Feral Hogs: An Aquatic Nuisance Species Weakens the Resiliency of Coastal Marshes

By Rebecca Brown and Jim Page

Wilbur.  For many of us who grew up watching Charlotte’s Web, the site of America’s Favorite Pig is a welcome one.  However, though Charlotte’s porky friend was certainly cute and friendly, we have come to learn in our adulthood that such is not always the case with pigs and hogs, specifically for those who have no farm to call home.  Feral hogs, or wild pigs, have caused some of the most significant negative impacts on our ecosystems.  In fact, some scientists say wild pigs are the greatest vertebrate modifier of natural communities in the United States. 

Their destruction isn’t just a byproduct of their rooting and feeding behavior; sometimes, it is a direct consequence of their feeding behavior.  Scientists have learned that one of the favorite foods of wild pigs residing on Georgia’s barrier islands is also one of Georgia’s most threatened species:  sea turtles, specifically their eggs.  Research has shown that wild pigs will often use their enhanced sense of smell to locate a sea turtle nest, dig them up, and eat the eggs, thereby negatively impacting a sea turtle population already struggling to rebound. Though such negative impacts on sea turtles along our coast have been known for years, it wasn’t until recently that additional coastal impacts by these pests were realized.   A recent study in the marshes of the Sapelo Island National Estuarine Research Reserve has discovered feral hogs can also reduce the resilience of our southeastern United States salt marshes.

Feral hogs have a hefty appetite for ribbed mussels, a bi-valve that grows together in mounds and is commonly found in the marshes of Georgia.  These mussels have a non-trophic relationship with cordgrass, or Spartina, that regulates the ecosystem structure and resilience of salt marshes.  Scientists have learned that cordgrass and ribbed mussel have a positive mutualistic relationship in that the waste produced by the mussels provides nutrients for the growth of cordgrass and the cordgrass provides substrate and shade for the mussel.

Though their aesthetic beauty is well documented in the poetry of Sidney Lanier, cordgrass serves a much more important purpose.  Cordgrass is the base of the coastal marsh ecosystem that provides many ecosystem services. 

Additionally, cordgrass are essential for saltmarsh recovery after a catastrophic event such as a severe drought.  Recovery time after a large die-off of cordgrass can be a few years when ribbed mussels are present, as compared to many decades to recover when mussels are not present.

The discovery of the impacts of increased mussel predation by wild pigs along the coast is certainly alarming.  The loss of ribbed mussels can significantly weaken the resilience of our coastal marshes and thereby reduce the ecosystem services these marshes provide us.  Our coastal ecosystems are already facing increased pressure as global climate change increases the length and severity of droughts, increases storm intensity and frequency, and causes sea levels to rise. The facilitating species in non-trophic positive interactions can buffer against abiotic stress, widen niches, increase population densities, and strengthen ecosystem multi-functionality.  As a result of the learned negative impacts these pot-bellied pests can create, management plans created by resource managers need to adjust accordingly.  This means taking a wider approach to factor in how invasive species like wild hogs can alter non-trophic positive interactions (e.g. cordgrass and ribbed mussel).  We must consider how we as resource managers can prevent when possible and overcome when challenged with these unfortunate scenarios.  If we don’t, we may be left with less than nothing, and even a pig like Wilbur knows that’s the lowest you can go.

More Information: https://www.nature.com/articles/s41467-021-26504-4