Ballast

By Kirsti Scott

Cobble stone walkway in Savannah, Georgia (Phillip Salvador / Shutterstock.com)

The stones you find in towns along the coast or underwater just offshore may have traveled a long way before landing in the U.S. Some of these stones may have started out as ship ballast stones from Europe, used to stabilize ships during long voyages across the ocean. Once the ship landed at its destination, the ballast was commonly thrown overboard or piled onshore and replaced with more valuable products to be shipped back to Europe or on to another destination.

People living in the American colonies typically bought fewer manufactured goods from abroad, so ships traveling to the colonies were not filled with products for sale. Instead, the space in the hold of incoming ships was filled with ballast, usually stones. When the ships returned from the colonies with lumber, grain, tobacco, and other products, there was no need for the extra ballast.

When ships arrived at a harbor, they would jettison their stones in the water. In 1734, South Carolina’s legislature passed a law requiring ships to transfer their ballast stones to a barge that took the stones to shore. In 1769, a bill was introduced in North Carolina to appoint a ballast master to regulate the dumping of stones near harbors, which was so common that ships began having difficulty getting into the harbors. In 1784, the General Assembly passed an act to prohibit stones being dumped in river channels, requiring ships to jettison their ballast further out to sea.

Some of the discarded stones that ended up on beaches or in towns did not go to waste. Locals used the rocks for foundations of riverfront warehouses, retaining walls, and other rough structures. In the 18th century, most coastal roads were made of mud, sand, or crushed shells. However, in the 19th and 20th centuries, some of the smooth ballast stones were used as cobblestones to pave streets in towns up and down the East Coast. While they were a free resource, the stones were not shaped specifically for building use, so their use was usually limited to projects that did not require regular-shaped pieces.

Old San Juan city with colorful houses and cobblestone street (Nancy Pauwels / Shutterstock.com)

Most bricks are made with inexpensive, easily sourced materials and used for projects very close to where they were manufactured. However, in some cases, instead of stones sturdy, inexpensive bricks were used for ballast in ships sailing from Europe. Made from the waste from iron smelting, inexpensive bricks were used as ballast in ships traveling from Spain to the world’s oldest colony, Puerto Rico. You can still find remnants of this ballast in the cobblestone streets of old San Juan. These cobblestones, known as adoquines, help absorb and channel water through the pavement. Over time, the moisture has turned the bricks their distinctive blue color. Though not technically ballast, which would be dumped automatically when a ship reached its destination, these blue slag bricks could be dumped if necessary, without the shipper losing much money.

Blue cobblestone paved street in Old San Juan, Puerto Rico (Kirsti Scott).

Contrary to popular belief, pottery, marbles, or other finished products were not used as ballast, primarily because ballast is added or jettisoned as needed. The items used as ballast were meant to be disposable. Any goods in the ship were meant to be sold, and ballast was meant to be loaded or discarded depending on the circumstances.

Large cargo ship discharging ballast water (StockStudio Aerials / Shutterstock.com).

Today, commercial ships use sea water as ballast instead of stones. Large steel ballast tanks take on or dump water as needed during a voyage, which is more efficient than loading and unloading stones.

While discarding ballast stones rarely affects the environment, when ballast water is pumped into the tanks in one body of water and released in another, it can harm the ecosystem. Viruses, bacteria, algae, jellyfish, crabs, mollusks, and fish that survive the trip can be released where they don’t naturally occur. According to the National Research Council, more than 3,000 species of plants and animals are transported daily around the world in ballast water. These organisms can create havoc, becoming invasive species or harming the local ecosystems.

The International Convention for the Control and Management of Ships’ Ballast Water and Sediments was adopted in 2004 to control the transfer of potentially invasive species. With the treaty now in force, ships need to manage their ballast water, hopefully reducing the problems created by using water instead of stones for ballast.

A cluster of invasive zebra mussels and barnacles attached to the bottom hull of a ship (Dolores M. Harvey/Shutterstock.com).

When ships discharge ballast water, it can release potentially invasive species and bacteria into a new marine environment. Below are some of the species that have spread to bodies of water through this mechanism, according to the International Maritime Organization.

Undaria pinnatifida seaweed growing at the beach (Kelly Headrick/Shutterstock.com). Vibrio cholerae bacterial colonies on blood agar plate (Chansom Pantip/Shutterstock.com). Carcinus maenas on a fish farm structure surrounded by mussels (AlDigital On/Shutterstock.com). Asterias amurensis, a serious environmental pest in Australia (David Lade/Shutterstock.com). Jellyfish in the Adriatic sea (SaskiaAcht/Shutterstock.com).

Asian Kelp

Undaria pinnatifida

Also known as wakame, this edible seaweed is commonly used in Japanese and Korean cuisine and is native to cold-water coastal areas of Japan, Korea, and China. It has spread to New Zealand, France, Great Britain, Spain, Italy, Argentina, Australia, Mexico, and the U.S. The kelp was discovered in San Francisco Bay in May 2009.

Cholera

Vibrio cholera

Port areas near the mouths of rivers are prime breeding ground for cholera bacteria, especially in countries where sanitation is poor, and water has been heavily polluted with raw sewage. These bacteria attach to the surfaces of waterborne microscopic organisms and enter ballast water, traveling to new areas around the world.

European Green Crab

Carcinus maenas

This species has spread from its habitat in the northeast Atlantic Ocean and Baltic Sea to Oceana, South Africa, South America, and the Atlantic and Pacific Coasts of North America. This carnivore preys on clams, mussels, oysters, and gastropods, costing fishing industries millions of dollars and endangering stock.

North Pacific Seastar

Asterias amurensis

Native to Japan, North China, Korea, and far eastern Russia, this starfish is now found in estuaries and intertidal zones in southeastern Australia and Tasmania, after having been carried as larvae in ballast water. In Australia North Pacific seastars eat the eggs of the endangered handfish and other fish.

Sea walnut

Mnemiopsis leidyi

The sea walnut is native to the eastern coast of North and South America, but has invaded the Black, Azov, Aegean, and Marmara Seas; the west coast of Sweden; and the Southern and Northern Baltic Sea. These carnivorous jellies feed on zooplankton, crustaceans, fish eggs, larvae, and even their own species.

This article appeared in Beachcombing Magazine Volume 46 the January/February 2025 issue.