What’s That Smell? Stinky Potato Sponges Cover Sandy Hook Beaches

On August 14th, COA received a message from a concerned beach-goer about something unusual and smelly on the beach. On the bay side of Sandy Hook, there was a large wash up of gray, softball sized objects with a very rotten stench. As it turns out, these objects are part of nature!

Mystery objects washed ashore on Sandy Hook (Picture Credits: Twitter @kimhalligan1)

 The mystery debris that lay scattered over the bayside beaches of Sandy Hook was identified as potato sponges, a group of demosponges within the genus Craniella. Potato sponges are animals, Porifera, that call our precious waterways home. These creatures use their needle-like spicules to attach to the coarse sand at the bottom of the marine environment that they inhabit. While attached to this spot, they feed by drawing water in, filtering out the nutrients, and forcing the water back out. 

Sponges can be forced to dislodge from their stationary location and float to the surface of the water where they will eventually be carried to wash-up on land. The most common causes for the dislodgement of these sponges are strong currents. This kind of movement is most commonly associated with powerful, up to hurricane level, storms. Once the sponges have been displaced and washed ashore, these animals are no longer alive. When they die, the organic material inside begins to decompose, which is what generates the smell that is commonly reported. This stench, however foul, is just part of a natural process as the bacteria break down the sponge and the cycling of nutrients continues. 

Dissection of a potato sponge specimen collected by the COA crew

From what we can tell, there have not been any official reports of potato sponges in the Sandy Hook Bay previously. However, there was a wash-up event in the nearby Barnegat Bay in 2011 after Hurricane Irene hit the area. This indicates that potato sponges are common in the type of environment that the NJ bays provide and are not invasive to the area. Whether they have been inhabitants of Sandy Hook Bay for months, decades, or centuries remains a mystery as this is the first reported wash-up event of this scale. 

Potato sponge (bottom) floating nearshore in the Sandy Hook Bay

There are a few theories that could explain why this die-off of potato sponges occurred in a healthy bay with no recent hurricane activity. Although there was not a hurricane, the week preceding the wash-up event was very stormy. There were multiple heavy rainstorms that passed over the bay in a few day period. This repeated strong storm activity could have been a cause for the dislocation of the sponges from their substrate. Another possible theory is that the sponges were dislodged due to dredging. There has been dredging activity in the Sandy Hook Bay, which disturbs the sandy bottom, and the sponges may have been forcibly detached as a result. Dredging, storm currents, or a combination of the two are the most probable causes for these smelly visitors making their way onto our beaches.