//
you're reading...

Ecology

Consider the marsh crab: Climate change shifts which species are key

The marsh crab, Sesarma reticulatum, is helping to shape marsh environments during climate change. Image by Esuglia at Wikimedia Commons.

Munching, nibbling and burrowing their way through life, the humble marsh crab can now add “keystone species” to its ecological resume. As sea level rise has inundated shorelines on the East Coast of the United States, marsh crabs have emerged as important players in shaping how marshes respond to climate change. A new study suggests that these little crabs, once relegated to the bench to watch other heavy-hitting species play the most impactful ecological roles, are now changing the way creeks flow through marshes, what other animals live there, and maybe even the way marshes will function in the future.

A drowning land

Sea level rise is one of the more immediate impacts of climate change, and nowhere is this more evident than in salt marshes. In general, as the sea level rises, marshes spend more time underwater. This may seem like no big deal since marshes are tidal anyway, spending hours underwater every day. However, this can be harmful for the plants that  grow in marshes, specifically cordgrass Spartina alterniflora – food for marsh crabs.

To determine how much sea level rise was impacting salt marshes in the southeastern United States, the researchers examined hourly historic sea level data in salt marshes between South Carolina and northern Florida. They found that sea level rose at a rate 2.2-2.6 times greater from 1999-2019 than it had from 1940-1998. Even worse, they estimated that salt marshes spent between 2 and 55 times more time underwater from 1999-2019 than from 1940-1998. Altogether, the marshes were submerged from 219 to 402 more hours (that’s nine to about 17 more days) in 2019 than in 1999. The marshes are essentially drowning.

Consider the marsh crab

A creek running through a marsh at low tide. A creekhead is the highest point where a creek begins to flow through the marsh out to the sea. Image from John Myers at the Geograph Project.

The marsh crab, Sesarma reticulatum, has historically been a relatively small part of a salt marsh community, but researchers noted that over the years, creekheads with dense marsh crab populations have become more common in marshes. Suspecting that sea level rise might be driving this change, the researchers used aerial images to look at nine sites along the coastline between South Carolina and Florida. They found that creekheads with visual signs of grazing from marsh crabs increased in all sites. Where there were marsh crabs, creeks grew longer each year and drained more water out of the marsh.

How are the marsh crabs able to make such big changes? The researchers found that marshes that had the most marsh crabs were those that had the most drainage problems to begin with. Marsh crabs preferred creeks that were too small to effectively drain the marshes between tides. The more time the soil spends underwater, the softer it gets and the less work marsh crabs have to do when they burrow. However, as the marsh crabs eat away at the cordgrass around the creek and burrow, the soil is further weakened and the creek grows as more water flows in from the marsh and erodes the banks.

No place to hide

By settling along the creekhead and eating the cordgrass, marsh crabs actually make it harder for other animals, primarily other invertebrates (animals without a backbone like mussels or snails) to live there with them. Cordgrass serves as a physical barrier between hungry animals swimming in the water and the animals living along the banks of the creek, like mussels. When the crabs eat the cordgrass, this barrier is removed. The researchers found that the total mass of animals living along the borders of ungrazed marshes was more than a whopping 600% higher than in marshes that were grazed by marsh crabs. The missing cordgrass meant that snails, mussels, and other invertebrates had nowhere to hide from their predators, like fish or other crabs.

A creek runs through a salt marsh in New Hampshire with cordgrass, Spartina alterniflora, along its banks. Picture taken by Katherine Whittemore at the US Fish and Wildlife Service.

Marsh crabs are key(stone)

The small but mighty marsh crabs now have a disproportionately large impact on their environment. Sometimes they directly impact the marsh – they reduce cordgrass by eating it and burrowing into the mud. However, many of the things they do indirectly (reducing the number of mussels in the marsh, helping creeks grow and drain marshes more efficiently) may have an even larger impact. This power to shape the foundations of their environment means that the marsh crab could be a new keystone species, or a species which others in the ecosystem rely on. In the past, scientists viewed cordgrass alone as the defining species of salt marshes due to how it provides shelter from predators and also controls water flow through the marshes. By controlling cordgrass, however, the marsh crabs have become more important than ever in these drowning ecosystems.

The times they are a-changin’

Climate change is the reason why marsh crabs are becoming a keystone species. Without it, the soil along creekheads would be too dense for marsh crabs to have a large impact, but as marshes become more swamped by sea level rise, the soil weakens and the marsh crabs can do their work.

This is, however, a temporary condition. Marsh crabs ultimately improve the drainage in marshes by helping to expand the creeks, and the soil eventually hardens again, making it less hospitable to marsh crabs.

Yet this does not necessarily mean that marsh crabs will save salt marshes from drowning. The rate of sea level rise is increasing, and in many places, marshes have not been able to keep up. Coastal ecosystems are in flux, and the future of these lands and their species is still uncertain. Still, as the climate changes, the relationships between species may as well. Who knows? Maybe somewhere else, another small, humble animal has suddenly become key.

Reference: Sinéad M. Crotty, Collin Ortals, Thomas M. Pettengill, Luming Shi, Maitane Olabarrieta, Matthew A. Joyce, Andrew H. Altieri, Elise Morrison, Thomas S. Bianchi, Christopher Craft, Mark D. Bertness, Christine Angelini. Sea-level rise and the emergence of a keystone grazer alter the geomorphic evolution and ecology of southeast US salt marshes. Proceedings of the National Academy of Sciences, 2020; 201917869 DOI: 10.1073/pnas.1917869117

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 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 9 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 10 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 12 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