Ballast Water and the Transport of Harmful Algae
Commercial ships transport oil, iron ore, grain, and other cargo to ports worldwide. Most of these ships have large steel tanks, called ballast tanks, located along the sides and bottoms of their hulls. The ballast tanks contain seawater, or ballast water, which is pumped into or discharged from the ship during cargo transfer, usually in harbors and nearshore waters.
When cargo is unloaded from a ship, the weight of the ship decreases, so seawater from the surrounding waters is pumped into the ballast tanks to compensate for the decreased weight. When cargo is loaded onto a ship, the weight of the ship increases, so ballast water from the ballast tanks is discharged into the surrounding waters to offset the increased weight of the cargo. Modern ships depend on this exchange of seawater to regulate the ship's stability and operate safely.
The water pumped into a ship's ballast tanks may contain numerous aquatic organisms, including viruses, bacteria, algae, jellyfish, crabs, mollusks, and fish. If the organisms within a ship's ballast tanks survive the trip to the next destination, they may be released with the ballast water into waters in which they do not naturally occur. If these nonnative organisms survive and spread throughout their new environment, they may become invasive species. In this way, ballast water can accidentally introduce harmful microalgae and other organisms into the environment.
"Every minute, 40,000 gallons of foreign ballast water is dumped into U.S. waters."
Source: James Baker, U.S. Department of Commerce (Invasive Species Council 2001)
Invasive species may be harmful to a new environment for several reasons. They can negatively affect human health and economic activities. Invasive species can decrease the abundance and diversity of native species and damage the ecological stability of native ecosystems. Invasive species are transported through ballast water and create environmental problems throughout the world:
European zebra mussel (Dreissena polymorpha)-The zebra mussel was introduced into the Great Lakes in the mid-1980s through ballast water collected at a freshwater European port. Zebra mussels clog water pipes and foul underwater structures, resulting in billions of dollars in control and cleanup costs.
Harmful algae (e.g., Pyrodinium sp. and Alexandrium sp.)-These dinoflagellates, which can cause red tides, were transported to Australian waters from Southeast Asia. Some species can cause paralytic shellfish poisoning and harm local shellfish industries. More information about HAB Species.
Asian green mussel (Perna viridis)-Green mussels have recently become established in Tampa Bay and Charlotte Harbor. Green mussels clog the pipes of power plants and desalinization plants and can compete with native species.
It has been estimated that more than 3,000 species of plants and animals are transported daily around the world in ballast water. ~ Source: National Research Council
Study of Ballast Water in Tampa Bay, Florida
The Florida Fish and Wildlife Conservation Commission's (FWC) Fish and Wildlife Research Institute (FWRI) is investigating the potential for nonnative harmful microalgae to enter Tampa Bay through ballast water. Foreign vessels entering Tampa Bay are routinely inspected by the Foreign Vessel Port State Control Branch of the U.S. Coast Guard Marine Safety Office in Tampa, in compliance with international regulations for maritime safety, port security, and environmental protection. FWC personnel accompany Coast Guard staff members on some of these inspections, and, together, they meet with the captain of the vessel to discuss ballast water sampling.
As part of the FWRI study, researchers collect water, sludge, and sediment samples from the ballast tanks of commercial vessels visiting the Port of Tampa and Port Manatee.
Samples are examined for the presence of potentially harmful, nonnative microalgae that may pose a threat to Tampa Bay. Species found will be identified, cataloged, and tested for toxicity.
Once this project is complete, the collected data will be used for many purposes:
- Assessing the public health and natural resource risks associated with introducing potentially harmful algae into Tampa Bay
- Identifying needs for future monitoring
- Providing sampling protocols
- Providing lists of species that pose potential risks and determining the sources of those species
Sampling Methods and Laboratory Analyses
Ballast tanks typically have an open pipe-called a sounding pipe-that is used to measure, or sound, the amount of water inside a ship's ballast tank. To sample through the sounding pipe, a long piece of tubing is inserted into the sounding pipe and lowered to the bottom of the tank. Water is pumped out through the tubing and filtered through mesh sieves, which retain and concentrate small algae and particles. Sampling through the tank's sounding pipe is the easiest way to sample ballast water.
Researchers also sample ballast water by removing the hatch cover of a ship's ballast tank. They use a pump and tubing to pump ballast water out of the ballast tank and into a series of mesh sieves. Occasionally, a technician may enter an empty tank and collect sediment sludge that has accumulated at the bottom of the tank.
Live algal cells may be readily identifiable using a light microscope, or they may Using a microscope and mouth pipettor to isolate single algal cells and cysts from a ballast water sample require further examination using scanning electron microscopy. Genetic analysis may also be used to confirm species identification. Some cells and cysts may need to be grown in the laboratory, which is a process called culturing. In this process, live cells and cysts are removed, or isolated, from the sample and are placed into individual culture dishes. Researchers provide the cells and cysts with nutrients and light conditions that simulate the natural environment of Tampa Bay.
If the nutrients and light conditions are suitable, the live cells may reproduce, and the cysts may emerge from their resting stages and begin to grow. These growing cells can then be used for a variety of purposes:
- Genetic confirmation of species identification
- Scanning electron microscopy (the cell can be magnified more than 10,000 times, which aids in proper identification)
- Toxicity testing
- Physiological studies
Cysts that do not emerge from resting stages may still be identified by light microscopy, genetic analysis, or scanning electron microscopy.
Funding provided by the Pinellas County Environmental Fund.