Observations and Experiment:

Morphologies and Life History

Native vs. Invasive

Tunicates in Immunology

Organisms of the Intertidal Zone

Photo Galleries:


            B. schlosseri
and B. violaceus showed little preference to the substrate on which it settled upon. The majority of settlement was on rocks, though that is most likely due to the fact that much of the land cover consists of that substrate. Also, it wasn’t as common to find tunicate colonies on Ascophyllum nodosum. This is most likely due to the higher location of the Ascophyllum zone. Tunicates must be submerged for the majority of the day, thus areas where desiccation would occur (the high intertidal zone), fewer tunicates were found. The most telling aspect about the observations made is not what was settled on, but rather, the vastness of the number of colonies. According to Stoner et al. (2002) European populations of B. schlosseri are commonly found in natural environments like those of the intertidal or subtidal zones, whereas in other locations around the world, the species is greatly limited to ecologically impacted marine environments. This, however, was not the case in Nahant.

The next question that can be considered is whether these invasive ascidians are out competing or replacing a native species. In the case of B. schlosseri and B. violaceus in the Nahant intertidal zone, B. schlosseri may be considered the resident species, while B. violaceus may be considered the invasive species. B. schlosseri generally had smaller colonies, while B. violaceus often was the dominant mat, encircling the former. This theory of a resident species (see Carlton, in press or Stachowicz, 2002) could be defended with statistical data of the numbers of colonies of B. schlosseri compared to those of B. violaceus.        http://www.stanfordalumni.org/news/magazine/2006/janfeb/farm/news/squirts.html
                                                                                                                             Botryllus schlosseri, Tony de Tomaso

                 Temperature data supplied by the iButtons for the three days shows minor variations in temperature daily. It was expected that the temperatures from September to November would decrease, but in order to make an analysis, more complete observations and information is necessary. Stachowicz (2002) inferred that the climate change and the increase in water temperature expected in the Northern Hemisphere will increase the number of nonindigenous species invasions in coming years. Attempts were made to study the affects of temperature variation in a controlled experiment, but unfortunately, the tunicates did not survive the transfer from ocean- to aquarium- life.  Below is a reassessment of the experiment.  

In an alternative field experiment, several changes would be made to the procedure and the analysis of data. A search would again be made for preferred substrate by the tunicates; however, instead of solely observations supporting the research, statistical data would be collected. Three transect lines would be placed randomly; one in the lower intertidal zone, one in the middle intertidal zone, and one in the higher intertidal zone. Along each of these, a quadrat would be placed every three meters. The number of colonies and the substrates that they are on would be recorded. If limited to a semester, data collection every 10 days or every two weeks would be sufficient. Statistical analysis could then be attempted in order to find whether there was a significant difference between tunicate settlements on various substrates.

            If repeating the controlled experiment in a lab, changes would initially be made to the procedures, and depending on the results, further testing could be executed. To begin, the location of the lab would need to be near accessible salt water, as well as in a facility that could support flowing water. Collections and tying of the tunicates to the slides would be similar to the procedures described in the Methods. However, instead of being placed in an aquarium with an aerator, a source of flowing water would be supplied. The colonies on the slides would be placed vertically, and the tunicates would not be moved or handled for at least two weeks. This was a concern with the controlled experiment over the semester. While recording data and observing the newly transferred tunicates on their slide, they were exposed to direct bright light and heat of the dissecting scope in minimal water. Following the initial two weeks, if the tunicates were still living, observations and further research would be done concerning growth influenced by varying temperatures or growth influenced by varying light cycles.