//
you're reading...

Biological oceanography

Eating Snow: How detritus gets broken down

Nishibe, Y. et al. Degradation of discarded appendicularian houses by oncaeid copepods. Limnol. Oceanogr. 60, 967–976 (2015). DOI: 10.1002/lno.10061

 

The world’s oceans are teeming with the goo produced by microorganisms. Scientists refer to this detritus by the improbable name “marine snow.” Unlike the trash humans put in the water, marine snow is vitally important to the habitat: it links surface waters to the deep ocean, forms a component of the biological pump, and provides habitat for diverse microbial communities.

“Marine snow” encompasses a range of sinking, mostly organic, matter including dead plankton, plankton feces, and aggregates of tiny organisms. These carbon-rich globs are degraded by microbes and eaten by plankton as they drift toward the ocean bottom, providing energy to denizens of the deep. Bacteria decompose some of the nutrients in marine snow and, in the process, recycle it into a form usable by primary producers. The rest ends up on the sea floor and, eventually, in ocean sediments.

The details of this process, such as how quickly the snow gets processed by organisms, are difficult to study because snow is very fragile and often breaks up when collected with bottles, nets, and sediment traps. To get around that problem, a group from the Japanese Fisheries Research Agency (JFRA) led by Yuichiro Nishibe recently set out to examine one part of the cycle using a special in situ imaging system called the Video Plankton Recorder (VPR). The group also preformed experiments in the lab to compare to the data.

Figure 1 Image of an appendicularian taken with an in situ microscope off the coast of California. The head is the oval pointing toward the top right corner of the image. The tail is the long, thin line pointing back from the head. The rest of the material is the goo-house the appendicularian uses to capture food. All the little dots are bits of carbon rich particles it has picked up. (Scripps Plankton Camera; spc.ucsd.edu)

Figure 1 Image of an appendicularian taken with an in situ microscope off the coast of California. The head is the oval pointing toward the top right corner of the image. The tail is the long, thin line pointing back from the head. The rest of the material is the goo-house the appendicularian uses to capture food. All the little dots are bits of carbon rich particles it has picked up. (Scripps Plankton Camera; spc.ucsd.edu)

Nishibe and his team set out to measure how quickly copepods, a common type of plankton, eat the discarded houses of appendicularians, a planktonic filter feeder (fig. 1). “House” is the genteel term given to the ball of mucus appendicularians produce to collect food. When the house gets clogged up, the small zooplankton discard it and build another, repeating the process as often as 40 times a day. Some studies have found that the number of discarded houses per cubic meter of surface water can reach into the thousands. Scientists know that plankton eat the discarded houses, and they estimate that between 20 and 70% of the carbon in marine snow could be degraded by feeding. This rate needs to be pinned down to better evaluate how much carbon ends up sinking to the deep ocean.

To estimate the rate of consumption, the JFRA group towed the VPR behind a research vessel off the coast of Shikoku, Japan, raising and lowering it seven times from the surface to a depth of 100m. This process was repeated over two transects. The VPR was equipped with a camera and programmed to snap 15 pictures per second. In-focus objects were automatically extracted from the full images using real-time image segmentation software. These objects were then hand-sorted by an expert to identify appendicularian houses and copepods. The copepods were then further separated into three categories: individuals attached to houses, those attached to other particles, and those flying solo (fig. 2). The group then estimated the abundance of organisms in each of these classes at a variety of depths and averaged the abundances over each profile.

 

Figure 2 Images that Nishibe et al. captured using the Video Plankton Recorder off the coast of Japan. Panels a and b show discarded appendicularian houses. c-f  are examples of copepods attached to the houses (arrows highlight the copepod). g-j are images of free swimming copeopods. Scale bars all equal 1 mm. (Adapted from Nishibe et al., 2015)

Figure 2 Images that Nishibe et al. captured using the Video Plankton Recorder off the coast of Japan. Panels a and b show discarded appendicularian houses. c-f are examples of copepods attached to the houses (arrows highlight the copepod). g-j are images of free swimming copeopods. Scale bars all equal 1 mm. (Adapted from Nishibe et al., 2015)

The JFRA scientists were able to use these numbers to tease out the relationship between the copepods and the appendicularian houses. They found there is a tight coupling between the two groups. The VPR images showed that the proportion of copepods attached to the houses increased with the concentration of available houses up to about 2000 houses per cubic meter. Even when there were many houses in the water, copepods were only associated with a house about 35% of the time. Further analysis revealed that most of the consumption by the copepods took place in the upper 50 m of the water column. This result was consistent with the group’s observation that copepods did not attach themselves to houses as frequently at depths below 50 m.

To corroborate and better understand the field data, Nishibe and his team performed feeding studies in the lab. They grew copepods and fed them appendicularian houses. Behavioral observations were also conducted by video taping the feeding habits of an individual copepod in a chamber with a single house. Eight, one hour videos were made of different copepods eating new houses.

The video recordings from the lab revealed that the copepods spent about 6 minutes feeding on a house in a single sitting. The individual would swim away from the house and then return, paying many short visits to the house over the duration of the recording. This suggests that the in situ data could underestimate how often copepods eat the houses since they spend so much time swimming from place to place.

The estimated rate of house consumption by copepods from the field data came in at just under 10%. This may seem like a small number, but as Nishibe points out, it can make a big difference on a larger scale. Other studies have found that appendicularians can account for the vast majority of all organic carbon getting fluxed to the deep ocean. In that global context, 10% degredation represents a huge break down of material. It is certainly important enough to consider when discussing and studying oceanic carbon cycles.

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 5 days ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 2 weeks ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 3 weeks ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 1 month ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 3 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 3 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 4 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 4 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 5 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 5 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 6 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 6 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
  • by oceanbites 7 months ago
    Feeling a bit flattened by the week? So are these summer flounder larvae. Fun fact: flounder larvae start out with their eyes set like normal fish, but as they grow one of their eyes migrates to meet the other and
  • by oceanbites 7 months ago
    Have you seen a remote working setup like this? This is a photo from one of our Oceanbites team members Anne Hartwell. “A view from inside the control can of an underwater robot we used to explore the deep parts
  • by oceanbites 8 months ago
    Today is the day of  #shutdownacademia  and  #shutdownstem  and many of us at the Oceanbites team are taking the day to plan solid actions for how we can make our organization and the institutions we work at a better place
  • by oceanbites 8 months ago
    Black lives matter. The recent murders of Ahmaud Arbery, Breonna Taylor, and George Floyd have once again brought to light the racism in our country. All of us at Oceanbites stand with our Black colleagues, friends, readers, and family. The
WP2Social Auto Publish Powered By : XYZScripts.com