you're reading...


Menacing microplastics hamper hermit crab choices

Crump A, Mullens C, Bethell EJ, Cunningham EM, Arnott G. 2020 Microplastics disrupt hermit crab shell selection. Biol. Lett. 16: 20200030. http://dx.doi.org/10.1098/rsbl.2020.0030

Microplastic intrusion 

Marine debris like this will eventually break down to form microplastics which are a threat to ocean organisms. Image credit: NOAA Marine Debris Program

Tiny plastic particles of varying shapes and sizes saturate waters from the depths of the ocean to its sandy shores. These microplastics can infiltrate the bodies of marine animals, disrupting their lives in ways we are still only just beginning to understand.

Many of these microplastics have spent a lifetime breaking down.  Minute plastic fragments may start off as full-sized water bottles or plastic packaging or any number of other pieces of plastic which were disposed of but which in reality found their way into the sea. Very slowly, plastics are weathered by ocean waves and the sun’s intense UV rays, getting smaller and smaller without disappearing altogether. While some microplastics are fragmented bits of larger objects, others are microbeads or tiny pellets intentionally manufactured to such a small size. Regardless of their origin, microplastics are gradually becoming ubiquitous within the world’s oceans and their inhabitants.

It seems intuitive that tiny plastics making their way into an animal’s body would have negative physiological impacts – animal bodies, their organs and tissues, were never intended to encounter these unnatural bits and pieces of plastic which take so long to decompose. But how might microplastics affect an animal’s behavior and cognition, their ability to gather information and make decisions?

Hermit crab shells

In a recent study, scientists investigated this question by looking at how hermit crab shell selection is impacted by exposure to microplastic-filled water. To conduct their experiment, researchers collected European hermit crabs from the beaches of Northern Ireland. This species, and all other species of hermit crabs, must change shells as they grow, and choosing an optimal shell is essential for survival.

A European hermit crab, Pagurus bernhardus. Image credit: Hans Hillewaert via Wikimedia

When a hermit crab encounters a shell, they assess the inside and outside, collecting information in order to determine if the shell is adequate, to decide whether it is time to leave their current home and move into a new one. Hermit crabs use their small claws, called chelipeds, to inspect a new shell, exploring whether it might be worth a move. This process requires proper cognitive functioning; in order to accurately assess the shell, the crab must be able to collect and process information before making a decision. Would hermit crab shell selection and cognition still function the same when subject to microplastic pollution?

It looks like the answer, based on the scientists’ experiments, is no.

Impaired shell swapping

The researchers placed hermit crabs in suboptimal shells before putting them into a tank and giving them the option of a new, better shell to move into. Half of the crabs tested were placed into microplastic-laden water, while the other half were not exposed to any microplastics. As part of their experimental design, the researchers made sure that the levels of microplastics they exposed the hermit crabs to mimicked the amount of plastic they might encounter in a natural setting. This is different from past studies, which often exposed marine organisms to higher concentrations of microplastics than those found in most coastal habitats.

Hermit crabs which were exposed to microplastics touched the new shells less frequently, took longer to come into contact with the new shell, spent less time assessing the shell, and swapped suboptimal for optimal shells less often than their counterparts in the control experiments.

An assortment of microplastics. Image credit: 5Gyres.

More research is necessary to figure out exactly what changed the hermit crab’s behavior and ability to select a better shell, but the authors of this recent study suggest that it may have been due to changes in energy levels after ingesting microplastics. The microplastics used in this study were likely too large to have entered the bloodstream and made their way to the brain where they could impact cognitive processes directly. Since this study’s microplastics were used because of their similarity to those found in the crab’s natural habitat, it seems unlikely that the brain would be directly impacted in the wild, either.

What may have happened instead is that the crabs’ brain functions were impaired by decreased energy levels brought about by consumption of microplastics. When marine organisms consume microplastics, they feel full even though they have consumed particles which don’t provide them with any nutrition. They then stop eating, but the lack of nutrients means that their body is not getting the energy that it needs to get from finding food. Decision-making by the brain requires adequate amounts of energy, something which a crab with a stomach full of microplastics cannot provide.

Cutting down on plastics

Survival in the ocean is a difficult task, involving everything from searching for food to finding the perfect shell for protection from predators. With more research, it’s becoming more and more evident that microplastics and a variety of other forms of pollution can impact all of these different aspects of survival for a marine organism. In order for organisms to continue to survive and thrive in the ocean and around the globe, we need to cut down on microplastics at the source, reducing plastic production and usage before it finds its way beneath the waves.


No comments yet.

Post a Comment


  • 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 8 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 11 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