and is floating toward the Great Barrier Reef off Australia. Scientists believe that the pumice raft may actually help the Great Barrier Reef by collecting marine creatures as it floats, and then depositing them on the GBR, helping to repopulate a reef system that has suffered tremendously from climate change-related coral bleaching.

Zippy reappeared at the surface to an albatross welcoming party.

Yesterday we observed a different example of aggregation when we retrieved Zippy the Zooglider from his two-week excursion! Zippy had been doing continuous underwater up-and-down sampling patterns, so to recover him we had to program him to come up to the surface and float while we tracked down his GPS coordinates and spotted him from the ship (without running him over). But our human party wasn’t the first to spot him. We found Zippy by steaming toward the aggregation of albatrosses we saw sitting in the water nearby. Just like they had when we deployed Zippy, the albatrosses wanted to know why there was a giant orange missile-shaped carrot floating at the surface. We think one even took a bite – Zippy came back missing a small piece of wing! But somehow, even though they weren’t tracking GPS coordinates like we were, those albatrosses spotted Zippy before we did. Aggregation: it’s a marine life instinct.

Zippy gets picked up by the small boat crew.

We all participated in another form of aggregation two days ago: we had our third all-night sampling transect across another part of the (now evolved) ocean filament we are sampling. The transect was a typical all-night party/race of drawing water from CTD casts; filtering rapidly for carbon, nitrogen, and iron; and deploying zooplankton nets and preserving specimens – all before the next station 20 minutes away! We moved through everything successfully, though, and even managed to finish by dawn. Then most people slept all day.

Dolphins sometimes aggregate around our ship, too!

Wrangling the MOCNESS monster

by Laura Lilly

Recovering MOCNESS nets can be exciting in rough seas. They really do look like creatures from the watery depths!

When you do zooplankton tows, you bring a lot of monstrous-looking creatures onboard. Sometimes we get Phronima hyperiid amphipods, which were the inspiration for the 1979 movie Alien; occasionally we pull up red tuna crabs, small lobster-like crustaceans with very sharp claws; and the other day we caught two vampire squids, small purple creatures with big black eyes, Dumbo ears, and tissues between their tentacles that resemble vampire cloaks. But one of the craziest monsters we have is the net we use to capture and sample these organisms: the MOCNESS!

A Phronima hyperiid amphipod curled up in a hollow salp ‘barrel’ (body case). Phronima carves a salp’s body out and uses the barrel as a house – like a slightly morbid version of a hermit crab. Photo courtesy of Pierre Chabert.

Assuming you haven’t been living under a rock for the past hundred years, you will probably recognize MOCNESS as a play on Scotland’s Loch Ness Monster. MOCNESS stands for Multiple Opening/Closing Net and Environmental Sampling System, and was developed by Peter Wiebe at Woods Hole Oceanographic Institution. If you can process that behemoth of a name, you will get clues about what the MOCNESS does. Most of our plankton nets have simple circular ‘mouths’ that stay open for the whole net deployment: they go down to depth open and come back up still open, so if we sample down to 200 meters we are actually collecting animals everywhere between the surface and 200 meters. That comprehensive sampling is fine for a lot of the research questions we ask (aka: “Who is present in the upper ocean off San Diego versus Monterey?”), but sometimes we want more information about which animals live at specific depths. As its name implies, the MOCNESS has multiple nets (10 on our current setup!) attached to one frame, and they can be opened and closed in sequence to sample different depths. If you want to compare the zooplankton living at 1000 meters versus 100 meters, you can program separate nets to close at each of those depths. The MOCNESS also has oceanographic instruments to measure water temperature, salinity, oxygen, and fluorescence, so we can get information about the physical water profile in addition to zooplankton specimens.

A vampire squid underwater in Monterey Bay. The squids we pulled up in our nets were on their last legs (tentacles), but they had the same distinct Dumbo ears. Photo: MBARI.

Most of our MOCNESS tows on this cruise sample down to 450 meters, although occasionally we sample to 1000 meters. Those deep tows can last over three hours, which doesn’t even include the net washdowns afterward! The majority of the sample from each net filters down to a plastic jar attached to the end of the net, but once the nets come back on deck, we hose them down to make sure we collect all the animals that may have gotten stuck in the net mesh. Net washdowns sometimes feel like they go on forever, but they can be very important: one of the vampire squids we caught a couple of days ago was stuck halfway down the net, and we wouldn’t have collected it if we hadn’t done the net washdown.

Getting the MOCNESS overboard can be quite a process! Fortunately we’ve had mostly calm seas and a very helpful deck crew. Photo courtesy of Lance Wills.
Each of the ten MOCNESS nets has a plastic ‘cod end jar’ attached to the end. These jars collect most of the organisms that get caught in the nets, and bring them back to the surface for us to sample. Four cod end jars are visible here as the grey cylinders with drainage holes and duct tape bumpers. Photo courtesy of Lance Wills.

Net washing time is also essential for taking in the afternoon sun (or sometimes early morning pre-dawn air) out on deck, and for keeping an eye and ear open for passing whales. Today we started our third cycle, and we were graced all day by the presence of several fin whales. Their broad backs and deep exhales were sometimes just 50 feet from our ship. The sound of a fellow mammal emerging from the depths of the ocean to release a breath of air never gets old. Plus, all those whales are a sure sign that there are zooplankton around to feed on!

The cloudy skies finally parted for a brief sunset. Our red drift array buoy is visible in the foreground, flashing its red light. During each cycle, we follow this drift array as it floats around in the ocean, which allows us to track the same single water parcel for several days.