Conducting the Environmental Impact Analysis and Assessment - Environmental Impact Analysis: Process and Methods - page 208

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

Coal Limestone Taconite Native sediment

FIGURE 5.15
Attachment of invasive mussels (zebra and quagga) to DCR and Native Sediment Phase II
Investigation: U.S. Coast Guard DCR EIS (see text for reference).

A series of veliger studies was designed and conducted to evaluate the
potential impact of spreading and increasing the density of the invasive mus-
sels in the Great Lakes via larval dispersal. Veligers (both zebra and quagga)
were introduced to aquaria with native sediment and the three DCR types:
some uncovered, some covered with 1 mm of sediment, and others covered
with 3 mm of sediment. The results showed that up to 6% of the veligers pres-
ent in the experiment attach to DCR, compared with virtually zero percent
attachment to natural sediments (Figure 5.16). Even a 1 mm cover of natural
sediment over the DCR, which is less than the cover observed on the lake bot-
tom greatly inhibits veliger attachment to DCR to less than 0.2% of the veli-
gers present and a covering of 3 mm is an even greater attachment inhibitor.
Full evaluation of the literature, laboratory study, input from the expert
committee, and field evaluation provided a hard look at the impacts associ-
ated with invasive mussels from past and future DCR management practices
and alternatives. This hard look reached the following conclusions, which
were presented in the DCR EIS and used to evaluate alternatives, and ulti-
mately for the USCG to issue a Record of Decision (ROD) and promulgate
DCR management regulations:

r The preferable adult mussel attachment to DCR compared with native
sediment was a concern. However, the adults have limited mobility
and if they are already present in an area, new adults can attach to
old shells or even other live mussels. Thus in areas where mussels are
already present in dense concentrations, the addition of DCR is unlikely
to increase mussel distribution or density via adult attachment.