Grade 9 | Rhode Island
Grade 9 | Rhode Island
Exotic species are species that are non-native and have been introduced to a new ecosystem and are thriving in it. An example of problems caused by marine exotic species is something called biofouling. Biofouling is an accumulation of organisms (plants, animals, algae, etc.) on a surface, either man-made or natural. Exotic marine species contribute to biofouling on boats, docks, shellfish, plants and other organisms. The purpose of this research was to determine whether or not different floating dock types (plastic and cement) affected the number and density of exotic species. Exotic marine species were sampled using a quadrat design on floating docks in a coastal pond on the south shore of Rhode Island. This study was successful in determining that there are differences in the density and number of exotic species living on different man-made floating dock substrate types. This research showed that the density of exotic species was greater on the plastic substrates compared to cement. It may be useful to continue research to determine if plastic materials should be used less in marinas, and whether in the future, dock owners should switch to floating docks made of cement only. This type of research may also help set government regulations about man-made dock substrate types and the regulation of exotic marine species.
While walking along a dock or next to a piling, you may notice just below the water line an odd cluster of creatures mixed with the luscious layers of seaweed. Bending down to take a closer look, maybe even poking a squishy-looking specimen with curiosity, you notice how many there are. There are hundreds of them standing upright, with layers of blobs smothering all forms of native marine life. What are these alien-like creatures? These mysterious organisms are mostly exotic tunicates and other marine species carried in from the western Pacific and thriving in our waters.
Exotic species are species that are non-native and that have been introduced to a new ecosystem and are thriving in it. These species are a threat to our economy, health and ecosystems because they are often able to out-compete native and rare species. Exotic species are often very successful reproducers and are able to adapt easily to new environments, displacing native species. One major problem caused by exotic marine species is something called biofouling. Biofouling is the accumulation of organisms on a surface, either man-made or natural. Exotic marine species contribute to biofouling on boats, docks, shellfish, plants and other organisms.
The main way exotic marine species are introduced to a new environment is through ballast water. Ballast water is the water stored in the hull of ships; it is used to weigh them down when they have no cargo. In the past, ships used cobblestones instead of water. When cargo is emptied from a ship, the ballast water is sucked into the ship’s hull in order to weigh it down so it doesn’t tip or heel in high winds. When it is time to load the ships with cargo, the ballast water is emptied into the water, dumping marine organisms with it from different parts of the world. Each year, 21 billion gallons (2.4 million gallons per hour, or 4,000 gallons of water per minute) are discharged into U.S. waters, carrying marine organisms such as plankton and tunicates and small fish from oceans around the world (U.S. Federal Aquatic Nuisance Species Task Force).
Last fall, as part of my high school internship with the National Park Service Ecological Inventory and Monitoring Program, I participated in a marine-invasive-species monitoring program. Floating docks are often sampled as part of exotic marine species monitoring programs (Salem Sound Coastwatch). Many marine organisms require surfaces to attach to, and floating docks are ideal because they are submerged even at low tide. After spending my fall days along the docks of a marina in southern Rhode Island, I started to notice that most of the floating docks in the marina were made out of either plastic or cement. This made me wonder whether exotic marine species prefer a certain kind of dock surface to attach to. I decided that I would study exotic marine species on two common floating dock substrate types, plastic and cement.
The density and number of exotic marine species will be greater on floating docks made of cement compared to plastic, because cement has a texture similar to the natural substrate of rock.
What is the difference in the number of exotic marine species found living on floating docks made of cement compared to plastic?
I collected my data using a random quadrat sampling method. I first numbered all the cement and plastic dock locations and then randomly selected six locations for each substrate type. I then randomly selected the specific sampling location along each section of the dock in order to collect my data. I used a quadrat sampling method. My quadrat size was 9 by 14 cm. I chose to use a small quadrat due to the large number of species within each quadrat and the extensive time it takes to identify such a wide variety of marine organisms. To sample from the docks, one person would have to lie stomach-down and hold the quadrat completely flush to the side of the dock and submerged in water. With the other hand, the quadrat was scraped clean using a putty knife. A second person would catch the marine organisms with the net and put them in the tub for easy identification.
I then identified every species to at least the genus level, as well as counted the individuals of each species. One small quadrat often took me two or more hours to identify all of the species and determine whether or not they were the native or exotic species of that genus. As part of my training with the National Park Service and my own research, I spent time with a tunicate expert from the Woods Hole Oceanographic Institute (Dr. Mary R. Carman), learning how to identify tunicates, as well as with Dr. Niels Hobbs from the University of Rhode Island School of Oceanography, learning how to identify a variety of shrimp species.
The results of my study show that the density of exotic and native marine species was greater on the plastic substrate than the cement substrate (Figure 1). Cryptogenic species are those for which it is not known whether they are native or exotic.
The density of cryptogenic species (species of unknown origin) remained the same on both substrates. Both substrates had the same number of exotic species, although the plastic substrate had more native and cryptogenic species than the cement substrate(Figure 2).
The plastic substrate had more individuals of amphipods, bivalves, colonial and solitary tunicates, Nereidae species and seaweeds than the cement substrate, although the cement substrate had more anemone and hydroid species than the plastic. Both substrates contained only one bryozoan species and the same number of crustacean species (Figure 3).
Both substrates had many more exotic colonial tunicate species than solitary tunicate species. However, there were more individuals of colonial tunicates found on the plastic substrate than the cement substrate (Figure 4).
To help determine the density of organisms within each sampling quadrat, I placed the organisms collected within each quadrat in a flat white tub and placed a clear plastic grid containing 16 squares over the top. I estimated how many squares out of the 16 contained organisms. I then used this number to calculate the percentage of cover by the combined organisms in one quadrat. I then averaged all quadrats for each substrate type. The percentage of cover was higher for the quadrats laid over the plastic dock substrate, and had a lower standard deviation than the cement substrate, which had a smaller average percentage of cover and a larger standard deviation (Figure 5).
The experiment I conducted measured the density and number of exotic marine species found on two different man-made substrates commonly used to build floating docks in coastal marinas. I hypothesized that there would be more exotic marine species living on the cement substrate than the plastic substrate, because cement is the same texture as the natural substrate rock. The independent variable in my experiment was the substrate type, and the dependent variable was the number of exotic marine species. Following data collection and analysis, I proved my hypothesis incorrect. After conducting my experiment, the results indicated that there were more exotic species living on the plastic than the cement substrate. The plastic substrate was also more densely populated than the cement substrate (Figures 1 and 5).
From my research I also learned that Mytilus edulis (common mussels) attach more often to plastic substrates than cement, which may have been one reason why there were more colonial tunicates on the plastic docks, because colonial tunicates often grow on top of mussels. The plastic substrate housed many more individuals and colonies of exotic marine species than the cement substrate, but it also provided footing for more native species. For example, there were more solitary and colonial tunicates on the plastic substrate than the cement substrate (Figure 4), but there were also large numbers of the native species Ulva lactuca (sea lettuce) and Mytilus edulis (mussel), more than on the cement substrate.
In every experiment, there is experimental error. If I were to conduct this experiment again or continue the current experiment, I would take more samples and test at different locations in the salt pond at different salinity levels. For this project, I only collected data at one marina. I might also test the organism density and species richness at different salinity levels or at different water temperatures and see if there is a difference.
My study was successful in determining that there are differences in the density and number of exotic species living on different man-made substrate types on floating docks. Because my study
showed that the density of exotic species was greater on the floating docks made of plastic compared to those made of cement, it may be useful to continue research to determine if plastic materials should be used less in marinas, and whether in the future dock owners should switch to cement floating docks to lessen the growth and spread of exotic marine species. This research may also help set government regulations about man-made dock substrates.
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Carman, Mary R. Woods Hole Oceanographic Institute. Personal interview, 13 Oct 2012.
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