In 2008, the United States and Canada required all ocean-going vessels entering the Great Lakes to manage ballast water discharges to prevent the spread of invasive species. Are the regulations working?
by Antoine Ricciardi(McGill, The conversation) Freshwater ecosystems are threatened by a host of environmental stressors from human activities. Among the most insidious and impactful of these is invasion by non-native species.
Over the past two centuries, established populations of nearly 190 non-native species invertebrates, fish, plants and microbes have been discovered in the Great Lakes Basin. They were introduced by multiple sources and pathways including canals, the release of pets, the dumping of bait buckets, aquaculture escapes and, most notably, the discharge of ballast water from transoceanic vessels.
Ballast tanks vessels can contain various life stages of invertebrates, fish larvae, and huge amounts of phytoplankton and zooplankton. Ballast water discharge is responsible for thousands of coastal invasions worldwide. It was the most significant cause of invasion in the Great Lakes since 1959when the modern St. Lawrence Seaway was opened to accommodate larger ocean-going cargo-carrying vessels.
In the mid-1980s, a freighter from Eastern Europe began an overseas voyage to the Great Lakes. Before the ship left its home port, water was pumped into its ballast tanks to add weight and stability in order to cross the Atlantic Ocean safely. The water contained larvae of an invasive freshwater mussel. After crossing the St. Lawrence Seaway, the ship spilled some of the water — and mussel larvae — into a Great Lakes port, introducing the zebra mussel in North America. This scenario has happened for many other species.
Effective management of the ballast water pathway is critical to slowing the rate of invasion into the Great Lakes and protecting its resources. Here I describe an intervention that apparently achieved this goal.
Gaps in ballast water management
From 1959 to 2006, a new invader has been discovered established in the Great Lakes basin every six to seven months, on average. No other freshwater system on the planet has been invaded so frequently.
Almost two-thirds of these species were delivered in ballast water. They include invaders who have reduced native biodiversity, impaired fisheries and caused other ecological problems and socio-economic impacts in the Great Lakes.
In 1993, Canada and the United States attempted to control ballast water invasions by requiring incoming ships to exchange their freshwater ballast with saltwater before entering the Great Lakes.
The logic behind this regulation was that freshwater organisms in the ballast tanks would either be purged or killed by exposure to salt water, and any marine organisms randomly captured during the process would be unable to breed in the Great Lakes.
Surprisingly, new non-native freshwater species, such as the fishhook water flea, Ponto-Caspian amphipod, and blood-red mysid shrimp, continued to be discovered in the Great Lakes more than a decade after the settlement.
The effectiveness of the regulations was undermined by incoming ships not being required to undergo a ballast water exchange because they declared they had no pumpable ballast on board, despite there is residual water in their “empty” tanks.
Indeed, such ships, which constituted the majority of ships entering the seawaywore on average 47 tons of residual water and 15 tons of sediment in their ballast tanks and contained various living freshwater invertebrates.
After visiting a Great Lakes port to unload their cargo, these unregulated ships pumped in water to replace lost weight. Then they would go to another port to pick up a new cargo and discharge the water, now contaminated with organisms. Several invaders have been introduced to the Great Lakes by this route.
An unprecedented reduction in invasions
To remedy this problem, a procedure called a salt water rinse was developed. Onboard experiences showed that flushing ballast tanks with seawater to the point where the salinity of the tanks reached oceanic concentrations significantly reduced the abundance and diversity of organisms in the tanks. https://www.youtube.com/embed/KYIJdhw8NcA?wmode=transparent&start=0 Ballast water is recognized as a serious management issue for the Great Lakes.
In 2006 and 2008, Canada and United States, respectively, mandated all transoceanic vessels to perform a saltwater flush to ensure that partially filled ballast tanks contained water corresponding to ocean salinity before entering the Seaway. The regulation was enforced by inspection on board each ship.
My colleague, Hugh MacIsaac and I tested the effectiveness of this regulation using historical data. In our study, we compared the number of newly detected non-native species recorded in the basin over three separate 13-year periods: 1981-1993, when ballast water was unregulated; 1994-2006, period of partial regulation; and 2007-2019, the period of strict regulation which applied the new procedure.
We detected 19 invaders and 26 invaders in the first and second periods, respectively. After saltwater flushing became mandatory, the number dropped to just four new invaders in 13 years. Since 2008, new invasions recorded in the Great Lakes basin have decreased by 85%. The frequency of invasion is now at the lowest rate ever recorded in the basin.
We took into account changes in water temperature, search effort and vessel traffic during these periods. None of them can explain, even in part, the abrupt drop in the invasion rate.
While other management efforts – such as public education and laws prohibiting the possession and sale of particular species — could have contributed to the decline, the empirical evidence cited in our study points to ballast water regulation as the primary cause.
The risk of invasion is reduced, but not eliminated
The Great Lakes remain under threat of invasion by various other waysespecially those associated withlive trade» ornamental plants for ponds, aquarium animals, bait fish and live animals sold in food markets.
One of them is tencha European fish illegally brought to a Quebec fish farm in the mid-1980s and whose population is now expanding in the St. Lawrence River.
Meanwhile, four species of non-native carp (bighead carp, silver carp, grass carp, and black carp) raised on fish farms in the southern United States have spread throughout the Mississippi basin in recent decades. and pose a problem. continued risk of invading the Great Lakes. Grass carp was found spawning in tributaries of Lake Erie and is about to invade parts of the basin.
Finding new strategies to manage these risks is vital to conserving biodiversity and protecting a multi-billion dollar fishery. Our study has shown the benefit of collaboration between researchers, governments and industry towards this goal.