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
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.
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
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
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.