Aquatic Invasive Species

Ballast water is used by cargo ships to help stabilize the ship and help maneuverability during long voyages. Generally, ships intake ballast water while in port, and release it once they’ve reached the destination. During this process, the sediment and everything else in the water is released into the port along with it. We now know that this is a very common pathway for aquatic invasive species to spread across the globe and establish themselves in new habitats. The introduced species can range from microscopic zooplankton to animals like crabs and mussels, all of which can have negative impacts in new habitats. Because of the danger posed by ballast water transfer around the globe, various treatments are being developed to prevent the introduction of invasive species. The International Marine Organization (IMO) has headed the regulation of ballast water issues and treatments since 2004, and currently approves 30 different treatment methods being used and developed across the world (Kim and Lee, 2009). Unfortunately, the best combination of ballast water treatment methods is still yet to be found. This is a problem that Andre May hopes to solve.

Having an interest in civil engineering and shipbuilding, May also has an interest in the ballast water issue. He felt that there is a knowledge gap as far as economic and energy efficiencies are concerned. May says that as far as what has currently been looked at, “Cost was more on consumer side, not manufacturer’s side”, and he hopes to delineate the latter half. In his proposed study, May will look at the following criteria for ballast water treatment: “the method’s cost and effectiveness, ease of installation and operation, health and environmental risks, corrosive potential (to the ballast tank’s walls), and ease of monitoring and regulation.” In particular, May will focus on three of the most auspicious treatment combinations supported by the IMO. They are filtration and water heating, electrochemical treatment and water heating, and filtration and UV radiation. By measuring the energy usage per amount of invasive species removed in laboratory conditions, May will determine the best combination for use after subsequent analysis and comparison of economic and mechanical efficiency.

Ultimately, May hopes that the proposed experiment will shed light on the most useful and practical ballast water treatment combinations. While his study will illuminate the cost-benefits of three treatment combinations, there are still many more that can be researched. However, the results of his study should give future research a strong direction, regardless of the outcome. When asked how realistic he thought implementing the best combination or combinations for ballast water treatment globally would be, he replied, “Each region has to tailor a product. It’s not something that can be mass produced easily. Different countries use the same equipment, same combinations, but don’t get the same efficiency. It depends on the environment, Arctic versus Mediterranean, etc., and geographic location for the efficiency.” Personally, his method of choice is filtration. There are few risks to consider, and there is a higher level of control in screening for invasive species. However, May also advocated for water heating as a potential treatment. He thinks that the water used to cool the engines can be recycled for use in ballast water treatment. Finally,  when asked about the future of ballast water treatment and privatization versus nationalization, he supported nationalization, because in his mind it is more efficient. But those are debates for the future, and we look forward to the results of his study to lead ballast water treatment on.

Reference: Kim EC and Lee KP. 2009. Development of ballast water treatment system based on electrochemical disinfection technology. Oceans-Europe. 2009: 1-8.

The April lab group swiftly counted their very dense sub-samples this afternoon.  Jordan Lake surface water was 17 degrees Celsius today (pretty warm!), but Daphnia lumholtzi is still not present in our samples.  But the seasonal shifts in the densities of the two main taxonomic groups are striking!  I’ve included both linear and log plots of the Jordan Lake zooplankton trends:

The red swamp crayfish, P. clarkii, is one of the most ecologically damaging aquatic species. A native of Louisiana, this freshwater crustacean has invaded Mediterranean ecosystems in 5 of the 7 continents, imposing detrimental effects on each.

Scott Valentine of Duke University has proposed a study to determine the mechanisms by which P. clarkii reduces biodiversity in invaded ecosystems. Valentine hopes to find major differences in the food preferences of the native and invasive crawfish. He is confident that he will find sufficient support since many faculty members from the University of Florence and other universities throughout southern Europe have expressed interest and dedication to the study of P. clarkii.
Valentine believes the study will take approximately 15-36 months to complete. Field collections in two northern Italian streams, one dominated by P. clarkii and the other by A. italicus, will take about a year and may enlist supplementary assistance from citizen scientists. The bulk of the work, however, will take place in the lab as scientists analyze the stomach contents of the different species collected to determine the contrasting diets of the native and invasive crayfish species. Organic material found in the stomachs of each will likewise be scrutinized to ascertain the major ecosystem differences resulting from the P. clarkii invasion.

P. clarkii is a keystone species which further complicates the establishment of effective removal methods. This invasive species fills the niche originally held by the native crawfish species in each habitat but causes all sorts of problems because it is not a perfect match. “Ideally we would want to remove all P. clarkii and replace them with the native A. italicus species, but it is not that simple,” reports Valentine. The balance previously maintained in this ecosystem cannot be achieved because of the environmental alterations that have begun because of the P. clarkii introduction. On the whole, Valentine is referring to the “crawfish plague.” One of the most unfortunate consequences of P. clarkii invasion is its simultaneous transportation of the fungus A. astaci. When this fungus is brought in to foreign ecosystems that haven’t been acclimated to it, the local crawfish die.

“What we really are hoping to achieve is the reduced spread of invasive species, specifically the red swamp crayfish. This is a slippery slope, however, because native species are having difficulties reestablishing themselves due to the fungi transported via the invasive crayfish,” says Valentine. In addition to the stress placed on the environment by P. clarkii who dominate the native population and upset the natural balance of resource chains, the fungus serves as a major impediment. In order to return to the initial conditions before the invaders scientists would have to do more than just eliminate P. clarkii entirely, since the fungus spreads to the native species which in turn either die or subsequently serve as carriers for many years. Complete extermination of both the native and non-native invasive species as well as eradication of the fungi would all need to occur for a return to normalcy.

Biodiversity loss is a major factor contributing to the problem with this invasive species. Specifically, the loss of biodiversity after the invasion of P. clarkii caused a decrease in the freshwater volume of detritus, small fishes, and benthic organisms (all part of the P. clarkii diet), all of which contributed to a decrease in the water quality. P. clarkii burrow in the sides of streams where rice plantations are located and they caused a widespread decline in various countries’ rice production. Humans are inherently linked to the environment and thus also bear the repercussions of this invasive species.

In sum, Valentine’s study will enable scientists to learn how the P. clarkii changes an ecosystem by examining its food sources and the overall mechanisms by which it invades and dominates foreign habitats. More effective control methods can eventually be developed to end the invasion and continued eco-trauma delivered by the red swamp crayfish.