Global Shipping’s Aquatic Stowaways Wreak Havoc in Local Waters

Nov 20, 2015Fall 2015

The cobblestones that line the historic thoroughfare that is Thames Street in downtown Newport, Rhode Island, are remnants of the city’s seafaring past. Some were once used as ballast to stabilize large, seafaring vessels from Europe in the 1700s and 1800s, and today are evidence of a long-standing heritage of marine transportation and trade in Rhode Island.

Today, there are about 22,000 ships, at any time, coming and going from New England waters. It’s not uncommon to see transatlantic cargo vessels and tankers delivering material goods and fuel to Newport or Providence, the second deepest port in the region and the energy hub for southern New England, as well as to the port of Davisville, the 7th largest auto importer in North America. Daily, 200-foot commercial tankers and bulk cargo carriers travel into Narragansett Bay delivering over 2,000 tons of petroleum, scrap metal, automobiles, food, and dry goods from all over the globe.


Ships converge in Providence Harbor, the energy hub for southern New England. Photograph by Michael Cevoli

But since the introduction of steel-hulled vessels about 120 years ago, ballast tanks filled with millions of gallons of seawater have replaced large stones to stabilize oceangoing vessels in transit by weighing down the vessel’s center of gravity.

When the ships reach the shallower waters close to the destination port, they discharge some of that ballast water, and along with it, any tiny living things that stowed away for the voyage. Most of these organisms—ranging from crabs and fish to microscopic plants and pathogens—will fail to gain any foothold in their new environment, but those that do can end up radically changing the marine landscape and can mean disaster for the local environment, economy, and public health.

“When the contents of Tokyo Harbor dump out in Narragansett Bay, most of it dies, but a small percentage lives,” says Kevin Cute, marine resource specialist for the R.I. Coastal Resources Management Council (CRMC), explaining that the local conditions may either be too hot, cold, or inhospitable for non-native species. “Most non-native species don’t survive, but when they’re successful, they’re famously successful.”

Some of these newly introduced species are better equipped at competing for food and space than native species, and some are able to spawn for longer periods of time. Also, native predators often don’t recognize these new species as potential prey. Soon, these “invasive species take over critical habitat for native species,” Cute says.

Aquatic invasive species (AIS) are one of the leading threats to biodiversity and to the world’s oceans, according to the International Maritime Organization (IMO), the United Nations’ agency responsible for improving maritime safety and preventing pollution from ships.

The zebra mussel, native to Russia and introduced to North America in 1988 via a transatlantic freighter, is one of the most well-known invasive species for having spread to all five Great Lakes within 10 years of its introduction, causing about $5 billion in damage to harbors, waterways, fisheries, recreation and water treatment systems according to the U.S. Fish and Wildlife Service.

This prolific species out-competes native species and attaches to manmade structures, particularly pipelines, impeding water movement through hydroelectric turbines and intake structures for drinking water and irrigation systems.

Although they have not been documented in Rhode Island, zebra mussels are a species of concern because they are found in the Connecticut side of the Housatonic watershed and near the Massachusetts border, and are expected to invade every freshwater habitat in the nation within the next 20 years.

The primary threat for spreading zebra mussels in Rhode Island is now the recreational boater, according to the R.I. Department of Environmental Management.

Additional studies suggest that other invasive mollusks cost the U.S. more than $6 billion per year in environmental damages and losses, while some estimate a $120 billion financial loss every year in the United States alone due to “bio-invasions.”

For Rhode Island, the most problematic invasives thus far, which were introduced directly by ballast water in state waters or in neighboring waters, include the European Green Crab, the Asian Shore Crab, the Chinese Mitten Crab, several types of colonial tunicates, and the Oriental Grass Shrimp, according to Cute.

Colonial tunicates “are really impacting eelgrass, which is scary,” Cute says. These marine invertebrates, also known as sea squirts, wreak havoc on shellfish and eelgrass beds by growing rapidly to form colonies of hundreds of organisms that spread like mats, engulfing their surroundings. They don’t directly kill shellfish or eelgrass, which provides essential nursery habitat for healthy fisheries, but they can block out sunlight and out-compete for vital oxygen and nutrient resources, changing the entire ecosystem.



The European green crab is one of the most successful coastal invaders and has established itself in coastal habitats on the East and West coasts of the U.S. It’s been over two centuries since the green crab ventured from Newfoundland waters to establish itself on five continents. With an epic appetite—able to consume 40 clams in a day—these 2 to 4-inch critters destroy eelgrass beds and shellfish populations and have been implicated in the destruction of the soft-shell clam fisheries in New England, according to the U.S. Geological Survey.

It is estimated that between 1997 and 2005, East Coast shellfishermen lost between 67.5 and 77 million pounds of quahogs, soft-shell clams, blue mussels, and bay scallops to green crab predation every year, according to the U.S. Environmental Protection Agency (EPA).

Even though the European green crab has been taking up residence in local waters since the mid-1800s, squatter rights do not apply.

“Invasions are invasions, no matter how long ago they occurred,” said James Carlton, the world’s leading expert on aquatic invasive species and professor emeritus at Williams College, at a 2012 aquatic invasive species conference held by CRMC. “Invasive species do not become native or naturalized, even after hundreds of years. An understanding of ‘historicalinvasions’ is critical for interpreting community and ecosystem history.”

In other words, says Niels Hobbs, a Ph.D. student at the University of Rhode Island studying the impacts of invasive species, it’s important to see how the morphology of native species changes in response, as well as the environment as a whole, so when another new species does arrive, “we have a better idea of what to expect, and how to better manage those impacts.”

“We need to keep a fairly fine finger on the pulse of change in biodiversity,” says Carlton, whose recent work has taken him from Maine to Long Island Sound surveying ports, docks, harbors, and marinas to obtain a baseline of current invasives. He says the “hope” of the survey team is not to find anything new, but he adds that if they do, they must study the new species, its distribution throughout the area, and its impact on native species.

About one to two new species are discovered in Rhode Island waters each year, according to Cute, who says it’s difficult to know when they were introduced since the state only started a volunteer monitoring program in 2009 at docks located at five sites: Save The Bay in Providence, Allen Harbor, Point Judith Marina, East Bay Yachting Center, and the Fort Adams Boat Basin.

“These floating docks are excellent proxy habitats and are the foundation of our understanding of invasive species in the bay,” says Cute, explaining that one of the main purposes of the monitoring program is to determine whether these species are spreading
in Narragansett Bay. “We need volunteers to find that answer.”

Invasive species are spread throughout the world via ballast water in addition to aquarium and ornamental trades, aquaculture and recreational boating, as well as expanding ranges due to climate change.

Invasive species are spread throughout the world via ballast water in addition to aquariums and ornamental trades, aquaculture, and recreational boating, as well as expanding ranges due to climate change. Photograph by Michael Cevoli


While many non-native species are beyond eradicating, efforts are being made to control current populations and prevent the arrival of new species. Understanding how these species arrive is the most crucial part, says Carlton.

In addition to ballast water, invasive hitchhikers have many means of transportation to local waters, from aquariums and ornamental trades to aquaculture and recreational boating, as well as expanding ranges due to climate change.

But ballast water management has been given greater attention in recent decades because of the sheer volume—more than 2 million gallons of ballast water (equivalent to three Olympic-sized swimming pools) are released in U.S. waters every hour—that is 555 gallons a second—according to the Narragansett Bay Research Reserve.

Currently, mid-ocean (200 miles out from shore) ballast water exchange is the only internationally accepted, and required practice. This involves either overflowing the tanks or emptying and flushing them with mid-ocean water taken from at least 200 meters deep. If done correctly, this can eliminate nearly 99 percent of the biological content. However, this process can be dangerous and ineffective in inclement weather and rough seas.

Other factors impacting the effectiveness of mid-ocean exchange include equipment failure and biota living in sediments that accumulate in ballast tanks that may not get flushed out. Onboard alternative treatment systems that either use chlorine or UV light to render organisms harmless are encouraged for this reason.

But even now, when ships are required to dump and exchange their ballast water out in the open ocean to rid themselves of potentially invasive species, the spread of invasives continues to grow. This is because, in a new globalized economy, shipping accounts for 90 percent of the world trade.

“It’s Russian roulette,” Hobbs says, explaining that increased commerce ups the odds on invasive species establishing themselves. “It’s stacking the deck in favor of more successful species.”

Since 2012, all oceangoing freighters entering American waters are required by the U.S. Coast Guard to install onboard treatment systems that filter and disinfect their ballast water. This final ruling sets the upper limit for allowable concentrations of organisms in ballast water depending on species type and size, as well as vessel size and design. However, there are currently no treatment systems that meet the Coast Guard’s standards, says Gavin Black, legal counsel for Moran Shipping, based in Providence, explaining that there are procedures for vessels to receive a “temporary pass,” if outfitted to international standards, which have yet to be formally instituted.

While Carlton admits current regulations and technology haven’t “nailed the lid” on the introduction of invasive species from ballast water, he believes that other factors, such as biofouling (where organisms attach to the hull of the ship), climate change, and other vectors beyond shipping are contributing to an increase of invasive species.

With global climate change, Carlton says, Rhode Island can also expect to see southern species crop up in Narragansett Bay in a “Chesapeake [Bay] invasion.”

“We have to know how they’re getting here,” he says, explaining that understanding all the ways in which invasive species are transported is crucial for management. “The real question is, is it preventable or inextricable?”

And if we can’t control invasions, we’ll have to adapt, says Cute. And how we adapt will be based on what we know ecologically about these species, which in many cases is nil.

— By Meredith Haas
     Photographs by Michael Cevoli

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