//
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 3 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 4 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 5 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 6 months 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 7 months 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 7 months 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 7 months 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 8 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 8 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 8 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 8 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 9 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 9 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 10 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 10 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 11 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 11 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 12 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 1 year 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 
WP2Social Auto Publish Powered By : XYZScripts.com