you're reading...

Invasive Species

Builders or Opportunistic Squatters? Invasive Species Drives Ecosystem Change on Georges Bank

See article here: https://link.springer.com/article/10.1007/s10530-017-1517-y

Colonial tunicates, Nick Hobgood

Tunicates are underappreciated seafloor animals. Living sedentary lives and resembling some kind of marine slime, they don’t usually make it into headlines or flashy ocean documentaries. They are, however, important components of marine ecosystems (super cute ones too, like these bright blue ones), building bottom habitats and providing food for a number of fish and other marine animals. As adults, many tunicates are glued to the seabottom, filter feeding on passing plankton and doing their best not to breed with their siblings. Larvae, though, are free swimming and more closely resemble tadpoles than adult tunicates. Released larvae swim for a couple of hours to days until they settle down somewhere new and form their own colony.

Didemnum vexillum is a type of tunicate scientists think is native to the Pacific Ocean off Japan. Since the mid 1900s, it’s been making its way into the east and west Atlantic, North Sea, and Mediterranean, supposedly transported by imported oyster stock for aquaculture operations. Commonly known as carpet sea squirts, carpet tunicate, or, my personal favorite, Marine Vomit, Didemnum has slowly made itself a pest to benthic ecosystems throughout the world. Growing at depths of 200 or so feet, Didemnum forms coral-like colonies of relatively small but connected individuals that collaboratively envelop entire rocks, coral formations, shellfish beds, and other hard surfaces. If smothering wasn’t enough, Didemnum also secretes a toxic substance over its substrate to prevent predation and the settlement of other larval species. It is The Blob, only underwater and lacking it’s own blockbuster.

Marine Vomit, Dann Blackwood, USGS

Invasive species are a hot topic in ecology and evolution. Most scientists define invasive species as non-natives (or aliens) that have become a problem in their newly colonized homes. They may be really good at eating native species, competing with natives for space, or otherwise excluding natives from their habitats. Sometimes, aliens get blamed for the degradation of native species that are actually failing in response to other changes, almost always rooted in human interference (pollution, habitat degradation, fragmentation, etc.) Though, if Donald Trump tried to implement an invasive species travel ban it would probably be widely endorsed by the scientific community for the much needed research funding it would open up. But I digress… On short time scales, those important to us humans, the introduction of a new species can seriously alter the normal functioning of an ecosystem we depend on. The number of “invaders” has also dramatically increased in the last 50 years. Where humans have benefited from increased international trade and complex world transport systems, so have alien species. It is therefore important to understand when and why they become invasive; whether an alien is causing ecosystem change or if they’re just moving into available territory.

Scientists are concerned about Didemnum because, where it’s found, many other previously abundant species tend to disappear. From the Mediterranean to the Atlantic, Didemnum arrival seems to exclude a variety of seafloor organisms. Kaplan et al. asked whether the seemingly unstoppable Didemnum is the driver of the ecosystem change noted widely across its invasion track, or if it’s just an opportunistic squatter taking advantage of space opened up by other human activities. It’s an important question, because the answer could give scientists clues to the best course of restoring these ecosystems.

They took a vessel-towed underwater camera called a HabCam to the bottom of Georges Bank to investigate the causes of bottom system decline there. Georges Bank has a long history of bottom trawling, a destructive fishing method that scrapes the ocean bottom of most coral and other habitat-forming species. It’s also the site of a number of protected areas where bottom trawling is no longer allowed. This makes it the perfect spot to compare Didemnum colonies and see what’s causing decline in bottom communities: Trawling or Didemnum.

Photos from the Habcam, Kaplan et. al. 2017

Kaplan et al.’s underwater camera found a variety of native sea sponges, sea stars, cnidarians, polychaete worms, various shellfish, and Didemnum in both the open and protected areas on Georges Bank. Didemnum presence, especially in large colonies, was correlated with decreased biodiversity of other bottom species. Interestingly, this decline did not differ between the open fishing area and the protected area under study. Species composition differs between protected areas and those open to fishing, as a direct result of bottom trawling, but both areas decline in biodiversity when Didemnum is present. This supports the hypothesis that the invasive Didenum tunicate drives ecosystem change, and isn’t just riding on the back of another destructive human activity. Builder, it is!

Kaplan et al.’s study is important for informing the builder vs. squatter debate in invasive species biology, but also because it profiled a section of a highly altered bottom site on Georges Bank, one of the most important fishing areas in the world. Future studies in seafloor community dynamics could benefit from the success of this study’s use of the towed underwater camera to collect abundance data. Follow up studies on the role played by Didemnum in seafloor communities could look at larger study areas, multiple protected areas, and regions more intensely fished. It will be important to repeat Kaplan et al.’s approach to monitor changes in the Didemnum-macroinvertebrate relationship over time. Even though Didemnum may have arrived on Georges Bank as long as 50 years ago, community ecology works on spans of hundreds of years, and continued monitoring for Didemnum (as well as other newcomers) will be important to inform future seafloor management.


No comments yet.

Post a Comment


  • by oceanbites 2 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 3 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 4 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 5 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 5 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 5 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 6 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 6 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 6 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 7 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 7 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 7 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 7 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 8 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 9 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 9 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 9 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 10 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 11 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 11 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 
WP2Social Auto Publish Powered By : XYZScripts.com